METALLURGICAL PRACTICE SOUTH DAKOTA SCHOOL OF MINES. Department of Metallurgy. Rapid City, South Dakota. JUNE, 1904. ERRATA 5 %. 1. Page 23, foot note, third line: Read bromine for brome. 2. Page 28, line 30: Read zinc bromide for zinc bromo. 3. Page 28, line 32: Read bromo for bromide. 4. Page 28, foot note: Read Simpson for Sampson. 5. Page 29, line 12 : Insert bromo before the word cyanogen. 6. Table III, test No 5, column Time of Treatment: Read k ‘and 48 hours standing” for “48 days standing.” 7. Table I, test No. 4, column Time of Treatment: Read “41 hours agi- tation and 31 days standing” for “60 hours agitation.” 8. Table I, test 8. column Time of Treatment: Read “22^ hours agi- tation for “same.” 9. Page 35, first table, Ore C, column “Increase in Extraction,” last line: Read 6 per cent for g per cent. 10. Page 35, second table, in second column heading: Read “31 days contact” for “3 days contact.” 11. Page 52 Table, Dakota Mill: Transfer figure “86 tons” in column “amount of solution passing while filling” to column “amount of battery solution.” Oak Street JNCLASSIFIED BULLETIN NO. 7. OF THE SOUTH DAKOTA SCHOOL OF MINES Department of Metallurgy. l. , 2 . 3 . Sulphide Smelting at the National Smelter of the Horseshoe Mining Company, Rapid City, South Dakota. By Charles H. Fulton and Theodor Knutzen. Laboratory Experiments on the Unoxidized Siliceous Ores of the Black Hills. By Charles H. Fulton. The Crushing in Cyanide Solution Process as carried on in the Black Hills of South Dakota. By Charles H. Fulton. Rapid City, South Dakota JUNE, 1904 THE RAPID CITY DAILY JOURNAL PRINT- Letter of Transmittal. South Dakota School cf Mines, | Rapid City, June 5, 1904. j Sir: — I have the honor to transmit herewith a series of papers, by Charles H. Fulton and Theodor Knutzen, on Met- allurgical Processes in South Dakota. I submit them with the recommendation that they be pub- lished as Bulletin No. 7 of the School of Mines. Respectfully, Robert L. Slagle, President, Hon. Ivan W. Goodner, President, Regents of Education. Digitized by the Internet Archive in 2017 with funding from University of Illinois Urbana-Champaign Alternates https://archive.org/details/metallurgicalpraOOfult Introduction. The successful treatment of the unoxidized siliceous ores of the Black Hills is a subject of vital interest to the mining frater- nity of the region and the experiments on these ores were taken up by the Metallurgical department of the School of Mines with the idea of rendering what assistance it could in this direction to the millmen, knowing that very often their time and opportunity for this kind of work is limited. The crushing in cyanide solution process has within the last two years assumed great importance in the Black Hills, and for that reason a detailed description of the process should prove of interest. The writer wishes to express his obligation and thanks to all those who have so kindly and freely furnished him with informa- tion; his especial thanks being due to Mr. John Ingersol, Mr. J. V. N. Dorr, Mr. Freeman Steele, Mr. G. Howell Clevenger, Mr. John Cross, Mr. Baldwin, Mr. James Hartgering and Mr. John Millikin. He wishes also to acknowledge the indebtedness due to Mr. William Bowman, his assistant, for the faithful and careful work done in the experimental tests on the unoxidized ores of the Black Hills, also to acknowledge his indebtedness to Mr. S. S. Arentz for much aid in the same work. Lundborg, Dorr & Wilson Cyanide Mill, near Terry, South Dakota. Sulphide-Smelting at the National Smelter of the Horseshoe Mining Co-, Rapid City, S- D.* * BY CHARLES H. FULTON ANDTHEODOR KNUTZEN. The plant of the National Smelting Company, a corporation controlled by the Horseshoe Mining Company, was built during 1901 to smelt the dry siliceous ores of the northern Black Hills, extracting the gold and silver values in a matte of low copper- percentage which is shipped to Omaha and Denver for refining. Originally, the plant was designed to collect the values of the siliceous ores is an iron-matte, which was to be resmelted with lead-ores, in a lead furnace, the lead-bullion produced to be re- fined into Dore bullion in English cupelling-furnaces, How- ever, the scarcity of lead-silver ores in the Black Hills, owing to the present non-productiveness of the Galena district, led to the abandonment of this plan; and both shaft-furnaces of the plant were run as matting-furnaces, the mattes produced being shipped as above stated. It is not our intention to present anything very new, but rather to supplement the interesting and valuable paper, Pyritic Smelting in the Black Hills, by Dr. Franklin R. Carpenter. 1 Smelting in the Black Hdls is a difficult matter from a com- merical point of view, owing to the fact that the only produc- tive material going into the furnace, generally, is the siliceous ore and a little copper-ore, the pvrite, or pyrrhotite, and the limestone, being barren of values, and no lime-ores, or gold or silver-bearing pyrite being at present available in the Black Hills. The recent price of coke from the east or from Colorado has also been prohibitive C$9.50 per ton), and Cambria, Wyoming, coke ($4.50 per ton) is of such inferior quality that it cannot be used alone, but has to be mixed in the proportion of 2 to 1 with x Trans . , xxx., 764. * [Reprinted from the Transactions cf American Institute of Mining E~ gineers February, 1904.] 8 eastern or Colorado coke, to be able to smelt with it nt all. The National Smelting Plant is situated at the eastern end of Rapid City, on a terrace site on a spur of the Fremont, Elk- horn & Missouri Valley Railroad, a branch of the Chicago & Northwestern Railway system. Directly below the railroad- trestle are nine 125-ton bins: Three for siliceous ore, 2 for lime- stone, 2 for coke, and 1 for coal. The bottom of the bin slopes 50° , the planking being protected from wear by railroad- iron, placed transversely every foot. The material is shipped to the smelter in 20-ton ore- cars, usually having a bottom-discharge. It is sampled by shoveling on a sampling-floor at the top of the bins. Lots of 60 tons or less are sampled by taking every fifteenth shovel, while those in excess of 60 tons are sampled by taking every twentieth shovel. The sample is thrown down a shute at the side of each bin, carried by a barrow to the sampling- works, and is there crushed in a 9-by 15-in. Blake crusher which divides it into halves by an ‘‘A” discharge, one-half going directly to a pair of 24- by 12-in. Allis-Chalmers rolls. The discharge from these rolls is re- shoveled, every fifth shovel being taken as the sample, or every tenth shovel, if the ore lot is more than 60 tons. The sample ob- tained in this way is crushed in a pair of 12- by 12-in. sample- rolls, then coned and quarted on a plate-floor, and the resultant sample ground in a sample-grinder. The moisture is determined at once on the sample-floor, in a specially provided drying-cup- board. FURNA CES — There are two blast furnaces, one, a copper- matting furnace, 144 by 38 in. in cross section at the tuyeres, and 15 ft. in height to the downtake, and the other, a lead-furnace, 120 by 36 in. in cross-section at the tuyeres, and of the same height as the copper-matting furnace The lead-furnace is used as a matting-furnace by bricking up the well. Both furnaces have removable hearths placed on trucks, and the off-take at one end just below the feed-floor. They are charged by a specially designed bottom-dump charge-car, running directly over the furnace-top, In our opinion this method of charging is the most desirable one. No trouble from fumes is experienced on the charge-floor. The furnaces, however, could easily be in- creased 4 ft. in height, which would enable better work to be done in them. Steam is furnished by two 200-h. p. Stirling water-tube 9 * * boilers, .-with a steam -pressure of 125 lb. per square yich. A No. 8 Green blower furnishes blast for tiie large furnace, and a No. 7 blower of the same. type for the small furnace. Both blowers are directly connected to horizontal engines on the same bed- plate. The blowers run from 130 to 150 rev. per min., furnish- ing blast at a pressure of from 14 to 18 oz. per square inch. The blast main from the large blower is 30 in. in diameter, and that from the small one 24 inches. The coal is of a very poor grade, being slack from Cambria, Wyo., which costs $2.75 per ton, delivered at the plant. The ashes are sluiced from the boiler-plant through lauders to the slag-dump. The water-supply of the plant is obtained by pump- ing from Rapid Creek, a few hundred feet below the plant. SLAGS — Table I, gives the analyses of typical slags made at the plant. Table I — Analyses of Slags. 1 Kind. Silica. Ferrous (xid». Lime. I Alumina Zinc Oxide. Blowing in sing Per Cent. 42-65 47-5 50.2 42.86 Per Cent. 16 67 18.7 16.35 f 17.24 Per Cent. 3°-7 28 25 28.30 26 . 