International Library Of Technology Surface Arrangements Ore Dressing And Milling Sampling Ores Roasting And Calcining Ores The Cyanide Process

Name: International Library Of Technology Surface Arrangements Ore Dressing And Milling Sampling Ores Roasting And Calcining Ores The Cyanide Process
Author: International Textbook Company

International Textbook Company

International Library Of Technology Surface Arrangements Ore Dressing And Milling Sampling Ores Roasting And Calcining Ores The Cyanide Process

International Textbook Company · 1902 · Historical

Book Source: Digital Library of India Item 2015.169817 dc.date.accessioned: 2015-07-07T02:12:53Z dc.date.available: 2015-07-07T02:12:53Z…

Public-domain full text preserved in the Mountain Man Mining Library. Original source: archive.org.

INTERNATIONAL LIBRARY ofTECHNOLOGY

SERIES OF TEXTBOOKS FOR PERSONS ENGAGED IN THE ENGINEERING PROFESSIONS AND TRADES OR FOR THOSE WHO DESIRE INFORMATION CONCERNING THEM. FULLY ILLUSTRATED AND CONTAINING NUMEROUS PRACTICAL EXAMPLES AND THEIR SOLUTIONS

Surface Arrangements Ore Dressing And Milling Sampling Ores

Roasting And Calcining Ores The Cyanide Process

Scranton :

International Textbook Company

Copyright, 1899, 1900, by The Colliery Engineer Company. Copyright, 1902, by International Textbook Company.

Entered at Stationers' Hall, London.

Surface Arrangements at Reduction Works: Copmight, 190;i, by International Textbook Company Entered at Stationers' Hall, London.

Ore Dressing and Milling : Copyright, 1898, 1899, by The COLLIERY ENGINEER Company.

Sampling Ores : Copyright, 190'2, by International Textbook Company. Entered at Stationers' Hall, London.

Roasting and Calcining Ores : Copyright, 1902, by INTERNATIONAL Textbook Company. Entered at Stationers' Hall, London.

The Cyanide Process : Copyright, 1902, by International Textbook Company. Entered at Stationers' Hall, London.

ima

Burk Printing House, Frankfort And Jacob Streets, New York,

Preface.

The International Library of Technolog-y is the outgrowth of a large and increasing demand that has arisen for the Reference Libraries of the International Correspondence Schools on the part of those who are not students of the Schools. As the volumes composing this Library are all printed from the same plates used in printing the Reference Libraries above mentioned, a few words are necessary regarding the scope and purpose of the instruction imparted to the students of — and the class of students taught by — these Schools, in order to afford a clear understanding of their salient and unique features.

The only requirement for admission to any of the courses offered by the International Correspondence Schools is that the applicant shall be able to read the English language and to write it sufficiently well to make his written answers to the questions asked him intelligible. Each course is complete in itself, and no textbooks are required other than those prepared by the Schools for the particular course .selected. The students themselves are from every class, trade, and profession and from every country; they are, almost without exception, busily engaged in some vocation, and can spare but little time for study, and that usually outside of their regular working hours. The information desired is such as can be immediately applied in practice, so that the student may be enabled to exchange his

Preface.

present vocation for a more congenial one or to rise to a higher level in the one he now pursues. Furthermore, he wishes to obtain a good woi*king knowledge of the subjects treated in the shortest time and in the most direct manner possible*

In meeting these requirements we have produced a set of books that in many respects, and particularly in the general plan followed, are absolutely unique. In the majority of subjects treated the knowledge of mathematics required is limited to the simplest principles of arithmetic and mensuration, and in no case is any greater knowledge of mathematics needed than the simplest elementary principles of algebra, geometry, and trigonometry, with a thorough, practical acquaintance with the use of the logarithmic table. To effect this result, derivations of rules and formulas are omitted, but thorough and complete instructions are given regarding how, when, and under what circumstances any particular rule, formula, or process should be applied; and whenever possible one or more examples, such as would be likely to arise in actual practice — together with their solutions — are given to illustrate and explain its application.

In preparing these textbooks, it has been our constant endeavor to view the matter from the student's standpoint, and to try and anticipate everything that would cause him trouble. The utmost pains have been taken to avoid and correct any and all ambiguous expressions — both those due to faulty rhetoric and those due to insufficiency of statement or explanation. As the best way to make a statement, explanation, or description clear is to give a picture or a diagram in connection with it, illustrations have been used 'almost without limit. The illustrations have in all cases been adapted to the requirements of the text, and projections and sections or outline, partially shaded, or full-shaded perspectives have been used, according to which will best produce the desired results. Half-tones have been used rather sparingly, except in those cases where the general effect is desired rather than the actual details.

Preface

It is obvious that books prepared along the lines mentioned must not only be clear and concise beyond anything heretofore attempted, but they must also possess uneqiialed value for reference purposes. They not only give the maximum of information in a minimum space, but this information is so ingeniously arranged and correlated, and the indexes are so full and complete, that it can at once be made available to the reader. The numerous examples and explanatory remarks, together with the absence of long demonstrations and abstruse mathematical calculations, are of great assistance in helping one to select the proper formula, method, or process and in teaching him how and when it should be used.

Two of the volumes of this library, of which this is the first, deal with the metallurgy of gold, silver, copper, lead, and zinc. In the present volume the following subjects are treated : Surface arrangements at reduction works, ore dressing and milling, sampling ores, roasting and calcining ores, and the cyanide process. The subject of ore sampling treats both of mechanical and hand sampling. In Ore Dressing and Milling the reduction and concentration of ores and also the amalgamation of gold and silver ores are treated. The papers on the Cyanide Process are very thorough and complete, and every precaution was taken to insure that the information given was accurate and practical. This volume, together with the other volume treating on the same subject, forms the most thoroughly up-to-date and practical work that has yet appeared on the metallurgy of the metals specified.

The method of numbering the pages, cuts, articles, etc. is such that each subject or part, when the subject is divided into two or more parts, is complete in itself; hence, in order to make the index intelligible, it was necessary to give each subject or part a number. This number is placed at the top of each page, on the headline, opposite the page number; and to distinguish it from the page number it is preceded by the printer's section mark (§), Consequently, a reference such as 16, page 26, be readily found by looking along the inside edges of the headlines until § 16 is found, and then through § 16 until page 26 is found.

International Textbook Company.

2G

Hydraulic Classifying Machinery , .

2G

Settling Ponds

Concentrating Machinery

2()

Compartment Jigs

Jig Discharges

u

Stationary and Revolving Buddies . .

Evans's Buddie

Dolly Tubs

Theory of Concentration

Concentrators

Frue Vanner

Dry Concentrators

Pneumatic Jigs

24

Magnetic Concentrators

Amalgamation

Losses of Gold in Amalgamation . .

Amalgamating Apparatus

Patio Process

Modern Amalgamating Machinery .

Chemical Reagents for Pan Amalgamation

Boss Continuous-Process Mill

Barrel Amalgamation

f)

Stamp-Mill Amalgamation

Cleaning and Dressing Plates

Devices for Saving Gold in Amalgam .

Huntington Mill

General Mill Arrangement

Amalgamating Mills

Removal of Mill Tailings

Practical Hints in Connection With Concentration

Surface Arrangements At Reduction Works

1 . Definitions. — Reduction plants are usually distinguished as ivct and dry. In the first instance the plants are supposed to use water and chemicals for reduction purposes, while in the second they use fire to obtain metals fx'om the ore. The dry process would include magnetic concentration and the concentration of minerals by air, were there at this time any other than experimental plants existing for the latter. The wet process is made to include all those plants that reduce the bulk of ores by means of water, whether chemicals enter into the reduction or' not. Concentration from a metallurgical standpoint, is defined as a separation of ore or metal from its containing rock ; whether water or heat is the more convenient and suitable agent for concentration will depend on the location of the mill and the character of the ores, for in some cases one method would answer while the other would be entirely unsatisfactory and too costly.

' 3. Hydro metallurgy. — The process of reducing metallic ores by means of liquids is Termed liydrometq.ntirgy. Hydrometallurgy includes both cwcentfatipn by means of water and reduction by means of chemical solutions. It also includes amalgamation and such method,Sj.as are termed combination processes., Hydopietallurgy, as it

§ 24

For notice of copyright, see page immediately following- the title page.

2 Surface Arrangements § 24

is understood today, embraces both chemical and mechanical concentration wherein water enters as a factor.

3. Hydraiilicking is a term given to mining, transporting, and concentrating metal mineral by means of water. The term to within a short period referred entirely to the operation of concentrating gold by means of a stream of water, which mined the ground and gravel containing the gold, transported the same, and allowed the gold to become massed at one point and thus made recoverable. This principle has been extended to mining other minerals, such as iron, phosphate, rock, zinc ore, and platinum, and the term should no longer be limited to gold mining, but it should be extended to such operations as use the same stream of water for mining, transporting, and concentrating minerals.

4 . Dredging for minerals approaches hydraulicking as far as concentration by water enters into the operation, but differs from it materially in that the excavating is accomplished by other means than water alone, such as centrifugal pumps or dredging buckets. While water in some measure assists the dredging apparatus in excavating, nevertheless it would not transport and concentrate the mineral, as is done in hydraulicking, without the use of a water elevator. Hydraulic elevators, such as arc used in the West for placer mining, belong to dredging rather than to hydraulicking.

5 . Hydrometallurgleal Apparatus. — Various mechanical devices ai'e used to concentrate minerals by washing them free from dirt or other impurities. Such machines arc not classified with hydraulicking, as they are not mining machines; but although they wash and concentrate minerals, they come under the head of hydrometallurgical apparatus. Mechanical devices, such as jigs, trommels, log washers, hydraulic classifiers, and other similar machines, are not to be placed in a separate class, as they may be made adjuncts to several operations that differ completely in their ultimate method of obtaining the desired results. This character of

§24

At Reduction Works

hydrometallurgical apparatxis is described in Ori' Dressing and Milling and will not be specifically explained here; but it is well to understand that such apparatus may be used for concentrating secondary products of milling, as well as the primary products of mining.

6. A second class of liydrometalliirgical apparatus includes wet crushing as a preliminary operation, followed by sizing and concentration. Water forms the medium through which the decrease in barren mineral becomes possible. This operation is treated in Ore and Milling and includes such machines as jigs, trommels, spitzkasten, cone classifiers, bumping tables, concentrators, buddies, and vanners.

Concentration by the use of such machines is for the purpose of obtaining mineral matter in small bulk and then subjecting it to some other treatment. The milling ores thus treated are usually sulphuret and lean ores, which must be concentrated to a small bulk and treated at some distant point. Concentrates containing sulphur are more easily and economically reduced when freed from barren vein material, and in some cases if the ore were not concentrated no values could be obtained.

This system is used to separate lead from zinc in the Missouri-Kansas zinc districts of the United States, where zinc and lead are found in the same ore, and as they do not alloy they cannot be concentrated by fire so as to obtain each separately without making the cost of the concentration exceed their value. The only other means left, then, is a system of hydrometallurgy that will separate the two as far as possible, owing to their difference in specific gravity. This process is not practical when pyrite is associated with blende and galena. The same system is also practiced with the native copper ores in Michigan, where, on account of the difference in specific gravity between the rock and the native copper, they are successfully separated. The process was attempted at the Huston Mines, near Nace, Virginia, in order to separate manganese from limonite, but on account of the

Surface Arrangements

nearness of the minerals in their specific gravities, it was a complete failure.

7. A third hydrometallm-gical process includes wet crushing with amalgamation, such as is usually practiced in stamp milling. This process may be extended to include pan and barrel amalgamation. In case there is any considerable loss of gold from incomplete amalgamation, the process may be followed by that previously described or the fourth process.

The operation is hydrochemical in some instances, but not in the sense of lixiviation, for chemicals are not added in the pan process to extract the precious metals, but for the purpose of keeping the almalgam quick and preventing its sickening, flouring, or becoming incorporated with copper.

When the mercury becomes sickened it refuses to act upon the gold, and hence the gold is not recovered by this process. If, therefore, it is possible to keep the mercury bright and active, as may be done by adding chemicals, a larger percentage of precious metals can be recovei'ed.

8. It often happens in stamp milling that only about 40 per cent, of the precious metals in the ore is recovered by amalgamation, and it is seldom that the recovery exceeds 75 per cent. In the case, then, of a $12 ore, the value remaining after amalgamation would be $7.20, if the recovery was but 40 per cent. If by grinding the tailings in pans containing mercury a further percentage of the values may be recovered at a cost that will prove profitable, it is generally done, provided this system of recovery is cheaper and more profitable than some other. Again, if the ore will leave a profit after concentration and shipping expenses to the smelters are deducted, that method will prove advisable provided pan amalgamation does not yield as large returns. In some cases lixiviation may prove more remunerative for a secondary operation than the methods set forth; in any

At Reduction Works

case, the method adopted should be tested by practical experiments, which will also in a great measure be dependent on local conditions.

It is not good metallurgical engineering to adopt an expensive process that in a short time may become worthless on account of such a change in the character of the ore as to require its abandonment for some other; yet the West is dotted with just such near-sighted experiments, which would not have occurred had some metallurgical engineer been called in to treat the ore experimentally before the mill was erected.

9. A fourth, hydrometalliirgical process consists in the reduction of minerals by chemical solutions. The factors entering into such processes, if not well known and recognized, will cause failure. It is seldom that an ore can be obtained which does not require some preliminary treatment before leaching, and in some cases the preliminary treatment becomes a part of the chlorination and Russell processes. In nearly every case, except that mentioned, where tailings are treated, crushing precedes leaching. In case the ore is refractory, roasting must precede cyaniding; and it is an absolute necessity where chlorination is practiced oij. sulphurets. There are other chemical processes that have been conditioned to the metals they are to extract, such as the leaching of lead, zinc, and copper ores. So far, they have not come into general use because the expense connected with the recovery of the last-named metals by leaching their ores, with other necessary treatment, amounts to more than the value of the metals after recovery.

Eixiviation is defined as a process by which a soluble alkali or saline compound is extracted from an earthy mixture by washing out. As this does not cover the case of such metals as native gold, silver, or copper, the definition must be adjusted to include the term leaching*, by which is meant the separation of soluble matter by percolation or drainage. The distinction between lixiviation and leaching would then be that the former was a process and the latter

Surface Arrangements

a part of that process. A further distinction can be drawn from the fact that lixiviation includes dissolving with special solutions, while leaching is a matter of draining off the matter dissolved.

10. Ore Dressing and Milling. — The definitions given show that the four different hydrometallurgical processes mentioned require different milling methods and that their subdivisions also require different apparatus to carry out the particular processes involved. As an illustration, the cyanide mill requires very different arrangements and machinery from a chlorination mill, but since nearly every kind of apparatus that is used in hydrometallurgy has been discussed in Ore Dressing and Milling it is unnecessary to go into the details of their construction and workings. In the case of that metallurgical apparatus which is to be described under particular headings, such as tanks, barrels, pumps, filter presses, etc., it would simply be an unnecessary repetition to describe them at this time. Their description is given under the processes in which they are employed and which are included in this Course.

11. Roasting fuimaces are described in Roasting and Calcming Ores, These form a very important adjunct to milling and smelting arrangements, few metallurgical plants being able to do without them. They are, therefore, mentioned, but not described in detail.

13. The question of water supply enters into the subject of mill location, and if not always for power, at least for milling and smelting purposes. In some cases it may be the only means available for power, and in any case no mill or smelter can be run successfully without a supply of water. The subject of water supply for power has been fully discussed in Hydraulics and Hydraulic Machinery,

13. Economic Arrangements. — In case there is not sufficient water to furnish power, but fuel for steam boilers is available, the position in which the steam boilers are to

At Reduction Works

be placed at the mill is one worth, consideration. The situation of the engine room will be a matter of some moment for the reason that line shafting and belting must, as a usual thing, extend to various remote parts of the mill. The more distant it is from the power, the more difficult it becomes to maintain and keep it in repair. If it is possible to arrange a mill so that fuel may be delivered direct to the boiler house, considerable labor will be saved, and if by the expenditure of $1,000 the labor of one man can be saved, it will prove economical in the end. At small works, where it costs 20 cents per ton to load, cart, and unload coal, and this is in most instances a low figure unless done by contract, a saving of 1146 per year can be accomplished when 2 tons are used daily, provided the delivery track can be laid directly to a trestle adjacent to the boiler room.

14 . In the arrangement of a mill, ore delivery is probably one of the most important items. If it is possible to place the mill near the mine whose ore is to be treated, an ideal location would be a side hill, provided the ore could be delivered at the top of the mill In a situation of this kind gravitation can be made to assist and thus avoid the expense of raising the material. Advantages of this kind would not always apply to those mills that use driers before crushing and Screening-

Calcining furnaces are sometimes built high up in a mill, but there is less danger from fire and they are generally better located with regard to fuel and general handling of hot material if they are on the lowest floor of the mill. Even in case it is advisable to drop the ore to the drying furnace, there still remains certain advantages if a side hill is used for a mill site, as it usually furnishes a tailing dump, besides affording easy methods for dealing with slimes, tailings, and exhausted liquors.

15. Should the ore be delivered to the mill in lumps, so that it requires crushing, it is considered by some to be a disadvantage to have the mill on a side hill. This objection

Surface Arrangements

arises from the fact that some one once placed a crusher at the top of the mill, without first making allowance for vibrations and thrust from loaded ore bins, besides not properly anchoring the crushers. Some will smile that such claims should be advanced as a drawback to placing the crusher at the top of the mill; nevertheless, the position of the crusher is one that requires serious thought and much careful work, in order to obtain a firm foundation and prevent excessive vibrations. If the crusher or the stamps cause a water tank to vibrate in unison with them, the building will be seriously affected and weakened to its foundations.

16 . In case the mill is to be built on comparatively level land, the location should be chosen first with preference to the ore supply and then with reference to transportation of products and the delivery of fuel. In case it is to be a custom mill, similar preferences should be shown. The disposition of tailings is very important, but, like the water supply, it is considerably more flexible than the delivery tracks at a mill. The ideal location for a mill that must receive ore from different mines would be the brow of a hill, whez'c the water supply might reach it by gravity, ore be delivered into bins from railroad cars, and tailings leave the mill in such manner that the expense of handling them would be practically nothing. There are instances where mills have been very favorably located, but it is simply impossible to find every advantage in one mill.

In case the mill can be run by water-power furnished by some stream in the vicinity, it may be advisable to transport ore to a mill so located. On the other hand, it may be advisable to locate the mill near the mine and transmit the power generated by water to the mill. This second arrangement would cause a great loss of power, but it may so happen that the location of the water-power was practically inaccessible, to transportation facilities and mill construction. There are several instances on record where the power has been carried to the mill in the form of electrical energy.

§24

At Reduction Works

LAWS EELATIlSra TO WATEU RIGHTS

Bitches Anb Water

18. The laws passed by the United States Congress to encourage mining and assure to citizens agrarian rights are given in the following sections as far as they have bearing upon water rights, mill sites, etc.

'Whenever, by priority of possession, rights to the use of water for mining, agricultural, manufacturing, or other purposes, have vested and accrued, and the same are recognized and acknowledged by the local customs, laws, and the decisions of the courts, the possessors and owners of such vested rights shall be maintained and protected in the same ; and the right of way for the construction of ditches and canals for the purposes herein 'specified is acknowledged and confirmed; but whenever any person, in the construction of any ditch or canal, injures or damages the possession of any settler on the public domain, the party committing such injury or damage shall be liable to the party injured for such injury or damage.'' — Sec. 9, Acts of Congress (A. U. ), July 1866.

19. Excepted in Patent. — ''All patents granted or preemption or homesteads allowed shall be subject to any vested and accrued water rights, or rights to ditches and reservoirs used in connection with such water rights as may have been acquired under or recognized by the preceding section." — Sec. 17, A. C., July 9, 1870.

30. Claims Subject to Ditches and Elmnes. — "All mining claims now located, or which may be hereafter located, shall be subject to the right of way of any ditch or flume for mining purposes, etc. Provided always, that such right of way shall not be exercised against any location duly made and recorded, and not abandoned, etc. without the consent of the owner, except by condemnation, as in the case of land taken for public highways. And provided further, that such ditch or flume shall be so constructed that

Surface Arrangements

the water from such ditch or flume shall not injure vested rights by flooding or otherwise."

31. Ditch Rights. — "Ditch rights are located and a notice posted, after which a certificate of ditch and water rights is made out by the locator and sworn to before a notary public. The ditch should be staked and work commenced and prosecuted with reasonable diligence, otherwise the record and notice amount to nothing. Different States have different forms upon which the locator of a ditch is to record his statements. As these can be obtained from the Secretary of State, they are not given here."

33. " The right to clump is but little, if at all, affected by statutory regulation, and the right to dump, as of necessity or by custom, across lower claims, has been looked upon as custom or subject to only nominal damages. The exception in such cases would be where damage was done to mining operations on the claims below or to improved lands. The dump, when placed upon another's claim, is considered real estate by law ; hence, tailings or piles of lean ore dumped upon another claim belong to that claim and cannot be removed by the miner from whose mine it came." — Morrison.

MUm SITES

33. A mill site for purposes incidental to mining may be located on government lands, provided the United States statutes are complied with. There are, under United States laws, two classes of mill sites, which comprehend two classes of mills— private and public. The first class, that is, a mill site with lode, being of a private nature, is of greater interest to the miner than the second class, or the mill site that is intended to serve as a place for erecting a custom mill. Such sites can be patented in a manner similar to lode claims.

§24

At Reduction Works

34. How to Patent Mill Sites. — ''Where non-mineral land, not contiguous to the vein or lode, is used or occupied by the proprietary of such vein or lode for mining or milling purposes, such non-adjacent surface ground may be embraced and included in an application for patent for such vein or lode and the same may be patented therewith, subject to the same preliminary requirements as to survey and notice as are applicable to veins and lodes; but no location hereafter made on such non-adjacent land shall exceed 5 acres, and payment for same must be made at the same rate as fixed for the superficies of the lode.

"For filing claim, a charge of llO is made; for mill-site survey and platting, IBO; for mill site, including United States survey with a lode, $15. The owner of a quartz mill or redaction works not owning a mine in connection therewith may also receive a mill site, as provided in Sec. 15, A. C., May 10, 1872."

Location Aj!D Recokb

25. American Practice. — Mill sites are located by posting a notice in some conspicuous place on the claim, after which the locator records his notice with the proper county or State authority in which his mill site is located.

Location Notice

"I claim the Juanita mill site (GOO feet northeast by 200 feet southwest) as staked on this ground. Date of location, September 4, 1901.

" G. C. Munson."

Record Location Certificate

" To AH' Whom These Presents May Concern : Know ye that I, G. C. Munson, County of Arapahoe, Commonwealth of Colorado, do hereby declare, and publish as a legal notice to all the world that I have a valid right to the occupation, possession, and enjoyment of all and singular that tract or parcel of land not exceeding 5 acres, situate, lying, and

A-

Surface Arrangements

being in the Empire Mining DivSlrici, County of Clear Creek, vState of Colorado, bounded and described as follows, to wit: The Juanita mill site, beginning at corner No. J, from which a line north east 100 feet, etc,, to of beginning. Together with all and singular the hereditaments and appurtenances thereunto belonging or in anywise appertaining.

"G. C. Munson. [seal.]

''Witness my hand and seal, this fourth day of September, A. D. 1901."

36, Non-Miiieml Affidavit. — It is sometimes customary to make a non-mineral affidavit that no portions of the mill site contain minerals. In such cases, on two days' notice parties who own the land make affidavit to that effect; the claimant is not required to file his own affidavit to the same effect. The claimant must, however, make affidavit in regard to his being a citizen of the United vStates and finally publish his notice. After the application for survey has been made and the land surveyed, the patent will be given for the mill site, provided everything has been regular and the law complied with. Where a mill site is applied for in connection with a lode, a second affidavit (according to some authorities) of stated form, and which can be obtained by applying to the proper official, is required. This latter affidavit is a brief of mill site used for mining or milling purposes. In case a patent has been granted for a mill site and mineral should afterwards be discovered, the probabilities are that the patent would be good to cover both mill site and mineral, it having been received in fee simple.

37. Staking. — The locator of a mill site, before he makes claim to any portion of the land, will proceed to mark its boundaries by means of suitable stakes, or, if stakes are not possible, by means of monuments of rock or stone. A stone or boulder properly marked fully answers the purpose of a stake, or even a pile of stones in such

§34 AT REDUCTION WORKvS 13

places where stakes cannot be driven. A stake is set at each angle of the claim, marked with the name of the mill site and the number of the corner. Whenever it is possible, one corner should be tied to some natural landmark, government survey, or if that is not possible, to a natural permanent monument. If on account of the precipitous ground it is impossible to set the stake where the* claim corners, a witness stake suitably marked to designate the position of the corner should be set at the nearest available point along the lines of the survey.

BRITISH COBUMBIxVlS MILL. SITE

38. Britisli Columbian laws require that the land for a mill site be unoccupied public land, and as far as known, not to contain mineral. British Columbian statutes entitle the owner of a mill site to surface rights only, reserving all minerals that may be subsequently discovered on the land, together with the right to enter the property and mine such minerals for the government and its licensees. They also require that the mill site shall be as nearly square as possible.

Aside from the difference already mentioned, the British Columbia statutes are very similar in intent to those of the United States, as in the United States the area of a mill site is limited to '5 acres. The corners are marked by legal posts, with the notice on each post, stating, first, the name of the locator; second, the number of his Free Miner's Certificate; third, the intention, within 60 days from date of notice, to apply for the land as a mill site; and fourth, the date of notice.

39. foi* Uease. — Having properly located and staked his mill site, the locator, within the 60 days specified, applies to the Provincial Land Surveyor for a lease of the property, and on depositing duplicate plans and making affidavit as to the location of the claim, is granted a lease for 1 year. If in that time the lessee has placed or

Surface Arrangements

§M

constructed machinery or done other work on the property for mining or milling purposes to the value of $500, he can obtain a Crown grant (equivalent to the United States patent) to the mill site at the expense of $5 per acre. The interpretation of the term ''mining purposes" is not so broad as in the American practice. It includes only the erection of machinery and buildings for transporting, reducing, crushing, and sampling ores, or for the transmission of power for working mines.

Plaistt Foe Teeatment Of Oee

30 . General Considerations. — In a matter of this kind, the first thought should be the supply of ore. Mills have been erected almost simultaneously with the operation of breaking ground at a mine, irrespective of the quantity and quality of ore that the mine would produce. In some cases, the mines proved to be merely pockets, so that all moneys expended for mills have been entirely lost. In other cases, there was not sufficient ore for one-third or onefourth the capacity of the mill erected, and yet again there have been mills built at great expense to treat ore by a certain process, which proved complete failures, since the process was not applicable to the ore. It sometimes happens that the character of the ore completely changes with the dejdh, in which case the method of treatment must change in order to work economically and satisfactorily.

31 . The erection of a plant for the reduction of ore Is a matter of considerable importance to mine owners and is not one to be guessed at or to be the subject of ex])erimentation by ordinary mine managers. The West is full of good little mines that have failed to pay the owners interest on the capital that they have invested, although interest and capital have been made from the mine. The natural inference when one regards such results coolly is that the returns have been misapplied, and upon an expert examination it

At Reduction Works

has been found that usually they were squandered in some character of unsuitable mill or process, and in many instances the profits were lost in the tailings.

33, The first general thought relative to the erection of a mill is the question of a suitable ore supply. The second thought is the kind of power most readily available. The third, the location of the mill. The last, the character of the mill suitable for treating the ore mined.

Assuming that we have a free-milling ore, the question of the mill to be used is narrowed down to the stamp mill, as that, although primitive, has been ascertained by costly experiments to be the one best suited for that ore. This being the case, there are two classes of mills to choose from : The California mill with heavy stamp (weighing with stem, head, and shoe 950 pounds) and short, quick drop and the Gilpin County, or Colorado, stamp mill, with light stamp (600 pounds) and long, slow drop. These two mills, from their different modes of working, require different mortars — one a low discharge, the other a high discharge. The arguments for and against these mills have been long, sometimes bitter, without either side gaining an advantage ; but with the disappearance of the old guard, there seems to have been a compromise, in which the tendency is towards heavy stamps and quick drop — that is, from 60 to 95 drops per minute.

33. Arrangement of Bnildlings. — Mill buildings should be arranged with reference to the ore coming from the mine, the handling of material in the mill, the fuel supply, railroad connections, and tailings dump. The plant, if simply intended for coarse-crushing ore, which is subsequently to be picked for shipment, should be at the mine, since in that locality dumping ground for lean ore and rock is usually available and transportation of barren stuff is avoided. If such a plant is located so as to have railroad connections, the work may be conducted in the cheapest manner possible, advantage being taken of gravity to load the cobbed ore directly into cars from storage bins. In

Ig Surface Arrangements § 24

instances where the mine is almost inaccessible for machinery or erection of proper milling machinery, the ore must be trammed to the mill.

The mill may be a simple crushing plant, but if of large capacity, it should have a steady delivery of ore, possibly

Pig. 1

obtained through the use of a wire tramway, such as that shown in Fig. 1.

The illustration is of a wire tramway whose length is 9,000 feet, with a span of 1,173 feet across the town of Wardner, Idaho. Wire-rope tramways arc more expensive to operate than railways; however, in some situations they are" imperative, railway construction being out of the question. They may be made to work up and down hill, across ravines or rivers, and are very useful adjuncts to mining.

34 . Picking' Pelts. — Simple crushing mills, where ore is assoi'ted for shipment, should be provided with a picking belt. The Robbins picking belt, shown in Fig. 2, has proved successful both as a conveyer and as means for assorting

§24 At Reduction Works 17

and cobbing the ore. The ore is cobbed with a hammer on the belt as it travels along. One of these belts is said to have conveyed 350,000 tons of heavy crystalline ore, in

Fig. 2

pieces about 3 inches in diameter, at the Franklin, New Jersey, Zinc Mines.

By careful hand picking, the value of rich mineral in ore has been raised 26 percent., a matter of considerable importance, since if ore transportation is $2 per ton, $2 will be saved on every 4 tons shipped. One advantage of a movable picking belt lies in its serving the purpose of a conveyer. Another case is that of the Ferreira Company, in South Africa. The value of the ore as it comes from the mine is $17.17. After assortment the ore is worth $25.78, the increased value, due to sorting, being $8. 61. The increase in value leaves but $.84 per ton in the waste rock, although the latter is 36 per cent, of the ore mined.

18 Surface Arrangements § 34

35* It is advisable that mill building's sliould be erected with a view to economy; nevertheless, they should not ])e so arranged as to increase fire risks. At some plants the storage bins are connected with the head-gear above the shaft. This is a faulty arrangement, provided the shaft is perpendicular, for then the head-house must be above the shaft, and in case of fire the miners are cut off from escape. Many lives have been lost by this arrangement of buildings.

Fig. 3 shows the plant at the Mother Lode Mine, Anaconda, British Columbia. The head-frame and gear a is

Fig. 3

seen in the background. The ore when dum])cd at the head-house passes over the grizzly bars, the finer, dropping on to a 13-inch belt conveyer, which carries it to the ore bins shown in the foreground. The coarse pieces are delivered to the crusher, located in the building c in the back of the illustration and to the right of the head-frame. A 3G-inch sorting conveyer, 111 feet between centers and located in building d, receives the ore as it falls from the crusher and carries it to the bins. The waste and lean ore

At Reduction Works

§

to be discarded is assorted by hand labor and dropped into chutes, which deliver it to a IG-inch conveyer c having 540 feet between centers, which carries it to the rock dump. This conveyer may be seen to the left, connecting the ore bins with the dump.

Construction Op Miuts

36, Masonry. — The supervision of mill construction is generally one of the many duties intrusted to the metallurgical engineer. The design, as well as the kind of mill to be constructed, is a matter usually left for the metallurgist's decision ; therefore, he should be able to draw up plans and specifications in order to estimate the cost of construction. For this purpose he must know the cost of labor and materials delivered at the mill site, and which involve an estimate of the cost of transportation, a matter varying widely in the mountainous districts. The cost of masonry is particularly difficult to estimate in a new country, for at times, with good stone quarries near by, it may be economy to import stone or bricks from a distance. Masonry should not exceed 11 0 per cubic yard, and from that price it can be made to taper down to 11.50. In estimating the cost of buildings and masonry, labor should not exceed 00 per cent, of the cost of the materials used, otherwise something is wrong. This rule one may say is flexible enough to fit into any district where labor is dearer cheap, as in such situations materials are correspondingly high or low in price. Masonry depends on the price of stone and labor.. In some instances stone can be quarried and delivered to the masons for 75 cents per cubic yard. Under such favorable circumstances, the wall in place should not cost over $1.50 per cubic yard. The above figure for masonry is exceptional; a usual figure for a good cement mortar wall, pointed and well bound, is about $'2.50 per cubic yard. The stones used for mill foundations are not dressed, that is, cut to size, but are usually faced and split by the mason as he lays them, in order to keep a line and bind the wall.

Surface Arrangements

§ 24

37. Masonry at metallurgical works is usually confined to building foundations and engine beds, although at times it extends to vats, chimneys, and the construction of the entire plant. When constructing simple foundation walls for heavy buildings and loads, a good rule to follow, either for temporary or permanent masonry, is to give the stones plenty of binding material, such as a mixture of two-thirds cement and one-third sand, and also to have all spaces well grouted and spalled. Headers and corner stones should be properly laid to strengthen the bond and course joints should be properly broken. The batter given to foundation walls is about 1- inches per foot, from the surface up, and while such walls should go to bed rock, it is not necessary to batter them below the surface, unless it is desired to give them an extra wide base. A firm foundation wall whose top is less than 20 inches wide cannot be I'eadily built. Walls 18 inches wide and possibly less can be constructed for dwellings, but this will not answer for heavy mill construction. Sometimes it becomes necessary when erecting mills on side hills to build retaining walls which answer as building foundations and at the same time keep the earth from sliding or moving the building.

38. Retaining Walls. — The usual form of a retaining wall is shown in Fig. 4. There is no fixed rule for

At Reduction Works

§ 24

determining the dimensions of retaining walls, but the one given below will in all probability meet every requirement.

Rule. When the backing' is loose a wall of first-class large stones laid in mortar should have a base CD equal to one-third its vcrticccl height; a call of bricks laid in mortar should have a base of tzvo-fifths its vertical height.

Retaining walls must have a firm, wide foundation and must be constructed in the manner explained for dams in Hydraulics and Hydraulic Machinery . In case they are built up against shaly or other rock, they should be well backed by loose stones, and in instances where the rocks carry water, all spaces should be filled with cement to hold back the water or a drain made to carry the water away from the masonry.

Probably the latter plan will be better in case the wall is placed at the foot of a high hill or where the water is likely to come from a high elevation and create a great pressure against the wall. If, however, there are other avenues of escape for the water, which is easily determined by examination of the strata, it will not matter if the backing is made water-tight.

39 . Guarding Against Frost. — Where freezing occurs, the back of the wall should be sloped, as shown at a Fig. 5, and smoothly finished to lessen the hold of the frost, which might otherwise displace the masonry. The foot of the slope b should be at the frost line, usually about 2 feet below the surface in moderate climates and from 4 to 0 feet in climates above the forty-fifth parallel of latitude.

High altitudes will also affect the frost line.

40 . Having proportioned a retaining wall by the rule given, its stability may be increased by stepping it in back, as shown in Fig. 6, without adding to the volume of masonry.

The offsets are determined as follows: Through the middle point of the back, draw any Hney From /"erect

Surface Arrangements

§

the perpendicular f h. Divide into any even number of parts, in this instance four, and draw through these points of division lines parallel to f Ji. Then divide f h into one greater number of equal parts than gli and through these points of division draw lines at right angles to forming the offsets shown in the figure. By increasing the thickness of the wall at the base, the center of gravity is lowered and the stability consequently increased. The backing included between the lines gli and fJi exerts only vertical pressure against the offsets, which tends greatly to prevent the overturning of the wall. The theory of retaining walls differs little from that of dams and consequently is not repeated here, the student being referred to Hydraulics and Hydratilic Machmerjr

FRAMING OF TIMBER STRUOTITRES 41. Trestles. — As most reduction works require railroad tracks, and as it is frequently necessary to construct trestles, either leading to bins or clumps or during the I'egular construction of any mine railroad, illustrations arc given for framing some simple forms of trestles. Fig. 7 illustrates the various parts of a trestle; Fig. 8 two forms of bents and a side elevation of a poiTion of a pile bent trestle. The various parts are numbered and their names given in the following list :

i, a bent framed; S, a pile bent; S, cap piece; 4, cross-tie; 5, dapping or gaining; d, guard rail; 7, jack stringer ; longitudinal brace; 9, mortise; 10, mudsill; ii, packing block; packing bolts ; JS, a pile given a batter, an inclined brace ;

14 , a vertical, plumb, or upright pile ; 15, a vertical, plumb, or upright post; 16, a post with a batter, or inclined; 11, sill;

15, stringer; 19, sway-brace; W, tenon.

24 At Reduction Works 23

The portion of the illustration at Fig*. 7, shows the arrangement of a pile bent trestle, while that at ib) shows the arrangement of a framing bent trestle. In case the trestle

Fig r

is not very high and piles are used, they may be driven vertically, but it is always best to have the outer piles driven at an angle so as to form batter braces. Fig. 9 illustrates a

Fig. 8

pile having a tenon formed on the upper end to receive the cap. When this method of securing caps is used, a hole is drilled through the cheeks of the mortise in the cap and through

Surface Arrangements

S 24

the tenon* It is well to have the hole in the cheeks of the mortise so placed that when the pin is driven two holes it will tend to draw the cap down on to the top of the pile.

Fig. 9 Fig. 10 Fig. 11

The pin used for this purpose is commonly called a treeiiaiR and should be made of hardwood, locust wood if possible, and slightly tapered, as shown in the lower part of the illustration. Sometimes the caps are not mortised and tenoned on to the piles, but may be secured by means of drift bolts, as shown in Fig. 10, or by means of dowels, as shown in Fig. 11.

42. Caps. — Another arrangement is shown in Fig. 12. This is called the split '' cap ; in place of using one 10" X 10" timber, two 5" X JO" timbers are employed and the top of the pile is cut as shown in the illustration. 1410 timbers can be seen at a and while r is a tenon, the full width of the pile, that is allowed to project up between the timbers. No notches are cut in the timbers where they rest on top of the piles, but they are secured in place by means of a bolt wliich passes through both timbers and the tenon. Some of the advantages of this method of framing the caps are as follows:

1. On account of the smaller size of the cap pieces, it is possible to obtain better timber.

§24

At Reduction Works

2. Repairs can be made with greater ease than where caps are mortised and tenoned or fastened with drift bolts to the top of the piles, for either of the caps can be removed- and replaced without interfering with traffic or cutting any portion of the timber work.

43. F r a mod Bents . —

Where it is not possible to drive piles and form pile bents, framed bents are used. Fig. 13 illustrates a framed bent in which all the timbers are simply secured by means of drift bolts. fig. is

44. Fonndations for Sills. — The sill of the bent should always be placed upon some form of foundation. This may be composed of timber mudsills, as shown at 10 , Fig. 7, but it is a better practice to construct stone or masonry walls under the sills and to see that the latter are well bedded. When masonry is used as a foundation for sills, care must be taken to see that the stones are well laid; it is never good practice to construct these foundations of round stones laid up like rubblework, for the constant passage of trains over the trestle is liable to break up such a foundation.

45. Plaeing Timbers. — The batter braces should have a uniform angle of 3 inches per foot. Fig. 14 illustrates the method of framing on the ends of batter braces

Fig. 14

Fig. 15

and posts in framed bents and also shows a drainage hole bored in such a manner that any water collecting under the

2G

Surface Arrangements

§24

jointing will immediately flow out throug'h the drain and thus reduce the tendency that timbers have to rot. It may be well to mention here that green oak timbers or wet oak timbers spiked or bolted with iron soon decay in the vicinity of the iron. Fig. 15 (a) and (/;) show the method of mortising and tenoning the legs to bents.

46. Ill list ration of a Framed Bent. — Fig. 16 is a dimensioned drawing showing a timber bent as used on one

line of railroad. The gauge of the track is the standard for the United States, that is, 4 feet inches, and the dimensions on the drawing fully explain the various parts.

47. Elevation of Outer Kail. — Where the ti'castle comes in a curve on the railroad track, if it is intended that

§ M AT REDUCTION YvORKS 27

the cars should move at any considerable speed, it is necessary that the outer rail be elevated. This may be accomplished by wedge blocks placed on the top of the cap and under the stringers; usually, however, the cross-ties are cut wedge-shaped to give the desired elevation.

48. Framing Buildings. — Small buildings about mills can be framed of small stuff, without any special framing, the pieces simply being spiked together to form a balloon frame, which is covered with either siding or corrugated iron.

Fig. 17

When it becomes necessary to build somewhat heavier structures, some form of framing may be used. The different joints used in framing are all similar to those illustrated in connection with trestlework and consist mainly in the use

of tenons or notching the timbers together. When timbers must be joined in the direction of their length, special joints or a different method may be necessary. When two timbers are joined without an increase of size, it is called a '' scarfed " joint.

Fig. 17 illustrates one form of scarfed joint in -which the timbers a and h are joined as illustrated, and are held in place by means of the key Fig. 18 illustrates another form of scarfed joint, which is better adapted for resisting end

A. M. Ill— 3

28 Surface Arrangements § 24

thrusts and in which the timbers a and b arc held together by two keys c and c. Usually scarfed joints are strengthened

§24

At Reduction Works

bolted on to the outside, as illustrated in Fig. 19, the joint becomes a pure fished joint, and the plates c and c are called fish-plates.

49. Heavy by Cutting Joints. — One form

of heavy framing is illustrated in Fig. 20. The heavy sill timbers a are secured to the timbers b by notching into each timber, as shown in the illustration, and also by the use of drift bolts. The posts c are fastened to the timbers b by means of tenons and treenails, or pins. The timbers for the second floor e and d are united by notching and by drift bolts, while the posts /"for the next upper story are secured by tenons and treenails. The braces g are notched into the posts and sills and secured by heel tenons and pins.

Fig. 21 illustrates a tenon on the end of one of the braces. The floors may be formed by using a joist i the same depth as the timbers b and notching them on to the sills a to the same depth the timbers b were notched down. After this the floor k can be laid on top of the joist and the timbers A Where the braces do not extend the full width of the post, they can be placed either flush with the outside of the building, as illustrated, or centrally on the timbers. The manner of placing the braces flush with the outside as illustrated has the advantage that whatever form of siding is used, it will be secured to both the posts and the braces, and will thus aid in stiffening the building.

50. Heavy Framings Without Cutting Joints. — Fig. 22 illustrates another system of framing which is to a large extent on the balloon-frame order, for it has no mortiseand-tenon joints and very little framing of any kind. The sill timbers a and b may be notched together and secured by means of drift bolts ; the posts c may be slightly notched into the timbers b and secured by drift bolts. The braces g are simply pieces of plank cut and spiked as shown in the

Surface Arrangements

illustration, the pieces h being spiked against the posts or sills in such a manner as to fill the space between the ends of the braces. Where the floor joists vi rest upon the sill it may ' be necessary to use a narrower piece between the braces, as at 2, or to saw notches into the piece z, into which the joist can be placed. The timbers d and e for the upper

Fig. 22

floor of the mill are fastened together and to the posts f and c by slight notching and drift bolting. In some cases no notching is done, the posts simply being sawed off square and secured by large spikes or drift bolts. The floor in this style of construction is laid exactly as in the previous case and is shown at k.

At Reduction Works

51. — Where it is necessary to join sills or large horizontal timbers on top of posts, corbels may be used, as shown in Fig. 23.

The corbel a is bolted to the two timbers b and and the post d is usually tenoned into the corbel, while the post a may have a wide tenon and be secured to the timbers b and c by means of two treenails or pins. By making the corbels fairly long, they will help support the timbers b and <f, thus relieving them of a portion of the weight they would otherwise have to carry. On this account, corbels are sometimes used whether joints occur above the corbels or not.

The Stamp Mile

52. The gold stamp mill has been described in Ore Dressing and Milling. Fig. 24 shows one, in cross-section, situated on a side hill, for the convenience of receiving its ore by tram cars that dump over a grizzly. The ore that passes over the grizzly passes to a crushing floor and thence through a crusher to the ore bin, where it again mingles with the ore that passed through the grizzly. From the ore bin, the ore passes through a gate into an automatic ore feeder, which supplies a stamp battery composed of five stamps. The crushed ore passes from the stamp-battery mortar, as pulp, over amalgamating plates; then from the launder at the foot of the plate it passes to concentrating tables, an arrangement not used with free-milling ores, but quite natural with a rather refractory ore.

At Reduction Works

U

Fig. 25 shows an elevation of a. double g'old stamp mill, by which it is meant that the stamps are placed

in double rows, m order to , increase the number of stamps and lessen the lengths of single-line shafting, a are the

Fig.

At Reduction Works

comparatively level, double stamp mills are preferable to single stamp mills.

Silver stamp mills do not differ from gold stamp mills until after the pulp reaches the settling tanks. At this point the excess of water is drained and the thick pulp shoveled in regular charges into amalgamating pans, in which it is worked several hours in order to obtain as much of the precious metals in the form of amalgam as possible. The pan digestion being completed, the contents are run into large settlers, where the quicksilver, in the form of amalgam, and the free mercury settle to the bottom. The quicksilver and amalgam are separated from the rest of the pulp by a trap and the amalgam is finally separated from impurities by treatment in the clean-up pan.

A wet-crushing silver mill, such as has just been described, is shown in Fig. In the figure, a is the grizzly, the rock crusher, c the ore bin, d the ore gate, e the automatic ore feeder, f the stamp battery, g the plate, Ji the launder leading from the amalgamating plate to the settling tank /, m the amalgamating pan, 7i the settling pan, and o the mercury and amalgam trap.

54. Dry Criisliiiig Silver Mill. — This character of mill is intended for refractory ores that must be roasted prior to amalgamation. It differs from the mill described by having a drier placed between the ore crusher and the stamps, which in this instance crush dry. The ore may be run in chutes, lined with sheet iron, from the driers to the automatic feeder. The pulverized product from the stamps is carried by conveyers to bucket elevators, which discharge into the hopper of the roasting furnace. The ore in the furnace is desulphurized and also chloridized by the addition of salt, thus preparing the pulp for what is known as barrel amalgamation. In Fig. 27 is shown a dry-crushing silver mill, in which a are the grizzlies, b the crusher, c the ore bin, d the drier, f the stamp battery of 20 stamps, g the screw cdnveyers, one on each side of the battery, the mortar

./Vt Reduction Works

in this case being of the double discharge pattern ; h the furnace, i the amalgamating pans, j the settlers.

At some dry-crushing mills the ore is crushed by rolls and properly sized for tlie furnace means of rotary screens. One great objection to this method is the dust created by the several crush ings and resizings, but it produces an increased amount of fine ore in a given time, though at the expense of power.

55 C o n e e n t r a t i n g mills are for preparing ores for s u b s e q u e n t metallurgical treatment. They may be divided into two classes: One reduces the bulk by the elimination of worthless gangue; the other not only does this, but it also separates those minerals that have different specific gravities, for instance, zinc and g a 1 c n a . U sually water is the separating medium, but lately a form of air jig has been quite successful as a

Surface Arrangements

§ 24

c()iu\*nl rator. 4'h('. ('oiuanitratinj;* mill has so

thorotijiy in DrrssiuX' 4/////;/i,'' that it will not taken up luuat in

In h'ig*. 28 is shown a plant in tint JopHtp Missouri, (listriih. In a iTw in this or<' litdd it is to a hillside, so as to lak( advantajt'(' of jTavity, hut in most instances the oia is hoist('d from tlu'. shaft hij;*h enougii in the head-hous<' permit its heini* tramnuul diretdiy to the top of tlui mill, whii'h is fnxjiumtly 1 story hi'lu .hVom the erusluu' room in tlu toj) of tlu mill tin* ore downwards durini;* the various optu'ations of concentration until i t rcatdics the j'roiuul (loor. In ('.ase coiu!(mtratioi is md. com|)lete, it is ait'nin elevated to the top of tlu building and again through tlu various proo esscs by g'ravity* In. mills, portions of tin* ori is elevated three four tim<'S, but as a rule two or '(i times is sutliciimt aftm* it once descxmds from the crusher romiL When (Concentration has been

§24- AT REDUCTION WORIvvS 39

the tuilino's g-o to the wastes pile. Water is iuniished irom llu' creeks, when they arc accessible, and Iroin niiiuis when no ether source is available; in the lattiu* ('ast' tht water is impounded and used over and (jver ai>'ain, it lunussary. Centrifug'al [)umps raise the water from ponds to tardvs situaUul in the building's or elevated on towers. Ch'eek or well water when not contaminated with sulphates of linui is used for steam production. In many instances, howenau*, spriiyg water and city water must be used and in (cxtrenuj cases water is hauled in barrels several miles to tlu'. mill.

In the head-houses are seen at the extreme

rig'ht and Ud't, the mill // being* locatcid between them and, as shown, ('onnected by trestles c over which tram cars movci. In the foreground is seen a waste rock pile d; to the extreme left, part of an ore pile c. The tower back of the mill, c'ontains an elevator for raising* the tailings, which arc'. run out .automaticudly fi*om it on s})ecial cars, whose traedvS arc; supporU;d by the skeleton towers The tailings art; automatic'ally dumped, as shown by the white pile 2 back of the; liead-housc on the left. Between the rock pile in the; foreground and the mill is a settling pond, which may be distinguish;d only by the bank ;//, whic:h serves to im{)ound the water and slimes. The slimes that accumulate are sometimes (piite rich in mineral and are treated in separate mills, ('allcul inills. In Fig, 29 is shown a

group of mills and head-frames at the Mastin diggings, ( hileua-J oplin district.

57. Dievniors and C-onveyors. — Since the introduction of elevating and conveying machinery, the handling of material at reduction works has been revolutionized. The c'ost of handling material has been lessened, thereby increasing profits and making it possible to treat and handle larger cpiantities of materiaL

Surface Arrangements

The term' conveying and hoisting machinery includes bucket conveyers, wire-rope tramways, elevated railways, cableways, and cantilever cranes. These various devices have numerous modifications to condition them to the work to be performed. The introduction of this class of machinery has made it possible to place reduction works on ground that would at one time have been considered unfit for the purpose. Occasionally mills are seen almost entirely hemmed in by waste rock and tailing piles, so that it looks as if they must be covered over if work is to be continued. This state of affairs is now past, owing to the improved machinery for handling the waste tailings and rock. Conveying and hoisting machinery is used inside the mills as well as outside; moreover, its flexibility permits it to be applied to new and various conditions that are continually arising.

58. Cliain-belt coiiTeyers were probably the first in the field and have held their own in most instances against new devices intended in a measure to supersede them.

Fig. 30

In Fig. 30 is shown a Jeffrey 'ore conveyer as used at a cyanide-process mill for filling the vats. The carriers are so

§ U At Reduction Works 41

arranged that they may dump their buckets into any vat or any particular place in the vat. Bucket elevators for unloading vats and delivering tailings to conveyers that run to the dump are also made. The same elevators can be made to deliver into tram cars. Where the roasting furnace is separated from the mill, conveyers may be used to move the ore to the place it is to be treated, thus avoiding the

Fig. 31

otherwise necessary haulage, loading, and unloading. Fig. 31 shows a refuse conveyer much used in the anthracite fields of Pennsylvania, where it handles veritable mountains of refuse termed culm.

59 Hoisting and conveying machinery is sometimes used at smelters for the purposes of conveying ore, fuel, and flux to the furnaces. Fig. 32 shows an elevator building containing a bucket elevator, which is 60 feet between

wSURFACE ARRANGEMENTS

§

centers and intended to lift granulated slag and water to a height that will permit them to flow to the dump or deliver them to the dump pile through troughs carrying scraper

Pig. 33

conveyers. Sufficient water, with a slight inclination, will move the slag along and a considerable saving may be effected by getting rid of furnace slag in this way. Besides,

Pig. 33

44 Surface Arrangements §M

the necessity of a slag dumping* ground is obviated if there is a good-sized stream or river to dump into.

In the figure, is a hole leading to a sump which answers as an elevator boot and is kept flushed with water. The slag is dumped into this well from slag carts b and, becoming granulated, is carried by the elevator buckets c to the bucket discharge in the house d. The water and slag that the buckets discharge flow together down the trough c to the slag pile or river, as the case may be.

60 . The Ligerwood cableways have two towers, between which is stretched a wire rope. In Fig. 33, the poles a will answer for towers. Upon the wire rope b a carriage c runs back and forth, carrying with it a bucket d. The traveling

Pig. 34

rope e is attached to one end of a bucket and passes over a pulley f and then between the span and over another pulley leading to the engine room. It is given two or three

At Reduction Works

turns around the drum, then passes up to another. pulley, and so on back to the bucket, making virtually an endless rope. This rope moves the carriage back and forth on the cable b.

The carriage shown in Fig 34, is another arrangement for dumping refuse. The carriage runs on rope there is a fall rope which is connected with the engine at one end and with the bucket e at the other. The fall rope passes half around pulley then half around the block d, up to pulley and then, as shown, down to the bucket at e. The traveling rope moves the carriage back and forth to the dump, and when it is desired to dump holds it there. The rope c then comes into play and tilts the bucket, allowing the contents to fall on the dump pile. The bucket is next pulled into its normal position and moved back for more refuse by the traveling rope moving the carriage a.

In Fig. 35 is shown another carriage which travels down an inclined rope b. The loads are raised by means of the fall

Surface Arrangements

§24

rope which also acts as a haul rope and brings them from a lower level to a higher.

61. Rope Sag Calculations. — While a cable may be made sufficiently taut to answer as a runway for the carriage and car, nevertheless there will be a certain amount of deflection that must not be neglected, otherwise it will

Fig. 36

necessitate the shortening of the span or require the tower away from the mill to be the higher. This deflection can be estimated if the length of the span, the weight of the rope, and the weight of the load are known. In Fig. 36 let j span or the distance A B between supports ;

in and n arms in feet into which span is divided by a vertical through required point of deflection ;r, m representing arm corresponding to loaded side ;

y — horizontal distance from load to support corresponding with in'; w weight of the rope per foot in pounds; g load ; t tension;

h — required deflection at any point

Deflection due to rope alone :

It — - at X, or-- at center of span.

Deflection due to load alone :

r guy zy

h at X, or at center of span.

If j/ -, A at Xj or at center of span.

At Reduction Works

it f Ji — — — at or at center of span. t s '% t

Total deflection ;

n — — at or ' , - at center of span.

If -S' Pin+gn ws"- +

at JT, or —

at center of

span.

, Winns gmn

it y Jl — — — at or

fy t s

ws 2 gin

87 '

If tension is required for a given deflection, transpose / and Jl in the above formulas. (Trenton Iron Company I)

Weight Oe Wire Rope

62. To obtain the weight per foot of wire rope of any diameter,

let zv — weight per foot ;

D diameter of the rope in inches.

Then

For ordinary wire rope with hemp core, w For ordinary wire rope with hemp core, w For patent locked -iron rope, w

For solid round bar, zo

The Hunt Elevator And Automatic Railwax

63. The limit elevator and automatic railway is operated by gravity, needing neither steam, horse, nor manual power. It requires power, however, to raise material to the car. This car, Fig. 37, is arranged to run on a railway track, as shown, and is discharged by means of the tripping block 2 , placed on the track where the load is to be dumped. The sides are not fastened to the car, but to each other, so that if one is unfastened both are. The load is thus evenly discharged and without danger of overturning the car, although

1.57 1.7 2.62

Surface Arrangements

§24

the gauge is but 22 inches. The bottom of the car has a center ridge so arranged that the material runs entirely out

when the sides are unfastened. The bearings on some of these cars are so made that the car runs around a 30-foot radius with comparative ease.

Fig. 38

64 . In Fig. 38 is shown the car at work removing coal from a boat to the dump pile, a is the trolley and automatic

Surface Arrangements

bucket that raises the tailings to the dump car above the car is a pocket c into which the bucket dumps automatically. From the pocket the ore slides directly into the car, which runs down a narrow-gauge track laid upon the trestle, to the dumping ground /, after it has been loaded and started by the man at the loading chute.

The chief peculiarity consists in storing the energy that the loaded car creates in descending the inclined track, so as to return the car to the loading chute after it has emptied itself. This is accomplished by the car picking up a cable which is attached to the weight g in its journey down the incline. The car raises the weight g only a limited distance, and that by a gradual movement, so as to prevent strains on the various parts as far as possible. When the car has dumped, the weight falling gives the car sufficient momentum to run up the plane to the chute, after which it is ready to receive another load. This arrangement is probably best suited to unloading vessels or cars, but may, by having movable towers, be applied to almost any character of loading and unloading.

65, Another method of disposing of tailings is shown in Fig. 39. This arrangement is shown in the cantilever crane, that when used on the Chicago drainage canal had a length of 353 feet over all and a maximum height of 80 feet for a dump. It was arranged to travel upon a truck whose wheel base was 37 feet. This truck ran upon a portable track, so that the entire structure could be moved with comparative ease. The cars or buckets could be loaded, then raised by a fall rope, and hoisted up the incline to be dumped automatically. With such an arrangement, a dump pile 80 feet high could be made and continued indefinitely along the canal.

66, Centrifng'al pumps are sometime used to raise the exhausted tailings from leaching vats. When used for this purpose, care must be taken to give the bends of the tail-pipes and the delivery pipes as large a radius as possible

M

At Reduction Works

to prevent friction. When the pump shown in Fig. 40 is stationary, so as to require long suction pipes, the latter must be air-tight and given a gentle rise towards the pump. They will elevate 50 feet to a launder large quantities of sludge, but are probably most efficient when elevating about 20 feet. As the construction of centrifugal pumps was fully described in Hydratilics and Hydraulic Machinery Part 4, only the work that can be done by them will be discussed here. Ordinarily a pulp 'consisting of 2 pounds of water to 1 pound of solid matter can be handled by a centrifugal pump when there is but a slight head to be

Fig. 40

overcome. This quantity of water must be augmented, as the elevation is increased above 10 feet, to from 3 to 10 pounds of water to 1 of mineral matter. It is to be understood that mineral matter of a coarse nature is more difficult to raise than fine but that there is a limit to the density of the sludge for good work, no matter how fine the sands may be, and this limit is its mobility. The necessity for having the foot-valve of a centrifugal pump well submerged in the sludge arises from the fact that the tailings sand will not otherwise enter the tail-pipe and the pump will draw only water.

The objections to the use of centrifugal pumps for this purpose is the large quantity of material that must be

62 SURFACE ARRANCxEMENTS § 24

handled to attain the desired end, the hindi power required to drive them, and their low efficiency. Their advantage, however, is that they are capable of handling very large quantities of material in a comparatively short time. Their use effects a saving in time, but a loss of power.

67. In South Africa the ore is stamped and amalgamated previous to cyaniding. The tailings from the stamp mills are conducted in launders to large tailing wliocls, sometimes 60 feet in diameter, which lift the tailings in buckets on their inside peripheries and dump them into a' launder leading to the leaching vats.

At Reduction Works

m the wheel, and raised by the wheel so as to dump into the launder c. The boxes are V-shaped spitzkasten to catch any sulphides in the tailings. Large wheels for handling tailings were probably first used at the Lake Superior Copper Mines, although the idea no doubt originated in Cornwall, England.

68. The Cliiiiese immp shown in Fig. 42 may be used for handling tailings and water with probably more economy than any of the wheels, pumps, or other devices so far described, provided it is intended to charge the lixiviation vats by launders and with tailings.

These pumps require comparatively little power to run them.

Smelting Plants

69 . General Considerations. — Sm e 1 1 i n g plants must be located with reference, first, to water supply; next, fuel and flux; and lastly, ore.

Furnacescannot be worked without water ; it is needed

for boilers and the mod-

. , . Fig. 42

ern economical furnaces,

which are constructed with water-jackets. The supply of water required for furnaces will be found in Art. 88. Fuel and flux are both necessary items and furnaces should be located so as to have, if possible, railroad transportation for these materials; or if that be not possible, to have good wagon roads at least. Custom smelters are usually situated where cheap fuel can be obtained, for, as the ore must come

Surface Arrangements

§24

to them, they care naught for the location of mines. This is due to the fact that the miners must pay the freight on ore and the smelters the freight on the coal and the flux. Private smelting plants can in some instances afford to pay more freight per ton for fuel than for ore, from the fact that much more ore is handled at the furnace than fuel.

70* The ideal furnace location is one where water is abundant and where fuel, flux, and ore can be delivered with a short haul into the stock piles without extra handling. This, of course, requires a system of railway tracks and trestles connecting with the main haulage railways. It was customary in the past and is so yet in some instances to regard 36- and 42-inch gauge tracks as the proper width for furnace delivery tracks. This idea is erroneous, for it is possible to put in a standard railroad track which has a gauge of 4 feet inches where it is possible to put in the above. If narrower than standard-gauge tracks are used, it causes the rehandling of the fuel and sometimes of the flux and ore. The idea prevailed in the past pretty generally that curves on narrow-gauge roads could be given more curvature, so as to take up less room. The wheel base on two-wheel mine cars of any size is nearly the same as for four-wheel trucks on narrow-gauge cars and the latter is about the same as on broad-gauge cars. The small difference in curvature required for standard-gauge car trucks will not take up much more room than ordinary mine cars, such as would be used to transport ore to the furnace a mile or more.

71- Ideal furnace locations are not always obtainable; but whenever it is possible, locations should be picked where nearby ground will furnish a dumping place for slag. Granulating slag and having it floated away by some stream has been spoken of as an economical method of getting rid of a troublesome furnace product. When such locations are not convenient, but water is abundant, granulating slag and then floating it, as described in Art. 59, to some depression in the ground near by is to be recommended. Again,

§34

At Reduction Works

the molten slag may be granulated and elevated to dump piles by some of the methods described for the disposal of tailings. Lastly, the slag may be removed to dumping grounds in a molten condition and used for filling up depressions in the surface, if convenient, and if not, for creating slag heaps.

73. Arrangement of Fnrnace Plants. — The location of the plant having been determined, the next step is the arrangement of buildings, stock piles, and furnace flues with reference to the furnaces and roasters.

The furnaces and roasters must be located with regard to the quantity of ore that may be delivered and also to any possible increase that may occur to double the output in the future. The actual number of furnaces erected should not exceed the output of the mines, but space should be left for additional furnaces and stock piles, should the ore come in greater abundance in the future than the original furnaces can manage.

Flues, water, and steam supply should be considered with an eye to an increase in the number of furnaces, and should in each case, whether an increase occurs or not, be in excess of the actual requirements of the plant. The reasons for this are obvious : For instance, if one boiler should give out, there would be too little steam ; or if an auxiliary engine of some kind were needed, there would be too little steam power ; or, again, in case a furnace were to work badly, it might require an additional blast pressure to cure the trouble ; finally, it is economy to have an overabundance of steam supply, rather than a shortage or just enough. The same method of reasoning will apply to keeping an additional furnace in the plant, even though it is idle three-quarters of the time, also reserve engine power, blowers, and water supply. The first cost in such cases will be greater, but it is, nevertheless, cheaper in the long run, because fixed charges about furnaces do not decrease when something goes temporarily wrong, and in furnace work it is a steady output that keeps down expenses.

5G SURFACP: ARRANGEMENTvS §24

73. While the arrangement of a furnace plant will depend somewhat on the location, it will also depend in detail on the metallurgist in charge. Details of requirements will necessarily vary, but general details will not.

74. If the plant is to be permanent, the buildings should be of stone, brick, and iron ; but if it is a temporary affair, the buildings may be constructed of light framing and rough boards. Sometimes corrugated iron is used for sidings, but it is not as durable as wood; neither will an iron or steel roof last as long as a first-clas? shingle roof. But a smaller fire risk, which even then is large, ofttimes causes the management to favor the metal construction.

In case the capital necessary for a large furnace plant is not available and must be derived from profits, any temporary structure will suffice; but while the building may be ramshackle, the furnace and appliances should be first class in every respect. The general plan in this latter case should be thought out as if the structures and entire plant were to be erected at once.

75. Tlie Ore Beds. — The space for ore beds must be large enough to permit one to be building while the other is being drawn upon to supply the furnaces. Two beds, each containing 3,000 tons of ore, are sometimes planned. In such cases all the furnaces in blast are fed from one pile while the other is being made up. In case furnaces are running on one character of ore, ore beds are not necessary, ordinary stock piles being sufficient ; but wheix furnaces are receiving ore from many mines, bedding piles are a necessity. Sulphides and carbonate ores are kept in separate piles, the former usually being dumped in close proximity to the roasting furnaces, from which they are transported to the bedding floor and spread. The carbonate and oxidized ores are dumped nearer the furnace and, consequently, the bedding floor. The beds should be protected from snow and heavy 1 'ains.

At Reduction Works

The manner in which the ores arrive is of much importance ; that is, whether they come in large or small consignments, at regular or irregular intervals. In case all ores arrive during the summer months, large stock piles may be necessary; this calls for a series of railroad trestles and tracks, if the furnaces are to run throughout the year. In cae the ore comes in small quantities at regular intervals,, the various ores can be carried, unless they need roasting, direct to the bedding pile.

The question of room for the bedding floor requires particular attention only when various ores are to be mixed and smelted.

76. Lioeation of Smelting Plant. — Whenever a hillside is decided upon for a furnace site, the questions to be considered are, can one terrace be obtained for the ore supply, another for the products of the furnace, and yet another for the slag dump ? With insuflicient fall, the main stress will be laid on having at least two terraces — one for the ore floor and one for the furnace floor. In case but one terrace is possible, preference should be given to the slag dump ; the trestles should then be raised to such a height that the stock piles or at least the fuel piles will be above the top of the furnace. In some instances the furnaces must be situated on perfectly level ground, which requires elevators for nearly every product going into and coming out of the furnace.

77. Handling Materials. — The principal aim at smelting plants should be to simplify the handling of materials, both loading and unloading, as well as charging. This is done by handling the materials to be moved from one place to another in such a manner that they will fall from and into trucks by gravity. The runways between loading and unloading points should not be long, but still they should not be so short as to crowd and prevent the free movement of apparatus. Tracks, elevators, and scrapper lines should all be arranged with this object in view.

Surface Arrangements

§ 24

Water Supply Eor Stamp Mills

78 . Water for stamp mills should be free from grease and should contain as little mine water as possible, if that is acid, as is usually the case. The average quantity of water used per stamp per hour in California is about 190 gallons and about 2,600 gallons per ton of ore crushed. The average fineness to which this ore is crushed is 40 mesh. The average quantity of water used per stamp per hour in Colorado is given as 125 gallons, and for each ton of ore stamped about 2,400 gallons. Clayey ore requires more water than harder ores, while the degree of fineness to which the product is crushed also decides the quantity of water that must be used.

79 . Toss of Water. — The water mentioned in the above cases is that necessary for stamping where the water runs to waste. For instance, in Colorado a 20-stamp mill would, if each stamp pulverized 1 ton of ore, consume 48,000 gallons per day. It is possible by means of settling ponds to economize in the use of water and use the water over and over again in the battery, less the loss from absorption by the ore and evaporation. The absorption by ore is considered to be 66 gallons per ton for hard quartz and 96 gallons per ton for soft ores. The total loss of water will in no case be less than 25 per cent.

80 . Water for tlie Combination Process. — In this instance, the stamps will require as much water as formerly, say, from 125 to 190 gallons per stamp per hour. Each amalgamating pan will require at least 125 gallons per hour and each settler 65 gallons per hour. These quantities are subject to variations and may be more or less, according to the character of the ore being milled.

81 . Xieacliing* processes require water in considerable quantities. Even though the weak and exhausted solutions are used over and over again by being standardized, the fact remains that a 25-per-cent, loss from absorption and evaporation will occur under the most favorable circumstances, On the Rand, South Africa, it is estimated that

at reduction works 59

the tailings after cyaniding retain 30 gallons of water per ton, while the "slimes" contain 240 gallons per ton. The Russell process of lixiviation requires from GO to 75 gallons of water per ton of ore.

8. All leaching processes require an easy-flowing pulp and then water for wash purposes. In case the ore being treated is silicious and comparatively coarse, not more than 80 gallons per ton will be required, while if heavy concentrates are being treated, probably as high as 120 gallons per ton may be required. The quantity of water required for the treatment of any ore should be determined by experimental tests, and the quantity used will not vary much from those tests.

83 . In the eliloriiiation process, assuming the quantity of water found to be 80 gallons per ton for lixiviating and to make an easy-flowing pulp, the wash water required will be 140 gallons per ton of ore. This quantity of water is for barrel chlorination and is double that required for tank chlorination, where only enough water is required at first to make the ore wet and porous. The wash water in both cases will probably be the same, from 80 to 140 gallons per ton of ore.

84 . Water for the cyanide process varies according to the character of ore being treated. The quantity of water for weak and strong solutions, also for wash water, will probably approach 240 gallons per ton of ore treated, assuming 80 gallons sufficient to form an easy-flowing pulp. For each additional wash 80 gallons per ton of ore in the vat will be required, all tons being those of 2,000 pounds.

85 . Water for Concentrators. — The quantity of water that will be necessary for concentrating machines, such as Frue vanners, will be 1.5 gallons per minute of clear water and from 1.5 to 3 gallons per minute with the pulp from the stamps. The quantity of water required for jigs is variously given and the same for classifiers.

N. 71//.

Surface Arrangements

The only true way to determine the quantity for any ore is to experiment with the ore and machines. Where there is an unlimited water supply, not much attention need be given to the water that concentrators of this class require, but where water is to be bought, it is good policy to ascertain the quantity required at some mill in the vicinity, or if none, to experiment before jumping at conclusions in regard to the machines.

Water For Smeltikg Peakts

86. This subject is of considerable importance for modern smelting practice, as the quantity of water recpiired by a water- jacketed smelting plant depends on local conditions. The direct object in supplying water to a waterjacket furnace is to prevent the jacket from burning, if of wrought iron or steel, or from cracking if of cast iron. The water should be discharged from the jackets below the boiling point, in order to prevent steam generating in the jackets. No more coke should be supplied to the furnace than is sufficient to smelt the flux and charge, otherwise more water will be required per minute to reduce the surplus heat to normal. The water supply will also depend on the blast pressure, for if that is too strong the heat will be moved upwards towards the tnnncL hcad and less water may be needed. Again, if the ore smelted is of such a nature that it clings to the sides and forms a coating, unless this coating is a good conductor of heat less water will be required than if the jacket walls were perfectly clean.

87. Hoffman states that a furnace 86 in. x 92 in. at the tuyeres, making a silicious calcareous slag, requires under normal conditions 11 gallons of water per minute. This figures out 15,840 gallons per day, which is considerably less than furnace builders recommend. It must be understood that the water supply here spoken of is for silver-lead furnaces.

In blowing-in and blowing-out furnaces tlie quantity of water must be increased. Mr. Hoffman suggests doubling

At Reduction Works

the regular quantity, or 22 gallons per minute. It must be explained in this connection that the jackets during* the warming-up period or "blowing-in " are subjected to a very strong, hot coke fire with little ore to reduce the heat, and that just before the furnace is stopped or " blown out" ore is not charged into it, but coke, until all the material in the furnace has been drawn off, when the furnace is allowed to gradually cool off.

88. Peters, in his book on "Modern Copper Smelting," gives the following quantities of water for furnaces properly managed :

Hearth Area. Square Feet

Water per Hour Normal Running. Gallons

1,100

1,300

1,500

1,800

2,000

2,200

The above table is, of course, assuming that the water is delivered to the furnace at 60° F. Should the temperature of the water delivered to the furnace be 120° instead of 60°, the quantity of water must be increased, for a cool jacket depends on the temperature or heat units per pound of water, and hence the quantity of water necessary for the furnace. Assuming the water left the furnace at 200° F., the heat units per pound of such water will be 168.7. If the water is delivered at 60° F., the number of heat units it will contain will amount to 28.12; the furnace will then have

G2 Arrangements At Reduction Works § 24

been cooled 140.58 heat units by each pound of water. Sup posing the water to have entered at 120" F., it will contain 88.00 heat units per pound, and the water leaving the furnace with 168,7 heat units will have cooled but 80.64 heat units. Referring now to the Peters table, it will be found that if 460 gallons of water were required for the furnace when it was delivered at 60° F., 800 gallons will be required when the water delivered is 120° F. to accomplish the same cooling effect.

Ore Dressing And Milijng

(Part 1)

Ore Dressing

ORE DRESSIISTG IVIACHmERY

Rock Breakers

1 . Classification, — Under the heading of ore dressing are included those processes by which the miner prepares bis ore for milling, smelting, or sale. The old method of cobbing ore is practiced in the mine and on the dump, consequently does not enter into this discussion, since it is presumed that ore has been assorted before it reaches the mill. There are two classes of machines used in ore dressing: one class break coarse material and are called rock crushers ; the other class crush fine material, that is, pieces smaller than

inch in diameter, and are termed fine crushers.

It is true fine crushers sometimes approach pulverizers in their product, but it is not usual or desirable to pulverize ore to impalpable powder for milling purposes, consequently pulverizers are seldom needed.

3, RocK BieaRers. — Ore as it reaches the mill is usually in lumps varying in weight from a few ounces to many pounds. To reduce the size so that fine crushers can work it finer, it is usual to employ a class of machines known as rock breakers. These machines are limited to two classes, termed jaw and gyratory crushers, on account of the movement of their parts in performing work.

§ 25

For notice o£ copyright, see page immediately following the title page.

Ore Dressing And Milling

§ 25

3, Blake Cinisher. — The Blake crusher shown in Fiij;. 1 has the entire frame cast in one piece. The swinging jaw b is pivoted at //, so that its greatest movement is

Fig. 1

at the discharge opening. At each full throw of the jaw the discharge opening varies, thereby causing a corresponding*

Ore Dressing And Milling

§ 25

variation in the size of the product, and the only control the operator can have over the latter is to set the jaw by means of the wedge a' and setscrew jt, thus fixing the maximum size of rock that shall pass through the opening. The pulley r, which travels at the rate of from 225 to 250 revolutions per minute, operates an eccentric on the main shaft As the pitman d is raised and lowered with each revolution of the eccentric, the toggle plates p impart a reciprocating motion to the jaw b. The steel bearings e are lubricated through the tubes t. A tension rod vi connects the jaw b with a coiled steel or rubber spring, insuring a rapid return of the jaw after each stroke. The jaw plates shown at c are usually cast with vertical corrugations, in order to give them a larger crushing area and better bite. The stationary jaw k, against which the plate c is held by the check plates /, is bedded in zinc inch thick, directly against the frame.

Table I

THE BliAKE CRUSHERS

Size of

Receiving Capacity

Trade Number of Crusher

Weight of Heaviest Piece

Total "Weight

Extreme Dimensions

Proper Speed

Horsepower Required

Breadth

Height

Inches

Lb.

Ft. In.

Ft.

In.

Ft.

In.

s X li

Laboratory

Ox 3

One

1,200

Three

1,800

4,900

O

Five

3,800

8,000

Eight

7,400

15,500

Nine

7,800

16,000

Ten

5,300

11,200

Ten

8,100

18,300

Sixteen

14,200

33,000

Twenty

14,200

35,000

4 Ore Dressing And Milling S 25

Bodge Criislier. — The Dodge crusher shown in Fig. 2 has an eccentric c on the shaft g which gives a rocking motion to the lever /. The lever is cast in one piece with the

Fig. 2

jaw b and pivoted on the shaft h. The stationary jaw d, as in the Blake crusher, is cast as part of the frame. The jaw shaft rests in sliding boxes, provided with setscrews to regulate

Table H

The Dodge Crtjsiier

Size of Jaw

Opening.

Inches

Diameter of Pulleys.

Inches

Width

of

Belt , Used.

Inches

Horse-

power

Required

No. Tons per Hour.

Nut Size

1 Weight

lulions

Corn-

Minute

2 to 4

375 1,300

4 to 8

1 to 3

335 4,300

8 to 12

2 to 5

330 5,000

4 10 X 16

12 to 18

5 to 8

300 13,000

the size of the product. The setscrews should always be set tight, with locknuts set, while crushing. Packing strips p are used between the frame and the shaft boxes to take up

Ore Dressing And Milling

§ 25

wear. The shaft makes from 200 to 850 revolutions per minute. This crusher has the discharge opening near the center of motion of the movable jaw, hence the variation in the discharge opening is so slight that a practically uniform product is obtained. This feature of the Dodge crusher has led to its adoption as an intermediate crusher between the coarse and the fine crushers in large mills. The vibration caused by jaw crushers is sometimes destructive to the building. They should be therefore set on timbers or foundations independent of the rest of the framework, especially where there are leaching tanks; otherwise they may throb in unison with the crushers.

5. The capacity of the Blake crusher is much larger, on account of the variable discharge opening, which reduces the tendency of the ore to clog; but at the same time this render's crushing to any degree of fineness and uniformity impossible. The Blake crusher is therefore used where the

Fig. 4

§25

Ore Dressing And Milling

amount of material handled is large, while the Dodg*e type is limited to mills of moderate capacity, or to secondary breaking in large mills, as previously mentioned.

6. Roll- Jaw Rock Breaker. — In the Schranz rock breaker, shown in section in Fig. 3, the motion, instead of being reciprocating, as in the types previously described, is rocking. The same principle is employed in the Sturtevant roll-jaw eruslier. The advantages are that owing to the peculiar motion of the movable jaw the material is crushed with comparative ease and the product is approximately sized. The disadvantages are that as the discharge is small there is danger of blocking the machine and their capacity is limited.

7. Multiple -Jaw Crusliers. — For special work, multiple-jaw crushers are used. The movable jaw in such machines consists of a number of segments, each of which is worked independently. They are but little used in gold or silver milling, but give a uniform product which makes them desirable crushers for lean magnetic iron and zincblende ores, especially where magnetic concentration is practiced and it is not desirable to break the mineral crystals.

8. Gyratory crusliers have a large capacity and continuous action. They consist of a heavy cast-iron frame, the upper portion of which is a conical hopper /z, shown in Fig. 4. The hopper is lined with a ring of steel, against which the material is crushed by a conical steel head c which fits on a shaft g, the bottom of which is placed in an eccentric bearing so that the amount of space between the hopper and head varies as the head rotates. The material is dumped into the receiving hopper and when crushed passes downwards through the machine and out the spout shown in the cut.

The advantages of this style are that the large pieces of material are received at the top of the jaws, where the motion is the least and the leverage or purchase greatest, thus reducing the work necessary in this heavy preliminary crushing. The relative movement between the crushing members is maximum at the discharge opening, but the

8 Ore Dressing And Milling § 25

amount of this movement is so small that the pi'odiict is approximately sized. The fact that the maximum movement is at the point of discharge assures a free discharge. There is practically no jerking imparted to the building by the gyratory crushers. Their capacity is very great and besides a large-sized material may be dumped into the liopper 1l directly from the cars. For small capacity, a gyratory crusher is more expensive than a large crusher. Sometimes where there are large amounts of material to be crushed, a large gyratory crusher is used as a secondary cruslier after jaw crushers of the Blake pattern, the product from the jaw crushers ranging from 3- to G-inch cubes and that from the gyratory crushers from 1- to 2.-inch cubes.