6 t Per Cent, 6.85 3-5 4.2 9-39 Per Cent. Typical slag Typical slag High alumina a r d zinc 2.28 The precious metal-content of the slags given in Table I are usually, gold 0.01 oz. , and silver 0.20 oz. per ton, a trace of copper also being present. The limestone used as a flux is very pure, as shown by the analyses given in Table II, and contains only a trace of mag- nesia. Some magnesia, up to 8 or 10 per cent replacing lime, would be desirable, owing to its greater silica-saturating power, anddhe lesser^specific gravity of the resultant slag. The Golden Reward plant at Deadwood uses a magnesian limestone success- fully. At the present time- no limestone containing magnesia is available in the vicinity of Rapid City. The slags are fluid and flow readily from the furnace with a slight arch. They chill quickly, which indicates a rather high temperature of formation. Water-cooled slag-spouts have been tried on the furnaces, but had to be discarded owing to their « marked chilling-effect on the slag. The greater part of the slag " is granulated by waste, water from the furnace-jackets and dis- charged to flat-cars, of the railway which utilizes it as road- i IO ballast. The slag flows from the settling^pot in a thin stream, falling f rom a height of 4 ft. and strikes the water which flows in a heavy cast-iron gutter of semi-ellipsoid section, 8 in. wi.de and 6 in. deep, inclined 3 in. per foot for the first 10 ft. The section of the gutter beyond the first 10 ft. is of a larger cross- section, and inclined but 1 in. per foot. Owing to excessive wear, the section of the gutter where the slag strikes it has to be frequently renewed. Heated blast is used in smelting. The blast heating appa- ratus is a U-pipe stove, containing 12 U-pipes each 16 in. in diameter and 10 ft. high. This type of stove is not as efficient as it might be owing to the difficulty in preventing leakage. The stove is placed in the dust-chamber directly beneath the down- take, it being intended to heat the blast only by the waste heat from the furnaces. Under ordinary conditions the temperature of the blast, taken at the tuyeres, is 1 3 1 0 Fahr., with the outside air at 65° Fahr. With the cupelling-furnaces. running on some experimental work, the temperature of the blast at the tuyeres was as high as 320° Fahr , with the outside air at 77 0 Fahr. The flue of the plant is of the zig-zag type, 350 ft. long, ex- tending up hill to a plate iron stack, 10 ft. in diameter at the top, and 166 ft. in height from the bottom of the flue where it merges into the stack. The total height from the tuyere-level to the top of the stack is 275 feet. Table II —Composition o f Materials of Furnace-Charge. Name of Material. Silica. . ! 5 i i fl ■ jo 6 o i 5 i Carbon V ZK 0. 0 w .< £ w Per Per Per « er | Her Per Per Per per j Cent. 1 Cent. Cct. Cent ! Cent. Cent. Cent. Cent Cent. Monteeuma pyrite ... > 0.35 | 7 63 3 <- 7 ^ ! 2 57 0.30 32-3 6.50 Bion pyrite 2 7.0^ ‘ 3 1 . 7.5 I 37 °3 Penobscot ore . Hen Hur ore 61.44 1 62.56 7 3.11 29 2 (a) 10.7 (a) 12.36 0.68 (a> trace 3.01 Ben Hut ore 7" 1 3 (b) *T * O *t . . . 7.2 Limestone /O* A A 1.94 31.62 5 ,.6, o .63 Montana copper-ore. . , *. Ashes: 2147 22 85 24 .i 6 Cambrig coke, 30 per ce^it 36.57 4°- 35 i4 . .... a. 01 1 2.75 t race Fail mount coke 60.46 37.-09 * • A-shas, 12.5 per cent. 1 b U ■ (a) Includes feme oxide. ** (’>). Fernc oXide . The Penobscot ore contains from 0.88 to o .<)6 oz. gold and from 1 to 2 oz. silver per ton. The Ben Hur ore contains from 0.73 to 0.80 oz.. gold and 1.5 oz. silver per ton. It is generally aimed to keep the ore-value not less than $20 per ton. - 1 1 MA TTE — The first matte produced is low in copper, con- taining from io to 14 per cent copper and from 4 to 5 ox. gold and from 6 to 7 oz. of-silyer per ton. The matte-fall figured on the total furnace-charge is from 4 to 5 per cent, this fall being amply sufficient to collect the values. We believe a 3 per cent matte-fall would be sufficient. It was found by experience that some copper was absolutely essential in order to have the matte cpllect all of the values and at the same time to produce suffi- ciently clean slags. In ipoi, shortly after the plant was started, it was endeavored to run without copper-ores, owing to the difficulty of procuring them. Mattes were made with only a trace of copper in them, but the slags invariably contained from $i.oo to $2.50 in value per ton in gold. This loss being too great for profit, copper-ores had to be procured. Upon the addition of copper-ores to the furnace, the abnormal loss of value in the slag disappeared, dropping to the normal value of from 20 to 30 cents per ton and often less. It has been demonstrated by Dr. R. Pearce 2 and E. G. Spillsbury 3 that iron sulphide will not collect gold and silver Metallic iron will collect gold, but prac- tically no silver, as Dr. F. R. Carpenter has pointed out 4 — a fact which is amply proven by the sows, or metallic-iron accretions, formed in the hearth of the furnace as well as in the fore-hearth. The matte formed rarely contains more than 30 per cent sul- phur, while the iron monosulphide contains 36.36 per cent, so that the matte is evidently a subsulphide. It also contains me- tallic iron, which can readily be abstracted by the magnet. We agree with Dr. Carpenter that it is this metallic iron in the matte which collects the gold, but, unfortunately, it is rarely in the matte in sufficient quantity to give clean slag^. Paradoxical as it may seem, the quantity of metallic iron formed in the furnace is due to a large extent to the amount of oxidation which takes place in the furnace. This point is referred to later in this paper under the section devoted to sows. The amount of oxidation being difficult of control, thematte- composition and matte-fall vary from time to time. There are occasions when practically no matte is being made, but the Same time the slags do not increase in value, showing tha t while no matte is made, metallic iron is being produced. This? condW* tion of affairs occurs during periods of much oxidation, and is usually remedied by the charging of extra quantities of pyrite, 2 J'ntf/s.y, xviii'. 4.54 s Trans. I xv. , 767. 4 Ob cut. 12 „ ' . i 'i . in order to furriish mor.e sulphur, and leave ; some to remain in the ma'tte. *- Accretions^on the furnace-walls will decrease tne quantity of matte made, by raising the zones of oxidation. Of course, the quantity and pressure of the blast, also, greatly influence the matte producion. f DESULPHURIZATION — The matte-fall being generally but 4 or 5 per cent, shows the great desulphurizing action of the furnace, which amounts ordinarily to from 70 to 77 per cent. To take the workings of a typical day, the quantity of sulphur fed into the furnace in the shape of pvrite was 7,350 lb. and the sul- phur in the matte was 2,100 lb., showing a loss of sulphur of 5,250 lb., which is equivalent to 71.5 per cent of the total quan- tity in the materials charged into the furnace. The desulphurization-figures for December, 1903, were as follows:—The quantity of sulphur fed into the furnace in pvrite, 175 tons; in matte, 37,5 tons; in copper-ore and concentrates, 27 tons, a total of 239. 5 tons. The sulphur in the matte produced was 52 tons, showing a loss of sulphur of 187.5 tons, or 78 per cent of the quantity charged into the furnace. The sulphur in the materials carried over mechanically in the flue-dust may be disregarded on account of its relatively small quantity and the fact that much of it is in an oxidized con- dition. The total quantity of flue-dust produced in treating 3,- 952 tons of charge amounted to 10 per cent, or 395.2 tons, hav- ing an average sulphur-content of 3 percent, which is equivalent to 1 1.8 tons of sulphur, a large portion being in an oxidized form. The matte produced without copper-ore was made with the furnace running on pyritous material of the following composi- tion. Iron, 24. 52;. silica, 27; lime, 3.06; lead, 5.82; zinc, 8. 55 ; sulphur, 28.03; arsenic, 3-4 P er cent; copper, trace; gold, 0.04 oz,, and silver, 2.86 oz. per ton. Table III .—Composition of Mattes. Kind. Iron. Copper. Sulphur. Zinc. Gold. Silver. Made without copper ore Ma’te made with 1 ttlc topper-ore .. Mat,te Per Tent 6i. r 68.5 Per Cent. . 1.6 • 3 . 5 Ca) ‘ 5. s'? Per Cent. - 2 7-9 Per Ct. 2.18 Ounces Per Ton 7.1 4.2 17-65 - 17.ll IT-73 II.62 " Ounces Per Ton 9.7 8.7 10.25 2 i .4 I9.7 i 8.76 Typical 'Matte 7 * . 22.6, . - 26.5 I 9-3- 30.0 1 ypical Matte Typical Matte. . f (a) Ttiesla^ acco'mp.mying this matte had an ^ssay vaftie of $1,40 perton. 