These crushers are made of a capacity varying from 1 ton to 200 tons per hour. They have not come into general use in the West, owing to prejudice against any new and untried machinery, but wherever they have been introduced they have been found to answer as well as any.

fie'critsiihstg machine rt

9 . Rolls. — The degree of fineness to which

crushing is carried depends upon the screen the ore particles are to pass through. Ore is said to be fine crushed when the particles will pass through a one-half- inch-diameter screen and from this point to an impalpable powder.

The principal representative of this type of machine is the ordinary Cornish roll, having a fairly wide face and rather small diameter. The' diameter of these rolls was kept down for a number of years on account of the fact that cast-iron shelves properly chilled couldn't be obtained enlarge sizes and were expensive and hard to handle. With the advent of the rolled-steel shells it became possible to employ lax"ger diameters and higher speeds. Rolls of the Cornish type vary from 4-inch face and 9-mch diameter to IC-inch face and 42-inch diameter. The distinctive feature of the Cornish roll is a comparatively wide face, compared with the diameter, and a rather slow peripheral speed. Many of the

Ore Dressing And Milling

modern Cornish rolls are provided with rolled-steel shells, especially when employed for very fine crushing, owing to the fact that these shells are of a more uniform texture, work more evenly, and can be worn much finer before being discarded and can be trued up with less difficulty than is the case when chilled iron is employed. The large-diameter rolls with narrow faces are usually employed as finishing rolls, while the rough rolls have wider faces and are not intended for fine crushing, but to crush the product coming from the rock breakers.

10 . Tlieoretical Capacity of Rolls. — The amount of material that can pass between any pair of rolls is proportional to the number of square feet of working surface passing per minute. Hence, the capacity of wide rolls may be increased by increasing the speed, or the

same capacity may be obtained by reducing the face and increasing the speed. If the distance between the contact points of the material with the rolls be Fig. 5, the distance between the crushing face of the rolls be re', the angle be as shown in the figure, and A be the radius of

the roll, then ,-r-7- r. The amount of material Q

' 2 (1 — cos a)

that may be crushed by a pair of rolls in a given time is equal to one-fourth of a layer whose length is the circumference of a I'oll multiplied by the number of revolutions, whose width is the length of the rolls, and whose thickness is equal to the space or distance between the rolls.

// TT 77 / 'iO

Or, 0 — , where d diameter of rolls; 3.14;

Ore Dressing And Milling

§25

7 number of revolutions in a given time; length of rolls; "zc/ space between rolls; and one-fourth coefficient to allow for the irregular feeding of the haaterial and the space between the pieces. The Denver Engineering Works Company gives the following formulas for the capacity of crushing rolls:

T tons per hour ;

R — revolutions per minute;

5 mesh of screen in inches.

For 14" X 27" rolls, T 7.725 R 5; for 16" X 36" rolls, 11.775 RS\ for 12" X 20" rolls, :m RS. The pressure on the bearings necessary to crush ore depends directly on the face width, and hence if the capacity can be kept the same and the face width decreased, it is evident that there will be less pressure on the bearings and less loss in friction.

11. Holls. — The difficulty experienced with the old Cornish rolls in keeping the bearings cool when crushing hard rock led to the introduction of high-speed, narrow-faced rolls for certain classes of work. One objection to running small diameter rolls fast is that the larger pieces of ore have a tendency to dance off the face of the rolls rather than be crushed, while the bite is better when the speed is slower. The advantages of high-speed, narrowfaced rolls are greater capacity for a given bearing pressure, less loss of power from friction, and less dancing of the ore on the roll face, owing to the fact that the angle of approach between the surface of large rolls is more acute than with rolls of a smaller diameter.

High-speed, large-diameter I'olls will also handle coarser material and hence make a greater range of reduction than small-diameter rolls.

One disadvantage of high-speed rolls is the tendency to hammer and pulverize the ore, and this feature, with brittle minerals, may be a detriment. In general, it may be stated that for crushing to any definite size with the least possible production of very fine material, rolls are the best form of

Ore Dressing And Milling

machinery on the market. For crushing brittle material fine, quite slow speeds may give the best results. The accompanying table gives some facts in regard to the crushing-roll practice of several manufacturers, data having been taken from information furnished by them.

Table Iii

Name

Size.

Inches

Peripheral Speed in

Ft, pel- Min.

Sprinij Pressure in Lb. per 111 of

Face Width

Chai acter of Rolls

Frazer & Chalmers. . .

600-1,500

4,000 for hard quartz

Cornish

Frazer & Chalmers. . .

2,200-2,800

Narrow face, high speed

Earle C. Bacon

1,000

Cornish

Sturtevant Mill Co..

27 X ' 5

3,000

Special Centrifugal

E. P. Allis Co

26 X U

Cornish

E. P. Allis Co

1,885

Narrow face,

high speed

4, 000 for hard

Iron Works

rock

4, 800 for very

Cornish

hard rock

Denver Engineering Works Co

to

350-1,000

3,500,500

Cornish

Gates Iron Works. . .

2,266-8,383

Cornish

Ore Dressing And Milling

13. Oonstriietioii of Rolls. — The ordinary form of crushing rolls, shown in Fig. G, consists of two cylinders set in a strong cast-iron frame, with their axes parallel and in the same horizontal plane. One roll has fixed journal bearings, cast as a part of the frame. The other roll has adjustable bearings arranged to slide horizontally and take

up wear and also prevent rupture

of the machine in case some very hard substance, such as a hammer head, should accidentally get into the ore and pass into the rolls. The adjustable roll is held in position by rods which terminate in some safety device, so that in case of such an accident as mentioned, the pressure will force the rolls apart and allow the obstruction to pass through. This was formerly done by means of cast-iron breaking cups," used as washers for the adjusting rods.

When the pressure became excess-

I ive, the cups would break and allow the roll to slide back.

The cups were inexpensive, but whenever one broke the rolls had to be stopped, and frequently the

whole mill had to wait until it could be replaced.

Springs placed in frames /, shown in Fig. 7, compressed, say, to %o000 pounds and then fastened in place by means of nuts on the rods r, so that they cannot relax, are now generally used for crushing rolls by placing them as washers on the rods that draw the

adjustable roll into position. The roll is thus held in place by a force of 50,000 pounds (35,000 pounds on each side).

N. M. JlL-6

Ore Dressing And Milling

In the rolls the axes of the rolls are not in the same horizontal plane, but are in a plane inclined at an angle of about 45°, so that the upper roll practically rests upon the lower while the machine is in operation. The upper roll is an idler, being driven by friction from the lower roll. It is set in a sliding bearing and is held in position by its weight alone, no rods or springs being used except in the small sizes, in which the weight of the roll is not sufficient to perform the crushing satisfactorily. Rolls of this type are only adapted to crush fine ore particles, as they would have to be built inconveniently heavy in order to get weight enough in the idler roll to satisfactorily crush coarse ore.

One of the latest improvements in the construction of rolls dispenses with the sliding journal, its place being taken

by the swinging pillow-blocks h, shown in Fig. 8, which are pivoted at p and carry the adjustable roll in fixed bearings g,

1 3. P o w e r of Rolls. — The power for driving may lib applied to the shafts of either roll or to the shafts of both rolls. With geared rolls it is almost invariably divided between the two, but with belt-driven rolls it is frequently applied to the fixed roll, and the adjustable roll is driven by friction. It is preferable, however, to have both rolls driven directly, particularly when crushing comparatively coarse material, as this reduces the slip and also avoids the heavy blow resulting from the sudden starting of the idler roU while the driving roll is at full speed— something

Ore Dressing And Milling

that is very apt to happen when idler rolls become stopped by clogging. When both rolls are driven directly by belts, the pulleys are placed on opposite sides of the machine, one being driven by a crossed belt and the other by an open belt from the same countershaft. This practice secures the reversed motions.

14. The wear on roll faces is necessarily very great, so that for economy they are made as interchangeable chillediron or wrought-steel shells which fit on over a turned core, usually tapered. When the roll shells become so worn that they can no longer be used for fine crushing, they may be used on the coarse crushing rolls until worn out, or the faces maybe turned down and the rolls readjusted. With chilled-iron shells the amount which can be thus removed is limited to the depth of the chilling, but steel shells may be turned down until they are f of an inch thick; below this they will not be safe. When a shell is worn out, it should be removed and replaced by a new one.

15 . Application of Rolls. — While rolls may be used for any purpose for which approximate sizing is necessary, by far their largest application is in preparing ore for the jigs, lixiviation, and roasting. As before mentioned, they are frequently used, instead of the jaw crusher, for secondary crushing, even when uniformity is not a desideratum, or for roasting. Dry-crushing rolls must be completely covered, or housed," with wood or sheet iron, to confine the dust. It is usual in the case of dry crushing for lixiviation to calcine the ore, as that makes it more friable and prevents ore sticking to the face of the rolls. The product is better for crushing and also leaching, but the dust is correspondingly increased.

16 . Dimensions of Ilili-Speed Rolls. — In Fig. 9 is shown an elevation of a high-speed roll, with a section of the housing a thrown back to show the roll b. This, it will be seen, is a narrow roll. The rigid roll, being the main driver, is supplied with two heavy pulleys c of large diameter, while the adjustable roll receives its motion from a smaller

Ore Dressing And Milling

§25

pulley d. A test of 56'" X 8" rolls showed that they could easily crush SOO tons of hard granite in 24 hours, when material was fed at l|--inch ring and rolls set inch apart;

of the product in this case, 10 per cent, ran over i inch 90 per cent, passed -inch screen, 60 per cent, through -inch, 37 per cent, through -iich, 27 per cent, through iV -inch, and 12 per cent, through a 30-mesh screen.

"s-VEIGHTS, DIMEKSIONS, ETC., EOB HIGII-SPEEB EOEJLS

Size of Rolls in Inches

Size of Large Pulleys in Inches

Size of Small Pulleys in Inches

Revolutions per Minute

Total Weight Roll Complete Without Housing

i Additional Weight for

1 Housing

15,500 28,000 1

1,550 , 2,400

17, Speed of CimsWng Bolls. — The most advisable speeds for different sizes of crushing rolls, to give the most satisfactory product and best economy in operation, are based on data furnished by extensive investigation assuming that every size of ore particle fed to the roll should have a certain speed.

Ore Dressing And Milling

gas

18. Theoretical Capacity of Crushing? Ilolls. — Fig. 10 is a diagram which shows the theoretical capacity in cubic feet and tons of ore crushed per hour for 14" X 37" crush ing rolls, through screens from 4 to 40 mesh. Referring to the diagram, suppose it be desired to find the cubic feet of ore which will be crushed to 10 mesh when the rolls are running 90 revolutions per minute. Find the number 90 in the left-hand column of figures marked ' ' Revolutions of roll shells per minute;'' follow the horiz'ontal line, passing

22 18 Mssii of Screen to wh/ch Ore is crushed.

Fig. 10

through 90 out to the point of intersection with the diagonal line marked 10 in the row of figures marked Mesh of screen to which ore is crushed." This point of intersection lies nearest the vertical line marked 200 in the line for '' Cubic feet of ore crushed per hour." Therefore the theoretical capacity for 90 revolutions and crushing to 10 mesh in 14 X 27 rolls is 200 cubic feet per hour.

A second row of figures at the bottom of the diagram gives the '' Tons of ore crushed per hour/' assuming

IR ORE DREvSvSING AND MILLING § 25

100 pounds to equal 1 cubic foot. The actual capacity for several sizes of rolls will be about 60 per cent, of the amounts shown in the diagram.

The Gravity Stamp Battery

19 , Stamps are under certain circumstances the best of the fine-crushing machines. On account of their simplicity of construction and operation, they are peculiarly adapted to enterprises in which the seat of operations is remote from railway facilities, while their comparative cheapness recommends them for operations of a temporary nature or where capital is limited. As a means of saving the mineral values of ore by amalgamation and concentration, they give a fair efficiency, varying with the character of the ore, the completeness of the plant, and the skill of the operator. The relation between their efficiency and that of a smelting or leaching process, in conjunction with the freight rates, frequently determines whether the ore is to be treated on the spot or shipped to the nearest smelter or reduction works.

In the case of gold-bearing sulphides, the combination treatment is commonly employed. The oi'e, if it contains any free gold, is crushed under the stamps, and any gold which may be freed from the pyrite is caught and held by the amalgamated plates of the battery. The rest of the crushed ore is passed over suitable apparatus, by means of which the light gangue materials are washed away and the heavier sulphides left, thus greatly reducing the ore in bulk, while retaining practically all the values. The sulphides, or concentrates," are then shipped to the nearest smelter or reduction works for the final treatment.

30 . Stamp Slices. — The stamp consists of a wroughtiron or steel "stem," 10 to 14 feet long, a cast-iron " head " or "boss," and a chilled-iron or steel "shoe." The two ends of the stem are interchangeable, being slightly tapered to form blunt conical wedges, one of which fits tightly into a hole in the upper end of the boss. In the bottom of the boss

ORE DRESvSING AND MILLING

is another hole, similar to that in the top, but larger, into which the conical shank of the shoe fits loosely, being wedged in by strips of wood for wet crushing, or by iron for dry work. In the latter case, the head is strengthened by a ring shrunk around the bottom. The construction of the shoe is shown in Fig. 12- and constitutes the striking surface of the stamp. The

Pig. 11

Pig. 12

Fig. 13

shoe and stem may be released from the head by means of drift keys driven in through the slots k, Fig. 11.

31 . Dies. — The stationary die upon which the stamp falls is of chilled iron or steel, with a striking surface whose diameter is equal to that of the shoe and a rectangular or octagonal base, Fig. 13.

The latter is preferable and is now almost universally used, as it saves iron and renders the removal of the dies easier when ''cleaning up" the battery or making repairs. For dry crushing, round dies are used — preferably with lugs cast on the bottom, as shown in Fig. 14. By giving these dies a quarter turn in the recess in which they

20 ORE DREvSSINCt AND MILLlNO §2.

rest, the lug;s catch and bind them firmly in position. Dies are also made with wedge-shaped biases, dovetailing into a socket in the mortar. There seems to be considerable difference concerning the merits of steel and cast iron for stamp shoes and dies. Some millmen use chrome or manganese steel; others prefer cast-iron dies and steel sh(;es; still others condemn this practice and state that iron should not be used in conjunction with steel. In com])etitive trials cast-iron dies and shoes crushed 1,(>80 tons, while chromesteel shoes and dies crushed 1(),800 tons. The wear on iron shoes and dies is between 2 and 3 pounds per ton of ore crushed in California, while in Colorado it is about 1 pound. When the boss is worn down to within 1 inch of the footplate, it is to be replaced. Dies wear more slowly than shoes because protected by a layer of 2 or 3 inches of pulp, but they are replaced more frequently, because of their small height. A small loss of metal in a die renders it unfit for use. '' Dies should all be renewed at the same time ; if one breaks, one worn as much as the others should take its place in preference to a new die.

33, Cams. — The stamp is raised by means of a doublearmed cam keyed to a revolving shaft and catching under a

tappet fastened to the stamp terri. The curve of the cam is laid off as the involute of a circle, the radius of which is equal to the horizontal distance between the centers of the

ORE DREvSvSING AND MILLING

cam shaft and the stamp obtained by attaching to circular disk of the proper diameter one end of a piece of string, which is then carried around the circumference of the disk to a point b diametrically opposite the first point. By holding the disk still and unwinding the string, at the same time keeping it taut, the point b will trace the line b which represents the lifting curve of the cam. In practice, however, the curve is slightly flattened at the end. Fig. 16 shows right- and left-hand cams, the upper cam being constructed to revolve to the right, the lower one to the left.

Cams are usually fastened fitted steel keys. There are

stem. The curve may be any point Fig. 15, of a

O O

L_V

Fig. 16

to the cam shaft by carefully usually two key seats in each shaft, one-third of the circumference of the shaft apart, though formerly one seat sufficed for all the cams of a set. A later form of fastening is a taper bushing fastened to the shaft by means of pins, as in the Blanton cam, Fig; 17. The shaft has corresponding holes bored in it to receive the pins from

Fig. 17

ORE DREvSSING AND MILLTNCi

the bushings. Another device is shown in Fig. 18. The bushings tighten automatically and give a more even bearing than the ordinary key. They possess the further advantage of being much easier to adjust and remove than the old form ; in fact, an entire set of cams with this fastening can be

removed and replaced in the same length of time that is frequently required for the removal of a single cam with the old fastening.

The cam shaft, usually of turned wrought iron or mild steel, is driven by a belt from a countershaft. The cam-shaft pulley is of wood, on an iron hub, while the countershaft pulley is iron. The countershaft pulley is either fixed or has a friction clutch. The belt is kept taut by ordinary tightening pulleys.

As the cam shaft revolves, the cam lifts the stamp gradually, and at the same time gives the tappet a slight rotary movement, so that the stamp does not fall in the same place on the die twice in succession. When the stamp is raised to the end of the stroke, or '' drop," the cam slips from under the tappet, and the stamp, weighing from 000 to 1,000 pounds, drops.

The new Blanton cam is shown in Fig. 19 and the cam shaft in Fig. 20. This arrangement permits the cam to be secured to the shaft without keys or loose parts of any kind.

The cam is notched to fit the shaft, which has ten taper-

faces made with mathematical precision, thus insuring a proper fit and division of the cams on the shaft.

§ 25 ORE DREvSvSING AND MILLING 23

It is only necessary to place the cams on the shaft in their respective positions, and tighten on the taper faces sufficiently to hold them in position until put in operation, when

Fig, 20

they will tighten themselves further on the shaft in proportion to the amount of work they have to do.

23. Tappet. — The tappet, shown in section in Fig. 21, is made of cast iron, bored true inside, and is fixed to the stem by means of a gib which is pressed firmly against

Pig. 21 fig. 22

the stem by the keys shown in Fig. 22. The wear on the stamp and die is met by raising the tappet so that the drop is kept constant. Each time the cam raises the tappet it imparts two motions — namely, a lifting or vertical and a rotary or horizontal. This rotary motion is due to the cam's curve sliding upon the plane surface of the tappet. It is very important to have this slight horizontal turn given to the stamp.

Ore Dressing And Milling

§25

When a battery is liim up*" for cleaning up or repairs, the stamps are supported by hardwood Angers," shown in Fig. 24, tipped with iron, which are fixed in sockets on a jack-shaft, usually at the back of the battery. There is one jack-shaft to each battery of stamps. The fingers are moved independently of one another by a handle in the back. They hold the tappet high enough to clear the cam in its revolution. To hang a stamp, a tapering stick faced with iron is inserted between the cam and the tappet, raising the latter so that the finger can be slipped under.

24 , Arrangement of Stamps. — Stamps are usually arranged in batteries of five each, working in a heavy castiron mortar, in the bottom of which are placed the dies. Two- and three-stamp batteries are made for prospecting purposes; while steam and pneumatic stamps have only one stamp to the mortar. There are few permanent stamp mills of less than 10 stamps. The number of stamps at mills is usually increased in multiples of 10, the batteries being set in pairs, with the middle battery post common to the frames of both. The cams of both batteries are fixed on the same shaft, which is supported in the middle by a bearing box on the common post. Instead of the double shaft, two short shafts are sometimes used with one common bearing.

25 . Tlie Frame. — The frame in which the stamps move is usually made of well-seasoned heavy timbers bolted tightly together. Iron frames are also made, but they are not to be recommended where timber is available and the battery is intended to stand any length of time, as the jarring works the bolts and rivets loose and crystallizes the iron of the frames, rendering it brittle and apt to break. They are very convenient, however, when a portable battery is desired.

Wood frames are of two general types: the A frame and the knee frame. The old A frame is, however, being rapidly superseded by the knee frame. In the A frame, shown in Fig. 23, the countershaft is usually placed on the battery sills, almost directly under the cam shaft, and the belt runs

§35

Ore Dressing And Milling

nearly vertical. With the knee frame shown in Fig. 34 the countershaft may be set level with the cam shaft, if desired, the tightener dispensed with, and each battery driven independently by a friction-clutch pulley on the countershaft.

so that it may be stopped and started without affecting the rest. The knees support a floor convenient in hanging up stamps and in inspecting and repairing the batteries. The frames are braced either on the back or front, according as the countershaft is set behind or in front of the battery.

Fig.

Ore Dressing And Milling

Fig. 25 shows a back-knee frame with the countershaft on the battery sills.

The battery posts are usually of 12'' X 24" timbers with their lower ends framed into the 12" X 12" sills. They are

bound together by cross timbers, of which there are four sets, as shown, the upper two being used as supports for the guide timbers, while the two lower ones act as binders for the battery blocks. The frames are strongly braced for both tension and compression.

36. Tlie Oiiides. — The stamps are directed in their fall by t;wo sets of guides bolted to the cross timbers of the battery frame. The lower set is generally about 18 inches above the top of the mortar, and the upper set about 7 feet higher. These guides are usually made entirely of wood, Fig. 26, though combination guides of

Ore Dressing And Milling

wood and iron shown in Figs. 27 and 2'8 present some advantages in the way of quick repairs and economy of timber, as scrap timber can be used for guide blocks, and the iron frame is practically imperishable. They also may have the friction along instead of across the grain, which increases the life of the block.

Iron guides have also been tried, but are not as satisfactory as wooden and combination guides.

Wooden guides for an ordinarv five-stamp battery are usually made of 4" X 12' hardwood plank, and consist of two timbers bolted face to face, with grooves on the inner faces for the passage of the stamp stems. The grooves are not cut hemispherical, but are left slightly shallow, with thin strips of wood placed between the two timbers, so that as the grooves wear deeper lost

Fig. 25

Pig. 20

Pig. 27

motion may be taken up by removal of the strips and by then drawing the timbers towards each other. The wear

Ore Dressing And Milling

§25

may be still further taken up by planing off the inner faces of the blocks. The guide blocks fit in between the battery posts and are held firmly against the back of the cross timber by bolts passing through all three timbers. In case repairs are needed, the back block can be removed by simply taking off the nuts and drawing it off.

Guides should be kept well lubricated with a paste of graphite and linseed oil, care being taken that none of the lubricant gets into the mortar, as it would interfere seriously with the recovery of the gold.

2'7, Sectional guides of both wood and iron are also made, as shown in Fig. 28. This construction permits of

Pig. 28

their adjustment, so that lost motion caused by the stamp stem may be taken up as desired. In Fig. 28 2 :) the guide blocks b are held in place by two clamping plates c and d, which in turn are held against the girth a by the bolts c and nuts The back plates c are dipped rearwardly to fit snugly into the girth beam, so that there will be no lost motion. When it is desired to change a stamp guide or take up lost motion, the plate c is loosened and the block b is either taken out or moved forwards with shimmers. If the guide is badly worn, it is discarded and a new one put

§ 25 ORE DREvSSING AND MILLING 29

in its place ; if only slightly worn, it is shimmered to lit snugly.

Siiig'le-JDiscliare Mortar. — In Fig. 29 there are two styles of mortars shown in cross-section. In shape they resemble cast-iron troughs. The ore is fed into a slot / at the back, and the crushed ore finds its exit through the screen in the front of the mortar, bn to an apron plate or into collecting troughs called launders. The left-hand

Fig. 29

mortar is arranged for inside amalgamation, both at the front and back, while the right-hand mortar in the figure is arranged for amalgamation on the screen side only. The chief difference between them is in the feeding arrangement. The back amalgamating plate, being put in a recess, is protected from the falling rock as it is fed into the mortar. There are many styles of mortars, some high and some low discharge, some with straight-screen fronts and others leaning outwards, as shown. Each style has an advocate,

N. ill ///.—/

Ore Dressing And Milling

because that style may be particularly adapted to the work in hand; but the best mortars are built to meet the circumstances of high and low speed, inside and outside amalgamation, high and low drop, also convenience, and all these particulars cannot be embodied in one mortar,

29 . Double-Discharge Mortars. — In Fig. 30 {a) and {b) two double-discharge mortars are shoAvn, Such mortars are used where dry crushing is practiced — that is, no water enters the mortar to assist in washing the ore through the screen. For wet crushing they might increase the product where the ore was coarse, but it would be done at the expense of screens.

30 . Feeding Ore to the Battery. — To obtain the maximum crushing duty of a battery, feeding should be carefully regulated and kept just short of the point where the striking of metal on metal is noticeable. If it is allowed to get below this, breakage is apt to follow the uncushioned fall of the stamp upon the die, and even if no break occurs,

Fig. 30

energy will be wasted to no useful purpose. On the other hand, if too much ore is kept on the dies, the cushioning is so great as to lessen the crushing efficiency of the stamp,

§25

Ore Dressing And Milling

the drop is shortened, and the packing of ore and pulp around the stamp between strokes causes an appreciable suction at the beginning of the up stroke. Usually in wet crushing, 2 to 21 inches of ore on the dies is sufficient.

31. Splash Boards. — The top of the mortar is covered tightly by "splash boards," which are two boards resting on narrow ledges /, /, Fig. 29, cast on the inside of the mortar, their edges meeting in a close joint down the middle of the mortar, with semicircular notches in each board for the passage of the stamp stems. These splash boards are best set slanting slightly towards the center, as in Fig. 31, with

their edges beveled to make tight joints. The feed opening has a piece of canvas hung inside of it, which prevents the splash from coming in there, and another strip of canvas is hung in the upper part of the discharge opening above the screen frame, which prevents the pulp from splashing out there and at the same time permits the insertion of the hand to examine the condition of the inside amalgam and to

Ore Dressing And Milling

§25

clean the screens when they become clogged. A board is sometimes used instead of canvas over the discharge opening.

32 . The height of discharge of a mortar is the perpendicular distance between the tops of the dies and the bottom of the screen. It may vary from 4 inches to 16 inches in the different types of mortars. To regulate the height of discharge, chuck blocks" Fig. 32, usually of wood, are placed between the bottom of the discharge opening of the mortar and the bottom of the screen frame. As the dies wear away, these blocks may be replaced by lower ones, thus

Fig. 32 Fig. 33

keeping the height of discharge nearly constant. In amalgamating mortars, the front amalgamated plates are fastened to the chuck blocks shown in Figs. 32 and 33, while the back copper plates are under the lip mentioned. An iron chuck block made of |-inch iron plate is considered by some to be better than wood, as the copper plate is then If inches farther away from the shoes, and the scouring action is consequently less, allowing the retention of more amalgam on

ORE DREvSSING AND MILLING

35

the plates. The copper plates are riveted to the iron with rivets, which will not rust out, and the iron itself will last as long as the battery.

33. Sectional Mortal's. — In some localities where transportation even by wagon is impracticable, mortars are cast in sections, no part weighing over 300 pounds. The sections are carefully planed and bolted together, as shown in Fig. 34. The upper part of the mortar is built up of wrought-iron or steel plates and angle irons.

Fig. 34

34. Jjined Mortars. — Mortars are subjected to a splash as each stamp falls and are gradually scoured by this action until in time they become too thin or too wide to work well. For this reason they are sometimes fitted with steel linings, which when worn may be replaced without heavy expense.

35. Screens. — The maximum size of the crushed product of a stamp battery is regulated by the size of the mesh of the discharge screens, and the efficiency of the battery depends to a considerable extent upon the care exercised in the selection of the screens. The size to be used on any ore should be determined by experimental '' mill runs," with different mesh screens.

Ore Dressing And Milling

Screens made from steel or brass wire cloth are suited only to wide mortars with a high discharge; in such cases, they allow a freer passage of the pulp, which would be apt to clog in punched screens. In low-discharge, narrow mortars, punched screens are used almost entirely, as the increased force of the splash overcomes the tendency of the screens to clog, and they wear much longer than would wire screens, which, even in the wide, high-discharge mortars, last on an average only about one week. A Russia-iron screen is supposed to last at least two weeks before it cracks. Five per cent, of aluminum in copper makes an alloy termed aluminum bronze that lasts several times as long as Russia iron and does not crack, and when the holes are worn large, the screen can be remelted and made over.

Pig. 35

Screens are punched either with slots or round holes as shown in Figs. 35 and 3G. The slot screens are generally considered the better form, with the slots running diagonally. Screens are also made with the slots in vertical or horizontal rows, parallel and alternating, and in ''burred'* or " burr-slot " screens; the rough edge is left on the inside of the slot, and can be closed slightly as the slot wears by striking with a mallet- The slots are generally made about inch long and are punched as small as 60-mesh needle, which is equivalent to .014 of an inch.

§ 25 Ore Dressing- And Milling 35

36. Screen Frames. — Screens are fastened to rectangular wooden frames, which fit into the discharge opening of the mortars. For wire screens, the frame is divided by inch strips into three or four panels to prevent bulging, and diagonal-slot screens are strengthened by a mid rib. A patented screen is also manufactured, with the screen fitting into the frame in sections which are independently removable. This effects a considerable saving in screen cloth, as the bottom sections, which wear out faster than the top, may be renewed independently of the top panels, whereas in the single screen, the life of the bottom is the life of the

Fig. 3G

screen. The frame is placed in the mortar with the screen on the inside, and is usually held in place by one horizontal and two or four vertical keys, Fig. 31, the frame being protected from the keys by strips of sheet iron screwed to it.

37 . Ortlei* of Drop. — While the cams of a battery are all on one shaft, they are set so that the stamps fall one after another, usually in the following order: 1-4-2-5-3, supposing the stamps to be numbered consecutively from left to right, looking at the battery from the front. This order is preserved with a twofold object: first, to have the " swash" from side to side, so that each stamp as it falls will drive the ore and pulp under the one which drops next in order; and second, to distribute the pressure as evenly as possible and avoid any tendency towards rocking.

Sb

Ore Dressing And Milling

§25

With a double battery (10 stamps), the scheme of dropping is extended to the whole ten stamps. Thus, starting at the left as before and numbering the stamps consecutively from 1 to 10 , the order of drop would be as follows: 1-8-4-10-2- 7 5 9 3 0 . This order is sometimes varied according to the fancy of the designer or superintendent, but the idea is always to balance the strains throughout the battery, and have the pulp flow from the mortar in a series of waves.

38, Battery Blocks. — On account of the continuous and heavy jar to which the mortar is subjected, the timbers on which it rests must be very strong and have a very solid foundation. The usual arrangement of the foundation timbers or '' battery block " is as follows : A trench is excavated down to solid strata, if such can be found at a reasonable depth, but in any case at least 7 feet deep and about 3 feet larger both ways than the battery block. In the bottom is laid a horizontal timber, or mudsill, of the same surface dimensions as the horizontal section of the battery block; this is carefully leveled and tamped and upon it are stood the vertical timbers which make up the battery block. The contact sui'faces should be carefully planed (not sawed) to a perfect bearing. In very loose ground, where a good natural foundation cannot be had, it is customary either to sink piles or to put in an artificial foundation of concrete.

The battery block proper is made up of planed timbers bound firmly together by bolts. Modern practice favors the use of smaller timbers, or even 2 -inch plank, spiked together, with joints lapping, and held in place by horizontal binding timbers, which are fastened by transverse bolts. There are usually two sets of these binders, the upper set — made of 8 '' X 12"' timber — being usually just above the battery sills and framed into them, and the lower set — usually ma,de of 12' X 12"' timber — 3 or four feet lower down. When plank is used in building up the block, the two upper binders are put flush with the top of the block. When large timbers are used for the block, the lower binders are sometimes omitted.

Ore Dressing And Milling

§

Plank blocks were first built with the faces of the plank parallel to the short dimension of the block, but this arrangement has given way to that in which the width of the plank runs lengthwise of the block (see Fig. 25), as this form is more convenient for repairs, it being only necessary, in replacing a block, to open up the front of the block and raise the mortar, when the plank can be torn out with picks. Plank blocks are much cheaper than the old form of block, made up of two or three huge timbers, which were clumsy to handle, awkward to work, and, moreover, expensive and difficult to obtain in clear lumber.

39 . AncLor and Tie-Bolts. — The battery block being in position, the tie-bolts are screwed up until there can be absolutely no play between the various members. Dirt is then thrown in around the bottom and tamped lightly to hold the block in position and the top is planed perfectly level. The holes for the anchor bolts are then bored and the pockets for the nuts chiseled out. A sheet of rubber

inch thick is usually next laid on the block, with holes for the passage of the anchor bolts ; the latter are put in and the mortar is set in place and bolted firmly down. The pit is then filled and firmly tamped.

The anchor bolts, 3|- to 4 feet long and inches in diameter, are usually threaded at both ends, pockets being cut in the block for the lower nuts. The lower ends are sometimes turned into rings instead of being threaded, and 2-inch iron bars running horizontally through the block from side to side pass through these eyes, each bar serving for two anchor bolts on opposite sides.

40 . In erecting a battery, all bearing surfaces should be planed perfectly true and level, and the centers of gravity of both mortars and stamps should be as nearly as possible in the same vertical plane as that of the battery block, to avoid rocking, which would tend to throw the battery out of line and cause the parts to wear unevenly, greatly shortening their life.

Ore Dressing And Milling

§ 25

Stkam

41 . Construction and Capacity. — Besides the ordinary ''gravity-stamp" battery just described, there are in use

Fig. 37

Steam stamps. In the steam stamp, the stamp stem is the piston rod of a piston moving in a vertical steam cylinder. The stamp is raised by the steam entering through

40 ORE DREvSvSlNO AND MILLING § 25

the lower ports, and when it reaches the top of the stroke the bottom exhaust opens suddenly and at the same instant live steam is admitted through the upper ports, adding impetus to the fall of the stamp. The valve mechanism is such that the piston descends under full boiler pressure of steam, while the pressure on the up stroke may be regulated at will. Steam stamps dispense with the use of a mortar block (battery block), the anvil on which the mortar is built being set on spring timbers, as shown in Fig. 37, with 1 inch of rubber between the timbers and the anvil ; or the anvil may be set on a solid cast-iron anvil block, Fig. 38. It is claimed by the manufacturers of the latter style that it increases the crushing capacity; but while this is probably so, it also increases the jar on the frame, and consequently the tendency to crystallize and break.

The crushing capacity of these stamps is enormous, one steam stamp with a 15-inch piston and a 30-inch stroke doing the work of 50 or 60 ordinary gravity stamps. At present the chief use of steam stamps is in milling free copper ores, but they bid fair to be an important factor in gold milling, as these stamps with their heavy blow, strange as it may seem, make less slimes than the ordinary gravity stamps — a great consideration in crushing before concentration.

4 : 2 Tremain Steam Stamp. — For prospecting or for small mines where an extensive stamp battery is not required, or where it is simply desired to develop the mine and test its value, the Tremain steam stamp has come into very general use. It consists of two steam cylinders, which operate two stamps, the heads of which are located in a single mortar, as shown in Fig. 39. In the Tremain steam stamp the pistons are turned from solid metal on the stamp stems, so that the area exposed to the steam on the up stroke is smaller than the area exposed to the steam on the down stroke by an amount equal to the area of the piston rod. This area on the up stroke is simply a ring about f of an inch wide around the piston rod. Live steam is employed in raising the pistons, it being introduced on the under side,

Ore Dressing And Milling

and, acting on the small area, raises the pistons and stamps, which weigh only about 300 pounds each. As one piston ascends, it moves a valve which admits live steam to the bottom of the other piston and vice versa, so that the valves of one stamp are operated by the piston of the other in such a manner that the stamps always alternate, one ascending as the other descends. After the steam has raised the stamp, a passage is opened which allows it to expand around, and acting on the greater area of the top of the piston, it urges the stamp down very much more rapidly than it would fall by gravity, so that the blow actually struck is equal to that of an 800- or 1,000-pound stamp. After the steam has urged the piston down, an exhaust valve is opened and the steam exhausts into the atmosphere as the stamp ascends.

On account of the fact that these stamps are operated positively by steam, they can be run at a very much more rapid rate than ordinary gravity stamps, it being possible to use a speed of 00 or more drops per minute for each stamp, and hence the crushing power is very much increased.

Some of the advantages of this style of steam stamp are that it is comparatively light and portable and requires no extensive foundation. The stamp can be run by steam from the same boiler which runs the hoisting engine and mine pump, so that it does away with the necessity of an extra engine or separate motor for operating the stamp iqil}. The capacity of a two-stamp battery on average

Ore Dressing And Milling

ore is greater than that of an ordinary five-stamp gravity battery, and in some cases mines have been operated for a considerable period with Tremain stamps only. In case it is found desirable to move the mill from one location to another, the battery can be taken up and transported with as great ease as either the boiler or engine, and this portable feature is one of the most important factors in the selection of this style of mill. Where the Tremain stamp is used without a crusher, it will be necessary to break up the coarse rock with sledges, but steam stamps can handle much coarser material than the gravity stamps. Owing to the fact that the Tremain stamp, like other steam stamps, produces less fine or slimed material, it is especially applicable for cases in which it is desirable to concentrate ores after they have been passed over the amalgamation plates.

43 . Pneumatic Stamps. — The style of stamp usually called by this name is not driven by compressed air, as its name would indicate, but usually consists of two stamps, the stems of which are attached to pistons of small diameter which work in pneumatic cylinders. These cylinders have a reciprocating up-and-down motion given to them by means of a crank-shaft, with which they are connected by means of ordinary connecting-rods. When one of the cylinders is raised, the air beneath the piston is compressed and so lifts the stem and stamp; similarly, on the downward stroke of the cylinder, the air above the piston is compressed and the stamp driven down more rapidly than it would have descended by gravity alone. The stamps are provided with a means for rotating them, so as to give better or more even wear to the shoes or dies. This style of stamp has been used principally for working the tin ores in Cornwall, and their output is from 20 to 30 tons per head per day, using a 36-mesh screen. The power required is usually about 25 H. P. per head. Like the steam stamps, these pneumatic stamps produce less slime than ordinary gravity stamps.

44. Quick and Slow Drop Stamps. — Stamp batteries for the treatment of gold ores are divided into two

Ore Dressing And Milling

§ 25

general classes, according to the kind of work for which they are intended. For ''free-milling" ores, in which the gold occurs native in comparatively good-sized grains, unassociated with pyrites, or " sulphurets," the California battery is used. The stamps in this type of machine are very heavy — 800 to 1,100 pounds — the average weight being about 950 pounds. They fall through only a short distance, from 4 to 8 inches being the average, but they make from 80 to 100 drops per minute. The mortar is built with a low discharge from 4 inches to 8 inches, and in the original form no battery plates (amalgamated copper plates placed inside the mortar) were used, all the gold saved being caught on the apron plates. In most modern batteries of this type, however, an effort is made to save part of the gold in the mortar.

When the discoveries of rich veins of gold-bearing pyrites were first made in Colorado, batteries of the California type were put to work on the ore. They gave very unsatisfactory results, however, compared with the assay value of the ore, and in the attempt to increase the saving, the millmen evolved the so-called Gilpin County battery. The weight of the stamp was gradually cut down and the drop lengthened, and the width and the height of 'discharge of the mortar were at the same time increased, finally resulting in the typical Gilpin County battery, with stamps averaging about 600 pounds in weight and falling through a height of from 16 to 20 inches into a roomy mortar with a high discharge (12 to 16 inches) and battery plates. The stamp battery averages about 30 drops per minute.

The reason for the change lies in the fact that in goldbearing pyrites the gold is in a very finely divided form, lying in the cleavage planes of the pyrite. In crushing this ore, a great deal of the gold is set free, but is so fine that it is apt to be floated away without coming in contact with the amalgamated plates. This fact was not known to the early millmen, and at first they put up mills designed to amalgamate all the gold on the apron plates, as they had been accustomed to do in milling free-gold ores, but cleanups failed to give the proportion of the assay value of the

44 Ore Dressing And Milling §

oie that they had anticipated so they concluded that Lhe gold must be combined very closely with the pyntesj and turned their attention to the concentration of the latter, with little or no attempt at amalgamation The results were still unsatisfactory, but the true condition of the gold at last became known to them, and to meet it they first put amalgamated plates into the mortar This was an improvement, but It was found that with quick drop and low discharge, the battery plates were not given time enough to satisfactorily perform their work, so, step by step, the weight of the stamp was diminished and the depth and width of the moitar increased, until the extreme type of high -drop battery was obtained As is usual in such cases, the changes were carried rather to exti ernes, and modem batteries are usually a compromise between the two old foims. About 75 per cent of the total gold saved by amalgamation is now caught in the battery The pyrites are concent! ated and shipped to the nearest smeller or reduction works for treatment, and at some large mills the tailings are leached by potassium cyanide solution

45* Cliiliaii Mills, — The term roller mills, as here used, comprises all the modern forms of crushing machinery in which the crushing is done by rollers moving m a horizontal pan These machines are constructed on the same general plan as the ancient Chilian which crushed oie by heavy stone rollers in a stone pan

The modern machine of this type is essentially a steel oi iron pan with a vertical spindle passing up through the center and bearing two or more radial aims, at the extremities of which are the rollers of chilled iron or steel The pan in the path of the rollers is also lined with chilled iron oi steel, furnishing a durable crushing face Crushing is done eithei wet or dry, the crushed pulp being discharged through screens in the sides of the pan.

Roller mills are of two general types those m which the taxis of the roller is a continuation of the radial arm, and

§ as ORE DRES.SING AND MILLINfi- 46

which may, for convenience, be caXi&d i dial toller milh, and those in which the roller i evolves on an independent vertical axis, which may be called centrifugal rollct nulls

46 . KacTial Kollei' Mile;. — home machincb of this type, the cential shaft is sLatioiiaiy and the pan i evolves, in otheis the loan is i evolved in a direction opposite that lu which the rollers aie moving

The rollers are usually cylindrical Moving as they do in a circular path, the outer end of each i oiler has to traverse a longer arc in the same time than points farther in towaids the central spindle, the distance any point traverses being proportional to its distance fiom the center of revolution The various points on the surface of a cylindrical roller all revolve at the same velocity about the axis of the roller, and the outer end of a horizontal cylindrical roller revolving about a vertical axis is obliged to slide in order to make up the difference between its linear velocity aiound its own axis and its velocity around the central vertical spindle The msidcend, on the other hand, probably drags somewhat, and at only one p;)int along the whole line of contact between the roller and the pan is the motion purely rolling As the idea of the machine is to crush entirely by rolling contact, this lb theoretically very bad, but practically it answers very well for all ordinal y work, the only seiioub objection being the uneven wear on the ciusliing faces But when it comes to crushing ore to a very fine, uniform size, as for leaching, the difficulty assumes a piactical aspect, the amount of sliming due to the slip of the i oilers being consideiable

This difficulty is somewhat overcome by making the i oilers and pan bottom conical, and having the apex of the cone angle of the rollers correspond with the apex of the cone of the bottom In this form every point on the roller along the line of contact with the pan moves with the same velocity as the corresponding point on the pan bottom, and consequently without slip In the vSehtanz mill the cential spindle is stationary and the pan bottom revolves, dnvnig the rollers by function Other ludial lollei mills use cylindrical rolls H U HI —8

Ore Dressing And Milling

§25

with a coin par atively nanow face, so that the difference in velocity between the two ends of the loll is veiy small, and there is consequently little slip

4:7* Model'll Clillian Mill* — As has been explained in the pievioiis article, the i dial roller mills do not crush the ore pnmai'ily, but both crush and trituiate, or grind, it Theie are certain cases in which this triturating action is veiy desirable, as, for instance, m the preparation of clay material, and

hence most, if not all, of the clay mills are of the Chilian mill type In Old Mexico and other locations whei e rich gold and silver ores occur in legions containing practically no water, it is often necessary to 1 educe the oie by the patio process, and for this puipose the material is ground in Chilian mills driven by mule power The mills were originally of the old crude type, but at present the greater number of them ai*e of improved construction, and many of them are similar to that illustrated in Fig. 40, which shows a plan and section of a Chilian mill provided with three 1 oilers Silver oies intended for pan amalga- FiG 40 mation may also be

§2.5

Ore Dressing And Milling

ground oi pulverized in Chilian in ills, and a large number of millmen prefer this style of machine, even foi use with gold ores which are to be amalgamated on plates outside of the machine They have also been employed lor the regnnduig of middlings in concentrating works, but aie not as well adapted tor this purpose as the Huntington mill The Chilian mill usually has but two crushing rolls or wheels.

Fig 41

48* Oontrifugal lioller Mills. — The second type of roller mill is termed centrifugal, because the crushing action IS largely due to the centrifugal action of the rollers, which are hung so that they are tree to swing outwaids in a radial direction, the rapid i evolution of the spindle causing the rollers to press against a hardened ring die in the side of the pan, immediately below the discharge screens, These mills are used for wet crushing and amalgamation, also for legnnding the intermediate products in concentration mills The type is repieseuted by the Huntington roller inili which

Ore Dressing And Milling

§25

will be debcnbed m clet.iil, as its success and extensive adoption ui gold nietalluigy have placed it upon a high level as a crushing and amalgamating machine

4:9i Mill,' — -The Huntington mi 11, shown

in Fig 41, consists of an iron pan, through the center of which passes the vertical shaft The arms a extend horizontally and terminate m a ring 1), from which the lolleis c are hung so as to swing freely in a radial direction on the yoke which is shown in detail m Fig 42 The rollers are also free to revolve on their own axes In fiont of each

roller is a sciaper /, which keeps the ore fi om packing The rollers are hung so that they clear the bottom of the pan by about an inch The central shaft, revolving at a rate of from 45 to 75 revolutions per minute, causes the rollers to swing outwards against the ring the pressure varying as the squaie of the speed of the mill The crushing power of the mill, being equal to the product of the pressuie and the velocity, consequently varies as the cube of the velocity, that is, twice the speed gives eight tunes the crushing power- The ore, which has been previously broken to inch in diameter or smaller, is fed into the hopper Jl on the side of the

Fig IS

§ 25 Ore Dressing And Midtjng 40

pan The rollers and scrapeis throw it out to the nm of the pan, and as fast as it is ciushecl it passes through the discharge screens and trough shown to the left of the figure on to the amalgamated plates, not shown in the figure The greater pai'tof the gold, on being liberated from thegangue, sinks to the bottom of the pan, and is caught there by the quicksilver, ot which there aie fiom 17 to 2n pounds The clearance of the rollers prevents then flouting '' the mercury, and at the same time they aie close enough to keep the surface of the met cury agitated and in the best possible condition for amalgamating

This mill IS pai ticularly adapted for the tieatment of brittle sulphide oies, which under the stamps are apt to shine

It IS made in three sizes, 3, o, and 6 feet in diameter, the second being the most commonly used A 5-foot mill will crush from 10 to 20 tons of rock m 24 hours, through a 30-inesh scieen, at an expenditure of from 10 to 12 horsepower The first cost of the mill is considerably less than for a stamp mill of the same capacity, and the parts are faiily cheap and easil}'' replaceable The power pei ton of ore crushed is much less than foi the stamp mill, the pulp is in better condition fox concent! ation, and the loss ol mercury is mmimized Its disadvantages are that the wear on the parts IS great — particularly on screens, dies, and shoes — and that the corroding action of the acid in some mine water and in decomposing pyritic ores soon renders the machine unfit for use This latter source of trouble is qlso piesent m the stamp battery, but the great thickness of its permanent parts makes it of less moment than m the Huntington mill

Huntington mills have an especial field in the regnnding of intermediate products m concentrating mills

50 . The KinRead Mill — This mill is simply a large automatic mortal -and-pestle arrangement The mill is shown in Fig 43 The uppei portion a of the spindle is vertical and revolves in fixed bearings directly over the center of the pan, which is shaped as shown in the figure.

ORE DRESvSING AND MILLING

g 25

The portion d of the spindle is connected to the lower end of a by the offset cranks:, and slants slightly inwards towards the bottom, wheie it connects with the shoe or pestle the offset giving the shoe a gyratory motion The machine IS driven by a belt on pulley r As the ore comes from the crusher it is fed into the hopper h The corrugations shown on the under side of this hopper cause the rock to be rapidly crushed to a small size, which can conveniently work down to the rim, where the final pulveiization IS accomplished The large screening area allows the pulp to escape as soon as it is sufficiently reduced, and this, together with the fact that the action of the machine is almost entirely a pinching action, reduces the sliming to a minimum The pulp passes into a discharge launder, which extends all round the mortar and carries all the pulp to an amalgamated plate m front All crushing parts of the machine are made of crucible steel and are replaceable

The feeding of the machine is entirely automatic , The hopper slide j is pulled out to allow the desired amount of ore to fail on to the feed plate/ This plate is connected through the gears g to the friction plate e Poi a short time, in every revolution of the mam spindle, the disk d

62 ORE DREvSvSING AND MILLING g 26

presses on c and i evolves it slightly aiound, this motion is tiaiismitted to /, which also turns ior a shoiL distance, the ore on the plate being pushed against a sheetuion guide and a portion of it forced off the plate each time the disk moves The shaft on which the disk e is fastened is hung fiom a springy to prevent any excessive pi assure between and c/, which would be apt to break one or the othei

51. Mill.— A somewhat similai mill, shown

m Fig 44, has the power applied to the central shaft from below by means of bevel gears The motion is transferred to a crushing shoe by an iron disk set eccentrically on the shaft and having on its penpher? two loose rollers, which as the shaft revolves are carried along with it, pressing against a ring on the inside of the shoe and causing it to oscillate without revolving

BATAa PUnVEIlIZiEKS

52 Ball Mill. — Ball pulverizers comprise all machines in which the crushing is done by means of balls rolling m a cylinder. The Kiupp ball mill is of the multipleball type and is used for dry grinding The machine consists of a revolving ciium made up of haid-steel plates, inside of which are a large number of chrome-steel balls of various sizes Outside of this drum are first a pci f orated sheetsteel cylinder and then a cylindrical sieve, concentric with the crushing drum and i evolving with it The whole is housed carefully with sheet iron, with an offtake for dust at the top and a discharge funnel at the bottom The crushing drum is made up of segmental steel plates a and shown in Fig 45 The plates a are perforated ovei the front half of their area, and the back portion is thickened and bent spirally, as shown in the cioss-section, causing a slight step between the adjacent ends of segments. The ore is fed into the drum through the hopper h Attached to the shaft of the drum at the feed opening aie a set of helical spokes which act as a screw conveyer, feeding the ore gradually into the dium as it revolves, and at the

§ 35 ORE DRESvSING AND MILLING

same time rcndeuii it impossible fot the balls or the oie to escape back into the hoppei As the oie is broken up by the tumbling balls, it passes thiough the holes in the plates on to the sheet-iron screen r, the holes m Avhich aie considerably smaller than those in the drum Thiough these

holes the finer stuff passes on to the outside wire screen and the material too coarse to pass the screen rolls back as the mill revolves on to the plates and thence into the drum to be recrushed The plates h are strips of sheet non extending the full ividth of the screen from the fiont end of each crushing plate, thiough a slot m the first screen, to the outer or battery screen d This slot also alloAvs the return of the coarse mateiial from the battery screen to the drum for further reduction The oie which passes d finds its exit through the chschaige funnel The mill is run at a speed of from 20 to 45 revolutions per minute, according to the size of the machine, Avhicli varies ordinarily from 63 to inches in diameter

53, Alslng Piilverlzei'. — This is another form of multiple-ball machine used for very fne crushing It is, in

Ore And Miliand

fact, a pulverizer in the tiue sense of the word The material IS crushed to 10 mesh oi hiier before being intiodiired into the pulverizer and is discharged from it as an impalpable powder

' The machine, as shown in Fig 40, is automatic and has a continuous discharge The material is fed in at one end by a screw feeder s m a hollow tiiiiinioii and is discharged through the trunnion at the opposite end, the size of the

product being regulated by the rapidity of the feed — the slower the feed, the slower the dischaige, and consequently the more complete the pulverization The cylinder is 8 feet long and 3 to G feet in diameter, lined with hard, vitreous porcelain, and makes from to 35 i evolutions per minute. A large number of spherical flint pebbles constitute the crushing apparatus It would seem at fiisl thought that the size of the product could not be uniform, but in practice this mill has ground lo tons of oie in 24 hours fiom 10 mesh, and 99 pei cent of the piodtict passed a 125-mesh scieen The rolling of the machine works the laiger pai tides towards the bottom, so that by the time the ore has traveled the length of the cylinder it is pretty thoroughly crushed. The machine may be used for either wet or cli y work, Ther

ORE DREBvSJN( AND MILLTNC

are a number of patent mills which woik on the same plan as the Alsiiig, the moie reeent being improvements upon that machine They aie used chiefly foi giinding cement and pigments

54. Allis- Clialniers Ball Mil I.- — Fig 47 illustrates a ball pulverizing iniU which has been quite extensively

Pig 47

employed in preparing ore for cyanide and chlorination tieatment when they require that the ore bepulveiized very fine The ore is first reduced to about four-mesh size, or smaller, afte: which it is fed to the pulverizing machine, Avliich consists of a sheet-steel shell having cast-iron heads on which aie cast tiunmons that work in bearings so as to support the cylinder One of the heads is provided with a gear for driving or rotating the cylinder The heads are lined with plates in the form of sectors, bolted to the head near the center as shown and seemed at their outer ends by the linings of the cylindrical portion The cylindrical poition IS lined with curved plates, held in place by means

Ore Dressing And Milling

§26

of wooden strips or steel wedges driven between them after they are set in position The shell linings are so ai ranged that they form a senes of ridges which have a slightly spual course m such a diiection as to feed the oie and cuishmg balls towards the feed end of the cylindei The mateual to be crushed is fed into one end of the apparatus through the hollow trunnion and crowds its way to the other end, where the dischaige takes place thiough another hollow tiimnion The late of discharge is governed by the Kite of feeding, on account of the fact that the oie natiually tends to move towards the feeding end, and travels in the opposite cluection only when forced to do so The balls which accomplish the crushing aie about in dies in diameter, are made of chilled white iron, and weigh appi oximately pounds each It requnes about thiee tons of these balls to each crufehing barrel, and m order to make up foi weai, It IS necessary to occasionally charge new balls in with the oie The feed end of the machine is provided with spiral arms which prevent any material inside from backing out through this end A series of expenments to test some of these machines gave the following results The material fed to the Cl usher consisted of (jOper cent ore broken to screen four mesh, 30 percent to eight mesh; and 10 per cent finer than eight mesh The product from the barrel which passed through lOO-inesh screen amounted to thuty tons in twenty-four hours In pulverizing ore this fine, about 50 per cent of it was lediiced as fine as J50 mesh, and the remaining 50 per cent varied between 150 mesh and loo mesh The wear and tear on the balls amounted to only three pounds pei ton ot mateual pulverized. The crushing was done wet and the wear on the balls made up by charging new balls into the machine without slopping The speed of the pulverizing barrel was fiom V? to 15 revolutions per minute, reqnnmg about 17 H P

One great advantage that this style of pulverizer has over other crushing machines is that no sizing or screening is necessary The mateual fed to the crushing barrel is passed through finishing rolls first and discharged sufficiently

Ore Dressing And Milling

tiiiifonn in size for its desired puipose AVhen crushing wet in the above expei iments, fiom five to seven gallons of water per minute were requited for each barrel The crushing may be accomplished diy, and when this is the case, the wear on the balls is increased

In the illustration the disthaige arrangement has been removed from the front end of the machine and a poition of the casing broken away to show the inside of the barrel

55. Globe Mill. — The mill shown in Fig 48 differs essentially from those described, as only one ball b is employed

Fig 48

to do the crushing, and the cylinder a is stationary The ball moves about in the cylinder, motion being imparted to It by the frictional contact of two steel disks c fastened to the main shafts, and flaring slightly away from each other, but pressing lightly against the ball The machine i evolves

58 ORE DRESvSING AND MILLING § 25

at the rale of about 300 i evolutions per minute, giving the ball in a 5-foot mill a velocity of about 75 Icet per second, so that after it once gets well in motion, veiy little iiiction froira the disks is necessary to keep it going, and the wear on the disks is, consequently, vSUipnsingly small The ore IS fed into the machine by an automatic feeder at the top and falls into the grooved path of the ball which is pissed strongly outwaids by the centrifugal force clue to iLs lapid motion The Cl ushing action occuib along the whole path of the ball, as its rapid motion draws the oie around with it The mill is adapted foi either wet or dry clashing The pulp IS discharged through screens in the ends of the chum, against sheet-iron splash plates, whence it falls into the dischaige boxes The wet-crushmg mill can be fitted with inside amalgamated plates if desired, and the coarser gold saved inside the mill

AUTOMATIC ORiE FEUDISTIS

56, Objects Attained, — Automatic feeclcis for stamp batteries have almost iinivei sally replaced hand feeding When running with a uniform oie, automatic feeders, once carefully adjusted, will work day in and day out with very

little attendance, giving the maximum capacity of the stamps and the m i n i m u m wear, besides saving the wages of the feeders Modern feeders cut out a certain amount of ore at each stioke of a certain stamp and push it off into the motor, making the feed regular

57., The K oil CP Peeclep, — Another and more modern form of lollei feeder

Fig. 49

§ ORE DREbSING AND MILLING 59

IS shown in Fig 49 The lollei, like that in the previous machine, revolves a little with each drop of the driving stamp, and carries out with it a little oie each tune The feed from this machine is apt to be inegular, as the roller may slip without bringing out any ore, and large pieces may clog the machine

58 . Tullocli Feeder. — The Tulloch feeder, shown in Fig 50, feeds perfectly, is cheap, light, and so very simple

Fig 50

in construction and operation that any blacksmith can make whatever repairs may be necessary The feeder is of the shaking -tray type The hopper a holds about 1,500 pounds of ore, which runs into it directly from the crusher or is dumped m from a car

The tray b is hung from the frame timbers in such a manner that it swings foi wards of its own weight until lugs beneath strike the jar lod It is swung backwards by an arm on the rocker-shaft connected to the under side of the tiay The crank-arm d of the locker-shaft is connected with the bhoit arm uf the lever the long arm of which is connected with the tappet rod / This tappet lod of 1-inch

60 Ore Dressing And Milling §

steel IS opposite and parallel to the middle stamp stem and passes till oil gh a hole bored thiough the lower stem guides The head ot the lod, upon which is set a lubber biiffei is stick by the stamp tappet towaids the end of its fall, and pressing down the lever tiiiows the tray back Some of the 01 e in the tray in front of the dooi h is pushed off, the amount coiiesponding to the length of the swing of the table, while the tray, falling back mto position again as soon as the tappet rod is released by laismg the stamp stem, carries forwards an equal amount of ore from the inside of the hopper A spring is sometimes used at the back of the tray to assist the forward motion The fiame of the feeder is mounted on rollers, so that the machine can be readily moved about The feed regulates Itself automatically, if the bed of ore on the dies becomes too thick, the lowest position of the stamp is raised in consequence, slioi tenmg the length of the stroke of the tappet rod, and consequently diminishing the feed of the machine, until the bed has worked down again If the bed gets too thin, on the other hand, the feed of the machine met eases correspondingly

59. Cliallene Feeder, — The Challenge feeder, shown m Fig 51, IS particularly adapted for very wet and sticky ore, on account of the fact that the ore is scraped off m place of being shaken off It is heavier and more expensive than the Tulloch and much more mtiicate in construction, but is very strong and durable and feeds well The hopper feeds on to the inclined cast-uon plate or disk which is revolved by a bevel gear beneath, diiven by a friction disk f — or, m a modification of the Challenge, by a ratchetand-pawl arrangement — which is connected by a system of levers to a tappet rod, as in the Tulloch feeder, and turns a short distance with each blow on the rod The fiiction disk (or pawls) and the levers and tappet rod are brought back into position after each blow by a flat steel sjiring a and Imk I With each partial revolution of the plate, the wing h scrapes oft a little ore into the machine being fed. The highest

§ Ore Dressing And Milling 01

pobition of the tappet itxl is cunt oiled by the hand wheel while the length of its stroke vanes with the length of the

Fig 51

drop of the stamp, which in turn depends on the thickness of the bed of ore on the dies, so that the machine is selfregulating

60 , Belt-Briveu Feetlci*s. — Automatic feeders weie formerly driven by the blow ot one of the outside stamps, either No 1 or No 5, but the ore was found to be distributed better if the blow was given by the middle stamp , therefore, all feeders are now constructed with the tappet rod opposite the middle of the machine, under the center stamp tappet, unless otherwise ordered

Both the Tullochand the Challenge feeders can be adapted to feeding Huntington or other roller mills, the levers being operated by cams on belt-driven shafts instead oi by tappet locks, Belt-diivcn feeders are not self-regulatmg and must be very caiefully adjusted

N M

Ore Dressing And Milling

(Part 2)

OLASSIFYma MACHIlSrERY 1 . Tlie ore as il comes from the crushing machines ranges in size fioin impalpable dust to the laigest pieces winch can pass the machine In all processes of treatment, uniformity in the size of the product is sought, as such ore makes an open bed, through which the leaching gas or solution and the wash water can leadily permeate, and thereby a more uniform extraction be obtained For this reason, screens or other sizing appliances aie placed between the crushing machines and the apparatus for the further treatment of the oie The oie which passes the screens goes on to the leaching vats or tanks, while the coarse ore passes thiough another crushing machine or else goes back into the original machine to be further reduced If, on the other hand, the entire product of a crushing machine, as a set of rolls, for instance, were conveyed directly to a leaching vat, the bed would clog m some places, fiom excess of fines, and at others be too open The leaching solution would then merely travel up and down through these open spaces and never fairly permeate into the clogged spots, so that their values would be practically untouched And even if the ore bedded well and percolated evenly, nevertheless, since the time of extraction is the time lequiredfor the solution to thoroughly penetrate the coarsest particles, the operation would be unduly prolonged By screening the ore and recrushing the coai'se particles, the maximum size of the product can be reduced as much desired without

§36

Foi notice of copyright, see page immediately following the title

ORE DRESvSING AND MIELING § 20

affecUng the mimmuni — the practical limit of this recrushing being the point where the cost of lecrushing balances the gain in time and exti action This point varies with different 01 es, and can be determined only by experiment In preparing oiesfor coiicentiation, also, a certain amount of sizing is necessary for, while the fundamental principle of all concentration is that the minerals of higliei specific giaviLy will sink to the bottom and those of lower specific gravity will range themselves above in inverse older of their specific gravities, yet there are complications which entei into and modify this hypothesis Of two mineials of different specific gravities that are bi oken up into particles of a uniform size, the heavier aviH i*eadily arrange itself m a layer below the lighter, nevei theless, if they be of varying sizes, they will have a tendency to ai range themselves not only according to their specific giavities but also accoiding to the latv of iqiial falling particles. This law is that bodies falling f7Ce\ in a fluid, fall at a speed proportional to the %vcight divided by the resistance Now, the weight of a body IS proportional to the volume, and hence increases much more rapidly than the resistance, which is made up of three separate — namely, the frictional resistance of the fluid, which IS proportional to the total lateral surface exposed, the vertical reaction (floating foice) of the fluid, which IS equal to the weight of the fluid displaced ; and the cohesive foice of the water, which must be overcome m order that the body shall sink Therefore, if a lot of unsized oie IS thrown into watei, the particles will sink with a speed proportional to their weight divided by the resistance of the water This will result in a bed of mixed ore at the bottom, the lower portion being composed mostly of the coarser particles of heavier mineial, but mingled with these will be found many coarse fragments of gangue rock and mineral not wholly freed from gangue These latter particles will be largei than the pure mineral pai tides, but the proportion between their weight and the resistance they met in falling will be the same as m the case of the pure mineral lying at the same level This arrangement will

Ore Dressing And Milling

continue up through the bed, the proportion ot oaiigue, however, becoming greater towards the lop layer, which will con&ibt almost entirely of fine gangue The separation IS known as liyclraiilie classiflcatioii.

In most apparatus the fall is too short to allow of complete separation of the equal-falling classes, and the fall is further letaidecl by the friction of the particles upon one anothei, but the law, nevertheless, enters indisputably into the action of all concentrators Indeed, these imfavoiable conditions for concentration make it doubly desirable that the sizing should be uniform, m order that the separation shall be as complete as possible, for, incomplete as is the concenLiation accoiding to this law, it is still a step in the right direction, and the moie uniform the me, the longer the step Were peifect uniformity of product possible in crushing, a practically perfect separation of the minerals by water alone might be expected, the only drawback being the impossibility of entirely disengaging the mineral from the gangue In actual practice, this incomplete separation gives rise to a product known as micXcIliiig's,'" or iinseparated oie and gangue, which m such a bed as the one mentioned above will occupy a position between the pure mineral 'nieadiugsi''' and the pure gangue tailings."

STZmG MACHINERY

2 Drum Screen or Sizing Trommel. — The sizing apparatus most commonly used, in fact, the only purely sizing apparatus, is the screen In the case of jaw Cl ushers, rolls, and gyratory crushers, separated screens must be used to properly size the material crushed The most common way of doing this is by winding screen cloth on a

Pig 1

i ORE DRESSING AND MILLING § iiC

cylmclrica] ot polygonal frame, ab shown m Fig 1, which revolves slowly on an axis slightly inclined from the horizontal, and running the oie from the crnshei into this drum The mcluiation of the dunn allows the coai se muteiial. which will not pass the meshes of the screen, to run down to the lower end, where it runs into a chute a, and is either retiiined by a belt or chain clevatoi to the original crushing machine, or, as in large mills, is earned to a finei crushed The screened product is conducted by means of a hopper and a trough d to another apparatus foi finlher tieatment, or, as IS frequently the case, to a second, and sometimes third and fourth screen, as shown in Fig 4., each of somewhat smaller mesh than its piedecessoi This limits the variation in the size of the product from any particular diura to the diffeience between the diametei of its meshes

Fig %

and of those of the preceding drum Such multiple screening IS leborlecl to only when sevei'al distiucL sizes of piocluct are desired, or, m fine crushing by successive stages, to lessen the duty and increase the effectiveness of each crushing

Conical lievolvin ScTcens.— Drum screens are bometimeb set with then axes horizontal, doing away with end thrust in the beaungs, the slope necessary for the dis charge of screenings being obtained by making the fiame conical or* pyramidal with the discharge at the wide end In Fig % IS shown a conical revolving scieen with longi ludinal straps foi stiffening the consUuction and holding

Ore Dressing And Milling

the wire cloth in place In case one section of screen cloth needs replacing, it can be accomplishecl without as much delay or expense as when a scieen cloth is one entire piece

4, Tarlable-Meli Screens. — To save the room and expense of a multiple-screen system, vaiious schemes have been devised for crowding the entire senes of screens on to a single frame The simplest of these is to divide the drum into sections, each of which is covered by a screen of different mesh, making practically a series of separate screens

Fig 3

upon a common axis, the fine screen being at the head and the coarse screen at the mouth of the drum The laige leceiviiig hopper is divided into sections corresponding to the divisions of the drum, with delivery pipes from each section This scheme is open to the objections that if more than two sizes of screen aie desired, the drum must be made inconveniently long or the screens will not have time to do their work fully, and that the most wear falls on the finest screen

G

ORE DRESvSING AND MILLING

A better scheme is to ai range the screens in a senes of

concentiic drums, as shown iii Fig 3, each with a separate discharge trough for its screenings In this arrangement the coarse screen IS in the center, next to the shaft, where the mat enal IS coarsest and the meshes of each consecutive screen become smaller towards the outside Conical screens of tins type are sometimes made with every other cone reversed, so that adjacent screens discharge at opposite ends of the drum In this case, aa in simple conical screens, the axis IS horizontal

5, Wet Siziiig and Washing; Screens. — Revolving screens are sometimes made with hollow shafts having small holes

§ 20 ORE DREvSvSINO AND MILLING 7

bored at light angles to the length of the shaft and connecting Its inner and outer circumfeiences One end of the shah is closed, so that when water is forced into it through the other end it spirits through the holes into the screen, washing the material inside These tiommels may be revolved in a trough containing water, besides using the jets Such trommels are used in gold dredging and in iron and phosphate mining to remove clay that adheies to the lock The revolving screens shown in Fig 4 are for wet sizing where coarse concentiation is practiced The treatment depends upon even sizing, which the wet sizing screens are quite effective in producing The screens shown are connected by gearing a The first screen removes all the pieces too laige for treatment, by passing them out into the hopper Z?, from which they are returned to the crushing machmeiy The particles which go through thefiist screen are washed down the trough c into the next screen, where they are sized again, the coarse pai'ticles passing out of the hopper corresponding to and those that go through the screen meshes travel into the next finer screen by way of the though €

6, SliaMug Screens or Box Scx*eens* — Shaking screens aie but little used in ore dressing, the simple consti action of drum screens, together with their economy of space and admirable working qualities, having led them to supersede all other forms for automatic sizing Shaking screens are piactical, howevei, and are used to some extent in coal screening A recipiocating motion is given the screen by means of an eccentric or by a cam and springs The mechanism in either case is much more intricate than that of a drum scieen to accomplish the same work, and the shaking screen occupies considerable moie space Moieover, drum screens are frequently hung from overhead timbers, leaving the floor beneath clear for any purpose desired, while shaking-screen frames are usually set on the floor, taking up room at the expense of other machinery or the convenience of the workmen The greatest objection to shaking

8 ORE DRESSING AND MlLLINGx

screens in concentrating woiks is that they have such a jarring eftect upon the building, and the average concentrating mill has enough jarring without inti odiicing any more The capacity of shaking screens is greater for equal aieas of surface than the capacity of revolving screens

7. Wet aiicl Dry Bereeniii. — Scieemng, like all other work about a mill, is preferably done wet whencvei consistent with the further tieatment of the oie, as the water facilitates the operation, lessens the wear on the screen, and renders housing minecessaiy Jets of water are sometimes played on the screen to pi event clogging, when there is not sufficient water in the pulp as it conies from thcciushing machine In case the oie is damp oi wet, it cannot be screened satisfactorily without first being passed through a drier Drying, while it makes moie dust, lenders the ore friable and permits the lolls or stamps to crush it quicker.

8. Screen €lotIis. — The materials used for covenng screen frames aie punched sheet metal and woven-wire cloth Both materials may be used for all sizes of product, but as a rule the sheet-metal screen is better adapted for coarse mateiial, while wiie screens wotk best on the fine stuff, as their open area per square inch is greater for the same size of mesh For wet crushing, the screens can be made of brass wire, which does not rust. The relative merits of pinched-metal and wire-cloth screens are a subject of dispute, but the round-hole 301*0611 is the commonest form for punched sheet-metal screens, and after it the longitudinal, oval, or rectangular slot Square holes and diagonal slots are also common Wire screens are almost invariably made with the meshes set square with the frame.

9. Grizzlies. — As the ore comes into the mill, it is dumped on to stationary inclined gratings, termed 'grizzlies,'' and shown in Fig 5. These are usually made of flat

Ore Dreing And Milling

f)

§

steel bars, set edgewise, about 1 oi "finches apart, and running lengthwise down the grating As the ore slides down the grizzly, which is

inclined at an angle

of from 45 to 55 de glees in the direction of Its length, the ore which is small enough calls between the bais into an oie bin below, while the coarse stuff slides down on to the feed fiooi The rock breaker located here clashes the oie to the proper size and then discharges it into the bins, where it mixes with the oie that passed through the grizzly

The grizzlies vary fiom 3 to 0 feet m width and fiom 8 to la feet in length, 4 tt X lOtt being the usual size The bais are held in position by i*ound-iron rods, usually three in number, one in the middle and one near each end, they are spaced by cast-ii on washers, through which the rods pass The bais are sometimes made with the lower edge thinner than the upper, the idea being to have the openings slightly wider at the bottom than at the top, and thus prevent ore sticking in the grizzly

CLASSIFYING MACnnSTERY

10 . Object of Porting'. — vScieens ot very fine mesh cannot very well be used foi automatic Avork around a mill, as they are expensive, delicate, and altogether too slow in then action Now, in the operation of any crushing machine, however coarse the maximum or average size of the product may be, there aie produced a consideiable pioportion of '' fines," the propoition increasing rapidly as the crushing faces of the machine are brought closer together These "fines " are made up of particles varying in size from

10 ORE DREvSvSING AND MILLING § 2G

fine sand to an impalpable dust or slime In character they are, like the original ore, a mixture, more or less intimate, of gangueand mineral, the only difteience is that the more brittle portion of the ore (usually the mineral portion) is present m larger proportion, as its biittleness tends to make It break up fine This makes it doubly desirable that these fines should be saved, and to that end many machines have been devised Most of these machines depend for then opei - at ion upon the specific gravity of minerals and the tenacity with which the various minerals of an ore cling to a smooth surface against the force of a current of water The machines were at first fed with the screen-sized material direct fioin the stamps, but this resulted in too wide a lange of product from the concenti'ator, while the saving was not what It should have been, so that at present a classifying apparatus is usually interposed between the battery scieen and the concentratoi s, assorting the viaicrtal mto equal failing classes and each class is earned to a separate concentrator The duty of each concentrator is thus lightened and the separation made much cleaner; foi not only is the lange of size of material to be treated by any one machine thus decreased, but the heavy, pure mineral in each class is confined entirely to the smaller particles and the pin e gangue to the larger, with the combined mineral and gangue landed in between m sizes relative to the proportions of mineral and gangue present The smaller particles present much less surface to the water, in pioportion to their weight, than the larger particles, and consequently tend to cling moie tenaciously to the surface of the concentrator, and by regulating the current any proportion of the material desired can be kept from washing away

11 . Bpitzlrasteii. — Spitzkasten, shown in Fig 6, are troughs with pointed bottoms, arranged in a senes, with settling pits at intervals, m Avhich the various classes of material settle These pits are allowed to fill up with sediment and are then cleaned Each box discharges mto one somewhat larger than itself As the pulp stream flows

Ore Dressing And Milling

§ 9Ji

tlitough the seitcs, each class of mateiial bettles out as it comes to a certain box, accoidmg to the stiength of the current at that point

In all modern machines of this type, the separation is made by inttodncmg a using cm rent of water at the bottom of the box, as shown in Fig (5 The inateiial settles against

this current into the tee below and is washed out at the orifice In this way all slimes are washed out, and the concentrates aie very clean A partition or ''diving boaid " is set in a box to divide it into a downward and upward curieiit and prevent surface currents from traveling directly across the box.

The level of the water m the trough from which the wash water is taken is somewhat higher than that in the boxes, giving the desired pressure for an upward current, and the force and amount can be regulated by valves m the pipes, as

12 and MILLING § 26

shown The fiist boxes of the senes arc usually quite small, and the current of the pulp stream as it passes through is correspondingly swift, so that only the heaviest oie particles settle out in the first box As the boxes increase in size the force of the current diminishes and the hnei pulp settles out, the size of the material settling in each box becoming successively smaller down the senes

13 . Allis Classifier. — The Alhs classifier shown in peispective and section m Figs 7 and 8, respectively, is a

Fig 7

modification of the spitzlntte. Refening to the section, Fig, 8, the pulp flows through the trough and scieen as indicated by the arrows The pai tltion a divides the machine into two main divisions, corresponding to the down-flowing and up-flowmg aims of the spitzlutte. The up-flowing ann, which extends under the main box like the tail of aji, is divided by partitions and d parallel to a — there being

Ore Dressing And Milling

§ JiO

as many of these partitions as there are to be classes of products formed The wash water enters thiough a pipe at the side of the box into a compartment behind the classifying though propel and passes down and undei the partition through a space left for this pm pose, and rises on the other side The pulp flows thioiigh the trough and screen down one arm ol the apparatus and up the othe: The lighter

Fig 8

particles of gangue are carried up with the ascending stream through the space between a and b into the tailings box A metal hp at the top of a, extending over the top of the tailings slot, prevents the overflow from the receiving trough or down-flowing aim from lunning back down the tailings slot m case the machine gets too full The heavier mineial particles settle to diffeient depths according to their

Ore Dressing And Milling

densities, before they aie carried up into their respective spouts, the wash current flowing stronger as they descend The tops of the discharge spouts are all nearly on the same level, so that all classes aie discharged with the same force The tongues shown at the ends of the partitions regulate the size and amount of each class, or the partitions may he made with slides which aie adjustable to different depths by rods with thumbscrews attached, running up through the tailings though

13. Cone Classifier.-— The cone classifier is the apparatus shown m Fig. 9, and is made entuely of iron The

Fig. 9

outside cone is of cast iron; the inside cone, usually made of boiler iron, is open at the bottom and can be adjusted by means of a hand wheel and screw The construction is shown in Fig 9 (a) The pulp flows into the inner cone and down thioiigh the open bottom, here it meets a lising

§ 2G ORE DREBvSING AND MILLING U

cinrent of wash watei and flow s up through the space between the two cones The particles of mineralb have to against the combined upward foice of the 'wash w'-atei and the rising pulp stieain Those pai tides which have weight enough to do this settle to the bottom alid are discharged through pipes onto then i respective concentiatois, while the hghtei particles are earned over with the main pulp stieam into the launder and thence into the next laigei classifier, wheie the whole opeiatioii is repeated, but with a slowed CLiirent, on account of the greater size of the apparatus, the average size of the product being propoi tionately smaller By varying the width of the space between the cones m each classified and the amount of wash watei, the separation may be made as close as desired and may he earned through a number of classifiers — more than three, lioivever, is unusual The old-style wooden classifiers in Ameiican mills have been laigely replaced by these cone classifiers, as they are much more convenient and compact Cone classified s range in sizes from 12 to 40 inches m diameter and weigh from lOO to 635 pounds

14 . Troxtgli Classifiers* — In the Lake Supeiior copper regions, classified s of another form, known as trough

Fig 10

sepal atoms, are used for a rough classification of the native copper ores, preliminary to jigging The La/e Superior t7 ough separator shown in Eig. 10, is a double V trough, the space between the inner and outer troughs being divided at intervals, so as to make the apparatus in effect a series of double V boxes Towards the lower end of each box a slot is cut in the bottom of the inner trough to allow communication between the two. The pulp is run m through the

iV U 111— 10

Ore Dressing And Milling

§ 26

inner trough m a continuous stieam, while the outer though contains the wash water, which ib kept at a level somewhat highei than that of the pulp in the inner though, in oidci to maintain a steady upward cm rent of water through the slots, against which cunent the mmeial must settle The coarser particles naturally settle to the bottom first and sink through the slots into the outer trough, and thence through the dis~ chaige openings to the jigs, the finer stuff being earned farther along before settling The slots of the inner trough are madelongei towards the lowei end of the trough, sotliaL the smaller pai tides shall have more time m which to find their way through into the lower trough

15. The Cahiinet classtfn\ shown m Fig 11, is another type of trough classifier It consists of a trough which

widens slightly towards its lower end and has a senes of boxes or pockets in the bottom The pulp flows through the entue seiies, the stops deflecting the sti'eam downwards into the bottoms of the boxes, so that all the material is subjected to the action of the wash water which enters through the pipe a and discharges directly against the discharge spigot d The spigot IS not large enough to carry off all the pulp directly,

w

Ore Dressing And Milling

so It swirls and eddies in the bottom of the box keeping the sand stiiredup, and allowing only those heavier pai tides winch have weight enough to settle in this commotion to be washed out through the dischaige The shield c deflects the cull ents set up by the wash watei and prevents them from rising to the surf acOj thus confining the agitation to the bottom The force ot the wash water can be regulated at will, the classes issuing from the spigot responding readily to any change in the force of the wash water The force of the wash water in the lower boxes is less than in the upper, and the average size of the product propoitionately smaller By using for the discharge spout a veitical pipe with three or four openings at different levels, the amount of water discharged may be regulated — the dischaige being more rapid when the lowest hole is used and slowest Avhen only the top hole is open

16, Hydraulic classifieis are, as a matter of fact, concentratois, but aie tieated under a separate head because they ai e invariably used in preparing ores for further concentration The ]ig, on the other hand, is just as essentially a classifier m its action as the hydraulic classifiers just described, but the classes which it yields are treated as final concentrates, hence the machine is always classed with conceiitiators,

sifiTamrisra boxes

17, Object of Settlers — It is always desirable, if possible, to crush and size ore with a large excess of water, as this greatly facilitates both operations This excess of water is, hovvevei, frequently undesirable, or at least unnecessary, in the subsequent treatment of the ore If a too thin pulp interferes with the subsequent operations — as is the case with many conceiitiators of the vanner type or in the pan amalgamation of silver ores — the battery pulp is run into settling boxes, wheie the suspended mateiial settles out and is withdrawn at the bottom with just sufficient

18 Ore Dressing And Milling § 2G

watei to give it the proper consistency for concentration or amalgamation, as the case may be The concentrates from some machines are delivered with a gieat deal of watei, and are usually settled out and drawn off very thick, to be clued for further ticatment, storage, or shipment Tailings from concentrating and amalgamating mills are likewise sometimes settled out and dried and then tieated by the cyanide process foi what gold remains in them

In case of a scanty water supply — quite a common drawback to milling operations — the necessity for dry crushing may be avoided by drawing off the superfluous water from the pulp and tailings and using it over and over again The adoption of this scheme has alloAved the working of many large deposits which would otherwise have remained untouched.

18 . Settling Ponds — Pulp settling is a very old practice. It was formerly done in large settling pits sunk in the ground, through which the pulp stream flowed The sediment was allowed to accumulate until it came so near the surface of the water that the surface cniieiiLs commenced to cut channels in the deposit, when the pulp stieam was deflected into another pit and the sediment m the first pit shoveled out The pits were usually rectangular, with steep, sloping sides The large settling tank oi vat which has replaced the settling pit is a huge rectangular pointed box, set on a framework above the ground These tanks aie sometimes set in series, beginning with tanks only a few feet long and wide, and ending in tanks of enormous dimensions, somewhat on the plan of spitzkasten, but on a much large! scale The larger the tank, the greater the diminution in the velocity of the pulp stream on flowing into it, consequently, the boxes ananged m series in this way would be in effect classifiers as well as settlers, the heavier and coarse equal-falling particles settling out in the smaller boxes, while the finer and lighter particles would remain in suspension until they reached the almost motionless bodies of water in the larger tanks.

§36

Ore Dressing And Milling

19 . Automatic Settling Boxes. — Besides the trouble of hand cleaning, which necessitates either the construction of two tanks or sets of tanks, to be worked alternately, or else the shutting down ot the mill while the tanks are being cleaned, the old settling tank, as well as the more primitive pit, presents several other disadvantages Their size and consequent cost is one great drawback In addition to this, a great deal of fine material is floated across

by surface currents, and when the deposit of sediment appi caches the surface, more or less of it is washed over the lower edge of the box The continuous, aiitomatic-dibcharge settling box removes all these objectionable features at a single stroke The size of the box is reduced to reasonable proportions, surface currents are prevented by the use of a diving board, and the operation of the apparatus is continuous, the sediment being removed as fast as formed and not being allowed to accumulate in the box

30 Ore Dressing And Milling §

The construction of the settling box is illustrated m Fig 12 A box of the dimensions given in the figmc will handle the pulp fi om five stamps, or even ten nndei favorable conditions The sides should slope at least 50 degiees from the horizontal, or the sediment will stick to them instead of sinking to the bottom and discharging The pulp IS fed in through a distributor at the head, with holes and guide tongues, and the clean water clischatges ovei the lower edge — which is cut 2 oi H niches loci than the sides for this purpose— into a tioiigh, and thence into the water launder

AH the pulp must pass under a vertical diving hoard across the tank near the head, and this seives the pin pose of preventing surface currents, that is, it prevents the pulp stieam from running light across the tank and ovei the other end in a narrow current between banks of quiet water instead of spreading equally over the whole box This diving board also selves the purpose of completely submerging the particles of oie, thus pi eventing their being floated off on the suifacc of the watei, supported by a film of air — the source of considerable loss in milling The sediment discharges through a 1-|- oi 3-inch siphon discliatge, a few inches above the bottom of the box The upper poi - tion, or, better still, the whole, of the discharge pipe is of rubber hose, and the pressuie of dischaige can be altered by simply raising or lowering the mouth of the hose, which is closed by a slicing-gate tap The pipe is connected to the box by a nipple and tee, or, if a hose be used fot the full length of the pipe, the tee can be dispensed with, as the only reason for using it is that an opening may be had at the bottom of the box so that it can be completely emptied it desired, and with a hose discharge-pipe this can be had by merely dropping the nose

The form of the settling box has consideiable influence on the size of the box required If the location is such that the number of square feet is limited, it will be found better to employ a wide short box than to employ a long narrow box, on account of the fact that the relative percentage of

§ 2C Ore Dressing And Milling 21

the materials settling fiom the water depends upon the degree to which the velocity of the cuirent is retarded or, in other words, the nearer the flow is brought to rest, the more thorough will be the settling of the contents If two boxes can be employed, it is usually better to divide the flow and send half of it tliiotigh each box than to place the two boxes one aftei the other and depend on each of them to extract a portion of the material from the flow

CONCENTRATING MACHINERY 30. Coneeutrator is the general name applied to all machines for I'educing the mineial values of an. ore into smaller bulk, in older to get iid of as much superfluous material as practicable Among the Western smelters it is customary to vary the smelting chaige with the chaiactei of the ore as regards fluxing, oi, what is practically the same thing, to have a uniform charge for a neutral oie (one in which iron oxide and silica are present m pioper proportions), and then pay a fixed premium for every additional unit (per cent ) of iron, or require a bonus or excess charge on every unit of silica beyond neutrality Foi instance, if a mine at a considerable distance from a smelter is pi oducmg aquaitz ore carrying 10 pei cent iron pyrites — the other 90 -per cent being quaitz — and $12 per ton in gold, the owner would be apt to find, if he shipped the ore direct, that, after paying the freight and the smelting charges, including the bonus on the silica, there would be little left of his $12 But the quartz being much lighter than the pynte, he finds that after crushing he can, by the use of suitable apparatus, wash away the greater pait of the gangue rock, leaving behind the pyrites, m which all the values are contained In this way he dispenses with a great portion of his fi eight charges, and if he carries the concentration far enough, he may, instead of paying a bonus on excess silica, receive a premium on excess non Thei*e is always more oi less loss of mmeial m concentrating, but by the careful use of good apparatus this can be kept down to a

22 ORE DREvSSING AND MILLING § 2G

nominal figure The limit to which concentiation, may be profitably earned is the point beyond which the cost of concentiatioii, together with the inevitable loss of values in the tailings, exceeds the saving in freight and the treatment charges

2t, Concentiating apparatus may be divided into two general classes First, machines in which the separation is pei formed by means of an intermittent upward cuiient oi water, which tends to anange the particles in layeis, m the order of their specific gravities. Tins class comprises all jigging apparatus Second, machines in which the separation IS mainly due to the supei'ior tenacity with which the particles of the heavier mineral cling to a smooth suiface against the force of a stream of waiei This class includes buddies, belt and tabic concentrators

22* Jigs . — Jigs aie almost uni vei sally used for concentrating the coarser sizes of ore, but are inefficient foi oie which will pass through a screen having less than 30 openmgs to the linear inch, oi 900 lioles per square inch; oies below tins size are usually concentrated on bumping tables, vaniiers, or buddies, or other shine concentiators, accoidiug to the fineness

All hydraulic jigs woik upon the same principle, that is, the tendency of ore particles in water, when approximately of the same size, to arrange themselves in layei*s, accoiding to then specific gravity, when the bed of material is kept sufficiently open to allow the particles to move freely among themselves. This is accomplished in jigs by giving a column of water a pulsating motion or by giving the grating and screen upon which the oie lies a shoit lecipiocating motion, the resistance of the watei lifting up the ore on the down stroke of the piston or grating and the particles assorting themselves as they settle back The pulsating motion of the water makes the operation of the machine continuous, as the particles of a certain density are never allowed to get below a certain level , for, so long as the bed is properly preserved, there will always be a layer of heavy mineial upon

§ 20 Ore Dressing And Milling 23

the screen which it will be impossible for the lighter mineral to displace, so that the latter is confined entirely to a level above the bed of heavy mineral, though the particles of heavy minetal may work down thioughit, a little at each stioke, to the bed below In Jigging coarse material, the holes m the scieeii upon which the bed less aie made smaller than the ore to be jigged, and the latter forms its own bed as described, the different classes being discharged through various forms of pipe and slide discharges above the screen Mateiiai has been successfully jigged in this way as coarse as inches in diameter and as fine as 10 mesh For jigging the smaller sizes, however, it is customary to have the meshes of the screen ratliei laigci than the particles of ore to be Jigged, so that the whole sttiface of the screen may be utilized for discharging the concentrates Abed 1 to d inches thick, of coarse mineral, of the same oi slightly greater specific gravity than the mineral to be concentrated, is ananged duectly above the screen This bed is usually made up of coaise pieces of the same mineral as that to be concentrated The fiagments composing the bed are all too large to pass through the scieen Through this bed the fragments of the mineral to he concentrated work their way, and passing through the screen, fall into the hutch below, where they accumulate and are discharged at intervals This method is used very largely in American gold milling, where sizes seldom lun above or f inch

33, — Crushing can nevei completely disen-

gage the ore from the gangue, nor can screening or even hydraulic sizing be made so close that there will not be a considerable variation in the size of the particles making up any one class, so that in jigging it is practically impossible to get a perfectly clean separation of ore and gangue Even among the cleanest concentrates there is always some gangue and ore combined, and also in the cleanest tailings, and in all concentration, by jigging or otherwise, there is always an intermediate product between concentrates and tailings, known as middlings,'' which is made up of combined

u

Ore Dressing And Milling

§30

gangue and ore In Jigging, these middlings form a bed or stiatum between the clean concentrates and the tailings — or, in the case of Jigging through a bed of coarse material, just above this bed— winch is discharged separately If

Fig 13

practicable, theiTiiddlings are usually re crushed and returned to a finer jig to be further concentrated

34. 8 tatlonai-y- Screen J'igs.— The ordinal y type of jig

belongs to the class in which the grating supporting the

Ore Dressing And Milling

§

screen is stationary In construction, all jigs of this type are essentially the same The machine consists of a rectangular box or tank, divided, for the up pel pait of its depth, into two compartments by a vertical partition A

Fig 14

space IS left open below this partition to allow free passage foi the water between the two compartments In one compartment IS a stationary gratings. Fig 13, of wooden bars supporting a wire screen upon which the ore is bedded, in

26 ORE DREvSvSING AND MILLING 2(>

the other is a piston or plunger, which is moved usually up and down, as m Fig 13, hut sometunes horizontally, as in Fig 14, by a crank, eccentnc, oi othei lecipiocating device on the shaft The hoiizontal-plunger jig is not very extensively used, as it presents no decided advantages ovei the vertical-plunger type, lequires moie flooi space, and it IS haid to keep the packing about the piston lod watertight Jig plungers are made to fit loosely, and in the veitical-plunger type of jig are sometimes perforated with auger holes, in order to i educe the suction on the back stroke

In starting a jig, the bed is first ai ranged on the screen as nearly as possible in the older the particles would arrange themselves iindei the action of a ]ig in operation; water is then run into the tank until the ore bed is completely covered, when the piston is started up, giving the water column a quick, dancing motion, which keeps the bed open and assists in the separation of the classes Ore and water aie fed in, either logethei oi separately, at a laLe to keep pace with the discharge of the machine and make its operation continuous If they are fed separately, the oie is fed in at the head of the machine on to the scicen and the water lb fed into the piston compartment, othei wise both are fed on to the scieeii The bottom of the tank is made hoppei -shaped, with a hole and plug or a discliaige gate for removing the concentrates The middlings weie foimerly allowed to accumulate, and weie cleaned off at intervals by hand, but in most modem jigs they are discharged through automatic, continuous-discharge gates The tailings discharge over one end of the box, left lower than the other for that purpose

25. Gompartixieiit Jigs. — Jigs aie frequently made in sets of two, three, or four, or what are known as two-, three-, or four-compartment jigs, one long tank being partitioned off into that many main compartments Each one of the latter is furthei subdivided into scieen and plunger compartments. The grating and the tailings clam of each

§ 26 Ore Dressing And Milling 27

bULcebsive mam conipaitment are somewhat hover than those of the piecedin compartment, so that the overflow and tailings fiom each compartment aic earned on into the next and further concentrated These multiple-scieen jigs aie used when several grades oi product aie desired or when the oie contains moic than two minerals Avhich it is desned to separate fiom one another more or less completely For instance, if an oie contains galena and pyiite, with a quartz gangiie, a three-compartment jig would be used The concentrates from the first compartment would be galena, almost ptue, fiom the second, mixed galena and pyrites , and from the last compartment, nearly pure pyrites If the gangue is a heavy one, like baryta, or theie IS anothei mineral in the ore which it was desired to separate, as zmc-blende, another compartment would be added, the concentrates from which m the latter case would be mixed blende and pyiites, with some gangue, particularly if the latter is heavy The separation of three mmeials may also be accomplished m a two-sieve jig, the mixed galena and pyrite foiming a middlings class m the first compartment, above the bed of heavy, coaise mineral, while the concentrates from the second compartment are neaily pure pyrites

The force of the water column in the diffeient compartments IS regulated by varying the length of the stroke of the piston The plungers, m jigs of less than four conipaitments, are all operated fiom one shaft, in four-compartment Jigs two shafts are generally used, with two pistons on each, the shaft for the last two compartments revolving somewhat more rapidly than that for the first two It is in the method of varying the length of the piston strokes on a common shaft, independently of each other, that the chief diffeience between the jigs of this type lies

36 . Uax'tz fTlg. — The Hartz jig is the commonest foim of jig, and IS typical of the vertical-plunger class Fig 13 shows a three- compartment Hartz jig The stroke of the piston IS regulated by means of a double eccentnc made

2S Ore Dressing And Milling § 20

up of two eccentiics, one withua the olhei Ei It) shows the constiuTCtion and principle ol the eccentric The inner

eccentric c? is fixed on the shaft nsualiy 4'' inch out of centei The outer eccentric d is set the same amount out of centei with i efei - ence to about which it may be turned, being held in posiLion while m operation by set" screws When d is turned so as to carry Its center on the outside of the center of a, opposite the shaft center, the total throw of the whole eccentric is equal to the sum of the throws ot a and d Thus, with a and I? each inch out of centci, the entite eccentric would be 1 inch out of center, with a consequent throw of 2 inches But if b be tinned half way round a from this position, so that the center falls on the same side of the center of a as the shaft center, the centei of d will coincide with the shaft center — each being the same distance from the center of a and on the same side — and the throw will consequently be reduced to zero, as shown by the broken lines in the figtiie* By tuning 5 to any desiied position 'between these two extremes, the throw can be varied from 0 to 2 inches

37. Quiclr-Retuim Jig'. — In the ordinary Haitz

]ig, the up and the down stioke requue the same length of time, and consequently on high-speed jigs the suction on the back stroke is considerable But by the use of a countershaft

L-soi Fig 15

Ore Dressing And Milling

§2G

and the aiianqemcnt of ciank, level, and connectingrod shown in Fig IG, the down stroke of the piston is made to occupy only one-thud of the tune of the full double stioke — or one-third of one of the counter shaft — the othei two-thuds being consumed on the up stioke The diagram, Fig 17, shows how this is accomplished The small circle is the path of the ciankpin / in the crank c. Fig IG, and the large circle represents the path that would be described by the pm / in the end of the lever / in one complete i evolution of the rocker-shaft c The connectingrod r, being fixed at one end to the crank and at the other

Pig 16

to the lever, must necessarily, m any position it can possibly take, have one end somewhere on the circumference of each of these circles The lengths of r, r, and / being known and the paths to which the connecting pms on c and I ai e confined being fixed, by assuming p at any point of the circumference of the smaller circle, and laying off the length r from this point to the circumference of the larger circle, we obtain the coiTespondmg position of the connecting pin on the level /. On the diagram, the corresponding points on the two circles are mmibered alike, It will be

Ore Dressing And Milling

noted that the level travels on the down stroke between its two extreme positions, indicated by the points I and S on the ciroumteienee of the largei circle, while the crank moves between the corresponding positions on the smaller circle, and that the latter distance is only one-thud of the ciicumference of the circle The leturn stroke of the piston occupies the other two-thirds of the revolution of the crank-shaft (While p travels from i to m this particular instance,

t remains nearly motionless, and points 1 and 2 on the larger circle exactly coincide, so that the down stroke of the piston really occupies only one-sixth of a revolution of the crank shaft ) This device is used only on high-speed jigs with a short stroke, as the eccentric moves only thiough a quarter of a revolution, and m order to get a long stroke, the eccentric would have to be of quite large diameter and considerably out of centei A similar scheme is also applied to

ORE DREvSvSING AND IMILLING

other type of jig;& using' cranks instead of eccentncs on the counter shaft

28, Slide Jigs '—The slide jig shown in Fig 18 illustrates another adjustable lecipiocating device In principle

it IS somewhat similar to the quick-return Hartz jig, the down stroke occupying a shorter poition of the revolution of the shaft j than the up stroke The lever I is slotted and keyed on the rocker-shaft In the slot of / is a freely moving block which also serves as a bearing for the free end of a crankpm p extending out from the wnstplate d. As the shaft j revolves, the block b slides back and forth in the lever slot, and at the same time causes the lever to oscillate, tins motion being transferred to the rocker-shaft, and from hei e through the crank to the piston

The two extreme positions of the lever I are the points where the center line of the lever is tangent to the circle described by the center of the pin / in its revolution about the shaft as shown by the dotted lines in Fig 18, It is N M III 11

Fig 19

ORE DRESSING AND iMrLLING 33

apparent that the largei the cude described by the pm, the greater will be the diffeietice between the dmation of the up stroke and the down stroke Consequently, in oidei to make this difference adjustable, as well as the length of the stioke, the pm p and wiistplate i/ are so constructed that the distance between the Centex s of the pm / and the shaft can be varied at will The plate d is slotted diametrically across its face, and in this slot p slips and is held in place by a nut If p is moved over to the center of the plate, the pm will merely revolve m the block /?, without any up or down movement, and the level and rocker-shaft will remain stationary But if the pm is moved ever so little away from the center of the plate, it will have some throw and will start locking the lever and rocket -shaft As the distance of the pm from the center of the plate increases, the throw of the level increases also, and consequently the length of the piston stroke, while the duration of the down stroke is deci eased as the angle thiough which the lever moves increases These jigs are suitable foi coarse ores

39* Collom Jig. — The Collom jig, shown in Fig 19, illustrates another method of operating the pistons In this method the pistons axe not connected with the shaft, but are hung independently and held in position by springs and collars, as shown in the figure The pulley p is set on a crank-shaft jt, from which a connecting-rod c runs to the level tappet r, giving the latter a locking motion As the tappet oscillates, the levers press alternately on the heads of the piston rods on either side of the shaft, the rods pressing down as the aims descend, while the springs return them to their normal position as the arms rise and release them. The length of the stroke may be varied by raising or lowering the set collar on the piston rod, against which the spring presses, thus lowering or laisuig, respectively, the normal position of the piston As the lowest position of the piston is always the same, being the point to which it is depressed when the lever arm is in its lowest position, while the highest position is the normal position in which it is

34 ORE DRESSING AND MILLING § SfJ

held by the alone, it is obvious that by raising or lowering the latter, the stroke is consequently increased oi diminished, respectively, the motion of the lever tappet being entirely independent of that of the pistons Two ]igs of this t 3 pe aie sometimes operated from one diiving shaft, as shown in Fig 19 (a), by means of a connecting-rod between the two level tappets, the motion is thus transmitted from the , oi head, jig to the tollowmg, or tail, jig The tail jig in this case is set at a slightly lower level than the head jig Collom jigs are quite largely used for the concentration of copper ores

30. Reeiproeatliig -Screen Jigs — Recipi ocatmg-screen Jigs are very little used, particularly in Ameiica They get out of order more easily than piston jigs, the wear IS greater, and the increased suction on the back stroke is also a disadvantage They do away with the extra width required fur piston compartments, but in all other i aspects are infenoi to piston jigs The best example of this type is Green's jigger, in which the screens are moved up and down by double eccentrics, like the plungers of stationaryscreen Jigs

ora BISCHAJIGES

31. Pipe Piscliarge. — The simplest form of pipe discharge IS a pipe running up through the jig box and sieve The lower end maybe left open for continuous dischaige, oi kept closed and the concentrates discharged at intervals, as desired The latter scheme presents two disadvantages The first of these is that, the ore bed remaining on the screen for some time, the particles rub against one another and wear away a fine shme of rich ore, the greater part of which IS lost The second objection is that, to be sure that the concentrates are completely discharged, the discharge must be continued till the gangue commences to come thiough the discharge pipe, and the pipe will necessarily be left full of gangue, which will come out the next clean-up.

Ore Dressing And Milling

2G

On the other hand, when the contimioiis dischaige ib employed, the sepaiation is not quite so clean, and the discharge must be very carefully regulated, but this can be done by means of slides ni the lower ends of the pipes, by which the area of the discharge orifices may be adjusted The use of continuous discharge saves the time that is lost, 111 dischaiging intermittently, by stopping the machine, and on the whole it may be considered the best practice under ordinary conditions

33. Scope of Pipe Discharge. — The opening of the discharge pipes for the screen concentrates is flrish with the top of the screen If more than one class is to be concen trated m the same screen, as galena and pyrites, the pipe for the discharge of the lighter concentrates (pyiites) is carried up through the bed of galena Three pipes aie sometimes used in tins way, two of them dischaigiug clean minerals, and the third (the middle one) dischaiging a class composed of the two minerals mechanically combined Middlings of gangae and ore may also be discharged thiough pipes, and the scheme may be employed foi amiddings dischaige in jigging through a bed by extending the pipe up through the bed of coarse, heavy material Pipe discharges are laigely used for fine and medium sized ore, but if the oie is very coaise, the pipes are apt to clog, and some form of dischaige must be adopted that is less liable to pack and is more accessible for cleaning in case it does pack Various devices have been invented with these objects m view, but the Hi berle gate lias superseded all othei s and is almost exclusively used m America for coarse jigs, and has to a great extent replaced the pipe dischaige for the finer sizes

33. Hebex-le Gate.— The beds of ore on the jig sieves, being kept loose and full of water, flow back and forth like heavy liquids, they can be run or siphoned off, and have, in fact, all the characteristics of fluids The Heberle gate takes advantage of this fact The gate, as illustrated in Fig 20, consists of a rectangular opening / m the side of the jig box

36 ORE DREvSSING AND MILLING § SO

above the screen and an adjustable slide r, through which the concent! ates dischaige Sometimes a double slide is used

at c, so that both the top and bottom of the opening through which the concentrates discharge can be controlled Behind the apei - ture theie is a U-shaped piece a This is secured against the side of thejig by means of the band b, which terminates in bolts that pass out thi ough the side of the jig and aic secured by nuts on the outside By loosening these bolts, the shield can be moved up and down in such a manner as to regulate the distance between its lower edge and the face of the screen Oiclmarily for discharging concentrates, the shield a is placed so that the coarsest material can just pass undei its lower edge without clogging between it and the screen e The thickness of the bed of concentrates is controlled by raising and lowering the slide r, which regulates the height of the discharge opening This can also be effected by regulating the supply of ore The shield a prevents the tailings and middlings from flowing out through the opening in the slide r, but allows the concentrates to run tmdei , and the weight of the oie and gangue on the bed forces them up inside of lire shield, on the principle of the siphon, to a level considerably above the concentrates on the screen, but necessanly lower than the top of the material on the screen on account of the fact that the material on the jig is composed of heavy and light particles, while the concentrates are all heavy particles A gate constructed on this principle can be used as a middlings discharge by simply raising the shield to a sufficient height above the screen so that the middlings will flow over the concentrates and out through the siphon discharge The

Fig 20

§ 26 Ore Dressing And Milling 37

lift being veiy shoit, the dischaige ib, not apt to clog, and the top of the shield or gate being open, the jigman can tell at a glance ]iist how the machine is workings and, if the gate clogs, can reach his hand in and clear it out In the illustration, 'Aepresents the Avooden grating Avhich supports the screen c on which the ]ig bed less, /('represents the bed of concentrates, Avhile t represents the gangue material above The opening f in the side of the jig box is usually provided with a small spout over Avhich the concentrates discharge as at p

34, Tailings Discharge. — The ]ig tailings ordinal ily dischaige at the loAvei end of the box, over a tailings dam, the lattei being one side, or a part of one side, cut lower than the lest of the box

In the method kuoAvn as the Hartz discharge, both the tailings and the conceiitiates from each compartment floAv on to the screen of the next compartment — the tailings over the dam and the concentrates through a slit iindei it There is a drop of about inches betAveen each screen, to pi event the material fiom backing up through the concentrates discharge, and the slit is protected by an apron Avhich prevents the tailings from mixing Avith the concentrates as they floAv over

When Avater is scarce, and it is desirable to use as little as possible and still have automatic discharge, mechanical means are used to dischaige the tailings The most common mechanical discharge is a revolving paddle Avheel which scoops the tailings over the dam as it revolves, or a scoop at the end of a suspended oscillating rod, Avorkmg in the same Avay The Archimedean helical scrcAV has also been used foi this purpose

35 . Stay Box. — -Another Avater-saving device is a box or extra compartment built on at the lower end of the ]ig, called the stay box The tailings discharge into the >stay box thioiigh a sht Avhich is 2 oi 3 inches loAver than the overflow of the stay box This gives a constant head or back pressure against Avhich the tailings must discharge, The

38 Ore Dressing And Milling § 20

box albo acts as a settling box or hydraulic dassifiei , any heavy particles which may be in the tailings settling to the bottom, while the lighter tailings pass away with the ovet - flow Another form of stay box discharges entii ely tin ough a hole m the bottom, the opening being regulated automata cally by a plug attached to a float which uses and falls with the watei in the box As the float uses or sinks, the discharge opening is altered to correspond The tailings sink to the bottom and discharge, most of the watei being retained*

36 . Jigs are usually built of wood, held together by bolts and iagserews, and if well constructed will last for S or 10 years— working a single shift Sheet-iron pgs, though sometimes used, are not practicable for ore milling m general, as in the majority of mills the only watei obtainable IS pumped eithei directly from the mines or fiom stieams into which the acid wateis from the mines diain, and this corrodes the iion and soon renders it rotten and worthless Moreover, the constant vibration shakes non jigs to pieces in a very few years unless they are veiy stiongly made

Jig boxes are usually 3 feet to feet square in the clear The areas of the piston and screen compartments are usually equal, though for coarse jigging the piston compartment is sometimes reduced to J or of the area of the scieen The space beneath the dividing partition should nevei be of less area than the piston coxnpaitment, to avoid conti action of the water column The bottom of the jig box in fine jigs is sometimes built semicirculai*, as this form obstructs the water less than sharp angles and gives a more even flovc The speed of the jig vanes from 75 strokes per minute for coarse ore to 200 and even 300 strokes for the separation of the very fine sizes Strokes with a length of 5p inches are used in Europe for very coarse Jigging, but m Ameiica these coarse sizes are seldom jigged, except at anthracite collieries, and % inches is usually the maximum stroke The plunger compartment is usually covered by splash boards

§2G

Ore Dressing And Milling

If chips of wood 111 the oie cause trouble by cloomg the screens of the fine jigs, they may be collected by placing a strip of screen just back of the overflow of the coarse jigs, with its edge dipping slightly beneath the surface of the watei

37 Stationary Buddies — The buddle is one of the oldest f 01 ms of slime concentrators Buddies are particularly efficient in treating slimes too fine to work well on belt or table concentrators, and are used chiefly for ti eating the tailings from othei concentratois The principle of the buddle IS that of all concenti ators — the settling of minerals m the 01 der ot their specific gravities

From plane tables down winch the pulp flowed to round buddies was a short but impoi tant step Round buddies aie merely circular tables, with the sui faces inclined either inwaids or outivaids at a slope of fiom 1 to 2 inches per foot They aie usually made of wood oi sheet iron, with a wooden or cement working suiface The pulp is fed eithei at the center or at the iini, accoiding as the buddle is an out wardflow or an nward-fioW machine, and flows down the table, depositing its contents as it goes, in the order of their specific gravities The out waid-fiow buddle is superior m operation to the inward-fiow, as the pulp stream spreads out as it flows, consequently diminishing the force and allowing the inateual to settle out more completely, Avhile the pulp stream on the ward-fiow buddle contracts in its downward flow, giving a deepei and stronger current towards the tailing sluice and washing away considerable fine mineral with the tailings Each form, however, has its advantages

The feed of the inward-flovv table being at the circumference, the area over which the headings are deposited is veiy much larger than in the case of the outward-flow table, where they are deposited near the apex of the cone A great deal of gangue is also deposited at the head The middlings product of the ward-flow table is smaller, coat set, and

40 Ore Dressing And Milling § 26

Fig 21

§ 2G ORE DREvSvSING AND MILLING 41

richer than the con ebponding class fiom the outwarcLflow tablCj and the tailings aie apt to lun lather high

The outward-flow table, on the other hand, tends to produce a small, clean head class, shading off rapidly into a large, low-giade middle class, while the tailings are nearly barren

38# Paine and Slepliens Buddie. — The original foim of round huddle was a stationary, convex, or concave conical table, 11 to 30 teet and upwards in diametei, upon which the pulp was fed, in the case of the inward-flowbiiddle, from slowly revolving feedpipes running fiom a main pipe in the center and dischaigmg at the circumference, and, in the outward-flow huddle, fiom a slowly revolving central feed The Paine and Stephens huddle, shown in Fig 'iil, illustrates the best type of stationary inward-flow buddies The brushes which are used on all inteiiiiittent-discharge

buddies, are for the purpose of spreading the deposits evenly over the suifaceof the table They radiate from thecenti'al shaft and i evolve with it The pulp on eithei maid-oi outward-flow buddies flows down the inclined table, the heavy particles depositing first, and the light, or tailings, last The huddle IS usually ai ranged so that the feed and discharge gates and the brushes are raised automatically by a woimgeaiing as the deposit accumulates

When the huddle is full, which will occur in from 8 to IS houis, according to the coaiseness of the sand, the inachine is stopped and the table cleaned The bed is usually divided into three classes — heads, middlings, and tailings — the three rings are shoveled off separately, and both the heads and middlings, and sometimes the tailings, ai e retreated The middlings are rewashed as before, and again divided into thiee classes, the heads going in with the first headings and the middlings mixed with other middlings and retreated The headings are huddled again, the huddle discharge being raised about 3 inches, and the huddle covered with middlings from the tossing tubs The heads aie then charged When this is completed, the deposit is again

Ore Dressing And Milling

divided into three rings and cleared off, the heads being carried to the tossing tubs for further -vvasliing and the middles again huddled

39 . KeyoMng 33 ucMles, American milling pi'actice has always been remarkable lor an aversion towaids intermittent-dischaige machines, hand cleaning, and retreatof pioclucts It was this dense to avoid the formation and retreatment of middlings that gave use to the invention of continuous discharge }igs, belt concentratois, etc , and it naturally showed itself in regard to the stationary-table buddle with its intermittent dischaige and mamtold retreatnients, and the invention of the revolving continuousdischarge buddle was the result

The sorting action of the revolving buddle is the same as that of the stationary type, but the operation is quite diffei - ent The table itself is given a revolving motion, the rate var 5 nng from one revolution in 5 minutes for very fine slimes to revolutions per minute for pulp carrying 8 or 9 per cent of fine sands The higher the speed of the table, the greater is the capacity — the limit of the speed being determined by the grade of the tailings as compared with the gam in capacity The feeding apparatus is stationary, and the pulp feed extends only about to of the way around the table, the lemainder being fed by wash watei The maid-flow buddle is comparatively little used except in connection with the outward- flow machine Reyohing tables are made, like the stationary tables, of wood or sheet non, with a working surface of either wood or cement The frames are sti ongly braced. The tablet range from 12 to 30 feet m diameter and are driven by bevel gears or worm-gearmg, usually from above

40 . Inwaid-lTow Btidcllos. — The revolving buddle difteis from the stationary buddle only in that the table is revolved, while the feed is stationary, and that the operation IS iTiade continuous by the use of wash Avater, ivhich cleans the vaiious classes off the table as fast as they are

§ 26 ORB DRESvSING AND MILLING 43

formed and canies each to its respective launclei The upward-dow revolving huddle is fed from aUough or launder at its ciicuiiiference, which is divided so that pulp is fed about of the way round and clear water the remainder Flowing down the table, the pulp stream deposits its contents The different classes are washed into their respective sections in the central pit by jets of water from stationary pipes running radially oi diagonally across the zone on the table in which they aie deposited Thus, supposing there were three classes, headings, middlings, and tailings, a jet or senes of jets about -J- of the way lound from the forward end of the pulp-feed box, and extending diagonally up from the discharge pit as far as the layer of tailings is considered to leach, will wash this layei off coiitmiiousl}, for the table is revolving and constantly bringing fresh matenal midi the jets A second jet f of the way round, and extending across the middlings zone of the table, will carry the middlings to their laiindei , and a third jet, at the top of the table, washes the headings down just befoie the particulai portion of the table upon which they are deposited comes again into the pulp stream A revolving bustle brush is frequently used with the jets to clean the material off, as when water alone is used a slime forms on the surface of the table, which diminishes its efficiency

41, Outward-Flow Buddies —The outward-flow huddle is the type most geneially used in Ameiica, as it produces barren tailings, and the product does not have to be put through so many operations and reti eatmeiits Moreover, in American gold milling, buddies are used to treat only very fine slimes, such as the tailings from ffne jigs and vanners, in which the greater pax't of the valuable mineral is extremely fine — much finer than the greater poi - tion of the gangiie — and the pai tides are earned some distance down the table befoie they have time to settle through the pulp stream. In this case, if the current gained velocity as it descended, it would sweep these tiny particles along with It and carry them over the tailings gate

U Ore Dressing And Milling § 20

The feed of the outlaid- flow huddle is at the ceulei, usually from a round non box siuroundmg the shaft This box feeds pulp through onfiees ui the bottom extending from to -J- way lound Us cucumteience and cleai water the lemainder The pulp and water fall on to a fixed apron extending a short distance out ovei the table, and fiom here flow on to the slowly revolving table, wheie the mineial duly sorts itself. The table is cleaned by jets and blushes in the same manner ae is the inward-flow table

43, The Oollom biitlclle is a notary buddle, which is in form only a slight modification of the old stationary machine The pulp is fed in thiough a trough instead of fioin a cential distributor, and is spread by brushes, which aie sometimes given a leciprocating motion to prevent the pulp from packing aga-inst them The wash water is dehveted from a central box or fiom an annular pipe at the head of the table The table is cleared by jets, as m the other forms described These tables are sometimes made in two or more annular sections, with a slight step between each, the sections sometimes have different slopes They aie also used for amalgamating tables, by cutting a senes ot annulai grooves in the surface and filling them with meicury, which will amalgamate any gold coming in contact with It

43. Evans Buddie. — It is sometimes desirable to protect the headings from the action of the wash water, and in such cases either a sphal apron is used, as in the Evans huddle, or the wash water is not fed over the apron, but issues from holes m a spiral pipe hung in such a manner that the best headings aie not subjected to the action of the wash water

The slime table, shown in Fig 23, known as Evans huddle, protects the headings by means of a spinal apron placed at the center of the table. The pulp flows over half of the surface of the apron a through holes m the bottom of the chs' tnbutor which is partitioned so as to feed pulp half way round and clear water the other half. From the apron the

Ore Dressing And Milling

§ 36

pulp flows on to the i evolving table b Owing to the spiral form of the apion, the top headings, as they sink, passatonceimdei.it, and aie protected fioin any furthei action of the pulp stieatn and wash watei until they leappear, at the end of the revolution, fiom iindei the widest patt of the apion, when the jet from f washes them dovn into a division of the launder The middlings me washed off by the jets fiom the perforated pipe just ahead of the

headings jet, into another division, and the tailings how off through the remainder of the launder The position of the slime and water feeders on the api'on is regulated by the division boaid k The feed apron is hung from the frame I and can be readily adjusted relatively to the table The speed of a 14-foot machine of this type is about 1 revolution in 80 seconds, and the capacity 25 to 30 tons per day of 24 houis. The slope or pitch of the table is about inches per foot and of the apron IJ inches The table revolves in the

44, Mixltiple-Declc Biicldles. — A frequent device to save expense and economize m flooi space is to place one huddle above another, as shown in Fig 23 Each table may be fed separately, or the lower table may take the tailings from the upper and f ui ther concentrate them This latter scheme is especially applicable when both inward and

Ore Dressing And Milling

§80

4r)

outward flow buddies are used The inw aid-flow table is placed above and the rich tailings from this table discharge directly on to the outward-flow table below, which catches most of their values and delivers a barren tailing In this way the best points of each tyie are applied This scheme IS employed with both stationary and i evolving buddies

FtO 23

Fig-, 24 shows a sectional view of a triple-deck Linkenbach buddle This huddle is stationary, but differs fioni the ordinary type in that the discharge is contmnous, both the feed and receiving launders i evolving Each table is about feet wider than the one above it When two oi three grades of slimes are to be treated, the coarsest grade is treated on the top table and the finer grades on the lower tables Referring to the figure, the pulp is fed on to the tables A from pipes / The wash water is fed thiough the hollow

Ore Dressing- And Milling

spindle and the pipes c, which are attached to it and revolve with It This spindle also caiiies the revolving cylmdiical gates g-, which deliver the pulp successively to all points around the ciiciimfeience of the distributing apions Jets of water from the pipes e dean the classes off the table as fast as they a:e formed, carrying them down to the laundeib /, / The launders for all but the bottom table aie stationary and are made up of a ring of fiat funnels, about 2 teet apart, delivering into pipes leading into the laundei of the next table below In this way all the tables discharge constantly into the lowest launder, which is supported on wheels and i evolves at the same rate as the feed gate and cleaning ]ets The revolving laundei is divided by adjustable partitions into as many segments as it is desired Loform classes of mineral As this trough revolves at the same late as the cleaning jets, any poitioii of it is always at the same position with reference to the discharge of the table and consequently catches the same class of material Suppose, -for instance, we are forming three classes— heads, middles, and tails— on the table That portion of the trough closest behind the cleaning jets will catch the taihngb which are at the lower edge of the table By the time the highest of the tailings has washed down the table, the trough will have traversed some distance At the point where the tailings end, we put a partition The length of the tailings segment of the launder will be proportional to the width of the zone of material we desire to consider as tailings The middlings will wash down into the trough behind this partition, another partition being placed between them and the headings which reach the bottom last, and consequently settle in the last portion of the launder The use of openbottom launders for the upper table is equivalent to having all the tables discharge into one revolving launder, as the classes, as fast as they are washed down the tables, flow right on through the funnels and pipes into their pioper sections of the bottom launder as it revolves Any overflow m the wash-water feed box b is taken care of by the oveiflow pipe 0

§ 26 Ore Dressing And Milling

Concentkatiisg Tubs

45, Tossing Tul)& — The tossing tub, or keeve, is little used in America, but m Europe it is quite common m connection with huddle, paiticulailf with those of the stationary type, the headings from which are always further concentrated and cleaned by tossing It is simply a round

[ill

wooden tub, shown m Pig 25, about 4 feet in diameter and 2i feet deep in the clear, made usually of 3-inch material This tub IS stationary, but a vertical shaft or spindle passes up through a cast-iron sleeve or cone extending up in the center nearly to the top of the tub and is operated by a

50 Ore Dressing And Milling § 26

bevel gearing- belov On thi spindle and revolving with it IS the yoke2 bearing the staring paddles b This yoke may be lowered and laisecl into and out ot gear by a light tackle over the tub On opposite sides oC the tub aie two weighted bell-crank levels with light hammers attached to their upright dims These bell-cranks are pivoted uudei the lowei edge of the tub, and their horizontal arms extend nearly to the center, whcie they aie engaged by pins set in the two Vertical bevel wheels c, on opposite sides of the hoiizontal bevel wheel d Thei-e are tAvo pms in each wheel As the wheels revolve, these pms raise the ends of the levers As soon as the lever is leieased by the pm passing from under it, the Aveight causes it to drop back suddenly, and the hammer head on the other arm is brought up against the tub with a sharp blow Each hammer stakes tivo bloAvs at each 1 evolution of the shaft, Avhich is run at a speed of trom 25 to 50 revolutions per minute — the usual speed being about 4:8 revolutions

The tub befoie starting is Med about one-third full of water, the yoke is let doAvn into gear, and the hammers are blocked back by wedges between the hammer aim and the side of the tub. The stirrer is then started up The huddle headings are fed in till the tub is nearly full or the pulp reaches the proper consistency The yoke is then lifted out by the block and tackle above it and the hammers thrown into gear by knocking out the Avedges between them and the tub. The pulp is then allowed to settle Avliile the hammers are tapping away on the sides of the tub at the rate of 50 to too blows a minute each This rapid airing keeps the water agitated, and the mineral settles in layers of equal falling particles This settling operation requires from 15 to 20 minutes The machine is then stopped and the water siphoned off The upper 2 inches of the bed are usually thrown away as waste The remainder of the bed is divided into two beds of equal thickness The headings are set aside and the middles are retossed The headings from this second tossing are combined with those from the first and sent to the roasters preparatory to some other treatment*

Ore Dressing And Milling

The second middles are letiuned to the buddies and are lebuddled along with the huddle middlings, and the iippei layer of tailings is tliiowii away The tossing tub is suitable only for the treatment of medium-giade slimes Sand slimes coaiser than IG to 20 mesh are too coaise to separate properly, and very hue pulp shines do not settle well

46, Dolly Tuh, — The Dolly tub is anothei form of slime-concentrating apparatus It consists of a stationary

wooden or iron tub, having preferably a conical bottom, slanting from the center to the sides, as m Fig 26, with a

Ore Dressing And Milling

26

raised funnel dischaige at the center, a suspended veitical shaft driven by a bevel gearing above carries foui arms on which are fixed paddles fitting loosely into the annular space between the sides of the tub and the central discharge cylinder The feed and dischaige ot the machine may be either continuous or intermittent The pulp in the continuous-discharge machine is fed into the tub near the side The heavier pai tides sink to thebottom and the centrifugal force set up by the revolving paddles, combined with the sloping bottom, carries them to the outside edge, wheie they dischaige through or holes The lighter particles, on the other hand, aie kept m suspension by the motion of the water and are gradually diawn into the dischaige funnel at the center The paddles are sometinies dispensed with by delivering the pulp stream tangentially into the tub, the force of the stream thus delivered setting the water m the tub m motion in a circular direction The whole ot the water may be introduced along with the slimes, or part may be delivered through separate pipes, at different points in the circumference of the tub.

Ore Dressing And Milling

(Part 3)

Table Oonc'Ent Ration

1. Tlieory of Oonoentpation* — All concentration, whether .wet, dry, or centritiigal, depends upon specific gravity primarily and upon size secondarily, the two together agreeing with the law of equally falling bodies Assuming all particles to be of practically uniform size, the sorting power of water, for instance, will arrange particles falling through it in layers according to their varying specific giavities, the heaviest going to the bottom and the lightest arranging themselves on top with intermediate ones between in their oi der The law of equally falling bodies, falling free in a -fluid, as water, may be represented by the formula

wheie S speed, — weight, r — resistance, friction, c — cohesion, and b buoyancy Now, in unsized ores the separation will not be so satisfactory, for in any case the following is true, because f and c vary as the surface and b as the volume, the volume varying more rapidly than the surface, since

tt and surface 4 r

Foi notice o£ copyright, bee p ige iranicdiately following the title page

a ORE DRESSING AND MILLING § 27

Suppose r (the radius) 1, then tt X 1® and the surface — 4:- x V

But suppose r 10, then 77 x 10 1383- tt, and the

surface 4x x lO"" 400 x, so that r /+ c 1? vanes less than the volume, while zu vanes directly as tJie volume,

therefore varies faster than r, and the ratio y S inci eases,

and presently a point is leached m unsized 01 es where a comparatively large body of gangue, 01 gang tie with ore attached, will fall as swiftly as a smaller body of greater specific gravity, or more swiftly than a body of ore smaller still This results m some gangue in the lower layei and some fine ore in the superposed layer, the 01 e deci easing and the gangue increasing m quantity upwards In each layer the particles of ore and gangue, though diffeung in

size, have the same ratio of This law also holds in sized ' r

ores, but is unaffected by the complications stated above, and the concentrates should be, therefore, comparatively clean

2. Bnnipin Tables. — Bumping, or percussion, tables are largely used for concentrating ores, in which the gold is so intimately associated with iron pyrites that it is not freed by stamping The bumping table is essentially a suspended table which is capable of a limited movement, and is subjected to a senes of blows or shocks m the plane of its motion The shocks are delivered by drawing the whole table back by means of cams, and releasing it, when strong springs Will throw it f 01 wards suddenly, and the end of a beam, which is a part of the table, strikes against a fixed block or buffer, bringing the table up with a jar The table IS slanted away from the head or bumping end, and the pulp IS fed on at this end, running down m a thin sheet The heavier particles in the pulp settle to the bottom and cling to the surface When the table strikes the buffer, the sudden jar causes the mineral to creep a little farther up towards the head of the table Such pai tides as are heavy enough, in proportion to the amount of surface they expose,

§ 27 Ore Dressing And Milling 3

will resist Lhe down-flowing sheet of watei, until finally they reach the head The shock also serves to separate the pai tides from one another and to completely submerge all pai tides, and then vei y little mineral is floated away by a coating of air

The surface of the table should be absolutely true and even, so that all the pulp is subjected to the same action, and the top should be as thin as possible without danger of buckling under the jar, then the shock of the bump will send a violent tremor tliiough the whole sheet If a table be watched while clean water is being run over it, at each blorv myriads of small drops of water will be observed to jump up from the plate at light angles This action, in the regular operation of the table, keeps the pump agitated and exercises a certain amount of classifying action on Lhe particles Bumping tables have a large capacity, make a fairly clean separation, and are simple in construction and operation; but as the loss of slunes is heavy, they are not to be used for veiy close concentiation

3 , Gilpin County Bumping Table. — This table, although one of the earliest of the many forms of peicussion tables, is still one of the most commonly used, and the oiigmal design has remained practically unchanged The table IS typical of the end bumping class The consti uction IS as previously described The cam for driving the table may be exthei above or below The icturn is accomplished either by fiat steel bar springs or by coiled sjorings, rigidly fixed at one end, which are forced back by the table on the back stroke, and forwards as soon as the cam releases them The double table is about 4 feet wide and 7 feet long There are two plates, one on each side of the bumping beam, set on a slope of inch per foot for the greater portion of their length On the last 3 feet, at the head of the table, the slope is increased to 1 inch per foot

The is run into the rectangular feed box, towards the head of the table, and flows gradually on to the table The wash -water box is set above the feed box in order that the concentrates may be washed clear of slime and gangue

4 Ore Dressing And Milling § 27

before passing over the dischaige The head of the table is always away tiom the battery, and the concentrates, which die comparatively diy, aie allowed to accumulate on the door at the head ol the table The capacity of a table IS tioni 10 to 20 tons pei day

4, Perfection Concentrator. — This inacbine is meiel} a modification of the Gilpin County bumping table The bumping beam is placed underneath the table, and one single sheet of copper is substituted for the two plates in the Gilpm County bumping table The height and slope of

Fig 1

the table can be adjusted by means of nuts on the hangers. The coiled- return is used The table is shown m Fig 1 Its capacity is about equal to that of the double Gilpin County bumping table, but it weighs only about two~thirds as much

5. Itittingei' Slde-Pereiission Table. — The side-per cussion table is but little used in America, though it is quite common m Europe. The table is hung on a slope, which is adjustable between 3 degrees and 0 degrees As the name indicates, the swing and shock are lateral, the beam running across the table on the under side The table IS driven by cam and springs, as in the end-bump table, the amount of the swing being also adjustable The pulp is

ORE DRESvSTNO AND MILLING

§27

uni m at the uppei corner of the table, on the side opposite the buffer, and flows downwards m a thin stream The wash water is also inttoduced at the head, between the pulp feed box and the buffer side of the table As the pulp and water flow downwards in a thin sheet, the heaviei mineial sinks to the bottom and is gradually woiked ovei towaids the buffer side by the side jais Those particles of mineral which, m proportion to their weight, piesent the least suilace to the down-flowing stream naturally require the longest time to traverse the length of the table, and are consequently exposed to a greater number of shocks than the iightei particles and are woiked farther over towards the buffer side In this way the discharge over the lower end of the table may be divided into any number of classes desired, ranging from very poor tailmgs on the feed side of the table to rich concentrates on the buffer side Each class discharges into a separate trough or compartment The tables are visually double and are divided by a strip down the middle, each vSide having a separate feed Many materials have been tried for the surface, but cast-iron, slate, and marble slabs aie found to give the best lesvdtb The table performs a very good separation, but the product of pure concentrates is comparatively small, and the formation of middlings is undesirable m the class of work for which bumping tables and vanners are used iii America, moreover, the product is mixed with large quantities of water and requires settling after it comes from the table, so that the side-percussion table can hardly hope to supplant the end-bump table to any extent in America The wear on the cams and tappets of percussion tables may be reduced by the use of roller tappets

Vanning Iviachines

6 . The principle of all vanning machmes is the same as that of the gold pan and batea, namely, separating the heavier mineral from the lighter by gently shaking or vanning the pulp, the mild agitation keeping the particles of the lighter mineral in suspeiibiun, while the particles ol the

Ore Dressing And Milling

(j

heavier mineral sink to the bottom A constant automatic dibchaige is accomplished with vanning tables by suspending the table and giving it a houzontal jerking motion by means of cams and springs or by eccentrics The table moves slowly out to the end of the stroke, and returns with a jerk which gradually works the heavy mineral which has settled to the bottom oi the stream of pulp running over the table, along oi across the table, in a direction opposite that of the jerk The Wilfley table is the best example of this type ot machine In the belt vanners, the operation is made continuous by precipitating the mineral on a slowly moving endless rubber or canvas belt, so that the whole precipitating surface is constantly advancing, carrying with it the mineral accumulated on it Of this type are the Fine, Embrey, and Lung vanners and the Woodbury concenti'ator,

YAlSlSflNO TABLES

7. Wilfley Table. — The Wilfley table, shown in Fig 2, IS a fiat linoleum- CO vexed table, 10 feet long by 7 feet wide,

Fig 3

set on rollers, and slightly mclmed from front to back The table IS moved forwards by a togglejomt arrangement, and IS brought back by springs with an endwise jerk, which gradually works the concentrates down to the discharge end

§27

ORE DRESvSrN(; AND JIILLING

The feed box at the back of the table extends ftom cud to end, and is divided by a movable gate, the pulp being fed in one end and clear watei along the rest of the length, keeps the headings clean, so that the operator can tell at a glance how the table is woiking

A set of cleats, 2 to 7 in number, according to the chaiactei of the ore, is nailed along the table paiallel to its length These cleats tape giadiially fiom 4 inch thick at the upper, or tailings, end of the table to a feather edge at their lowet end The fiist and longest cleat is put on towards the lower edge of the table and luns up to wilm 2 feet of the head The other cleats are successively shorter, the top one being about 4 feet long The pulp is fed in as near the tailings end as possible, and the heavier mineral sinks to the bottom and clings there The cleats prevent it from sliding straight across the table and oft, and at the same time allow the particles of lighter minerals, which are held m suspension m the water by the jerk of the table, to pass over and off The tape mg of the cleats provides tor a considerable range m the size of the particles of gangue and lenders the extremely careful sizing, which must be done for most concentrators in order to get the best results, altogether unnecessary The finer gangue, which is held in suspension in the stieam of water, is carried over the cleats with It, but the coaiser pai tides sink At each jeik of the table, however, they are thrown momentarily into suspension, and as they work towards the end of the cleat, they finally come to some portion which is low enough to allow them to pass over This operation must be repeated at each cleat The space between the end of the lowest cleat and the head of the table allows the middlings, or unseparated ore and gangue, to pass over the edge of the table into a middlings trough, through which they flow to a wheel conveyer, which raises them into a launder returning to the feed trough, to be retreated This insures a clean heading and at the same time prevents the loss of the mineral m the middlings An inclinect shield prevents the tailings from entering the though This table has shown a

ORE DREvSSING AND AIILLING

§27

remarkable saving, taking the oie right from the stamps, like the bumping table, without previous classification ; and It has been proved that it can compete, at least on even terms, with the best of the belt vanneis on coarser piodiicts and has a much larger capacity — 15 to 25 tons in 24 hours, or equal to the best bumping tables, with a much better separation,

8. Oammett C one entratoi\ —This machine is constructed on the Rittmger model and has recently leceived

much praise for accomplishing good work. It has also come into prominence owing to its being able to closely separate different metal minerals, such as zinc, iron, lead, and copper sulphides, from each other The designer of the Wilfley concentrator imagined that the Cammett was an infringement upon his table, and so brought suit against the latter While the suit was pending the Wilfley people bought 'out the Cammett people, whereupon the Court decided in favor of the former against the latter The table is shown from the operating side in Rig 3

9. Oonsti'uction of the Canunett Table. — Tlie top of the table consists of redwood boards tr, m which longitudinal riffles are cut These riffles are said not to warp,

Ore Dressing And Milling

break off, tuin up at the encL, or split It wiil be noticed that the riffles aie continuous from end to end oi the table and that they gradually become flattened until, at the clischaige end, the grooves aie scarcely noticeable The pulp distributing box b is constructed on the principle of delivering the coarse oie at the head at the table and the tine ore neai the tail end The box is suspended on brackets and moves with the table top, tlius insuring agitation necessary for classifying and to prevent clogging. The table is moved by the cone pulley which is connected by a belt 2 inches wide to a similar pulley on a counter shaft, winch should make about 250 i evolutions per minute The floor space occupied by this table is feet 4 inches wide by 10 feet 1 inch long The height of the table ovei all is 34 inches

To further insme that the table top retain its original shape while m motion under its load of pulp and water, the proper points at which to place the bearings weie determined by a system of balancing, by which parts remote from the bearings balance eachotliei, producing equal pressure on each bearing and relieving the middle portion of the table top from strains The satisfactoi y result obtained can be seen in the absolutely quiet state of the water on the table top when the table is m operation

The pulp distributing box is one of the special features of the table and has been designed after many extensive experiments and practical working testa This distributing box is a modification of the well-known spitzkasten, which classifies the pulp, delivering the coaise at the head end of the table and the fine near the tail end The box is suspended on brackets and moves with the table top This insures the necessary agitation requisite for a classifying action and also prevents clogging at the discharge outlets, a grave difficulty encountered m other forms of distributing boxes With each box is provided a set of various sized outlets, made of a non-wearable mateiial

The wash-water pipes, three m number, are connected to the mam water supply pipe by angle valves, enabling the flow of wash water to be regulated to any degree andfor any

ORE DRESvSING AND MILLING

n

part of the table These pipes dischaige the watei into separate compartments of a wooden trough, which distiibutes the water in a uniform sheet over the table sui face

It requires one-half horsepower to drive a Cammett concentrator by an electric motor, and this power will give about 10 tons of fine slimes in 24 hours, while on coarse ore the product will be very much inci eased The size of the pulp may be fiom 3 mesh to the finest shines, although such a mixture cannot be treated without previous sizing, as slimes are moie difficult to concentrate than coarser material The water required for this table will vary from 5 to 20 gallons per minute Middlings must be recrushed before placing them back on the table

10 . Belt Vamiers. — Belt vaiiners are of two types the side-shaking and the end-shakmg The principle, however, IS the same in both The end-shaking vannei is comparatively little used, as the side-shakmg machine is the better, both in principle and construction End-shaking machines, however, are still used in some mills where the conditions are such that they do practically as good work as the side-shaking machines, but they lequiie a largei amount of water, a greater inclination of the belt, or a more rapid shaking motion than the side-shaking machines, in order to do the same work

11 . Erae Yaiinei\ — The True vanner, shown in Fig 4, iS the original side-shaking machine, and is typical of the class It consists essentially of a continuous rubber belt traveling slowly up a slight incline and shaking rapidly back and forth sideways The belt is usually 4 feet wide — though 6-foot belts have been used™and has elastic raised edges It runs over two large galvamzed-iron rollers

13 inches in diameter and 12 feet apart from center to center, set at either end of a slightly inclined frame. This frame is supported from the fixed frame or table of the machine by eight flat steel rods or springs, which allow it to swing back and forth laterally, and eccentrics on a

§ ORE DREvSHlNG AND MILLING 11

Clank-shaft give it a rapid side shake — abnut ISO to *300 elouhle strokes per muiute being the average speed, the displacement or throw being 1 inch A number of small rollers along the top of the shaking fiame support the belt between the mam rollers and keep the sniface smooth and even The pulp flows on to the belt from a distiibutmg box about one-fourth of the way down from the head, and flows downwards in a thin sheet

The heavy mineral settles to the belt and clings theie, while the gangne mineuil is earned down with the stream into the tailings launder, the separation being greatly facilitated by the lapid side shake The belt moves slowly upwaids, carrying with it the clinging particles of heavy mineial These pass through the wash watei, which is delivered in a series of jets across the belt just below the head roller, cleaning the headings so that the woiking of the machine may be easily watched, and such pai tides as withstand this are gained ovei the head of the machine into the concentiation box wheie the concent! ates are washed off and settle to the bottom, from which they are scraped every thiee or four horns into the box E, which is sometimes set on wheels for convenience in removing the concentrates The guide rollers B and C cai ry the belt in and out of the concentrate box and also control the tension of the belt, being adjustable vertically on either side A second senes of wash- water jets is sometimes played against the belt from beneath as it leaves the box to clean off any mineral which might cling to it, and the oveiflow selling boxes F are set after the concentration box The faces of all the rollers except C are slightly longer than the width of the belt, C, however, bears on the upper oi woiking surface of the belt, which must run between the flanges, and it is consequently made iiarrowei, with its corners rounded or beveled off

13. Driving Arrangements for Ernie Aanner. — The stationary frame of the vanner consists of two long timbeis G, bound together by thiee cross timbers The

iV U III —13

n ORE DRESSING AND MILLING § 27

Cl OSS tunbeis aie extended on. one side to form a support for the ciank-shaft S This frame less in shoulders cut in the four uprights P The shoiildeis m the posts at the lower end of the machine are deeper than in those at the head so that the whole fiame has an inclination from head to foot, and this inclination is fuither adjustable by means oi wedges underneath the lower end of the frame at the shoulders The eight beatings d for the rods supporting the shaking frame aie bolted underneath Gy the bolt holes in the bearing being oblong, so that the bearing can be adjusted The end bearings each have two bolt holes, the intermediate bearings one each

The vanner is driven by a belt with a quarter twist fioin the countershaft pulley to the crank-shaft pulley p On the crank- shaft are three small cranks each inch out of center, which connect by fiat steel rods or pitmans to the middle of iron pipe girts extending across the shaking frame The crank-shaft also canies two small flywheels f The driving arrangement for the vanner belt is peculiar A narrow belt i passes from a cone pulley C on the crank-shaft to a flanged pulley d on a worm-shaft t The worm on t slowly turns a worm-wheel %v driving a short shaft, which is m the same line as the axis of the head roller of the belt On the end of the -worm-wheel shaft is a crank which connects with the free side of a flat spring 4, the other side of which IS firmly fixed to the end of the roller shaft between the two shafts This spring forms practically a flexible crank connection between the two shafts and yields to the swinging of the frame The worm and worm-wheel aie covered by a cast-iron casing, which has a limited motion about the ivory-wheel shaft on an independent bearing bolted to the stationary frame This casing also forms the bearing and support of the worm-shaft and its adjusting rod When the machine is idle, a hand screw draws the casing around and throws on the casing the whole weight of the worm-shaft, flanged pulley, and adjusting rod, but when it IS in operation, the screw is loosened and the weight allowed to fall on the belt keeping it tight

Ore Dressing And Milling

13. PvLlp Dlstrlbiitlng T3ox — The distributing box: fur the vanner is shown in Fig 5 It is attached to the frame and shares with it, the feedpipe being flexible The spi eading blocks aie fastened to the top board of the spreader, shown upside down at {a) The distributor should be close to the surface of the belt, in order to get a gentle feed and avoid washing away mineral In treating the pulp from an amalgamating battery, a silvered coppei plate is sometimes used, which sets m the bottom of the box and catches nearly all the amalgam and mercury coming over in the pulp Or, again, the meicury and amalgam may be caught m a copper well shown at (6) which sets in the box directly undei the pipe, so that all the pulp fiom the battery must fall into it This Avell can be removed and emptied at any time

The wash-water distributor is usually a narrow wooden trough with holes 3 inches apart, through which the watei discharges on to the belt Iron troughs are also used, with spouts of brass inches apart, by stopping up every other hole, the effect can be made the same as that of the wooden trough The wash water should fall upon the belt from a height of not less than inches, m order to secure the best effect The trough is supported on standards on the stationary frame and the height is adjustable by hand screws

14. Tanner Belts, — There are two styles of belts in use on Frue vanners, the plain and the corrugated The latter, called by the manufacturers the improved helt has a senes of low, fiat corrugations or riffles across its woikuig surface It is claimed by the makers, with apparent justice, that this belt doubles the capacity of the machine, or that one improved vanner, which is only a little more expensive than the ordinary machine, ivill do the work of two of the

14 Ore Dressing And Milling § 27

latter. New con ugatecl belts are much inoie expensive than plain belts, but weai well; so that, when the capacity of the mill warrants it, the improved vanner should be given the prefeience Practically the only difference m construction between the two forms is m the belts, but this necessitates several slight changes in the adjustments The improved vannet allows the use of a steeper grade and requues more wash water in pioportioii to the inci eased capacity The geneial grade of the old vanner, or the grade of the fiame,

15 usually from to 4 inches m the length of the frame, with C inches as a maximum, and in addition to this the head-roller bearing is about inch highei, with reference to the frame, than the lower hearing, and the small guide roller next to the head is also raised a little, slightly increasing the grade at the head of the belt. With the improved belt, the average grade is to niches, the shoulders m the lowei posts being cut correspondingly deeper, and the head roller is raised f inch above the tail roller, increasing the grade at the head by that amount, The plain-belt vanner is better for saving very fine shares than the improved or corrugated belt vanner

15 . Adjustments of tlie Erne Tanner. — Belt A plain-belt Frue vanner running on oidmaiy oie should have a speed of about 190 shakes a minute and a belt travel of 28 to 34 inches in the same tune The grade of the fi'ame should be about 3 or 4 inches The amount of wash water used vanes from 1 to gallons per minute — just sufficient to keep the field between the water and pulp distributors covered, with no projecting fingers of sand — and there should be from 11 to 3 gallons per minute in the pulp The belt should be smooth and even and should run true on the rollers , there should be a slight corner of sand along each edge of the belt, as Jloppy corners cause a loss If the corners are sloppy, there is too much watei in the pulp, and either the £)Upply must be diminished oi less water must be drawn off with the pulp from the classifiers If they are too heavy, however, more water must be added to the pulp

§2T

ORE DRESSINCx AND MILLING

coming: into the distributor If one corner is heavy while the other is sloppy, the distiibutioii of the pulp is uneven This maybe due to looseness ot some of the paits, causing ajar, but if evei3Thing is working noiselessly" and the feed is even across the belt, the fault lies m the adjustment of the hitteij-and is corrected by during the slotted bearings h ot the flat steel iipiights //, supporting the shaking frame, either m oi out by light bloivs ot a hammer, until an even distribution ot the pulp is seemed The same result may be accomplished by bending the end ot the driving spring in the collar over towards the side of the belt having the heavy cornel The adjustment of the guide rollers also has a slight effect on the comers

The condition of the sand corner's is also affected by the giade and travel of the belt and the speed of the shake — a slow travel or shake or a slight inclination lending to give a heavy corner, and a swift travel or shake or a high inclination tending to give a sloppy corner , but the giade, travel, and speed of belts are determined by the amount and cliaiactei ofc the mineral in the ore and the size of the particles, and the foiegomg adjustments refer to the working of the machine after the giade, travel, and speed of the belt have been fixed The speed of the side shake of the machine depends on the coarseness of the material, varying usually from about ISO strokch per minute for fine shmes to 500 or 10 foi coarser sands (30 to 40 mesh) While vauners will handle ore, with good lesults, directly fiom the stamps, it is always best, if the capacity of the mill warrants it, to classify the pulp and carry each class to a separate vanner, as the best possible conditions for woiking the machine aie thus obtained .

The upward travel of the belt should be adjusted according to the amount of mineral in the ore The belt is supposed to carry off only the pine mineral in the concentrates The rate of deposit of the concentrates upon the belt depends upon the grade, the pulp, the wash- water feeders, and the side shake These being adjusted, the travel of the belt must be made just sufficient to cairy the headings off the

Ore Dressing And Milling

§27

table at the same rate as they aie deposited. I£ the travel is too fast, bane band is earned over with the headings; if it IS too slow, the mineral will accumulate on the belt and some of It will wash over with the tailings As the headings are earned up thiough the wash watei, they are cleaned of the last gangtie matter and aie washed up into little longitudinal piles between the ets, the piles varying in size with the proportion of mineral in the ote These headings can be watched as they go over the head of the vanner and should be free from gangue There should be a slight " head " or ndge of mineral just below where the wash water strikes the belt If the belt is traveling too fast and is dischaigmg a greater weight of mateiial m a given time than there is mineral in the pulp treated, sand or gangue will be found m this head and m the concentrates as they go over the head of the vanner If, on the other hand, the travel and dischaige of the belt is too slow, the head below the wash jets becomes heavy and gradually extends down towards the pulp teed, and even through it, and a great deal of mineral washes ovei with the tailings The travel of the belt is regulated by the adjusting rod and hand wheel k, the thread on which passes through a tapped hole in the worm casing Turning the hand wheel carries the flanged pulley d and with it the belt t up or down the cone pulley Thus, if it is desired to mci ease the travel, the worm-shaft and flanged pulley are drawn back towards the head of the vanner and as the belt creeps farther up the cone pulley, the distance thiough which it travels with each revolution of the crank-shaft is increased, the opposite effect is obtained by moving the flanged pulley m The grade of the belt is adjusted by means of the wedges under the statioimry frame, where it rests in the shoulders of the posts Increasing the grade of the belt gives a thinner

and more swiftly flowing steam of pulp down the belt and a cleaner heading The feed, grade, and side shake should be adjusted so that the minei'al does not pack on the belt below the pulp feed; but if the fingers arc placed in the stream on the belt, the coarse sands can be felt rolling slowly downwards

§ Ore Dressing And Milling 17

Any looseness of the belt is taken up by the guide rollers B and C By lowering or raising A, the length of the belt m the concentrate box D may be inci eased or diminished, thus regulating the tune for washing the concentrate

The bearings of the head and tail I'rollers at opposite ends of the shaking frame are bolted to it through slotted holes and can be drawn in or out by adjusting screws If the belt shows a tendency to creep over to one side, the bolts of one 01 both of the bearings on that side aie loosened, the healings drawn out as far as desued by screwing up the adjusting screws, and then the bolts tightened Oi, if tins would make the belt too tight, the bearings of the other side may be let in a little instead

16 Corrugated Belt. — The mechanism of the corrugated'belt vanner is the same as that of the ordinary machine, and the adjustments aie performed m the same manner, but the working of the machine is quite different, on account of the shape of the belt The gi ade is steeper than in the ordinary vanner and about double the quantity of wash water is necessary. The heavy mineral settles in the corlugations and lemains theie until it passes over the head roller into the concentiatioii box, the light sands washing down over it The speed of shake should be just sufficient to settle the mineral and keep the sands in suspension, not allowing them to pack on the belt There should be slight indications of sand corners in the corners of the belt — neLlher too decided noi, on the other hand, too sloppy The methods of adjusting to meet the various conditions are exactly the same as m the oidinary vanner

17 . Speed of Tannei's. — The speed of the vanner is usually predetermined by the coarseness of the material, and when once set up, neaily all the regulation of the machine consists in adjusting the grade to fit the character of the pulp The amount and cleanness of the concentrates are regulated by the travel and wash water An experienced vannerman can tell at a glance how his machine is

ORE DRESwSING AND MILLING

working, and if anything is wrong, knows ju&t how to correct it; if there are several ways in which this can be done, his experience will indicate to him the most suitable foi the case This is a knack which can be acquit ed only by experience A good rule to observe in the care of vanners IS to keep all parts of the machine clean There should be no splashing of pulp over the sides of the belt All ivorking parts in parUcular should be gone over frequently with cotton waste, to prevent any grit getting m the beaimgs Good care results m a considerable saving of powei If the power of the null, and consequently the speed of the vanner, is constant, vanners once adjusted will run right along with very little attention except that necessary to keep them clean, and one man can tend to as many as sixteen machines ; if, however, the power is constantly changing, one machine will sometimes give a man more than he can do To get any machine to work properly, it must work undei the proper conditions

There are many other concentrators of this type, all more or less of the same design, but as none have succeeded in displacing the vanner to any extent, and as they all are really forms or imitations of the vanner, they will not be described

18 . Lulling TTtnner.— The Luhrig vanner is a accent machine of a type intermediate between the side-shaking and end-shaking machines It is practically a continuous - belt bumping table of the Rittinger type The belt is not flanged and is horizontal in the direction of its travel, with a slight incluiatioii sideways at right angles to the travel End blows are delivered to the vanner at the rate of from 150 to 10 strokes per minute, according to the ore, the bumping mechanism being similai to that of the bumping table The stroke can be varied from J- inch to 1 inches, according to the nature of the ore and the size of the particles The belt is of rubber, 4 feet wide and 19 feet long (total), and has a travel of 18 to feet per minute The pulp IS fed in thiougli a distributing box at the upper

§27

Ore Dressing And Milling

right-hand coiner — the belt traveling fiom light to left — and flows down the belt, wash watei is distributed fium a perforated pipe running diagonally across the belt The heavy mineral sinks to the belt and clings to it, and the end jar and the ti avel of the belt combine to can y it along to the left-hand end, at the same time the mineial works slowly downwards, under the co;nbined uifliience ot the wash water, the jai, and the inclination of the belt In this way the pat tides of the greatest specific gravity are canted neatly oi all the way down the lower end of the machine before they discharge over the side ot the belt The tailings, which remain in suspension or cling very lightly to the belt, discharge near the right-hand end, while one or moie classes of middlings discharge at diffeient points along the belt, according to their specific gravity The receiving trough along the lower edge of the belt is divided b}- movable gates or partitions, so that the amount and range of each product can be readily adjusted This production of middlings is one of the puncipal features of the Lung vanner The capacity is about equal to that ot the Frue vanner, and the machine uses about twice as much wash watei The relative ments of these two machines aie still a subject of dispute The Frue vannei maintains the supremacy in this country, veiy few of the others being used, while the Luhiig IS rapidly gaining a foothold abroad, where the production of middlings is not considered an objection

19 . RmbueT Coiicenti'ator — The Embrey concentiator or vanner is typical of the end-shaking vanners Like the Frue vanner, it consists of an endless rubber belt, i unrung over rollers on a shaking frame, the essential diffeience being m the direction of the shake. The driving shaft is placed across the lower end of the stationary fiame, as shown in Fig G On it are a tight and a loose pulley (to which the mam driving belt extends fiom a parallel countershaft above), two flywheels, two eccentiics r, e for driving the shaking frame, and a cone pulley from which a narrow belt extends to a second cone pulley on a shaft below the

Fig

§27 Ore Dressing And Milling

driving shaft This shaft drives the worm-shaft t thiougli a bevel gearing, and the worm-shaft iii turn drives the wormwheel and the driving idler which gives the belt its forward motion The belt is kept tight by the adjustable roller D The beaimgs of B and C are also adjustable The shaking frame is supported by six upright legs or toggles three on each side, resting in stumps b fixed to the stationary frame The frame is diiven by the two eccentrics r, which have a throw of about J inch and are connected by the rods r with the tail-iollei hearings The legs supporting the head end of the shaking frame are longer than those at the tail end, giving the belt a uniform grade of about 3 inches in its length This grade can be increased or diminished at will by means of wedges under the ends of the table

The shaking frame is kept m line by four cast-iron standards c bolted to the stationary frame, with pi ejections on the inside pressing against the shaking frame One of these standards at the head of the table is lengthened and serves as a support for a bell-ciank that gives a slight motion across the belt to the water pipe which is supported on spring legs, the other end of the belLciank is connected by a strap to the shaking frame The pulp distributor IS practically the same as that on the Fi ue vanner In another form of Embrey vanner, the crank-shaft passes under the shaking fiame, upon which falls the entire weight of the belt and lowei rollers, causing the machine to run more heavily

30* The Tinmnpli coticeulmtoi* is an end-shaking machine, somewhat similar to the Embrey in construction and operation The travel of the belt is regulated by a friction roller, however, instead of by cone pulleys The distributing trough IS of iron and contains quicksilver All the pulp passes over this quicksilver, which is kept agitated by a shaft, with stirrers attached, running through the distubutor

ru

31* The Woodbtii*y concent i*aloi* is another end-shaking vanner, similar to the Triumph in construction, but

ORE DRESSING AJD MILLING g 27

having the tubbei belt oi apt on divided into seven parts by longitudinal partitions

The end-shaking concentiatois all lequiie a moie lajiid shaking -motion than the side-shaking machines to accomplish the same ivork and aie i an at an aveiage speed of 220 to 2dt) double strokes per minute

23. Oaie of Tanners— It is absolutely necessaty for the efficient operation of concentrating machmeiy that it be kept clean The opeiatoi should go ovet all woiking parts frequently with cotton waste, so that no clu&t or grit will have a chance to woik into the bearings, and the entire frame should be wiped off at least once a day Belt vanneis are not suitable for working sizes coaiser than 30 mesh, while a still smaller maximum size, say 40 mesh, is pieferable As the sizes become finei, the slope of the belt and the speed of the shake aie diminished

Concentbatobs

33* Ceixtrlfag'al Pry Conceuti'ator. — The Claikson & Stanfield dry concentrator separates oie fiom gangue through the agency of centrifugal foice The carefully sized ore is fed on to a rapidly revolving houzontal disk or shallow pan, the iim of which is perforated with a large number of small holes The ore is thrown through these holes by centrifugal force and falls into a seiies of annular troughs surrounding the central disk As centrifugal foice vanes directly as the mass (or as the specific gravity), the particles will be discharged from the plate with a force pioportionate to then specific gravity, and the heaviest particles will therefore be thrown farthest In addition to this sorting effect of centrifugal force, the pai tides of heavy mineial present less suiface to the resistance of the an, m proportion to their weight and momentum, than the gangue and middlings pai tides, consequently, to a certain extent, the law of equal falling pai tides enters into the action of

Ore Dressing And Milling

2

the concenti atoi\ bat this is much less maiked and important than in the hydraulic concentiatoiSj an being a inudi later (thinner) mediiuii than water This coneentiator has given good results in experimental luis, but has not been adopted in practice to any extent

34. Y"oo:Ts Dry Placer Miner — Wood's diy placer minei is a form ot dry concentratui designed for treating gold-beainng placer sands without the use of water, the absence ot winch has heicLotoie lendcied worthless many otherwise valuable placer fields The machine is allied to the pneumatic jig, the sand being separated fiom the gold by a blast of air

The material must be quite dry m older to obtain satisfactory results It is passed over a gnzzly, which removes the larger stones and boulders The finer mateiial falls through into the disintegiator trough, through which iiui two shafts carrying paddle blades or beaters These blades are curved like the blades ot a screw propeller, so that the diit is fed ahead as well as broken up From the disintegrator the material passes on to the inclined table on which the separation is performed This table consists of a perforated metal sheet, forming the stationary cover oi a bellows, and IS covered with a blanket or carpet of such texture that It allows the passage of air without permitting any diit to fall through into the bellows Copper iiffles aie placed at intexwals across the table and seemed in position by the side boards, which are held m place by clamping screws, so that they may be readily removed foi cleaning up A sheetsteel cover slides up between the side boards, about h inches above the surface of the table, to pt event the escape of dust The bellows and table are hung fiom fiat steel- standards and are given a sliort longitudinal shake by means of eccentrics on the driving shaft, which runs in bearings across the lower end of the frame The disintegrator and bellows are diiven from the same shaft through a system of gears and counter shafts The bellows are operated by connectmg-rods to slotted crank plates at either end of a

U Ore Dressing And Milling §

cotiutershafl The throw of the ciankSj and consequently the stroke of the bellows, may be regulated

The blast of air from the bellows thiough the holes in the table blows away the dust and carries the coarse, light sand to the top, like a hydraulic jig, and the shaking of the table carries it down and discharges it The grains of gold, however, sink to the bottom and catch on the blanket and behind the riffles, together with more oi less sand and heavy minerals These concentrates are cleaned up at least once a day, by removing the oovei, side boards, and riffles, and brushing the concentrates fiom the blanket, and are cleaned by panning or amalgamating The machines aie provided with link-beit feed and tailings elevators, if desiied The capacity is given as from 8 to 13 tons per hour A smaller machine is also made for prospecting, with the construction modified to adapt it to hand labor, with a capacity of from 1,500 to 2,000 pounds an hour

These machines have given satisfactory results in test runs, and their invention may mark the birth of a new era for the hitherto worthless desert placers of Arizona, Utah, New Mexico, and other Western States and Territories

25, Pneumatic Jig, — The Krom pneumatic jig, shown m Figs ? and 8, is essentially a dry concentrator, the gangue being separated fiom the ore by means of lapid puffs of air up through the oie bed No water at all is used, and the ore must be perfectly diy The ore bed o, Fig 7, IS only about 5 inches wide and extends the full length of the machine The thickness of the bed is regulated by the height of the tailings-discharge dam which extends along the front the entire length of the bed, as shown in Fig 8 The feed is regulated by a similar veitical gate b m front of the opening of the hopper k, extending, like a, the full length of the machine

The sieve compartment is connected with the fan chamber by a narrow vertical slit Fig 7, extending the full length of the bed The sieve is made up of inverted troughs of wire gauze, open at the end next to c These troughs are

Ore Dressing And Milling

§7

placed fiom to of an inch apait, accoulmg to the size of the oie to be jigged

The fan f ih u. flat, horizontal vane, extending the full length and width of the fan box Theie aie several flap valves in it that open on the downstioke, preventing suction and reducing the resistance It is keyed to a rocker-shaft m the back, upper angle of the box, and this shaft is

operated by a lever /, A projecting roller tappet on

the lever is held by a spring d against a latchet wheel t on the end ot the driving shaft As the driving shaft revolves, the lever is forced back until the roller passes the ratchet tooth, when the spring draws the lever sharply back into position, throwing the fan upwards A strap e checks the lever fiom striking the wheel on the in stroke The trip

Ore Dressing And Milling

wheel has six teeth, so that lot every revolution of the driving shaft the fan makes six strokes The shaft is dnven at a speed of fiom 80 to 00 icvolutions-per minute, consequently the machine gives from ISO to 510 puffs pei minute

The rate at which coiicentiates discharge beneath the screen is controlled by a long, horizontal gi coved i oiler 1 Fig 7, having a fine-tooth ratchet at the lowei end This ratchet is duven by pawl / from the trip wheel /. The bearing pm of this pawl is fixed in a radial slot m the trip

FlO 8

wheel, so that the tliiwv of the pawl, and consequently the rate of dischaige, may be adjusted independently of the speed of the other parts

Though this Jig has received the endorsement of many good engineers and has given good experimental results, it has not succeeded in displacing the water jig to any extent It works best on very fine sizes, much below that at which tlie efficiency ut the hydiauhc jig* ceases. It may eventually find a field of usefulness m x eg ions where water is veiy scarce.