13 It is worthy of note that while some of the zinc enters the matte, practically no lead does. The analysis of the slag corre- sponding to this matte is given in the Table I under the name, “High Alumina and zinc.” The quantity of copper in this matte, r. 6 per cent, is insufficient to give a clean slag, which in this instance had a value in gold of $1.20 per ton. When opera- tions were first started at the plant an experiment was made of adding lead-ores in quantities equaling those of copper-ores now added, to ascertain whether lead would enter the matte and re- duce the abnormal losses in the slag. However, no lead was found in the matte, for the reason that the conditions under which the furnace was operated precluded its entrance into the matte. There is so much oxidation that most of the lead be- comes volatilized to the great detriment of the yield of silver. Lead, even in small quantities, is very undesirable in sulphide smelting. The first matte produced is generally resmelted twice, the third matte being the shipping- matte. The Table IV shows the concentration: Table IV. — Concentration of Gold and Silver in Matte. Matte. Copper. Gold. Silver. Per Cent. Oz. Per Ton. Oz. Per Ton. F rst 13.5 4.04 6.03 Second 21.5 10.05 15.6 T! ird 22.6 17. 1 1 21.4 The matte is cast into slabs in cast-iron molds, in order to break it up readily and have it in a convenient form for shipping. AMOUNT OF COPPER NECESSARY TO MAKE CLEAN SLAGS — At the present time, copper-ore for the matte is brought from Montana at a considerable expense, and is added in just sufficient quantity to produce the desired effect. It is aimed to have at least io lb of copper in the charge for every ounce of gold present, and more, if a supply is available. The silver is much more affected by the lack of a certain proportion of copper than is the gold. The ratio of silver to gold in the ore is from 1.5 to 2, to 1, and, with an equal saving of both metals, this ratio should be preserved in the matte. Mattes containing less than 20 per cent of copper show a distinct loss of silver. In general, we do not think that sulphide-smelting is adapted to a close saving of the silver. FUEL — Owing to the high melting-point of the siliceous slags, the quantity of carbonaceous fuel is considerable. The 14 fuel expressed in percentage of total charge seems very high, but is explained by the very poor quality of the Cambria coke used, the ash amounting to about 30 per cent. Generally a mixture of two-thirds of Cambria coke and one-third of Eastern or Colorado coke is used. The quantity of coke used varies from 14 to 18 per cent of the ores and flux charged into the furnace. Table V. — Composition of the Coke Used at the National Smelter Kind of Coke. Fixed Carbon Volatile Carbon Ash, (a) Water. West Virginia PerCent. 8 5 .8q 65.22 86 86 Per Cent Pi r Cent. 10 12 42 3-93 29 93 1 7 lo .7 Per Cent. 0.69 O.Q2 1.6 Cambria, Wyo Colorado (a) The analysis of the ash is given in Table 1 1 . The statistics givea in Table VI show a capacity of the small furnace of about 105 tons of burden per day. The large furnace has a capacity of about 130 tons of burden p«r day. Both furnaces operate under the disadvantageous condition of treating a very large quantity of fines, aside from using such very poor and friable coke. COWS — In our opinion the production of sows is practically inseparable from sulphide-smelting when high concentration is done. The sows are due to the strong oxidizing effect of the Table VI, — Capacity of the Furnaces of the National Smalter. Material. Smaller Furnace. November, C903. Smaller Furnace- December, 1903. Ions. Pons. Siliceous ore 1,100 <380 Pyrite 5 12 , 548 Limestone... 1,058 1,070 Copper ore etc 70 9 o Flue-dust (a) 250 348 Matte 136 125 Total burden 3. 126 3 .j 6 i Coke. Cambria 510 517 Eastern 180 162 Fuel percentage 18 17 (a) Including accumulated flue-dust from the chlorination works. furnace, as shown by the following data. A desulphurization of 80 per cent; the production of copper sulphate, found in layers in the accretions of the do wntake; no evidence of carbon 'mon- 15 oxide in the furnace gases; the volatilization of all the lead fed into the furnace, and the facts that no iron goes into the furnace as oxide, and the slag contains from 18 to 20 per cent of iron oxide in the form of silicate. These data make it difficult to imagine that the reducing conditions in the furnace could exist sufficiently strong to produce metallic iron. We believe that .the -sows are produced by oxidation in a similar way that metallic copper is produced during bessemeriz- ing, taking as the first stage, the melting of the pyrite, FeS2; and the loss of the one atom of sulphur forming the monosul- phide FeS; the second stage, the gradual oxidation of the sul- phur in the monosulphide, producing a subsulphide; the third stage, the production of .some ferrous oxide, part entering the slag, and part reacting with .the sulphide present, producing sulphurous acid gas and metallic iron, according to the following chemical equation: FeS + 2FeO = jFe SO 2 . Experience has shown that a larger quantity and higher pressure of blast result in an increased production of metallic- iron sow, and, from its analysis, it is seen that it contains prac- tically no carbon, which apparently should be present if the metallic iron was due to the reducing action of the coke. In the large furnace (38 by 144 in. in cross-section at the tuyeres), a 15-ton sow was produced in a 7-months’ run, having an approximate value of $5,000 in gold. In the smaller furnace in a 3-months’ run, under a lower blast-pressure, a 5-ton sow was produced, having an approximate value of $1,500. The sow, as a whole, is not homogeneous, and consists mainly of metallic iron containing intermixed slag and a little matte. The metallic iron contains practically no silver, but con- siderable gold. The iron has a crystalline structure similar to that of pig-iron, possesses a distinct silver color and is practically pure metallic iron. In the large sow some pieces of copper were found. Rarely a small button of lead is found in a sow. Table VII. — Composition of Sozv Produced at the National Smelter. Material. • Iron. Sulphur. Gold. Silver. Copper. Average Sow Per C ent Per Cent. Oz- Per Ton. 20.3 29.6 35-8 134-17 83.8 Oz. Per Ton. 2.4 4.4 nil 27 3 .4 5 nil Per Cent. Crystalline iron- F ore-hearth sow (a) , 99 68 0,2 trace 14.19 Lead in sow Copper in sow (a) A true sow. 1 6 Material from the fore-hearth resembling a sow contained, iron, 72.3; sulphur, 19.19; copper, 6.94 per cent; gold, 6.3 oz ., and silver, 5.2 oz. per ton. It is usually through the accumula- tion of this material and that of the true sow that the fore-hearth is lost. The top layer of the sow, as well as that partin contact with the fire brick, is usually of an oxidized appearance. The treatment of the sows for the recovery of the gold and silver values in them is a difficult problem, especiallv when no reverberatory furnaces are available. The National Smelter has not this valuable adjunct which is practically necessary for the treatment of the sows and the flue-dust. At the present time the sows are broken up by blasting, a very expensive opera tion, and re fed into the furnace a little at a'time with the pyrite in order to resulphurize the iron.' FLUE-DUST — Owing to the absence of reverberatory fur naces, the flue-dust made amounting in quantity to about 10 per cent of the charge is resmelted in the blast-furnace, a rather un- desirable procedure. Aside from this flue-dust, the plant has treated at times considerable quantities of concentrates from stamp-mills, and accumulated flue-dust from chlorination-plants, so that the quantity of fines was really more than the furnace could profitably handle. In order to put this material through and keep the quantity of flue dust produced within limits, the furnace low in itself, was operated with a low charge, and con- sequently with a fairly hot top, which accentuated the losses in fume. The flue-dust increases in value as the stack is ap- proached. Table VIII . — Analysis of Flue-Dust, Material. K, 2 0 3 . Sl0 2. Lime. Sulphur. Copper. Gold. Silver. — * Per Per Per Per Per Oz. Per Oz Pei .Lent. Ce t. Cent. Cent. Cent, Ion. Ton. From dust-chamber . .. 0.88 1. 02 4 1 Beginning of Hue (a) iC.14 35*7 4 . 12 5.60 0.80 1 17 12.60 Average flue-dust(b) 2^.13 34 463(c) 0.80 1.25 * 3-55 (a) Contains also AI2O3 4.07 per ( ent. (b) Contains also 9 per cent carbon (c) Considerable of which is Milan * . n wat; . Table IX . — Analysis of Accretions in the Dust-Chamber . Place. Curb n. Copper. Gold. Silver. Per Cent. Oz. Per Ton. Oz. Per Ton. From the bottom of downtake Considerable i 4 . 1 0.70 8.80 On the blast-heat; ng apparatus Considerable. 16. Ha) o. 4 o 5-1 (a) All soluble in water, lor the most part being present in the form of copper sulphate. 17 The ratio of gold to silver in the ore is usually about i to 2, so that the analysis of the accretions shows a heavy loss of silver by volatilization. In fact, the process as a whole is unfavorable to a high recovery of the silver, especially if high concentration is carried on. LOSSES IN FUME— It has been the experience at the National Smelter that there is a considerable loss of values by smoke and fume, especially in silver, and gold, under certain conditions; as, for instance, when operating with high concentra- tion and lead or zinc in the charge. Lead is not at all desirable in the furnace, most of it being volatilized, carrying values with it. Table X . — Analysis of Condensed Fume from the National Smelter. Place from which Taken. Gold. Silver Copper. Remarks Flue near the s ack Oz. Per 1 on 1 5 o i .6o 1 .60 2.00 Oz Per l'on t 5 . 