Ore Dressing And Milling

§

26. Tlio lloopei* Riieuiiiatie Coiiceiitrator. — This machine like the Kioin pneumatic concentrator, will not treat impalpable powders Fig 1) shows a pei spective view of the machine set up ready for operation It will separate at one operation as many as five minerals, some of whose variations in specific gravity may be less than one point, for instance, feldspar or quaitz from mica One separation gave a 98-per-cent pme product between quaitz and corundum In the illustiation the concentrating table and

skimmers are shown on top The rods on the apion are movable and may be adjusted to guide the different products of a machine to their respective bins As the rods aie placed in the illustration, the products will be concentrates, which form at the light of the machine looking from the apion end, next the middlings, and to the extreme left the tailings The machine is made of iron throughout, with the exception of valves, diaphragm, and dividers, but there is no reason why it should not be so constructed that no section should weigh more than 125 pounds.

Ore Dressing And Milling

2S

A sectional elevation is given m Fig 10 (a), in which a is the machine shaft having a belt-driven pulley at one end and a balance wheel c at the other The eccentric shown in Fig- 10 (i) and (i) is rigidly fastened to the shaft a, while an eccentric sleeve r may be turned and fastened to vary the stroke from 0 to inches The sleeve to lengthen or shorten the stroke is turned to correspond with the marks on the dials, Fig 10 (t), and then held in the desired position by a setscrew, shown m Fig 10 (n) and (t) The

eccentric collar in revolving on the shaft works the rod / up and down at a speed of from 350 to 450 strokes per minute The rod / works on the spungy at the lower end and is attached at its upper end to a frame Zf having a perforated leather diaphragm j upon which sheet rubber is fastened tiansversely to form five double flat valves that open on the down stroke to admit air and close on the up stroke to compress the air between the cast-iron cover and the diaphragm j The cover is also partly perforated and supplied with rubber valves /, raised by the compressed au

Ore Dressing And Milling

above the diaphragm j, admitting that au into the chamber w It is evident that the an comes into the machine from below on the down stroke and escapes above the machine on the tip stioke The concentiatmg table u foims a universal joint with the cover k o The table bed consists of a cast-iron grating shown in Fig 11, with Its bars and an space arranged at an angle of IS'' with the sides of the table Around this grating a fine woven broadcloth IS stretched and held in place by a frame shoivn in Fig 9 Upon this cloth the frame r, Fig 11, is placed, which IS crossed diagonally with strips of steel of an inch m height, spaced so to rest diiectlyupon the grating/

Pig 11

beneath the cloth The weight of the frame r is sufflcieat to form a tight joint and cause the cloth between the two bars to vibrate with each pulsation of the machine and allow the compressed air from chamber w to escape through the meshes of the cloth The strips s form riffles m which the heavier mineral particles gather and move towards the right-hand Side of the table At right angles to the strips and above them, the skimmers are fastened These are given an angle of 45° with the sides of the frame and are made of cast iron inches high, thus forming diagonal channels Ihrongh which the lighter minerals travel to the left or tailings side of the table The crushed ore is fed from the

ORE DRESvSING AND MILLING

§7

hopper at the upper end and passes on to the cloth, which, being agitated, throws the inmeial slightly upwards The air escaping as the mineral settles pi events the lighter particles from teaching the cloth as quickly as the heavier The heavy particles, therefore, arrange themselves next the cloth and fill up the riffles s The lighter particles accumulate on top of the heavier, and being unable to settle m the riffles, they follow the channels formed by the skimmeis i By the time the ore has reached the line tiv Pig 11, ail the minerals of the same specific gravities have separated and the heaviest will be found on the concentrates side, the next heaviest will follow the line n-/, while the tailings will he discharged between y and provided there are but three minerals to separate The table is given an inclination upwards, 11° being the most allowable, to facilitate the passage of the ore from the feed to the discharge end The side inclination has a direct effect upon the character of the concentrates, some minerals requiimg more than others, this matter, therefore, is to be determined by examining the concentrates as they pass over the table The table may be adjusted when running, and should, when m proper adjustment, give a clean product The capacity of this concentrator vanes greatly, but actual working results gave from 8 to 22 tons daily per concentrator.

27, Magnetism of Minerals. — All substances of whatever nature are to some extent sensible to magnetism, that IS, they are either attracted or repelled by the poles of a magnet In the case of only a few, however, is this pioperty appreciable under ordinary conditions Substances that are attracted by the magnet are called paraviagnetic those that are repelled, dtainagiieitc Iron is notably paramagnetic, nickel, cobalt, and chiommm are feebly, but appreciably, attracted by a hand magnet Manganese, titanium, cerium, platinum, palladium, uranium, and

§ Ore Dressing And Milling 31

osmium, though geneialiy considered non-magnetic, arc paramagnetiCj and can be sensibly attracted by very powerful electromagnets All the othei metals are more oi less diamagnetic The minerals of the different metals show the same magnetic characteristics as the metals themselves, but m a much smaller degree Of the non minerals, magnetite IS quite strongly attracted by a hand magnet, and pyirhotite somewhat less strongly, while the rest, with occasional exceptions, are apparently non-magnetic Some of the nickel, cobalt, and chromium minerals are very feebly attracted by a hand magnet, but most of them are apparently non-magnetic

The apparently non-magnetic minerals may be made quite strongly magnetic by eithei an oxidizing oi a reducing roast This fact has been taken advantage of m the concentration of lean hematite, limomte, siderite, and pyrite ores The roasted ore is passed through the fields of strong electromagnets, sepal atmg the magnetized minetal from the non-magnetic gangue, and thus raising the grade of the ore to a point where it can be profitably smelted The tendency at present, however, is to do away with the trouble and expense of roasting and to concentrate directly, by increasing the strength and modifying the design of the electromagnets Magnets are now made which will attract any of the iron minerals except pyute without previous roasting, and manganese minerals have been successfully concentrated by magnetic concentration

When concentrating an ore of iron by means of magnets, not only is the percentage of non m the resulting product raised, but in some cases deleterious elements, such as phosphorus or sulphur, may be removed This IS especially true m the case of ores which are naturally magnetic and m which the phosphorus occurs in small crystals of apatite and the siilphur in crstals of pynte

When the magnetic process is used for concentrating any mineral, the material should be crushed to the size of the average particles to be separated before it is fed to the machine The results will be high-grade concentrates,

32 ORE DRESvSING AMD MILLINO § 27

practically barren tailings, and a inicldle product which will require further crushing and reconcentiation

38. Among the successful applications of magnetic concentration may be mentioned the following The sepaiation of magnetic iron oies from gangue matenals, the separation of minerals containing iron from puie or nearly pure zinc minerals, the sepaiation of the various materials in monazite sands, the separation of garnetiferous rocks where it is desired to obtain pure garnet , and the removal of garnet fiom corundum ores

By a pioper adjustment of the machines, it is possible to make separations between two compounds having diffeient magnetic properties.

39. Comparison of Magnetic Concentrators. — New machines are constantly being brought out for use in connection with magnetic concentration But all machines can be divided into two general classes one in which the material is brought within the field of the electromagnets, and the magnetic material thus deflected far enough from the path of the mam stream to be deposited in a separate receptacle; and the other in which the magnetic material is actually picked out of the stream of ore, carried off, and deposited

The first class is used only for quite strongly magnetic material, such as magnetite or roasted ores In a typical machine of this kind, the stream of ore falls past a senes of electromagnets, set off to one side, and the attraction of these magnets draws the magnetic material somewhat out of the path of the mam stream, so that it falls into separate concentrates chutes

In the machine of the second class, the material falls or IS conveyed by a belt conveyer into the field of the electiomagnets, which pick up the magnetic material The nonmagnetic material goes on and is discharged practically freed from iron The magnetic material is earned along on the under surface of a continuous traveling belt or on the surface of a cylinder encasing the magnets, until it passes out of the field of the magnets, which remain stationary, and

§27

Ore Dressing And Milling

then It drop oft into a concentrates leceptacle or on to a conveyer of some sort

30. Theory of Manetic Separation. — The chief minerals of importance to which magnetic concentiation is applied aie zinc and non Iron is not wanted in zinc concentrateSj and as it exists in the form of pyiites in connection with zinc sulphide, it becomes necessary to i educe the iron sulphides to oxides by roasting and without appreciably affecting the blende

(a) (bj

Fig Is

The intensity of a magnet for the purpose of magnetic separation depends upon the 'Mines of force'* radiating from a unit surface of area, rather than upon its size To obtain this, specially constructed machines, of which the Wetherill and the Cleveland-Knowles are types, must be used and they belong to the second class of magnetic concentrators mentioned.

31. Fig 12 shows two different views of the Cleveland- Knowles magnetic ore separator Fig 12 (rt:) is a side

ORE DREwSRING AND ]![rr.LIN(

Jd

elevation, in which a lepiesents the magnets, which aie suspended by shafts b and which aie rotated by means of suitable belts and pulley wheels A ci oss-section of one magnet is shown in Fig 12 {b) and consists ol a coie and a casing / The space between the core and the casing is filled with a coil z, the ends in of the true which foims the coil are carried up through the top of the magnet and aie connected to the slip rings which make contact with the brushes to which aie attached feeding wiles leading to the dynamo Beneath the magnets and in pi*oximity to then lower faces an endless belt conveyer s passes so as to leave a magnetic gap .c The ore to be separated IS fed into a hopper which distributes it evenly over the belt in a thin layer The belt carries it under the first magnet, where, owing to the "intense magnetic field formed between the two poles tt and all the particles of sufficient permeability are attracted as the magnets rotate and are carried to one side of the plate, wheie they ate removed by revolving brushes not shown m the figuie, but nevertheless situated just above the angular i evolving drum x As the belt passes over the angular drum a-, material clinging to the belt is detached by the corners of the drum striking against the belt, and thus particles which have been covered up and so prevented from adhering to the magnet will be brought to the surface and adhere to the magnet towards which the belt moves So far, this sepaiator seems to have given general satisfaction m several different localities

33, Tlie TVetlierill Magnetic Coiioeiitratox\ — This machine is fairly well known and is used m Europe, Africa, andAmeiica The concentratoi gives general satisfaction in zinc separation in New Jeisey The machine shown m Fig 13 was built for the De Beeis Consolidated Mines, Ltd , Kimberley, South Africa, where it is employed to remove magnetite, ilmenite, chromite, garnets, olivine, etc. from diamonds

The ore is delivered crushed to a proper size from a feed hopper a on a mam conveyer belt which passes

Ore Dressing And Milling

thiough the magnetic field of the magneto i The magnetic minerals are attracted and raised to the upper traveling cross-belt d, and by iL are removed from the magnetic field and fall into a hopper not shown in the cut

By properly adjusting the cuirent strength and by regulating the distance between the poles the ore on the mam belt passes fiom weaker to stronger magnetic fields, so that a separation of the minerals ot different magnetic attractabihty IS readil} effected A sepaiator like that shown m the illustration treats from 2 5 to 5 tuns of Bioken Hill tailings per hour, removing about 25 per cent of garnets as a magnetic product

33* Pan and Batea. — There aie, besides the concentrators already described, various concentrators of miscellaneous forms and minor importance In placer mining and in cleaning up around amalgamating plants, the pan and batea, both m the hand and as mechanical forms, are frequently used for cleaning the amalgam from the plates The hand pan is usually made of either Russia iron or agate ware It is a shalloAv pan, to to 12 inches in diameter on the bottom, 17 to 20 inches at the top, and %l to 3 inches deep, pressed out of a single sheet of metal The amalgam is placed in it, softened with quicksilver, and washed with an excess of water The pan is

grasped by both hands, on opposite sides, and given a gentle, circular, swinging motion, iindei the influence of which the mercury and amalgam settle to the bottom, while the lighter material uses and may be poured off with the water

The batea is a shallow wooden bowl, usually about 20 inches wide and 21 inches deep, used by Mexicans and South Americans It is made out of a solid block of green wood, the cavity being dug out with an instrument resembling a shoemaker's hammer The bowl is buried until seasoned, after which it

IS smoothed and sandpapered It IS shaped somewhat like a sheetiron or agate-ware gold pan and is used in the same manner and for the same purpose

34. Mechanical Pans.' — The object of mechanical pans and bateas IS to imitate as closely as possible the motion and action of the hand articles in the ti eatment of much larger quantities of material than can be handled m the latter. This is accomplished by various mechanical devices for giving the pan either a shaking or a gyratory motion The device for driving the mechanical batea, described m the next paragraph, is of the

latter class

Fia IB

ORE DREvSvSINO AND MILLING

§7

The mechanical batea is shown in plan in Fig 14 and in elevation m Fig 15 The pan is of cast iron, about 4 feet wide, with a rounded bottom and a plug m the center The front end or spout is set on a roller, allowing the pan to slide back and forth, while the back is supported by two light iron rods, allowing the pan to swing freely. The pan is given a rapid gyratory motion by a ciank at the rear, on a short, vertical shaft diiven by bevel gearing

35. Log Waslier*— AYhen ores are encased in clay or other adhering substance, they may be separated from it b) means of the log washer shown in Fig 10 This consists of cast-iron or wrong ht-irori tieesiipon which blades are bolted in such a way as to form a screw conveyer One end of the

log (so called because the original apparatus was a log with blades) works in a gudgeon placed below the water in the box containing the ore to be washed , the other end works m journals The logs, which are driven by gear-wheels, as shown in Fig 17, work the ore towards the head of the box and discharge it into a bm. Water is introduced at the upper end of the box, while the ore is fed at the lower end;

the clean water thus meets the ore and discharges when it becomes dirty at the lower end, taking away at the same time the clayey sediment There is no general standard for thee washmo 1 ? ers The box IS about 4 feet deep

§37

Ore Dres.Sing And Milling

at one end and two feet at the other, according to the length of the logs, which vary from Ki to 30 feet and are pitched at an angle sufficient to give a rise of li inches to the foot A pair of logs usually woik together and can wash from one to two hundred tons of iron or phosphate lock per day, ivith from 50 to 300 gallons of water per minute, according to the nature of adhering material

36 . Anialg:aixL. — Mercury (quicksilver) rapidly dissolves gold at ordinary temperatures, forming an amalgam \wliicli IS liquid, pasty, or solid, according to the proportion of mercury An amalgam contammg 90 per cent of mercury IS liquid, while one containing 85 per cent crystallizes in yellowish-white prisms Silver and also the base metals, copper, lead, and zinc, are likewise soluble in mercury, and any or all of these metals can exist in an amalgam at the same tune as gold The excess of mercury in a liquid amalgam may be strained through cloth or buckskin, leaving the hard, dry amalgam behind The mercury from amalgam may be distilled off by heat — 'applying at first a gentle heat and gradually increasing it, if the heat is stopped at any point, the distillation ceases, but recommences if the heat is again raised, at a bright-red heat all but a mere trace of the mercury is expelled, and if the heating has been gradual, the vaporized mercmy carries off but little of the precious metals with it A piece of gold readily absorbs mercury and becomes brittle, this brittleness sometimes remaining after the mercury has been volatilized by heat The fumes of volatilized mercury are exceedingly poisonous, producing serious salivation if breathed even in comparatively small quantities, hence the distillation should always be performed m strong, hermetically sealed retorts,

40 ORE DREvSSING AND MILLING § 27

and the fines condensed by passing them through a watercooled condensing tube or coil

The amalgamating property of meicury, together with the ease with which it can be separated fiom the amalgamated metals by distillation, condensed, and used over ana over, makes it a veiy important factoi in the metallurgy of gold and silver, particiilai iy the former Amalgamation is one of the principal processes of recovering free gold and silver f tom then ores The ore is crushed up fine enough to free the metals from their gangue, and the pulp, mixed with water, is passed over copper plates which have been coated by quicksilver, or over a bath of liquid mercury, or the gold and silver may be amalgamated by giindmg the ore or pulp together with mercury, ui machines like the arrastra, amalgamating pan, and Huntington mill, oi the mortal of a stamp mill Mercury is also used in placer mining, being placed in the sluice riffles to catch fine gold, which might otherwise be earned on down the sluice by the swift current and be lost Chloride of silver is also soluble in mercury, and in the case of silver ores in which the silver is present as a non-amalgamable compound, the ores are crushed, lasted with common salt to bring the silver into the form of a chloride, and the chloiidized ore, mixed with warm water, IS introduced into cast-iron pans, around which revolving arras carry mullers or mixers; a little clean mercury is pul m the pan and amalgamates the silver chloride, the mullers insuring the contact of all the ore with the inercury

In America, mercury is sold m 'fiasks" containing 764 pounds, the Australian "bottle"' of mercury contains 75 pounds of the metal

37. Tosses of Mcrctii'y. — The mercury used for amalgamation should be as free as possible from base metals A little gold or silver in the mercury is a decided advantage m amalgamation, as mercury containing a trace of gold or silver amalgamates much more rapidly than perfectly pure mercury, this advantage is so marked that, when a new lot of mercury is received at a mill, it is either mixed with old

Ore Dressing And Milling

mercury that has been strained off of amalgam and always retains a little gold and silver, oi, if there is no old mercury obtainable, as installing a new mill, a little silver is dissolved in the new metcuiy Copper plates are silver-played foi practically the same reason

38. 8ickeiiinjg. — Mercuiy is said to be ''sick" when It contains some substance which coats it with a film and prevents it from amalgamating the gold and silver When the mercury becomes separated into fine drops, this film prevents their leunitmg, and they aie broken up finer and finer, and finally washed away with the tailings, the film preventing their catching on the apron plates This is one of the principal sources of loss in gold and silver amalgamation Sickening is caused by certain base metals and their compounds in the mercury Lead, coppei, tin, and zinc in mercury oxidize rapidly and cover the mercury with a film of their oxides Lead and copper are the worst of these, because the most common They also make the amalgam pasty, necessitating the use of inordinate quantities of mercury, and consequently increasing the loss If an ore contains soluble salts of any of these metals, it is very apt to be unfit for amalgamation, at least by the ordinary methods, such as amalgamation in the stamp battery oi pans or on copper plates, as the iron and copper piecipitate the metals from solution by galvanic action, and the precipitated metal IS at once dissolved by the mercury, soon causing it to sicken For this reason, the old-fashioned stone arrastra is better suited to working some ores than the improved modern machinery

Arsenic, antimony, and bismuth also cause a great deal of trouble Whether they occur in the metallic form or as compounds, are dissolved by the mercury, and then a black, crystalline coat of the metallic element foims on the surface of the mercury. Easily decomposable sulphides and sulphates reduce and form sulphide of mercury This IS the case with sulphides of arsenic, antimony, and bismuth, and more or less with the sulphides of lead,

4

Ore Dressing And Milling

coppei, and silvei' Clean iron pyiites is not affected by mercury

Sickening, when due to the formation of metallic oxides, may be remedied by the addition ot a little sodium amalgam This is prepared by adding metallic sodium, in pieces about the size of a pea, to a bath of mercury heated to about 300° F Each piece of sodium causes a slight explosion and a bright flash of flame The reaction becomes less violent after about 3 per cent of sodium has been added, and the amalgam is then poured into a shallow pan and allowed to cool, becoming solid when cold It is then broken up and kept under naphtha m closely stoppered bottles, to prevent oxidation A little of this amalgam, added to a lot of sick quicksilver, will reduce the coating of oxide, the oxygen combining with the sodium and forming a soluble salt, while the metal is absorbed into the mass of the mercury, leaving the surface clean and lively This will cure nearly all sickness of the quicksilver except that due to sulphides of antimony and bismuth, but is applicable only to pans, mercury wells, and iiffles, and not to plate or battery amalgamation, where the mercury is in a thin film

39 FlorLi*iiig. — When mercury is broken up by the machinery into very fine globules, while a film of air around each globule prevents their reuniting and permits them to float away in the waste water, flouring is said to occur If this film of air be broken in any way, the particles instantly unite, but a considerable proportion of the total mercury unaccounted for is lost in this way, particularly in stamp milling Flouring can be prevented to a considerable extent by passing the pulp through mercury wells or troughs, where the air films around the minute globules are broken by agitation and the globules unite with the mass of the mercury

nossies Gonu

40* Float Gold, — Clean gold is readily amalgamated by mercury Very fine gold particles, however, may become surrounded by a film of air (like floured mercury),

§ 27 ORE DRESSING AND MILLING Li

which prevents their being amalgamated, and floats them EAvay with the tailings Finely divided pyrites are floated off in the same way, but cannot be strictly considered as "float gold/' although frequently no distinction is made This floating away of gold and mineral is one of the chief sources of loss m gold milling

4 : 1 . Gold.. — Some gold that is not directly amalganiable, being coated with or surrounded by some substance which pievcnts it coming in contact with the mercury, is also a source of loss This includcb gold m pyiites, "lusty ''gold (gokL surrounded by a film of some oxide or sulphide winch pi events its amalgamation), greasy gold (the particles of gold being prevented fiom amalgamating by a film of greasy material), and gold in chemical combination, as tellurides

4 : 2 Gold, ill pyrites is mostly, if not wholly, in the form of native gold m minute crystals in the cleavage planes of the pyiites Some authorities claim that the non-amalgainable gold in pyrites is in the form of a sulphide, but the majority of the evidence is in favor of its being native gold Examined undei a powerful microscope, the gold can always be seen in the cleavage planes, gilding the edges of the little streaks or strise on the sides of the crystals maikmg the edges of the cleavage planes By leaching with potassium cyanide, this gold can be dissolved, leaving microscopic crevices between the cleavage faces and pitting the faces themselves The crystals of gold are so minute that a large proportion of the gold leinains with the pyrites, even when the ore is crushed very fine The very finest slimes of pyiites, even when ground m pans with mercury, will seldom yield more than 40 per cent of their gold by amalgamation If the pyrite is oxidized, either by weathering or roasting, the pioportion of amalgamable gold is considerably increased, but, on the othei hand, a great deal of the gold IS apt to become coated with a film of iron oxide, particularly when the pyiite is oxidized by weatheiing and is rendered unfit for amalgamation The plan usually followed

N M III—ip

U ORE DRESSING AND MILLING § r/

with sueli ores is to save what gold is possible by amalgamation lu the stamp battery and on the plates, and then concentrate the pyntes and extract the gold fiom them, eithei by smelting or by chlorination oi biomination In the latter two piucesses, the pyrites are first lasted, to drive off the sulphuL, and then moistened and tieated in closed vats or ban els with chlorine gas or a solution of bromine The action is veiy similar in both cases The gold is brought into the form of a soluble chloride or bromide , this is leached out of the pulp by water and the gold then precipitated as a brown powdei, usually by ferrous sulphate (copperas), sulphureled hydrogen, or charcoal, and the precipitated gold is melted and molded into bars

Even when concentration is employed, more oi less pyntes IS inevitably gained over with the tailings, but by careful work this loss can be reduced to a minimum

43. lUisty gold is native gold the scales of which are coated with a thin film of some mineral substance which prevents them from amalgamating The film is usually oxide of iron, silica, or some sulphide oi arsenide The films are frequently perfectly transparent, so that the gold appears to be perfectly clean and pure, and the existence of the film IS indicated only by the failure of the gold to amalgamate If the scale of gold be broken or cut so that the least surface of clean gold is exposed to the mercury, the scale will amalgamate at once, but otherwise it will be carried over with the tailings

Roasting or calcination is a process usually beneficial in the case of rusty gold Calcination is merely roasting to drive off water or decompose carbonates, and is so called to distinguish it from the oxidizing roast to drive off sulphur and arsenic If the coating of the gold scales is a sulphide or an arsenide, it is leadily decomposed by an oxidizing roast A calcining roast is frequently effective in treating hmonite (hydrated iron oxide) gold ores, m whicli the particles of gold are coated with a film of the iron oxide The heating drives off the watei and leaves the ore open

Ore Dressing And Milling

§

toi amalgamation Inbtances are known wlieie ores in the raw foiin would yield only from 30 to 40 per cent of then gold by the most careful and elaborate amalgamation, but after calcining would yield fiom 80 to 90 per cent With ores of this type, however, it is usually advisable to employ some other process, such as chlonnation or biomination

44. Clayey Gold Oies. — When the gangue of an ore is talcose — i e , like talc (soapstone) — the gold scales are apt to be coated with a slime which prevents then amalgamation and boats them off A somewhat similar effect lesnlts when grease nr oil gets into the ore The scales of gold become coated with a thin film of grease — a condition known as greasy gold — and refuse to amalgamate A very small quantity of grease will do the mischief— a little tallow from the mmeis' candles or a few drops of oil m the mortar or pan being siillicienl to cause considerable loss and trouble The effects of the grease may be counteracted by the use of a little potassium cyanide, caustic soda, or potash m the water, to cut the grease

45. Telliiride Gold Ores. — Tellurides of gold are of a greasy, talcose nature, and are exceedingly difficult to amalgamate They frequently contain free gold, but even this is apt to be coated and non-amalgamable They may be rendered amalgamable by roasting, which volatilizes the tellurium, but the volatilized tellurium carries off with it a great deal of gold — altogether too much for practical working — so that amalgamation is practically out of the question for telluride ores Chlorination and bromination are open to the same ob 3 ectioii, as the ore has to be roasted preparatory to leaching, and even smelting is unsatisfactory on account of the large gold loss by volatilization In some cases the cyanide process, m which the gold is dissolved out of the me by leaching with a veiy dilute solution of potassium cyanide, has given the best results on tellurium ox*es Theie are so many factors entering into the case that it is impossible to make any general statement as to ivhich is the best method for telluride ores.

4:0

Ore Dressing And Milling

46* Loss of Ainalgain, — More or less gold is lost in the shape ot finely divided particles of amalgam This can be remedied by careful working, not allowing the amalgam to get too hard oi to accumulate m too large quantities, and by placing amalgam traps below the apparatus, such as mercury wells, shaking coppei plates, or the amalgam savers on vanners — vanners themselves \vould catch most of the fine amalgam, but as it would go m with the concentrates, the mercury m it would be lost, the amalgam saver is not expensive, in view of the saving it will accomplish

AMALGAMATIlSra APPABATU8

PHIMITIVJE APPARATUS AlB METIIOBS

47. AiTastra, — The arrastra is similar in construction to the Chilian mill, except that, instead of stone rollers, flat

stones, usually four m number, are dragged around the pan by the radial arms, to which they are fastened by ropes or chains The front ends of these stones or millers are raised a few inches from the floor by the suspending ropes or chains, insuring their hiding on the ore and grinding it instead of merely plowing through it The mnliers, which weigh fiom GOO to 1,500 pounds each when new, are used till they wear down to about 400 or 500 pounds , they are then renewed one at a time, so that there are always old mullers in the pan Power for the arrastra is obtained from a mule at the end of a pole or from water or steam. Fig IS shows a mule-power arrastra Small portable arrastras with iron pans are made for prospecting purposes,

ORE DREvSvSING AND MILLING

4'

§

In many ways the aruistia is an ideal amalgamating: machine, in spite of its ciude consti iiction, and on certain classes of ore it will save a laiger proportion of the values than the more modern machinery, notwithstanding the loss of mercury and amalgam through the stone bottom If the gold is rusty, for instance, the giindmg action is almost certain to break the film suri'ounding the scales and give the mercury a chance, and, again, m the case of ore containing easily reducible salts of lead, copper, oi other base metals, as there is no metal about the machine with which the pulp comes in contact, there is no reducing action and the metals remain m solution instead of i educing and sickening fhe mercury As the ore is ground to an impalpable pulp, theie is considerable flouring of mercury and amalgam, but subsequent settling and washing save a great deal of this

The arrastra is too slow in its working to be applicable to any but very rich ores The ordinary ariastra will grind from 800 to 1,500 pounds of ore in twenty-four hours, using about twice that amount of watei in the pulp About one ton IS usually charged at a tune in an ordinary arrastra Enough mercury is added to have the amalgam contain not more than 20 per cent of gold and silver The mercury IS usually alloyed with silver, copper, or zinc, both to keep it from breaking into globules and running into the crevices and to make it amalgamate moie rapidly In starting up an arrastra, about 5 or 10 pounds of mercury are added at once, and then about half a pound is added every other day The amalgam is cleaned np at intervals, varying from twice a month m the rudest arrastias to twice or four times a year m those of the best construction It is washed, with the addition of fresh mercury, then steamed and retorted

4 : 8 . The Patio Process, — In the patio process for the extraction of silver the ore is first crushed in Chilian nulls and then ground in the ariastra, where any free silver and gold or other directly amalgamable forms of the metals,

ORE DREvSvSTNG AND MILLING g M

such as hoin silver (silvci chloride), bioiiiides and iodides of silver, etc , are extracted by amalgamation The slimes from the aiiasttaare then Gained to settling pits, where the pulp IS freed irom suipius water, and from here are conveyed in the form of a liquid mud to the patio

The patio is simply a court oi enclosure, usually fiom acre to U acres in extent, which has been carefully gilded and paved with stone, cement, asphalt, or even matchboards, made as neaily as possible impervious to merciuy The court has a slight inclination, so that the water readily drams off from the pulp beds The pulp is brought on to the door from the arrastra in a semi-fluid state, made up in piles containing from 30 to 130 tons, and allowed to dram and dry for several days, dams of sand, wood, or stone being built around the pile to prevent it spreading all over the floor, in large woiks, permanent circular walls oi dams aie sometimes built for this pin pose The piles are about 1 foot thick and 20 to 50 feet m diameter When it becomes stift enough to work, it is spaded ovei thoroughly, and then from 2 to 5 per cent of salt is scattered over its surface and worked m thoroughly by spading and by mules or horses driven around in it This operation of spading and treading the pile or forfa is known as repaso

Aftei the salt is thoroughly worked in, the pile is once more spaded over and the magistral added The essential constituent of the magistral is copper sulphate Magistial was formerly made by roasting copper pyrites, converting the sulphide to sulphate of coppei, or by roasting togethei iron or aluminum sulphate and insoluble copper salts, converting the copper into sulphate and spreading this over the torta Of late years, however, it has become customary to leach the copper sulphate out of the roasted ore, crystallize It, and use it pure as magistral The office of the magistral IS to convert the non-amalgamable silver salts into an amalgamahle form The reaction is as follows The copper sulphate reacts with the salt (sodium chloride), forming copper chloride and sodium sulphate The copper chloride then reacts on the silver salts, forming chloride of silver, which

§ 27 Ore Dressing And Milling L)

IS readily amalgamable The cupper sulphate of the magistral also reacts upon any soluble lead and zinc minerals in the torta, converting them into insoluble forms, and thus preventing them from being i educed and sickening the mercury The amount of magistial added is carefully pioportioned to the character of the ore and its silver contents, any excess of magistral causes a loss of meicury The proper proportion may be detei mined by the way thetoita works The magistral is spread over the surface of the torta and another lepaso made, and this is repeated every second or thud day, about eight houis at a time, until the operation is finished The chemical action of the magistial generates heat, and the pioportion of magistral necessary IS indicated by the temperature of the pile If the pile gets too hot and steams, there is an excess of magistral and a loss of mercury, while if theie is not enough magistral, the pile IS too cold and the action slow An excess of magistial may be corrected by the addition of a little finely gioiind ore containing oxide of copper, oi by adding lime or wood ashes to decompose the excess of copper chloride

About 0 or 8 ounces of mercury aie added to the toita for every ounce of silvei it contains Usually one-half to three-quarters of the total mercury is added at first, along with the magistral, and the remainder added in small quantities fiom time to time, always sprinkling thiough a strainer in ordei to get the meiciuy thoroughly clistributed in as small globules as possible The mercury is spaded m, a hot solution of copper sulphate added, and the pile trodden for 8 or 9 hours the first day, and again the next day, and then every second or third day until the pile is finished The average time is about 20 or 25 days

When the tests of the pulp and amalgam show that the amalgamation is completed, a considerable excess of mercury is thrown m to thin the amalgam and catch floured mercury, and the treading is continued for a while longer The pulp and amalgam are then washed, usually in very primitive box settlers built of stone or equally primitive

50 ORE DRESSING ANt> MILLING §

tubs 01 pans The pulp ib kept in motion m the bcttleib by men dancing and wading m the watei The tailings from the settlers aie furthei concentrated on mcliiied planes of masonry The amalgam from the settles us collected, strained, and retorted

The losses in the patio process are very high There is always a loss of merciny ot at least 1 ounce for every ounce of Sliver in the pulp, and even the best woik seldom saves more than 00 or 05 pei cent of the silver The system is only applicable to fairly rich ores, in remote regions, wheie labor is veiy cheap and machinery very expensive and difficult to obtain

49. The ca55o is a round pan or tub, about 1 meter (39 37 inches) in diameter, made entirely of coppei, or of wood or stone with a coppei bottom This is set ovei a rude fireplace, the thin pulp with o to 15 pei cent of salt Eidded, and the imxtme brought to a bod, the meicmy is added as soon as the salt is dissolved, and a man stus the pulp with a piece of wood, rubbing the bottom to keep it clean of amalgam and assist in the amalgamation of the rich Sliver minerals

50. The foiidou is a foim of the cazo, but much larger, being about 7 feet m diameter, and the mulling is done by two copper muliers revolving about a spindle in the center of the pan If the mercury is added caiefully and the muilers kept moving at the pioper speed, the amalgam will not cling to the copper bottom and mailers of the fonclon

51. The tiiia is even more like the modem amalgamating pan; m fact, it is practically identical with it, except that the bottom and ixiuUers aie of copper instead of cast iron and wood, and are operated by a bevel gearing above instead of from beneath The operation is the same as that of the fondon and cazo These machines are suited only to very rich, easily amalgamable silver ores, such as chlorides, bromides, and iodides of silver.

ORE DREvSIN( AND MILLINCi

Modern Amadguevtino Mach Inert

53* Amalgamating' Pan. — The am alga mat mo pan is an adaptation of the pimciple of the aiiastia to the requirements of modem metallui gy The prospecting arrastia pievioiisly mentioned is really a crude amalgamating pan, a connecting link between the arrastia and the modern pan The amalgamating pan is essentially a cast-iron pan m wliiLh the pulp is gioiind and amalgamated by means of mulleis of cast iron tiavehng about a vertical shaft or spindle, passing up thiough a hollow cone in the middle of the pan and diiven by bevel gears imdeineath The gimdmg faces aie leplaceable The bottom, or muller path, is made up of a senes of dies, which fit together to form a closed ring, the joints between them being filled in with hardwood strips They are usually held in place by dovetail lugs on the hier side, which set into corresponding grooves m the bottom of the pan and tighten automatically, the lugs and gi coves being nairowei at the end towards which the dies are drawn by the motion of the muller, or they may be bolted down The muller shoes are usually fastened into the niullei ring in the same manner, but with the nairow ends of the slots m the opposite direction, so that the forward motion of the muller tightens both the shoes and dies in their places, while a reversal of the motion will loosen them when for any reason it is desired to remove them The muller ring is a wide, horizontal flange on the bottom of the hollow cone oi hub on the driving spindle, through which the motion of the spindle is transmitted to the mullei

The mullei must be attached to the spindle in such a man™ ner that it can be readily raised from the dies without throwing the machine out of geai while charging the pan or Avhile amalgamating, when a stirimg action only is desired

A number of wings of iron oi of amalgamated copper, usually something in the shape of inverted plowshares, are set around the sides ot the pan, above the level of the miilleis, and deflect the pulp inwards and downwards as it uses towards the rim of the pan by centrifugal force, carrying it

52 ORE DRESvSING AND MILLING § 27

in thiough the openings in the miller cone and under the inullei again and ag;ain, till it is all thoioiighly i educed and amalgamated In the Stevenson pan, curved mold boards, which guide the pulp upwards and inwards, on the principle of a screw, are used instead of wings

The pansaie made eithei entirely of iron or with a castiron bottom and wooden-stave sides, bound together by iron hoops, the latter form is used more particularly when working strongly acid ores which would corrode iron pans The pans are usually about 5 feet m diameter and 2- to feet deep The shoes used in the different pans vazy considerably 111 shape, size, and number The minimum number is three, the maximum, twelve They are usually fiom 2 to 3 inches thick, and aie so designed as to draw the pulp under them.

53 . Heating Pulp in Pans. — The pulp m the pans is sometimes heated neaidy to boiling point (to about 200° F ), the heat being supposed to assist greatly in amalgamation The heating is done either by passing live steam duectly into the pulp or by exhaust steam in a space between the bottom of the pan and a false or steam bottom The sides, too, of iron pans are sometimes picketed. The use of steam passed directly into the pulp is gaining popularity in the later models, as it accomplishes the heating so much more rapidly It is, however, open to some objections, which are made the most of by the advocates of the other system In the first place, it requires the use of live steam right Lorn the boilers, as exhaust steam always contains more or less oil, and gi'ease of any sort m the pulp will cause a gieat deal of trouble The second objection, which is not a very serious one, is that the watei from the condensation of the steam thins the ptilp and makes it too tlun to work properly The use of jackets allows the utilization of waste steam for the heating, but it is lather slow and unsatisfactory in its operation A compromise between the two methods is a good idea, the pulp being brought up to the proper temperature by direct steam and maintained there by the heat

Ore Dresstno And .Millino

§ 27

fiom the exhaust steam in the false and steam jackets, if the latter are used When live steam is used, the pans should be sealed with a ca&t-iron or wood covei , the steam being introduced thiough a hole in the top Covers are useful in any case, as they letaui the heat and confine the splash

54, Forms of Pans. — There are a number of different forms of pans in use, though the idea is the same in all The pan is essentially an amalgamating machine, not a crushed, and the giindmg action should be of secondary importance By far the greatei pait of the wear on the machine arises from the grinding, and foi this reason it is advisable to ci ush the ore as fine as practicable before it enters the pan jMoieover, the longer the pulp has to be ground, the greater is the loss of mercury from flouring In some mills the ore is ground or crushed to the desired fineness before entering the amalgamating pans, eithei by the oi diary crushing apparatus or, as m the Boss process, m special grinding pans , in such a case, the iron shoes iii the amalgamating pans may be replaced by wooden ones

Pans were formerly made with conical bottoms, with the idea that they requiied less power, but this construction is now practically abandoned, as it has been proved that for the work done the comcahbottomed pan requires as much power as the flat-bottomed pan, and that flat bottoms wear more evenly, and consequently longer, than conical bottoms, and aie more easily repaired When the sides of the pan are of wood, the bottom is usually cast with a nm inside of the staves, against which they are drawn veiy tightly to prevent leakage of mercury and amalgam, and the pan is sometimes also covered on the outside with a tight casing of sheet iron The pans discharge at the bottom A common and convenient scheme is to have the dischaige through a flexible hose, which can be tied up against the side of the pan when not m use In some mills the meicury and amalgam are withdrawn by themselves into an amalgam kettle, and the pulp is then discharged into the settlers , in others,

bi

ORE DREvvSWa AND MILLING

the entire contents of the pan aie conveyed at once into the settles, and all the amalgam and meicury collected there Withmobt fiat-bottomed pans there aie always 50 or 60 pounds of met ciiry left in the bottom of the pan, but this is really an advantage rather than a disadvantage, as the mercury IS not lost, but IS utilized in the next charge, and the silver and gold it may contain make it amalgamate moie readily and alloy any new mercury which may be put in the pan

55 . The Wheeler pan, though one of the oldest forms, IS still quite extensively used The general details of the

construction aie the same as those previously given in the general description , the method of suspension, however, differs somewhat The pan IS shown in section in Fig 19 The upper portion of the spindle g- IS threaded, and a corresponding thread is cut m the muller nut so that it can be screwed up or down on the spindle when cleaning up, putting in new shoes, etc A keyway cut in the muller nut receives a key which locks the muller at any desired height on the spindle The position of the muller on the spindle is only altered when a large movement is required, as when the muller must be raised above the top of the pan, in cleaning up or m order to change shoes or dies All small alterations in the height

§ 27 Ore Dressing And Milling

of the mullei, such as raising it fioiri the dies when chaigmg or amalgamating, aie made by means of a hand wheel h on a vertical rod r at one side ot the pan, the rod r connects with one end of a bent lever /, underneath the pan, the other end of the lever being suspended from the frame of the pan The lever passes under the center of the pan and forms the support for a pm ivhich m turn supports the lower bearing of the spindle The bevel gear-wheel on the spindle is attached in such a manner as to allow the spindle a slight vertical displacement without affecting the gears, and the shaft and muller can be raised oi lowered as desiied by scieAving the hand wheel to the right or left, respectively

The sides of the pan aie variously made of cast or wrought iron or wood, m the latter case, the bottom is let slightly into the sides The pan has a double, or steam, bottom for heating the pulp The shoes are from 6 to 12 in number, and are wedged into the muller plate with wooden wedges The dies, 4 to 1:2 in number, aie in the shape of sectors of a circle, and are fastened ui the bottom of the pan by dovetail wedge joints, the radial spaces between the dies aie usually filled in with strips of hard wood The shoes and dies usually last from 3 to G weeks Very hard dies may last considerably longer, particularly with good care, but many millmen prefer rather softer shoes and dies, made of a mixture of equal parts of white and soft iron The space left between the muller and the sides of the pan is considerably larger than m most of the other pans

56, The Varney pan is somewhat similar m construction to the Wheeler The shoes, however, are much larger and of a peculiar spiral outline, and the shoes and dies are bolted to the muller and the bottom of the pan, respectively, making them rather inconvenient to insert and remove The suspension of the mullet also differs somewhat from that employed m the Wheeler pan The muller is merely keyed firmly on the spindle and not threaded on, and when for any reason it is desired to raise it any considerable dis- t£vnce from the dies the key must be loosened and tle

5G ORE DRESSING AND MILLING g

raised by overhead tackle Any small vertical movement of the mullei, however, is accomplished by the hand wheel and level underneath the pan, as m the Wheclei pan The pulp IS heated by dnect steam, there being no steam bottom oi jacketing The guide wings are not attached to the sides of the pan, but are suspended fiom lods passing thiough the wooden cover of the pan and thtough castnion sleeves bolted to It, and are raised and lowered by means of hand wheels threaded on the upper portion of the rods The cover lb bolted to a flange on the nm of the pan when the machine is m operation

57. The Horn, Greeley, Patton, and McCone pans are all double-bottom pans, and daher essentially from the Wheeler pan only in the method of suspension of the muller, which is the same m all The nniller nng and the suspending cone oi driver are cast separately and either boiled or wedged together in the chfterent pans The shoes and dies are held in place by self -tightening wedge joints The appal atus £oi raising or lowering the muller is all above the pan, as shown in the illustration ot the McCone pan,

Fig 20 It consists of a vertical screw turned by a hand wheel at the top The lower end of this screw rests upon the top of the driving spindle, and a thread is cut on the inside of the muller nut corresponding to that on the screw, and the mullei is raised and lowered by tuning the wheel The muller is free to slide up and doivn on the spindle, but is caused to rotate with it by a vertical key fixed in the

Fic so

Ore Dressing And Milling

'.puiclle and working freely in a blot in the muller hub r The muller in the Horn and Patton pans is not fastened tightly to the driving cone or hub, but is caught in grooves, so that it tightens when the diiver is turned foi wards and is loosened when the motion is reversed, and can be readily detached from the driver All these pans differ more or less from one another in unimportant details, such as the shape of the false bottom and muller, the shape, weight, and number of the shoes, etc , the difference being in many instances barely sufficient to characterize the pan The lountalii and Stevenson pans dispense with the ordinal y guide wings, having instead fiaiing lips on the muller which guide the pulp dowiiwaids through radial slots in the plate beneath the lips A similar device is sometimes used on the McCone pan A method ot suspending the muller sometimes used IS similar to that on the Wheelei pan, except that, instead of keying the muller at the desired height on the spindle, it IS locked in position by a hand wheel threaded on to the upper poition of the spindle and screwed firmly down on the muller nut when the latter is in the desired position The muller nut is made as a hand wheel, for convenience in raising and lowering the muller

58- The Bossi pan, used in the Boss continuous process, presents some characteristic features One of the most important of these is the extension of the steam bottom up into the central cone of the pan, as shown in Fig 31, thus greatly increasing the heating surface The cone of the false bottom is extended up beyond the top of the mainbottom cone, and foims the sleeve and upper bearing of the spindle A rust joint is made between the two cones The steam enters on one side of the bottom and exhausts on the othei, and is regulated by a horizontal valve operated by a hand wheel on a rod extending out to the side of the pan The pans are set in senes, the pulp flowing from one to the other, and the driving shafts of the entire senes are coupled together and driven as a whole, and any pan m the senes can he thrown in or out of geai by a friction dutch

Ore Dressing And Milling

§37

without disturbing the rest The friction ring which the clutch engages is cast separately from the driving bevel gear and bolted to it, so that it can be replaced independently when worn out or broken The step beaimg of the spindle

Fig 21

IS caniedon a bracket cast on the driving-shaft box in such a way as to allow the removal of the shaft without disturbing the spindle The mercury bowl m front of the pan (see Fig % 2 ) has a siphon arrangement, by means of which the pan may be readily drained of amalgam and pulp, if desired.

Ore Dressing And Milling

59t Cliemicals.,— In the eaily dayb of pan amalgamation, all sorts ot mixtures weie employed in pans, with the idea of assisting the operation These nostrums weie mostly harmless, but some of them were highl} ndiculoub and nearly all of them absolutely useless They weie hit upon with about the same authority as the ''charms" of a negro "voodoo doctor", and once an old-time millman conceived the idea that tobacco juice, sage tea, or some othei equally iionsenical substance was an aid to amalgamation, It was as difficult to shake his faith in it as it is to undermine that of a superstitious negro in his "chaimL' However, new blood and modern education have now almost completely displaced this class of " rule-of-thumb " metallurgists, and out of all the motley collection of nostrums foinieily used, only those remain whose chemical reactions are known and which are used to obtain definite effects Thus, salt and " bluestone " (sulphate of copper) are always used, for exactly the same reasons as they are employed in the patio process Lime is used to counteract the sickening effect on the mercury of too much acid in the water, dilute sulphuric acid is used when the ores are too strongly basic , lye and potassium cyanide and niter are used to cut grease, and cyanide and niter to clean i usty scales of gold and silver Sodium amalgam is used, as m all processes of amalgamation, to clean and enliven sickened mercury

60. Cliarguiig' tlie Ore. — While charging the pan, it IS customary to raise the muller about inch from the dies and use it at first merely as a stirrer or mixer If the charge is of dry-crushed or roasted ore, water is first run into the pan until the muller is covered The muller is then started up, running at a speed varying, m different mills and with different pans, from 60 to 90 revolutions pei minute, and the ore is then dumped or shoveled in TJie muller must be in motion %hile charging or the ore will pack on it and hold it down, and it will either be impossible to start It or the force required will be so great that there will be consideiable risk of breaking the macbiuei The charge N M. lU—i6

00 ORE DREhSINQ ANp MILLING §

varied fiom 800 or 1,000 pounds, in the old -type Wheeler and Vaiaey pans, to 4,500 pounds or even more m laige pans treating slimes Modern practice favors the use of pans of large capacity, as they do nearly, if not fully, as good Avoik as the smaller pans, require but little more time to grind and amalgamate the charge, and the additional power necessary to drive them is small in proportion to the increased capacity

The pulp m the pan, when the charging is finished, is about the consistency of batter and fills the pan about half full The motion ot the mullei causes the pulp to rise nearly to the top of the nm of the pan, sloping inwards towards the center, and the guide wings or mold boards, as the case may be, throw it back again to the center As soon as the charge is all in, the muller is lowered until the shoes and dies almost touch and the ore is ground to a fine pulp The grinding usually requires from 1 hour to hours, the end of the operation being recognized by the feeling of the pulp when rubbed between the thumb and finger Rebellious ores sometimes require as long as 4 houis Towards the end of the gimding, steam is turned into the pan or into the steam bottom, as the case may be, and the charge brought up to the proper temperatuie, about '00° F , and this temperature IS maintained thioughout the amalgamating operation

To obtain the best results in grinding, the pulp should be moderately thin, while the best amalgamation is obtained with the pulp somewhat thicker — about the consistency of honey, The pulp, for good amalgamation, will thicken up sufficiently during the grinding if not made too thin at the start

61, Cliai?g:ltig tlie Merciix*y.' — There seems to be no general rules for the addition of the mercury, either as to the amount or as to the time of addition The chaige of mercury is usually a fixed weight per pan, the amount varying in different mills from 300 to 350 pounds per ton of ore m the charge; as a rule, the greater the capacity of the pan, the smaller the proportion of quicksilver required In some

§ 27 Ore Dressing And Milling 01

millb, indeed, the amount of quicksilver added is pioportioned to the amount of silvei in the oie, which ib determined by a&say, but even these lules aie empirical and applicable only in the practice of these particular mills The addition of meicuiy is geneially made aftei the grinding is completed, and the mallei is raised from the dies duiing the amalgamation Occasionally, a mill will be found where the meicury is charged and ground with the ore, but this is extremely bad practice under oidmary circumstances, as it does not appiecuibly increase the amalgamation, and il causes excessive flouring and loss of mercury and amalg-am The mercury may be all added at once, or a pait of it reset ved till the amalgamation is completed and then added to thin and collect the amalgam.

The mercury is scattered over the top of the pan chaige through a ckith strainer placed over the top of the flask, or poured from the flask between the closed fingers, or in some nulls It IS squeezed through canvas, the object in all cases being to break it up into very fine globules The motion of the pulp and the miiller further breaks up the mercury, the thick pulp holding the minute globules in suspension, and they gradually circulate thioughout the entire charge, amalgamating all the gold and silver they meet The amalgamation usually requires from 4 to 5 hours, the additional saving from lengthening this period seldom compensate for the loss of time. The entire time of the ore in the pan is usually from 4 to (3 hours, in some cases it runs as high as 8 hours

62 , Cliargdng the Chemical Reagents. — The essential chemical reagents — salt and bluestone — are charged at different periods in the operations lu different mills, and in quantities varying with the character of the ore The amount of each reagent necessary must be determined by experiment The charge of bluestone seldom runs higher than 4 pounds per ton of oie; the salt is about twice or three times as much They may be added with the mercury or at any time previous Some miilmen charge the salt and

G2 ORE DRESvSING AND MILLING § 27

bluestone with the ore, otheis chaige the salt with the ore, and the bluestone at some time during the grinding, there IS no fixed iiile, and the time of the addition seems to make very little diffeieiice with the amalgamation The longer the chemicals aie in the pan, the greater will be the conosion of the iromvoik — vi strong argument for postponing their addition till towards the end of the gi Hiding operation, when there will still be plenty of time for their chemical action on the oie

In combination mills, woikmg ores containing both gold and silver m amalgamable torm, and amalgamating both metals in the pans, the mercury is allowed suMcient time to amalgamate the gold before the addition of the bluestone, as the latter hinders rather than aids the amalgamation of gold, though It is practically indispensable in the amalgamation of silver minerals

The anxilm?y reagents — lime, cyanide, sodium amalgam, etc — are added as required When the character of an ore lequires the constant use of any of these reagents in definite quantities, they may be made up into a stock mixture or solution with the salt and bluestone, to save time and trouble. The quantities used aie, relatively to the size of the charge, usually very small — a few pounds to the ton of ore being sufficient in most cases to produce the desired result

C3i When the amalgamation m the pans is completed, the speed of the mullers is usually reduced to about 1:0 i evolutions per minute, the steam shut off from the pans, if it is on, and the pulp thinned with water to cool it and allow the suspended globules of mercury and amalgam to settle They are run for 15 or 20 minutes m this way, and then the mullers are stopped and the pans drained into the settlers The amalgam in the bottom of the pans may either be withdrawn separately or the entire contents of the pans may be run into the settlers, where the mercury and amalgam remaining in suspension are settled out

64* fcjettler&,— The settlers used for this pin pose are merely large tubs of wood or iron — or with a cast-iron

§ 27 ORE DRESSING AND MIELTNG li:]

bottom and wooden or sheet-iron sides — usually 7 or S or even 10 feet m diameter, in whuh the thinned pulp is slowly agitated by stuieis resembling the miilleis of amalgamaUiig pans The whole construction of settlers, indeed, is quite similar to that oi amalgamating pans, except that, as no grinding is reepured, the shoes on the stiiiei aie usually made of wood, and no dies aie used on the bottom of the pan The geneial construction of the settle is also consideiably hghtei than that of the amalgamating pan, as the speed of the vStnrers and the resistance of the pulp aie both very much deci eased

The stirrer usually has four radial aims, on which the shoes are arranged as in Fig 22 , the path of each shoe on the short arms thus lies between the paths of two other shoes on the long arms, and the width of the shoes being equal to the width of the spaces, the entire bottom of the pan comes under the action of the shoes, up to the base of the central cone The stirrer is hung like the muller of an amalgamating pan and is raised and lowered by a hand wheel The shoes never quite touch the bottom, but are worked to within j- inch or less of it, and the currents set up by them keep the pulp from packing on the bottom

vSettlers vary little in their essential details, m fact, most of the ordinary forms aie practically identical in construction, the only radical departure from the construction here described being m the case of the Boss settler

65. Discliavglng Settlei*s — The pulp is discharged fiom ordinary settlers through a number of orifices in the side of the pan at different levels, as shown m Fig 22, the lowest being about 8 inches above the bottom of the pan, these are closed by wooden plugs, and are opened one at a time, beginning with the top one The pulp being discharged by layers, the lower portion is undistuibed by drawing off the upper portion, so that settling and discharge go on together, thus saving considerable time in the operation The dischaige holes are placed diagonally down the side of the pan, so that the lower plugs will not become covered

§ 21 ORE DRESSINOr AND MILLTND

with the slime fiom those ab()\e The bnttinn of the settler usually slopes from the center A groove d m the bottom of the pan collects the amalgam and nieicury, from which It can be tapped as desued, into the mercury bowl in front of the pan In some of the latei designs a small bowl or hollow in the bottom of the pan, near the side, replaces the outside mercury bowl, and the amalgam discharges automatically, through an inverted siphon, as tast as it forms The excess of mercury m the amalgam is stiamedoff and returned to the le&ervoir for further use

66 . The pulp is oidmarily discharged from the settler through the side holes alone, leaving about 8 inches, more or less, of the heavier sand and pulp packed in the bottom of the pan , and the next charge from the amalgamation pans IS tut ned m on top of this In starting the stirrer on a new charge, it is raised so that the shoes ate at about the level of the lowest side hole, just clearing the top of the packed sand fiom the previous charge, and is run m this position for about half an hour before adding any water, in ordei to get the heavy sand into suspension, or water may be added slowly, in a senes of fine jets, about 1 inch apait, from the under side of a pipe extending radially from side to center of the pan The stirrer is then gradually lowered, reaching its lowest position about 2 hours after starting The addition of water through the jets is continued meanwhile, and IS kept up until the contents of the pan are within about 6 inches of the top, when it is shut off The stiner IS run m its lowest position from 1 to horns with the pan full, the top plug IS then removed and clean watei allowed to flow through the hole for about half an hour, then the next plug below is removed, and so on, the stirring continuing all the while The entire time consumed m the settling IS gauged to correspond with that required foi the amalgamation, so that neither the pans nor the settler will be obliged to stand idle, waiting for one another Each settler usually handles the pulp from two pans, though sometimes a single small settler is used for each pan

ORE DRESvSINO AND MILLING

(U)

S i i

67. Cletiu-Up. — Once a week the settles aie completely drained till ough a hole in the bottom of the meicuiy well, and all tiie amalgam caiefully collected m an non vessel and washed In this tune ftom :J00 to 400 pounds of mercury and amalgam will have collected, unless a continuous siphon discharge is used

The amount of water used m the settlers should be carefully regulated, for if the pulp is too thick the meicuiy will not settle completely, and if it is too thin, the coarse sand will settle along with the mercury and prevent the globules from uniting Beyond a certain point all fiuther addition of watei IS useless, as at this point the mercury separates as readily from the pulp as it would if the pulp were thmnet, and any further addition of watei only thins the pulp unnecessarily With ordinary care, the settle is not apt to clog , if, however, the sand shows a decided tendency to pack on the bottom, the settler should immediately be cleared, to avoid any risk of breaking the apparatus

68 . Affltatoi's. — The pulp from tlie settlers is sometimes run into still other settlers, called agitators, or dolly tubs These are simply large wooden tubs, from 8 to 20 feet m diameter and fiom to 4 feet deep, with foui radial arms, hung and driven like the arras of a settler, revolving about m the tub at the rate of from 10 to 20 revolutions a minute Each of the arms carries from six to eight vertical wooden staves, reaching nearly to the bottom of the tub, and these keep the pulp m a state of gentle agitation, allowing the fine shots of mercury and the coarse sand to settle A constant stream of water is kept running through the agitator Every three oi four days the accumulated matei lal is shoveled out and worked over in pans One agitator will handle the pulp for five or six settle s

These are now seldom used, having given way to modern concentrators or to various modifications of the ordinary settlers.

69. A few years back it was customary to build long blanket sluices below the agitator, through which the tailings

§27 ORE AND IILLINCi

fiom the agitatoi ueic iim These slices icsenibled the underciiri ents used in hydiaiilu mining They iisually consisted of a number of shallow tioughs, IS to inches wide and 'i oi o inches deep, placed side by side, un a giade of from n to 10 inches in 12 feet, and valuing in length fioin 75 to 1,700 or 1,S{)0 ieet The bottoms (jf the sluices weie coveted with blankets, tuned on the under side to prevent then rotting, oi, in the short sluices, riffle bais weie sometimes used The sluices were cleaned at intervals, either by sweeping or by removing the blankets and washing them Both blanket sluices and agitatois have ot late }eais given way almost entirely to improved modem slime washes such as buddies andvanneis

Ore Dressing And Milling

(Part 4)

SII/TEB xOIAIiGwtUIATIOjSr

ii OSS-PROCESS MTEI.

1. Boss Contlmzous Bx'oeess. — The Boss continuous process for the amalg-amation of silver ores is a comparatively new process, which will in time piobably supersede all the older processes The adoption of the Boss system eliminates a considerable portion of the hand labor ordinarily required about a silver mill The operation is entirely continuous, and, except where the ore requires roasting, it need not be handled from the time it is fed into the stamps until the mineral and amalgam are cleaned out of the settles When the ore is roasted, the pulp fiom the stamps (crushed dry) IS conveyed to a roasting furnace, and fiom there to the cooling floor, where it is Spread out and allowed to cool before charging into the grinding pans, in which the ore is mixed with water and ground to the proper fineness before entering the amalgamating pans A Boss-process mill section IS shown m Fig 7

2 , Grinding Pans, — The grinding for this process is done in small iron pans 4; feet in diameter and 1 foot 4 inches

§28

For notice of copv rislit, see immedinteK following the title page

Si ORE and § 2.S

deep, oonstriu tefl soinewliLit similarly to the giindmg and amalgamating pans previously desciibcd The diivmg anangeinent is the same as that used on the Boss amalgamating pans, with this exception there is a compressed spiiiig m a sleeve atonnd the mullei nut, which keeps the adjusting screw pressed down finely on the spindles

The mallei ring and driving cone aie cast in one piece The ring is a Hat, veitical iim, connected to the cone by horiiiontal spokes, and the shoe is bolted to lugs projecting outwards from the sides of the iim, opposite the ends of the spokes. The upper edge of the iim is turned inwards at right angles, forming a fiat, horizontal flange, ot hp, about 5 inches wide 1'he shoes and dies aie both solid, flat imgs, but have oblique slots on then innci edges, extending a short distance into the rings, in ordei to get the same effect of suction that is obtained when the shoes are in segments, with oblique slots between them The pulp is fed into the mailer ring, and is obliged to pass under the muller in order to get to the outside of the pan, since the joint between the muller iing and the shoe is made water-tight by a rubber gasket, and the flange at the top of the ung prevents the pulp from splashing over the sides and turns it back to the middle of the pan Crrinders are usually placed in pairs, two for each ten stamps, one being set slightly lowei than the other The pulp from the entire ten stamps passes into the first pan, where it is ground , thence it passes on into the second pan, where it is still further ground , from here it discharges into the first amalgamators — or in some mills into a chemical imxci\ which is interposed between the grindeis and the amalgamators, and in which the chemicals are mixed with the ore befoie it enters the pans The grinding pans are on a higher level than the amalgamators, and behind them, and ai'e dnven by fiiction clutches on a separate shaft, the clutches being thrown in and out of geai by levers operated from the pan floor

The amalgramating* pans used in the Boss process are described in Art 58, Ore Dressing and Ahlltng Part 3

§ Ore Dressing And Aiilling 3

The number (jf pans in the senes depends both on the capacity of the mill and on the character ot the ore Thus, the renter the cvqiacity of the mill, the larger must be the number ot pans m the senes, siolc the ore must be in the pans a certain length of time m order to obtain a percentage of amalgamation As the operation of the mill is perfectly continuous and all the pulj) has to pass thioiigh every one of the pans in the senes, the greater the quantity of pulp, the less time it will be in each pan, consequent!}, if the amount of oie handled by the mill is increased, the number of pans m the series must be increased proportion* ately, in order to the material exposed to the actum of the mercury foi the proper length of time Oi, again, if one ore amalgamates more leadily than another, it will require less time in the amalgamating pans, and allowing both ores the same time in each pan, the first would require fewer pans in the series to treat the same amount of pulp than the second The same is true of the settles The pans settlers, and — when one is used — the chemical mixer aie all in the same line and on the same level and aie driven from the same shaft, each machine being thrown m or out of gear independently of the rest by means of the friction clutches shown in the illustration of the pan m Fig 21 Ore Di essing and Millings Part 3 To avoid the necessity of stopping the whole mill when pans are cut out for cleaning or repairs, steam siphons are used, which carry the pulp past the idle pans and into the next pans beyond them, and the operation of the mill proceeds without interruption The shaft is made in sections — one section to each pan — coupled together Every other coupling is a clutch coupling and the rest are ordinary flange couplings Between the faces of each flange coupling a ring or washer is inserted, the thickness of which is a trifle greater than the distance it would be necessary to draw the two portions of the clutch coupling apart m order to disengage them When it is necessary to remove any section of shafting, the cover of the shaft box is removed, the flange coupling at one end is unbolted, the washer

Fig 1

§ 28 ORE DRESvSING AND xMILLING 5

removed, and the bection diawn back till the clutch coupling disengages, when the shaft can be lifted out of the box.

4, The Boss settler, winch is used in the Boss con-

tinuous process, is shown in Fig 1 This settler differs from those previously described mainly m the shape and airangement of the stirier and shoes The pan is 8 feet in diameter, with a cast-iron bottom and wrought-iroii sides The bottom of the pan is fiat, and the central cone has a much wider base than is usual m the ordinary forms There is a slight trough in the bottom, next to the sides of the pan The shoes are of non and are much larger than those used in the ordinal y settler, each shoe extending across the bottom from the base of the cone to the edge of the outside groove, at a slight inclination from the radial line instead* of 1 adially They ai e bolted to a muller ring oi plate, which

IS in tuin bolted to the three legs of the driver The shoes do not touch the bottom of the pan, but work quite close to It The angle at which the shoes are set induces a strong current on the bottom and keeps the pulp from packing The driving and following gears aie proportioned so that the stirrer makes about 20 revolutions a minute (The speed of the amalgamator mullers is about 00 i evolutions ) As a rule, no additional settling apparatus is used in Bossprocess mills

5. The clieiiilcal mixer, which is frequently used m the treatment of somewhat lefractory ores, is of the same size as the settler and nearly identical in construction It has, however, wooden sides, as they withstand the reaction of the chemicals much better than wrought iron, and a steam cone is run up inside the mam-bottom cone, the heat from It greatly assisting the action of the chemicals. The chemicals are relatively light and the motion of the stirrer slow, so that the solution is strongest m the top of the charge, where the pulp meets it on entering the mixer, and the dischaige is practically from the bottom, a vane or wing ]ust m advance of the discharge pipe deflecting the

c, ORE DRESSING AND illLLING §

pulp into It ub it rises tiom the bottom at the outside of the pan In this way, the chemicals are retained longer in the pan and the necessary chemical action on the oie is completed sooner The number of niiveis used in the senes depends on the character of the ore and the capacity of the mill The moie refiactory the ote, the long-er must it be exposed to the action of chemicals, consequently, very lefractory oies sometimes have to be passed through several mixes in order In give the chemicals sufficient time to act on them The chemicals are fed into the mixers by an automatic chemical feeder When mixers ate not required, the chemicals (salt and bluestone) necessary foi amalgamation are fed into the first pan by one of these feeders, which is placed between the first two pans of the series, and if any additional chemicals are necessary, they are fed in by another feeder farther down the line, usually between the last two pans

6. The mei'ciiry system is entirely mechanical The mercury is stored in an iron reservoii and is run into the pans through pipes having inverted siphon tips, where they connect with the pans to exclude the pulp The amount being charged into each pan is regulated by a gock m' the pipe near the pan The total amount of mercury used is shown on the dial over the reservoir The shaft which carries the hand on the dial has a small sprocket on it, over which passes a link-belt chain, one end of which is fastened to a cast-iron float on the raercuiy m the reservoir, while the other end carries a counterweight which keeps the chain taut As the mercury falls in the reservoir, the float sinks with It and draws the hand around on the dial The mercury bowls of the pans and the first settler are connected by pipes with a receiving tank, into which the amalgam may be run by merely withdrawing the plugs m the bottoms of the bowls The amalgam can be drawn at will from the receiving tank into canvas straining bags, from which the excess meicury drains off The stained mercury luns through pipes into the boot of a small link-belt elevator, by which it

g ORE DRESSim AND MILLING 7

IS raised and dumped back into the stoiage reservoir, to be used again

7. In the Boss process, when the ore is crushed wet, the pulp runs directly from the stamps into the giinding pans The propoition of watei ordinanl} used in wet crushing in stamp mills would render tUe pulp altogethei too thin tor amalgamation , so the size of the screen meshes is increased considerably and the water cut down to the pnjpei proportion foi pan pulp In this way the same crushing capacity and the aveiage size of the product is practically maintained, while the pulp can pass to the gi Hiding pans without intermediate settling

When the ore is very lefractoiy and has to be crushed dty and roasted, the roasted ore is mixed with water and fed continuously into the grinding pans by a screw feeder Oidmarily the roasted ore is spread out on cooling floors to cool before going to the pans, but in the moie modern continuous-process mills there is no handling of the oie fiom the beginning to the end of the process The oie passes from the bins into I'evolving drying furnaces; itom the driers it goes directly into the automatic fecdeis of the stamp battery, the pulp from the battery is elevated by a continuous-belt elevator into the hopper of the roasting furnaces — which are generally of the revolving type (Howell- White continuous or Bruckner cylindei) — where the salt IS added Lo chloridize the ore, after passing through the furnace it goes to the mixing pan, from which the screw conveyer carries it to the grinders, and from here on the operation is as previously described In old-style mills the roasted ore is spread c ;it on a cooling floor and cooled, and IS then carried to the mixer by hand

8, Clean-XJp Pans — Clean-up pans are small amalgamating pans, used in gold and silver amalgamating mills for cleaning dirty or impure amalgam before retorting, and for working up small quantities of heavy blanket concentrates, battery sands, etc They aie made m vaiuous sizes fioiu

][I HI —If

Ore Dressing And Milling §

15 incheb to 5 feet in diameter, Lfoot pans being* the most commonly used in laige mills The construction and mechanism are the same as those of oidinary amalgamating pans For cleaning amalgam, wooden muller shoes are generally used, as they are lequired more foi stirring than for grinding The dirty amalgam is charged into the pan with enough additional meicury to make it perfectly duid and it IS then tluiroughly stirred The foreign matter uses to the top of the liquid bath of amalgam and is washed away by water running through the pam

For treating concentrates and battery sands, iron shoes are used, as it is necessary to grind the pulp, and iron shoes not only wear better but clean the surface of the gold, so that It amalgamates moie leadily When the pans are used for both purposes, the deep wooden shoes are shod with cast iron The wooden blocks extend above the surface of the amalgam, so that no amalgam will be deposited on top of the shoes when the pan is drained

In many small mills, amalgam is still cleaned by hand, grinding with more mercury in iron pots or hand mortars, and concentrates and battery sands are panned with an ordinary miner's gold pan, to recover free gold and amalgam. All modern mills, however, are fitted with some form of mechanical clean-up apparatus — usually pans. A cleanup pan known as the Berdan pan is considerably used in Australia and New Zealand It is merely a revolving pan, slightly inclined from the horizontal, and containing an iron ball, which naturally stays at the lower edge as the pan revolves, grinding the oie as it is earned around by the pan

9, Clean- [Ji> Barrel. — The clean-up barrel is made and operated in the same way as the amalgamating barrel shown m Fig, 2, but is unhned, and not so large — being usually 3 feet in diameter and 4 feet long. The amalgam and mercury are charged into the barrel, the barrel is then nearly filled with water, closed, and revolved for several hours at about 20 revolutions a minute Scrap iron IS sometimes added, but tbis flours the mercury and

ORE DRESSING xVND MILLING H

does not materially assist the opeiatton, and its use is now being generally abandoned At the end of the agitating period the barrel is opened and washed out with water — the

Fig 2

tailings being run over amalgamated plates or through some other form of amalgam saver — while the amalgam in the barrel is removed, strained, and retoited

10 , Banrel Amalgaination. — The Fieiburg, or barrel, process ot amalgamation is not much used in America A few attempts at ban el amalgamation have been made, but 111 most cases they have given way to the pan process, which IS somewhat quicker, and by most inetalliu gists con* sidered superior to the barrel process However, a description of the barrel and a brief outline of the process will be given

11, Tlie Barrel. — The amalgamating barrel is cylindrical m shape, usually about 4- or 5 feet long inside and the same m diameter Fig 2. shows one form of barrel Some barrels have a replaceable lining of wooden blocks, about o inches square and 3 or 4 : inches thick, set on end, as shown in the illustration, this lining can be replaced when it wears out, and thebairel will last indefinitely The barrel IS made of soft pine staves, 2 or 3 inches thick, bound together with iron bands, and the joints between the planks forming the heads are grooved and fitted with tongues of bard wood. When the barrel is not lined, the staves are

It) ORE AND MILLING §

from 4 to I) inches thick when new, and are replaced aftei they have worn down to about "I incheb The ends of the ariel aie stiengthcned and braced by a cast-non spider, through the endb of whose arms aie passed tie-rodb which draw the bairel heads fiuuly up against their seats These spiders are east m one piece Avith the trunnions on which the barrel revolves In some mills steam is used in the bairel to heat the pulp, m which case one of the trunnions lb made hollow and the steam pipe is passed through it with a gland to prevent leakage

13, The geneial plan of <>peratioa in the bairel process lb practically the same as in pan amalgamation — drying, crushing, roasting, and amalgamation — but the details of the process die entirely difterent and necessitate much expensive machinery, while the process extends over a longer peiiod than would be required to treat the same ore by the pan process

13, Drying?. — The ore from the mines is run through a jaw crusher and then conveyed directly to the drying floor or kilns, where it is spread out to dry as rapidly as possible The drying floor is usually a floor of cast-iron plates, forming the covering of a sei les of flues about 8 inches deep, through which the smoke and waste gases ot the roasting furnace pass , or the floor may he heated by a special fireplace The ore lb constantly raked and turned on the drying floor until perfectly dry

14. Iloasting- —From the drying floor the ore is carried to some form of dry-crushiug apparatus, usually a stamp mill, where it is reduced to a maximum size of 40 mesh, or, in some cases, to fJO or even 70 mesh The crushing and screening to such fine sizes naturally consume considerable tune From the crushes the ore goes to the roasting furnaces, which are ubually either leverberatory or cylinder furnaces The 01 e is roasted with salt until the silver is all in the foim of chloride, and any sulphur and arsenic are volatilized This usually requires G or 8 hours; in the case of very rebellious orcb, it may require as much as lO lioiiis

§2S ORE DREvSSTXG AND MILLIXO 11

or even longer The nie ih roasted several houis befoic adding the salt, m oidei to volatilize the sLilphiii, etc as the chloride oi silver is slightly volatile, and a smal amount of it IS apt to be Gained oft in the fumes, particularly in the first pait of the roasting operation, when copious fines of sulphur, arsenic, and antimony are passing oft

15 . Screening;. — When the roasting is complete, the roasted charge is withdrawn and spiead out on the Lonhiig floor to cool as rapidly as possible, m order not to foim lumps As soon as it is cool enough, it is run through a 40-mesh screen, or finei, and all lumps which refuse to pass this screen are lepulveiized The leason tor this screening IS that the ban el pulp is mixed with only enough watei to make a lather thick mud of it, but not sufficient to soak into and disintegrate clots, so the mixing must be extremely careful It is this fine crushing and repeated screening that consume so much tune m the barrel process and make it so much slowed than the pan process

16 , Oliaring, — The roasted oie is thoroughly mixed with sufficient water to make ,a fairly thick mud, and this IS charged into the ban el, together with fiom GO to 300 pounds of scrap non and the barrel revolved for or 3 hours, the object being to allow the iron to reduce the chlorides of silver, lead, and coppei to metals, ivhich the mercury would otherwise have to do From 2o0 to 500 pounds of mercury is then added and the barrel again revolved for from 12 to 10 hours at the rate of 15 revolutions per niuiute A small quantity of bluestone or magistral is usually added with the mei cm y for the same reason as in pan amalgamation

1 7 . Diseharing;. — When the amalgamation is complete, a plug in a hole m the barrel is removed when the hole is m Its lowest position, and the mercury and amalgam are withdraAvn into a receiver beneath As soon as the pulp commences to follow, the plug is replaced The amalgam js then removed and the pulp from the ban el is run into a large agitator, where the fine globules of amalgam are settled out The rest of the process is the same as m pan amalgamation

U Ore And Milling § '28

Mihi, A'.o vmatiox

18* Amalg:anialin>' Stamp Battery. — The amalgamatiii stamp battery is specially designed for the recovery of victallic gold aad stiver from their oi es It is the simplest appatatiis known for this purpose, and with proper care one of the most efficient The pan and barrel systems just described are desig'ned especially for the tieatment ot silver ores, in which the metal is in the ctnnbined torm, either as minerals not susceptible direct amalgamation— as the sulphides, arsenides, etc, — or as mineials, like the chloride, bromide, and iodide of silver, which although amalgamable, are, fiom their comparative lightness and other physical characteristics, not leadily brought into direct contact with the amalgamated surfaces of the battery and apron plates The slow and long-continued working of such ores in pans or barrels gradually brings every particle of ore m contact with the meicury — a thing practically impossible in the comparatively swift moving and turbulent water in the battery and on the apt on plates

19* Aiixalga mating* Mortal*. — The mortar of the amalgamating stamp battery differs yery little from mortars used sirnply as crushers, except that amalgamated copper plates are placed the mortal The amalgamating mortal must be made somewhat wider than is necessary if the mortar is to be used for crushing alone, m older to get the plates fa: ther away from the stamps and dies, and thus dec: ease the foice of the splash The same thing may be accomplished by deepening the mortar, using a highei discharge, and setting the plates higher above the dies, but this either deci eases the capacity of the battery or necessitates the use of a coarser screen or more water, and is less satisfactory generally If the plates are too close to the stamps, the splash will scour off the amalgam and greatly injure the efficiency of the battery as an amalgamating machine

30. Wet crushing is absolutely essential for successful lirect amalgamation in the battery, as the pulp must be

Ore Dressin( And Milling

1,3

very thin and open tn insure the fold coming m contact with the plates Even when the pulp is very thin, the battery screen of quite fine mesh, and the gold comparatively coarse, there is always more less gold which escapes from the mortar without amalgamating, and Avitli it consideiable finely divided amalgam, in order to catch these pai tides, copper apion plates aie placed in front of the battery Apion plates aie usually thm sheets of coppei, from 8 to 12 feet long and the full width of the mortar, set on an incline of about I in 12 The pulp falls from the battery screens directly upon the plates and flows over them in a thin, rippling stream, the gold and amalgam sink to the bottom and are caught by the amalgamated surface of the plate If the gold IS very fine or is rusty, some of it will not be caught on the plates, but will be floated on with the tailings Formeily this loss m the tailings was overlooked, but close competition and low-grade ores have forced it upon the notice of the millman and metallurgist, so that at piesent there are a number of devices m use designed to save float gold

31* Battery Plates. — Figs 32 and 33, Ore Dressing and Millings Part 1, show amalgamating gold mortars Inside the mortar there are usually two copper battery plates — one at the back, bolted to the inoitar, as in Fig 33, or held in place by taper keys, as in Fig 32, and one in front SCI ewed on to the chuck block and msei ted and removed with it Occasionally end plates are used, but they aie not common Some mills, working base ores by combined amalgamation and concentration, use only the front plate The plates are generally from to inch thick and are usually not silvered

In most modern amalgamating mortars, the back plates are protected from the scouring of the ore, as it is fed into the mortar, by projecting shelves or lips, as shown in Figs 32 and 33, Ore Dressing and Millings Part 1, but there are still many mortars muse in which the back plates are set directly in the feed opening When the plates are protected

U ORE IJRESSINO AND MILLING g

by a tipj the moi tais aie sometimes made with a second opening at the Ua('k, extendmo the full length of the moitar, through whi( h access may be had to the plate in the place beneatii the lij} This opening is kept closely covered while thebatteiy is in operation by a tightly httiiig splash boai'd On an aveiage, about Id pei cent of the total gold saved as amalgam is caught on the inside plates of the batleiy The pioportion in a tew instances urns up to a little oyei DO per cent Most of the gold that escapes the battery plates is caught (ni the apron plates, and a Uttie on the blankets, bumping tables, or othci concentiatmg apparatus

32. Apron Plnte'. — Apion plates are set immediately in front of the mortal, fitting snugly up undei the cast-iron hp oi apron They are usually of or -J-inch copper, and in some mills ai e electi ophitcd on the upper surface with silver — from 1 to 3 ounces of silver to the squaie foot of surface — as the silvei amalgamates much more readily than pure copper and works well from the very beginning of theiun, while it reqiuies seveial days' rim and elaborate pielimmaiy cleaning to get the surface of a plain copper plate into fit condition for amalgamating the gold to good advantage Plates of !Miiutz metal — -an alloy of GO per cent copper and 40 per cent zinc, used for ship sheathing — been tried in some localities, and on certain qualities of low-grade ores give better revSults than plain copper plates and do not foul so readily, probably on account of a weak galvanic current formed by the copper and zinc with the acid water The plates amalgamate more readily than plain copper and Avork Avell from the very start, but the coat of amalgam is very thin and superficial and easily removed , hence, they are less advantageous for rich ores, as they have to be cleaned up too frequently Fui~ther experiments Avith this metal aie desirable

23- The plates are fastened to carefully planed tables by .copper screws or nails or are held doAvn by cleats, and arc beaten to a perfectly smooth, even surface by means of hardwood blocks, Avhich are placed on the plate and

§2S Ore Axd Millino R)

stick with heavy mallets It is highly important that the suiface of the plate be perfectly smooth and set horizontally paiallel to its width, so that the pulp will be evenly distiibuted over the entite surface The table may be made of nairow widths of heavy pLuikmo spiked firmly to the inclined framework, but a better design is made up of narrow strips of wood, set edgewise, lengthwise of the table, and bound togethei every two oi three feet by light iron tierods A table built m this manner will not warp and the even surface of the plate is moie easily preserved Tables made of sections of cast iron are sometimes used, but wood IS cheaper and lighter and answers the purpose just as well.

24. California IMilling Practice. — In the California milhng practice, a very peculiar and unpractical aiiangement of the outside plates has been m vogue for yeais, and, though rapidly dying out, is still retained to a considerable extent The length of the apron plate proper, which is ordinal ily fiom 10 to feet long, is cut down to from 10 to 4-S inches, and from it the pulp is rim into sluices from 11 inches to feet wide and 10 to 10 feet long, paved with copper sluice plates Besides being much narrower than the apron plates, the sluice plates aie given a slightly gi eater inclination, usually inch moie to the foot In spite of the increased speed and scouring action of the pulp stream after leaving the apron, as a result of the contracted channel and increased grade, the California niillinan of the past imagined that he was saving in the sluices gold and fine amalgam which could not be caught on the apron plates Notwithstanding the fact that on its ver' face the whole idea is contrary to all leason, California inillineii, being governed by precedent rather than by reason, clung desperately to it for years, refusing to see what one would suppose impossible to overlook

25. Preparing Plates. — As has been stated before, quicksilver, which already contains some gold or silvet, catches gold or silver more readily than mercury alone If the surface of the plates be amalgamated with pure

IfJ ORfi DRESaiNf AND §

mercury, they will allow considerable gold to escape at iirst, but will steadily impiove as the amalgam grows richer, until they are Avorking normally But if the surface be previously coated with a gold or silver amalgam well worked in, the plates will do full duty from the start For this reason, new copper plates are coated with gold or silver amalgam before being used, or else plates electroplated with silver are used, the silver plating amalgamating with the mercury used in dressing the plates and giving the same effect as preparing with amalgam, with much less time and trouble Gold amalgam works somewhat better on the plates than silver amalgam, but is seldom used, on account of the great expense

To prepare plates for amalgamation, they are first scoured with sand or emery paper until they aie clean and bright They aie then washed with a strong soda or lye solution to remove all traces of giCwise Dilute nitric atid — 10-percent solution— or a comparatively strong solution (about percent ) of potassium cyanide may be used instead of lye or soda After washing with the chemicals, the plate is well washed with water and then a mixture of equal parts of sand and sal ammoniac and a little mercury is rubbed on with a scrubbing brush The sand and sal ammoniac are used to keep the plate clean while the mercury is being rubbed in Enough water is used to make a thick mud More mercury is sprinkled upon the plate from a flask with a piece of cloth tied over the top, and the i ubbing is kept up until the surface of the plate has absorbed all the mercury it will hold The plate is allowed to stand for about an hour and is then washed clean with water or Avith cyanide of potassium and water, and more mercury is added if the plate will hold it. If the plates are plain copper, they aie next given a coating of gold or silver amalgam and are then ready for use. The amalgam is rubbed in with a piece of, rubber belting or cloth, the plate meanwhile being kept wet with sal ammoniac When rubber belting is employed, a piece IS fastened between two blocks of wood, so as to leave about i inch of the belting projecting from the wood The

§:i.S ORli AND MILLING 17

entire block, belting and all, is sometimes called the rubber If old merciiiy js used in piepaiingthe plates, the use of special amalgam is unnecessary, as mercury strained, or even distilled, from amalgam retains enough gold or silver to start amalgamation at once

26. Cleaning' and Dressing: Plates. — The plates are cleaned up at mteivals varying with the richness of the ore being treated, the idea being to let as much amalgam accumulate as possible without loss fiom scouring The amalgam does not accumulate evenly all over the plate, but in ridges, which grow steadily, and if left too long commence to scour off If the mill is running on iow-grade oics, the outside plates are usually wiped twice a day — morning and evening — or only once a day if the ore is very poor

As the richness of the oie increases, the interval between clean-ups shortens, and for very rich ores it is sometimes necessary to clean the apron plates every hour, or even oftener The battery plates are not cleaned until the amalgam stands up m thick ndges ; with very rich ores it may be necessary to clean them once or twice a week, or even every 48 hours, but they are usually cleaned every two weeks, when a general clean-up of the whole mill is made

27. The plates are cleaned by rubbing' the amalgam loose with a wiper made by fastening a piece of rubber belting between blocks of wood, with about half an inch of the rubber projecting, or with a whisk-broom, cut down to make It stiff The apron plates are wiped fiom bottom to top, the men using bits of plank to kneel on while working If necessary, fresh mercury is sprinkled on the plates after wiping and is rubbed m with a piece of rubber In a general clean-up the stamps are hung up, two batteries at a time, and the screens, battery plates, and dies are removed and carefully cleaned of amalgam The battery sands are removed and ai e either fed into one of the other batteries or are panned, bits of iron removed by a magnet, and the concentrates transferred to the clean-up pan ; or, in some mills, they are saved and returned to the mortar on starting

Is Ore Dressing And :\Iilling §

up ag;ain All amalgam slicking to the stamps and to the inside (if the mortal is caiefully collected, and, with the rest of the amalgam from the clean-up, is Erst stained to remove the excess of mei cm y and then transferred to the clean-up pan, oi — m small nulls — to a hand mortar, where It IS ground with tresh mercury and cleaned The amalgam from the pan is again strained, and the balls ot dry amalgam are then leady for retorting

28 Scmphi Every three to six months,

according to the richness of the oie, the plates are scraped with a piece of steel or a spatula, leaving only a very thin film of amalgam on the plates In some mills the plates are 'sweated," in older to get more gold out; but the plates frequently have to be lesilveied or reamalgamated aftei sweating, and the operation involves much moie labor than simply scraping, the thm film of amalgam left after sci aping IS, moreover, very advantageous in starting up again, Sweating is merely heating to loosen the amalgam The plates are removed from the tables and heated over a wood fire, expelling most of the quicksilver, and the gold scale remaining behind is then scraped off Practically the same result IS accomplished without removing the plates Irom the tables by washing them with boiling water or playing a jet of steam on them to soften and loosen the amalgam, which is then scraped off In some mills, chemicals are used in the sweating, the plate being fiist heated to expel the quicksilver and then rubbed with a solution of mter and sal ammoniac and again healed, when the gold rises in scales and blisters The plate is sometimes plunged into a tank of boiling water on being removed from the fire, when the gold scales off " Skinning " plates in this manner is not usually advisable during the life of the mill, as the plates are very apt to get buckled and be irreparably ruined, and there is then nothing left but to melt them up and get new plates The gold recovered from the old plates is usually more than sufficient to pay for a new set, but it takes some time to get new plates to work properly, and they will soon absorb

Ore Dressing And Milling

practically as much as would have teinained lu the old plates aftei sciapmg, so that theie ib really little or nothing gamed financially, even if we do not considei the time lost m changing the plates, and the time and amalgam lost in breaking in the new plates

39, Dressiuji; Taeuisliod Plates. — New plates lap idly become tarnished tiom the action of the acids m the pulp, timing a thm film of coppei salts, or 'Merdigna," over the surface of the plates, which prevents them fiom catching the gold and amalgam flowing over them The tarnish appeals in spots — yelloAV, blown, or greenish — and spreads rapidly if not removed at once To remove the stains, the battery is stopped and the spots scrubbed with a solution of sal ammoniac, this is left on foi a few moments to dissolve the coating, then it is washed oft and the plate scrubbed with a potassium cyanide solution to brighten it, this lb finally washed oft, more mercury added if necessaiy, and the battery again started up Aftet the plates have once acquired a thick coating of amalgam they do not tarnish very leadily, for this leasoii silver plates give less trouble from tins source than plain copper Plates dressed with nitric acid tarnish more rapidly than those dressed with soda and cyanide In some nulls, a little cyanide of potassium IS fed into the mortar from time to time to prevent the plates from tarnishing, and soda or lye is frequently used in the mortar to counteract trouble from grease

30, Mercury Feed aiid Loss. — The amount of merciuy used depends upon the richness of the ore The quicksilver does not wholly dissolve the gold scales, but only foims a coating of amalgam on the surface , consequently, weight for weight, the finer the gold the moie inercuiyis necessary to amalgamate it, as the smaller particles present more surface m proportion to their weight than the larger ones Generally speaking, with a clean gold ore, about 1 ounce of mercury should be charged into the mortar for each ounce of gold in the ore treated Impurities alter the proportion greatly, however, and it is someluneb necessary to chaige

20 Orb Dressing And Milling § 2S

two or thiee limb as much mercury as there is gold m the ore, in order to preserve an amalgam of the proper consistency 111 Amei lean practice no mercury is charged on to the outside plates, except a mere sprinkling aftei cleanups, all the mercury for the amalgamation being charged into the mortar It is charged a little at a time, at mteivais of fiom half an hour to two hours Automatic mercury feeders are made which dip up and feed small quantities of mercury into the mortar at proper intervals, but most millmen prefer hand feeding, as the feed is more easily regulated, and the work amounts to practically nothing, m fact, the regulation of an automatic feeder to suit the varying conditions in many mills would consume moie time than would be required to feed the batteries by hand

The rate of feeding mercury to the battery is regulated according to the appearance of the amalgam on the apron plates About half of the quicksilver fed into an amalgamating mortar escapes through the screen on to the api on plate, and if the battery has no inside plates, practically all the quicksilver sooner or later finds its way on to the apron plate This mercury catches on the amalgamated surface of the plate and then amalgamates with any free gold oi amalgam coming in contact with it The propoition of mercury fed should be kept such that the amalgam thus formed on the apron plate is pasty If too much is fed, the amalgam becomes liquid and is apt to gather into globules and run off the plate or scour off easily , if the feed is too slow, the amalgam becomes too hard and does not catch gold well

31 . On an average, from 20 to 30 per cent of the mercury used m stamp-battery amalgamation is lost — mostly through flouring and sickening Of course, the loss depends largely upon the character of the ore and the experience and judgment of the amalgamator, m many instances it runs much above 30 per cent , either unavoidably or through carelessness, By careful amalgamation and the use of pmalgam shyers below the apron plates, it can be reduced

§ Ore Dressing And Milling '21

to a minimum The loss of mercmy vanes from of an ounce to 5 ounces per ton of oie crushed, and in exceptional cases it IS more

rOR RI.OAT GOLI> AMALGAM

32, fctep Plates, — One of the chief sources of loss is from float gold and floured amalgam being carried away m the pulp stream without coming in contact with the platCvS at all In stamp milling, various devices are adopted to overcome, or-at least to mitigate, the losses from this source The step plate is one of the most common of these The apron plate, instead of being one continuous sheet, is divided lateral}' into two or more segments, and between the foot of each segment and the head of the next one below there is a step or drop of 1 or finches — just enough to cause a slight splash and free floating particles of gold and amalgam from their buoyant film of air, submerging them and bringing them into contact with the plates, but not enough to scour the plates

Sometimes the plates are placed directly under one another and zigzag, the alternate plates slanting with the same gradient, but in opposite directions The pulp stream falls from one plate to the next one below, reversing its direction each time This arrangement allows the use of a great length of apron plates on a limited floor space, and is advantageous when the gold is very fine, as the drop from plate to plate tends to submerge float gold and amalgam, while the increased length of plate surface gives the suspended particles of gold and amalgam more time to settle, It is rather inconvenient for cleaning up, however, and has not been generally adopted

33. SliaMng Plates — For saving fine amalgam that may escape the apron plates, shaking copper plates, placed below the apron plates, are much superior to the blanket sluices sometimes used Sheets of copper — preferably silvered — usually 4 feet square, are set on light frames, with a grade of about f inch per foot the frame is ifher

Ore Dressing And Milling § '18

sii'?pendecl, or, better, mounted on locking legb, and is given a rapid side shake by (.onnecLing-iods operated byeocentiics on a belt-driven shaft at the side of the frame The shaft has a speed of from 180 to '200 revolutions per minute The throw of the table is about 1 inch At the upper end of the plate, which is about a foot shorter than the table, there is geneially a cleat or iiffle about + inch high, extending from Side to side In case the amalgam on. the battery plates gets too hard, any lumps of amalgam escaping from the battery will be caught behind tins riffle, the shaking motion of the table lolling them up into little balls, which gradually pick up more amalgam and increase in size, like a snowball rolled in the snow Two shaking plates will handle the pulp from five stamps, after it has passed over the apron plate

Shaking plates need not necessarily be used aftei stationary apron plates, but may take the pulp directly from the battery The Gauthier shaking table is designed especially for this purpose It has an end shake instead of a side shake, and is practically only a shaking apron plate, mounted on rocking legs and driven by an eccentric on a rapidly revolving shaft extending from side to side, underneath the table If desued, this table can be used below the ordinary apron plates

34. Coimugated nates. — An effort has been made to save flour gold and amalgam by the use of corrugated apron plates The corrugations extend horizontally from side to side, and form a series of parallel troughs or traps, ui which mercury settles and catches the gold and amalgam passing over It m the pulp stream It is doubtful if corrugated plates have any advantages over the ordmary flat plates If much gold is escaping as float gold, a second corrugated plate, amalgamated on its lower surface and placed immediately above the first, with just space enough between them to allow the pulp stream to pass through without being backed up at all, will accomplish a considerable saving by amalgamating a good deal of the float gold and amalgam on Its own surface, and forcing the rest to become submerged

§

Ore Dressing And Milling

v"i

111 Older to escape it, aud once wet, the particles will sink quickly and amalgamate on the lowei plate

35, Meiviiry Wells. — Mercuiy wells, or traps, are merely horizontal troughs parallel to the discharge of the moitai , a bath of liquid amalgam is placed in these tioughs and the pulp btieam either passes ovei or thiough this bath When It passes through the bath, a vertical iron partition IS run along the middle of the trough and dips beneath the suitace of the bath, forcing the pulp stream to pass under It and up thiough the meicury on the other side, in older to get past the tiap The mercury-trap system us open to criticism at many points A comparatively large quannty of amalgam is used in the traps, and the amount of capital locked up in this foim is consideiable Again, this disposition of the mercury is not neaily so advantageous foi amalgamation as the use of amalgamated plates, since it is much more difficult to secure the proper contact of the pulp with the mercury in the baths than on the plates This IS true even of those wells in which the pulp is forced to pass through the mercury bath, as it goes through in lumps or bubbles, and only a comparatively small poition comes in actual contact with the amalgam bath The use of mercui y wells is being gradually dropped from American stamp-milling practice Single troughs are sometimes used below the apron plates, where they save some amalgam , but in all cases they could be advantageously replaced by shaking plates Occasionally a mill is found in which mercury wells are used above the apron plates, but this is bad practice, as It makes it much more difficult to detect overfeeding or underfeeding of mercury m the mortar, conditions which, with the ordinary arrangement of the apron plates, become apparent at once in the condition of the amalgam on the aprons

In Australia mercury wells are still retained to a great extent The battery pulp passes through a senes of wells and then usually over blanket tables — amalgamated plates, in many cases, not being used at all In some mills, working uch free-millmg ores in which the gold is very coarse

N. M i5

Ore Dressing And Milling

§8

no iiierciu'y is tisccl at all except in the clean-up, the heavier gold sctthni, 111 the moitar and the finer gold being caught on the blankets Tlie whole practice is lathei piiniitive in many of its details, and not up to the Aineiican standaid

36, Plates.— A form of amalgam saver used in many California gold mills is the swinging plate Curved plates ot amalgamated, copper, about fi inches deep, are hung on wires across the sluice box, with their lowei edges dipping beneath the surface of the pulp btieain, and the concave, amalgamated side facing up stream The cuirent keeps the plates swinging gently back and forth, and float gold and amalgam are forced to pass undei them to get down the stream A great deal of the and amalgam lb thus caught by the plates themselves, while the rest, once wet, will sink to the bottom and catch on the sluice plates or blankets A tide of amalgam accumulates on the bottom of the sluice immediately under each plate The plates are placed a few feet apart along the sluice They are comparatively inexpensive and go a long way towards correcting the faulty design of the sluice Straight plates would answer the purpose, but a slight curvature makes them more effective, drawing the pulp into the center and creating an eddy that aids materially in submit gmg the floating particles

37 . Miscellaneous Appliances,— In the early days of gold milling in Califoima, before the blanket table had given way to the amalgamated copper apron plate, Atwoods amalfnmatox' and the Eurelca were quite generall} used below the blankets for the purpose of saving amalgam. The former has now given way almost entirely, with the blankets, to amalgamated copper plates, and the work of the rubber is much better performed by the grinding pan The blanket conceiitiates were treated m the Atwood amalgamatoi This was merely an mclmecl table with two horizontal mercury wells or troughs, over which the pulp was run Two revolvmg paddle wheels, one over each well, with their blades barely clearing the bath of mercury, forced the concentrates to pass through the mercury,

g 28 ORE DRESSING AND MILLING 2o

where the gold, on account of its weight, sunk and amalgamated Aftet passing the arnalgamatoi , the mateual ran over a simple riffle sluice, and any esia[)ing amalgam was caught in the 1 1 flies The skimmings the u elL ot the arnalgamatoi and the tailings fiijin the blankets were passed thiough a rubber, wheie they were gioiuid between iron surfaces, cleaning the gold and fleeing it fiom gangue, as soon as it was cleaned it was amalgamated on copper plates in the lubbei The lubber was merely a fiat box with a false bottom of alternate strips ot wood and cast non, extending across the box tiom side to side; above this v as a miiller, shod with plates of cast iron simifai to the bottom plates, bolted to level nairow, amalgamated copper strips were fastened on the sides of the blocks The muller was hung fiom foui swinging lods, so that the shoes barely cleaned the bottom, and was given a slioit hackwaid and forward motion by a connecting-rod and an eccentnc on a shaft at the lower end of the box The stroke of the muller was about 4 inches and the faces of the shoes and dies were 4 inches wide

38. Besides the foregoing machines, there are numerous patented amalgamatois used occasionally here and theie, none of which, howevei, gives any promise of diiving amalgamated plates and pans out ot the inaiket, although some are founded on theoretically correct piinciples A great many of these make the galvanic or electuc current an essential feature, the idea being that galvanic or electiolytic actions keep the merciay clean and live}" — -which is perfectly true, but mechanical drawbacks prevent the general adoption of these machines To this type belong the jMoIloy liyclroen amalgamalor and the J?a55iii amal|?ainator.

iniTIMJTOX MILL,

39* It IS not probable that the Huntington mill will evei generally displace the stamp battery, though it may to a considerable extent

20 '

Ore Dressing And Milling

§ 28

When It IS desu*ed to amalgamate as much gold as possible inside the Huntington mill, the watei -supply should be kept down low, but not so as to clog the screens The pulp then remains in the mill longer before discharging and the gold lb given more tune to amalgamate in the stamp mill, a decrease in the water-supply is attended with a corresponding decrease m the capacity of the mdl On the aprons, a model ately thin pulp, flowing readily, is best, too thick a pulp will clog the plates with sand

Acc'Kssoiit Apparatus

40. Araalgani StTuincrs ami Hnfes. — In silver pan amalgamation mills, wliere laige quantities of amalgam are

handled, the liquid amalgam is poured into an amalgam safe himu lai to the one illustrated in Fig 3 The top and bottom of the safe are made of cast iron and the body of wrought iron The top is concave, with a hole m the middle through which the amalgam drops into the conical canvas bag or strainer beneath The hole is protected by a raised cap, cast on the cover or bolted to it, to pieveiit the theft of amalgam The excess of meicuiym the amalgam IS stained through the canvas by Its own Aveight and falls mto the bottom of the safe, leaving the lumps of nearly dry amalgam m the bags The strained mercury IS drawn off mto flasks or reservoirs, or, m the continuous-system mills, is raised by a quicksilver pump or elevator to the receiving reservoir The cover is hinged, and can be lifted to obtain access to the strainer

Ore Dressing And Milling

17

The strained is fastened to a rinjt, and can be taken out and cleaned A dooi m the side g:ives access to the bottom of the safe without lemnving the strainer Both this doui and the cover are kept locked

41. Retorts. — Meiciiry is separated fioni the o'old in the amalgam by distillation In small silver or gold mills,

Fig 4

where the amount of amalgam handled is comparatively small, cast-iron retorts of the type shown m Fig 4 are generally used, but m larger silver mills, where a laige quantity of amalgam is produced, retorts of the type shown in Fig 5 are necessary The small pot retort, Fig 4, does not require a special fireplace, although one is generally

ORE DRESSIXCr AND MILLING

provided for large retorts. A melting furnace, in which the bullion IS melted to be cast into bricks or bars, is frequently

§ 28 Ore Dressing And Milling 20

built in connection with the retortinj fuinuce, as shown in Fig 0 The letoit, 12" in diametei, is usually plac eel immediately above the giate, but wheie laige cpiantities ot amalgam aie retorted, if the furnace is left unattended for any time, a letort which is set immediately above the fire is apt to become overheated, and the weight oi the metal inside then causes it to sag, luimng it completely To prevent this, the letoit IS sometimes ai ranged with the fire at one side and a fire-bridge between, the letort being supported at several points

In most modern retorting furnaces, a numbei of small rectangular openings, connecting the fire-chamber with the flue at intervals along the top of the arch, causes the heating to be distributed evenly along the length of the retoit, and the draft can be very delicately regulated and the heat localized, if desued, by the use of indivKlual dampers ovei these holes Many furnaces are still built, howevei, with only a single due connection at the front end

4:2, Charging the Retort. — Befoie charging the retort with amalgam, the inside suifaoe is chalked ()r coated with a thin wash of clay or is lined with a few thicknesses of paper, the ashes of which effectually prevent the gold fiom adhering to the sides of the retoit In laige stationary retorts, the amalgam is placed in iron trays which slip into the retort and save much trouble in charging and handling The lumps of amalgam from the strainers aie broken up, placed in the letort or m trays, and pressed down firmly In many the amalgam is packed with the head of a holt, but most millmen disapprove of this practice, as packed amalgam requires longer to retort and is apt to hold some imvolatilized mercury m the center of the lumps The condenser pipe shfjuld he carefully cleared of all obstructions, and if the amalgam is put directly into the ictort, it should be spiced evenly and in such manner that by no mischance can this pipe become clogged, as an explosion would be apt to result, filling the retorting loom with poisonous meieiiry fumes and greatly endangering the health and lives of the

;jO ORE DRESvSING AND MILLING § 28

men In retniting imptue amalgam containing solid substances -which volatilize and recondense in the condenser tube, clogging is very apt tooccui, and the condenser should be so an anged that a rod may be slipped through the tube from time to time to keep it open The heating should also be veiy slow at fiist, as a further precaution against explosions

After the retoit is charged the cover is put on The cover and its seat aie carefully faced, and in addition to this a luting of clay or an. asbestos gasket is placed between the cover and the retort to pi event the escape of mercury fumes The cover is held firnily on its seat by clamps, tightened eithei by wedges or by clamp screws The pipe to the condenser connects with the neck at the back of the cylindrical retort or screws into the cover ot the pot retort The condenser is merely a water-jacketed pipe ; a constantly chaiignig supply of cold ivatei keeps the pipe cool and the volatilized mercury is reconclcnsed and runs into a basin of cold water at the lowei end of the condenser pipe Thus there is very little chance of any mercury vapor escaping condensation Caie should be taken that no water ib drawn back into the retort by sudden cooling, as the steam generated might cause an explosion Some millmen use a rubber or canvas sack over the end of the condensed tube beneath the watei, to avoid risk from this source, the condensed mercury running into this sack

43, Heating; the Retort, — -The heat is gradually raised under the retort until the boilmg point of mercury is reached and active distillation commences. It is kept at this point for one or two hours, according to the amount of amalgam, and is then again gradually raised to a bright red heat and held there for some time, to expel the last of the mercury The fire is then drawn and the retort allowed to cool After it is thoroughly cooled, the cover is removed and the metal withdrawn. The trays used in large retorts are divided into small compartments by partitions, so that the retorts," as the masses of retorted metal are called,

§28

Ore Dressing And Milling

will be of a convenient size and foim tor intinducingf into the melting crucible without bieakmg up The letoited metal IS poiotis and spongy, and usually contains a consideiable proportion of impunties It always retains a small amount of mercury, which is only expelled m the final melting

44. Melting tlie Bullion. — The melting is done in clay or graphite crucibles, with boiax and bicarbonate of soda; and if the letoit " contains much sulphur oi base metals, a little niter is also used to oxidize these impurities The fluxes aid in the fusion and slag off the impurities The fluxes are added a little at a tune , as soon as their action has ceased and the slag becomes quiet, it is skimmed off and more flux added This is continued till the surtace of the melt remains perfectly cleai and shiny, when the crucible is withdrawn and the bullion quickly poured into an iron ingot mold, previously warmed and greased on the inside with heavy mineral oil or beeswax Most large mills do their own melting and refining, but many small nulls sell their "retorts " to private i*efinenes or directly to the mint

45. There should be a "hood" above the melting furnace to carry away the fumes that arise when the crucible is uncovered foi skimming and prevent their spreading through the loom This precaution is very frequently neglected, but the many cases of salivation among the melters are proof of the necessity of observing it

aEOTBAL MELL

Mld Site

46. Gravity Assistance.— One of the fiist considerations in the erection of a gold, silver, or concentrating mill, next to the certainty of an ore supply to keep it i unning, is the selection of an advantageous location In order to avoid mechanical handling of the ore and to keep the expense of pulling down as low as possible, the mill

ORE DRESSINf AND MILLING

S3

desi£nei takes achantaoe ot the fouc ot [cavity and places the successive machines at successively lower levels, so that the material luns duectly fiom each machine to the next one m order To secure the necessarv diffcicnce in elevation between the ciiishei and the final apparatus for this ariang;ement, without building the back oE the mill very high, it IS always desuable to place the mill on sloping ground The slope should he clmsen to correspond as closely as possible with the calculated sltjpe of a line from the gates of the ore bins to the tailings dischaige of the mill, in order to avoid all imnecessai y building oi excavation When giound has to be cut away, strong retaining walls should be built at the back of the excavation and between the benches, as shown in Fig 0, to prevent caving

47- General Arranenient of Bitikliiigs and Apparatus. — Mills aie usually ai ranged so that the mine cans 01 skips, or the oie wagons, it the oie has to be hauled to the mill, can run into or alongside the mill on an elevated track or staging (see Fig i\) In most m<')fern mills the me IS dumped on to grizzlies, and only the coarse lumps go to the rock biCcikers, the smaller stuif falling tin (nigh the grizzlies into the ore bins below, this greatly lightens the duty of the crushci Many mills are still found, however, where all the oie enteimg the mill is put thioiigh the rock breaker, regardless of its size The coarse ore fiom the grizzlies passes on to the ciushmg floor, oi, m most laige modern mills, to a coarse storage bin, the gate of which opens upon the crushing flooi By keeping a supply of coarse ore m this way, the crusher may be kept steadily at work, and the power used by the mill kept more nearly constant This IS particularly desirable m concentrating mills where vanners are used, as these machines aie veiy sensitive to change of power, a variable power makes their regulation much more difficult and lenders constant a ttentujn necessar} , and even if every possible precaution is observed, they will not do nearly so good work as when running under uniform power In small mills the power consumed by the crusher is often

84 Ore Dressing- And Milling § 28

about one-fourth of the total power of the mill, so that throwit in and out makes a decided diffeience m the speed of the other machinery With large mills this is less impoitant than in small mills, but, nevertheless, it is a notable factor in the working of a mill

18. Roolt Breaker's, — The mouth of the lock breaker IS set level with the feed floor, so that the ore can be shoved into It and need not be raised, thus saving the feeder much work Gyratory criishets are gradually displacing ]aw crushers for laige mills, both on account of then great capacity and the comparatively small jai and vibration In modern milling practice, the rock breaker is frequently placed at the mine, and the ore comes to the mill bins already crushed This relieves the mill of the strain and jell of the crusher and makes the consumption of power, and consequently the running of the mill, more uniform The proper place for removing ruck from ore is at the mine, and this can be better accomplished there when the ore IS passed through a crusher

49* Ore Bins. — The sills of the framework of the ore bins should all be on the same bench or terrace and should not be set on different levels along the slope The bottom timbers of the bm pioper are usually set sloping at an angle of about 45 degrees towards the gate, so that the ore will run down to the gate by its own weight Bins are sometimes built flat-bottomed, but tins necessitates shoveling the ore to empty the bm and thus offsets the increased capacity The bins are double-boarded with heavy planks, usually with a layer of building paper in between to prevent the loss of fines The inside bottom planks should be laid lengthwise down the slope, as they wear better this way and the ore slides more leadily Oak, beech, and birch make good orc-bin floors, the ore sliding over them making them smooth The bm linings should be renewed as fast as they wear out When large amounts of ore are handled through the bins, they are frequently lined with plates of iron Owing to the fact that ore slides better on iron than on wood, it is

§ 38 ORE DRESvSINQ AND MILLrNG :?5

possible to give the bottoms of the bins a 85" lathei than a 45" slope, and hence a somewhat largei storage capacity may be had when iron linings aie employed

50. Water Tanks — In most mills the water supply runs into Avooden or iron tanks — usually circular and from 8 to 20 feet in diameter — and isdiaAvnfrom them as desired By this means a practically constant head or presaiiie is obtained j and there is always a reserve supply of seveial thousand gallons — enough to run the mill fur several hours if necessary Some mills use tAvo tanks, one of Avliith is filling Avhile the other is m use These tanks are usually set outside of the mill, on the ground In cold countries, Iioavever, this is not always practicable, as the tanks Avould freeze up during the cold weather In such cases, the tanks should be put in a separate room AVith its floor sills independent of the rest of the framework of the mill, or if set m the mam building, they should at least be set on independent timbers , for if the tanks are set on the mill timbers, the jat of the crusher and other machinery is communicated to the Avater in the tanks, sets it in rhythmic motion, and the vibration of this immense Aveight of Avater IS transmitted to the mill timbers, and Avill, burner or later, if continued, rack the building to pieces

61. Amalgamating iVnils. — The general arrangement of the rock breakers and ore bins is practically the same for all classes of gold and silver mills BeloAv the bins, however, the machinery and airangement vary Avith the amount and nature of the Avoik required of the mill Thus, the machinery of a concentrating mill differs in kind and in arrangement from that of an amalgamating miU, as Avill be seen by comparing Figs and 8 Of course, all mills should be designed to make the operation as nearly as possible coutmuous and automatic For instance, in an amalgamating .mill the are bins discharge directly on the feed floors of the stamp battery, Huntington mill, or Avhatever fine-critshmg machine is used, oi, if automatic feeders are employed, into the hoppers of the

ORE DRESSING AND TvFILLING

feeders The battery oi mill discharjet. on the ajDian plates and the [nilp flows troni them dnectly on to any subsefpient gold- or amalgam-saving apparatus that may be used, and wlucli is on a level 3 oi 4 feet lowei than the battery flour If the mill is a combined amalgamation and concentration miU, as m Fig 0, the concenlialmg appalatus — vanneis, humpino, tables, <n' similar machines — is put on the flour below the battery fiooi If hydraulic dashifleis are used, they can be suspended from the lool tunbeis oi set on frames, usually paiallel to the battery

discharge, and receive the pulp diicctly from the plates, disch*urging the sized ore through pipes into the distubuting boxes of the concentratois Slime-savmg apparatus below the vannors oi othei coiicentiatois is seldom used, but the tailings watei may be run into laige settling vats and the slimes settled out This is particularly applicable in dry countries, wlieic the water supply is united, as the water from the settled tailings may be pumped back to the tanks and used over again, with a loss of perhaps 20 or

ORE DRESSINOx AND MILLING

5 *2S

15 per cent The tculiiigs, if they con tarn mucli value, may be treated by the chlonnation oi by the cyanide prucebs In the very diy regions of Austialia, the watei is sometimes i'emovecl tiom the tailings by means of fiftet piesbCb The design of siivei amalgamating mills is still different from that of gold amalgamating and ('oiicentratmg mills Fig 7 shows a Boss continuous-jirocess mill in Dection

52* Coiieeuti'ntiuijr Mills. — The objci't ot t'oncentiaang woiks is meicly to get the values in an ore into anallet bulk, in older to diminish the and expense shipping and further tieatment, and not toi the immehate actual exti action of the metals m the ore

The operation is purely mechanical, the ore and gang tie jemg separated by crushing, and the gangue, owing to itb owei specific gravity, being washed away Tins being the :dbe, crushing and careful sizing become highly important

53. No definite scheme can be laid down for the arrangement cone entiatmg mills This depends largely upon .he nature of the ore and stiU more upon the ideas of lie designer vSeveral methods, each leqiuimg diffeieiit apparatus and anangement, may be equally well adapted .0 the concentiation of an oie, and the selection ot any one nctliod lies with the designer, who is supposed to take into consideration local conditions as tar as po'nsible Thus, ocal factories, if there are such, are usually given the reference, if their machines can compete on anything like qual terms with those of outside nianufactureis The pei- >onal preferences and prejudices of designers aie frequently mportant factors m the designing oi mills

The concentrating gold mill is for several reasons usuilly much simpler in design than concentiators foi copper, ead, and zinc ores In the first place, the out-of-the-way ocation of the average gold mill makes the freight on apparatus an impoilant consideration in the first ost and runung expenses, and, again, such mills aie usually only temporary stiuctiires, doomed to abandonment as soon as

§28 ORE DREBSIISRx AND MTLEINO

the oie body is exhausted As a i tde, gold mines aie exhausted after being woiked continuously tor a tev 3 "ears, and the oie body may play out unexpectedly at any time, so that it IS desirable to put as little extra expense into the mill as possible It is seldom with while to dismantle an old mill Nevertheless, the mistake ot putting too little apparatus m a mill is much moie common than that of putting in too much Additional machines, it of good design and within reasonable limits, will usually pay for themselves

With immense low-grade deposits, like those nf Dakota, Idaho, and Douglas Island, Alaska, it will usually pay to put m more elaborate concentrating plants, as a veiy small increase in the saving per ton counts up rapidl} where seveial hundred tons of low-grade material aie being treated dally and the ore bodies are practically inexhaustible Fig 8 IS a cioss-section of an Idaho concentrating mill, showing Jigs 7 , hydiaulic classifiers //, buddies b, and vanners v In the Butte (Montana) copper legion, concentration has reached its highest development in America The ores of this region, though containing small quantities of gold and silvei, are essentially copper ores, the gold and stiver being obtained merely as by-products

54. Roll GriisMng Coiiecnti'ating* — Roll crush-

mg is almost mvaiiably adopted m concentratois, though steam stamps have replaced rolls to a considerable extent in the Montana and Lake Superior coppei regions The usual anangement of concentrating mills is somewhat as follows The grizzlies, lock breakers, and bins aie piactically the same as fur amalgamating mills From the bins the ore goes to the coarse or roughing rolls or to a second rock bleaker, set closer than the first, which fills the place of the roughing rolls In many mills a second rock breaker is placed between the main rock breaker and the rolls to lighten the duty of the latter In such a case, the product of the first rock breaker usually goes to a tioinmel whose meshes correspond to the maximum size of the product of

40 Ore Dressing And Milling § 28

the second breaker, and the mateiial winch is ah early fine to pass the second ci-usliei is taken oat, only the oversize product of the scieen (the poition which will nut pass thioufjh the screen) going- to the vsecoiid bicakei

The product of the second cuisheris elevated by a belt or chain elevator bark to the trommel, which is the fiist of a series of three oi louie The iiudeisizc piodiict of trommel No 1 includes the uudeisize product fiom the fiist t lusher and piacLically the entire product of the second cuisher, this tails into the hopper beneath the trommel and passes through a chute into tiominel No 2, whose meshes correspond to the maximum size of the product of the loughmg lolls The oversize from this trammel goes to the roughing rolls, while the undersize goes to trommel No Sj whose meshes correspond to the maximum size of the product of the fine or finishing rolls The product of the loughing lolls is elevated back to trommel No 2 and rescieened The oversize from trommel No 3 goes to the finishing rolls

The product of the finishing rolls may be elevated directly back to tiommei No 3 or may be taken off by a chute — or, if the lolls aie on the same level, by a horizontal traveling belt — and combined with the product of the roughing roils and elevated with it to trommel No. 2 The latter arrangement saves one elevator, but it throws more work on trommel No 2, without appreciably lightening the work on trommel No 3, and necessitates a horizontal traveling belt or chute between the roughing and finishing lolls

The undersize from trommel No 3 goes out to the next machine In most gold-concentrating mills this is the coarse jig, but m many large mills the undersize from trommel No 3 IS earned to a fourth trommel, only the oversize fiom which goes to the coarse jigs, the undersize from trommel No 4 maybe further sized by going thiough moie trommels, each additional trommel giving another jig size, or it may be carried directly to the intermediate jigs and the work of sizing thrown upon them,

§28

Ore Dressing And Milling

55. When oie is clashed hne and sued thiough screens,

the undeisize fiom the last s.ieen ii'iuilly toes tn clabsiheib, which remove the slimes The spigot dischaige oi the classifieis is gained to the finislim; and the

oveiflow, with the siimes, [cjes tr) settles, \\heie the superfluous water is removed, and then to the slime coiicentra' tuis — vanners, huddles, etc In the Butte concentratois, trommels are replaced to a lai<;e extent clas-ifleis ot the type shown in Fig 31, Ore Dusujuf tuuf PaiL I,

with two or moie spigots, tlie discdiaige fiom the spigots going to the respective 3 igs in to Aanniis, and the oveiflow going either to the settling tanks, and thence to the shine concentrators, or to waste This ariangemeiit is common among those mills using steam stamps instead of rolls for the comminution of the oie

56. Troatiiient of Pioducts, — The treatment of

the jig products depends upon the character and giade of the ore When the mineial occurs in bunches, rather sparsely scattered through a t lean gangue from which it separates readily, the me is usually crushed rather coarse, and after screening out the flues, goes to the coaise jigs The deal mineral headings from these jigs aie a flnished product containing very little gangue, and go to the drying floor, and thence to further treatment toi the extraction of the values The tailings from these jigs are usually quite clean and go to the tailings dump The middlings are mixed gangue and mineral and aie lecriidieil in fine rolls, stamp batteries, or some patent mill, like the Heberle, Stuitevant, or Huntington, to fuither hbeiate the enclosed mineral In the recrushing of coarse-jig middlings such as we have been considering, lolls would be pieteiable, and the recrushed material would be sized by tiommels, the oversized going to the next jig beloiv in the series, and the undei sized going on to the finei jigs and subsequent apparatus.

57. When the mineral is distuhuted quite uniformly through the guingue, and particularly when the gangue is

43 ORE DRBvSSING AND MILLING § 3S

tough and intimately associated with the mineial, the crushing must be iTiLU h finer to begin with than in the previous case, in ordei to secure a clean sepaiation, and we will get a small headings class, a large middlings class, and a more or less rich tailings class Frequently, m working mediumgrade ores, It IS found advisable to recrush the jig tailings from the coarse jig and sometimes tiom the fine ]igs as well, in some fine-crushmg machine, and then classify and concentrate them on vanners, buddies, etc As the grade of the ore improves, othet conditions remaining the same, the loss in the tailings, of course, increases

MISC'Et-OAItEOirS jVPPAltA.TirS

58. Elevatois.— Belt elevators and Imk-helt (cham-andsprocket) elevators are largely used in mills for automatically raising the matei lal from the crushing machinery to the screens, oi to samplers, etc , or, m geneial, for delivering material to higher levels These elevators are merely continuous belts, to which sheet-iron or steel buckets are fastened at intervals The belts in gold and silver mills are uniformly lun at a speed of about 300 feet per minute, the capacity of the elevator being regulated by the size and spacing of the buckets.

The belts commonly used are 5- or C-ply rubber belts or link belts Leather bells are used to some extent m drycrushing mills, but would soon stretch out of shape if used for elevating wet material When elevating hot material, such as ore from driers and roasters, cham-and-sprocket elevators are used exclusively The buckets are fastened to rubber and leather belts by countersunk rivets The belts run on pulleys (or sprockets) on countershafting The entire apparatus — unless it is to be used for handling hot material — is enclosed in a tight wooden casing or housing, to prevent splashing or dust, as the case may be, with then attendant inconveniences and loss of material The material falls into the boot of the elevator — which is usually

ORE DRP:SSING and iMILLlNG

§

made, like the rest of the casing, of wood, but some- Limes of heavy sheet lion — and the buckets scoop It upj elevate it, and discharge it into a chute or spout leading to the next piece ot apparatus, as shown in Fig 9

Chain-a n d~spi ocket elevators are of two general types — singlechain and double-

chain In the ill St

type, the buckelis are bolted at then backs to the links of a single chain, while in the second type the buckets are hung between two parallel chains Link-belt machinei y has been generally adopted for conveyers of ail kinds

Fig 9

59. Sand AYlieels, — Frequently the taihngs-discharge opening of a mill or conceiitiatmg works in time becomes blocked by the tailings backing up from the dam or tailing dump, so that it becomes necessary to lift the tailings as they leave the mill This may be accomplished by a bucket elevator similar to that shown in Fig 9, but when an elevator IS employed, it requires a belt, and the expense for the belts in the long run is considerable On this account sand wheels are frequently employed They are really nothing but overshot waterwheels in construction, which are given a reverse motion by machinery, so that in place of the descending water operating the wheel, the rotating wheel lifts the water and tailings in its buckets The buckets are placed on the inside of the nm of the wheel, as shown in Fig 10, and are filled from launders or sluices a at the

44 ORE'dRESSINCJ AND MILLING §

bottom and dischaicd into laiuideis c at the top, which cany the tadinis to the dump tailing dams, oi lixiviating vats The wheel m the illustration is one used in South

Fig 10

Africa The spitzkasten shown in the discharge launder is for the sulphurets or heavy particles of ore to settle in, while the lighter particles gu to then proper leceptacies The sand wheels aie driven by belts or gearing

60. Sand Puiniis. — Sometimes tailings are discharged by means of centiitugal sand pumps, which force the material mixed water up and into the launders on a higher level, so that it can flow away

In cases wheie plenty of watei is available at the mill, the tailings may be removed by means of an hydraulic elevator,

ORE DRESS 1 and MILLINO

§2S

which IS really a watei ejcctoi, and which takes advantage of the toixe ol a comparatu ely small stieam of uatei iiialei a great velocity and makes it move a large sticam of water and sand at a comparatively slow veloeit) and raise it to a moderate height This device is fiequcntly employed for handling the tailings in placer-niining voik, and will be

found equally efficient foi handling the tailings at mills

1 . Dischavgiiig- Tailiiifts 4 Vitli()ut VVater. — In regions

h e 1 e tv a t e 1 is s c a 1 t e , some arlangement must be made foi removing the tailings aftei the w a t e 1 has been drained or filtered out of them This may be accomplished by means of a i abroad track and cars, or by conveyeis, eilhei of the chain - and-bu( ket or endpattern One great difficulty m regard to all foi ms of conveyers has been that as the tailings pile me leased, it became necessary to lift either the track or conveyer so as to keep it being

buried under the

Pig li

4n

Ore Dressinc And Milling

tailings To overcome this, tiipods canyon the conveyer may be siippoiied on screw piles, which can be lifted as fast as the pile nl material ijiows One of these adjustable supports foi a conveyed is shown in Fi 11

62# DilTerontUil lullers — Differential pulleys are indispensable aioLind mills tor hitting heavy apparatus, such as stamps, mulleis of amalamaiing pans and settlers, etc By then use one man can raise easily, and with no risk of dioppmg and breaking, weights which several men could not move by mam strength ahme

GB, Cra'. — Oveihead ciawls oi tackle-block carnage are merely movable hangers m supports for the differential pulleyb. They are usually made entirely of iron, the

Fig is

most common form being the four-wheeled carriage shown m Fig 12 There are various other forms m use, however, — four-wheeled carnage, with flanges outside, running on a single horizontal timber, with iron or steel strips for tracks, two-wheeled carnage running on a single track, and a single wheel carrying a hook

§ 28 ORE DRESSINfx AND MILLING 47

The tracks on which the ci awls run ai e susjicuded from the timbeis above the stamp batteries, pans, etc , so that the crawl With its pulley tMu be lun back and faith to any point, and the stamp oi mullei lilted and swung' out of the way One Cl awl and one piille\ aie supplied for eac h low ot appa latus The tracks most commonly used are made by fastening flat steel or iron by screws to heavy honzontal timbeis, which aie suspended by vooden hangers from the overhead fiame timbeis Flat iron bars, suspended edgewise by iron hangers, are aLo common

64. Exhaust Fans. — Exhaust fans are used in all modern dry-ci fishing mills to draw oft the dust, moie oi less of which will escape even from the most carefully housed machinery The tans are placed at advantageous points in the upper part of the mill and keep up a draft thiough the , drawing in the dust and discharging it outside or into a settling loom They are indispensable to the health and comfort of the workmen m diy-crushing mills In addition to these, fans aie connected sometimes by pipes directly to the housing of the machinery, drawing oft the dust before It can get out into the mill

SPECIkD BXAIMFI/ES OF COTSTCENTTlATTOlsr

65. Concentration and Preiiaration of Cojpei' Ores* The coucentiation of copper ores naturally divides itself into two distinct methods (L) The concentration of those ores m which the copper occurs m metallic form, as, for instance, the ores of the Lake Superior region m the United vStates (2) The concentration of ores in which the copper occurs as a copper mineral, usually one of the compounds with sulphur or oxygen

66. Native Copper Ores- — In the first case, the .copper IS all in metallic form, and hence it is practically impossible to produce slimes from the metal itself, also the great difference in specific gravity between the copper and the associated gangue renders the separation much easier than

IS the case with the copper minerals Owing to these facts, a special system of comcutiation has been developed in the Lake vSupeuor legum The old gravity stamiiis have been abandoned and heavy steam stamps mtioduced

The copper oie as it comes from the mine is, to a certain extent, hand sotted in older to icmove any laige masses of the metal Theoieisall stamped through coarse set ecus and is sized by means at hydiaitlK classifieis As a lule, no screens oi tiommcls are used for sizing the material, which upon leaving the hydiaulic classifiers passes to CoL loin jigs These Jigs usually pioduce three classes of material fine concentrates passing through the jig sieve and into the hutch box undei the jig (commonly called hutch woik), barren tailuigs the end of the Jig, and a bed of inineral on the sieve, composed, in the case of the coaise jigs, mainly of miggets of metallic copper, and on the jigs farther down in the senes, a mixture of gangue and metallic coppei, called ragging, which i eqini es further ciushmg The beds of the Jigs are cleaned out at mteivals, the metallic copper being placed with the concentrates, and the ragging being returned to the stamps fur further reduction The hutch work passes to other jigs or settling boxes and is worked over again The slimes passing through the screens of the fimshing Jigs are worked on buddies or shine tables and in tossing tubs The slime-concentrating machinery at many of these copper mills appears vei y complicated, and yet it is mostly composed of such simple machines as buddies and keeves, which have vciy few paits requuing renewal

67, Ores Containing Coppev Minerals. — Ores of the second class pieseiit a very different pioblem, for the copper mineral naturally crushes finer than a large portion of the gangue rock This results in the production of a great percentage of slimes The , engineers m charge of concentration works in the West have followed two lines in dealing with this class of material In some cases they have introduced the steam stamp on account of its gieat capacity and the low cost per ton tor which it will crush the material.

§ 28 ORE DRERRINf AND ADLLING

Where steam stamps have been intiofUiced, an attempt has been made to follow the Lake SupeiKji stem of concentration as closely as possible , but most nulls have inti ochiced some moie expensive machine! y foi dealing with the slimes (such as Flue vanneis and othei special concentrating raachiner}"), m addition to buddies oi slime tables They have also been forced to introduce Utge slime pits, m uluch an attempt is made to catch the valuable portions earned off in the fine slimes The overflow tiom these pits is carried out of the mill and saved behind dams The pits are cleaned and the mateiial mixed with lime before it is fed to the furnaces The mateiial which settles behind the dams IS cleaned out every few jeans and either allowed to dry m solid cakes or is mixed with lime and charged into the furnaces This method of handling slimes is very expensive and leaves a laige amount of copper locked up tor months or years before it is lecoveied

68. The other general method followed by engmeeis in charge of this class of concentrating works is that of successive reduction and separation, the ciushiiig being accomplished by means of lock breakers and tolls and the material being sized by means of trommels oi screens. Hydraulic classifiers are also used to make mtei mediate classifications The material is passed over jigs, and any of the middle products (corresponding to the raggings of the Lake Supetior ore) at'e leciushed by mils or special machiiies (such as Huntington mills) The jigs used foi the coarse concenliation work are usually of the Hartz pattern, those for the finei work being the Collom, Evans, or Slide pattern* The work is cai ried on very much as described under the heading of Concentrating Mills ''

69. Points to he Ohserved in Coiiecntration.—In concentrating any oie of coppei, the object is to pioduce a product suitable foi the copper furnace, and on this account iron pyrites is not unwelcome, as it will assist in forming the matte, and the iron is useful in the subsequent processes of

50 ORE DRESSINtJ xVND MILLINO § ;J8

treating the matte In coneenttatuig oreb of tin, lead, or zinc, It is of cotisidei able importance that the difteient nnneialb be seiiarated, foi iron and lead will injure the ictorts or fiunaces in which the zinc is treated, while zinc in the lead ftunace renders the smelting veiy difficult and tends to cairy off both lead and silver as fumes or to carry them into the When it becomes necessary to separate two mm-

eralb which have specific cavities varying but little, the material must be closely sized before it is passed to the jigs or other concentrating machines

70- Before any ore can be concentrated, it should be crushed to such a sixe that the grams or crystals of the different muieials are set fiec, and the first cuishing should be such that the average size of the product is the average size of the mineral grains The lesult of concentrating such a product will be pure grains of the mineral and bari'en tailings, also a thud or intermediate product, consisting of pat tides which contain both the mineral and the gangiie and require furthei crushing before they can be concentrated This rule applies equally to the methods of dry, magnetic, and wet concentration

71f When gold and silver are present in the ore to be concentrated, they may have a decided effect upon the method pursued, for if the gold oi silver occuis m one particular mineral, the concentration will be earned on with an idea of saving the greatest possible percentage of that mineral

73, Coneentxation of liOad Ores* — Lead ores which occur pure, that is, free from other metals, are frequently hand-picked or washed on hand jigs to separate them from the gangue Where the ores occur in somewhat harder formations, they require crushing and sizing previous to jigging, and if the mineral is finely disseminated through the ore, fine crushing and close sizing will be necessary, especially if zinc ores occur associated with those of lead

§38

Ore Dressing And Milling

Some concentrating mills also use biuldles or other slimewoiking machines foi coriLentrating the fine oie Whete the lead oies aie associated with some zinc ores oi with non pyiites, a sepaiation may be eftectcd by closely sizing the 01 es and then caiefiilly Jigging them, but unless the zmc crystals aie comparatively coaise, it beruincs dithciilt to make a first-class separation by hydiauhc means Theie is only one mine m the United States for lead alone, and that is Mine LaMot in Missoni i jMost lead is deuced from silver lead ores

US. Conceutratioii of Zinc Ores — Where the oie of zinc IS blende, either asscjciated with lead ores or occmrmg by Itself, It may be separated to a certain extent under certain conditions only by picking and by crushing and jigging When the zinc oies contain iron or manganese minerals, they may be magnetically concentrated Where the objectionable material is franklinzte, it may be separated from such minerals as willemite or zincite by means of magnetic concent ratios, as is clone at the New Jeisey mines, the oxide being removed and employed for the manufacture of zinc pigment, the lesidiie fiom this process being used m the manufacture of spiegeleisen The non-magnetic portions, consisting mainly of willemite, are used for the manufacture of zinc The non-magnetic portions carry more or less gangiie material with them, and this has to be separated by means of ordinary wet concentration on jigs Some ores of zinc have been freed from iron by loastmg the oie until the iron is x'entered magnetic and then separating it on magnetic concentrators

74, Concentration of Tin Ores. — Tin ore should be free from other compounds before it is introduced into the smelting furnace These facts rendei the concentration of such ores somewhat more difficult, but by taking advantage of the difference in then specific gravities, the problem is by no means impossible

52 . Ore Dressing And Milling §

Oidiaaiily tin is Lonitiiitratticl by hancLsoi tmg ui ciiisliing and stainptni* Ihc ore, aftei which it is sized and sepal ated liy means ut jigs, huddles, and keeves The concentrates of tinstone and minei'als cairymg iron associated with suiphui and aisenic The sulphur and ai seme are driven oft by i ousting, after which the iron oxide is removed by fiirUiet concentiation The fact that timstone IS already in the form of an oxide keeps it from being changed during an oxidizing lasting

When tinstone is associated with large amounts of mica and close sizing is not desirable, most ot the conccntiates of the Jigs are foimed as hutch work, that is, the concentrates pass thiough the sieves ot the jig and the tailings over the endSj AVhilc the material forming the ordinary concentrate, discharged over the bed, is middlmgs or raggings, which require furtbei treatment

*75. Coiiceiilralion of Mercury. — As a rule, the ores of mercury are separated entirely by hand picking and sorting, no concentrating machuieiy being employed

76, Concentration and Preparation of Ivon. Ores. Most of the iron uics need no preparation before they are charged into the furnace, but there are great deposits of lean ores, or ores containing certain ingredients which it is desirable to remove, and various processes have been introduced to prepare these oies fur smelting These operations or processes may be described as follows

1 Separation of the ore from barren rock or gangue by means of ordinary wet concentration

2 The separation of ore from clay by washing

8 The elunmation of sulphur or carbonic acid

4 Magnetic concentration

77. Wei Coiieeui ration and Sorting*,~Under the first operation can be considered all ores m which the iron mineral is fairly hard and the gangue consists of quartz or

ORE DRESSlNC'i AXE MILLLNO

othei worthiest material Sin'h oils rue c nminunly and separated by hand this special soiling floors aie sometimes the bet oi clean oil btinp picked out in the mine, jots diiedly to the cai-* oi stuck pile, while the ore which is mixed with nioie (n* less gLinoue IS suited into two or muie classes ot mei chantable tire (the niimhei of classes depending upon the ot cue in eachjj and a Avorthless lass ut the bant n lotk or gang Lie The sorting oi picking mac be done on fltaus from tables, or picking belts A gieat many plants hare been introduced foi the pieparalmn ot oie by oidinaiy wet concentration, using lock ciiishei s and to reduce the material, bcieens or hydiaulic classifiers to sue or suit the crushed materuil, and jigs or other concentrating machines to separate the ote fioin the vvoithless mateiial Giving to the extremely low price per ton which non oie brings at the present lime, it is impossible to concentrate most low-grade oies at a profit This is especially true in cases ivhere both the ore and the gangue are haul and cause excessive wear on the rolls, crushes, and olhet machinneiy, besides reqtiiimg a laige amount of power The expense per ton is often moie than the price of the ore wan ants, and as a result neaily all of the plants which ivere operating upon the harder non-magnetic oies, by means ot wet concentration, have been closed

YS, Iron Oreek Containing* Cltiy , — Many of the iron oies, especially those of the Eastern and Southern vStates, are associated with more or less clay A number of machines have been devised to wash this matenal from the ore, but the primitive log washed has developed into a form which seems the best adapted fur this purpose Figs* 13 and It illustrate a log-washing plant that luis been m successful operation for a number of years Fig 13 is a front and Fig It a side elevation; tlie engine u not shown m the plant, but is an automatic Buckeye giving H P with 00 pounds of steam when luiinmg at revolutions per minute The plant is dnven by a 1 Finch lielt passing

54 ORE DREvSSING AND MILLING § 28

ovei a 3~foot piillfy on the engine shaft The washed proper IS dll ven with (1-nit.h lubbci belts luniiingovei the pulleys D and A, Fig 14, A and U in the same figure being the loose pulleys on to which the belts can be shifted when

It is desired to stop the engine The logs are arranged m pairs, and as they are alike, a description of one pair will be sufficient

To the end of the shaft //", Fig 14, on which is fastened the pulley is keyed the small pinion /, which meshes into the spur wheel J. This drives another pinion at A", and this in turn gears into the spur wheels L and which drive the logs in the two washers N and 0 at the rate of 12 revolutions per minute

The gear is connected to the logs, which are on a slope of g'Unch per foot, by cast-iion clutches, one of which IS shown at A, Pig 14

Ore Dressing And Milling

The real beanti! is inches m diametei and is of cast iron It IS cast solid with a Hange, on the face of which is turned a shoulder This shoulder lits into a coricsponding

S

recess turned in the similarly flanged end of the log Th( two flanges are bolted together and make a very stiff joint as the shoulder prevents any lateral motion

A M Iii —0

ORE DREvSHINPr AND MILLING

g

The 'dVL simply pieces of cast-iion pipe, 17 feet inches loner ILI inches in diameter, with metal inch thick, and tinged at each end This makes a splendid log — one that is stiff and wears well

The method of attaching the spoons is shown m Fig 15 They aie put on m two spiral threads, ISlF apait, and with

a 5-foot pitch They are set 45 apait on the ciicumtcrence, thus making (S spoons to each 1 evolution, as shown lu Fig 15 By this method ()i laying out, theie are, at every t of a revolution, two spoons opposite each other and 1S0" apait If, now, holes he bored through the pipe, under the two holes with which the toot of each spoon is provided, two thioiigh bolts will fasten on two spoons These bolts aie inch in diametei and are made with nuts at each end as shown

At the upper end o£ the log theie is a gudgeon, similai to the one at the lower end, except that the bearing is only inches in diameter and extends 2 feet beyond the box To this end the revolving screen Q, Fig 14, is attached The screens are made of steel plates perforated with

--inch holes, 4 inch from center to center

The tioughs in which the logs woik are made of a wooden frame, in which aie fastened the iron plates constituting the trough proper The bottoms and sides of the frames are of 3-incli pine, thoroughly braced by the yokes shown at 5, Pig 13 Both bottom and sides are bolted to iron end pieces, m which are cast seats for the chilled-iion gearing boxes The iron plates constituting the though proper rest tipon the sides ot the frames, to which they aie attached by J-mch lagserewb As indicated at A, Fig 13, they are oL the usual semicircular pattern and aie cast in sections only 15 niches long. This permits them to be made as open-sand castings

In the operation of tliL* [haiU, the nie is bnmijht tiom the mines in sidL- c ars, hoklini> about tons eai h The cais aie pushed out past the wasiiei on the tiestle 7, Fig ly, whith is built with a guide asienduu; in the direction ot the arrow shown in the diawimi The cais are then allowed to diop down, two at a tune, until they come the chutes U and which are lined with 1-inch iron plates

The ore, falling thiougli the chutes to the hgs, is caught by the spoons, which voice it up against a descending curlent of water from the though f", Fig Id, until it reaches the i evolving screens (2, into whudi a stieani of water fiom the same trough is tiouing There the ore is fuitlier washed and at the same tune sepmated AH uvei u-int h diametei passes along the screen and tails into the " chute to cars," Fig Id

The dues, which diup through the [lei forations, fall on the Id-mesh wire-cIoth screen IF, Fig Id, where the} aie fiuthei ashed and screened, all over 1 t mesh going to the cais, while the sludge falls on the apron A' and is thence carried away m the trough I", which also conveys away the water from the lear end of the washers

The cuirent of watei descending in the troughs is apt to cany off more or less oie thiough the lear end, and to prevent this loss, two perforated screen plates (not shown in the draivings) are used The muddy water the trough passes through a gate upon these screens, through which it falls and is earned away into while the ore lemains upon the screen Only one screen is used at a tune, and as soon as 01 e enough has accumulated upon it to stop the perfoia- Lions, the water is shut off and turned into the other The ore IS shoveled back into the washers This device saves a great deal of ore at a \eiy low cost, as it requires the attention of one man for only pait of his tune, thus leaving liim free to help at other points

79* When day is the only material removed from an iron ore, the percentage of impiiiities will inu be much affected, that IS, the phosphorus and sunilar unpuuties, as a ruiCj

58 Ore Dressing And Milling § '28

occur in the iron me and not in the associated chy, hence the washing will not increase the grade of the oie matei rally, except m its percentage ut iron Washing plants are sometimes introduced to clean ore from clay before it is put till oiigh some othei fuirn of concentrating machinery, such as Jigs, etc , or before it is hand-picked

80, Ores Contiiiniieii' Sulphur or Carbonic Acid, These impurities have to be removed by loasLiiig, and as this IS usually done at the smeltei, the apparatus need not be fully described in a woik on Mining It will be sufficient to say that the roasting kilns now in use for this class of wmik are fired with gas and that the ore is fed to the kilns and the roasted mateiial cliawn fiom them continuously, much as m the case of a lime kiln or an iron blast furnace This continuous action greatly increases the capacity of the kilns, and the firing with gas lesults in a inoie uniform roast than was possible m lhe old style of intermittent kilns m masters

81, PrexKii'atloii of vSalt. — As lock salt comes finm the mine it usually canies moie or less foreign mattei, and if it were ground to a fine powder for table use, it would have a dark color, and hence would not find a leady market For this reason, the greater poitionof the tabic salt of commerce IS made by the evaporation brine solutions obtained either from salt wells, salt lakes, or from the sea There are a few rock-salt mines which produce perfectly clear crystal bait, and from these table salt can be manufactured without the intermediate stages of dissolving and reevaporation The regular product of salt fiom any mine is treated as followb The large lumps are laid under sheds to undergo a process called weathering, for the salt attracts moisture, and if the lumps are not properly weathered, they are liable to breakup more or less during shipment The water which the salt absorbs from the air forms a brine on the surface which effectually cements all crevices and readers the masses solid pieces The portion of the salt intended to he treated m the mill lb crushed m rock breakers and toothed rolls, after which it passes over shaking screens which separate the

§2S Ore Dreestno And :Itllixo .9

diftcient giacRs Tht. mtiRiuil (up Dinch cubes) IS used tot cappings in packing meal These appings aie added the biine uu In]) oC the meal in onlei tn maintain the brine at its full stiength The hner grades of salt are used in the inaniitacliire of ice eieam, foi preserving hides, and for similar commercial pin poses Tin large lumps of weathered salt aie shipped as cattle salt salt is prepared foi the table, it is giound fine and eithei separated by means of shaking screens m by a blowing machine, the different grades of salt being collected m various bins oi chambeis, owing to then vanuus sizes, the lightest mateiial being blown the gieatest distances

82. Points to Observe in Concentrating;

Works. — When au engineer is called upon to design a concentiation plant, he should be very caiefiil that he is not deceived by new conditions For instance, the condition of the mineial may be such that concentration is impossible, as in the case of a silver ore m a coinpaiatively hard gangue The silver sulphide would be pulverized so fine and form such bad slimes that it would be impossible to recover the gieatei part of the values from the ore

83. Aiiothei case which might be mentioned is that of the haid non oies banded with jasper The jaspei is frequently so Ultimately associated with the iron that it is impossible to separate them by crushing, and as the specific gravity of the jasper is fiequently very high, a separation of the two would be practically impossible On the olhei hand, the magnetic oies of iron being m the form of crystals can easily be separated from the gangue by crushing, and hence can be concentrated

84. General Kule. — .dj a rulc it may he stated

that tn orda to concentrate any tf must he of a nature that by crnsliinetthi mineral it sipatuits in the form of dutinct (lystals or distinct pieces Where minerals are practically of the same hardness and are intimately associated, it IS rare that concentiMtion by mechanical means IS successful

Sampling Ores

iTOli Y

1. Object of — The object of ore sain- xMing IS to obtain tor chenncal or mechanical tests a small quantity that will contain all the minerals in the same proportions as the original ore If the sample is not correct, there will be a loss to eithei buyer oi seller In concentrating mills and leaching plants, samples are also taken of the tailings, and in smelters of the slag, in order to deteimine how much value is being lost In concentrating mills, the different products of each machine are sampled, in oidei to know whether the machine is doing the woik expected from it In blast-turnacc smelting, samples and analyses of the oies, fluxes, and fuel are necessary in order to calculate the proportion in the charge that will make the furnace run properly Careful sampling is very often disregarded , but no furnace or mill manager can aftoid to guess at values when the exact knowledge can be so accurately obtained by SAinphng and assaying This is especially true in these days of close competition, when values are being profitably saved that could nut be recovered by the old methods It may be stated, as a rule, that the best extraction cannot be attained unless checked by cai eful sampling and assaying

Obtaining a Cox*rect Sample. — To obtain a correct sample, a systematic method must be used vSelecting lumps of oie haphazaid here and there will not answer, for however honest the sampler may be, it is impossible to

For notice of cop right, see pnge immedmtely following the title page

Sampling Ores

judge the right pioportion of iicli and poor oie by the eye The moje thoroughly the ore is mixed and sized, the moie certainly will a peilect sample be obtained

3. Sampling is done eithei by hand or by machine, machine sampling, howevei, is seldom completed by machine, the final process being done by hand

Although great improvements have been made in sampling machinery, metallurgical wot ks usually do their own sampling by hand, while public sampling mills do their sampling by machinery, which seems to give satisfactory results to both buyer and seller Public samplers really occupy the position of umpire between buyer and seller, the seller frequently believing that the buyer takes unfair advantage of him, especially if the latter is a public smelter or reduction mill Miners have been, known to send ore to smelters so lean that, if fi eight and smelting chaiges weie added, the miner would be m debt to the smelter The only way for a miner to be satisfied that he is getting full value for his ore is to sample his ore before he sends it to the smelter or else send it to a public sampling mill Sampling IS as important as assaying, and the hand sampler should have no interest whatever m the ore if he would obtain an average sample

Haot Samplintg

Saitpling Bumps

4. General Consideration. — The method of sampling dumps or any large piles of ore depends on the character of the ore, the amount to be sampled, and the disposition that IS to be made of the oie If all the oie is to be moved, the fit St sample may be obtained by taking a certain portion of the ore as it is being moved, as, foi instance, every fifth shovelful or every fifth car or wheelbarrow load. This is called fractional sclixtion

§29

vSAMPLING GRES

If the mam poition oi the uie is not U) be move, the first sample may be taken by 1411114 trenches m channels thiough the mass and either takin-4 all the 01 e from the channels or a ccitain piopoition ot it by fictional selection* This method is called

The fiibt sample from a large mass may also be obtained by sinking shafts into the pile 01 bydrivim; tunnels thtough it The sample is sometimes obtained by taking small portions ot 01 e from varions parts of the suiface of the pile A sample taken m this manner is called a sample

5 , Grah Sample* — When it is desned to get an approximate idea of the v'alue of a laige ore heap, a sample is sometimes obtained by taking a shovelful of the mateiial from various points, equally s])aced, all over the suiface of the heap This method should be used only for materials that are pretty imifoim in composition and of low value, such as iron 01 es, fuels, and fluxes Even with these care must be used to take coarse and fine pieces as they come and not to take all lump, foi the fines are quite certain to differ fioin the lumps m comprisition

An improved modification of this method is sometimes used when iinloadnig iron ore fiom a vessel When enough ore has been removed to expose a face of ore reaching to the bottom of the vessel's hold, small quantities of ore are taken from all over the face, the samples being taken in regular order from side to side and from top to bottom When consideiable moie ore has been taken out, samples are taken from the new face and so on. This procedure has the advantage of taking portions from all parts <')f the heap instead of merely from the suiface The sample may be further reduced by fractional selection, by quartering (which will be described later), or by a machine

G. Fi'actional Selection. — When a large lot of ore is being shoveled fiom cais or elsewhere, a sample may be obtained by throwing aside every third, fifth, tenth, or twelfth shovelful The richer the ore or the more unevenly the minerals are distributed through it, the oftener is a

SAHPLINa ORES

So

sample shovelful taken Each shovelful should be taken from the ilooi and from the bottom of the pile When the 01 e comes in sacks and is of a fairly uniform character, every filth oi tenth sack may be taken for a sample Fractional selection is probably the most accurate method of obtaining a sample fiom a large amount of ore

T. Clinnneliug.— Channeling, as applied to dumps or large piles ot ore oi other inateiial, consists in shoveling channels thiougli the mass and taking all or a portion of the ore ftoni the channels as a sample When only a poi tion of the oie is taken as a sample, the reduction is genetally made by fractional selection , that is, by thi owing every thud, fifth, oi tenth shovelful of ore fiom the channel aside as a sample When sampling du mps by channeling , cai e must be taken to see that the ore from the sides of the cuts does not fall into the channel to such an extent as to give an unduly laige pioportion of ore fiom the uppei pait of the pile

8 . SiKe oi Sample.— The size of the sample taken from a clump or any other large quantity of me should depend on the manner iii which the values are distnbuted through the ore In the case of ores in which the values are uniformly distributed, such as iron ores, a grab sample may be all that is required oi every twentieth shovelful may be taken, but if the values are not uniformly distributed, as in the case of 01 es cai 1 3''ing free gold ot valuable minerals, the first sample must be laiger and the ore must be crushed finer if coirect results ate to be obtained In some cases the first sample must be at least one-third of the ore After the first sample is taken it is reduced by fractional selection, channeling, quartering, oi by a machine

Sampling S 3 Lall Lots Op Oke

9 . General Couslclemtion. — The sampling of small lots of ore does not differ greatly from the sampling of dumps or large lots In dealing with a carload or other small lot of ore, it is generally necessary to handle all the ore.

30 Sampling Ores

heoLe a grab sample is lady taken If the <ne is being unloaded from cais, the hist sample is geiieially takea by fractional selection and then i educed by the same method or by quaitenng oi chamielmg

10, Rraetioiial Selection, — When this is used for sampling taiily laige lots ut oie, the hist sample is taken in wheelbarrows or cais and dum])ed in a pile When this pile IS completed, it is removed by shovdmg and a ceitain proportion of the matenal tliiuw n into anew pile, caie being taken to tin nw all the oie on the top of the pile, so as to thoroughly mix the sample ft is often that the second sample is so large that it has to be taken in wheclhai lows nr cdis and piled m another place When shoveling the ou\ caie must be taken to ste that the [dace wheie the sample is piled IS swept clean and that each shovtlful nt oie is taken from the bottom of the pile Fi actional selection is piobahly the most accurate method for obtaining a sample ot oi 00 pounds fiom a lot of oie in which the allies are not regularly disti ibuted thiough the ore The mm e ii reguhii ly the values are distributed tluough the me, thelargei should be the sample taken at each handling of the ore and the finer should the me be crushed Aftei the sam[)le has been reduced to 100 or 300 pounds by fi actional selection, it is generally still fiiither reduced by quaitenng or channeling,

11, CliaiiTieliiig, — For channeling, the oie is spread out m a flat heap or layei a few inches thick and the sample taken by shoveling out two or moie parallel channels, like paths through a bank All or a part of the ore from these channels constitutes the sample Sometimes two sets of channels arc made, one set at light angles ti) the other Channeling is fairly accurate if caiefully dfuic, but is little used, since it requires a large floor space In channeling, the ore does not require as much mixing as ui but there is sometimes considerable ditficully experienced lu making the channels without knocking down some ore, either coarse or fine, from the sides of the channels

Sampling Ores

§29

12. Qiiarteriiii>\---Wlien ore is sampled by quartering, aiso called the Comi>>h nxetliod of sampling, the ore is first thoroughly mixed and then divided into four parts or quarters and two of these parts taken as a sample, while two are discarded. , In order to thoroughly mix the ore, the work may be done as follows :

The ore is dumped in a large circle, as shoAvn at Fig. 1, and the samplers move slowly round the ring, shoveling the

Pig. 1

ore into a pile in its center. It is common for two men to work together, always keeping diametrically opposite each other. They drop each shovelful exactly on the apex of the resulting cone, as shown at b. This is done by holding the shovelful of ore above the apex of the cone and then suddenly pulling the shovel away from the ore in the direction of the arrow. This distributes the ore on all sides of the cone and gives a pretty thorough mixture. As another aid to complete mixing, the samplers do not shovel all the ore in walking once round the circle, but make at least two trips. Care must be taken to sweep up all the fine ore and place it on the top of the pile. It will not do to simply sweep the fine ore up to the edge of the pile, as this is apt to be the richest part of the ore.

HAltPLTNG ORES

In some cases, to iiisuie the ore ib shov-

eled from a ring to a pile and back to a iing again several times 01 it may be bhoveied fnjin one pile to anothei Atter the oie has been thoroughly mixed and piled up in a tone, the samplers walk round the cone umtinuously m one direction and with their shovels diaw the oie into ci wide, flat pile or heap The mannei of doing this is illustrated in Fig i, ivhich shows the cone paitly spread out It may sometimes be necessay to shovel the oie tiom this flattened cone into a second cone in order to make the mixing more complete

13. It IS hard to get a thorough mixtuie when very coarse and very fine material occur togethei, but this difficulty IS lessened by moistening the ore a little Water should not be added in sufficient quantities, however, to make the oie cake Veiy wet ore cannot be properly sampled by quartering, because the water washes the fine material away from the coaise and so prevents satisfactory mixing

Having spread out the ore flat, it is divided into four quarters, as shown in Fig 3 This may be done by pressing the edge of a board down through the heap on two lines that

pass through the center at right angles to each other If a comparatively large mass of ore is being sampled, the quarters may be separated by shoveling two channels across the pile at light angles to each other When shoveling these channels, the me removed is thrown alternately to the right and left After the quarters have

been matkedoft foi stpaiatin, two ojjposite qiuirlets, as, foi instance, /and III, aic shoveled auay, taking caie to remove all the fine pai tides belonging to them Theieinauimg twm qiiarteis are shoveled into a new cone and the process repeated This time, quaiteus If and //"are shoveled away instead ot / and II The object of this is to overcome any possible tendency ot the shovdeis to make one side of the heap richer than the othei The i eduction of quantity must not piocecd too tai hetoie the oie is crushed to a smaller size Even aftei fine crushing the sample is seldom reduced m size belt)\v S pounds by quaitermg

14* Kainxding Ploois— The floor on which the quaitciing is done should be smooth and fiee from cracks, and for tins learn it is best to have it covered with iron It

should be carefully swept before it is used, to pi event nth dust Irom pievioiis samplings being mixed the oie in hand When a floor is not available, a large piece of strong canvas may be spread out

15* iSpllt fcsUoveh — With lots weighing not more than half a ton and when the largest lumps are not moie than about 4 inch m diameter, the split shovel. Fig 4, is sometimes used This shovel consists of several long a, with open spaces b between them, the spaces being the same width as the scoops. The sampler takes the ore on an ordinary shovel and spreads it over the split shovel, moving hxs shovel back and forth across the bcoopb as the ore slides off When the scoops aie full, the shovel is lifted and the ore in the scoops is put one side as the sample, the rest of the ore leniammg on the floor The action of the split shovel is very much like that of the sample riffle or the Jones ore

sampler, both of which are described under

the head of Finishing the Sample

§39

Sajipling Ores

IG. A slotted -pixe is so me tunes used to sample fine matenal that is ot tan h tiaile, such as concentrates The best foim of this tool is n in Fn* a A 1-inch iron pipe a has a slot b cut in it from one end to within 3 or 4 inches of the other A T is screwed to the unblotted cndjfoi the insertion ot a handle c A second pipe just \aige enough toi the first to easily slip inside, IS also slotted, but this slot i does not extend quite to either end of the pipe The lower end of this largei pipe is forged to a point, so that It can be easily pushed into a pile of fine 01 e The tool, while held in the position by the

cross-section is forced into the material to be sampled, the inner pipe is then turned the position and is twisted back and forth until it fills with oie It is then returned to the position / and the sampler is withdrawn. To pull out the driven pipe d, a cast- ()r wioui;ht-iron cross Z; IS screwed to the pipe and a lifting handle / inserted through /i

ox* Budget Sample. — To sample any rimmng stream of matenal, such as the difieieiit products in a concentrating mill, a dipper or bucket may be passed through the stream at regular intervals, once an hour, for example The dipper must pass across the whole stream, because one side may be richer than the other It must not

Rampling Ores

bfc! allowed to dll and lun ovei, especially in the case of products caincd in a stieani of water, for this would cause a loss of suine of the finer pait of the sample

18 . In this connection, it is necessary to mention an impuitant point that is often disregarded When fine material earned in water is to be sampled, it is common to let a bucketful settle for 10 or 15 minutes, then to pour off most of the watci and dry the lesidue This is thought by bome to be a safe plan because, although the water poured off is ai some cases <[Uile tmhuh the quantity ot solid matter suspended in It IS apparently insignificant The trouble with tills reasoning is that this cxtiemely fine material is often veiy rich With most oies of silvei, gold, copper, lead, etc , the valuable mineials are pulverized more than the waste during the crushing, so that a sniall quantity ot veiy fine material may contain more value than a large quantity of the coarse part To show the importance of catching these very fine slimes, a case can be mentioned wheie material to the value of about St, 000 a day \vab going to waste in this form in the mill tailings the manager's knowledge Sometimes, howevei, the very fine slimes will not settle completely in several clays or even weeks, but right here an interesting scientific fact comes to our aid Small quantities of common salt, alum, and various other substances dissolved in the watei cause the finest slimes to settle much more lapicllythun otherwise, as is showui by the following expel iments

19 . The tailings fiom a gold stamp mill were run through a settling tank to remove the coarse portion and the overflow was allowed to fill a small tank After the water had stood undistimbedin the lattei for houi, a large sample was taken from the top of the tank and, of couise, It contained only extremely fine slim Numerous tests showed that 95 to 100 per cent of all the suspended slimes settled out in hour when as much as 1 per cent of salt or alum was dibbolved ; while only per cent settled out m the same time wheie nothing was added, in fact, 20 hours

Sampling Ores

§ So

were necessary fui DT) pet cent tu settle when nothing was added Lime uas still mote cftective, the equivalent of 05 of 1 pet cent, or less of burned lime added in the condition of cleai hrne water caused neaily ad the slimes to settle out in less than 5 minutes It should he noted tliat slimes from cliff eient ores act differently In some cases neither lime nor common salt gives good lesults, therefoie, the best substance to use in any case must be found by experiment Fan ly vigorous but not too violent stiiiiiig sometimes makes the particles that have been coagulated by lime or any other substance come togethei in large flakes and so settle more rapidly

SO, Geiieml Remarks. — When the sample has been cut down to a few pounds of finely cuished ore by successive crushings and i deductions of quantity, the final sample is prepared. In order to do this, the sample is geneially put through a sample gimder and then i educed to I pounds or less This small sample is then ground on a bucking boaid and passed through a fine screen, after which it is divided into three or four portions, one for the sclier, one for the buyer, and one for the umpire In some cases, a fourth sample is kept by the sampler for reference in case of need

Some ores contain metallic particles that cannot be ground and will not pass through the screen These Anetallics" and the ote passing through the screens must be weighed and assayed separately If this point is not carefully attended to, the value of the ore cannot bt correctly determined

21 . Sample Gvimler. — When the sample is ready for finishing, it generally consists of from 8 to I'i pounds of ore that has been crushed in some form of fine crusher or that has been passed through finishing rolL This sample is then passed through some form of sample grinder before it is stiU further reduced m bulk.