5 ° it 90 10.4® 16,1 1 er Cent Trace Middle of flue Near the beginning of the flue 'I Contains lead, so 1 u b 1 e 1 suphates, arsenic, ?ome 1 J calcium sulphate. Average value of fume from the steel roof of the flue The analyses show the relatively much greater volatilization with the silver suffers, although it is evident that the gold in the ore also suffers loss. As a matter of experience, it might be said that when the furnace is running low with a hot top, and some of the above mentioned undesirable elements present, the monthly account based on the ore-assays, will show a consider- able loss in silver, and a very appreciable one in gold, as well as some copper, which are not slag losses. Greater attention paid to the saving of fume in sulphide-smelting plants would lead to economy. Laboratory Experiments on the Unoxidized Siliceous Ores of the Black Hills. By Charles H. Fulton. It is well known that while the ‘‘red” or oxidized siliceous, or Potsdam ores of the Black Hills yield readily from 75 to 85 per cent of their gold value to the cyanide process as at pres- ent practiced in the Hills, the “blue” or unoxidized ores yield but from 30 to 50 per cent extraction, and are as a general thing the bugbear of the millman. Regirding the occurrence of the “blue ores” in the ore bodies, no distinct, line can be drawn sep- arating them from the red ores, the blue ores often being found in bunches and pockets in the red ores, in widely varying quan- tities. The amount of blue being mined is, however, increasing as the workings penetrate further into the ore bodies. This fact is amply proven by the extraction figures of the various mills which, as a general thing, have dropped from 5 to 10 per cent, within the last two years. While, as a usual thing, the siliceous ores present the same general characteristics at all of the properties yet ores from the individual mines will vary quite widely as regards amenability to cyanide treatment. The ores can be roughly divided into two general classes, the shale ores and the quartzite ores, of which usaully, though not invariably, the quartzite ores are the more refractory, generally on account of their greater compactness and density. There are some blue ores that will not yield more than 20 to 25 per cent of their values to ordinary cyanide treat- ment, while others will yield 50 to 60 per cent, although the latter percentage of extraction is rare. The gold and silver values are very evenly distributed throughout the ores as is shown by the assay of different screen sizes*. It is rare that the dust has a higher value than the coarser sizes, and it sometimes has a lesser value. As an exam- ple, the dust accumulated on the mill rafters from the dry crushing of ore at the Imperial mill, had a value considerably *F. C. Smith. The Occurrence and Behavior of Tellurium in Gold Ores, T. A. I. M. E. Vol. 26, p. 491. Similar Experiments made in the laboratory of the School of Mines more recently confirm these results. 19 less than that of the ore crushed during the time of its accumu- lation. These facts point to the occurrence of the gold in the ores in a comparatively non-brittle mineral. Just in what form the values do occur has been much speculated ont but it cannot be said that any definite conclusions have been reached. It seems a rather important point to determine, from a metal- lurgical point of view, as having an influence on the mode of treatment. F. C. Smith states that he has found tellurium in many of the Potsdam ores, and believes that the gold occurs in many instances as sylvanite, although this mineral has never been isolated except in ores from the Ironsides mine, Squaw creek. t However, the fact that many analyses made at the School of Mines recently, fail to disclose tellurium or but traces of it, in many ores, lead to believe that tellurium is not of such widespread occurrence in the siliceous ores, as believed, and that the gold bearing mineral is not in most cases a telluride. Experience at Cripple Creek, Colprado, and at Kalgoorlie, Aus- tralia, shows that the dust from telluride ores invariably runs higher in value than the original ore. As an example, a Crip- ple Creek telluride ore shows this result: t Original ore value — 0.82 oz. Dust, -f- 200 mesh, value =1.04 oz. Dust, 200 mesh, value =1.92 oz. This is due to the extreme sectility of the telluridei'minerals. As already stated the dust from the Black Hills®' siliceous* *ore rarely has a higher value than the sands. It has also been found that a cyanide solution plus ibromo cyanogen exerts a solvent action on calaverite and possibly sim- ilar telluride minerals, as shown by results on a large scale at Kalgoorlie, and by laboratory tests on Cripple Creek telluride ores. For example: A Cripple Creek ore (Vindicator mine) having a value of 1.09 oz. gold, gave 40.4 per cent extraction on raw ore by a 0.4 per cent cyanide solution. A 0.4 per cent cyanide solution plus bromo cyanogen, same time of treatment, gave 91.7 per cent.* fH. M. Change, The Discovery of New Gold Fields, T. A. I. M. E, Vol. 29, p. 229, 1033, 1037. fF. C. Smith, T. A. I. M. E. Vol. 29, p. 1033. {Figures furnished by Mr. John Millikin, Dead wood. The dust men- tioned is from the frame work of a Cyanide plant at Florence, Col- orado. *For data concerning Kalgoorlie ores, see “Jhe Diehl Process” by* H. Knutzen, T. I. M. & M. June, 1902. 20 An extended series of experiments with b'rcmo cyanogen (results of which follow) on the “blue” siliceous ores of the Black Hills fail to show such phenomenal results, although an increase of extraction of from 8 to io per cent is noticeable. These facts certainly throw doubt on the supposition that the gold in the siliceous ores is generally in the form of a tellu- ride. Below are appended a number of analyses of siliceous ores, in which particular attention has been paid to the elementary constituents present in small quantities such as arsenic, an- timony, etc. No. i f (blue ore.} Gold 0.63 oz. per ton Silver 2.00 “ 6 4 4 4 Silica 65-38 per cent ... Iron 13-40 “ “ Sulphur ti.40 44 Arsenic 0.90 Antimony. .. trace Tellurium. . .0.003 Zinc ,0.00 Copper .0 02. Manganese.. .trace Alumina.. 5.43 Lime 2.10 Magnesia.. 0.20 No. 2. f (blue ore.) .0.85 oz per ton .6.08 4 4 4 4 4 4 80.00 per cent 7.50 4 4 4 4 .4.40 44 2.00 4 4 4 1 0.00 .trace .0.00 . 0.004 .0.54 .1.79 1.70 .not determined No. 3d (blue ore.) Gold 3.35 Silver 1.7s Silica.... 80.90 Iron 9.94 Sulphur .4.53 Arsenic 0.29 Antimony. ... trace Tellurium . . ..0.007 Copper 0.013 Zinc tra^e Manganese. . Lace Alumina 1.70 Lime 0.5° per cen‘ . . . Magnesia. . . .trace Ore ‘‘A - ’ No. 5. ( blue ore.) Gold 0.78 oz, per ton No. 4 .t (partially oxidized )f 2.00 0.62 84.80 7-50 0.7s 0.00 0.00 trace 0.008 0.00 0.96 T 02 0.90 per cent not determined Ore 44 B” No. 6. ( blue ore.) 0.90 oz. per ton fKindly furnished by Mr. John Gross, Maitland, S. Dak. 21 Silver Silica . 77.38.. T ron Sulphur. . . . Arsenic .0.55.. Antimony.. • . trace. Telhirium . . . .none, Copper Manganese. .none. Alumina . . . Lime .0.56. . Magnesia. . . .trace. Phos. acid . . ..0.32. . Soda ..1.32. . Lead Thallium. . . . ? Tungsten. . . . . . 93*72 per cent .2.67 “ “ .o.6g “ “ .0.002 .0.0893 .none .none 0.082 ..3. 33 per cent .0.0059 .trace p none In the analyses, copper, antimony, arsenic, tellurium, will be noticed in small quantities in most of the ores. In the Mait- land ores bismuth also exists in appreciable quantities for at the Penobscot mill it is found in considerable amounts in the zinc precipitates. Certain peculiar facts are noticed in roasting; var- ious blue ores, as a general thing a fair extraction may be ob- tained on most of the blue ores if they be finely crushed and roasted at a low heat for a considerable time. If the heat be raised to a high temperature at once, with some ores but little better extraction can be obtained than from the raw ore. Other blue ores again do not behave in this way. It seems possible that the gold and silver are held in some complex mineral com- bination into which arsenic and antimony enter, so that a high temperature and oxidizing conditions transform this compound into stable compounds, failing to liberate the gold and silver. The gold and silver bearing mineral is also very uniformly dis- tributed throughout the rather dense ores, so that in most in- stances a comparatively fine crushing* is required to liberate the values from the rock mass. Roasting of the ores causes practi- cally no loss of values. The fact that the siliceous ores of the Black Hills were pos- sible telluride ores led to the rather extended series of experi- ments with bromo cyanogen, which while not giving the results hoped for, aid the extraction of the values somewhat, so that the publishing of the results seems justified. All the tests made were agitation bottle tests, which, is the usual starting point in *There are exceptions to this rule, as for instance, certain ores of the Wasp No. 2 mine, and the Ragged Top ores. 22 experiments of this kind. The results obtained by these were to be confirmed by tests on a larger scale, but unfortunately the time, means and apparatus for this work was not available. The tests were made practically all on the ‘ ‘blue ores” with the idea that the more oxidized ores would be tested later. The effect of bromo cyanogen on the extraction is soon to be tried on a large scale by one or two of the mills of the district, and the results will be watched with great interest. BROMO CYANOGEN — Bromo cyanogen and chloro-cy- anogen were first used unsuccessfully in the Cyanide process by Dr. William H. Gaze, in Australia in 1892. Later in 1894 the use of bromo cyanogen was patented by Messrs. Sulman and Teed in connection with zinc dust precipitation in England. It is at present used in Kalgoorlie, West Australia, in the Diehl process with success, on sulpho telluride ores.t Bromo Cyanogen above a certain temperature is a pun- gent irritating colorless vapor, extremely poisonous which affects the eyes and lungs in a very irritating manner. At 60 °C it sublimes into colorless needles, which afterwards change to cubes. The vapor and sublimate is soluble in water and methyl alcohol, more so in alcohol than in water. When heated in a closed tube to 140 °Cit is converted into CN3 Br3. It is decomposed by potassium cyanide with the fol- lowing reaction. KCN + BrCN = KBr + 2CN. With alkalies such as potassium hydrate, the following re- action probably takes place in dilute solution. BrCy + 2KOH = KBr + KCNO + H2O. PREPARA TION OF BROMO CYANOGEN— There are three methods of preparing bromo cyanogen. 1. By the Addition of Dilute Bromine Water to a Dilute Solution of Potassium Cyanide , the Last Being in Excess — The amounts of bromine and cyanide are best present in the theo- retical quantities expressed by the reaction. fThe Diehl Process, H. Knutzen, T. I. M. & M. June 1902. Metallurgical Progress in W. Australia, E. & M. Jour. Vol. 75, p. 18,251, also Vol. 77, p. 31. The Treatment of Sulpho-telluride ores at Kalgoorlie, E. & M. Jour. Vol. 76, p. 156. The Treatment of Telluride ores by Dry Crushing and Roasting at Kalgoorlie, T. I. M. & M. Oct. 15, 1903. Cyanide Practice, by Alfred James, 1903, 1 23 2 Br + KCN = KBr + BrCN. The bromine water may be added until a faint permanent yellow color appears. The cyanide solution during the addition of bromine water should be kept cold by ice water, as the heat developed by the reaction is sufficient to drive off the bromo cyanogen as a vapor from the solution. 2. Preparation by Means of Bromine and Mercuric Cyan- ide. — When one part of liquid bromine is allowed to flow grad- ually on 2 parts of mercuric cyanide (dry salt) in a retort* sur- rounded by ice, bromo cyanogen and mercuric bromide are formed with a great evolution of heat. Bromo cyanogen sub- limes in needles contaminated with free bromine, which, however, flows back into the retort and enters into complete combination. Gentle heat, by means of an alcohol lamp, is then applied and the BrCN sublimed into a receiver surrounded by ice water. Mercuric cyanide, if not available, can be made by dissolv- ing mercuric oxide, (which can be made from mercury or mer- curic nitrate) in a solution of hydrocyanic acid. The hydrocy- anic acid can be made with potassium Ferro cyanide or potas- sium cyanide and dilute sulphuric acid, by heating in a dis- tilling bottle and collecting the vapor in ice water, or water cooled by ice. When the mercuric oxide is all dissolved in the hydrocyanic acid solution in the cold it is gently evaporated to crystals on a water bath, care being taken not to remove the very last of the solution on the bath, but to let it evaporate in the air, or in an air bath at a temperature not exceeding 120 0 Fahr , otherwise there is danger of reducing the mercuric cyanide. Bromo cyanogen crystals obtained in this way can be kept in a tightly corked bottle in a cold place for use indefinitely. This method is the most difficult and expensive method of prep- aration, but yields the pure crystals of bromo cyanogen unadult- erated by any other salt. This may sometimes be desirable for certain tests, but for general experimental purposes bromo cy- anogen made by the first method, or still better by the third method, to be described, which is the commercial method of its production in Western Australia, is just as desirable. 3. Preparation by Means of Bromine Salts , Potassium Cyanide and Sulphuric Acid.— When solutions of potassium *The apparatus for this work is best a small retort and receiver, the re- tort having an openingfor a small thistle tube with stop cork for the introduction of brome. See Denver Fire Clay catalogue, p. 173, No. 1313. 2 4 bromide, potassium bromate, potassium cyanide and sulphuric acid are mixed in the proper proportions, bromo cyanogen in solution is produced according to the following equation: 2KBr + KBrOs + 3KCN + 3H2SO4 = 3BrCN + K2SO4 + 3H2O 238 167 135 294 318 522 54 1.4 2 1 1. 1 7 1.76 1.90 It is essential for success that the proportions of the theo- retical equation be followed closely and that the solution be not too concentrated. TO TAKE A DEFINITE EXAMPLE: Taking as the starting point 2 5 grms. of potassium bromate it will require 1.42 x 25 = 35. 5 grms. of potassium bromide 1.17x25=29.25 “ “ “ cyanide 1 76x25=44.0 “ “ sulphuric acid. This should produce 47. 5 grms. of bromo cyanogen. The Po- tassium bromide and bromate may be dissolved in about 400 c. c. of cold water. It will take some time to disolve the bro- mate, as it is rather difficultly soluble in water. The potassium cyanide can be dissolved in 200 c. c. of water, and the required amount of sulphuric acid diluted to 400 c. c. The strength of the sulphuric acid should be estimated be- fore dilution with an N-10 solution of sodium hydrate, 4 grams to the litre, one c. c. of which is equivelant to .0049 grams of sulphuric acid. The proper amount of sulphuric acid being* taken, containing 44 grins., this is diluted to 400 c. c. and al- lowed to cool thoroughly. In taking the amount of cyanide, care must be taken to allow for the amount of impurity in the salt. The solutions of potassium bromide, bromate, cyanide and of sulphuric acid are now mixed best by pouring the bromine salts and cyanide solutions simultaneously in a thin stream into a large funnel discharging into a bottle containing the sulphuric acid. It is essential to mix in this way Otherwise reactions oc- cur which occasion loss. The best way is to have the two solu- tions discharging simultaneously in a thin stream from large stop cock funnels. After the mixing of the solutions the resultant solution should be agitated for about six hours to complete the reactions. The solution is then ready for use, and will contain about 4/4 per cent of bromo cyanogen (theoretically in this example 4.75 per cent. ) 25 Pure potassium bromate is a rather expensive salt, $2.00 per pound if bought in small quantities (although in large quan- tities it can be had at about 50c per lb.), and in practice as men- tioned further on commercial mixed bromine salts are used. For experimental purposes the mixed bromide and bromate salts can readily be made in the laboratory by the addition of liquid bromine to a saturated solution of potassium hydrate. This solution after the addition of bromine is heated until the bromine disappears, when more bromine is added, this being re- peated until the red color stays permanently. The solution now contains a 'mixture of potassium bromide and bromate from which the bromate containing some bromide will separate out first when the solution cools, owing to its inferior solubility. This can readily be removed by filtration and the solution evap- orated to the dry salts. The reaction for the preparation of bromo cyanogen calls for a mixture of bromide and bromate, of which 41.2 per cent should be potassium bromate. If the solution containing the mixed salts made in the way described be evaporated down to dry salt, the mixture will contain considerably less than 4.12 per cent of bromate. For this reason it is desirable to remove successively the salt which settles out from the solution on evaporation and which is at first practically all bromate but gradually decreases in this salt until what precipitates finally is practically only bromide. In this way by having lots of salts, some high in bromate and others' in bromide, the proper mixture of the two salts can readily be made especially if some extra potassium bromide, a common saU in the laboratory, be at hand. The resultant solution should be neutral, as bromo cyanogen shows neutral to methyl orange and phenolpthalein, but may be slightly acid owing to the reactions being incomplete. If it should be acid, this acidity must be carefully neutralized by an N-10 potassium or sodium hydrate solution, care being taken not to add any excess, as this alkali decomposes bromo cyanogen, as already mentioned. The bromo cyanogen solution prepared in this way is quite stable and keeps a considerable length of time, several months, _ if kept in a tightly stoppered bottle. It may turn a brown color upon standing, which color is not due to free bromine. This color does not interfere with the reactions. Bromo cyanogen is made on a commercial scale, in West- ern Australia at Kalgoorlie as follows:* * A. James, E. & M. Jour. Vol. 77. p. 31. 