N M llL—ei

ores

sample ismtiodined mtolhc hoppei a and is aunuid bctwein

the head £: and the img After grinding the material is dlfechaiged through the spouts i/ and r and collected in pans The head c can be raised or Imveied by means of the hand wheel which controls the thrust beaimgAat the foot of the shaft yhy means of the lever ? It the head is raised the particles of the material will be ground fine , on the other hand, if lowered, the particles will be ground coarse

JiSJ* Cultinj Down tUe Sample. — After the sample has been ground it is cut down to about )l pounds oi less This may be done by quartering on the bucking plate oi on any other hard smooth surface ot by using some form of sampler, such as the iifHe or the Jones sampler

§29

Sampling Ores

33. lilffle, or Till Hamplor — This insists ot a seues of trouglib arrangfcid bide by bide with open spaces between

tlienij as shown in Fig 7 The width and number of the spaces and troughs can be so ananged that the sample will take out au}'' desired portion of a ci wished sample thuit has been spread evenly over it The nfflet. aie commonly made to cut the sample into two equal jiarts, halt lematning in the troughs and half falling through The oie is taken xiy on a scoop a and spread over the troughs, cate being taken not to heap the oie above the top of the troughs, the sampler IS then lifted and the poition m the tioiighs oi that which* remains on the plate taken as the sample

34. Joueb Ore Sampler.— In the c ase of the otdinaiy riffle, It lb necessary tr) lift the sampler out of the <n'e to sepal ate the samples, and care must he taken not to let the Die pile up above the top of the troughs The Jones sampler ov'ercomes these objections and makes provision for taking duplicate samples from much larger amounts of material than can be handled on the riffle at one operation Tins sample is illustrated in Fig 8 It IS really a riffle sample in which all the

Fig 8

Sampling Ores

§29

spaces aie connectetl tn spouts that clischatge alternately to the light cintl left The oicib distributed over the iitfles at d and two samples result, one being received by the tiay d and the othei by the tiay c

25. Eimil OrtiuliiiA— Aftei the sample has received its final cutting down, it is placed upon a biitking plate

(also called a bucking board) and gioimd with a inulhr until it will pass through cl sieve having the desii ed mesh, which IS usually one that has 80 or 100 meshes to the linear inch One form of bucking plate, or rubbing plate, is shown in Fig i) The muller with which the gi Hiding is done is shown at a The plate shown has two raised edges, though some rectangular plates have three raised edges. This foim of plate is best if the ore comes on to the plate m rather large pieces, so that they must be broken with a hammer or with a very heavy muller, for the raised edges tend to keep the ore from flying off the plate For reducing samples that are already comparatively fine, some persons prefer a circular bucking plate Such a plate IS usually about feet m diameter, and when m use is placed on a low table or bench so situated that the operator can walk around the table as he draws the muller back and forth These circular plates wear more evenly than the rectangular ones, because the rubbing takes place m different directions across the plate, and there is no tendency to wear grooves in the surface of the plate,

36. Sepaiatlon of the Namplc. — After the sample has been passed through the sieve, it must be divided into three or four portions, so that the buyer, seller, and umpire may each have one A common method of separating the

vSAMPLIN( ORES

lo

§20

sample is to place the oie on a piece oi oilcloth or ihized paper and to mix it thoroughly by duiwing tip liist one corner and then anothci the oih loth or paper in urdei to toll the material over Aftei the oie is mixed, it is spread out m a thin layer means ot a spatula and then small portions of the material are taken fuim vaimus parts of the mass, as shown at n, Fig 10, and placed in the dish // After

Pig 10

the first sample is taken, the process is lepeatcd to obtain the second and third samples Theie is some danger that this method will not give accurate results on account of the difficulty of getting equal poitions from the top and bottom of the pile Some pet sons prefer to thoroughly mix the sample and then to divide it by quaitermg

37. Probably one of the most accurate methods of dividing a sample is by means of the Bridgman mixer and divider, which IS shown iix Fig 11 In using this devucc, 2or impounds of finely ground ore is mixed m the funnel, or mixer the opening at the bottom being closed by one finger The finger is then removed and the mixer passed back and forth over the divider which discharges into the sample bottles as shown All the ore that is put into the mixed must be run into the bottles, or there may not be a proper distribution of the heavy and lighter portions A cover, which is nut

U) SAMPLING ORES g

shown in thc illustKition, is placed upon the mixed when the ore is being shaken

Fig 11

MOISTURl STOPPLE

38, Nearly all ores are more or less wet; and, since the moisture gradually evapoiates, the weight does not remain constant Hence, the only way to find the leal value of any lot of me IS to have the assayePs sample perfectly dry and also determine what the entire lot would weigh when perfectly dry For the latter purpose, a special sample should be taken when the ore is weighed This sample must be obtained as rapidly as pos'ible and put into a closely coveredLion pail or box to prevent evaporation It must not be taken simply from the top of the ore pile, because that Will generally be drier than the average The best way, if possible, is to dump the ore immediately after weighing and take a sample by rapid fractional selection

SAAIPLIXf; ORES

The moistuie .sample may he veiy much sinallei than the tewulai sampk As sjun as the moistuie sam[)le is all taken, It should be and dned, oi, it it is too bulky, it may be rapidly mixed and a poition taken toi hut it must be handled as little as possible befoie dryintJ. The dtffoiun iJic Ttv/ and divided by tin

7uef and ninitiphid by 100 in'is tJu pDLtntagi of

nioistu?L in tin zoit oie

Example — A sample nt 21) pounds of ore after weighed It) 0 pounds What peieentage of niiusture was in the oie '

Solution — 20 — tiJ ™ 4 and — 2 pti cent moisture

Ans

MECHA3sO.VL SAMPLIXa

39. General Considoratioii. — Sampling ores by hand lb tedious, slow, and expensive, besides the operator's judgment may be warped unintentionally m regard to the pioper pioportion of coaise and fine oie in the sampling It has been stated with considerable truth that a man who samples a mine should have no conscience, as he may en almost as badly by trying to be tair as by trying to be unfair This does not apply to oie sampling at metalhngical turks to as great an extent as at mines, ncverthelesb it docs in some measure, unless the operator acts in a mechanical manner and mciely directs the sampling according to some fixed method A machine has no judgment, still it has method due to Its construction, and while, if properly planned and constructed, it may prove accurate, on the other hand it may not be accurate, and then must be discarded The main objection to the most accurate mechanical sampler is the difficulty experienced in cleaning it after each sampling operation

30, I/imitingf Conditions.— Mechanical sampling can be used wherever the ore runs m a fairly steady stream A mechanical sampler has some form of diverting spout that delivers the sample in one direction while the bulk of the

Sampling Orls

Ole goes m another To give accurate lesults, it must take the zeholc stream part of tlu time and not a part of the stj cam all the tiuu, that is, it must cut out a iortion of ore across the whole stieam at leguku intervals The reason for this is that the large lumps of ore aie almost suie to roll to one side, away ftom the fine, and the heavy to roll away from the light, so that one patt of the stieain does not represent the whole The stationary devices, which take one part of the stream all the time, aie at present not used by careful operators If the divertug spout of a sample swings back and forth through an ore stream, it must move completely out of the stream in each direction oi xt will take too much fiorn one part of the stream and not enough from other parts The machine shoukl be simple in construction so that it can be cleaned easily, thus pi eventing rich particles of ore from one sampling getting into the next sample.

li'lG 12

31. Topham's and Siiydex''*s samplovs arc shown in Rigs VZ and It) Each of these resembles a pan with flaring sides, turned on edge and fastened to a revolving horizontal shaft. Near the circumference of the pan is an opening

Sampling Ores

thiough whicli the sample passes to a bin, but the main poitiou of the (lie is diverted into a separate bin by the flange In the

Tophain sampler, which is "

illubtiated m Fig l'i, the s ,

oie comes down a sloping Lo ''V;\

chute a placed at the

back of the pan /?, while Im c yi|[i

m Snyder's, Fig IB, the /i'l 111

oie IS fed to the front i

side Topham's sampler 11 1'

IS not on the maiket, but

Snyder's is made by the ''1

AUis-Chalmers Company b I

of Chicago It wull be no- /

ticed that the two sides of /

the opening foi the sample to pass through converge towards the axis of

rotation, so that the pait of the opening neai the center of the pan and the part neai the cirenmferenLe pass through the

stream in exactly the same time and take equal proportions

uf oic horn all [jails <ti the tieam This point is provided toi in all the met hanual samplcis that uill he desenbed

32. The sumptoi* in Fig; l-t has a lionzoiiUil aim tasteneid at its middle to a levolviug vertical shaft /r, on each uul of the arm is a diverting scoop f When these si'oops come under the end of the spout the ore falling fiom r/ i-, duected into the spout t, which leads to a sample box 01 bin At othei tunes the stream of oie passes thiotigh the s[)outytothc shipinng oi storage bin The slo[)ing Range pi o vents any ore tailing into the

sample spout t except when the sample scoops come i ound

33. The YezLii saniplor lb sinular the Collom m its essential feature, which is a clive ting scoop i evolving horn zon tally, as shown m Fig 15, but It differs in construction* Two truncated' cones made of heavy sheet iron are joined at then bases, wheie they aie attached to a set of spider arms extending horizontally from the vertical shaft From the upper cone, one or two radial scoops a project beyond tlie base of the The stieam of ore falls ftom the sp()ut and when the scimp a passes through this stieam a sample passes' inside the cones and is delivered through the small end of the lower one into a box or bm The mam portion of the ore passes to a storage bin

34-. Bi'anton! '-Simpler, showm in Fig 16, consists of an oscillating divided /; that swings back and forth beneath the end of the feed spout g. The divider is fastened to

Fig. 16

each oscillation and divert a sample to a sample bin ; but the lest of the ore is deflected in the opposite diieotion to the stock bill by the sloping faces b Theie are Uvo Bum*- ton samples, but the one described is the better

35. Constants '-ampler, shown in Fig L7, is a hollow cylinder fastened on a horizontal shaft and having openings d m the sides When these openings pass under the chute a, samples of the falling ore run inside the cylinder and are delivered from the ends into the hoppers t The rest of the ore rolls over the surface of the cyhndei into the hopper d This machine is arranged to take duplicate samples

36. Seir-Aeiing' Samplex's. — In some cases wheie tailings are to be sampled and there is no shafting from

Sampling Ores

§29

which to cluvc any of tlu machines described above, devices are Used that eithm by the force of the running stream of tailings oi by an auxiliary stieam of water. The

Richards sampler, Fig is a hollow cylinder made of sheet iron and having internal curved blades against which the tailings and ivater strike, causing the machine to revolve The axis of the cylinder is inclined so that the tailings pass between the blades and out the lower end of the cylindei A hole is cut thiough the cylinder between two of the blades and a tube is soldeied on the outside to deliver the sample that passes through the hole into the channel a of the casing The space bctweeu the two blades mentioned should be covered on top and at the lower end, so that whatever gets into this space can get out again only through the hole m the side of the cylinder The sample delivered into the channel a passes through a tube, at the point of the channel, into a bucket or box Professor Richards of the Massachusetts Institute of

SAMPLING i ORES

Tt;chnolo£>y has also dosincd an watriuiKcl to he diiven by the stream of tailings, <au of the biiekets having

Fig 18

an opening towards center of the wheel, through which a sample passes

37* The apparatus shown in Fig 11 is used to sample tailings at some of the gold mills of the Transvaal It is not strictly self-acting, but it does not have to be connected to shafting The pipe in which there is a longitudinal slot, lb attached to the shaft c by means of the arms d The box d is als<) attached to the shaft c. A small stream of water from the pipe r urns steadily into tf When d is filled, the weight of the water makes it tip over and the pipe a is thereby moved downwards through the

Pig lO

again passes through the stream One end of this pipe is closed, but the other end is open and delivers the sample into the box t

38. The Ijaiiib samples made by the Allis-

Chalmers Company, is shown in Fig The box b, Avhich IS arranged to rock endwise, has a central partition c When enough watei has run into one side of the partition, that end of the box tips down and discharges the Avatei at the end This allows the suspended spout e to run down to the lower end of the guide lods and thereby cut through the

Sampling Ores

2'J

stream of tailmys that tails fiom tlu launder and deliver a sample into a bn.\ oi haul When one tiul of the ho\ b tips down, the pipe d delivers its watei into the othei end of the box, which, m turn, jriadually tills and is

fict ;io

down, allowing the spout e to out across the stieani of tailingb again, but in the opposite diiection The frequency with which samples are taken depends on how fast the water IS aiiowed to flow from the pipe d and to escape from the box

39. RcTolAin Tailms .Sampler. — One form of sampler that IS operated the flow of the tailinjs is shown in Fig It consists of an undeislut ivateiwheel

driven by the flowing tailings, and which, in tuiii, diiveb the geai on the veitical pipe// The pipe /i is tamed in

vSAMPLING ORES

§29

bearings in the tLinges jr and /, and one end of the waterwheel shaft IS eat lied iii the veitical flange d The vertical pipe // IS connected to the horizontal trough so that whatever IS caught in 2 will flow down through h to the launder 7 The wheel causes the pipe h to revolve and the trough z to cut through the tailings as they flow from the launder a

The sample that passes through j must be caught in a large tank, so that none of the water will escape, for the ivater must be separated from the solid matter by means of a settling tank, but in all cases any water that is allowed to flov UAvay must be clear, so that it will not carry any values with it

40, Coin 3 aidsoiis and Gciiei'al Beinark&. — Hand sampling is gener'ally used for small lots that do not justify the outlay for a mechanical plant The latter, however, generally costs less for operation and saves tune Moreover, a properly constructed mechanical sampler always

§20

SAxMPLING ORES

gives correct results, but in hand samplin'; the may take an unfair sample if he is so inclined

In regard to difterent methods of hand sampling, it may be said that quartering is piobably more accurate than channeliug and requires no more laboi Foi very large lots of ore, neithei quartering nor channeling can well be used, because with such lots they would require too much hour space and too much labor Fiactional selection, liuwever, can be used foi a lot of any size The limitations of the grab sample are stated m Art S.

41. Some machines are ai ranged to take duplicate samples, but theie is no advantage m this, foi it has been shun m practice that with a properly con'll! acted machine the duplicates always check Indeed, if they did not check that would be conclusive proof that the machine did not take fan samples In some cases these duplicates might serve to detect any ''salting/'* but it would generally be a simple mattei for any one who tampered with the ore to add equal proportions of '"salt" to both samples The final small samples for assaying are made up m duplicate where ore IS being sold, so that both buyer and seller can have a sample Indeed, a third sample is commonly prepared, so that any discrepancies in assaying may he settled by an assayer who is independent of both buyer and seller

PKmCIPLES OP SAMPLma

42. General Consideration. — Since oies are never perfectly uniform m composition, a single shovelful taken from a lot is not at all likely to be a correct sample But if enough shovelfuls aie taken from regularly apportioned parts of the lot, as in fractional selection, the rich portions will balance the poor and give a connect lesult In the method of quaitermg, instead of many small portions, a

"Salting'* lb the unsci upuhms addition of rich mateiial, with a view to making the ore appear richer than it real ife-

iV iU. in—

as

Sampling Ores

§30

few laige portions aie taken, but this requires careful mixing before cutting out the sample Without this mixing, the chances of making the sample too lu'h will not be so well balanced against the chances of making it too pool as they are in fractional selection By toiisideiiiig this balancing of the rich against the pool, it will be seen that the accuracy of a sample depends not on the latin of its weight to the weight of the whole lot, but simply on the actual weight of the sample, whethei the lot is laige <ir small

4 : 3 . Effect of Size of Eniniis. — With any given ore. It IS cleai that a gi eater weight must be taken when the lumps are large than when they aie small, because in the toimei case the different grades of oie cannot be as uniformly mixed as in the lattei case The gieater the weight foi any size, the gieatei the accuracy of the sample, but for every case there is a weight that comes so near to perfect acciuacy that there is no piactical advantage in taking more In this connection, it may be stated that ore m any Sized lumps can be correctly sampled if a large enough sample IS taken, but if the lumps are too large, the sample will be mconveiiientl)'' bulky.

44:. Effect of Chai-aeter of Ore. — Larger samples must be taken of iich than of pool ores, because the foitner must be mure accurate in order to prevent losses When the rich minerals occur irregulaily, the sample must be larger than when those minerals aie uniformly distributed, otherwise there wull not be the propei balance of rich and poor

45, Size of Samiile. — If a 100-ton lot of ore was crushed fine enough add was perfectly mixed, a coirect sample would be obtained by taking a few ounces fiom any part of the lot, but this would be very expensive, both for the labor of mixing and for the power used m crushing, and would generally leave the ore too fine for any following treatment Moreover, we should never feel sure of getting a perfect mixture of such a large lot The method used is to crush the entire lot, leaving it as coarse as is required for

Sampling Ores

§29

concentrating,, smelting, or othei subsequent pioiess, and take a suitable weight foi a sample This is crushed finer and a sraaller portion taken for the sample

46* Rules for iiize of Sample. — To decide what weight to take foi lumps of a particular size, an approximate estimate of the quality ot the ore is made by judging from Its appeal ance or fioin previous knowledge of the mine from which it comes Having decided this for lumps of one size, the weight to be taken tor lumps of any size may be found by the tollowmg rule Tah luJi a wiiglit fioui each sie:e as zeili h equal to a fi.itd nitaibif of the pai'ticles j that is, if the weight taken after ciushmg to 1 inch IS equal to 50,000 1-itch lumps, then after ciushmg to I inch, the quantity taken should be equal to 50,000 -mch lumps Since the weight of a lump of ore is proportional to the cube of its diamctci, this lule may be stated as follows For a given ort the 'lecight takin for a sanipL should bt proportional to tlu cubt of tiu diamitt of flit laigist particle of the ort

47, This uile would be all right if the diffeient minerals were entirely detached trom one another and if all the pai tides of any given mineial weie equally rich But most oies have to be crushed finely beloie the minerals will be wholly detached fiom one another. Now, if the entire lot of ore Tvas in one laige lump, that single lump, of course, would be a perfect sample If, on the other hand, the ore was crushed so fine that all the minerals were perfectly detached from one another, a single particle could not be a correct sample, foi it would contain only one of the minerals Thus when the particles are large, fewer of them can be taken than when they are small The following rule conforms to this last statement and gives results that agree with good practice Fo) any given

the lOi ight taken for a savipk should be p? part wnal to the SQUARE of the dtanutc) of iJu largLst pat tick

48. This rule was worked out by Piofessor R H Richards, of the Massachusetts Institute of Technology, after

Sampling Ores

21 )

studying the piacticc ot seveial careful manages, and is given hete, together with the accompanying table, by hxs special permission

The accompanying table embodies this rule, and each column in the table is based on figiueb taken from practice Column 1 applies to such materials as iron oie, veiy low-grade lead or coppei oics, or even to low-giade gold ores when the gold is contained m pyiite and the pyiite IS evenly distributed through the ore Column 2 applies to ordinary low-grade copper, lead, and zinc uics, oi to any ores of not too high a grade m which the valuable mineials are uniformly distributed Columns 3 and 4 apply to richer ores in which the valuable minerals do not occur in nicgularly distributed spots Column 5 applies to native gold ores with fine nuggets of gold (these nuggets occurring in spots), to ordinal y telluiide oies, and to certain orch containing sulphide of silver Column 0 applies to native gold ores in which the gold occuis as large nuggets, also to rich tellunde ores, and to iich ores ot silver sulphide (silver glance) and silver chloride (horn silvei)

49. Such a native gold ore as that just mentioned cannot be sampled in the sense of gradually reducing the size of the particles and at the same time i educing the quantity of ore Suppose such an ore contained all its gold in nuggets no smaller than inch in diameter and theie was an average of five such nuggets in a ton of ore When the quantity of sample was reduced to 20 pounds, a single nugget in the sample would make the latter too rich , and it this 20 pounds contained no nugget, it would be too poor The only way to find the value of such an ore is to extract the gold from a 10- or 20-ton sample

50. In using the accompanying table, it is not necessary to pass successively through all the sizes shown m any one of the columns, but before taking any of the quantities given in the weight column, the ore must be reduced to the corresponding size shown jn one of the other columns.

Sampling Ores

§ 2.9

Weights To I5E Taken In Sasipltng Oke

Diameters of Largest Particles

AVeight.

Pounds

Very Low- Grade or Very ITniform Ores.

Low-

Grade

or

Uni-

form

Ores.

Medium Ores

Rich

or

"Spotted "

Ores.

Very Rich or

Excess-

ively

" Spotted" Ores.

Milli-

Alilli-

Milli-

meters

meters*

meters'*

20,000.000

'70.30

10,000.000

5,000.000

O

o

2,000.000

(jo. 60

1,000.000

2o.40

32.80 '

200,000

3,60

50. 000 :

! .27

5,000;

,57

.200:

,66

*2S.4 mm. (millimeters) 1 incli.

SAirPLING ORES

51. The following figures, based on piactical work, show Vihiit aie ronsideied pioper sizes and quantities foi ceitani kinds of oie, but they aie not to be taken as a iiniveisal guide In some cases smallei quantities may be sufficient, and in othei cases laigei quantities will be needed

53. vSizes of lumps and their conespondmg quantities for iron oies and othei low'-giade mateiial

With lO-inch lumps, take 10 tons fur a sample With (j-inch lumps, take a tons for a sample With o-mch lumps, take 1 ton for a sample With l-iiich lumps, take 00 pounds for a sample With --meh lumps, take 10 pounds foi a sample With jV-mch* lumps, take i to 1 pound for a sample. With -giy-mch'f lumps, take 1 to G ounces for a sample,

53. Sizes of lumps and their coi responding quantities for copper oi lead sulphide oies of a value not exceeding J50 or )7o cl ton (including silver and gold)

With G-incli lumps, take 15 to ZO tons for a sample With 3--inch lumps, take 4 to 5 tons for a sample With 1-inch lumps, take 1,000 to 1,500 pounds foi a sample With -inch lumps, take 200 to 400 pounds for a sample With --inch lumps, take 2 to 4 pounds for a sample With ;>-J-'iach§ lumps, take 4 to 6 ounces for a sample

SAMPIIKa MILLS

54. The arrangement of a complete mill depends on the opinions of the designer and on the character of the ore vSome manages prefer all hand sampling; but in most cases mechanical sampling is bettei, at least for part of the work, unless the ore comes in very

Through 16-meah screen t Through 80-mesh screen i Through 12-inesh screen § Through lOO-mesh screen

vSAMPLINCt ores

small lots The two methods aie ccanpaied la Ait 39. When the bulk ol the oie is to be Ictt eoaise foi smeltmj, the first sample is taken by fictional selection and crushed and the father sampling is done either by hand or by machine When all the oie is to be ciiished line foi treatment by vSome leaching pioeess oi when lead ores aie to be masted, mechanical sampling is most convenient, except foi the final steps m which the quantity is small

AJSLVIjIKG MIEE for a OOET) jmente

55. Gencriil Description — In Fig 22, is a plan, a side elevation, b) an end elevation of a sampling mill used by a gold- company The oie comes to the mill 111 cars and is dumped into oie bins shown m views and (I?) There aie several of these oie bins, so that each lot of ore can be kept separate The oie is drawn from the bins thiough gates b into ore bariows and is then wheeled to the platform scales r to be weighed If a moisture sample IS needed, a shovelful of ore may be taken from every fifth barrow after weighing The ore is then dumped into the coats-iock bteakei and is raised fioni the boot c by No, 1 elevator / to the revolving compartment screen The ore that sifts tin o ugh the fine scieen passes directly to No 1 sampler where a sample is taken and the discard carried by No 2 elevator A directly to the storage bins 2

56. Sizing the Ore £ina Talcing* the Fii*s,t SamiRe. The revolving scieen gives three pmducts the fine, which has just been disposed of, the intei mediate, and the coarse The oic that sifts thioiigh the intermediate screen passes to crushing rolls j, 30 inches m diametei, and then to No. 1 sampler where a sample is taken The discard is taken to No elevator A and by it to the storage bins ? The third, or coarse, product of the screen passes through a rock Cl usher termed the " fine crushed The ore is

Sampling Ores

taken from this crusher by a sciaper line to the boot of elevator No 1, IS raised by the elevator, sifted m the levolvuig scieen, and the product disposed of as described foi due and intermediate ore

67. The object of using the screen instead of passing all ore directly through the thiee ci ushers in succession is to leinove the fine ore from the coaise as soon as possible and thus prevent its being reduced to dust There are some cases where so much crushing as is dcsciibed above would not answer, for the reason that theie would be too much very fine ore for the subsequent operations Coarse sampling is, theicfore, used foi the product passing through the screen to the fine-rock ci usher mentioned

58. Kecliicllon of the Tirst Sample. — The ore that IS being sampled 'passes through the screen and the No 1 sample , where a rather large sample is taken This sample lb raised by No 3 elevator I to sample lolls ///, and passed from them to No % sampler ;z, where a sample is taken and the lemainder of the oie discarded The sample is next earned to an intermediate bin /, which is aiianged between No 2 and No 3 samplers in oixlei to give No 3 sampler a continuous feed No ciushmg is done between No 2 and No 3 samplers, but it is safer to take, say, a 20-pei-cent sample and then to take 20 per cent, of this, which makes 4 per cent of the oiigmal sample, than to take 4 per cent by a single operation In doing this, howevei, the intermediate bin is necessary, otherwise the sample from the No 2 sampling machine might all pass to the sample side or to the discard side of the No 3 sampling machmc The plant is so arranged that all discarded oie can be delivered from No 2 elevator h to anyone of the six storage bins t The final machine sample is earned by cai to the sample loom /, wlieie it is cut down by quaitenng oi fi actional sampling on the iron-covered floor q. A sample grinder r is provided so that the ore may be pulverized to reach the final sampling for the assayers

§39

Sampling Ores

59. Diagram of tlie Course of the Ore.— Fig- 33 illustrates the pi ogress ot the ore through the sampling mill into the sample bin From the sample bin it is taken to the sample room for further reduction by hand

60. Drying the Sample. — Borne form of drying table should be provided to diy the samples, foi, as stated in Art 38, the oie should contain no moisture when assayed

61. Kooin.

The door to the sampling room should have a lock, so that only the head sampler can enter Avheu the final samples of purchased ore are being prepared The room should he well lighted, and the windows should be so placed that interested peisons can watch the work from the outside

fig 23

THE TAXTOR-DTHESTTOT SAIMPEDSTG MIIjJj

63. General — In Fig 31 is shown a section of the Tayloi and Brunton sampling system, Avhicli is about as accurate and complete as any piesent automatic sampling mill, although some prefer the Vczin sampler In the figure, a broad-gauge box car is shown in a shed The ore IS shoveled out of this car into a steel hopper a The gate /; of the hopper is an anged with a notched lever, so that it can be opened to suit the size of the ore passing on to the shaking grizzly c. The grizzly is not placed at a steep angle, because it is desired to feed the crusher d slowly and it IS further deauable to riddle the ore and not crowd the

Sampling Ores

crushed with oie that is tine enough The ore that passes through the gnzzly falls into a steel hopper where it meets the ore that passes thiough the X ci usher d The 01 e slides down the steel chute and hoper into the elevator boot /, f 10111 which place it is raised by the elevator buckets to the top of the sampling null The elevator buckets discharge into a complete bucket dischaige at which, however IS not shown m the figure

63. TaMug tlie Sample- — From the complete discharge, the 01 e passes down a chute, wheie it meets the No ] sample /, which takes out 20 per cent of the ore, the leinaining 80 per cent is discarded Thiough the chute y into the ore bin Fiom the sampler the 20-pei-cent* baniple passes throtigh a set of 10' X 30' clashing rolls / to the No 2 sampler ///, which takes a -t-per-cent sample of the original oie and discards IG pei cent , in other woicls, 20 per cent of the No 1 sample IS retained and 80 per cent discarded

The No 2 sample now passes through 14'' x lolls ?i and then thiough No 3 sampler where .8 pei cent of the original oie is taken and 3 2 per cent discarded; that is, 20 per cent of No 2 sample isietaiued and 80 per cent dis- Cdidecl

The No 3 sample next falls to a rotating steam diner /, fiom which It IS fed by the feeder to a pair ot 12'' X 20" crushing rolls r From the cuishing rolls the oic passes to the No 4 sampler i-, which retains JO per cent and discaids 04 per cent of the original ore, i e , 20 per cent- of No- 3 sample is retained and SO per cent discarded

The No 4z sample passes to the sample safe fiom which It m removed and sampled by hand, so as to still furthei reduce the size of the sample.

64, Size ot Final Meelianieal Sample — If the cat contained 20,000 pounds of oie, the size of the mechanically obtained sample would be 32 pounds, which can be further reduced by hand Thus it is demonstrated that mechanical ore sampling is not entirely mechanical, but depends for its final stages on hand sampling. The

vAMPLING ORES

§ 29

sampled ore has now i cached the ore bin and is drawn off thionh the gate u and chute v into the car which removes it to mill oi furnace, as the case may be If 1 ton only were sampled, the fiist sample would be 400 pounds, the second 80 pounds, the thud 16 pounds, and the tourth 3 pounds from 1 ton In this case the ore could be finally divided by the Biidgman apparatus

65* of Helglit in a Mill. — It will be noted that the Tayloi and Bi unton sampliiij mill is highei than that shown in Fi This permits the oie to be

raised high enough to descend by gravity from one machine to anothei , thus economizing m power, as the second and thud elevators of Fig S3 aic not lequired In this plant, little bill capacity is needed, but by using a sciaper line undei the spout as the oie comes from the discard a scries of bins can be filled

66* Use of tlie Drier. — The drier is used only foi ores that aie quite moist, such ores foiinmg lumps when ground fine vSoft damp oies when passing thiough lolls simply flatten out m sheets, thus making it necessary to dry such oies befoie attempting to sample them by hand or machinery

Roasting And Calcining Ores

1 . Oro I'oastiiig' is the process by which certain chemleal chanjeb are pi'ocluced by the aid of heat, but at a tempeiatuie so comparatively low that the ore does not fuse It IS one of the most important operations in metalluigy, because the quality of the product from this process controls the lesulLs in the vaiioiis processes that follow

2, The most common example is the oxidizing roasts by means of which sulphides aie converted into oxides by the oxygen of the air, the sulphur passing oft principally as sulphm dioxide SO Arsenic and antimony aie also oxidized, the object being to form as much arsenic trioxide A or antimony trioxide as possible, because these compounds pass off by volatilization Other compounds of sulphur, arsenic, and antimony which are not volatile are also produced by roasting, these, however, can geneially be changed to a condition m which they can be volatilized by the reducing* x'oafet, which consists in the admixture of fine coal to take away oxygen, atmospheric oxygen being excluded during this operation When the sulphur, arsenic, and antimony have practically all been removed by a series of alternate oxidations and i deductions, the ore is said to be dead-i-wasted or sweet-roasted. For the siiljiliatizing: I'oast the operation is conducted at an especially low

§ 30

For notice of copyrig-ht, see page immediately following the title page,

ROASTING AND CALCINING OREvS § 30

temperature with a small supply of an and with the ore bed somewhat deeper than usual, by tins means consideiahle sulphur IS converted into sulphur tiioxide which com-

bines with the metals to foim sulphates

S. In the eliloi'idiziu roast, certain metals, especially silver, are changed to chlorides by mixing then oies with common salt NaCl aflei piacUcally all the sulphur, arsenic, antimony, etc have been expelled

Purposes Op Roasting

4. The object of loastmg the sulphides of lead and zinc IS to convert them into oxides, which aie aftcrwatds reduced to metal in smelting furnaces In the case of copper sulphide, the pin pose geneially is to bum oft the excess of sulphur, leaving enough so that when smelted it will combine Avith all the coppei to toim an iitificial sulphide called matte, which always contains iron Copper-sulphide ores with 4 per cent or less of copper aie often loasled to sulphates, or sometimes to chlorides, the copper being subsequently dissolved by some liquid

5. Silver ores aie often chloiidized so as to prepare them for amalgamation Gold oies that aie to be tieatecl by the chlorination process generally contain sulphides or arsenides, and as these minerals are detiimentaltochloiination, such ores are dead-roasted If oxides of copper, calcium, oi magnesium remain after this roasting, common salt is added to the ore towards the end of the last to convict them mto chlorides; otherwise they will absorb chlorine gas d ruing the process of chlorination It often happens that with finely pulverized oies and shines which are to be treated by the cyanide process, the solutions will not easily pass through the ore Again, some ores, foi instance tellurides, are so compact that the solutions cannot entei and attack the gold In such cases roasting will often remedy the trouble by producing physical changes in the ore

§ 30 ROAvSTING AND CALCINING OREvS 3

6. Iron ores aie sometimes roasted to remove caibort dioxide CO and water and also to remove sulphur Zinc carbonate is also roasted to remove caibon dioxide This kind of roasting is termed eal Lump ores are sometimes heated in order to eliminate moistuie and allow them to crush more readily The heat in drying sometimes expands the rock and produces small cracks Ores that are to be crushed fine and screened generally have the moisture driven from them by heat to render them more friable

7. Roasting is usually preliminary to some metallurgical process, but in some cases it is preliminary to mechanical concentrating Mixtures of blende and pyiite are roasted for the purpose of concentiation by magnetic concentrators

Experiments have been made with hematite and hinonite iron to convert the feme oxide into magnetic

oxide but they have not pi oved commercially success-

ful On the othei hand, magnetic non oie containing sulphur has been successfully converted into hematite by roasting to eliminate the sulphiii

METHODS OE ROASTma

8. The methods adapted fot ioastmg fine ore are not suitable for coarse ore, and the methods used for coai se ore are still less suitable for fine Fine ores are generally treated in beds only a few inches deep, which aie turned over and over to expose all parts to the an With coaise ores this would be troublesome in various ways, they ate, therefoie, roasted in masses fioin 0 to 80 feet deep, the necessary air passing ujd thiough the mass between the lumps Fine ore cannot be treated in this way, because it would pack so solidly that the air could not pass through it A diametei of inch is piobably the limit oi boundary line between coarse and fine ore for lasting purposes, and in most cases the largest pai tides in a lot of fine ore are much

§ 30 ROASTma AND CALCINING ORES 5

smaller Since in roasting one must deal with fine ore more often than with lump, the furnaces for the former will be described hist and the methods for roasting lump oie aftei wards

Boabtjn'G Finis Ore

Eiirnaces for fine oie maybe classified as haiid-rabhlcd reverber atones incchamcally rabbled r tverberatortes retwlving cyhndcrs and shaft fmnaccs

IIATO-R-iUBBLED FITIINACES

10, A liand-rahhlecl ievei'heratory fuimace is shown in Fig 1 In this figure, {a) is a hoiizontal section, (b) a vertical section through the line and (e) a vertical section through the line S-4 The fiiinace consists of a long hearth a (on which the oie is spread from S to 6 inches deep) with a fire-grate b at one end and a flue c at the other, leading to the chimney d The fireplace and hearth are covered by the arched roof e, shown m Pig I (d:) This atch is made as flat as is possible without danger of collapse, so that the flame and heat will spread to the sides of the furnace The top of arch c is commonly covered with sand / to prevent loss of heat by radiation

11 , The ore is dumped from the hopper, Fig 1 (b), on to the health dx, and is occasionally rabbled, or stirred, to expose fresh ore to the heated air and to pi event caking The ore is gradually moved by a paddle towards the fire end, where it is discharged through the openings h into cars The openings are closed when oie is not being discharged through them In order to expose as much surface as possible to the oxidizing action of the air, the workmen make furrows m the ore instead of leaving the suiface flat The labbles and paddles for working the ore are inserted through doors t on both sides of the furnace The bottoms of these doors are level with the hearth

N M Iii —2

roasting and calcining ores

The rabble lor b tin mg the ore ib shaped like a hoe, the

blade being about 4 niches by 9 inches The paddle for pushing the ore fon wards is bunilar but largei As these tools are long and heavy, an iron bar is placed across each doorway, a few inches higher than the lieai th, to serve as a rest oi £ulcmm on which to swing the tools from one position to anothei Rollers arc also used, but they are apt to get out of shape and not roll

ISJ. In Older to exclude cold an, the working doois are kept closed when the men are not labbling the 01 e or moving it forwards All the air for loasling should be heated Sometimes the whole air supply comes th: ough the

Roasting And Calcining Ores

fire, but for an oxidizing last, it is better to obtain a special supply of flesh an thiough openings jii the fiie-biidge j For the latter purpose, the bridge is made hollow horn end to end, and the an becoming heated while passing through this hollow space, enters the fiunace below the dames from the fire through several openings on the side towards the health

13 . For aieduciiig last, this fiesh air supply must not be used Indeed, the bed of fuel on the grate should foi the reducing roast be so deep that no flee oxygen will pass thiough It into the furnace On the coutiaiy, the gases fiom the fire should be incompletely oxidized, in ordi to assist in the reduction ot the oi e

14 . Lead oies aie often partially fused aftei roasting, so that they will be m better mechanical condition for smelting m the blast furnace Fine oie makes the blast furnace work irregularly and creates losses Foi the put pose ot fusing, modifications to the furnace shown m Fig t aie made The roasted ore is dropped about 2 feet from the roasting hearth Fig 2, to the slagging lieartli b (This name IS given to the health b because the oie is daggtd oi well fused on this health ) It will he noticed that the roasting hearth Is considerably wider than the slagging hearth By making it this way, the gases from the firebox which are hot enough to fuse the ore in expand when they enter a and are thus cooled to a suitable temperature for i casting When the ore is pi operly fused on the health it is drawn out through the side doors d into slag pots, cooled, and broken up

15 . The slagging volatilizes a consideiable portion of the lead, so that it cannot be recovered; therefore, this fiunace should be used only for low-giade ores For iich ores, the health Fig 3, is made wide, so that the heat from the file IS sufficient only to sinter or slightly fuse the ore, in this case b is called the sinter lieai'tlx. At some woiks for treating ores that are easily fused, the hearth b is omitted and the ore sintered at the fii'e end of the health a In these cases a depression is made in the hearth near the fiie-bridge,

:U) Roasting And Calcining Ores 9

ita which the sintered ore is collected When enough sintered 01 e has collected heie, it is scraped through the side doors into iron pots or barrows and is pounded m order to solidify It When cold, it is broken up If the sintering is done on the same health as the roasting, theie is no distinct line between the otc that is i ousting and the ore that is sintering, consequently, some of the galena may not be roasted before it becomes sintered, and in the latter condition roasting is very impel fectly done, if at all

16, Unless the ore contains a good deal of silica, some highly silicious ore IS spread on the slagging hearth before drawing the charge on to it fiom the preceding hearth This IS to pi event the corrosion of the hearth by the hot ore Some of this sihcious ore is also thrown on top of the charge on the slagging hearth if necessary and is well stirred m When this has been done, the file is made hot for several hours and the oie thoroughly rabbled at stated intervals

17* When a furnace is heated the brickwork expands, and therefore it must be bound with iron in order to prevent Its becoming distorted and falling to pieces One method of tying the walls of a furnace is shown in Fig 2, which is a perspective view of a hand-rabbled leveiberatoiy with a slagging hearth Steel rails or I beams termed states, are placed m veitical positions at intervals along the sides and ends of the furnace, their upper ends extending a few inches above the top of the furnace These buckstaves are held togethei by iron tie-iods o, shown across the top and through the foundation neai the bottom of the furnace The tie-rods aie loosened a little when the brickwork expands, to prevent their breaking, and are again tightened when the brickwork contracts on cooling

18. The sie of a furnace depends on the ore to be roasted therein For an ore containing much pyrite, the length of the hearth is commonly about 05 feet, but for an ore rich in galena or blende it does not generally exceed 40 feet The reason for this difference is that pynie generates so much heat m roasting that it is less dependent on

10 ROAvSTTNCt and calcining ores § ;]0

the heal from the giate fuc than are the othei miiieials The width of the health is usually about L5 feet It is difficult for the men to woik the ore if the width is much greatei than this Foi i casting zinc mes, it is quite common to have woiking doois on only one side of the furnace, m order to admit as little cold air as possible The width of the hearth is m that case i educed to 7 oi 8 feet, since a greater width would be inconvenient ioi the workmen

19. When ores are to be dead-roasted, more satisfactory results can be obtained with a hand-iabbled reverberatory than with any of the mechanical furnaces, because the ore is moie tmder control. In most mechanical furnaces the ore IS labeled with the same frequency at all stages of the operation, but with a hand furnace this can be varied to suit the condition of the ore at diflreient times Fig 3 shows apian, an elevation, longitudinal cross-section, also a cross-section through the line a fiont elevation, £ind a crosssection through the line 3-Jf.

20. If galena that is i casting on the surface is stored into the ore bed before it is properly oxidized, it is apt to form lumps, and these do not toast well Therefoie, rabbling should not be done too often during the first part of the roast , but lowaids the end of the roast it should he clone more frequently, in order to expose all paits of the charge to the heat from the grate fire As both galena and the oxide that lesults from roasting galena are quite readily fusible, an oie that contains any considerable percentage of this mineral is apt to cake and stick to the hearth It requires special care to prevent or connect this in mechanically labeled furnaces, but it is much more easily prevented in hand-rabbled furnaces For these reasons most metal- Im gists prefer the long-hearth, hand-rabbled furnace i oi lead ores Mechanical furnaces are, howevei, used in some cases

The fuel used for roasting should be one that burns with a long flame With a long flame extending some distance into the roasting hearth, the heat is generated in the hearth,

Roastinc And Cadcintng Ores

here it i'=i wanted With haid eoal, which bums without ly flame, the heat is all generated on the flic-grate Ithough the products of combustion such a file pass irough the hearth and heat it, the heating is not so well one as when the fuel gas burns in the hearth itself

MECIIArOAXiLY KABJlXiEl) HTVJRBlilKAXOTtY iUIlNACBS 31. In Fig 4 {a) is shown a hoiizontal section ot a mechanically rabbled reverberatoi y furnace known as the .ojip stifaig'Ut-liiie ruiniace. It has a long hearth a Lvided by a nanow slot d that extends tiom end to end elow the health of this furnace is a pitr, which is shown m ction in Fig 4 In this pit is a narrow track d, upon Inch several carnage are moved by a steel lope /, to which ley are attached Piom each carnage, a strong steel plate tend upwaids through the slot d foi the piupose of cai- /'ing the rabbles /i, which work the ote The rakes A reach le ASidth of the hearth and have their blades pitched at an iigle, so that when the rake is moved along, the oie is not tily pushed forwards, but is slirtcd and turned to one side, closing new surfaces The blades on one rake arc set in xe opposite diiection from those on the preceding rake, uts the ore is scraped first to one side and then back rake has the blades on one side of the health set m le opposite direction fiom those on the other side, in older ) balance the rake, 'if all the blades were set alike, the isistance of the ore to the inclined blades would force the ike and its carnage to one side instead of allowing it to run ue on the track

33. The steel lope to which the carnage are attached asses around large horizontal sheave wheels z and one eing placed at each end of the furnace The powei to love the rope and rakes is delivered to the sheave t' by evel gears, moved by the horizontal shaft j When the ikes come out of the furnace, they raise the two iron oors k and which are hinged at then upper edges die door k closes befoie opens, so that no cold air

Roasting And Calcining Ores

can enter the furnace The carnage and rake then pass round the sheave t and leturn to the other end of the furnace in the open an, on that pait of the track that is built outside oi the fuinace This gives the rakes plenty of time to cool and is an effective method of causing them to wear longer and lessening the expense for repairs On entering the furnace again, the rakes raise the doors I and V

33. The ore is fed into the furnace by two automatic feeders m , heal is supplied from one or more fireplaces n and the fumes made m roasting pass off through the fine o The discharge end of tins furnace is shown in elevation at Fig 4 (f) The rake pushes the oie under the doois k to aprons p, from which it slides into cars q This furnace is made in different sizes, varying from 100 to ISO feet long and from 11 to 16 feel wide It is used with good lesults for copper sulphide ores, for mattes (artificial sulphides produced in smelting) containing coppei and lead, and for dead -1 oasling either pyrite or blende

34* Brown's liorseslioe " furnace is built in the form of a ring, as vshowii m Fig 5 {a) The hearth occupies about five-sixths of the circumference, while the lemainmg sixth is an open platform extending from a to The rabble arm c is earned by trucks running m the side passages d, shown in the cross-section m winch is a seciion through the line The rabbles are opeiatedbya steel I'ope r,

winch IS guided by the pulleys /set in that passage / which IS towards the center of the ring The rope is driven by a suitable mechanism at £ Ore is discharged on the open platform by the automatic feeder at h and is moved into the furnace m the dii ection oi the arrow by the rabbles A door at i IS automatically opened for the entrance of the rabbles , there is also a similar door at wlieie the rabbles leave the furnace and the ore discharged into buggies, which are not shown. Heat is supplied from the three fireplaces y, while the gases pass off by the stack k

u

AND CALCININrx ORES

§30

25, When one of the rabble arms comes out of the furnace on to the open platform, it is automatically detached from the driving rope, at the same time another carriage, which has been standing on the platform, is automatically

Fig 6

attached to the lope. This gives the rabbles a chance to cool off, and they last much longer than they would without the cooling The fmnace is successfully used for pyritic ores, for copper matte (siilphatizmg roast), and for dead- roasting zinc blende

Roasting And Catxintng Ores

36, The \Tetliey heart li tiiriiaeo is made

either single or double Fig 0 shows a cioss-section ot the double torm, that is, two furnaces m one structuie The bottom healths are supported either on solid foundations or on brick riches a The othei hearths /i? are suppoitcd by means of strong cross-beams t of steel, which carry smaller beams d lunnmg longitudinally The brick hearths b are built on thick steel plates, which aie laid on the beams each health being 5 feet wide and ,50 feet long The rabble arms c aie earned by trucks which are drawn by chains ]i that pass over sheaves outside the furnace in a manner similar to that shown in Fig 7 The rabbles l pass through and out of the top health, over the sheaves, then through and out of the second hearth, ovei a second vset of sheaves at the other end, and back into the top hearth The two lower hearths are operated in the same way

Each rabble arm extends fiom the truck through a slut j running the whole length of the furnace This leaves one side of the aiched loof without any support from below, but it IS supported by a longitudinal I beam k hung on brackets / To prevent laige quantities of cold air lushing in through the slots just mentioned, they are closed by a senes of ovei lapping sheet-steel plates pivoted above, but not shown in the section given Each rabble momentauly lifts one of these plates, which, when the rabble has passed, swings into place again The hearths aie closed at the ends by doors (which are not shown) that aie hinged at then tops and which aie automatically raised and lowered when a rabble enters or leaves a hearth The ore is fed to the upper hearth by an automatic feeder (which is not shown) and IS gradually moved to the opposite end, where it drops through a slot to the second hearth In the same way it traverses the other healths and is finally discharged through the hopper in

For pyritic ores, each single furnace has a fireplace n leading into the upper hearth near the feed end The hot gases rapidly dry the ore and soon beat it to a temperature at

iS ROASTING AND CALCINING ORES § 30

which It begins to bum. The gases pass ofi. to the flue o at the other end of this hearth The combustion of the sulphur tiu'ashes enough heat to continue the roasting on the other healths without any other fireplace Eor ores that do not contain so much sulphur as pyiite, a fireplace is used for the bottom hearth also, especially if the ores are to be deadloasLed

27* Fig 7 {a) and iU) shows a modification of the Wethey furnace designed by Holt ho ff for the chloiidizing roast of Sliver ores oi for dead-i casting gold ores The piincipal feature to be noticed is the cooling health beneath the roasting hearth To msuie thorough cooling, pipes are laid in the health and cold water passed through them Sometimes, m place of a buck cooling health contaiiung water pipes, a special hearth made of coiiugaLcd non plates, supported on I beams, is used By this aiiangement effective radiation is obtained from the top and bottom of the health In common with the single foun of the oulinaiy Wethey furnace, the rabble ai ins extend thiough both sidewalls, as shown m section in Fig 7 (/;), each end being supported by a truck c There are two fireplaces and the gases pass off through the flue c The hoppeis f feed the ore automatically to the furnace, power being transmitted to them by sprocket wheels g and chains h

28. The McDougi'all iiiruaee, shown m section in Fig 8, IS designed to roast pynte FeS without using any heat except what is produced by the roasting ore itself Pynte generates more heat in i*wasting than any other mineral, indeed, it is the only mineral that can be lasted without the use of heat fiom some outside source To be selt-i casting, the ore should contain at least 50 or GO per cent of pynte Gangue minerals absorb heat, but do not contubute any This furnace is so const! acted that a huge part of the heat genet ated by the oxidation of the oie is absoibed by the brickwork and is given out again to the ore, to continue the oxidation after the sulphur in the ore has

§ 30 ROAvSTJNG AND CALC

been so nearly consumed that it ca necessary heat

Hi

iB

The furnace consists of a number of circular healths 2;, one above anothei, Avith a veitical 1 evolving shaft h extending throtigh the center The healths are made level by

ao ROASTIHG AND CALCINING ORES § 30

lettmg: the fine ore c fill up on top of the brick riches a The diametet of such f menaces varies fiom 1) to 18 feet For each hearth there aie two rabble arms fastened to the shaft chametncally opposite each other

39. To stait the furnace, a wood fire is made on the hearths and kept burning until the bnckwoik is well heated No more Avood is used after that, but ore is then automatically fed from the hoppers on to the upper hearth, where the rabbles gradually move it towards the circumference and drop it through holes f to the next health Ileie the rabble blades are set so as to move the oie towaids the center, where it drops through a hole g to the third hearth The movement continues thus alternately to the circtimfeience and to tdie center until the ore is finally discharged through the chutes ]i The necessary air enters through the openings % in the bide walls. The gases move in the opposite direction to the ore and are finally discharged from the upper hearth into the stack k

SO, It will be observed that the rabble arms are constantly exposed to the heat This made a great deal of repairing necessary m the original styles of this furnace, but m the more recent forms this trouble is overcome by circulating water through the arms and the vertical shaft, which are made of heavy tubes with small tubes inside Water flows in through the inner tube and out again between the inner and outer tubes The water is supplied fiom the pipe I and discharged through in This improved form of McDougall furnace has displaced the Bruckner in certain large works for roasting pyntic copper ores The capacity is two or three times as great as the Bruckner roaster and the moving tabbies give it a still further advantage by preventing the ore balling

31. Blalre's revolviiig-licartl:! fiinuace is shown in Fig y {a) and {h) It consists of a cncular, i evolving, firebrick hearth a about 16 feet in diametei, made m step

§ 30 ROASTIlSia AND CALCINING ORES 21

foim and resting on cast-iron balls b ananged m a circular ttaclc c These balls serve as an anti-fi ictiun beaiing on which the hearth i evolves The oi e is fed from the hopper

through the center of the roof on to the upper step of the hearth, and as the lattei revolves the ore meets one of the plows c, set at an angle of 4:5°, which scrapes it to the next

step The ore is thus gradually moved to the lowest step and discharged into the spout f The drop from one step to anothei is 6 inches or more , and the purpose of this drop is to make the ore fall m a shower This gives it a more thorough exposure to the oxidizing action of the hot air than it would have if the hearth was one continuous surface. The

M Iii —H

Roasting And Calcining Ores

oie IS heated fiom a fiiebox on one side and a supply of heated fiesh air enters through a nnmbei of holes (which aic not shown) arranged aiound half the cn cumfei ence The waste gases escape into the dust chamber h This furnace was especially designed to last a mixture of maicasite AhNj, blendCj and galena, so as to oxidize the first without changing the other two, and has given good lesults To do this, care must be ® used not to let the teni- 2 perature get too high Above a certain tempeiature the blende and galena will oxidize The purpose of this I'wasting IS stated in Ait

nosYonviNa boasting CYTaNOEKS

32. The Ilowell- WMte fuiniaee, shown m Fig 10, IS a long,

The good reailts weie not due to the special foim of the turnace, but to the fact that it was aiianged so as to permit accurate control of the draft and tempeiature,

§ 30 Roasting And Calcining Ores 23

slightly inclined, hollow cyhndei a, supported by and lolling on seveial huge rollers b On each side of the cyhndei are two guide rollers c The fuinace is made of cast-iron sections bolted together The lowei end wheie the hot gases enter from the firebox is lined with fitebiich, but the upper part f is not lined The shell of the lower part is just enough larger than the upper part so that, when lined, the mteinal diametei of the two pai ts is the same Oie fed into the cylmdei at the nppei end trom the lioppei IS gi actually woiked to the lowei end by the i evolution of the cylinder and the slight inclination that is given it and falls into the chamber Ji The f ui nace is fi om 20 to 30 feet long and trom 2 j to 5 feet in diameter On the inside there aie projecting ledges that raise the oie and allow it to fall in a shower through the hot gases This makes the i casting raox'c effective because it exposes a gieatei ore suiface Any dust that is carried out of the uppei end of the furnace by the diaft has a chance to settle in the dust chamber i This furnace is applied pimcipally to the chlondizmg last of silver 01 es, but similar furnaces aie in some cases used foi the oxidizing roast of copper oies and matte

33, The Bruckner roasting cylinder is shown in Fig 11 Unlike the other mechanical roasting furnaces that are described, this one is not fed and discharged continuously It IS a hollow cylinder a made of heavy iron plates and lined with bricks It is sometimes as large as 8- feet m diameter and 28 feet long, but by 18 is a moie common size Each end is slightly conical and has an opening in the center to admit the hot gases from the firebox b and to dischaige them into the flue t The cylinder is siiiroundecl by two heavy bands d that rest on friction rollers c These rollers are driven, by gearing not shown m the figuie, from the pulley /, thus giving the furnace a slow revolution

The openings being closed and the furnace not i evolving, ore IS fed from the lioppeis ]i into the openings, the covers of which are then fastenech

§30

Roasting And Calcining Ores

34. The furnace is noAV revolved and the oie is earned up a ceitain distance on the inside peiimetei of the cyhndei until it foiras a sloping sinface, and then the grams tumble down the slope so that fi esh ore is constantly exposed When the roast is finished the ore is discharged into the bin t The Brticknei cyhndei has been extensively used to roast pyiitic Goppei ores It has also been used with special precautions foi certain lead oies It is not generally successful for lead ores, however, because it is difficult to prevent the ore becoming pasty and forming balls The ore inside such balls escapes roasting The furnace has been used m a few cases to chloiidize silver ores

SnA3?T PUrnSTACE

35. The Stelefeldt roaster is a sliaft furnace from 25 to 50 feet high, used foi the chloncUzing roast of silvei ores Hot gases from the fiieplaces a of the Stetefeldt roaster shown in Fig 12, mixed with air from the passages b and 4, enter the shaft through c Pulverized ore, mixed with the proper percentage of common salt, is fed into the stack by the automatic feeder f and falls in a shower tlnougli these hot gases into the hoppei g The finest pait of the 01 c IS earned over by the diaft thiough h into the settling chamber i and is largely caught in the hoppers j To assist the chlorination of this material, an extra fireplace k is provided When cleaning is necessary, tools can be inserted through the openings /, and n Although the ore remains in the roasting atmosphere only a short time, the operation is successful because each small particle IS separated from all the others and is, therefore, thoroughly exposed to the hot gases

This furnace gives excellent results in cliloridizing silver ores, and has a much largei capacity than any other furnace for this purpose It has never been used for the oxidizing roast of highly sulphuieted ores, and piobably would not do good woik with them, because tlieie is not long enough exposure to the heat and an to sufficiently oxidize the sulphur

ROASTING AND CALCINING ORES § 30 ROASTING XrUlVtP ORES

36, Lump ores are usually roasted in heaps, stalls, or shaft fill naces If the ores arc high m sulphur and liable

is

to fuse, heap oi stall roasting is to be preferred; on the other hand, if the ore is an iron sulphide low in sulphur or

§30

Roasting And Calcining Ores

an iron or zinc caiboiiuile oie, the shatt furnace is piefeiable Many kiliih have been invented foi roasting, pyntic lump oie Very few of them, hfnvevei, have pioditced as satisfactory a product at as low a cost as heaps or stalls

37. Heap x'oastiiig lequires veiy little outlay for appalatus, but It IS expensive for laboi, requires careful supeiiiitendence, and takes a long time If propei care is taken, however, the lesults are excellent with suitable ores The most suitable oies are such as contain a large percentage of pyritCj because the oxidation ot the sulphur in the lattei fuimshes all the heat necessary after the roasting I's well staitcd, Pyirliotite and chalcopynte CnFeS also are soinetimeh loastecl in heaps As a matter ot fact, heap roasting is mostly confined to pyntic copper ores Lead ores are too apt to fuse Zinc oies lequiie too much fuel

38. Hcapg for loastmg are built on open ground, but this should be carefully piepaied The surface earth is removed and a foundation of broken stone or slag (the waste material from the smelting furnaces) is put in This is covered with gravel oi loam and is well rolled until the whole smface is solid and smooth On this is spread a thick layer of low-giade fine ore, the purpose of which is to prevent dirt being shoveled up with the bottom layer of ore aftei the 1 wasting is finished The surface should be made to slope slightly from what is to be the cential longitudinal line of the heap to the sides, in order to shed water in case of rain With the ground thus made leady, the area to be occupied by the heap is marked off This should not be more than or 26 feet wide, and a convenient length is 40 to 50 feet, though very much longer heaps are sometimes made Cord Av-ood in 4-foot lengths is placed all around the sides with the sticks pointing toivai'ds the middle of the area Inside of this border, the space is filled with wood laid parallel to the

§ 30 Roasting And Calcining Ores

long side of Uie area, as shown in Fig 13 In ordei to have the heap ignite satisfactonly when lighted, good, sound wood must be used on the outside , but fot the inside this is usually not important, waste ends, etc being considerably used there A second layei of wood is commonly laid on top of the first, with the sticks at right angles to those in the fiist layer, and still other laycis are put on if nccessaiy Small brushwood or sawmill slabs should be used for the top to fill up the cracks and so pi event the oie (that is to be piled on later) from falling in among the wood The amount of wood used depends in each case on the pei centage of sulphur in the ore, but it should be as little as will satisfactonly ignite the heap, not only to save cost, but also because too much heat will fuse the oi e and so hinder the roast

39# Along the longitudinal axis of the area a space a 6 inches wide is left in the bottom layei of wood and is covered by the second Itiyev At intervals of about 8 feet, similai spaces aie left leading from this central space oi flue to both sides These flues arc filled with small sticks, which aie to serve for kindling, Wheie the branch flues unite with the longitudinal flue at r, vertical chimneys are erected They are made simply by nailing togethei foiu old boards and arc tall enough to come a little above the top of the completed heap,

40 . The size oi the oie is impoitant, but it mtist be decided for each case It should generally be broken so that there will be no lumps larger than 2 oi 3 inches in diameter Aftei breaking, it is to be screened into three sizes, because, if all sizes were mixed together the air would not pass through the heap properly. The sizes might be coarser than 1 inch, from 1 inch to inch, and flnei than inch The coarse oie is piled on the wood, forming a truncated pyramid 5 to G feet deep, as shown at in the section of a pile, Fig 14 On top of this the medium-size ore b IS placed a foot or moie deep It is common and most convenient to distribute the ore from tracks elevated above the heaps

30 Roasting And Calcining Ores § 30

41 , If theoie contains only a small amount ol pyiite, small wood or sott coal is mixed thioiigh the pile to fuinisli the necessary fuel to keep up the heat alter the bottom bed of wood has burned out Such an ore should be piled deeper than one that is higher in sulphur, but the total depth of ore is seldom more than 9 feet Coal or wood scattered througli the heap is useful also when the ore contains any consideiable quantity of arsenic or antimony In such a case, the coal i educes ai senates and antimonates, which aie not volatile, to a condition m which the arsenic and antimony can be volatilized (see Aits 59 and 60)

42* The ore should be so arranged that about a foot of the wood bed pi ejects on all sides of the heap The sides of the heap are now covered with a layer of fines r, >say 4- inch deep, except near the bottom; and the heap is then leady to be bred The reason that fine ore is not spread near the bottom nor on top of the heap at this stage is that the small ail spaces between the large lumps must he left open m order to get the file well started The central wooden chimneys d are also important for this purpose The fire is started at the outer end of each of the Hues mentioned

§ 30 Roasting And Calcining Ores

above, and atter a period of some horns the heat fiom the wood will be bufhcicnt to stait the me roastinj neai the edges of the heap Fine oic is then spiead on these paits e to check the diaft, so that the roasting wdl not proceed so rapidly as to fuse the ore As the roasting gradually extends to the middle of the heap, fine oie is spiead over the entile surface, as shown at Fig 14

43. Fumes are now given oft ftom all over the sin face For several days the heap has to be closely watched, and wherever the burning is too vigorous mure fines are added to check the draft Much experience and judgment aie needed at this period As the bed of wood bums away the heap settles, causing vent holes through which there will be strong dials, if they aie not covered with fine oie These strong drafts would cause such lapid lasting as to fuse the ore Any huge cracks that appear aiound the sides of the heap, particularly at the bottom, should be immediately filled with fine me The completion of the last usually takes % 01 3 months and sometimes longer The outside layei of fines is only paitially lasted, but if proper caie is taken, the coaise and inedumi oie is veiy thoroughly roasted

44, In places wheietheie is likely to be much i am, it may be best to have rough sheds built over the heap Ram water peicolating through the ore will dissolve the sulphate of copper that is foimed during the lasting of copper ores If the sheds aie not provided, caie should be taken to have all water drained away from the heaps and passed thioiigh tanks containing scrap non The copper dissolved by this water will be precipitated by the non This precaution has sometimes prevented laige losses, since a large part of the total coppei IS converted into sulphate in heap i casting

STATjTj koastctg

45. A stall is an area enclosed by walls m which ore is roasted in small heaps The advantages of stalls ovei open heaps are that they requite less time, fuel, and labor

Roasting And Calcining Ores

One of the bebt foiins of stall ib shown in Fig LI Each stall IS made with two bide walls a and a back wall the front and top being open, the bottom is paved Two lows of stalls aie built back to back with a large flue c between them to cany the fumes into a tall chimney d In pre~ paling for a roast, large lumps of ore aie piled on the bottom of the stall, so as to form a small flue extending centially from the open tiont to the back wall, and with branch flues leading to the middle ot each side wall

'-IG* Small wood is placed inside these flues and a layei of wood is placed between and on top of them The stall is then pretty well filled with ore ranging irom 2 or 3 inches down to about inch in diametei, and this is covered with a layei containing lumps fiom to 1 inch m diametei This ore IS now covered with small wood and shavings and on top of all IS spread a layer of fine ore It is well to place some sticks of wood along the walls as the stall is gradually filled fldie fiont of the stall is built up eithei with lumps of coarse oie or with bricks loosely piled up The top may oi may not be covered with a piece of sheet iron , some stalls are permanently covered by a buck arch The oie is most conveniently brought to the stalls m cars on the track c tunning above the large flue c between the two rows of stalls The cais are run out over any stall by means of a turntable and branch track, which are movable and can be placed whenever desired

The oie is fired by means of the wood m the bottom, as 111 heap loastmg The air for roasting enters paitly thiongh the small flues made with lump ore on the bottom of the stall, partly through the loose front wall, and paitly thiough the passages f and g in the side walls The waste gases pass thiough the openings h in the back wail into the flue i

47. Stalls must be built with thick, substantial walls or they will soon fall apait The reason foi this is that sulphide ores expand considerably in i casting and will foice an unsubstantial wall out of place The walls m Fig 15 are about feet thick, The loose, tempoiaiy front wall should

Roasting And Calcining Ores

be biased with timbeis With these precdiitioiis, the expan- Sinn ot the oie will take place upwaids

The walls of a stall shoLild be plasteiecl ovci with day and tins coal of clay should be patched whete ne( cssary befme eadi roast The purpose of this is to pi event the oie sticking to the walls iii case of any slight fusum

4:8. In stall luasling, pyiitic oies that contain more than '-ifl per cent suliihur should be supplied with only sufficient wood to start the roast Too much wood wdi make too much heat and fuse some ot the oie Foi this reason, it lb best to use partly wood rathci than sound haul wood Moie wood is needed foi oies that contain a g;ood deal of gangue and so little pyiite that the oxidation ot the ore itself does not pioduce enough heat to mamtain a lasting temperatuie The size of the stalls is an nnpoitant matter, and must be decided for each oie by expein enced judgment The inoie heat the oie will generate in roasting, the smaller should the stalls be, since large heaps are not so leadily controlled and the oie may fuse, thereby causing future trouble The management of the draft IS also impoiiant and leqiiiies experienced judgment

419. As previously staled, stalls have the advantage over open heaps that they save fuel, time, and labor An oie that would lequiie % oi 3 months to roast in heaps can be roasted m as many weeks oi even less m stalls Sulphur is about equally well removed by either method, but stalls have the advantage of forming lessfei nc oxide because

the process is not-so long continued as in heaps (see Ait 57) Stalls, however, require the investment ot consideiable capital for then consUuc,tioii, while heaps do not The former also requne more careful superintendence For the lack of this care, stalls have in a numbei of cases been given up m

ejEKSi ximsr

50. The GJevs Idlii is a shaft fiiinace and is shown in elevation and in vertical section m Fig 10 It js used to last coarse iron ore. A similar furnace is used to lemuve CO

36 Roasting And Calcining Ores § 30

fiom calamine leaving ZnO It is fiom 10 to feet

in diametei at the widest pail and from 12 to 30 feet high The walls aie built of fiiebiick held in position by iron plates They rest on a cast-non iing a, which is supported by a number of cast-iron legs b The ore is bi ought in wagons or buggies on the tracks c and dumped into the open top 3 to 5 pel cent as much coal as ore is also used As the chaige descends, it is forced out in all diiections fiom the center by the cast-iron cone /and is drawn away between the legs b The air to burn the coal and to oxidize the sulphur 111 the ore enters partly through the spaces fiom which the 016 is discharged, partly between the cap and base of the central cone, and, if necessary, partly through the doors e The charge can be poked thiougli these cloois if it happens to clog Very little if any air would 1 each the central part of the charge if it weie not admitted at the cone/

The combustion of the fuel and the actual roasting of the

oie take place mainly in the central part (vertically) of the fiunace In the lower part, the cold an takes up heat from the roasted ore, and in the upper part, the cold ore is dried and heated by the hot gases

51 . Fig 17 shows a kiln in winch the fuel IS binned on an exterior grate instead of being mixed with the ore The flames fiom the grate fire a enter the ore chamber b and thus supply the necessary heat. The object of

Fig 17

COASTING AND CALCINING OREvS § 30

this IS to prevent the coal ash mixing with tin* oie This precaution ib necessary only with zinc oies, and even these are sometimes lasted in diicct contact with the fuel The ore IS fed at c and discharged at d The an for binning the fuel IS somewhat preheated by passing through the space c (just below the hot oie that is being drawn out thiough d) into the ash-pit /, the draft is conuolled by the damper g.

D A -OO n BY IC I LN

52. The Da vis- Colby kiln, which is also used for non ores, IS heated by gaseous fuel The special feature ol the kiln shown in Fig 18 consists m dividing the furnace into four independent sections means of the paititious a The purpose of this is to get a moie unifuim action than can be obtained with the ordinary constuiction in which the partitions a aie not used This furnace is about teet high Ore IS fed into the lioppei /? at the top of the fuinace and is drawn off through chutes c at the bottom Gas is supplied by the flue surrounding the furnace and enters the combustion chambers / through biaiich pipes which aie fitted with valves Air enters the combustion chamber through the ports and thebiumng gas and an pass thiough the openings z into the ore chambers y, Passing through the ore, the hot gases gradually raise the lattei to a red heat and arc diawn through openings I into the central vertical hue From tins flue the gases pass thiough the pipes in into the flue n surrounding the upper pai t of the furnace, and from theie into a suitable chimney When the ore is hot enough, it is diawn into the lower part of the ore chamber by discharging the ore that is already there The covers p are then tightly closed to exclude all an , and gas (unmixed with an) is admitted from the pipes r to the chambers and from there passes through the ore and into the exhaust flues This reduces the hot to according to the equation

The P'eO is then withdrawn through the chutes c

§30

Roasting And Calcining Ores

53, It will be noticed that the size of the ore chambers j enlarges somewhat from the top to the bottom This is to provide for the expansion that takes place in the ore while roasting

For calcining carbonate ores to remove caibon dioxide CO 01 roasting such iron oies as contain small percentages of sulphur that must be expelled, the radial partitions a are not used Also, foi such ores the combustion chamber / lb extended downwards to include the chamber because no 1 educing effect is needed

CHEMISTHY OE EOASTmG

54. In lasting sulphide oies, the sulphiu and the metals aie both oxidized, most of the foimer passing off m the gaseous state as sulphur dioxide while the metallic oxides lemain in a more oi less pious condition

PbS-\-W PbO +

ZnS ZnO -j- SO

CnS + C7ip+SO,

Cup w %Cu0 -h so

55. A certain amount of the sulphiu is burned to sulphur tnoxide SO vSome of this passes off m the draft, but pait of it unites with the metallic oxides to form sulphates, which are not volatile, foi example

PbO+SO:=PbSO, and CiiO + SO CuSO

The sulphur tnoxide SO also acts as a very efficient oxidizing agent, both oxidizing siilpliides and changing the lower to the higher metallic oxides, foi instance,

Cup -f ™ Cu„0 -f 450

56. In roasting pyrite theie aie seveial distinf't

stages One of the two atoms of sulphiu m this mineial is quite readily volatilized heat FeS -f- S) The first

stage in the roasting consists m the oxidatuni of this one

Roasting And Calcining Ores

atom of sulpliuij which burns with the chaiactenstic blue flame of sulphin In proof that tins atom of sulphur is actually volatilized, it is only neoessaiy to point to the fact that by scooping out small holes in the top of an open heap of lasting pynte and lining these holes with fine oie, a certain amount of bulphiii can be collected in them Indeed, this siilphui sometimes condenses in the tipper pait of the heap during the eaily stages of toasting to such an extent that It closes up the air passages and so hinders the lasting Any such cuist must be broken up This same crust forms on the suiface of the oi e when roasting fines in hearth furnaces Consequently the rabbling should be frequent during this period, but after the fiist atom of sulphur has been burned off, the rabbling need not be done so often

57. Dm mg the second stage of loasUng, the iron and the remaining atom of sulphur are oxidized, according to the following equation

FeS + 3d) FeO + SO,

Much of the ferrous oxide FeO formed by this reaction unavoidably becomes further oxidized to feiric oxide Fvfi, The ferric oxide is undesirable in smelting, because it has to be 1 educed again in the smelting furnace

58. As stated in Art 2, the quantity of sulphates pro-

duced is greatest when the temperatuie is comparatively low, when there is not too much draft, and when the bed of ore IS rather deep It is because these conditions aic so well fulfilled m heap and stall roasting that unusually laige amounts of sulphate are formed by those methods The temperature at which sulphate forms most readily diEeis for different metals Iron is sulphatized at a lower temperature than the other metals, yielding fcirous sulphate FeSO As the temperature increases, this is decomposed into ferrous oxide FeO and sulphur trioxide SO, or sulphur dioxide and oxygen O. The siilphatizmg and decomposition of the

other common metals proceed in about the following order copper, sdvei, zme, and lead It is to be understood,

§ 30 ROAvSTTNG AND CALCINING ORES

however, that one metal is not completely sulphatized before others begin to be, and the same may be said in regard to the decomposition of sulphates Zinc and lead sulphates are decomposed only at veiy high tempeialmes In the slagging oi lead ores, desciibed in Art 14, some sulphui is eliminated by the following i action

PhSO, + StO, Pb.StO, + + 20

59. Arsenic and antimony behave in roasting much the same as sulphui, but a larger pioportion of these aie oxidized to the non-volatile condition (arsenates and anti monates) than m the case oi sulphur On the othei hand, some arsenic and antimony may be volatilized as sulphide before oxidation takes place

60. In the reducing i oasts, oxygen is taken away from the higher oxides and from sulphates, arsenates, and antimonates by carbon, carbon monoxide, and sometimes by sulphur, where iron disulphide is used as a i educing agent The reactions differ with diffeient conditions of temperature, etc The following examples aie given of this reduction

CnSO, + %C CuS + %C0

CiSO + iC — O/S + 4:CO

61. In the chloridizing roast of silver oies, the principal reaction is

It often (and with the Stetefeldt furnace probably always) happens that the silver is not completely chloiidized in the furnace, but if the hot ore is left in a heap foi a numbei of hours, certain chemical reactions take place, which in cases greatly improve the chloiidization

63. The roasting of carbonate oi'es consists simply in calcining the ore , that is, driving off carbon dioxide by heat

FeCO, + heat rr: FeO +

4

Roasting And Calcining Ores § 30

In the case of iron

caibonate, it is practically impossible, commercially, to prevent the FcO being oxidized to though this IS not done purposely

In the various kinds of lasting theie are, in addition to the reactions given above, various others of a more or less complicated character, which it is not necessary to discuss here

63 . Eig. 13 shows the Argali limit! - tubular' roaster. It consists of four tubes, or cylinders, a arranged side by side and held togelhei by two heavy tires b Each of these tires rests upon a pair of grooved friction pulleys c set so that the 1 caster has a little slope from the feed end d to the discharge end c Each of the tubes a is 29 feet long and 25 inches in diameter inside the

§ :iO ROASTING AND CALCINING ORES 43

brick lining At the feed end, the tubes are set into the hood into which the oie is fed fioni the hopper / As the furnace is revolved by the friction pulleys the ore enters the tubes a The revolution, combined with the slope of the iurnace, causes the ore to gradually travel to the lower hood t', fiom which it discharges thiough the holes g into the receiving hopper h The Iurnace is heated from the fiiebox which is aiianged to burn oil, but can, of course, be modified to bum coal, The oil, mixed with air, is introduced through the holes k as a spray, and the hot gases pass into the hood c and thence thiough the tubes a of the roaster and pass off to the dust chamber vi and a chimney beyond

The object oi using four cylinders instead of one is to provide a larger amount of bnckwoik to absorb the heat fioin the firebox, this heat being again given out to the ore

The furnace has been used to roast some of the gold ores of Clippie Cieek, Colorado When treating 48 tons of ore in 24 houis ill one furnace, the 2 per cent of sulphur originally in the 01 e was reduced to 0 1 per cent , accoidmg to statements made If such is the case, the roaster is entitled to lake lank among the best

64. The Zellweger roaster has been recently introduced at Gas City, Kansas This furnace, while a straight- Ime reverbeiatory 135 feet long by 15 feet wide, has a rolling stirred that moves slowly from the feed to the discharge The stirrer coiisisLs of a heavy shaft earned by wheels, 0 feet in diametet, rolling on tracks in the depressed wheel pits on eithei side of the hearth On this shaft are a number of collars carrying blades foi rabbling the oie These collars lock on the shaft when traveling from the feed to the discharge end of the furnace, and as they revolve with the shaft, the blades scoop up ore during one half a revolution and discharge it during the other half, thus gradually moving the ore forwards During the return trip, the stiirers revolve around the shaft with the collar, but do not displace the ore more than to rake it. This furnace has external

Roasting And Calcining Ores § 30

fireplaces, and is said to roast 15 tons of blende to 1 per cent sulphur in 24 hours

65. The roaster shown in Fig 20 is known as the Herreshoff, although it is merely a modification of the

McDougall It has a cential shaft with a number of shelves which answer foi healths placed at right angles to it Attached to the shaft are Uvo arms v above each health, which cairy teeth so arranged that one set moves the ore from the center to the circumference of the furnace, where it fails on to the next lower hearth The set of ai ms on the latter hearth have the teeth arranged so that the ore is moved from the cnciunfereiice of the furnace to the center and discharged on to the next lower hearth, and so on to the ore dischaige at the bottom of the furnace, as shown by the arrows

Power IS transmitted to the shaft d aird arms c by the shaft h and gear-wheels f and g The ore is fed on to the top hearth from the hopper a and the gaseous pioducts of combustion pass out of the furnace through pipe The hollow shaft d is made large (14 inches in diameter) so that a large quantity of air is drawn up through it, this amount being increased by the sheet-iion stack extended above the

§30

Roasting And Calcining Ores

top of the fiiinace Between the shelves Lheic are cioss channels passing; diicctly through the sliaft at right angles, as shown in the veitical section di awing These cioss channels are about 4 inches wide and 5 inches high and allow ample space around them foi the passage of the ascending air Into these channels or sockets the arms r aie inserted, and by a groove and iib aic arranged to lock when horizontal and unlock when raised at their oiitei ends

By raising the outerend of the aim about 3 inches, the rib can be pulled out Practice has shown that these aims, weighing about 100 pounds, can be unlocked, removed fiom the furnace, and new ones put in and locked in place m about one minute Each furnace requires about horsepower The aims aie the most costly pait of the running expenses in regard to wear and tear, they are said to cost about $30 per year for each furnace,

COST OF T?OASTI2sra

66 . The cost of i casting varies according to the degree of roasting demanded, together with the price of fuel and labor The cost of roasting to eliminate sulphui to % per cent should not, with present mechanical roasters, exceed 50 cents per ton, howevei, to reduce the last traces of sulphur, the cosL will probably be foiu limes this amount

According to Doctor Phillips, sweet-roastuig cost IS at the Haile mine in North Carolina The cost of lasting at the Globe smelters in Denver was $3 075 in 1887 and 75 m 1898 for hand-rabbled leverberatory furnaces The cost of roasting in Brown-O'Hara mechanical roasters was 12.21 per ton of oie The cost of roasting at the Guggenheim furnaces, Monterey, Mexico, is given as $2 43 per ton of ore in hand-rabbled furnaces

While mechanical 1 casters give at first glance a cheaper product, the cost of roasting is higher when repairs and the quality of the product are taken into account

The Cyanide Process

(Part 1)

IlVOIiTITION XIIR CYANIDE PROCESS

1 , Cassell Process, — Recoids of gold being dissolved in solutions ot potassium cyanide and water extend back to The resulting solutions were first applied to gilding metallic surfaces That gold could be dissolved from some oies by weak solutions of potassium cyanide was known in 1807, and applied in that year, but without much success from a standpoint Doctor Cassell perfected a process which he sold to JMtssrs JfacA? and Fa? rest, who weie granted patents m 1800 fot what is known as the Ma.c.Vrtlim*"Porpest cyanide process. Messrs Mac- Aithui and Forrest demonstrated the practicability of the cyanide process, although since its introduction many useful improvements have been added to make this branch of hydrometalluigy a success The only patentable feature in the MacArthur-Fon est process was the method of precipitation by 5unc shavings, and even this is denied by some

2, IGlectrolyiic Px*ocess. — The application of mechanical agitation to assist m dissolving gold from ores was early lecognized by J H Rae, of Syracuse, New York, who made a test of his process in 1807 He applied to his

§ 31

Foi notice of copyugtit &Ge page immediately following the title page

2 The Cyanide Process §31

cyanide solution the clectnc current and precipitated the gold electrolytically in a bath of mercury

Many years afterwards, Pdaian and Clerict patented a similar process, which Avas more successful, howevei, for wheie Rae used an alternating current, they used a direct current Pelatan and Clenci introduced sodium chloride into their cyanide solutions, but this was also done by J W Simpson, of Newaik, New Jeisey, m 1885 There is probably nothing in the Pelatan-Clerici process that has not been patented or used prior to its introduction in this county The pneumatic-cyanide process was ougmated about the same time in New Zealand and the United States In this process, the agitation of the oie and aqueous potassiuin-cyanide mixtuie is accomplished by a blast of compressed air

Scope Op The Pbocess

3. Cyanide Solutions Ueflned. — Whenever cyanide solutions die mentioned in this woik, it is to be understood that they are those made by dissolving cyanide of potassium KCN in water The cyanide process lefeis to dissolving gold and silvei from ore by means of cyanide solutions and afterwards precipitating the gold by some one of the methods hereinafter described While the chemical reactions that lake place betAyeen gold and cyanide solutions aie knoAvn, the reactions between cyanogen and some other elements are as yet but slightly knoAvn, for Avhich leason the cyanide process has not been fully developed and its scope IS at the present time limited

4. Treatment of Rree -Milling Ores. — o? cs a?'e most svcccssfully treated by the cyamde procei ivhcn the gold IS tn a pine date or subdivision The cyamde process has a field of its OAvn in woiking tailings and concentrates resulting from wet crushing and plate amalgamation and can generally be applied to those ores that have their gold particles encased m some substance or have the gold so

The Cyanide Process

S 31

finely divided that it floats away ovei the amalgamating plates

5. Trea,tmeBt of Silver Ores — Oies conlammg silver are more or less soluble in diliiU* cyanide solutions, but not to tlic same extent as gold The chloride of silver AgCl and the subbulphide of silver Ag,S ate readily soluble, but silvci ores, as a rule, are slowly acted on by cyanide solutions Sodium chloride NaCl is sometimes added to cyanide solutions to hasten the reaction wbeie much silver is in the ore, the object being to form silver chloride, which, as stated, lb readily attacked by cyanide solutions The addition of sodium chloride to the solution takes place in the vSimpson and the Pelatan-Clenci processes

6. Treatment of Jinse-Metal Ores. — The base-metal ores or those containing iron, zinc, lead, copper, and antimony, combined with sulphur, aisenic, oi telluimm, sometimes cause a loss ot cyanogen by uniting with the cyanide solution and forming soluble cyanides This loss can be 1 educed materially by the use of weak cyanide solutions, as m that condition the affinity of cyanogen for gold and silver IS greater than foi baser metals The action ot weak cyanide solutions on lead and iron is piactically nothing The solvent action of weak cyanide solutions on copper and zinc in a metallic slate is little with gold present, but when their hydrated oxides and caibonates are present in the ore, the loss of cyanogen will be so gieat as to lender the cyanide process useless Paituilly oxidized pyntous ores cause a loss of cyanogen, but they aie sometimes leadily adapted to the cyanide process by a piehmmary treatment Those ores that contain a quantity of antimony oi tellurium geneially require prehminai y tieatment. Arsenic seems to have no iiijuuous effect on the cyanide solution When gold and silver are associated with ores of capper and antimony, weak solutions of cyanide exert a veiy decided action on gold and silver, but do not act on copper and antimony This fact is taken advantage of in the treatment of cupiiferous ores on a commercial scale

THE CYANIDE PROCEvSvS

4 :

§S1

ClTEMiyTllY OE THE THOCESS

7. Cyanide of potassinni is composed of the thiee elements pitcLbitim, LYiibon, and nitrogen, one atom of each combining chemically to foim a molecule of cyanide oi potassiiim Itb chemical symbol is written either KCiV or ATjf It IS an organic compound veiy active in combining with many base metals

A large iiumbei of cyanogen compounds aie toimecl with complex ores under diifcieiit conditions of tieatment The exact natuie ot many of these is as yet unknown, and it will require much careful leseaich m the laboratory by skilful chemists to determine then properties and reactions The cyanides of the heavy metals, with the exception of gold and silver, aie insoluble in watei, but they aie soluble m excess of cyanide The cyanides of the alkaline metals aie soluble m watei

8. Eisner's Eqnatloii. — When gold is Heated with a cyanide solution, oxygen must he present oi some other element that acts as an oxidizing agent The reaction, presuming oxygen to be piesent, is expressed by the following equation, known as AVw/erb* Equation, as he advanced the theory m 1S44

%Au u- 4KCN -h -j- %KOH

Gold Cyanide of Oxygen Watei An: ic-pota-sic Potassium potassium oyanide hydrate

The probable reaction is that the gold unites with the cyanogen, liberating potassium Part of the potassium immediately unites with the gold cyanide, tunning the double salt auric-potassic cyanide, the lemaindei uniting with the water liiieiates hydrogen and foims caustic potash oi potassium hydrate When such a solution is evaporated, it yields octahedral crystals, which show on analysis to be auricpotassic cyanide

9. Tiilliieuee of Oxygon Upon tUe Iteaclion. — In orclei to cany out the reaction indicated, Elsnebs equation shows that oxygen should be piesent That oxygen was necessary for the reaction was a1 first denied by some, but

The Cyanide Process

latei experiments have shown that Elsnei's theoi} was coirect Several devices lor the aitifieial intiodm tion of oxygen >nto the pulp have been invented

Agitation by means ot mechanical <le vices permits the oxygen of the atmosphere to come in contact with the pulp and theieliy hasten the operation Foi this put pose, inec ham ical stuiers, cenliitugal pumps, or comjnessed an rue employed Sodium dioxide is also used toi tuiinsh-

mg oxygen and mcLeasino the* tune of reaction, for the sooner the atoms ot o{>]cl, cyanogen and oxygen come in contact with one anothei, the quicker the operation of gold extraction will be completed Wheie tune is not an object, the oxygen piesent in thewatei and oie, togethei with bucli oxygen as is obtained iiom the atmosphere dining the 'operation, will be suhicient to cany out the chemical leacUon

10 , Coiabiiiiiiig Weiglits o£ Goltl and Potussiuiu Cyanide. — Taking the final leaction given by Elsnei's equation and applying the laws ot chemical combination, the molecular weights will express the weights of the elements that form the aunc-potassic cyanide compound The molecular weight of the two atoms of gold is 308 4 and the molecular weight of the foui molecules of piitassmm cyanide is As the molecular weights express the com* bining weights, 15 12 paits of gold will lequiie 10 paits of potassium cyanide, that is, 15 L2 ounces of gold will leqiuxe 10 ounces of potassium cyanide toi its solution It has been ascei tamed by practice that m treating tiee-milling oies, 20 to 40 pounds of potassium cyanide aie required to dissolve 1 pound of gold Tins may be paitially explained by secondary reactions that aie known to take place but aie not fully undei stood

llo Pate of the of Gold. — Researches by

various scientists have demoiistiated that the rate ot solubility of gold in cyanide solutions depends on the strength oi the solution and the supply of oxygen A piece of gold leaf may be immersed m a strong solution of cyanide of potassium and scarcely be attacked If, however, the piopei

6 The Cyanide Process § 31

amount ot oxygen be supplied by sodium dioxide, the gold leaf will be disbolved in a comparatively shoit time

Under oidinaty cucumstances, such as prevail when the MacAi thill -Forrest process is practiced, gold will dissolve quicker in dilute cyanide solutions than m strong solutions The maximum late of solubility for gold ina fiee-milling ore, under favoiable conditions, is reached with a :5-per-cent solution The chaiacter of the oic exerts an influence on the late with which cyanide will dissolve the gold, and this time can be determined by laboratory experiments

CAUSES FOE CYAmUE EOSS

13 . Cyamelcles, — Some of the losses of cyanide which occui when ores containing gold and silver are tieated by the cyanide process may be traced to the presence of mineral acids and salts, to minerals soluble in cyanide solutions, and to a certain percentage of waste caused by washing the tailings To these losses may be added those that are caused by evaporation or by carbon dioxide absoibed from the atmosphere

13 . liO&s From tlic Presence of Minea*al Ackls and Salts.— The ordinary gangue minerals associated with gold and silver ores are largely composed of silica and silicates of the alkalis and alkaline earths These substances are seldom of such a composition as to decompose a cyanide solution

The metallic mineials often associated with gold and silver in quaitz veins aie iron pyrites, copper pyrites, zinc blende, galena, and stibnite Iron pyrites, the most common and abundant of these, when undecomposed do not act on a solution of cyanide, but when exposed to the atmosphere in the presence of moistuie, they become oxidized into feiious sulphate and fiee sulphuric acid. The following equation shows the leaction

FeS + Hfi + 70 FeSO, + H,SO

§31

THE CYANIDE PROCEvSS

Iron pyrites, when exposed to the elements aliove water level, are often chcinged to feme oxide Feme oxide does not dsLompose solutions of cyanide, but its piesencc often causes very fine slimes, which retard the operation of draining the ore

The ferrous sulphate and tree sulphuric acid pioduccd by the atmosphenc oxidation of iron pyrites react upon solutions of potassium cyanide and may cause a loss of cyanide by the hbeiation of hydrocyanic acid oi by the foimatiuu of ten ocyanidevS and fenicyanides

14 . Alkali Treatment — TV; prevent loss of cyanide in ores or tailings containing aculs, iron salis and cariJiy sulphates they ai c treated with an alkali If the oie coiitaiiis a large percentage of fiee acid, it is washed with water before tieatmeut with the alkali If the oie is not too acid, a quantity of caustic lime is added and thoroughly mixed with the 01 e before it reaches the percolating tank Tf caustic soda or caustic lime is added to acid oies, it will neiiti alize the acids and will combine chemically with the objectionable salts

15 . Xiossj From. Minerals Soliihle in CyanidcH. — Potas- Slum cyanide acts on the oxide, sulphide, and carbonate ores of copper and the sulphides ol antimony and bismuth The loss of cyanogen, which will occur when oies of tins description are tieated by the cyanide process, depends on the quantity ot these minerals present in the ore

The selective action of weak cyanide solutions is taken advantage of in ti eating cupriferous ores There naay be sufficient copper present to decompose a 1-per-cent solution of cyanide and give a low exti action of gold, whereas a solution containing %6 pei cent of cyanide would dissolve more gold and less copper than the stronger solution

16 . Xioss From Ores. — To save as much

aunc-potassic cyanide as possible attei the oie has been treated, it is customary to wash the tailings with watei But as It is impossible to remove all the cyanide solution in this manner, some of it is lost in the tailings Washing the tailings causes a large accumulation of dilute cyanide

N M 111—26

8 The Cyanide Process § 81

solutionSj only a small poitioia of which can be used in making up new solutions, the balance being run to waste

17. Doss Absorption of Carbon Dioxide Fromtbc tinospliere.— Potassium cyanide is acted on by the carbon dioxide of the atmosphere causing the formation of potassium carbonate and the liberation of hydrocyanic acid, thus,

9.KCN-{- CO, + Hfi KCO, + %HCN

If the cyanide solution contained an alkali, the prussic or hydiocyanic acid thus liberated would be neutralized

The loss of cyanogen that occurs by evaporation is consideiable, free cyanogen CN also escapes fiom the solution through causes othei than those desciibed, but which have not yet been satistactoiily determined A small loss of cyanogen takes place when wooden tanks and vats are used to retain the solution, but only when the tanks aie new or leak With non tanks theie is no loss, except in the case of leaks

Application Op The Process

coismioioxs

18, Size of Gold lii Ore. — In deciding on the tieatment required for any given ore, it is necessary to considei whether the gold in the ore is coarse oi fine, whether the ore IS neutral or acid, and what objectionable metals or mineials, if any, the ore contains

19. Effect of Size and Condition of Gold Pax'tlclee. Ores containing gold in a fine state of division are usually good cyaniding ores If the gold is coarse, a longer lime IS lequired to dissolve it, and therefoie such ore is usually subjected to some method of plate or pan amalgamation before cyamding When the gold is in a fine state of Sion, It may sometimes be dissolved by a l-per-cent* cyanide solution m about hours.