26 It is made from imported salts (Germany) which contain ap- proximately 40 per cent of potassium bromate and the balance bromide. At Kalgoorlie to generate 100 lbs. of bromo cyanogen the following charge is used: Mixed bromo salts, 125 lbs. Cyanide, 100 percent 65 Sulphuric acid, 70 per cent 147 The bromo cyanogen is made in a wooden, plain or lead lined vat of about 200 gals.’ capacity, securely covered with a lid through which a revolving paddle or stirrer works, Above this vat is a smaller vat in which is stored the necessary charge of potassium cyanide dissolved in 40 gals, of water. The mixing vat is first three-quarters filled with water, the agitator is started and the sulphuric acid added slowly and carefully. The whole is now left to stand and cool for one or two hours, as the heat generated by the addition of sulphuric acid would vaporize the bromo cyanogen were the rest of the ingredients added at once. When the contents of the vat are cool the mixed bromo salts are added gradually and, simultaneously the solution of cyanide is run in with constant stirring. The reaction commences imme- diately, but is not thoroughly completed until six hours of con- tinuous agitation. The resultant bromo cyanide solution is then added in the quantities desired to the agitation vats. • METHODS OF ESTIMATING THE AMOUNT OF BROMO CYANOGEN AND POTASSIUM BROMATE.— For the quantitative estimation of both potassium bromate and of bromo cyanogen an N-10 solution of sodium-thio-sul- phate will answer. This solution will contain 12.4 grams of the salt. (Na 2 S203. 5H2O) and 1 c, c. will be equivalent to 0.00265 grms. of bromo cyanogen, 0.00142 “ “ potassium bromate. For the Estimation of Potassium Bromate in the mixed salts of bromide and bromate proceed as follows: Weigh out 200 milligrams of the dry salt, dissolve in 100 c.c. of distilled water, then add about 15 to 20 c. c. of dilute hydro- chloric acid, and 3 to 5 grms. of potassium iodide. Iodine will be liberated and the solution is then titrated to colorlessness by N-10 sodium-thio-sulphate solution. If greater accuracy is re- quired starch solution can be used as an indicator. The reaction taking place is as follows: 27 KBrC>3 + 6KI -f- 3H2SO+ = 3K2 SOi -f- KBr 3I2 -(-3H2O or KBrC>3 = 3I2 I2 — 2 (Na2S203. 5H2O) = Naz S* * Og H- 2NaI ~b 10H2O For the Estimation of Bromo Cyanogen take 5 to 10 c. c. of the solution to be titrated, dilute with 25 to 50 c. c. of water, add 5 c. c. of dilute hydrochloric acid and 4 to 5 grams, of potas- sium iodide. This liberates iodine and the solution is titrated to colorlessness by N-10 sodium-thio-sulphate solution. Or as above, starch solution can be used as an indicator. The reaction taking place is as follows: BrCN -f 2KI + 2HCI =' BrCN + 2HI -f 2KCI BrCN 4- 2HI = HBr + HCN + I 2 I2 “| — (Na2S203.5H2 O) == Na2S*OG 4- 2 Nal 4~ 10H2O. In estimating mill solutions, or solutions that have been used on ores experimentally, and which contain potassium cyanide, the presence of this salt does not interfere with the titra- tion for bromo cyanogen and in the estimation of potassium C3 r anide in these same solutions with silver nitrate in the usual way, bromo cyanogen does not interfere with the test except in so far as cyanogen, which may be present, due to the reactions between bromo cyanogen and potassium cyanide, interferes. Usually the presence of cyanogen gives somewhat low re- sults.t * METHOD OF MAKING BROMO CYANOGEN TESTS ON ORES . — In experimental work the general prac- tice is to add bromo cyanogen in solution to the test at in- tervals of 2 to 4 hours, the total amount of bromo cyanogen not to exceed one-fourth the amount of the potassium cyanide present in the experiment. As an example, suppose 16 assay tons of ore are treated with 700 c. c. of a 0.25 per cent, or 5 pounds per ton potassium cyanide solution, containing, therefore, 1.75 grams of cyanide. The total amount of bromo cyanogen to be added to this test is therefore 0.44 grams, and having a 3 per cent bromo cyanogen, solution each cc. containing .03 grms. the total number of c.c. to be added of this solution will be 15. If we make three additions at intervals of 4 hours, each we will add 5 c. c. each time. The theory of the reactions with bromo cyonogen is as fol- lows: f James, Cyanide Practice, 1902, p. 140. * James, “ “ 1902, chapter on Bromo Cyanogen. 28 BrCN + KCN = KBr + 2CN. Au + KCN+ CN = KAuCN 2 . The bromo cyanogen acts as a liberator of cynogen thus prac- tically taking the place of oxygen in the ordinary process. The nascent cyanogen acts as a hastener of the reaction and it is also probable that bromo cyanogen plus potassium cyanide may have a more powerful solvent action on certain gold minerals, such as calaverite, than the simple cyanide solution. The idea of adding bromo cyanogen in small amounts from time to time is to have the liberation of cyanogen going on dur- ing the entire treatment. The greater the amount of potassium cyanide present in proportion to the bromo cyanogen the more rapid is the decomposition of the latter. With additions of bromo cyanogen as described in the test above, there will prob- ably be no bromo cyanogen left in the solution after the ex- piration of 3 or 4 hours. Any bromo cyanogen left in solution after the expiration of the time of agitation is of course a waste and in tests following the amount may be cut down somewhat if this should be the case. The consumption of potassium cyanide is greater with bromo cyanogen than without, and this must be taken into account in experimenting, not using too dilute solutions, especially in agita- tion tests in which consumption is abnormally high. The solutions from the tests are very often a light brown or golden color, due probably to iron bromide, for more iron salts go into solution with bromo cyanogen than with plain cyanide. The earlier writerst dwelt at length on difficulties of precipitat- ing the gold from the solutions when bromo cyanogen is em- ployed, stating that bromo cyanogen has a decided action on zinc forming insoluble zinc bromo and zinc cyanide, which in- terferes with the precipitation. In the present state of the pro- cess there should be no bromide cyanide in the solution when it it goes through the zinc, ; s it should be all decomposed. This difficulty in precipitation seems not to be encountered in West Australia, where bromo cyanogen is used extensively.. t COST OF BROMO CYANOGEN — The mixed salts of potassium bromide and bromate, containing approximately 40 . - fGaze — Practical Cyanide Operations, 7898, p. 95. fFor certain minor troubles of precipitation, see “Treatment of Telluride ores by Dry Crushing and Roasting at Kalgoorlie, W. A., W. E. Sampson., T. I. M. & M. Oct. 1903. 29 per cent of the latter salt 3anbe readily obtained in this country* and can be delivered in 500 pound lots packed in barrels f. o.b. Deadwood at 25c per pound. Sulphuric acid costs at Dead- wood from 2.6c to 3c per pound and potassium cyanide 23c per pound. The cost per pound for chemicals, in making bromo cyano- gen will therefore be, taking the Western Australia charge as a basis: 125 pounds mixed bromo salts at 24c per lb. = $30.00 65 pounds of potassium cyanide at 23c per lb. =14 .95 147 pounds of 70 per cent sulphuric acid at 3c= 4.41 Total cost 100 lbs. cyanogen 49. 36 Cost per pound = . 50 The cost of labor, power, etc., of making may be estimated at 5c more, making a total cost of 55c per pound. The following tables show concisely the results obtained and the details of the experiments on the blue siliceous ores of the Black Hills. The ores are taken from the various districts, Bald Mountain, Ruby Basin, Maitland and Yellow Creek, so as to give a representation of most of the blue ores. *Can be bought from the Dow Chemical Company, at Midland, Michi- gan. 'i 30 0) 01 * CO to 1 - 'Haawn^ H H „ M 0 O 0 Ln O Ln O *8 :qsaux SuiMoqoj B 3 3 g 3 g 9qj jo uaaaog a cr in XT (0 Sn cr t/1 cr CD W nr B pass d 3JQ •uoi aad spunoj 0 0 0 0 0 0 •uoijnjog apiUB -Xq'jo qjguajjs & 0 3 73 p 9 in p $'<* s# 0 SJ 0 i ? p 5 * Oq § » oq 5‘ 3 a> cr D » cf- n p in 1 p 1 «> P Dh P nr b* O 3 p nr O J H. >5’ nr nr 3 cr 1 0> g nr a> P In p cfq" cr cr p £ rt O’ o' a cr to *0 CD p "2- t/) j f° •o So •B, 0 cr 0 Cu 0 2. p O us cyi hour* "2- HT 3’ 3 0 H n 3 a s_ B go.' 0 p l 3 n ns a s • 3 •0 n *2, a! ? c n e w •< ” p D cr 8sf O 0 51° « P 3 0 1'? X cu *d p o> 0 p o' P - • * 3 00 3 nr w •uoj aad 2.2 •sqi ‘uoxjduins -uoQ apiueAQ p o O O p b 1 p b O b 0 •uoj jad * zo sUuijtBj, vO O' 1 00 00 jo XWssy Cn 'o J° b vb bo b\ On ja»0 J3J Table IV. ORE “D”— A very dense blue ore, containing .22 oz. per ton. Tests made on 5 to 8 oz. lots, amount of solution 300 to Table I. ORE "A”-A dense blue silicious ore, containing 0.78 oz. gold per ton. For analysis, see previous pages. Tests made on 5 to 8 oz. lots, amount of solution 300 to 500CC. Number. I Ore p ssed a I Screen of the following mesh: Strength of Cy- anide Solution. Pounds per ton. Method of Treatment. Amount of BrCN Added. Time of Treatment. Cyanide Con- sumption in lbs. per ton. Assay of Tails. oz. per ton. Pei cent of Extraction 1 20 mesh 20 Plain Cyanide, no alkali added. 36 hours agitation 4.9 0.5a 33.3 2 40 mesh 20 Plain cyanide, no alkali added. 36 hours agitation 4.9 0.47 39.7 3 150 mesh ,0 Plain cyanide, ore treated 12 hours with KOH. previous to cyaniding. 60 hours agitation 2.6 °-35 55-1 4 200 mesh IO Same. 60 hours agitation i 2.9 0.36 53.8 5 40 mesh 20 Plain cyanide, with addition of small amount of lead acetate. 60 hours agitation 12.7 0.41 47.4 6 80 mesh 20 Same. 41 hrs, agitation and 31 days standing 13.3 037 52-5 7 150 mesh 30 Same. Same •.36 53-8 8 40 mesh IS. 1 Cyanide and bromo-cyanogen. 7 add’sof 3 >i c.c. Ea. of a. 3.3 perct.sol Same 4., o. 4 i 47;4 9 80 mesh 15.1 Same. Same 22X hours agitatioa 4-7 o. 4 o 46.1 1 O 150 mesh IS. I Same. Same 22H hours agitation 4.7 0-39 44.8 1 1 40 mesh 10.6 Same. 6 add's of 4 0.0. ea. of a 3.5 per oent sol. 22K hours agitation 7-5 0.42 48.7 1 2 80 mesh »o.6 Same. Same 4 o hours agitation 7-5 0 . 4 1 4 7 .4 1 3 150 mesh 10.6 Same. Same 40 hours agitation 7-5 0.40 46.1 1 4 40 mesh 20.0 Same. 0.98 grms in 3 additions. 40 hours agitation *14.0 0.39 44.8 1 5 80 mesh 20.0 Same. Same 41 hours agitation *13.8 o .41 47.4 16 150 mesh 20.0 Same, Same 4 i hours agitation *10.5 o.3 7 S z -5 1 7 150 mesh xo.6 Cyanide and bromo-cvanogen; ore treated with KOH. 12 hours before cyaniding. 6 adds.ef 4 o.c. ea of a 3.8 per oent sol. 60 hours agitation 3-1 0.28 64.1 1 8 200 mesh xo.6 Same. Same 60 hours agitation 4* 2 . O.3O 6r.5 1 9 130 mesh 8.9 Roasting, cyanide and bromo-cyanogen. Same 48 hours agitation 5-1 o.xo 87.1 20 150 me h xo.o Same, 4 adds, of 4 o. c. ea. of a 3 .J per cent sol. 1 24 hours agitation ,8 0.19 75.6 2 1 150 mesh 10.0 Same. 6 adds, of 4 c. c. ea. of a 5 pei cent sol, j 44 hours agitation r } 48 hours standing 0.14 82.0 22 150 mesh xo.o Roasting, cyanide & bromo cyanogen; ore treal edwith KOH for 12 hours before cyaniding. l Same Same o.il 85.8 23 150 mesh ,0.0 Roasting and plain cyanide; ore treated witfc KOH, for i2 hours before cyaniding i Same o- Is 80.7 24 150 mesh xo.o Roasting and plain cyanide. Same 0.14 82.0 26 150 mesh 10. 0 Same. 24 hours agitation i -5 0.I9 75.6 26 150 mesh 8.9 Same. 48 hours agitation 1.4 0.19 75.6 ♦Excessive consumption due to impure bromo-cyanogen. ORE “B.” A dense blue ore, containing; o.go oz. gold per ton. For analysis see previous pages. Tests mode on 2 to 5 oz. lots, amount of solution 200 to 400 cc. Per Cent 0 0 « VO 0 On CO 0 vO of d CO cJ vO \8 ro H >o Extraction. IO VO VO VO VO to to N 00 r* Assay of c* •O Cl o> VO Tf* Tailings lO OJ ci 0 CO PO m CO CO CO er Cl oz. per ton. o' d d o' d o' 6 O 6 0* d <5 d 0 6 C> anide Con- lO 0 Cl VO Os 00 Ov to sumption, lbs. per ton. co 00 H c$ co 10 d CO d co Jj T3 # a V S c _o c a ctf . c _o a .2 3 0 d O d 0 2 aS a 0 H 0 '5 ctf g Same bo •S *3 c a 3.2 .2 rt a a “ Same Same a '3d (4 3 Same Same. 1 u 3 O Same. a '1 (A 3 1 '« a u 3 a 1. S2 3 i Hi u d O S-§ -Is O co CD © A to 0 0 . t-©ft ■*0 a 41 C c bo O a O a § a Y <4 13 c* >x 0 6-S a^ 0 c c V a S IB 6 £ •° >> U a 0 x3 i*i s s ’OvS H 0 •a c4 .2 « bfl O § •a ‘S a d 3b V 0)43 E 13 •O T3 > 'S CO 0 43 0 s 13 0 e u d •2- '5 0 * 6 a 0 h 43 c "a "o. *G >» O C#1 • U B O 3 ^ •a S •a '5 T3 'S •a a J3 ■ 0 , d a a 2 a >> a O a 0 a V bo c be be'^ •St3 a a a d d 'S V V d d 'S ill 13 E a C/3 13 E 'a E a * C/3 1 c/3 a >> O £ C/3 a a C/3 £ aJ c n £ c8 c n £ c n a 0 pc! & O a c4 O V C * i3 Strength of Cy- anide Solution. to O O 0 O O O M . * VO Ov Ov Pounds per ton. « w W 10 10 d 00 00 " Ore p ssed a Screen of the X3 c/> £ mesh x: c/i a> £ mesh xs C/) 1) £ x: Hi 4) £ 43 <5 a X3 t/> (U £ ' mesh mesh mesh X3 V £ mesh 1 mesh X5 C/1 a following mesh: s O IO 0 VO O 0 00 0 to 0 0 00 O VO 0 Ss 0 10 0 to O to 0 to Number. - C/3 P - C/3 CT n> in cr 0 71 cr P - a Ml CT Ml O' a> P - O C/3 cr a> Ml cr n> 3 ‘ * passed 3JQ 00 00 1 •uoi aad spunoj vb VO ; 0 0 0 0 0 0 ON •uopnjog jptuB -^0 J° 'l.lSubi'jg s? >0 >0 Jd 0 ns 0 ft O 0 0 p - ST Jd O m> 5’ in S’ <*? cr «' C-t f/) 0-5- ►*(*? g S' h cro' 0 p 71 3 O C/3 *-t rt # H 3’ 10 crq jf £ p 3 cn >0 is. • a a Sg £ o. S' 0 V* p ■3 p p 5. p rr n or »q ir 3 * 00 S-o- 0 D- ^ vP 4 ^ 5* * 'H. Low heat, s f 0 3 tr heat plus cya anogen. heat, cyanide hrs before cy p "H- o£ 1 a *■* c.' E. *< £ P W 3 5 >sl plain cyanide 0 0 ^,3 3 0 tOv? s*g S w ? ~ 2^c- 0 S 1 p 0 £L 2- p Cu a. a> p* O CL O H Ml "2- sr 5* p 2. rT p 3 a 3 a P 3 CL < p- P 3 *5.' Of* 3 low heat for 4 en, treaied with s before cyanidin th KOH. solu c yaniding. 0 p- p 3 re P Oorp p tr OK? C. Vj ■ 0 CL 3 * O a ■3 fl) cr. ; ■3 » T3 Ct> 05 c* ss* S3 S g. 2 -g, O ? 9 * 5- B 2,5® g !J ' C ‘ C/1 P 3 s 2 ,“ J 0 & •pjppV 'N.) J a n 2- p 4 ^ ^ ^ jo junouiy 8 ’8 90 ' “8 00 • cn p s? -P 3" N O ro H? CT 00 cr £ cr &• s O 71 -L cr ON O tr S' cr kU 0 3 c 71 P K c p °S. e 7) P w. Same Same Same •t m 03 <2. £ p 3 - . B-g c Ml P ( S. p c 2. p in P C 2. 73 P OQ 0 H 0 p P p p 3 0 9Q p o’ &. s 3 o' 0* o' ' P 0 3 a 0 p 0 2 3 CL "oo •UOJ J3d *7* 00 ^0 * CO to 00 •sq[ ‘uopdmns 00 b 0 vb 451 -uoq optueAf) •uoj jad *zo t p M £ co io 0 0 OJ sSurjiB O cn 00 jo Aessy On On On Cn i •P In 0 ? Cn Ln •uopoBjjxg oj 00 vp ON vp O O 7 }° Cn b br b b O b Cn b b» JU3Q J3J Table III. ORE “C.” A dense blue ore, containing more sulphur than A. or B., containing 0.66 oz. of gold per ton. Tests made on 3 to 5 oz. lots, amount of solution 300 to 500 cc Miscellaneous tests. In the main to show efficiency of broinc- yanogen on certain ores. Tests made on lots, amount of solution 300 to 500 cc. 3 Percentage N rc | O | c O O of H M CO o O 0 0 O Extraction. o> 00 O' M 1 M w K Assay ■ f O' 1 tJ- O O Heads 0 "c 10 lO iG IO oz. per ton . H M 0 d d ■ °‘ O [ d Cyanide Con- sumption, lbs. CJ 1 vq CO M CO Tf vd 00 5-5 per ton. J c G • g G G g .2 *5 0 .2 .2 2 2 o3 d d aS 5 G G K be G g 3 £ G £ aJ be aS *5e G ‘So G ’be G c n u. ce. c/j g I ce c/5 jd rG 4 : 5 G 00 O O I 00 00 TJ 1 r- 0 00 • 00 6 ® Amount of ^ cc ^ *"■3 • '"c G E 0 ^ ^ s Added. •3 g 'd-g ^ ^ a 0 “ © rG X 0 ^ O ” fl U bS C/3 'S ^ s cS C/3 -^> > 0 G ’5 T3 O 0 6 > 1) JO G *2 G be «■ effi j d d EC aS O ‘3 S E.S E B! C/3 5.0 Sam g G if) e B) C« Passed through a screen of Mesh. s> 0 as O 2> J 0 . 0 1 C O 2 m 3 c M H I M 0 G rO 6 j (J d Cz « « 0 oT uT E O as s 2 E s a a 0 2 V .E bj c/3 p Bi C/3 G if) BJ C/3 BJ C/3 ctf C/3 in 0 JS> tn if E >.« S Q ts.s H E a bj Number. 1 OJ CO to (0 32 SUMMARY OF EXPERIMENTS. — Influence of the fineness of crushing. The size of the ore is stated by “mesh” in the tables which means that the ore passed an ordinary assayers screen of the mesh stated. For further information the actual size of openings or space and size of wire of these screens is given. Screen. Number of Meshes per inch. Decimal size of wire in inches. Actual Opening between wires or ‘pace in inches. 20 0.0I65 0 0335 3 o °- OI 375 0.0195 40 0.01025 0.01475 80 0.00575 IO VO O O 6 150 0.003 c.0033 200 0.002 0 003 Material called 30 mesh was sized and gave the following results: Per cent left on a 40 mesh screen “ “ “ “ 60 “ 80 ‘Too 4 4 4 4 4 4 4 4 4 4 4 4 150 “passed through a 150 = IO-4 I = 29.8 I coarser than 100 mesh — 16.7 f 66.1 percent. finer than 100 mesh 33.8 per cent. = 9-2 | = 1 1-7 ) = 22. 1 V Total 100.0 In order to show how this product compares to actual mill products made in the Black Hills the following figures are ap- pended: PRODUCT OF A S'X FOOT MONADNOCK ROLLER MILL. — Screen, wire cloth with space of 0.046 inches, equiva- lent to 18 mesh. Per cent left on a :o mesh screen = 1 per cent | “ passed a ‘40 = IO 1 1 coarser than 100 ‘60 = 1 O ( mesh 31 per cent. Too = lO ;; 1 ‘200 --- 19 \ finer than 100 200 =r 50 ) mesh 69 per cent Total 100. per cent. PR 0 DUC 1 OF STAMPS. — Weight, 950 lbs. Screen 10 by 4 mesh No, 18 wire, space 0.053 inches. Dakota mill, Deadwood. 33 Per cent left on a 20 mesh screen = 12.7 ) it < < < « 40 — 22.0 )- coarser than 100 mesh “ “ “ 80 “ — 14S J 1 55.5 percent. “ “ “ 100 = 6.0 1 it < . « < “ “ 150 “ = 14.8 >* finer than 100 “passed thro’i5o “ =-29.8) 44.6 per cent. Total 100.0 PRODUCT OF DRY CRUSHING ROLLS .