THE CYANIDE PROCEvSS

30, Time of Trccitment (governed Conditions.

iltc U eat input of comcnti ate lontaimn py lifts, the matertal must remain in contact ivith the cyanide soluHou a longer time than zvhen tailings aie being t? taped This may be accounted foi if there is a laige quantity of gold to be dissolved, it the gold is cuatse in the conceatiates, ui if there is some amalgam present It takes time for a cyanide solution to penetrate the pyiite crystals to get at the gold, for the solution that can pass into the small mteistices between the crystals will be held there by capiilaiity, resulting in a slow diEusion

31. Acid Ores. — The acidity of ore is due to the decomposition of pyrites The pioducts of such decomposition, which consists chiefly of fice sulphuiic acid and soluble sulphates of iron, are destructive to cyanide solutions The special treatment that is necessary to overcome the bad effects of acidity is discussed under the ti catment of acid oi es

33* Ckemical TAmltatlons of the Process. — In some oies the gold and silvci aie so imprisoned in the matrix that the cyanide solution cannot leacli them, even if the ore is crushed very hne Such ores can only be pailially treated unless they can be made pious by roasting, and as the latter operation is expensive, it may nut be worth while Again, theie may be substances that will unite with the cyanide and pi event cxti action of gold

33* Hllvor Extraction. — Silver occuis usually m com bmation with bases that decompose potassium cyanide When ores containing silver are oxidued or where the silvei IS 111 the condition of chloride, cyanide solutions will dissolve the silver On the other hand, when lead, oxide of copper, or certain oxides of iron arc present m the ore, the extraction IS so poor as to condemn the process

34* Slimes,, — By this term is meant fine, and sometimes impalpable, pulp that floats about in the solutions and IS very slow to settle When slimes dry, they form hard lumps If these lumps find their way into tailings and so into the vats, they will only be partially leached and

The Cyanide Process

§ 31

consequently yield but a part of their old and silver ShiTies are a source of annoyance from the fact that they aie a hindrance to pei eolation and often cntiiely prevent it They are not to be thrown away, however, bccanse they frequently contain a high percentage of the precious metals

35* Concentrates, winch are derived by exti acting the valuable minerals from a mass of barren lock, can be treated successfully by long contact with the cyanide solution Agitation has been used to successfully hasten the treatment In recent practice the concentrates arc roasted This affords an opportunity for the gold to be bettei attacked, as it changes the character of the ore Sulphide concentrates sometimes ariangc themselves m regular older, so that their cubes form a wall that prevents pioper peicolation

Laboratory Tests

36* Object of Tests.— Tests are made of oies to ascertain then fitness for the cyanide process Percolating* tests of ore made in the laboratory aie virtually similar to those earned on in practice, and consist in submerging ore in a cyanide solution, draining off the solution and finally wasting the ore A convenient apparatus for small percolating tests IS shown in Fig 1 It consists of a funnel-shaped vessel r, an iron stand and a beaker into which the liquid is dialed The ore a icsts upon a filter paper, which, in turn, rests upon a false bottom b

Fig 1

The Cyanide Process

§ 31

in the vessel A stop-cock c at the funnel end of the vessel e perraitb oi prevents the liquid in the vessel escaping into the beaker d The solution coming from the vessel may be tested foi any loss of cyanide that has occniied during the peicoLiting process and also for gold

Whenever iL is desirable to tieat largei quantities of oie than the glass vessel will contain, such an arrangement of

(d>

Fig s

glazed earthenware jars as is shown m Fig S {a) will answer A perforated false bottom /; fits into the jar a above the stop-cock c, as shown in section, Fig 2 (I?) This false bottom IS composed of slats rf, placed inch apart and surmounted by board upon which a piece of canvas is

n THE CYANIDE PROCESS § 31

stretched to act as a filter The solution is drawn from the jar a into the jar r, which answers as a gold-solution vessel The loss of cyanide due to pei eolation maybe ascertained from this solution The gold m the solution is precipitated on zinc shavings, which aie packed into a glass tube f 1 5 inches in diameter and about 18 inches long The lower end of this tube is fitted with a pertoiated cork //, into which IS inserted a glass nipple i pmvided with a rubber tube and clamp j for the purpose of legulaling the flow into the jar k The glass tube/' is supported in a vertical position by means of an non stand to which is attached the clamp I The testing jar described has a diameter of about 1% inches and is charged with 4 or o inches of ore

27. Testing Plant — In Fig 3 is shown an anangement for anothei small testing plant composed of tubs a

Fig 3

and a piecipitatmg box c, and a sump d for receiving the Altered liquor The tub a will hold XOO pounds of oie and sufficient cyanide solution to leach out the gold From tub a the gold-cyanide solution is di'awn into the tub d, fiom which It passes into the precipitating box r that contains zme shavings After the gold is precipitated the Altered liquor passes into the sump dj where it is tested for

The Cyanide Process

§31

la

cyanide loss, then strengthened or standardized by the addition of cyanide, and, if needed, pumped back to the tub a

28. Filters for Testing Plant. — A good filter bottom can be made for small testing plants by placing slats 1 inch apart across a hoop, as shown in Fig These slats do not reach down the entue width ot the hoop, but stop about 1 inch above the bottom to allow a free cii dilation of the liquor A strip ot canvas should be tacked between the circumference of the hoop and the inside of the tub to prevent sand from washing under the false bottom

liABOnATOUX A1PARATUS REQUIRED

29. The laboratory apparatus that will be lequiied to make these tests aie two burettes graduated to yV cubic centimeter, each having a capacity of 50 cubic centimeters and piovided with floats, one biuette stand, two pipettes having a capacity of 10 cubic centimeters, a giadualed cylinder having a capacity of 1,000 cubic centimeters and a glass bloppei , two titiating dishes having a capacity ot 120 cubic centimeters, six porcelain evapoialing dishes 5 inches in diameter, six non evapoialing dishes 5 inches ill diameter, one wedge-wood mortal 5 inches in diameter, one iron stand with three imgs, four flasks having a capacity of 8 ounces, and foiu flasks having a capacity of IG ounces, A desciiption of this apparatus is given m Assaying

DE/PERMINATION OE EREE POTASSIUM C YAISTIDE IN A SOEUTUm

30, HllAer Nitrate Test. — Several methods have been suggested for detei mining fice potassium cyanide in a solution. A rapid and accurate determination may be made by titrating a measured quantity of a solution with a standard solution of silver nitrate Silver cyanide is thus formed, which will immediately ledissolve if there is an excess of polassiiim cyanide The reaction is as follows

The Cyanide Process

§31

(1) AgNO, + ICCl - CN + KNO,

(a) AgCN + KCN [CN),

31 . Point.- — Titiatmg is fished when a peima-

nent white precipitate of silvei cyanide ib piodticed Silver nitrate is to be added from the buiettc until all the potassium cyanide has united Avith the silver cyanide to form a double salt of potassium silver cyanide If more silvet nitrate is added than is required to form the double sait a permanent precipitate of silvei cyanide is foimed, which shows that sufficient silver nitrate has been added for the leaction The end leaction is more distinct when two or three drops of a o-per-ceiit solution of potassium iodide is added to the cyanide solution before titration Aftei all the cyanide is converted into the double salt, any excess of silver nitrate will tniite with the iodide

33 . pj*eparatioii of tlie Standard Sllvei'-Nitrate Solution.' — A convenient standaicl for a silver-nitiate solution IS a solution m which the quantity of silver nitrate in each cubic centimeter represents 0 1 pQi cent, of potassium cyanide When such a solution is added to 10 c c ol a cyanide soluLion, it will eventually foim a permanent white precipitate To prepare the standaicl silvei nitiate, the equation of Art 30 is taken , it shows that it takes two molecules of KCN to unite with one of AgNO The molecular weights are as follows

AgAO - 108 +U + 48 1*70 2KCN " 7S + U + %8- 130

From this it may be seen that the two aie m the proportion of 17 to 13, so that it 17 grams of nitrate of silver be dissolved in 1,000 c c of pure water, 1 c o, of the solution will be equal to 013 per cent of KCN. This makes an unhandy number for quick calculations, therefore the mtrate of silver solution is reduced m propoitioii to 10 c c of KCN solution as follows

THE CYANIDE PROCEvSS

§31

and

13 17 H) 13 07

IV 13 07 13 lU

That IS, the staiidaid silvci-mtiate solution may be made by dissolving 13 07 grams of silvei nitiatc m 1,000 c c of distilled watei

33. To Caleiilute tlio Pei'eon tage of KCJVT in a Solution,— Fust fill two biiiettes, one with the standard silveinitidte solution and the othei with the cyanide solution to be tested Next, urn into a bcakei 10 c c of the cyanide solution , add cautiously the silvei -nitrate solution from the burette until a pei manenl opalescent precipitate remains aftei thoroughly agitating the solution m the beaker, If 2 or 3 drops of a polassuim-iorlide solution be added to the cyanide solution la the beakci, it will assist 111 determining the end leaction by forming a yellow precipitate Read fiom the biiiette the numbci of c c of stanclaid silver niliate used, divide by 10, and the lesult will be the avaiLible potassium cyanide in the solution in pel cent

To illustrate the above, suppose that 10 c o of the cyanide solution were used and that it took 0 c c of standard silvernitrate solution to form a permanent piecipitate, then

— 6 per cent KCN

34:. To Tost Cyanide Soixxtioiis, — To test a

sti ong cyamdt take S or c c and titrate it tvith

silvcr-nitrate solution It d c c of cyanide solution requiied G c c of silver niLiate, then 10 c c of cyanide would leqmre 15 c c of standaid silver nitrate, and 15 divided by 10 15 pel cent of potassium cyanide

In testing the sliength ot a strong solution in the dissolving tank, take 10 c c of the solution and dilute it with water to 100 c c Take 10 c c of this solution and titrate with silver nitiale, as described above The numbei of cubic centimeters lequued of the silver-niti ate solution will be the percentage of potassium cyanide in the strong

16 The Cyanide Process § 31

solution, for the 10 c c of the dilute solution only con tamed a tenth of the otinmal cyanide solution, hence theie is no need of dividing: by 10

35. To Test Very Weak Oyanltle Bolutimis.— Take 100 c c of the cyanide solution, initiate it with the silvcinitrate solution, and divide the number of c c of silvcn nitrate requiied by 100; the result will be the percentage ol potassium cyanide in the solution For example, suppose that ion c, c of a potassium yanide solution be used and it requiied o c c of silver nitrate to foim a permanent precipitate, then

5 — 100 05 per cent. KCN

30, To Test Polassiniu Oyaulde of Coimncrtc. — Cyanide of potassium when purchased fioin the dealers is not pure It may contain black carbide oi iron, alkaline caibonates, and small quantities of alkaline chlondcs and sulphides, foi which leason it is customary to test the unxtiuc to dcteimine the quantity of KCN it contains

In order to test the sticngth of solid potassium cyanide for the available KCN that it contains, proceed as follows (1) Sample the cyanide to be tested by taking a specimen across the thickness of the cake. (5i) Reduce the sample to a coarse powdei, mix thoroughly, take a small sanqile of this and reduce to a very fine powder (3) Weigh out 1 giam of the powdcied sample and dissolve it in distilled water, after which add sufficient watei to make 100 c c of solution, (4) Take TO c c of this solution and titrate it with standaid silvei niiiate The nunibei of c of silvci niratc i equired to pioducc the permanent piccipitatc divided by 10 will gave the amount of available KCN in 1 gtam of the salt For illustration, suppose that 10 c, of the KCN solution requiied 8 5 c c of standard silver nitialc, then 8 5-10 ,85 KCN in 1 gram, which is equal to 85 per cent, of /CfTAin the ciudc salt.

THE ('VANIDli VROCEvSS

AHHAA OK HOLUTIOIST KOU (,OhD ANf)

iVy* T:ik( Jillfl (' (' , ()i I pint, of the solution, ])lacc it 111 a lound non dish oven a iiic, and cva[)oiuLG to ri small bulk As Llu' (UMpoiation pious'cds lub the sides of the dish with a stiuinj; rod so as to eolleel the salts m the oL the dish. To this roneentrated solution add [0 plains of litharge Aftei mixing well, cvapoiaLe earefully to dryness Tiansfei the ('oiUtails of the dish to a ehiy ei LK'ible and add 15 grains of boiax glass, 5 grams of Imnirbonate ol soda, and )l grams of aigol, mix the contents eaiefuily with a spatula Cover the contents of the crneiblc with a little boiax glass and fuse Alter quiet fusion the contents and allow to cool the lead button and weigh the bead of gold and silver. If the oie eontains silver, pail the bead and weigh the

Load Evapo ration Trays. — In some cyanide woi'ks the >soluti()ns aie in trays made of thm sheet lead, which, with then eonlcnts, aie afteiwaids scorified and the insulting lead button cupeled

The lead tiay, Avait'h should weigh about 20 grams, is made of piue lead lod and is sha[)('d by laying a wooden block 'y X on the foil and folding (he load ition the sides the block so as to loiiii a tiay 1 inches long, 2 inches wide, and 1 inch deep Cate must be used'" in forming the cornets the tiay so that they will not leak Koi evaporation, the tray containing the solution is placed upon a piece of asbestos caidboaid and heated gently by a burner underneath.

iHh (n'ram and Tablen.-— "CkmsulL the following

tables to liiul the (puintity of gold and silvci pel ton of solution. When the gold and silver are weighed with giam weights, icfci to Table , and when with gram weights, refer to Table IT

The Cyanide Process

:n

TABXiTD I

von THE ASiSAY OE CYAMDE SO I ATTrOYH (PAKK)

236, (Ic c , oi 4 Pint, of Solution Givefa Pine Metal

1 Ton of vSolulion Gives Fine Metal

m 6 c c , oi Pint, of BolutuMi Give*' Fine Metal

t Ton of Solution Gives Fine Metal

Ct 1,1.111

Ounce

Penny-

weights

Cuains

Oiams

woihls

OOO'i

B

Is

0()00

f)

J4 fi

2iU)

u

18 !

Ooso

,0030 i

2] 0

if)

.0010 '

(5000

JiO

(Is

1,0

n

,0100

22,0

CRASSE'S METHOD OE TESTING CYAKIDIQ SOrAfTiONH EOH GOT-rl)

40* Take 33f] 6 c c, of the gokl-cyanide solution to be tested and add a solution of silvei nitrate until a piccipitate ceases to form* Add the silver nitrate a little at a time,

Tint: cyanide proceSvS h)

llu' soluUo]! afU'i cvirh addition The jold wdl pu'cipitati'd as aij'iMitu' auiiryanido Lot Llie pioc'ipttate sottU', oil tin* oltMi solution and (ilLoi Iho lonnuiuni piocipitalc j next diy the [)i oopillatc and mix iL with jams

TAIUJO ir

FOR TUK A4HV\ OF VNIDM SOLtITlONH (RAKK)

—

(i 1 , 1 ,

(i t' ( ,

ot t Pint,

ni Pint,

nl SoUi

1 (j 1 vSolulKin

(4 Solii-

1 ol Snliitioii

lion ives

1 (fives Kiiivi MeUil

lion (lives

(lives Fmt' IVJetal

Line

Fine

Metal

Oiitu i

Ponnv- w( i>.'hts

Uijims

(fi.iiiis

Pcjiinv-

(ll cVlIlS

ooo

(loa

Id

.OOIl

Oih)

,005

Is 0

, 100

?i0f)

! 0

,oos

4

]()

.001)

0

S

(i

n.o

of lilhaic, 15 nuns of lass, 15 jirams of bioaibonato of soda, and II grams of aigol; plane the; mixiui'c in a clay cuunbk;, fuse thoroughly, pour the contents into an iron mold, cupel the resulting lead button, pait the bead, and weigh the gokh From the weight of gold calculate,

The Cyanide Process § :]1

from tlie table, the amount of gold in a ton of the cyanide solution

Grasse's method is performed quicker tlian that dosciibcd in Alt 37, and gives reliable results where the value in only IS requiied, but if it is desired to know the amount of silvci 111 the cyanide solution, the fiist method must be used

TlilST POK OIUCS 031 TAUUmOS

41. All ores and tailings should be tesLecl m the laboiatoiy to determine their suitableness for cyanide tieatmeut. The principal items usually determined aie the rate oi percolation, the mimmiini extraction, the quantity of cyanide consumed, the acidity of the ore, and the neutralizing agents leqmrecl Other matters for considoiatiou aie economic, such as the strength of cyanide solutions for extraction, the time of contact for economic extraction, and the degree of precipitation fiom strong and weak solutions.

TEST Wll llATlfi OF PFIU'OL VTIOIST

43. Ore or tailings through which the solution wdl peicolate aL the late of fiom to 2 inches oi more an hour may be cyanicled by percolation When the pei eolation is inch per hour, oi less, economic pei eolation is practically impossible, unless the mateiial is veiy lich and will pay foi the long period of contact requiied. The same fact is true of oies and concent! ates

TKbT mil JERCKNTAGJfi OF tfiXTRACTrOTST

43. Take 4. kilograms of thoroughly dued and mixed tailings for the test Remove an assay sample and place the remamcler into a percolating vessel Level this charge and pour over it d liters of a (),Ji-]ier-cenl cyanide solution. Close the discharge cock ami soak the tailings ISi Iiouis in the solution, after which time allow tlic solution to dram below the surface of the tailings Aftei the solution has drained I hour into a vessel, close the discharge cock and

§ ;n THE CYANfDE PROCESS

poui the luiiujt on the tailnijs, open the disehaiie eock dinl liIIovv il to peienldle into the tec eivinu vessel ajax dMns process is to he lepeaLetl at mteivals oi 1 hoiii for 12 hoius, ufLei wliieh tlxe lujiKH is all drained oil, Tiie ULiliiij:>s aic iK'xl washetl with I htei s water, then diicil, and an assay taken fiom them I'he ('yanule solution IS drained into one vesstd and the wash water, wliieh now foi nis a weak eyanide solution, anothei vessel Each oi these solutions is assayed to asieitain the peri'cnlae ol (svti action Each solution is then passed tluouih 7Anc shavings, tlie wtsak solution being ptisscd inueli shower than the strong solution Assay the solutions aftei they have passed tluoiigh the Jiine shavings aiul the dilleicnce between the two assays will deteiinlnc the economic exliaetioii of gold All the gold in a cyanide solution is not tirceipitated by the/aue, anti foi that leason tests should always be atniliccl in older to icmeily any decided loss.

TO TnST YAMIDIO OONSTTMlUn 44. Idaee hi a stoppeied bottle 200 grams of Iheoie with 20{) e e, of .n-pei -cent, polassiiim-cyaiude solution and shake foi 20 mimites. Let the solution settle and then lilter off a portion Take 10 e. e. of this filtered solution and test it foi the amomit of cyanide it eonlains The difterciioe in the sticngtli of the cyanide solution befoie and aftei extraction shows tlie percentage oi eyainde eonsumetl by leaching 200 grams of oie. T1 the xSolution eoutamed 0 per cent, oJ cyanide befote Ireatment and 0 -ti) pel cent after tieatui cut, a consumption of O.OT) per cent of poLasHium cyanide would be indicated. The consumption of potassium cyanide at this late would be 2,000 pounds X 0/) per cent. ™ 1 jjoitnd foi a ton of oie

The of cyanide takes jiUice almost immediately after the solution comes in contact with the oic Aftci 20 minutes it is safe to consider that thcic will be no further reduction.

THE CYANIDE PKOCESvS § ;U

DICTKUMIN iTION OF At'IlUTl IN OKKN

45 If the of ('y.inidci ib high or above 4. pounds of KCN to the ton ol; uic, a poitiouol the mateual IS tested tor acidity oi 'H yanicides/ hy whudi is meant liec acid, soluldc melalhe salts, or any other hulistancc that will destiny cyaiingeii To dcteimiue the acidity in oies and tailings, the tollowiug Lest may be made

Place 14 0 grams oi oie and ''hO c ol Avaier in a tall glass jai and shake well Next fill a burette Aeitli a standard solution ot caustic soda NaOIJ dbtrate the sohiUoii m the jar with the eaiislic soda until it becomes ncutial to litmus paper to a solution ol litmus

Each c c of the soda solutions used will nubeate that 0 1 pound of eausLic soda is to be add<'d to each Ion ol oie oi tailings as a pi elmniiai y wash to netitializeeyameides befoie the cyanide solution is added

40. Pi'Cxjnratioi) oV a Standard Solution of Caustu* Soda - — Weigh 10 grams oi coinmeieuilly puu (e p ) iMustU' soda and dissolve in 500 c c of pine watci, aftei ivlncli add 500 G c. more of puie watei

TO NRUTUALizK voio <mm

47, The test foi acidity will show tile quantity of caustic soda to add to each ton of ore to ueutuihzc the acids, but caustic lime may be used sometimes to gieat advantage wheie soda is expensive and lime cheap. The of lime needed in practice may be calculated from the caustic soda used in the lest; toi example, the quantity of caustic soda expressed in pounds multiplied by 7 mil give the pounds of pure caustic lime that will be requiicd to neutnih/m the acids in the ore The caustic lime of commence is not ptue, so that a much huger quantity will he letpnied than is indicated by the above calculation La some mills the same number of pounds of lime me used as would be required of caustic soda.

§;]! TUK ovANinit: inioch: 2;?

Ctiuslio litue IS list'd in jixosl (cyanide woiks in pLcfcrcnco to caiislir soda. (Uuslit soda is ohjcrtlonabU' bct'auso t){ its itnulciK'y to Ihc lyaiiido solutions in Iho piooiiiilatin boos and to iorin ieirocyanulc of zmr, whcncvci [jyutu oics aio IJ tvLt<'d

Caustu lime is usually added to tlic oi e when IL is ])1aet'd in the k'tLehnpiJ vats Theie seems to be no bad clleet fioui eaustie lime on the eyanidc solution nor on the in the /aiic boxes, althoujfi it liy some that .in excess will iueteast' the e<)nHum])tion zini in the yanc boxes

J8* the ionsutnption of iainlu soda is more than J pounds per ton of oie it is usually advisable to Oist wasli tlu' ore with watei befoie adding the alkali, d'his is done by eovciingthe oui in the hsieiung vat with watei and allowing It to peieokite through the ore until the soluble acids aie leuiovc'd. The washed oie is then tieaied with a solution of taiustii' soda or lime o( the leituiied strengtli, which is dcLeiinmcd by the amoimt ol mad remaining in the oie

nn' NATION oif' siTieicN<"jTi of r vANion houution kou luoiriovr FXTU v<;TroN

diOni Idat'c I kilograms id oic oi tailings into eai'h ol six leiiehmg Uilis oi eitx'ks, alter mixing the ijuantity of lime ictiuiied Into the lust tub pLu'C A liLeis of a 0, 1-peiecaiL A'i 'A* solution, into the next 1 lilies of a 0 ATWsoliition ; and idac'e I'y.inide solutions in eaeli of the ioiu remaining tubs, having meieascd the stiengthof the solution 0. 1 percent, foi each tub. Let e.uh sample of oie soak bi houis, then preiadate foi hi houis, using the solution over and over again. Test the solution drained fiom eacdi tub for the cyanide coiisuitktI

Next, add 'I liUnsof wash water to each tub to displace the eyanidt' left in the oio, dramoif ami then take sam])lcs of the tailings from each tub foi assay Compai e the extiaetion in each ('ase with tlie amoimt of ('yanidc consumed. The point t( detcimme is the relation of the

N M, J/i—

24 T?IE CYANIDE PROCEvSvS § iil

nicrcasedexUaction to the inci eased consumption of cyanide The propel stieiigtli of cyanide boiuLion Lo select is tlie one that will give the highest exti action in a icasonablc length of tune with the least loss of potassium cyanide

TIMB Foil OOKTAC'l' WITH STllONCJ SOLUTION

50. To make a test foi time of contact between the oie and cyanide solution, take 24 kilomanis oi oie and add the necessary amount of lime, if the oie is acid. Divide the ore into SIX parts of 4 kilograms each Place t kilograms ol oie into each of the six tubs and add to each I litcis of cyanide solution of a stiengUi determined by the preceding pioecss to give the highest economic extraction Let the contents of each tub soak hours, then stait percolation on each tub Continue the percolation on the hist tub JS hoius, the second 30, the third 42, the fourth 54, the fifth and the sixth 78 hours Displace the stung in each tub nt the end of the respective peiiocls lor pei eolation with j liters of a cyanide solution one-fourth the slieiigth ol the original strong solution Let this pass through the mateiial, tlieii wash with 4 liters of watei. Drain and aSvSay the tailings.

The assay will indicate the time beyond which tlu* extraction IS not increased "f/u' time of ext nut ion will depend laricly on the fin cue isS of the gold whet Jur free or tonilnned and the presence of vitcrfering substances,

TBSTB OK XUOC( IPrrATIOJSr

51. To tost weak and stioiig solutions for percentage oi precipitation, the solutions from the previous tests may be taken. In some cases it is difficult to precipitate gold from weak cyanide solutions, This is one oC the weakest points iu zinc precipitation. The cyanide solution containing the gold IS passed through a column of zinc shavings. The tube should be carefully packed with fresh zinc shavings and the solution allowed to pass thiough it slowly If the piec'ipiiation takes place pxopeily, the gold is deposited as a daik,

§:u Tim PROCESS 2r)

('ovcniiii on iht' in the lop of the tulip iind [\ic (l('[)osit on lht' /.iiu IS kss lowaids Uk' bottom If the deposit is on to [3 tuul d.ii k lowai ds t he bottom, the mclications die iinkivoitibl{' lot pusniiildtiou

Take some of lh(' solution that has passed thitjuth the tiilu and assay it foi and silvei C'oinpaie Lius assay with whit the solution eontained oiitmally, and tlie dilfeieiiee will shtnvlhe deiee evil action With jood jnccipi- Lalion, tci h/i pei cent, of tiie is exti acted from the solution

If the piccipitalion is uiisalisiacloiy, jiass the solution thioufii two or Lhi<'(' tubes tilled with /am shaving's, and if It is still unsatisfactory, add potassium cyanide to the solutiond*' Pass the sUcntlumcd solution thioujtli the lilies and dctenninc hy assaying the solution the degiec of precipitation. KsUnmti' the ctuantity of tntassuun cyanide Lic('essary to biing the solution to the jiieeipilatmg point and Llui cost of (he additional potassnmi cyanide, and sec how it eom[>ai{'s with Ihtunxtia cjiuinlityof gold piecipitated, The addition ot ]>oLassium cyanide will jiay in some cases.

Impel feel pieeipitation ('an usually he collected by increasing the length of the /me column or by sliglitly tnei easing the sliength ui the solution with potassium cyanide.

Uoastiko

Ores coulamlng gold m with telUuium and antimony aio hcnciitcd hy a prcliminaiy roasting operation, as the loss oC ('yanidc is Lheieby reduced and the extraction of gold is inei eased,

111 thoCiipplc Cieek distiict, Coloiado, most of the Lelluride ores are found unsuitable foi cyanuling without a ju'e- liminary toast After lasting, a high extraction of gold has ])ccuo])taincd, with a small eousumpLion of cyanide, In bome ]ilaccs, concimtiatcs and pynticores that could not be

StKing 7v7'iV solutions alUfk /ini* and clicinico-eleclru al action between /Jnc ami cUnir-poUbbic-eyanidu solution.

U THE CYANIDE PROCESvS :U

treated ccoaomically in the law state have iiecai sucressfully treated after a dead last Roasting lias the (diet ol diivmg of! the cyamcides m the oie by vohLtiliyaiig stylist aiu es that destroy the cyanogen It seems also to lireak nj) iefiae toiy ore partieles by Ireciiig the gold and to lender the material more peimeable to cyanide solutions

53, After the ore has been tested liy the nudhods described for total extraction and eousuinptuin ol ( yaiiule, il the extiaciion is low, tiy Onei ciiishmg; and il the lesiilt IS still luisatisfactoiy, the difheulty may be cot looted by a roast, as already explained

The Ctanide Plant

54. til l-rodiic* tony. — The cyanide pioeess is varied to adapt it to the dilfcicnt metallmgieal and mcndianual problems that ause in diffeiout localities Tlieic are many matters which may interfcie with the siu'cesslul operation of a cyanide plant, theiefoie it is ini[)Oiative thal the oie fiom a mine be thoroughly tested in the laboratory befoie the erection of a plant Ores usually change with depth, a Cad that should be lemcmbeicd There ai*e oies that lie near the surface which yield up then gold leadily, while those* at certain depths on the same vein cannot tie ticaic'd by the cyanide process,

XiOCATIKG A OTAKIDE I'LAKT

55. Cliarnclei* of ilio Plant. — In selecLiiig the site foi a cyanide plant, the items to be considered arc:

1 Is the plant to tieat tailings as they come from the battery or a stock of accumulated tailings ?

2 , Is the plant to treat raw or roasted oie ?

3 The some of water supply and its sufhciciu'y

4 Method to be adopted for tianspoitmg ore oi tailings to the leaching vats,

IMlb:

;i7

o Mt'thodsof ihr Ic.k hin v.its and iumspoitinj 1 he icUlinu s to I ho diini]>

i>(J, oi (.IfontuL, — ff ihoio is a side

lull in iho ininiedtaU' vudmly wlnnai il has linen decided to i'H'el a plant, the ksu hmo vats and solution tanks maybe so anan[>(s! that the solutions will How by lavitatiou iiom one st*L tanks to the nest ci ushed ore can lie loaded

intodmiipiiyu t'ais and i iin by aviLation to theleachin vals, tind after it has bt'en leached it can he sluiced liom the tanks u[)on the lowei jtiound oi loaded into cais and nm by liivity to tlu' dump

i)'? ol ih riant. — The ap[)lianccs enter-

ing into ilu' (sinsluu'liou of c yaiutlc plants foi the treatment ol oics and tailings ddici both in si?ie and debit:>ii , but th(' jeiHsai involved m all JVIaeAi thur-Foircst eyiUude [ilanls arc' the same. 'Phe object of a cyanide plant IS to iHsil oit' oi tad in containing; silver with a W(*ak solutionkd ('ytinidc of potassium and water, for the [uirposeo! dissolviiti; them aiul then piccijiitaling the gold oi silvcn* fiom tlic solulion in a mclalhc loim,

lUdwccii Pla/ds.—'ro accomplish the objecUs inttnulcd, a c'yanidc plant must have Icachmg vats lor dissolving the gold, zinc boxes or tanks £oi pi ecnpilaluig llu' gold, and sloiagc tanks Jot the ('yanidc solutions The Impoilanl dilicucnu'cs jilaiiLs consist in the matelial, size, and sliajic of leacdiing vats, the methods foi dischaigtng the' tailing.s, and the iclative positions of leaching vats, stoiagc tanks, and jiiie boxes to one anothei.

55). A cmnM'ouiciil of a- Plant. — The most convenient arrangtmiciU joi a cyanide jiLiut is to have the vats in tiers, so that each of vats may be completely chained into the nc'xL liclow it.

By this means suhieient stoiuge room is oliUiined to enable work to proceed fiom 12 to 24 houis without pumping. Many plants have their vats on the same level, which

Till!: CYANIDH PR()(MCHvS

21)

§:h

that lilt' juiiup \)v kc*pl m opuaLinn most of Ihv UiiK', ill it) kc't'p ihc solutKHis in tut illation

I'ho (ijiunSj inlontltMl to illustiLLtc; Lbc tlchijns (>f pKiiils, die UiktMi /join W R lYidlinann's '' Notes (ioltl ICxUlkUoh by Mcsins ol Cyanide ol

In 1, the loa('lnni vats a aic jjhu'ed above the ziiic boxes b and i1k' sloraje lankst The solution jiav- iLates fiom a to the lattei lank, wlinli is virtually the sump tank, aeiiiig in tlu' dual ea])a('ity of slot aye and sump Lank Tlie holul)()ns die sti tniyllionetl in tank and wlien needed pumpeil to tanks n

The sketeii shows that the lis'ieliiny tanks aie lotided with oie fioin eais thid ]>ass over them on tu' if and are unloaded by shoveliny th(' tailinys ovei the side into tram ('UJs Altei load lily, the liameats aie i un to the tailings dump / and disehaiged 'Plus aiiangiuuent makes an mexpeusive plant, as it does <iway witli g( Id-sohttion and sioiago Uuiks; hilt lh(' method of handling the tailings uk leases the cost ol eyaniding

01 . The plant shown in Fig 5 is ai ranged so that the solution passes diieet fiom the Itauduiig vat a into an airtight sump A hioni the sump the solution is pumped up to the ;<ine-preci{)ilaUng boxes, horn whieh it urns by gravity into the sloragi' vats i In the storage' vats it is strengtln onccl for wlu'U wanted in tlie leaching vat a The tailings in this plant arc' disi'htirged thiough a door m the bottom of the vat n into the lais and thence uin to the tailings clum]) not shown m the figure, The pipe from the pump to the /due boxes is shown by the dotted lines / and the pipes iimn the vauous tanks by ///? The leaching lank IS centrally eliurgc'd with oic by the cai o

an. The plant shown in Fig, fJ is a combination of the plants shown in , I and 2. The leac'hing vat is centrally loaded witli <ne by tram (Xir b and the tailings are loaded into ears i through doois m the sides of the vats. The solution uins fiom the stoiagc tank Y into the leaching

30 The Cyanide Process § :>1

vat a, from the latter lank it luns by gravity to precipitating boxes and fiom e' it luns into the sump tank i*. The clotted lines in the figuie show the pipelines fioin the pump t to the stoiage tank, and fiom the storage tank to the various vatb The boiler k is shown to be under the same covet ae the precipitation and sump tanks, which is a good arrangement, since no one can get into the zinc boxes without the knowledge of the engineer

63. Fig ? {a) shows the plan and Fig 7 (d) the crosssection of a cyanide plant designed to treat 75 tons of oie a day The weak-soliilion storage tank cr' and the strongsolution storage tank a are each located on an elevation aboAe the leaching tanks /? The strong-solution storage tank is connected with the leaching vats at the bottom and top by pipe c Pipe c' connects the weak-solutioii stoiage tank with the leaching vats Over the leaching vats is a water pipe d for sluicing out the tailings The leaching vats b are on a level above the weak gold-solution tank and strong gold-solution tank h The pipe c is connected with the leaching vats b and the vacuum pump The solution passes from the vacuum pump to the Aveak goldsolution tank h' and the strong gold-solution tank h through the vacuum discharge pipe u In ordinary leaching, Avhere the vacuum pump is not used, the solution from the leaching vats b IS passed through the valves .v into weak goldsolution launder d' or the strong gold-solution laundei Y, depending on the strength oi the cyanide solution The weak gold-solution tank h' and the strong gold-solution tank h are connected, respectively, Avitli the precipitating boxes k' and k The solution passes thioiigh the piecipitatmg boxes into the Aveak-solution sump V or the strongsolution sump / The solutions from the sump are pumped to their respective storage tanks by the centrifugal pump w. The solution is standardized in the strong storage tank by adding the required amount of potassium cyanide The solution in the Aveak-solution storage tank is used as a wash to follow the application of the strong solution.

TTIE CYANIDE PROCESvS 31

The piecipitated gold and silvei is washed fiom the precipitating boxes k info a side launder communiLating with the launder thus allowing the piecipitate to pass into a movable laundei in and hence into the ac id tank o The piecipitate, aftei treatment with dilute sulphtinc acid, is thoroughly washed and partially dued by suction from the vacuum pump .v through tlie pipe J The piecipitate is washed in the acid tank o and the watci decanted into the setthno tank p Any precipitate floating m the watei settles to the bottom of the tank and is collected and put with the precipitate on the filLei box ;

04, Capueity of a Plant. — The capacity of a plant depends on the niunbei and size of leaching vats employed and the time required to ticat the oie The capacity of each tank should be either the same or one-half or one-third the daily capacity of the mill The mimbei of leaching vats will be Gilhei the same, twice, oi thiee tunes the numbei of days requiiecl to fill, leach, and empty a vat If a plant is dcbignecl for a 4-clay tieatment m foui leaching vats of 75 tons each, the daily capacity would be consiclerecl To tons If the leaching vats should take days on some ores, the plant would not have a daily capacity of 75 tons The capacity could be increased to this amount by adding 2 more leaclung vats, each of 75 tons capacity The remaining part of the plant would be the same as described in the specifications foi a T5-ton ])lant

The equipment and operation ol a cyanide plant, using a T5-ton plant as a model, will be illustiatecl and discussed

G5. Spcoiflealloiis lor a 75-Tou CyanLclxngi' Plant The following appliances will equip a plant foi a daily capacity of 75 tons, with 4 days' treatment in the leaching vats It IS assumed that there are good facilities foi charging the vats and dischaigmg the tailings

S sloiage tanks (foi strong and weak solutions), 13 ft diameter X 10 ft deep

4 leaching tanks, 24 ft diamctei X 5 it deep, capacity 75 tons 2 gold tanks (foi sti ong and weak sohitioas), 13 ft diametei X 5 ft deep.

The Cyanide Process

y

o

tJ s §2

5

CJl

s

2 for strong and

2 for weak solutions

3 for strong and

2 for weak solutions

4 for strong and

S foi weak solutions

s s £

B

o "d TCJ

K

rO +j 4-

t— 1

B

'-'f N

Hh Hh

0 lA

iH

d XJ xJ

N

01 lO

tH

d X X

IS; fSI

rO +J -u '-'J t4 m

/I

ja!

1

U 0 o

S y Ij

d 73 o

'O

o

8 Ok

to

j/j +j +j

Vt M-l

00 lO

Size,

10 ft diam

5 ft deep

8 pk

r/j 40 +j

H-l 4H

CM 10 tH

i S-

0) X X

N

4:; 4::

Co (A

iH

Ji

S

s) id

15

. 8 s

Cd T? Xj

N

2 4'

8 .So

(U Xj Xj

N

S

oT xs X3

M

8

to M

r /3 4-> +J

M-J Mh

Cq -4

rJ M

S B

(5 t-l TO

M ° e

1 i S

0 Co 03

o

8

. Ss S

Co

tH

Size,

IS ft diam

10 ft deep

id 0

(U X X

N

S3 ffl

' T— 1 1— i

Daily Capacity of Plant in Tons

lO

§

§ 31 The Cyanide Process 33

2 sump tanks (f 01 stionpr and weak solutions), 12 £t diameter X deep

1 acid tank, 0 tt diametei X ft deep, toi the i eduction of the zincold shmes

5 sets of zinc boxes, 9 m each set, 3 sets foi strong solutions, 2 sets foi \yeak solutions, making; 45 boxes 12 la high X 15 m long X 21 in wide, consti acted ot No 13 steel oi of wood 10 screens, No 18 wiie, 8 mesh

45 screens for zinc boxes, 15 in X 24 in , No 12 wiie, 4 mesh 45 SCI een frames foi zinc boxes 1 lathe with countci shaft, foi cutting zinc shavings 1 low-service duplex piston pump (all non), to pump solution, size G in X in X b m r

1 4' X 10' receiver oi vacuum chamber, foi exhausting moisture at atmosphei 1 C piessuie with Siiich pop safety \alve and vacuum gauge and fittings

1 C' X 8" X 12" vacuum pump W I piping, valves, and fittings for solutions, watei , and an, also steam pipes foi pumps Iionwork foi muffle fuinacc, including 3 non pans, 24 in x 24 m and 3 m deep Iionwoik foi IB-inch bullion fiiinace, 3 bullion molds, each to hold contents of No 125 plumbago crucible

6(). Spoeiflcatioiis for Plants of DiiTerent Capacities. By lefenmg to Tabic III, a genet al idea can be obtained of the size of leaching vals, solution tanks, precipitating boxes, and sumps, m plants of difieient capacities The general arrangement of smallei and laigei plants would be the same as in the 75-ion plant desenbed m Art G3, and illustrated by Fig 7 (a) and

Bjstails Ojt Cotstruction

67. Construction of Tats. — Any material that will make a water-tight vat may be used in its const: action Up to the present tune, brick and cement, wood and cement, concrete, wood, and steel have been used Where suitable ground can be found, cisterns lined with stone and cement or brick and cement, and having then mouths level with the surface of the ground, make seiviceable vats At the Langlaagtfe Estate of the Transvaal, in South Africa, circular brick vats 10 feet deep and 40 feet m diameter and having a capacity of about 400 tons are constructed. For

The Tyanide Process

small cyaniding plants, wooden oi steel vats arc belter suited to meet the i equireinents than the large vats mentioned The Pelatan-Cleiici, the Kendall, and the Pneumatic cyanide processes use small vats having a capacity of from 1 to 5 tons, as they are able to treat oie in from 12 to 18 houis The Pelatan-Clenci people use a wooden vat lined with cement Masoniy vats lined with cement are necessarily below giound, and in case they leak, the fact cannot be readily discovered, they ai'e thei'cfoie not to be piefeired, although they are in use at some large plants Wooden vats lined with cement will leak in case the cement is broken, but as they are above ground the leak can be detected and the lining repaired

68. Caliiornia redwood, cypress, cedar, and white pme are trees that make suitable tank lumber The timber trees mentioned have soft and compiessible fibres, well adapted to the tight joints necessary in cyanide tanks Wood used in vat construction should absorb and retain a certain amount of moisture, otherwise the vats will leak It is sometimes customary to coat wooden tanks with asphalt oi paraffin paint to prevent then leaking and absorbing the gold solution Wry little leakage will occur when a well-constructed and set-up tank is soaked, but should the tank be alternately wet and dry, it will leak Wooden tanks are purchased from dealers in the knock-down " form for transportation Each stave IS numbered, so that any intelligent carpenter can put the parts togethei

Wooden leaclimg* vats for cyaniding usually vary in size from 20 feet to 40 feet m diameter and from 3 feet to 0.5 feet in depth The staves shown in Fig S are about 4 inches wide by 2 5 inches thick, with a slight upward taper, so that the diametei of the vat at the top is about 4 inches less than it is at the bottom, The bottom b IS made at least 3 inches thick and of the same kind of wood as the staves The bottom pieces aie fitted to each other by dowel-pins They are then fitted into a groove cut in the staves near their lower ends, so as to leave a chime of

§31

The Cyanide Process

as

6 iiiLlieb The staves ai-e held m place by steel hoops No white lead or any packing should be used in making these vats, since if the faces of the lumber used are true, no amount of white lead can make them tiuer, and li they are

FlO 8

not true, no amount of white lead or any othei kind of packing will secure tightness The cyanide solution, being alkaline, will unite with the oil of the white lead and remove it, which Avould make the vat leak worse than if no white lead had been used

70. The liooiis used for vats are made of iron oi steel inch thick and 3 inches wide These bands ai e provided with a lug at one end for the reception of a bolt made at the other end The band is drawn tight by a nut working on the bolt and leenfoiced by the lug. The hoops are sometimes

The Cyanide Process

constructed of 'inch round iron, as shown at r, and fastened in place the same as the flat hoops In Fig 8 is the

side of the vat shown, b is the bottom of the vat, showing it to be drawn taut by countersunk bolt t and nut n For the purpose of making a tight connection with the filter, the wooden rings and t aie made around the inside of the tub In the space marked g, the filtei cloth is fastened by calking It in tight with hemp packing

Steel leaclilng vats are constructed in sections, so that they may be better transported In Fig 9 [a) is

shown a steel vat 20 feet in diameter and 1 feet deep The figure IS divided by the line a b, in order to illustrate both the exterior and mteiior The side r and bottom d of the vat aie of f%-inch steel plate, riveted to X V angleiron rings e The angle-iron rings are placed in the

The Cyanide Process

§ 31

positions shown, in oidei to stiffen the stcel-platc side A ling of iron r, bettei shown tn Fig 9 (/;), is iiveted to the lower angle ling m such a manner as to foim a lest for the filtei and allow the hltei covering to be fastened into the space .y by rope packing

72. CoaistTiietion of Filteis. — false bottom, such as IS shown ill Fig 10, is constructed foi the purpose of supporting a alter upon which the oie and tailings rest In Fig to, the wooden strips a, inches thick by 3 inches high,

aie ananged parallel across the floor of the vat and about 0 inches apait That side of the strip which rests on the bottom of the vat is notched at b to afford a fiee circulation to the liquids The ends of the slats are brought to the iron nng r, which ns 1 inch smallei m diametei than the tank On these strips a other strips d are nailed transveisely The strips t/, which are 1 inch square, are nailed t inch apart across the tank, to act as a support for the filter cloth f The filler flame in large vats is made in sections The sections when fitted togethei form a circular frame The space c between the filter frame and the vat permits the filter cloth to be firmly calked in its place by means of a rope passing around the inside cii ciimference of the vat and between it and the nng c. In vats with a bottom dischaige gate, the bottom can be arranged with an incline towards its dischaige gate

73 . Gravel Miter. — In Fig 11 is shown the construction of a gravel filtei These filters are used in some places wheie the tailings are shoveled fiom the tank In modern practice, the old gravel filtei has given place to latticework

The Cyanide Process

§31

and cIoLhfilteis in oidei td save time The sand hlLci consists of a oi wooden slats a lestnig on the tank bottom If On tlie slats, tiiaugulai wooden pieces aie nailed The wooden pieces c aie about B inches high and aie so nailed that theie will be l-ich spaces between them In the V-shaped space thus foimed, a 1-inch layer of coarse gravel cf is placed, above this is placed a 1-uich layer of hue giavel r, and on top a layei of sand/'

ra.)

Fig 13

lUniva Rilten — In Fig 1 2 (c?) IS shown the section of a perforated boat cl filtei which rests on grooved wooden slats d A portion oC the plan of this filter bottom IS shown in Fig 12 (I?) The perforated boards a arc covered with a filled cloth Cj fastened in place by a calking 1 ope The filtei cloth IS removed m Fig 12 (/;) in order to show the perforated boards

75. Filter Clotlis. — The slats or perforated boai ds of filter floors are covered with cocoa matting or the heaviest grade of hop cloth, the latter being the cheaper

§ 31 The Cyanide Process 39

This cloth lb tacked on the stave ends of the slats The covering lor this cloth filter is 8-ounce canvas and is made 12 inches greatei in diametei than the false bottom The edges of the lilter covering ate fastened in place by pressing a 1-inch lope into the space between the side ot the vat and the ling piece, as shown m Fig 12 (a) This ariangenient is veiy efficient in pi eventing the sand from washing undei the filtei

76* Wi'ou*lit-Iron Solution Pipes. — Each leaching vat has separate drain pipes for sting and weak solutions The pipe a, shown in Fig J3, is ananged to lead to the

strong"Solution gold tank and the pipe b is arranged to lead to the weak-soluiion gold tank These pipes are connected with the exhaust cylinder of a vacuum pump that is used to produce a partial vacuum under the filter bottom, in order to increase the i ate of percolation

77 . Eniiudeivs. — The wroiighi-iron solution pipes are arranged m Fig 14, with valves a and so that the vacuum pipe c may dram through the pipe leading to the laundei The laundei is divided into tivo sections and each 4 inches wide and 4 inches deep The section a is tor the weak gold solution and the section d is for the strong gold solution The valve a has a short rubber hose k attached.

jY M 111—8

40 The Cyanide Process § Ol

so that the solution can be dischai'ged into cither section of the launder as desired.

Fig IB

the cost of labor and others on the supply of water at command At some plants the tailings aie shoveled thiough gates m the bottom of the tank into dump cars Where

g31

THE CYANIDE PROCEvSS

il

there isgood watei piessuie, sluicing out the residue is found to be cheap and quick When the tailings contain coaise gold, the residues are sluiced slowly over amalgamated copper plates placed below the discharge hole

When large brick leaching tanks are used, they are sometimes unloaded with the aid of traveling cranes, which lower Ciiiply car bodies into the tanks, wheie men shovel tailings into them When the car bodies aie filled, they aie raised, placed on their trucks, and wheeled away to the dump

79* Dlisehax'e Doors. — In the case of bottom discharging, there may be from H to 8 openings, depending on the size of the vat In Fig 16, Buitei's bottom chschaige IS illustrated by a vertical cross-section In the figiue, a leprcsents the tank floor, /; a cast-iron ring that acts as a washed for the cast-iron cylindei r inside the lank, and a seat for the valve h The

ling b and the cylinder c arc bolted together so as to draw them tight against the lank bottom a There is a lug d inside the cyhnclei for the hanger to lest upon Thehangei at its lowei end is piovidecl with a screw thread/, upon which the butterfly nut woiks in order to tighten and hold in position the cast-iron valve It The faces of the cover h and ring b should be planed perfectly smooth so as to make a tight joint

80 . Bottom Discharg-e. — A simple foim of bottom-dischaige valve is that shown in Fig 16 It consists of a deep-flanged non collar which is placed in a hole in the bottom of the vat and fastened to the vat floor by bolts passing through the flange and floor The discharge valve b is operated from the top of the tank The valve seats on a rubber ring and is lifted by a screw at r, to leave a clear opening for flushing out the tank The opening should be about 10 inches in diameter.

the cyanide process

§31

81. The siile-clibelmre tloor ib shown lu Fig 17 It

consists of an iion fiame which is bolted to the side of the tank near the bottom This fiame supports a hinged irondooi h, A rubber gasket IS placed between the frame and the door to toi nr a watertight joint The loot when closed lb held in place hy a cross-bar c and the hand wheel and screw d The size of the opening in this door is 10 inches X 10 inches

82. Goia-Holutioii Tallies.— There aie two gold-solution tanks, which should be placed low enough to receive the solution from the peicolating tanks above and high enough to discharge by giavitation into the zinc boxes The tanks act as seitleis for solutions containing impiuities m suspension that would hiteifeie with the precipitation of the gold, if allowed to pass into the zinc boxes

83. Coiistriietioii of 55iiie 35oxes — Zinc precipitating boxes are usually divided into compartments having double partitions In Fig IS is shown an elevation, inFig 18 (d) a plan , and m Fig 1 8 (r) a cioss-section of a zinc precipitation box, The first partitions does not leach to the bottom of the box the next partition c does not reach quite to the top of the box, and so on, to permit the solution to enter each chamber from below and pass upwards through the peifoi'ated bottom d, which supports the zinc shavings The overflow from one box to the next occurs at the upper part of partition c

This arrangement for upward flow permits a free flow of solution, and the gold being deposited largely at the bottom of the box falls off, leaving the passage cleai for the solution The gold and zme slimes as they form pass through the false bottom d into the compartment below

Fro IV

44 THE CYANIDE PROCEvSS § Si

In the more recent zinc boxes a permanent discharge launder h, shown in Fig\ 18 (r), is fastened to the side of the box The box in this case is provided with an mclined bottom, to facilitate the removal of the slimes Each compartment also has a 1-aich discharge hole k neai the bottom, which, when not in use, is plugged with a rubber stopped

84* Detailed Armiiement of ZLiic Boxes. — When wooden piecipitatmg boxes aie caiefnlly constructed and put togethei , there is no danger of leakage They should be made of selected planks inches thick, tongued and giooved and fastened together with screws and bolts The pipe connections for zinc boxes are made with nipples and locknuts

The launder h, Pig 18 (r), on the side of the precipitating box should have a tight-fittmg hd that may be locked, to prevent the gold precipitates which it contains fiom being stolen The baffle boards a and c are made of l-|-inch plank The strapping plates m are made of X Y suitable holes iieai each end for -J-mch bolts The bolts are passed from plate to plate between the baffle boards, as shown m Fig IB

85. Size of Zinc Boxes. — ZinC boxes aie usually constructed of wood, and although iron is coming into use, it is claimed by some that the galvanic action between the zme and iron decomposes the potassium cyanide There is undoubtedly an action of this kind between iron and zme, but its importance has probably been exaggerated. At the Utica Works, Angel's Camp, California, iron precipitating boxes were used, and it is claimed there was no increased loss of cyanide Iron precipitating boxes have the advantage of being easily made water-tight, and as they can be coated with paraffin pamt occasionally, the galvanic action should be much lessened Zme compact meats in a precipitating box are usually 24 inches wide, 12 inches high, and 15 inches long The space left between baffie boards for the flow of the solution is about 3 inches

§31

The Cyanide Process

In a 75-ton plant, thiee precipitating boxes of nine zinc compartments each aie iibcdfor the sttong sokitioii, and two boxes ot the same size ate required for the weak solution A box IS feet long should have an inclination of 4 inches The object in using several boxes is to have a better distribution and siowei movement of the solution through the boxes to insure a better precipitation Another advantage is that the flow of solution need not be interrupted when one ot the boxes is being cleaned

8G* In Fig 19 IS an illustiation of precipitating boxes with the side launders a connected with an oidmary laundel b that leads to the acid tank below the floor The

cyanide solution after leaving the boxes d passes into a launder e and then through the trough c to the sump below the floor

87 # Protective Paints. — The outside and inside of solution vats should be protected Avith some kind of waterproof paint, such as asphalt, tar, or paraffin, m ordei to protect the timbers This paint is also used to cover the interior of vats made of galvanized iron.

§31

The Cyanide Process

VAC larivi SX.IMT5

88. 'Wasliing Slimes. — (xold slimcb are washed befoie refining in oidei to obtain as pure metal as possible The vacuum slim filter used foi washing slimes is an air-tight steel tank, as shoAvn m Fig 20 (fif) and (I?) The tank is 30 inches in diameter and 30 inches high, with the interior divided into two compai tments a and d by a filter bottom which IS about 12 inches from the top The filter bottom is made of wood inches thick, pciforatcd with j-mch holes IJ inches apart, and is suppoitcd by an non center post d and bais r The peifoiated false bottom is covered with a piece of wiie cloth a' having about 15 meshes to the inch On the wue screen is placed a heavy mill blanket m of one oi more thicknesses, as the case may retpure When slimes aie to be filtered, theie is a suction created below the filtei by a vacuum pump, which is connected with the filtei by a pipe flange at / and a pipe not shown m the figure This arrangement hastens the filtering In the lower iight-hancl corner of the filtei anothei pipe flange is shown This connects with a waste pipe and chains the solution which passes the filter out of compartment as that solution must not be allowed to rise high enough to entei the vacuum pipe p This height of solution in chamber b is shown by the watei gauge to the left of the filter tank.

The Cyanide Process

(Part S)

Practical Opjiirattons

ClIAJlGXlQ TJIE VATS

1 , The method used to chaise peicoiatiug vaLs with oie will depend on whether the ore is crushed dry oi wet. Diy 01 wet oie may be chaiged into the vats from iron cars that run upon trestles directly ovei the vats In such cases the ore must be leveled in the vat by hand, foi it is necessaiy to have an even surface for piopei lixiviation Large vats aie sometimes filled by biicketSj which aie moved in vaiious positions over the vat and dumped The buckets in this case either lun on trolleys oi are moved from place to place by the arm of a tiavelmg cane If the ore is dry, considerable dust is raised by the operation A thud method for chaigmg lixiviation vats is to connect them with the ore bin by means of a chute A canvas pipe connected with the chute allows the vat to be charged evenly This method is cheap, raises little dust, and permits an even distribution of ore about the vat

Vats Wltli Tailings. — The most sihcious ores when crushed wet will produce some slimes, and when clayey or earthy matter, iron or manganese oxides are contained in the oie, the quantity of slimes is increased

Slimes, which are sometimes the most valuable part of the ore, interfere with pei eolation in two ways If the slimes

Foi notice of copy ij'lifc, see papfc immeclmteU following* the title pag-e

§ 32 The Cyanide Process 3

die inegularly dibiribiited in the vat, channels thiougli which the cyanide will circulate without leaching all Iheuie will be formed and imperfect leaching wiH insult On the other hand, if they are in appicciable quantity and evenly distiibuted, they will retard drainage For the above causes the slimes produced by stamp milling and amalgamation aie separated as much as possible fiom the sands and lieated separately The tailings fiom a wet-crushmg stamp batteiy are conveyed to spitzlutten, wheie they aie classified into sands and shmes and concentrates containing some sands There aie two methods employed for disposing oi the fine slimes, known as the mtennedtate and direct methods of chaiging the vats

3. Tntcrmocliate Charging'. — By the method of intermediate filling, the fine slimes ate washed from the sands into a senes of intei mediate settling tanks To secure an even distribution of slimes and tailings, an automatic distributor IS placed ui the Centex of the vat on an non column j shown m Fig I [a) which is an elevation of the distnbutoi There is a hopper b on top of the distnbutoi, fiom which twelve or sixteen non pipes r, with the bent ends shown in the plan, Fig 1 (i), radiate The non pipes with the flat nozzles arc fiom to 21 inches in diametei, and as the stieain of shines and tailings issue fiom them, the escape causes the hopper and pipes to i evolve slowly The screen Y is placed ovei the hopper b to prevent lumps from passing into the pipe aims and stopping them up

The collecting vat is filled with watei befoie admitLing the pulp The water flows over the side ol the vat as the pulp enters, carrying with it the finest slimes The launder X receives the watei and shines of the overflow and conveys them to the slime pit

The settling vats contain filters, through which the water drams off, and when the oie becomes sufficiently dry it is discharged into the leaching vats through bottom clischai gc doors or it is loaded into cais and hauled to the leaching vats

The Cyanide Process

3

4. Iiitei-mediate Taiilcb.— The achantaoes of luLcrraecliate settling tanks aic that the sands aie collected and the slimes removed Again, when the intcimediate tanks are discharged, the sands become thoroughly mixed Pyi itcs aie oxidized very slightly, if at all, by this operation, congeqiiently, the cyanide consumption is low, the extraction high, and the cost of tieatment model ate

5. THi-eci Changing —This process consists m passing the pulp flora the amalgamating plates into a classi&ei The pulp IS divided into two sti earns The oveiflow stieain caiiies slimes and very fine sands to the slime pit, Avliere they aie stored for future treatment The oLhei stieam, containing mostly coarse sands with some fine sand and slimes, IS Gained to the leaching vat by a hose, winch is moved about to give an even distribution The excess of watei passes off through discharge gales fitted inside the vat

The advantages claimed for direct filling are that theie is piactically no oxidation of the pyrites m the tailings and that the tailings aie handled but once, besides, the slimes are separated by the rough preliininary classification

Some of the disadvantages of this method aie that the tailings pack, and then it is very difficult to remove the Avater; also that the tailings are unevenly distributed, thus favoung the foimation of channels during the subsequent leaching In some mills the water is drawn off through the filter bottom and the tailings are turned over by hand, so as to loosen and thoroughly mix them.

The Lixiviating Process

ORE 'WASTIIlSrO ATXD TIlFATMEUrT AVITR ALKAEI 6. Prellmlnai'y Washing —When oies or tailings contain sulphates, a preliminary treatment is necessary before percolation with a cyanide solution Whenever pyritic ore is kiln-dned previous to dry crushing, soluble sulphates are formed that are destructive to cyanide The

§ The Cyanide Process 5

producLs of the partial oxidation of iron pyiites are free salphuncacid and soluble bulphates Oies that contain acids and salts soluble in water are m general practice washed with water by pei eolation and the reniaiiiing acids neutialized by applying weak solutions of caustic soda that are allowed to lemain in contact with the ore several hours When a neutralizing solution is diawn oE, a standaid cyanide solution IS run on If the oie does not require more than '3 pounds of caustic soda to the ton to neutralize the acids and salts, the preliminary washing is omitted and theoie is tieated directly with unslaked lime The powdered lime is added to the ore as it is placed in the vat

LEAClIlNn WITH THE IHRST OXAOTDE SOLUTION

7. Tire Weak Solution. — The pi oper strength of the zveak solution should be such that all cyanic ides vill be exhausted The weak solution is taken from the weak-solution tank and run into the leaching vats underneath the filter. Experiments have shown that solutions will permeate the ore sooner and make fewer channels when introduced from below than when introduced on top of the ore The solution is allowed to pass upwards until it uses 2 or 3 inches above the ore m the tank, when it is allowed to remain in contact with the ore 2 or 3 liouis Percolation is then commenced, the liquor being drawn off into the weak-golclsolution tanks It is not always customary to use a weak solution first, but to run on the standard or strong solution as soon as the alkali wash water has been dialed off and then use a weak wash solution oi merely a wash, Undei ordinal y circumstances, it will require about 1 hour to charge a 75-ton vat with solution, and without suction it may not dram over 3 or 4 niches pei hour

liBACIIIISra VITH THE SECOOT) CYANIDE SOD0TTON The Strong Solution. — The time required for percolating with the strong or second cyanide solution is determined m each case by laboi atory tests. The liquor is allowed

G The Cyanide Process § 32

to enter the vat below the filtci and rise upwards tliiough the ore Percolation is commenced after several horns and continued until the solution coming from the vat reaches within 02 or 03 pei cent of the strength of the original cyanide solution.

Ill case the solution coming fiom the vat is less than onehalf the standard solution, it is run into the weak-golclsolution tank, but if it is more than oncdialf the stiength of the standard solution, it should be urn into the strongsolution tank

At the vStandard Woiks in Bodie, California, the oie is soaked 20 hums in the strong solution At the Mercur mill in Utah a series of strong solutions aie used and each time the solution is drained off before the fiesh is added This practice gives higher exti action than continuous leaching on this ore. In other mills, a solution is added to covci the tailings ui the vat seveial inches, then the solution is allowed to disappeai below the surface of the oie for an hour, when mote solution is added to cover the oic in the vat A succession of changes of this description is continued iinld the time allotted for leaching has been exhausted By this method of partially draining the vat at intervals, air is brought m contact with the material and the solution of gold is hastened.

9, Strong' Solution Hisfilacecl hy Cafe.™ The vStiuiig solution IS completely drained oft aftei the point of economic extraction has been leached In a new plant, watei is used to displace the strong solution until enough weak solution has accumulated When water is used, it may continue flowing thiough the percolating vat until the outflowing solutions indicate only 03 or 04 per cent of cyanide , this solution would not contain more than 30 to 50 cents with of gold per ton of solution After sufficient weak solution has accumulated, it is used to displace the strong The strength of the tweak solution is about onc-third that of the standard strong solution

The weak solution is usually di awn off as i apidly as possible, and the faster the solution comes off, the more efficient

§3? THE CYANIDE PROCEvSS 7

IS the washing The vacuum pump is oUcu used to facilitate the duunage, and the pei eolation is continued until the outgoing solution is of the same stienglh m cyanide as the solution when it eiiteis the peicolating vat

10 , WeaR Solution Displaced Willi Water— Water IS added to displace the cyanide solution lemaming in the ore As little watei should he used for this purpose as possible, in oidei to pi event the accumulation of huge quantities of the weak solution Weak solutions accumulate on account of the moistiue pieseiit m the ore fiom the wash water and fiom solutions that have passed thiotigh the 2 me boxes The excess of weak solution is disposed of by lunning It to waste

There can be no fixed lule for the exact amount of weak solution and water requiied to give the best lesults A careful study of all the operations is requiied and the effect of different washings deteimmed by careful assays of the residues and the wash solutions as they leave the vats These should contain no precious metal that it is possible to remove

HAiviPraxG TTip incvtiiKj> TAinmcfs

11 . A sample of the residues m the vat is taken with a 5-foot auger uitioduced W or 30 times through the charge at diffeient places iil the leaching vat The auger is carefully pulled out of the matciial, and brings with it cores of tailings, which aie collected in a bucket This sample is dried, qu altered, and assayed

13. Testing 8oliitiou for Cyanide. — The silVer-nitrate test IS used to deteimine when the cyanide is sufficiently washed out of the leached oie If a strong solution containing ,2 per cent cyanide and a gold value of about $-1 per ton is cliluLed with the displacing liquids, so that it contains 04 pel cent cyanide, its gold value havS been reduced in the same propoition It is clear, then, that the limit of the final displacement will depend on the cost of tieatment, and this must be deteimmed in each case by a series of tests

N M. Ill—sg

8 The Cyanide Process § 32

13 , Dlfecliargiug tlie Tat.— If the tailings are to be shoveled from the vat, the wash watei is dialed off until the tailings are dry enough foi shoveling If they aie to be sluiced out, the wash watei is drained off foi sampling The tailings are then covered with water, and aftei standing a short tune the plugs aie drawn and the residues sluiced out

14:, Stanclai' Sump Solutions. — The cyanide solution after having passed through the various stages m the process and i cached the sump has detenoiated in strength The solution is therefore titrated with standaid silver nitrate and the amount of cyanide it contains is determined, after which sufficient potassium cyanide is added to bring it to the standard strength The solution m the sump may be raised to normal strength by placing the required amount of cyanide in the last compartment of the zinc box or by placing it m a perforated tiay attached to a rope so that it can be immersed m the sump At some woiks a strong solution is kept in a tank and is drawn off into the storage tanks to raise the solution to standard sti ength

When pine potassium cyanide (i e , 98 to 99 per cent ICCN) IS used to strengthen the sump solution, it may be placed in a box with perforated sides and bottom and this box held under the discharge where the solution coming from the sump enters the storage tanks When adulterated potassium cyanide IS used, It should be dissolved in a small tank and the solution filtered as it enters the storage tanks, for the i cason that low-grade KCN contains a number of impurities that are insoluble

15 . To Standaiulize a Solution wltli Cyanide, — Storage tanks should be provided with a float that will register the depth of the solution within The number of pounds of cyanide to make 1 foot of standard solution in the tank should he calculated For example, a circular tank i2 feet in diameter would contain neatly tons of solution for each vertical foot If the standard solution contains 02 per

See Table HI.

§33

The Cyanide Process

cent of cyanide, each ton will contain 4 pounds, and 3- tons, or 1 foot ot solution, will contain 1 4 pounds

16 . Foriiiiila Jtbi* Stanclai'diziiig Soliitioiife* — Having determined the atienglh and quantity ut cyanide solution m the storage tank, the cyanide needed may be calculated from the formula

A'= [j - X 0] X D

In the above foimula,

A number of pounds of KCN m a solution whose bulk is the area of any tank multiplied by 1 foot ,

B percentage of KCN in any sump solution,

C percentage of KCN m any standard solution,

D numbei of cubic feet ot sump solution to be standai dized , X numbei of pounds of KCN to be added to the sump solution

Example —Suppose a sump, 12 feet in diameter, contains a 21-percent cyanide solution that measiiies feet in depth How much KCN must be added to bung the boUition up to the standard stienglli of 25 pei cent

Solution —Fust find the numbei of gallons in 1 foot of the tank, thus, 12 X 1 X 5 875 gallons This piocUict multiplied by will give 7,050 pounds of watei in 1 foot of the tank, and A V,O50 X 25%' KCN — 17 025 pounds ot KCN in 1 foot of solution Substituting these values m the above equation, the quantity of potassium cyanide to be added is found as follows

117 035 - 17 036 X J X 3 5 7 05 lb Ans

CimmSTEY OF ZINC PKECiriTATION

17 . Zinc SliaTings. — Zinc shavings in filiform oi threadlike turnings have been almost uni vei sally adopted for the precipitation of gold and silver from KCN solutions containing those metals The shavings should be fiee from arsenic or antimony A little lead in their composition is an advantage, as il promotes rapid precipitation by forming a voltaic

The Cyanide Process

couple with the zinc In usual practice, 1 cubic foot of zinc shaMngb will piecipitdte the gold from 2 tons of cyanide bolution Zinc sheets, amalgam, dust, and fumes have been tried, but zinc shaviugb seem to have the picfcieuce, because of the ease with which cyanide solutions attack them They also allow the free and lapid passage of the cyanide solution, and besides the screens thiough which the gold piecipitate falls aic not clogged by the zinc The action of the zinc on the gold solution is a simple substitution of gold for zinc, accoiding to the equation,

aunc-potassic cyanide zinc zinc-polassic cyanide gold

According to theory, 1 pound of zinc should piecipitate about G pounds of gold, in practice, however, it requires from i to 1 pound of zme for every ounce of gold piec ipitaled The double salt of auric-potas&ic cyanide is one of the most stable of gold salts, but its decomposition by zinc is piactically complete The piecipitated gold is not redissolvcd by potassium cyanide so long as there is zinc piesent The potassium-ziiic cyanide remains in the solution that passes to the sump tanks

18* Preparation of Zine Shavings. — Zinc shavings are usually cut fioin a cylindei composed of zinc disks Sheet zme of No f) Brown & Shaipe gauge, oi 111 inch thick, is generally used for this purpose Disks 12 inches in diameter, with an inch hole in the center, may be obtained fiom mill-supply houses They weigh about I pound each

The lathe on which these filaments are cut is veiy simple in construction, as is shown ui Fig 2 It consists of a mandrel thi ended on both ends and supplied with cast-iron disks and nuts In practice, twenty zinc disks are placed between the cast-iron washers a and aie held tight by a nut d The disks are placed in motion and thin shavings cut from their penphenes by means of any sharp steel tool steadied on an iron lest c The mandiel is given a speed of 350 revolutions a minute The zinc is thus shaved olf m fine threads, Guards, shown at prevent the shavings

§ THE CYAJSllDE PROCESS 11

gfetling under the belt of the machine Zmc shavings as ordinarily packed in a zinc piecipitating box weigh about

(J pounds pel cubic foot and should be thin enough to bum when lighted with a match

19 . billing tlxe Zinc Boxes* — Zmc shavings are placed in all the compai tments of the zinc box except the last one, which is left empty to collect any pai tides of zinc and gold that may be earned from the otheis The zmc shavings should be uniformly distnbuted and the coiners of each compartment well packed to pi event the solution passing through in channels The speed with which the solution should flow thiough the boxCvS can be determined by tests on the outflowing solution £oi the presence of gold

Where gold precipitation takes place undei pioper conditions, the metalhc deposit on the zinc is brownish black and precipitation should take place in the first compartments In impel feet precipitation, the deposit is frequently gray oi of a dull metallic color The dry piecipitate seldom contains more than 10 or 50 percent of gold and silvei, the remainder being finely divided zinc and its nnpuiitics The precipitation in the zinc boxes is influenced by the amount

THE CYANIDE PROCEvSS §32

of cyanide piesent in the solution, as there seems to be a selective action between the zmc and metals piesent It has been found that dissolved copper is pi ecipitated faster fiom a weak cyanide solution than fiom a strong one To oveicume this, a strong cyanide solution may be alloAved to diop into the first compartment of the zmc box fast enough to bring the solution to standard strength

30. Pre'enee of Copper —When copper is pi esent in the gold solution, it covers the zinc with a bright metallic copper covering This copper deposit is observed in the lower compartments fiist, from which it gradually works towards the first compartment The precipitation of the gold is very slow when the zmc is coated with coppei As previously stated, the copper may be laigely kept m solution by increasing the strength of the cyanide solution before it enters the zinc boxes

21 . Px'eTenting' Copper Deposits in Precipitation. To prevent deposits of copper m the precipitation boxes, the zinc shavings are sometimes coated with lead by being placed in a 10-per-cent solution of lead acetate This leadcoated zmc will precipitate gold from weak cyanide solutions and leave the copper m solution It is difficult to work ores containing much copper on account of their large consumption of cyanide and the difficulty of precipitating the gold in the presence of copper

33. Sciun on tlie Zinc Poxes. — In the treatment of pynticores and tailings, a piecipitate of zmc cyanide forms occasionally on the zinc in the precipitating boxes It is a grayish-white porous precipitate and the conditions of its formation are not thoroughly understood As a lule, gold is being imperfectly precipitated whenever it occuis. The formation can sometimes he prevented by using lime instead of caustic soda in 'the preliminary wash to neutralize the acids and salts. If, hoivever, lime is added in excess, it may form an incrustation on the zmc and also prevent satisfactory precipitation

The Cyanide Process

The presence of org;anic coinpotmds will sometimes cause excessive action on the zinc, generating hydrogen so vigoiously that frothing is the lesult The application of an oxidizing compound to the ore, such as sodium dioxide, wdl often remedy this condition If a scum forms on the zinc boxes, It should be removed and the cause of it corrected at once,

33. Care of Zinc Jloxes. — Piesh zinc shavings are added daily to the last compartment of the precipitating boxes The partly consumed zinc is brought up a step, so that the first chamber contains zinc partially consumed and rich in bullion, while the last chamber contains fresh zinc Zinc on which bullion is already deposited is more active than new zinc , it is, therefore, advisable to replace the dissolved zinc in the uppei compartments with zinc fiom the lowei compartments and add the fresh zinc to the last compartment

The hydrogen generated t7i the zinc boxes ts likely to retard precipitation by polar ization , to avoid this the zinc should be stirred occasionally

34. Zinc Boxes for Weak Holxxtions. — A longer column of zinc shavings is necessary for weak than for strong cyanide solutions; as the gold precipitates with greatei difficulty from them. The solution can be passed through two boxes of 9 compartments each, and thus come into contact with 18 compartments filled with zinc shavings

36. Percentage of Pi-eclpltatlon. — When good precipitation takes place, 95 to 99 per cent of the gold and silver should be deposited on the zinc Some plants do not leave more than 10 to 25 cents of gold in a ton of sump solution

Bhpining The Pbecipitate

36. Tlie Clean-IJp. — The clean-up takes place once or twice a month, and then the cyanide solution is shut ofifiom the zinc boxes A current of clear water is passed through the zinc boxes to remove the cyanide solution, which is injurious to the arms. The zinc shavings are stirred with a

The Cyanide Process

lod or the trays holding the zinc are moved up and down, which causes the precipitate and fine zinc to pass through the pelf orations of the false bottom into the box below After the gold has settled as a slimy mass, it is sluiced through the plug holes into the side launder The slimes and zinc are allowed to luii out of the laundci through a 40-mesh scieen, which catches fiagments of zinc that aie 1 eturned to the zinc boxes Each compai tinent is washed out in this mannei and the launder is next cleaned with a stieam of water from a hose The zinc fiom the lower boxes is moved up and fresh zme added to fill the remaining compartments The solutions containing the slimes is diawn from the laundei into the acid lank, where the precipitate is allowed to settle Aftei the piecipitate has settled the solution is siphoned into a settling tank The precipitate is now ready foi acid tieatment or the calcining process

37. Acid Treatnxout of tlxe — The tank should be located wlieic theie is a good diaft to cairy away the acid fumes In some mills, concentrated sulphuric acid IS added to the mass of wet slimes in the acid tank and then an equal volume of water is put on The mixtuie is thoroughly stirred and after the violent ebullition has ceased more strong acid is added, followed with an ccpial volume of walei Acid and watei are added until no effei vescence takes place on its addition , it may now be concluded that virtually all the zinc has been consumed The solution is now allowed to stand for a few hours with occasional stirring

38. ReinoTing Zinc SiiliJliate.— After the solution has stood a few hours the tank is filled with hot watei and the contents thoroughly stirred Tlie ziuc sulphate that formed by the action of the sulphuiic acid on the zme is soluble in the water The solution is allowed to stand until the precipitate has settled, when the clear liquid is siphoned into the settling tank and the precipitate washed from five to ten times with hot water to remove all the zinc sulphate

The Cyanide Process

§ 3a

S9. Eiltnition. — After the piecipitate is thoroughly washed it is removed to the filtei hox, the piecipitate from the settling lank is collected and added to the filter box, Avliere it is washed and dried by suction In some works filter presses arc used, into which the various dilutions of hot water may bediiectly pumped

30 . Drying, — The piecipitate is placed in iron pans and dried in a muffle oi over a tuinace arranged to remove the fumes The heat is kept loiv at fiist to drive oft the moisture It is then gradually increased to a daik-red heat and calcining earned on for about I hour, dining Avhich time the oxidation of the base metals, winch escaped lemovalby acid tieatment, is going on

31 . Eliixiiig tlie Dried Precipitate. — The diied piecipitate IS removed to the melting loom, where it is broken. into small pieces, weighed, and the necessary flux added The following mixture has given satisfaction when melted in a No GO plumbago crucible Precipitate, 100 ounces , borax, 30 ounces, soda bicaibonate, 15 ounces, silica, 7 ounces With some residues it Avill be necessary to modify this mixtuie to obtain good results

After complete fusion the molten mass is poured into proper molds Aftei cooling, the slag is removed and the bullion remelted with a little bat ax The slag can be ci ushed and melted with sufficient h that ge and argol to collect all the gold and silver in a lead button, aftei which the button is cupeled for gold and silver

33 . Calcining- Process, — The slimes are removed from the filter box and dried until just before they become dusty They are then mixed ivith powdered niter, m proportions varying from 3 to 33 per cent of their weight and gently heated in a tray of wi ought iron not above a dull red Less niter is used than is lequned foi complete oxidation of

See Table V

IG THE CYANIDE PROCEvSvS § 82

ail the base metals present, an excess of it would rapidly corrode the plumbago crucibles m the subsequent operations The niter not only assists m furnishing the oxygen for oxidation, but It assists in fluxing the zinc oxide, forming zmeate of potash, which is not so readily i educed as zinc oxide

33* Melting the Oscldizetl Precipitate. — The diy residue is broken into small lumps, weighed, transferred to a plumbago crucible, and mixed with suitable quantities of flux The fl.uxes commonly used are bicarbonate of soda, boiax, and clean quartz sand There is considerable variation in the proportion of fluxes and precipitates If theie should be much sand present (which would give a glassy but thick flowing slag), the best corrective is more soda with a little flour. When the slag is too basic (that is, a dull, lusterless one), additional borax will neutralize the base and improve the slag

34:* Pluxing Precipitates.— Some of the fluxes used are given in Table I Any one of them may have to be increased or decreased, according to the amount of impurities present

TABIiE T

Name of Fhix

Charactei of the Precipitate

1 Clean

Pounds

Veiy Zincy Pounds

1 Veiy Sandy Pounds

Bicarbonate of soda

J5

Borax

Sand

Flour ,

The whole of a charge as given m this table will go into two No 36 plumbago crucibles

See Table V

§ 32 The Cyanide Process 17

The crucibles aie placed in the fire and the contents fused until perfectly fluid The ciucibles are then withdrawn from the file and the contents poured into molds The metal settles to the bottom of the mold and after cooling is turned out and the slag lemovecl with a hammer The bullion thus obtained is remelted with boiax and run into an ingot The second melting should be conducted at as low a tempeiature as possible, since gold foims a veiy imperfect alloy with zinc

The slags generally contain a consideiable amount of gold, and should therefore be ciiished and melted with a little borax glass and poured when fluid into an ingot mold After cooling, the slag is removed from the bullion

MODTFTCATIOl OF THE CTANTIDE PROCESS

ACTION OF TIIB TUJjECTRIC CUEBENT ON OODD SOIiXJTlONS

35, Electrolysis. — When the electric cunent decomposes a solution of a metallic salt, the metal is carried to the negative pole, or cathode, of the electrolytic cell and deposited, while the metalloid is hbeiated at the positive pole, 01 anode In a given time a fixed quantity of current will release and deposit a definite quantity of metal The quantity of metal released at the anode and deposited at the cathode varies with different metals, being in direct proportion to their electrochemical equivalents This law does not hold good for solutions containing very small quantities of the metal m solution, as in cyanide solutions, foi the cunent does not find sufficient metal piesent at the electrolytes, consequently the water is decomposed To make the precipitation as efficient as possible, the solution is kept in constant diffusion by a steady flow through the precipitating box

THE CYANIDE PRDCEvSS

§

36. CoiKlltioiis that Hie Sleiacns-IIalslce Catliodo Mu=.t Fulfil. — The Ccithode should he u material to which the old will adhere, it should be capable of being i oiled into thin sheets, which aie of such a character that the gold can be lecoveied without loss or great expense The cathode should be inoie electropositive than the anode to pi event return cui rents being generated when the depositing current is stopped Thin sheet lead has been adopted as the most suitable metal for the cathode of the Siemens- Plalbke method of precipitation The lead sheets are fastened to light wooden frames Each fiame contains tliiee sheets of lead 2 ft X 3 ft , this gives each frame 18 square feet of surface Theie are 81 frames in each precipitating box, giving an exposed surface of square feet The three sheets of lead in each fiamo weigh 3 pounds, this makes 201 pounds of lead in each box

37. Carbon has been used for anodes, but it crumbles under the influence of the current that decomposes the cyanide Zinc used as an anode forms a white piccipitate of ferrocyanide of zinc when the ores leached contain iron Iron anodes' foim Piussian blue by the leaction of oxide of iron and ferrocyanide in the solution The non plates aie covered with canvas to prevent short-circintmg and to collect the Prussian or Turnbull blue that is foiincd by the ferrous and feme salts with cyanide solutions Iron plates are used in South Afiica as anodes and lead cathode plates are suspended between them

Cyanide can be recovered from the Prussian blue by dissolving It in caustic soda, evaporating the solution, and melting the residue with potassium caibonate

38. TSlcetrlc Current Kequli'ed for Precipitation. A weak current, one with a density of about OG ampere per square foot, is required for precipitation It can be produced by 7 volts when the cathodes arc about inches apart The advantages claimed foi such currents are that there is a firm deposit of gold and that the iron anodes are decomposed very slowly, thii waste being proportional to

The Cyanide Process

§ 32

Lhe cuiient Theoietically, 31 boisepower would be siifficiCQt to runu pLuit havinj a months} cupauty of 3,(H)()tons, but the amount actually icLpiired, liowevei, was 5 hoisepoYvei

39. AclvautcXes ol* Electrical — Gold may be precipitated from bolutions b) clectiolysib independent ol the btiength of cyanide solutions In the ti eaiment of tailings, theretoie, veiy dilute solutions can be used, the only limit being sufficient cyanide to dissolve the gold Electiolysis does away with ceitaui complications met with in zinc precipitation, such as the tormation of alumina, lime, hydrate of non, etc , besides, it is cleaiiei and simple, and gives a highei grade of bullion Its application seems to be limited to those plants where very weak cyanide solutions can be used successfully

4 - 0 , Working Itc&iilts. — At the Woi cester woi ks, South Afiica, the strong solution contains fiom 05 to OS per cent of /CCJV and the weak solution about 01 per cent Theie aie four precipitating boxes, 20 tcet long, B feel wide, and 4 feet deep Heavy copper wnes are fixed on the sides of the boxes to convey the cuirent from the dynamo to the electrodes The anodes are iron plates 7 feet long, 3 feet wide, and inch thick They stand on wooden strips that are laid on the floor of the tank and they aie kept in a vertical position by wooden strips on the sides of the box To facditate the circulation Thiough the box, each alternate plate IS raised 1 inch above the bottom, thus forming a senes of compaitixients through which the solutions must rise and fall alternately through the successive compartments

In a clean-up, the frames cairymg the lead are removed one at a time, the lead is removed and replaced by a fresh sheet, and the frame letiuned to the box, The lead that contains horn 2 to 12 per cent of gold is melted into hais and cupeled,

In treating 3,000 tons of tailings, 750 pounds of lead and 1,080 pounds of iron were consumed

The Cyanide Process

PBEOIFITATIOK WITH CTTAliCOAJj

41, Jolinson's rroce*=?s.— One of the many methods proposed to take the place of zinc shdvmjfci in the precipitation of gold fioin auio-potassic cyanide solutions was the use of dial coal It had been previous]]" employed for the precipitation ot gold fibm chloime solutions, and there was no chemieal reason why it should not be applied to a cyanide solution The process patented by a Mi Johnson consists in filtering a gold-cyanide solution thiough pulverized chaicoal, fiom which the gold is recovered by buinuig the charcoal and smelting the residues with suitable fluxes The process is considered too slow foi large plants The probable reaction that occurs may be expressed as follows

+ %Kco, + Wcn

43# The chaicoal filled used at the South Geiman

mine, Moldon, Victoria, is shown in Fig 3 It consists

of a tub a 2 feet i inches high, 2 feet 1 inch in diameter at the top> and

i foot 9 inches in chaineter at the boltom In the center of each tub and resting upon wooden cleats r IS a

glazed chain pipe d 4 inches in diameter The pipe and tub are nearly filled with chaicoal, after which the drain pipe IS placed under the mouth of a pipe c connecting with the gold-solution tank

The solution passes down the pipe d and out thiough the bottom, then rises through the chaicoal in the tub and flows

§ The Cyanide Process U

out at the pipe/ To prevent the chaicoai rising' and clogging the pipe / It IS confined by a board covei d

Theie are six of these filters in a set, so arranged that the oveiflow irom one will pass down the glazed pipe of the next, and so on until the solution is exhausted and passes to the sump About 300 gallons of solution can pass thiough each filter hourly

43, Cleaning tlie Eiltera. — The solution lemainmg in the tubs is poured off, then the charcoal containing the gold IS removed and sent to the fuinace loom

The first tub, or the one nearest the fiesh gold solution, IS removed after thiee days and its contents sent to the fuinace room The second tub is moved up to take the first tub's place, the third to take the place of the second, and finally the foiiner first tub is made the sixth of the senes by filling it with fresh charcoal A solution that contains gold and OO-f per cent of cyanide has the gold almost completely precipitated, rarely containing more than 22 grain per ton aftei leaving the filter

44 :. Recovei'ln tlie Bullion. — The charcoal is next burned in a leverberatoiy furnace The ash is then sifted with a 30-mesh tiommel enclosed in a box, and whatevei remains in the tiommel is returned to the furnace for reburnmg The ash in the box is fused in a graphite crucible with borax m about the following proportions box ax, 3 pounds, ash, pounds The cost of precipitation is said to he about 25 cents per ounce of bullion

Precipitation With Zinc Potces

45 . Definition of Prime. — Zinc fume is a product obtained in zinc smelting It is a blue powder containing about 90 per cent of metallic zinc. The cyanide solution containing the gold and silvei is placed in a precipitating tank having a capacity of about 30 ions The tanks have a 4:-inch iron pipe leading to the bottom, thiough which an is passed at a pressure of about 16 pounds, for the purpose of

§ 39. The Cyanide Process 23

tlie solution agitated dunng the time the zinc dust IS added

Tt takes about 5 pounds ot zinc dust to piecipitate the gold and silvei fiom 30 tons of C 5 ''anide solution The zinc dust IS sieved into the tank occasionally, from the time it is half full of the solution until it is full The pulp is agitated for a tew minutes after it is full of cyanide solution and all the zinc dust has been added

J.6, Collecting Zliic-Eume Precipitates. — The ruspended mattei, or piecipitate, is allowed to settle for 4 hour The solution is then decanted from the settled precipitate thiough a pipe that enters the piecipitating tank about 8 inches above the bottom As this solution contains some gold slimes, it is passed through a filter press to collect them The pi assure tanks aie located below the precipitating tanks, thus allowing the solution and precipitate to be drawn quickly into the pressuie tank and passed through the filter press, usually without the aid of pressure

The precipitation of the gold and silver with zinc dust IS almost instantaneous and very complete, not leaving ovei 20 cents in each ton of cyanide solution The consumption of zinc is about 14 pounds foi each ounce of gold precipitated

Oombinaiton Cyanide Ptants

4: Adviintagew of Agitation.— It has been said that by agitating the pulp, the cyanide process maybe hastened, and It may-! be added that agitation sometimes permits slimes to be treated directly

The plant dliisiiated m Fig 4 was constructed by D A Schiedel for the purpose of treating slimes by cyanide and agitation The plant, which was built of iron and steel, was composed of a tank a vacuum filtei piecipitating boxes c, sump tank/:/, and gold-solution lank f The machinery was to be driven by a watei wheel e

4 : 8 . Tlxe Sclileclel Tank. — The agitating tank is 5 feet in diameter and 5 feet high with a bunch steehplate shell N M III

24 The Cyanide Process § 32

and a -iion bottom 2 iiicbcs thick To the bottom lb cast a cone- through which passes a veitical shaft n, which cariios four arms o that hang down into the vat and have foul i-inch steel paddles r G inches wide fastened to them These paddles aie twisted like the blades of a propeller, and the arms to which they aie attached at right angles are sti'engthened by a collar The shaft with the paddles can be laisecl by the screw spindle t The driving gear is placed below the tank and agitator An opening 4 inches in diameter in the tank bottom discharges by means of a stop-cock the contents of the agitating tank through a pipe into a Schiedel patent vacuum hltei d A perfect separation of the gold-cyanide solution fiom the residues is heie elected

49. Description of Filter Box.— The filter box which IS shown m Fig 5 has i-inch steel plate for the sides and -inch steel plate foi the bottom. It foims a rectangular box 3 feet G inches deep, 7 teet long by 5 feet wide Two feet above the bottom, as shown in Fig 5 (a), is a perforated steel filter bottom a of g-indi boiler plate, made in three movable sections, supported by angle irons r attached to the sides, and by the vertical supports d The peiforatioas y shown m the hoiizontal section. Fig 5 are 4" inch in diameter and are arranged inch apait The filtei bottom fits closely to the sides of the apparatus , it is covered with a blanket which is kept in position by bars i tinning along the four sides and fastened by thumbsciews h A grating of |-mch rotmd-iionbars, placed 3 inches apart and made m three sections, serves to protect the cloth The space between the bars is filled with coarse sand The filter partition divides the apparatus into two compaitmeiits, one above the other The lower one / foims a closed box, which IS connected with a duplex vacuum pump by the pipe j By this means the an can be rarefied when the filter bottom is covered with pulp The part above the filter receives the contents of the agitatoi The bottom of the apparatus has a discharge pipe with a 3-inch stop-cock for

§ 32 The Cyanide Process 25

running ott the lilteieci bolution into eithei of the two solution tanks, which aie standing on the floor one step lower

The Cyanide Process

§32

with a gauge Fig 5 (c), to indicate the height of the solution within, a gauge ?i, to show the inches oi vacuum, an an tap o, to permit an influx of air when the filtered solution is being discharged, and a manhole g

50 . The rejiiiamdei of the process and the zinc precipitation tanks are the same as have been given in the geneial description The piecipitate is veiy slimy, and it is said that the freer it is of zinc, the more slimy it becomes The ti eatment of the precipitate is the same as has been desci ibed The steel tanks were but little, if any, alXected by the cyanide solution

51. Decluetioiis Erora ComMiiation Treatment. — The combination cyanide plant uas consti noted foi the pin pose of treating slim Q concentrates from the canvas plant Such concentrates contained a varying percentage of caibonate of lime, m some instances as much as 95 per cent , which, however, did not interfere mechanically oi otherwise with their sati&factory ti eatment by cyanide Such conditions would make chlorination all but impossible

It was found that for agitation the mateiial requiicd an amount of solution equal to 30 per cent of its weight and 6 hours' time tor leaching The plant clescubed is capable of Heating a much larger quantity of slimes Chain are usually pi od need per day by the canvas plant, its services are therefore only periodically required

53 . Eereenlage of Extraction — The average consumption of cyanide, calculated fiom a laige tonnage of slimes treated, amounted to 4 3 pounds per ton and cost $2 27 , the labor amounted to $1 ; and the total cost of treatment by cyanide amounted to 13 50 pei ton The average exti action amounted to 93 18 per cent of the gold and 90 per cent of the silver u*i the slimes, althougli as high as 96 57 per cent of the gold has been exti acted in some instances The extraction of the gold during the agitation goes on as shown by Table II

The Cyanide Process

§ 32

2?

TABJjE II

Tiealment af Sluiitis by Agitation

Gold per Ton

IexIi action pel Cent

Sample before tieatmeni

*8S 00

Sample after 1 hour's agitation

So 23

Sample after 2 hours' agitation

Sample aftei 3 hoius' agilalion

05

Sample aftei 4 hours' agitation

Sample after 5 hours' agitation

G 00

03 Is

Sample after G hours' agitation

Sample aftei Jioius' agitation

Sample after 8 hours' agitation

Within the first hour 85 23 pei cent of the gold was extracted ; dming the following 5 houis the mciease of exti action was slow and irregulai , after G hours no furthei exti action took place For experimental purposes, Doctoi Schiedel continued agitation up to 12 hours without improving on the le&ult The treatment of the slime concentrates by agitation was preferred on account ot its quicker, cheaper, and better lesults, as compared with percolation

53. Amalgam in Slimes. — Some concentrates contain a small amount ot amalgam, pait of which is found on the bottom of the agitating tanks, another pait leaves the woiks with the tailings and is lecoveied m Hungarian iiffles and on amalgamated silver plates

54, Treatment of Coiiceiitmtes — Sulphuiets, such as the concentrates of the Utica, Madison, and Eureka mines, of California, wmre treated on a more or less extensive scale at the same plant The results were not very satisfactory on account of the coarseness of the concentrates All sulphtirets of the Utica mine are pure sulphide of iron The fine canvas-plant concentrates alluded to, although less clean, gave an aveiage exti action of 03 18 per cent , whereas vaniier concentrates gave only 81 38 pei cent This later

28 The Cyanide Process § 82

exti action, although reasonably good, could not, at the cost of $4 per ton foi treatment, compete with chloiinalion, which yields 00 per cent of a $50 ore at a cost ol fJO

lisfoTE — The laige size of the Utica chloiinalion woiks oUeib special advantages and permits chloimation at this gine, which ib nnicli lowei than the cost anywhere else m Cahtornia

A laige ninnbei of tests proved that a high percentage of the gold IS contained in the coarser pai tides of the sulphurets; this will account to some extent foi the comparatively low percentage of cyanide extraction.

55, Cost of Plant, — The cost of this combination cyanide plant IS as follows

Grading and foundations

$ 300 00

Building.

Shafting, belting, and putting into place

Agitatoi

3G0 00

Vacuum filtei . .

Three tanks

Igo 00

Two zinc boxes

3G0 00

Two steel tanks

One vacuum pump

One liquor pump

Pipes, stop-cocks, faucets, etc

Total

$3,000 00

THE KENDADIi CYANIDE PROOEHS

56. The Kendall eyaiiitle process is based on the fact that oxygen is necessary indissoHing gold in acyanideof-potassium solution The inventor of the process claims that by the addition of a ceitam quantity of sodium dioxide to the cyanide solution, the necessary amount of oxygen is artificially supplied and the solution of gold is hastened The sodium dioxide is added to the ore as it is lulaoed in the vat

The following chemical changes are claimed by the promoters of the process to take place

§ 32 The Cyanide Process

%KCN-\-NaO + %IIfi-%AH %KOH-maOH+%AtiCN and 2/i u CN + %KCN ™ 2 A uK{ CN )

The plant and the method of leaching are similai to the MacAithur-Foirest cyanide process already described It was proposed at one time in the Kendall process to use sodium amalgam oi zinc amalgam tor piecipitatmg the gold fiom solution The only inducement tins process has to ofEei lb a saving of tune in lixiviation

THE PEIjATAN-CIEBICI CYANIDE PROCESS

57. Agitator. — The process known as the Pelatan- C] oriel cyanide process depends on agitation for quickly dissolving the gold in solution The process also involves elcctncal precipitation of the gold and silver dissolved by the cyanide solution In Pig 6 is shown the gencial aiiangement of the plant The ore and weak cyanide solution me thoroughly mixed in the tank by means of a cast-zron stirrer attached to the shaft 3 From the mixing tank the thin pulp IS run through a laundei to the lixiviating vats wliicli hold from 1 to 5 tonsof pulp and are provided with a cast-iron sill rei r fitted to the shaft/ Wooden pins aie inserted through the fotii blades of this stirred in order to prevent the sands settling upon the bottom of the vat The iron stirrer acts as an anode for an electrolytic bath or electrolyte as well as an agitator, the current being passed to it through the shaft / The bottom of the tank iscoveied with cement upon which rests a copper plate covered with live quicksilvei The plate and quicksilver form the cathode, or negative electrode, for the electrolytic bath The anode is connected with one pole of a dynamo and the cathode with the other, the aunc-polassic cyanide solution forms the electrolyte and completes the circuit

584 Qnicirsllrev Cailiode. — The use of live quicksilver above the cathode has a twofold object First, to catch and hold any coarse gold or silver that the cyanide solution

from a cyanide solution was patented by J H Rae, of Syracuse, New Yotk, in 18G7, but owin to the employment ot an alternating cnnent, the cation became au anion before the mercury could amalgamate the free gold The use of

§32 THE CYANIDE PROCEvSvS 31

the direct current convcitb the anion into a cation, which themerciuy araalgamateb without trouble The amalgam, however, is sometimes deposited veiy hard upon the copper plate, making the clean-up quite difficult Another objection to the use of quicksilvei in this process is due to the stirrers mixing it into the pulp, thus causing the loss of both quicksilver and amalgam in the tailings when they aie run off

59 . The tUeoi'y of electi*opi'eo1p1tatioii is based upon elect! olysis The gold is dissolved at the positive electrode by the cyanide solution m the piesence of oxygen, according to Eisner's equation It is presumed that oxygen IS liberated from the water of the solution by electrolytic decomposition and that the cation of aiinc-potassic cyanide formed makes a tour about the bath until it nears the cathode and is attracted to il and broken up The goldpolassiuin cyanide cation being broken up, cyanogen, potassium, and gold are liberated The cyanogen and potassium probably immediately unite, forming potassium cyanide, which again goes on a tour of the vat for more gold

60 . Claims for tlie Process. — It is claimed for this process that it economies m the use of cyanide, saves time and laboi, and takes only from 4 to 6 hours to lixiviate and run off the tailings The process may be adapted to slimes, as well as tailings from other processes, and to raw ore, provided they are suitable for cyanide treatment To get iid of the tailings, a side discharge door k is opened and the stirrer worked slowly until the vat is emptied The tank may now be washed out with a hose, the discharge door closed, and a new charge of ore immediately substituted The liquor from the tailings is drained off and strengthened for use again m some cases, as a rule, however, it is allowed to go to waste, it being low in cyanide and practically containing no gold

61 . Tlie Electrolytic Solution. — Salt NaCl is added to the bath foi the purpose of forming silvei chloride, if

Sa TELE CYANIDE PROCESS §

Sliver IS present in the ore, and thou aigentic-potavSic cyanide, accoiding to the following leaction

2Aga+UCCN:= %Ka f %KAgCN

111 the equation the chlorine iii solution has the same effect on the cyanide solution as oxygen, in that it hastens reaction between the metals and cyanogen The Pehitan- Clerici people also claim that the addition of sodium chlonde forms a stable electrolyte of sufficient density for the current used

It IS claimed by some that no benefit can be derived from the use of electricity in cyaniding, while otheis claim that there are so few particles of gold in a cyanide solution that few become cations and anions The fact remains, however, that under some conditions the extraction has reached 90 per cent of the gold in the ore The fact that this exti action was accomplished in from 4 to 6 hours, while the MacAitliur- Porrest process would require as many days, shows that the use of electricity saves time and possibly values

THE VimUMATIC CYANIDE PROCESS

63, for tire Process. — The presence of oxygen

being necessary for dissolving gold, unless some element of the haloid group, such as chlorine, bromine, oi iodine, be present, agitation was adopted as a means of fmnishmg a greater supply than was contained in the ore and water

Fta 7

The pneuxtiatic cyanide process agitates the pulp by means of compressed air rising through the solution, and which also furnishes oxygen for hastening the operation The pneumatic process reduces the time to 7 hours. The tanks a shown in Pig 7 are connected with a senes of pipes i?,

§ 32 The Cyanide Process 33

thiongh which compressed air is conducted to a seiies of pipes in the bottom of each tank The palp having been placed m the tanks the air is tinned on by valves c to the pipes m the bottom, winch have small apertures for its escape into the solution and thiough which it rises, thereby causing sufficient ebullition toi agitation

DTOSCIUPTION OF CYANIDE mELS

snncTPrcATioNS for a so-toiv ctaivibf

G3. Hxieeial Coiistriictiou. — Cyanide mills are sometimes designed foi special purposes A mill that was erected near Weaver, Arizona, foi the treatment of tailings had the following equipment* Pour leaching vats 12 feet in diametei and feet deep; two gold-solution tanks 8 feet m diamelei and feet deep, one sump tank 12 feet m diameter and 4 feet deep, one zinc box havingtwelve compartments, each having a capacity of 1 cubic foot. The entire plant was constructed of wood and covered with two coats of waterpi oof non-metallic paint

64.. Details of Wonlciiig; tlie Ore — The value m the tailings was largely in the dried slimes, which constituted 15 pel cent, of the dump These tailings were shoveled against a Junch screen, which broke the caked slimes into fine particles that were afterwards mixed with coarse gravel The oie was then chaiged into a 10-toii vat to be treated as follows

1 The ore is leached 12 hours with a of 1 per cent ( 25 per cent,) cyanide solution, which is then diawn off

2 The ore is leached 12 houis with a of 1 per cent ( 20 per cent,) cyanide solution run in fiom the top of the vat

3 A solution containing of 1 per cent ( 1G6 per cent ) cyanide is run on top of the oie aftei No 2 solution has been

34 The Cyanide Process § 32

di allied off and is allowed to stand 12 hours No 3 solution IS then drained off

4 The wash water from a previous operation containing I of 1 per cent ( 125 per cent ) cyanide is run on top of the oie and drawn off in 3 hours

5 Water is run on the ore and aftei standing 3 houis is diawn oft into a gold tank, to be used m the future as No 4 Solution

All solutions pass mto the gold lank, where they receive sufficient cyanide of potassium to give them a sit eng th of iof 1 per cent ( 25 pei cent ) before passing tlnough the zinc box The solutions after passing the zinc box are strengthened and used over and over again until they become foul, when they aie allowed to lun to waste

The amount of cyanide consumed is 1 pound per ton of ore The amount of zinc consumed is pound pei ton of ore It requires six persons to operate the plant ffoui men to shovel, charge, and discharge the vats by wheelbaiiows, one man to pump solutions by hand, and one assayer

MEXirOI3 OT CYANIDIISTG AT MTlBCTJBj UTAH 65 . Application of tlie Solutions. — The first solution, which contains 25 per cent of cyanide, is applied at the bottom and is allowed to saturate the chaige until it reaches the top of the ore, when it is shut off This takes about 8 hours The same strength of solution is run on from the top to covei the oie 2 inches in older to save tune It is allowed to stand 16 hours, after which time the percolaLion is started Fresh solution is added when the other is drawn off and the percolation continued 24 hours A weak solution, which contains about .035 per cent, of cyanide, follows the strong solution at the end of the 24 hours This solution is passed through the leaching vats from 4S to 72 horns, ot until the samples taken each day show that the ore charge is ready to be washed.

§32

THE CYANIDE PROCEvSS

Wash water is added to displace the weak solution, aii operation which takes about 24- hoiiis It acquires 0 oi days from the time the tank is filled with ore until it is discharged and leady to be filled again foi anothei leaching

G. Kesults from Boliitloiis. — All solutions, whethei weak or strong, flow into a common laundei that leads direct to the gold-solution tanks When a solution containing 45 per cent of cyanide is used, the mixed solutions will contain about 35 per cent , and this solution is pumped back and used as a weak solution without the addition of cyanide The best results aie secui ed when the total amount of cyanide liquor is about 2 tons to 1 ton of ore

67t Kate of Drainage. — The late of percolation differs, but the usual rate of drainage is from 2 1 inch of tank

depth per houi 'When the proportion of i ousted ore in the chaige is large, the ingredients present will make a good cementing mateiial This material will harden in the tanks in about 2 days, rendering sampling with an anger veiy difflcult and greatly impeding percolation When the percentage of limestone is high m the ore, a large quantity of lime IS pioduced m the furnace When the solution is added, it will hydrate, causing the mateiial in the tank to swell peiceptibly and make the leaching veiy slow

68. Discliarging the Tailings. — There is not vSufficient water available at Mercui to flush the tailings from the vats, hence they aie shoveled through the bottom gates into cars having a capacity of Batons The cai's aie tiammed out of the building by men Each tank has eight bottom discharge gates 15 inches m diameter, located above four tram roads, which permits the tanks to be shoveled out in from 5 to 7 hours, at a cost of ft om 6 to 8 cents per ton

69. Precipitation. — The gold at Mercur is precipitated fiom the solution by means ot zme dust The powder used IS imported from England or Germany and contains about 00 pel cent of metallic zme The solution is pumped from the gold-solution tanks to three precipitating tanks.

The Cyanide Process

§32

Gcicli of whicli liolds 30 tons of solution Whilo tlio thinks til G filling, till IS blown into ttiG tanks nt nbout 15 pounds piessiu-e througli a inch pipe This is done to sLii up the residues remaining in the bottom of the tames from foi iner precipitations, and which may contain some uiiconsumed zinc Five pounds of zinc dust is added to each tank containing 30 tons of solution The zinc dust is sifted into the solution at intervals fiom the tune the tank is half filled until it IS full The an pipe is moved about the bottom of the tank for a few minutes to stir up all the sediment and is then removed The suspended matter m the solution is now allowed to settle fot about hour, when the supernatant liquor IS drawn off through an opening 8 inches above the bottom of the tank As this solution contains some gold slimes, it is passed through the filter pi ess Usually the solution passes through the filtei press without pressure unless the press is well filled with slimes Piecipitation with zinc dust lb almost instantaneous, while its consumption is about pounds of zinc per ounce of gold tin own down

70. Pi'cssni'e Tanks. — Two pressure tanks, each having a capacity of 30 tons, are located below the precipitating tank These pressure tanks are connected with the precipitating tanks by large pipes, so that the solution can be run into them in a short time Pressure can be applied to these tanks and thus foice the solution through the filter press

The precipitating and filtering operation is continuous while one tank i& filling another is discliaigmg and the third settling

71. Moastmgr and Trcatlnsr Slimes Witli Acid. — The clean-up takes place monthly and requires about 3 days' time The precipitating vats are drained, as much as possible of the precipitates scooped into iron pans, and the remainder washed into the pressure tank

The gold slimes collected are refined in a separate building The iron pans containing the precipitate are placed m a laige cast-iron muffle furnace The cloths from the filter

§ 32 The Cyanide Process 37

prebb are allowed to burn in the pans and the whole is brought to a dull-red heat, by which most of the zinc in the precipitates is oxidized The roasted piecipitate is passed through a --mch scicen, after which it is treated with dilute sulphuric and nitric acids to remove the remaining zmc, zinc oxide, arbenic, and mercury, which aie piesent in Mercur piecipiLates Nituc acid is added to assist m the oxidation of the metals present, as well as to prevent the evolution of deadly aiseni meted hydrogen gas The acid or dissolving tank lb covered with a tight-fitting hood, which is connected with an exhaust fan, in order to remove the dangerous gases to the outside of the building The acid must be added gradually to pi event the solution boiling over the top of the tank When the addition of fiesh acid does not cause further eftei vcbcence, the tank is filled with watei and allowed to stand The supernatant liquor is diawn off thiough a prebsuie tank and filter press and the slimes again washed in the same way as before This is i repeated twice to free the slimes from soluble salts, as far as possible

73. Relliiing tlie Slimes. — The slimes aie next flushed into a pressuic tank, passed into the filter press, washed, dried into cakes, removed, coarsely pulverized, mixed with a flux of soda, potash, and borax glass, and smelted in two No 300 giaphitc crucibles (see Table V) Before melting the product contains 00 per cent of gold, the other 4.0 per cent, being largely silicious slimes The lesultmg bullion IS OoO fine This is the only mill in the district refilling its own bullion, all the other mills shipping to Eastern lefinenes The total cost of refining is about 15 cents per ounce of gold

Cyanijding Cuippde Creek, Colorado, Ores

73. Cripple CreeR Ores.— H Van F Furman states that ores of the Ciipple Cteek district consist of porphyry (andesitic bieccia), phonolitc, decomposed granite, and quartz, and usually carry on the surface iron oxide,

The Cyanide Process

manganese ojcide, anri oxide of telliuuim, below the watei level the gold occurs in the luineials calaverite and sylvanite and IS associated with moic or less iron pyrites The mineial fluor fiequeiitly occurs m the gold-beanng veins While the surface oies contain free gold, they do not yield their gold contents by amalgamation, the gold usually being coated with oxide or tellurium or some substance that interferes with Its extraction by this method The extraction of gold from surface ores by potassium cyanide presents no difficulties, but the treatment of the tellunde ores without subjecting them to a preliminary last has been attended with the drawbacks of extremely fine grinding and prolonged percolation m the vats (sometimes fiom 13 to 14 days 111 order to secure a fair extraction) At present all tellunde ores are roasted dead, i e , until the tellurium is oxidized completely before being leached in the vats "

74. Cripple Creole Cyanide Mill. — The process applied at the mill of the Biodie Reduction Company, situated about miles south of the town of Cripple Cieek, is typical of the method adopted for the tieatment of these ores The mill at present has a capacity of about iOO tons per day The ore as received from the diffeient mines is unloaded into bins, each lot being kept separate until it is sampled and paid for, the oie being purchased upon its value as determined by sample and assay, which is the invariable custom of the district Fiom the bins the ore is delivered by hand to a Gates crusher which reduces it to pieces not exceeding 1 inch, in diameter From the cuislier It is raised fay an elevator and passed through a Vezin sampler, which takes out a sample, on which the settlement as to the value of the lot is based The crushed ore passes through a 4-tube Argali dried to a Dodge crusher, iiimi which It lb raised by an elevator to a i evolving screen, the oversize going to a pair of Davis rolls, and aftei crushing it is returned to the screen, the undersize passing to 14" X 30" Krom rolls The product of the Krom rolls is elevated, divided, and delivered to four 40-me&h, brass-wire,

§ 32 The Cyanide Process 39

cloth revolving screens The undeisize is carried by a screw conveyer to the storage bins oi i casting furnace, as is desired The oversize passes to another set of Kroin rolls, whence it is elevated to the 40-mebh screens

75. The oxidized surface ores pass directly to the storage bins, while the unoxidized tellinide oies pass to the roasting furnace The furnace at these works is a Pearce till ret, 40 feet m diameter, with an annular hearth 8 feet wide, the rabble arms being watei -cooled Fiom the storage bins the ore is drawn into tram cars, each carload being weighed and dumped into the leaching vats The vats, which are circular, are constructed of No 8 steel (0 1285 of an inch thick), each vat being piovided with manholes for sluicing off the tailings after the charge is leached

76 . Bi'ollie lilill Practice. — The stock solution is slowed in steel tanks coated with paiafdn paint and is kept at the pioper strength by the addition of potassium cyanide The solution is lun in on the top of the ore to be leached and allowed to percolate Two solutions are used, the strong soluLion containing fiom 5 to 75 per cent of potassium cyanide* The time of treatment varies from 70 to 100 oi more hours, according to the ore Aftei the gold is dissolved, wash water is added to displace the cyanide solution, The strong solution is allowed to percolate for about 50 houis, when the weak solution is added and afterwards the wash water

The solution after passing through the tank's filter bottom IS conveyed by iron pipes to the zinc boxes for the precipitation of the gold There are two sets of zmc boxes, one set foi the strong and one set for the weak solutions and wash water After passing through the zinc boxes, the solutions pass to their respective sumps, from which they are pumped to their respective storage tanks The zinc slimes are washed, treated, smelted, and the resulting gold bars shipped to the United States Mint at Denver,

AT. M III — jr

4:0 The Cyanide Process § 32

Danger In Working The Cyanide Process

Pkopeeties Op Potassium Cyanide

77. The fact that potassium cyanide is a deadly poison was at one time considered a gieat obstacle m the way of the successful introduction of the process The solutions used in the process are so dilute that the hydrocyanic acid given off is of no consequence if the works aie properly ventilated All ore should be tested foi acids befoie tieatment and if necessary neutialized This will insure safety to the men and economy in the practical operations of the process Those working the process are not teqtiired to come into direct contact with the cyanide, either as a solid or with its solution Even the clean-up, when properly conducted, does not require contact with the cyanide solution

78. Symptoms of Poisoning. — Some men are very susceptible to the effects of potassium cyanide, and when the diluted solutions are brought into contact with their skin, an eruption is produced, which is not dangerous, but annoying on account of the itching Such men should not be employed in cyanide works If the works are not properly ventilated, the men will complain of headache, faintness, and dizziness If it be necessary to place one's hands in a cyanide solution, they should be protected by a coating of vaseline or by rubber gloves When the extensive use of cyanide is considered, the number of accidents is exceedingly small

79. Sources of Poisoning. — Poisoning may occur from hydrocyanic acid being liberated from the leaching vats or tanks In countries where the vats aie not covered, poisoning from the free hydrocyanic acid liberated by mineral acids IS unknown

The poisonous gases that are liberated when the slimes are treated with acid to dissolve the zinc are very dangerous, for the slimes after washing usually contain a little

§ 32 The Cyanide Process 41

insoluble cyanide that will yield hydiocyanic acid upon Heatment with sulpliiuic acid Respiiators should be woin in this case foi pioLection

Ores that contain arsenic are usually more oi less soluble in the cyanide solution The aisenic is precipitated on the zinc with the gold and enters the slimes When acid is added to the slimes, aisenuueted hydiogen, a deadly poisonous gas, IS liberated This gas, if inhaled, passes from the lungs into the circulation of the blood and rapidly attacks the tissue The symptoms are first nausea, then extreme languor with pain in the legs, and finally death

Slimes should be treated in a special chamber or cupboard connected with a chimney having a good draft when acid is used

80. Antidotes* — In case of internal poisoning, an emetic or physical means should be used to induce vomiting

In case of accidents, it is well to remember that peroxide of hydrogen is a pozverfiil antidote for cyanide poison-

ing. Hypodermic injections of solutions containing fiom 2 to 3 per cent of peroxide have been used successfully, especially when injected at difleient parts of the body At the same time the stomach was washed out with a 2-peicent solution of hydrogen peroxide Peroxide of hydrogen forms with hydrocyanic acid JICN '"oxanide" CONIfj which is a harmless compound, thus

2IICP/+ 2C0mf

DESIGN FOB A rWENTX-FIVE TON CYANIDE

Miee

81. Plan* — The plant to be described was designed by the Allis-Chalmers Company, of Milwaukee, Wisconsin This plant is shown by plan m Fig 8 The six lixiviating tanks a are each 16 feet m diameter and 4 feet deep , the solution tanks c and d are S) feet in diameter and 4 feet deep ; the sump tanks h ai e of the same capacity as the solution tanks Between the gold-solution tanks and the sump tank the zinc

42 The Cyanide Process § 32

boxes e and / are shown, each tank being divided into two rows of conipartmenls. The box is for the weaker gold solution The pump ib placed near the sump tanks for the purpose of forcing the solutions to the various vats, as lequired The leaching vats are under a roof 106 feet 9 inches long by 23 feet wide The remainder of the lixiviating apparatus is under a roof 53 feet 6 inches by 11 feet The boiler h and the engine t are separated from each other and the remainder of the machinery by partitions The milling machinery is contained in a ground space

The Cyanide Process

83. Elevation. — In Fig 0 is shown an. elevation of the 25-ton plant Avhose plan has just been described The section IS taken back of the line shafting in order to show the pi incipal machines The ore is first passed through the crusher / into the oi e bin a' below The ore runs down the oie-bin floor and is drawn off into a chute that feeds theoie drier k From the diicr at /, the ore falls into a screw hue n and IS conveyed to the boot ol the elevator m The elevator

raises the ore to a screen shown in Pig 10, at over which It passes by gravity The coarse ore passes down the chute zv to the rolls p and then down to the elevator, by which it IS raised to the screen again The fine ore from the screen passes to a bin, from which it is drawn as needed By an examination of Fig 9, it will be observed that advantage is taken of gravity, wherever it is thought desirable, for handling material and disposing of solutions The lixiviating tanks are above the gold-solution tanks, the latter above the

The Cyanide Process

§32

zinc boxes, and they, in turn, above the sump tanks The chai'ging track r has upon it a tram car ii above one of the leaching vats

83, Cross-Section — The cross-section shown m Fig 10 was taken thiough the plan on the line CD It shows the rolls p, elevator m, screen chute %v to the rolls and chute b' to the elevator boot C It also shows the charging cai li under the ore-bin chute

84. The cross-section shown in Fig 11 was tai-cen through the line A Fig 8 It shows m detail the boiler h, screw conveyer ?i, elevator m, drier furnace front /, crusher y, and ore bin with its chute leading to the drier

§32

The Cyanide Process

It will be noticed that the mill is built on a side hill, at an elevation that permits the oie cars to lun direct to the crusher. In some cases the ore is run above the crusher, so that it is unnecessary to handle it, as in this case.

Tabjle Iii

Co'S Tents 03? Tanics In Gaeeons At One Eoot In Depth

Diametei

Diameter

Gallons

1 Foot

Remarks

4)

in Depth

1,234 91

1,321 54

1,407 51

1,503 02

The number of gallons in a

1,600 00

leceptacle 1 foot in diametei

1,697 45

and 1 foot high is 7854 X 7 48

1,798 76

6 87 gallons 7 48 is found by

1,903 02

dividing the number of cubic

2,010 21

inches in a cubic foot by 231,

830 jB8

2,120 34

the number of cubic inches

2,233 29

m 1 gallon, thus, 1,728 - 231

2,349 41

" 7 48, 01 the numbei of gallons

2,468 35

ill 1 cubic foot The weight of

2,690 22 2,715 04

1 gallon of water is 8i- pounds ,

thus, 8 pounds

2,842 79

2,973 48

, 2 QOO lb o .. ..

1 ton g gg S40 gallons

in 1 ton

3,107 10

12

3,243 66

G

3,383 15

3,525 59

1,070 45

3,670 95

1,151 21

85, Fig. 12 IS a section through the plan E F and shows the leaching tank with the loading ti'ack r and

46 The Cyanide Process §32

unloading tracks s and /, also the gold-solution tank d and the sump tank d It will be noted that the leaching vats and the gold-solution tanks aie placed on a space leveled off on the side of the hill, m order to take advantage of gravity in drainage operations The car u runs on track r, which IS laid upon stringers over the tanks The stringers are placed upon bents, which are between the tanks, as shown by dotted lines

Tabde Iv

CAPACITY OP IvEACHIlsrO TANKS IN TONS OP DUX OBE

Diam-

etei in Feet

Height of Vat

3 ft

3 ft C m

4 ft

4 ft 6 m

5 ft

5 ft 6 in.

6 ft

14,5

50 j

86* Calculating' tlie Capacity of Tanlcs in Gallons anti Tons. — The capacity of a cylindrical tank may be calculated as follows Square the diameter in feet, multiply this product by the depth in feet, and this product by 5 87, which will give the contents of the tank in gallons.

Example, — What number of gallons will a tank 13 feet in diameter and 10 feet high contain

Solution — 13 x 13 X 10 x 5 87 — 8,453 gallons

Capacity m gallons 340 tons of water

8,453 gallons — 240 35 tons of watei Ans

§32

The Cyanide Process

Tabde T

SIZE OF GBAPiriTE OK-UCIBLES

Num

Bei

Holding Capacity, Liquid Measttie

Height,

Outside

Diameter at the Top, Outside

Diameter ; at the Bilge, Outside

Diameter at the Bottom, Outside

i Gal

Qt 1

1 Pt

Inches

Inches i

Inches

H

3#

If

n

If

H

a

Bi

4f

G

Oi

3f

Bi

n

9 '

Is

SO i

25 !

Ilf

13f

If

7f

lOf

Ilf

3 ;

ISf

8f

16|

llj

9f

16f

1S4

lOf

n5

16f

Crucibles for File Tempering

Note — Graphite ciucibles, being caibon, oxidize more oi less and should therefore be treated in a i educing and not in an oxidizing flame

Note —All item* in this index leEei first to the section (see the Preface) and then to the paie of the section Thus, Agitators 21 66" means that agitatois will be iound on page GO of section 27,

A

Sec

Page

Sec

Page

Acid oi es and liiiiding ,

Application o£ tolls ,

]5

" oies, NeuLialiring

Apion plates

Acidity in oies, Deteimlnation

Aigall loastei

ot

Ai rangement of mill apparatus

Acids and cyanide solutions

3Jl

" oC mill buildings

Adjustments of the Fine van-

" of mill buildings

m

nei

of stamps

Advantages o£ stalls

Ariastra

4b

AiRdavit, Nominineial

Assaying cyanide solutions foi

Agitatois,

gold

Alkali tieatment of oie in

" cyanide solutions for

silvei

Allis-Chalnieis ball mil!

Assorting ore

" classitiei

2G

Autonmlic dischaige jig

Alsmg pulveii?ei

" oiefeedeis

Amalgam . .

" tail way

" in shmos

settling boxes

,saving devices

Ainalgamntmg appaiatub

B

Sec

Page

" mills

Back knee frame , ,

Ball pLilveiizer ,

Amalgamation , ,

Bai 1 el amalgamation

Bai screens , , ,

and wet crush-

Base metal ores, oyanidmg ores

ing

Batea

Attwood's

Battel y blocks

bairel

plate cleaning ,, ,

retort, Charging

" plate SCI aping

" plates, Corrugated ,,

" stamp mill,

" plates, Dressed

Anclio! and tie-bolts

plates, Skinning

" bolts for battery blocks

" plates, Sweating

Anodes

plates, Swinging

Antidotes foi cyanide poisoning

" plates, Tainished

Appaiatns foi milling, Ai

" posts

langeinent of

3S

" step plates

vin

Index

Sec Pa-e

Sec Pam

Belt diiven orefeedeis

Cams

driven lolls

It

Capacity of ci uslnng tolls

elcvatois

" o£ leaching tanks ni

vatiiaers

sr

tons

Belt toi vannei

2T

of steam stamps

Bentfiame

Cap piece foi bent

Si

Berden pan

S8

Caihon dioxide. Cyanide loss

BUike Cl usher

fiom

a

'' 1 cvoh mgliearth futUdLe

foi anodes

Blanket tables

2S

2t

Cassell piocesb

Blanton cam

ai

Caustic soda, Amount of, Coi

Blend joabtmg

01 e

Blue powdei

ai

soda solutions, Btand-

Boss clietnical inixei

aidi/iiig ot

3t

clean-iippans

S3

CeiitiiEugal amalgamation, Ba-

Box scieenb

zin

Boxes for settling

S6

" pumps

Brace, Inclined

U

" lollei mill

Bteaking cups

U

Ceitificate for ftee minet

Ij

Bndgenian's mixed and divider

Cham and api ockct elevator s

Hiitish Coiambiati mill site

" belt con vejeis

laws

Challenge me feeder

Brodie mill practice . .

Channeling

Brown's lioisesboe fitinace.

So

Charactei of me in sampling

Bruckner raastiug cylindei

S3

Charconl precipitation of gold

Brunton's mechanical samploi

Chaigmg

Bucket sampling

" cyanide V Its

Bucking board

" cyanide its direct

" plate

" the chemical leagentb

Buck staves

" the meicury

Buddie, Collom type of

" theme

Evans type of

vats witli tailings

" Inwaid-floi\

Chemicals

" Linkeii bach type of

Chemistry of roasting

" Multiple-deck type of

of the cj amde pi oc-

" Paine and bteplieiis

2b

ess

" Outwaid-flov

" of zinc precipitation

Rcvob mg

Chilian mill

Jj

Stationai j

mills, Modem type

4G

BUhon melting

Chinese pump

" recovei v f i om charcoal

Chloiidizing mast

Bumping tables

Chlorination ju ooess, Watei toi

Burr alot sciee is

Chuck blocks

Butter's and Idean's reaction

Claikson and btaiiheld concen-

wheel ,

tiatoi

Classificatioii of lock bteakeis

Sec

Classifiei, Allis

Calcining ,

" Cahnnet type of

Ig

'' golci pi ecipitates

" Cone

Calculating sag of rope

Calculation of potassium cya-

Tiongh

H

nide m solution

Classifying macliinei , ,

California milhug practice

" machineij

" stamp miil

Clayey gold cues

Calumet classifier

Clean up

Cemuiett concentratoi

up bail el

Index

Sec Pae

Sec Fasrc

Cleaning alters

Convcyeis

up /inc bonces

Collom huddle

foi gramtlaled lab

" Jiff

3b

Si

Coppei and zinc boK

" mechanical sample

" apron plates

Coloiado stamp mill

" deposits in ptecipita-

Combination milluig

tion boxes

" process, Watei

' oie concent! atioii

loi

,58

" oie piepai ation

Combining weurlits o£ gold and

ores,

potassuun cyanulc

sulphide 10 i&tiiig

Compaitment jigs

3b

2b

Coi bels

ConceiitiaLes, Cyaniding of

Coi nish methods of Sampling

b

" Iheatment of,by

Coi iitgated vannet belt

Cost of cyanide agUation plant

Cnnccntiatuig maclilneiy

of masting

" mill, Design of

Ciassc's method of testing cya-

" milk

nide solutions

" mills

3.'

" method of testing foi

cue coiiLaming

gold .

clay

S8

Ciawls . .

" tubb

CiosS'lie for bent

Conccnti alien

Crown giant

'' Dry, process

Ciucibles foi melting bullion

" of cop pet ore

Ciushing x'olls

of lead and /me

" lolls, Capacity of

' of maiiganebe

lolls, Speed of

and Innonite

Cutting down the sample

Wet

Cyanide agitation plant, Cost of

ConcentiaLoi Cammett

GJcti action, Test fot

Diy centrifugal

liMviation process

Enibicy

" loss, Cause foi

Si

' (xilptn County

" loss fiom niineials

2.'

" mills, DcsciipLion of

" Ritt in gel's

" of potassium

" Tinimph

" oxygen and solution

" Wilfley's

" percolation, Test fot

" Woodbniy

" plant, Capacity of.,

" Wood's di>

" plant, Const! uction of

Conccntiatoi s

" plant. Location of

" Diy

plants, Airangemeiit

Magnetic,

of

" Water for

plants, Combination

Cone classifici

" plants, DilTei ences be-

Conical 1 evolving sci een

tween

Constanlk mechanical samplci

" plants, Object of

Const! uction of cyanide plant

plants. Specifications

" of heaps for roast-

fm

ing

poisoning, Antidotes

of Jigs

foi

' of mills

" process

' of rolls

" process, ( asseU'b

ai

" of steam stamps

" process, Chemistry of

Contents of tanks in gallons

" process, Kendall's

ConUnuoiis jig dischaige

" process, Modification

Conveyet for anlhiacite coal

of

Index

Sec Page

D

Sec

Page

CsratudepraGesfe, PeUtan-CIer

Dapping .

Davia-Colby kiln

piQcesSi Pneuinatic

Dead 1 oast

process, Scope of

Deflection of wiit ropes

process, Water £oi

Description of filtei box

solution for highest

" of Tailor Bnmton

extraction

sampling mill

Ih

soUition, Leaching

Designing roncenti ating works

with

Details ot hxiviation by cya-

solution, Pipes for

nide solutions

solution time of con

Determination of fiee potas

tact with oi e

Slum cyanide

solutions and agita-

Diagram of s iinpling mill

tion

Dies toi stamps

solutions and mineral

Dipper saiupimg

acids

G

Discharge doom foi vats

solutions and mineial

'' Jig tailings

salts

Discharging

solutions and oxygen

" settle! b

2r

solutions and the at*

'' tailings without

inosphere

solutions defined

" the leaching vat m

solutions, StancUrdi-

cyanidtng

B

Ditch rjglits

solutions, Testing

Ditches and water nights

Dodge crushed

sointjons, Testing

Dolly tubs

we ale

ai

Double discharged mmtais

"

sump solutions, Stand-

Dredging

aid j zing

Drcbsing and milling ore

(1

U

test

Di ler m sampling mill ,

21)

3T

''

test foi consumption of

Drum screens

((

test for ores

Di> concentiation

if

test foi percolation

concentiatoi , Claikson

tests, Objects of

and Stanfield,

vats

as

" concentratcus

it

vats, Chai ging

" concenliatois, Ceiiii ifiigal

it-

vats, Duecit-charging

" Clashing silver mill

Cyanides ,,

" milling plants

C /anidnig acid ores

" placet tnmpi, Woods

at Cupple Creek ,

" scieeamg

at Mecur, Utah

Drying gold piecipitates

base-metal ores . , ,

the 01 e

Cheinical limita-

Dump sampling'

jj

tions of .

Dumps .

CO irse gold , ,

Lombmation tieat-

B

Sec

Page

ment

Economic airangements

fJ

concentrates

EfftcL of lumps in sampling ,

tt

Details of

Electi 10 current and gold

flee milling ores

nide soUi turns

ft

ores

" current lociuijed foi

silver ores

gold pi ecipitation

Is

ti

Time of tieatmeiit

Electi icalpi ecipitatam, Advan-

foi .

tages of , ,

Cyliadei loasters

Electrolysis

Index

ec

Sec Pae

Glecti olysis in binding

Flue Vtinneij Adjustments of

Electiolyuc oyanulc piotess

Fuel for heap i casting

S9

EIllIi opiecipitation, Theoi y

" for level beiatouos

o£

tor stall loasLtn ft

Elevation of oiitei uul

2b

Fumes tioin heap i oabting

EJevatoi'i

Furnace, irdihcdf

Bolt .

Sk

" Plowed White

fenntl wliecl

location

lilsnci's eqinitHjn

liliiibiey eonccntiatoi

" pi ints

Evans btidclle

2b

" plants, Anangeinent

Evapoiation trays

oJ

Extraoil on by the cuinbiiuition

" Shaft Kitsting

So

cyanide ti eatmtiu

" Zellweger

F

Sec

Page

Fans, Exhati'it

a

Sec Pae

Feed and loss oL ineicui v

Is

Gaming

FLoding 010 in Uie b itLeiy

Galena toasting

F 'ifig claim foi mill site

U

Gate for , Plebetle type

Fillei boards

of

box t

Gates foi j igs

" box, Vacuum

Gilpin County bumping table

County cnnuentratoi

Eiltei s, Cleaning

" County staiui) mill

" Constiuctioii of

Gjet slain

ten testing cyanide

Globe mill

" foi vats

Gold assay

" fjiaiel

cyanide soluUoitb and

Vaeinuii slime

Filti iLioii of gold ptecipilates

" Cjatiidmg

Final ginuling ot sample

" in pytiLeb

2;

Fine-ci iishmg micliineiy

" oie sainplinf; ,

Finishing lolls

piecipitates, Calcining

' the sample

piecipitateb, Diying

Fust simple

Is

precipitates, hiltiation of

Fish plates , ,

2f

piecipitates, Fluxing of

Float gold

" piecipitates, Jleltiiig ol

" gold and amalgatii-sa'

" precipitation by/inc fmne

S3

ving devices

piuupitatiun, Elect lie

Flool forsimpling

cut lent fui

fi'loiiung , , ,,

precipitation fioin eja-

Fluxing gold ])! ectpilates

ntde solutions

Foot-powci pti miiuUu

Si

slmieb, Aud tiuatment of

Forms of pans

slimes, Wablniig

PoundaLimi Coi bunts

Grab sampling

Fractioiml selection

iTrani and grain tables

3t

Frame foi stamp mill

Gianulatiiig si ig

Fr amed bent

Giaphite GUtcibles ,

Flames foi sciuuns

Flaming buildings

Gravel iiltei s

limbei stuiutiues

Gieeleypan

Ftee-mdlnig oies, Cianidrng

)

Gietn'b Jiggei

2b

" millet's cel tifictite

Gi Hiding pans

Pttebuig band

S

" sample

Fnie vannei

Jo

Gii7/bes

S

Guaidiail

S£C

S4 a2

Gyi atory crualiei s ,

H

Page

Hand-rabble 1 e vei beratoi y furndLe

S

HandliniC battery

Oj #

aiatenalb

sUine'i

Hau Jig

Sb

Jig) Qnn-Jt letwrn

Head-house

Headmgii

Heap 1 casting

Heating pulp m pans

2T

theretoit

Heavi flaming cutting joints

" fjain.ng without cutting joints

Hebei le gate

Height of sampling mill

sr

Hem Uite roasting

High-speed lolls

speed rolls

Huffman barrel

M

HoUlioff furnace

Homestead iv'ater lights

Hooks foi leiching sats

Hooper pneuniatiu conuentiator

Hoi n's pan

Horseshoe fui inte

Howell-Wlnte fuinace. The

Hunt automata, railway

elevator

Huntington niitl

Hi di anlic ( classification

Jigs

Hyclraulickmg

Hydiogeti amalgamation, ifo!- loy

So

Hy d I om e tal 1 in g 1 c al app a 1 a t u s

Hydiometalluigy

Sec

Page

Inclined brace

Inside amalgamation

S'?

Invvaid flow buddies

lion for anodes

" me conoentiation

" me preparation

" oieioasting

stamp guides

S5

S7

J

Ssc

JacU-stiinger

Jig, CoUoni type

ditch 11 gc, Automatic

9G

" dibChat geil

Halts tipe

middlings

" pioducts, Tiuatmeiit oL

" quick 1 etui n, Hnica

" starting

2fj

tailings dischaige

3b

Jigs

" Compaitment

" Reupi locating sci een type

2b

" Slide type

" Stationaiy scioeii

Johnson's charcoal piecipita-

tion piocebs

K

Sec

Page

Kendall cyanide piotess

Kiln 1 ousting .

" masting, Colby

Km Head mill t

Knee £i o-me . ,

Kiom pneu/uatjo jig

Kiupp ball pulM,ii''el

Page

Kaboiatoi y flppaiatus leq tilled lor t-yamde ap-

paratus

3t

" tests for cyaniding

Like Superioi though classifier

Lamb's tailing sampler

Lathe for LUtting mwo shavings

Lauiidei s , , ,

Laws 1 elating to watei lights

L iving tiamway support

Le Idled tailings, tianipUng of

LeaUiiiig pi ocesses, Watei foi

" w 1 th a sUorig cyanide

solution

" with a weak cyanide

solution , .

vats

" vatb, Wooden

Si

Lead and zme scpai atbn by

concentiation .

S

" Gvapoiiition tiay

cue concen nation

Lease for mill site

Ligei wood cableways

limited conditions of nicchan-

ical sampling

Limoni te roasting

Index

xm

Sec

Pajre

Sec

Pa ire

Lined mortars

S')

Mt-Uing the bullion

Lmkiinb.ich buddLc

Meicuiy, Feed and loss of

Lixivi ition

" tips

Locating a cyanide plant

at

" wells

Lia-ation and leeoid of mill site

Si

Ifesh ot screens

'' ceilificate of null site

Metallic salts and cyanide solu-

" notice of mill sjte

tions

of Cl uslieis 111 mills

Si

a

'Methods of i ousting

" of ditch 1 ighti>

Middlings

" oi dumps

H Jijy

of tui paces in mills

Mill buildings, Ai t angemeiit

of mill sites

for

Ib

" of mill with lereience

" site. Clown gi ant

to powei

" site, Piling clnim loi

" mills witlirefei dice

site, Location notice of

to supplies

" site, Non-mineial affidavit

" of me bins

of

" of lock Ineakets

" site, Recoid and location

' of water tanks

of

Log wash 01

2/

site, Recoid and location

ceitilicate of

Longitudinal biaco

" sites

Lossfioni ininmals soluble in

sites, Bntish Columbian

cyanidfc ,

at

laws of ,

fi om washing 01 es

ai

" sites, ITow to patent

of amalgam ,

" sites, Private

ot cyanide

M

sites, Public

" of cyanide bi caibon di-

Mills, Amalgam at I tig

oxide

at

anddiensks

' of ineicin y iii stamp mill

" Concenli ding

mg

" Const! uc Li on of

" of watci

fm sampling

Losses of gold

Is

Miiieis' pan

of merely

3,*

Modern amalgauiaUug ma-

LUluig vannei

3f

cliineiy

B1

Liiinp oie roasting

ao

So

" Cliihan mills

3B

Lumps, Effect of, in suinphng

Moist me sample

So

Moitai foi amalgamating

M

Aec

Moi tise

Magnetic cmicentiatois

ao

Mud-sill

" conceiitiatms, Com-

MulUplc-deck buddies

parison of

" jiwctiisheis

" iron ore loasUng

" sepal ation, Theoiy

N

Sec

Page

of

sr

Native cop pel oies

Magnetism of miiieials

2,

Non-am ilgamablc gold

Masonry fm mills

in

J fat to roasting ,

ao

o

Sec

PtJ?e

McCone pan ,

Si

lie

Object of automatic ojc feecleis

9")

Bs

McDougall Ltinacc

ao

" of sampling ,

Mccli imcal pans

" of scttleis

sampling

Objects of making cyanide

" Sampling, Limiting

tests

conditions of

Obtaining a con eel sample

Ditecbanically tabbied Cuinaces

Older of stamp di op

Melting gold piecipitates ,

Ole, Alkali ti oatment of

Xiv INDEX

Sec

Ore beds at furnaces

Piecipitation boxes for cyanide

bins

pioccss

" (leJueiy at mills

" diesbing"

h

Pielimmai y oie washing

dressing machinery

Picssure tanks atMercui, Utah

3G

feeders

Piimitive amalgamation

" pulling

21

" appal atub and meth-

" roasting

ods

Principles of sampling

sampling, Small lots of

Ptivate mill sites

ObCiUating mill

Pioperties uf meicuiy

Ontward-flow buddies

Priisfaian blue

Is

Oxidizing 1 oast ,,

Public samplers ,

Pulleys, Diffeiential

P

Sec

Pulp distubution box for van

Packing block

net s

" bolts.

Pumps, Centiifugal

Go

Paine and fetepliens buddle

" foi sand

Paints, Protective

at

Pyute 1 casting

Pan amalgamation, Recoveiy

Q

Sec

Pans fot amalgamating by the

Qiiartenng

Boss process

Quick diop stamps

Patio process

Qiiicksilvei cathode fm cya-

Patton pan

5f)

nide process ,,

Pelatan-Cleiici anide process

Percentage of precipitation in

R

Sec

Page

zinc

3S

Rabble

Percolating tests

Rabbling

()

Peicubsion tables

Radial lollei mills

Pei fectioa concentrator

Rail, Elevation of

Picking belts

Reciprocating screen jigs

Pile bent

Recoid and location of mill site

" bent trestles

Recovering bullion fiomehai-

Pipe discharge foi jigs

2fa

coal

Placing timbeis

Reducing toast

Plane belt for vanner

Reduction of fii st s uncle

Plant foi ore treatment

Refining gold slimes at Moicui

Plants for wet milling

gold zinc precipitates

Pneiimaticconcentratui, Hooper 27

Removing carbon dmxidc ii om

" cyanide pi Dcesfa

ores

" Pg

" sulpliin from mes

" zinc sulphate fiom

Points to be obseivcd m con-

gold slimes

centiation

Retaining wall, Piopoition of

Poisoning by potassium cya-

walls and frost, ,

nide

walls foi mills

Ponds for settling

RLtoitchaiguig

9H

Posts of timber

healing

Potassium cyanide

Retorts for amalg iniation

" cyanide and solu-

Reveibciatoiy fuiii ice, Hand-

bility of gold

tabbled

cyanide, Process of

" furnace, &ie of

" cyanide test

" fiunaces, Me-

Powei of rolls

chanically

Precipitates, Acid ticatmentof

rabbled

Index

Sec

Revolving: bmldle .

Riibbei,

Eureka

" hcai tti f 11 1 n ace

Rule st7e of 01 e sample

blakes

2.)

Rusty gold

lo istmg* Lvlindeis

SCI tens

2b

'1

S

So.

'' taUuiRb sauiplet

Safes ioi amalgamation

S8

2G

Richauls tiainplei

Salt tonccntratinn

&K

Kiffle bamplei

Sample, Cutting clown ot

kiyhL to use w itei

2t

drying

RUtingei peieussion table

2r

Final gi uf

2)

lioasLin blonde and pJ lit

iO

gi inder

2d

n

" ChumisLi y of

"

Reduction ot

Cubtof

Sepaiation of

cyliudei, Bitlckner

Size of

" cyluideis

bi7e of, mechanically

" Davis-Colby kiln

taken

S9

" Dead .

"

Si7e of, Rule for

fine 01 e

Sciniplei

, Bi an ton's

" ftunace, Aigall

u

Col loin's

" furnace, Blown's

Constant &

Si

" f u i n a c e , R o p p

Jones's mo

straight line

"

Lamb s tailing

2d

Revolving, foi laii-

tiple-health

ings

furnaces

Richaids's

Gjeib kiln

'

Rime

U

" gold blfmesat ileicur

"

Snyder's

lieaps, Constiuctiou

tin

of

tl

Tophaui's

Hematite

Transvaal

ill heaps

Venn's

So

' in stalls

Sampleis, Compauson of

" iron 01 es

Public

" Limoulte

Sampling by channelaig

" lump oreb

C(

by Coinibh method

G

" magnetic non 01 e

(1

by fi actional -

" oic , . .

tion

' ptelimmaiy to cya

u

by hand

Hiding

u

by quarter mg

b

Pui poses of

chatactei of oie

" sulphide ores

a

dumps

" Sweet

(1

hooi

" tlicoie

((

for moistiiie

llohhms picking 'belts

Cxiab

Rock breakers

It

leached tailings

lump ore

Roll ciualung, Concenliating

It

miU, Diagiamof

If

mill drier

" ]ftW lock bieaket

u

mill for gold mine

So

RollSt Finishing , ,

l(

mil), Height ot

" Roughing

It

mill, Tayloi-Bi unton

Roller mills

It

millfa

" niillb, Ceiitufugal

2B

It

Object of

Ropp straight-Une fuinace

l(

Ptiiicipleb of

Roughing lolls ,

ao

(t

Reraai ks on

Round'flole btiecnn,

tl

loom .

Ndex

Sec

Sampling small lots oE ore

2 ')

tailings

" Weight of 01 e foi

With a split shovel

with bnchet

S')

" with dippci

with slotted pipe

S9

h ind- wheel elevators

sa

Seal fed ]oint

behiedel's tank

Scope of pipe dischaige jig

Sg

of the anide process

bcieen cloths

frames

2 S

" ]igs

Screens

'38

foi suing

fen washing

shaking

Sueellng, D 13

" the ore

" Wet

vSectional mortars

stamp guides

Self-acting samplers

Sepal dtiffti of the sample

Setting the apron plaLes

vSctrlei boss

Settleis

Settling hoses

' hoses, Automatic .

ponds

Shaft f III nace

So

shaking plates

screens

Shoes foi stamps

Sickening

siemens Hal&ke cathode

bills, Foundation foi

Silvei amalgamation

" assay

e sti action by cyanide

" mill, Diy crushing

" nitiate solutions, Siaiid-

" initiate teat of potassium

'' 01 ea, Cj'adding

stamp mills

Single discharge moilai

Sinter hearth

Site foi a mill

Sue of gold particles in

ding .

of mechanical sample

Sec

Size of rcverberatoiy furnace

" of sample

Si/es for sampling

Suing machinery

" Sc i eon

a

tiommel

2b

Skinning battery plates

Slag gianuJating

blagging heal th

Slide ]ig

Slime Loncenti atoi s

" m cyan 1 ding

" Tieatment of, by cya-

nide and agitation

Sloping gioiuid and cyanide

mill

Slot screens

blotted-pipo sampler

Slow diop stamps

Smelting plant, Lot.ation ot

" plants, W itei foi

Snyder's sainpiei

Solubility ot gold and potas-

sium cjanidtj

Solution pipes

3!

3!)

bolting 01 e

Speed of ciushmg rolls

" of van n 01

Splash boauls

Split caps

" shovel

shovel sampling

Spitakasten . .

Staking out mill sites

Stall consti notion

" loastmg.

Stamp battery

" cams

" die?

drop

" drop,Oideiof

guides

" mill

milling, Califoi ma pi oc

esb . . ,

m>, Rccoveiy

" mills, Watei supply foj

Pneumatic ,

" shoes

" tappet

Standard silvei intimate solu-

tions

Standaidi/mg cyanide solu-

tions , . ..

Index

Sec

Page

Stancldi cluing cyanide sunip

Testing ores foi the amde

bolutioiih

pt ooess

" Cot mu la Eoi cy-

" plant for aiding

n

anide solu-

" potassium cyanide

tions

" strong cyanide solu-

so 1 u tt oti s ot

tums

caufctiG soda

" tables foi the cyanide

Stai Ling a jig

process

So

SLalionai y buddies

" the woiking solution

SLieenjigb

foi cyanide

Stay-box

" weakcianidesolutions

Steam stamps

S')

Theoietical tapauty of crush-

" stamps, Tiemain

S'!

ing lolls

1(

Steel cyaniditig vats

3b

capacity of i oils

leaching vats

Xlieoiy of ciasstfving inacliiii-

3tep plates

2S

ety

2fi

g

fetetefeklE loastei

" of concentiation

2b

Si

Stiajnosfoi anmlgamation

2S

of concent! at I on

StiengtU o£ cyanide solutions

Tie-bolts for b ittety blocks

2,7

toi leaching , ,

Timbet foi cyanide vats

" of weak cyanide so-

" post

S2

lutions .

G

" sti LictLiies, Pi among of

Stnngei .

Tin oie concentiaLion

Sturtevant-ioll jaw crubhei

" sample

Sttlplmtiisingiaa&t

So

Topham eariiplei

So

Sulphide masting

So

Tossing tubs

Sway bjaco

Ti am ways, Wn 6-1 ope

Sweating battel y plates .

Tiaiisvaal sample i

Sweet roast

Ti dps fot catching mercury

Swinging plates,

Tieatineiit of concentrates by

agitation

T

bee

" of jigpiodiicts

of oie, Plant foi

Table conceiitiaLion ,

nr

" of slimes by agita-

" of Blake ci usheis

tat 11711

" of Cl ushnig 1 oils

S5

Ti eenails

" of Dodge Cl uivhei

Treinain steam stamp

" of weights and dimen

Ticstles

sions of high-speed i oils

Triumph concentiatoi ,

Tailings

Tioinmel

" Charging vats with,

Tiongh classified

Dibchaiged

Tub, Doliy type of

" Dlschaige, for jigb

Tubs forconcentiatmg

" Sampling

'' Tossing

3G

wheels ,

Tulloch oie feeder

Tank, Schiedel's agitating

Tunnel head

Tanks, Crold solution

ai

Turnbull's blue

Tappet

S5

Tellmide gold ores

Sec

Page

Tenon

Vacuum filtui box

Test for acidity in ores

at

" slime filters

fot cyanide consumed

Si

Vannei belt, Con gated

" foi precipitation

" belts . . .

U

of oxti action ,,

Flue

Testing for potassium cyanide

Liihng

'' for late of peicolation

'' pulp distribution bo's ,

iV M III —~$5

Xviu Inuex

Sc

Page

Vanner speed

sr

Weight and diinensionfo of high-

r,

speed lolls

S7

ofwirpiopo

Vanning' machines

Weights to he taken in sam-

" tables

2't

pling

So

Vai lable mesh screen

2G

n

Wells foi catching met cm y

2H

Vaiiiej pan

Wet ciusliing and amalgama-

Vat, Bottom discharge

tion

discharge doors

milling plants

discharging

" scieemng

Side discharge door

" sizing SCI een

Vats, Chaiging, with tailing

Wethei lU t onceiiti ation

Construction of

Wethey multiple health furnace

?o

" Diieot ctuiiging

Wheelei pan

O'

Intel mediate chaiging

Wilflcv table

fateel

Wueiopc, Defiecttoii of

IfJ

Vezm satnplei

rope tianiwa s

Si

" lope, Weight of ,

W

Sec

PajQ'e

Woodbury Concentiatm

Washing gold simies

Wooden jigs , ►

3B

" ores foi cyanide pi oc-

" leaching vatii

ess

r

" stamp guides

" ores foi cyanide proc-

Wood's diy placet inuici

ess

01 es piehminary to

Z

Sec

Page

cyaniding

Zellweger i oastei

" screens

3G

d

Zigzag Mttei y plates

Water foi chlorinition process

5D

Zinc bos, Filling the

" for conibination pi ocess

bases, Ai i angement ot

al

for coiicenUatois

busies, Caiu of ,

3S

" foi cyanide pi ocess

Do

" boses C'lemingup

n

" foi leaching pi ocesscs

" boses, Const! notion of

" for smelting plants

boxes fni weik solutions

3S

" Loss of ,

" bojk.es, fcize of

Right to use

boxes, Scum on

S3

rights, Homestead

" cai bonate i oastnig

So

' saving device foi jigs

2G

" disks

" supply for milling

" fume, De/lnitjon of ,

" supply for stamp mill

" fume precipitates

S3

" tanks

" Ole cohcenti ation

Wateipioof paints

" precipitation

Weak cyanide solutions dis-

" shaving lathe , .

sa

placed by wttei

shaiings

" cyanide solutions, Zinc

" shavings, Piepaiafion of

boxes for, . , ,

" sulphate in gold slimes