— Imperial mill, passed through a 16 mesh wire screen, 21 wire space .0305 inches. Per cent left on a 20 mesh “ 3Q “ 40 “ “ “ “ 60 “ “ “ “ “ 80 “ “ 100 passed a 100 screen coarser than 100 mesh 64 per cent. finer than 100 mesh 36 per cent. Total 100 The effect of the size of ore on the extraction is shown as follows, the results being averages of tests made under same conditions: Mesh. Ore A . Ore B. Laboratory Screen. 4o 46.9 per cent. 62.2 per cent . 80 46.9 “ 64.4 “ “ 150 47.8 “ “ 64.4 “ In order to test the effect of still finer crushing Ore A was passed through a 200 mesh screen, but the results were practi- cally the same as with 150 mesh, a trifle lower even. If. however, the ore is crushed so as to pass but a 20 mesh screen the extraction on all of the ores tested immediately fell off in such a manner that no further tests were made on such coarser sizes. The results of these tests are in accordance with the practice of the plants of the Black Hills, as will be seen by referring to the analyses of the mill products of several plants on the preceding pages. The product of rolls and screens at the Imperial mill is very close to that of a 30 mesh laboratory screen except that it contains a small percentage of somewhat coarser sands. The product of stamps at the Dakota mill, Deadwood, •4 contains a somewhat greater percentage of fines, (above ioo mesh) and less sands, but a considerable percentage of the sands is coarser than 40 mesh. In the product from the Monadnock Roller mill the sands are considerable less in amount than in the product of the 30 mesh laboratory screen and the fines considerably more. This product is probably better suited for extraction than the stamp battery product above mentioned. In general it is true that while indi- vidual blue ores will differ somewhat in the fineness of crushing required, material that is coarser than 30 to 40 mesh (0.0195 to .01475 inches) will show an appreciable decrease in extraction. Product finer than 40 mesh (.01475 inches) will in general show but little better extraction, perhaps 2 to 3 per cent, than 40 mesh material. It seems, therefore, that for the greater portion of the denser silicious ores very fine crushing presents no advantage whatever, but that efforts directed toward keeping practically all of the sands finer than 30 mesh and preventing excessive sliming as an unnecessary evil is what is called for. Tests that have been made on sand tailings at the Dakota mill show practically that all the sizes of sands, except the ones coarser than 30 mesh, have the same value. THE EFFECT OF BROMO CYANOGEN — The effect of bromo cyanogen while not what was hoped for is still very marked on all of the blue ores treated raw as the following table will show: Ore. Percentage of Extraction. Plain Cyanide. Percentage of Extraction. Cyanide plus Bromo Cyanogen. Increase in Extraction. ( 54 per cent J 63 per cent ( 7.0 per ct A ■J ■j ( 39 per cent ( 46 1 per cent ( 7.1 ; er ct. B 43 per cent 64 per cent 21.0 C ( 51 per cent j 57*5 per cent ( 6.5 per ct. ( 50 per cent l 57*5 Per cent ( 7.0 per ct. The effect of bromo cyanogen on roasted ore is not so marked, but still strong in evidence as the following table will show: Ore. Percentage of Extraction by Roast- ing plus Pla n Cyanide. Percentage of Extraction Cyanide plus Bromo Cyanogen. Increase in Extraction J j 75.5 : er cent J 75.5 per cent t no A 1 80.7 per cent I 85 8 per cent 1 5.1 per ct. j 75.6 percent j 87.1 per cent j n 5 per ct 1 82.0 per cent ) 82.0 per cent | no B 73.3 per cent 81.0 per cent 8 per cent \ 63.5 per c^nt 1 69.5 per cent ( 6 per ct. c •< 63.5 pei cent -< 68.0 percent \ 4 5 Per ct. ( 5o 0 per cent ( 56.0 per cent f 9.0 per Ct. The effect of bromo cyanogen on the siliceous ores of the Black Hills is to act merely as an accelerator in the solution of the gold bearing mineral as the following table shows: Ore Percentage ot Extraction by Plain Cyanid' , S days contact and 4 1 hours Agitation. Percentage of Extracts 11 ( , .ir.ide and Bromo C' amgen, 36 to 4 hours A. nation. Perc of Ex Plain Cy. 24 36 hrs. agi. A 53 per cent 48 7 per cent 39 per cent B 7I per cent 61. 4 per cent 43 per cent The effect of treating the raw ores for a considerable period with a dilute caustic alkali solution before cyaniding has a marked effect on the extraction in some cases. Extraction by Plain Cyanide With ut Alkali Treatment. Extraction by Plain Cyanide and Alkali Treatment. Ex. by Cyanic' e plus bromo cyanide plus 1 alkali treat. A 39 per cent 54 per cent 64 per cent THE EFFECT OF ROASTING . — The effect of roasting on the ores is of course pronounced, but in some instances does not accomplish by any means what might be expected of it. Some of the ores in order to get extraction must be roasted with great care as regards temperature. The temperature must be kept low, not above a very dull red heat for 3 to 4 hours, when it may be raised to decompose any sulphates formed. If the temperature be raised to a bright red heat, early in the " roasting, with some ores , but very little better extraction than on raw ore can be obtained. This is perhaps due to the presence of small amounts of arsenic and antimony that form stable insoluble compounds, locking up the gold and silver vaU 36 ues. The effect of roasting can be seen from the following table: Ore Extraction by Plain Cyanide, Raw- Ore. Extraction by Plain Cyanide, roast- ' edOre. 1 ncrease in Extracti n. A . J 39 per cent j 82 per cent j 43 per ct. ) 33 per cent 1 75 per cent 1 42 per ct. B ) 47 per cent j 76.6 1 er cent j 29,6 per ct 1 40 per cent 1 73.3 per cent I 33.3 per ct O j 50 per cent j 63.5 per ct.* * 50 rer ct.+ j 13.5 per ct 1 51 per cent 1 69.5 per ct.* 56 per ct.f ) 18,5 per ct With ore B,' roasting at a low heat for several hours, and then mixing with charcoal and reroasting was tried, but with no better effect than before. TIME REQUIRED FOR THE EX TRACI ION OF THE VALUES . — Twenty-four hours continual agitation is about the minimum limit of time in order to get the extraction the ore will yield. Below that extraction will suffer materially. In- creased time of agitation 36 to 48 hours, gives a somewhat in- creased extraction," but after that the increase of time gives but little increase of extraction, although of course a constant incre- ment of increase is noted, * if the formation of soluble sulphides be avoided by the addition of a soluble lead salt or zinc sulphate in small quantities. GENERAL . — A chlorination test on the ore B after roast- ing was made and gave an extraction of 75.5 per cent as com- pared to 81 per cent by roastmg, cyanide and bromo cyanogen. Ore B, 150 mesh material, was also treated with a solution of aqua regia with boiling to see the effect and an extraction of 84.4 per cent was made, showing the exceeding refractoriness of a portion of the values in this class of ores. From the experience gained in the tests made it seems that a portion of the values of the blue ores are practically insoluble in a cyanide solution, and that this insoluble compound is in many instances only partially altered by roasting. If a portion of the values were locked up in the gangue of the ore so that it could not be extracted for this reason, it would seem * Roasted at low heat. f “ at once at a hi"h heat. * See also Bulletin No. 3 South Dakota School of Mines. Cyanide ex- periments, by G. H. Clevenger and A. Forsyth. 37 that such fine crushing as '200 mesh would certainly liberate the greater part of it and thus permit a decided increase of extrac- tion. But this is not so as can be plainly seen from the experi- ments. For these reasons the low extraction in most cases must be ascribed the non-solubility of a compound containing a portion of the values, and any effort toward finer crushing beyond the limits specified above, or a continued contact or leaching for a longtime will be without results. However the time of treatment given the ores is a very important matter, as it must be continued long enough to be well above the mini- mum. There is also some evidence that when the time of treat” ment is continued for a considerable period of time that soluble sulphides tend to form which may lower the extraction unless some zinc be present in the solution to prevent their presence which, however fortunately, is usually the case in ordinary mill solutions. METHOD OF APPLYING THE BROMO CYANOGEN TO THE MILL SCHEME OF THE WET CRUSHING PLANTS. — This is largely a matter of experiment, but the first addition might take place just before the solution enters the battery. A 3 to 5 per cent bromo cyanide solution could be in- troduced by a small pipe into the battery mains and regulated to furnish an amount of bromo cyanide solution so that the bat- tery solution would contain, say, 0.01 per cent to 0.02 per cent of bromo cyanide. If added in this place the agitation given by the stamps could be taken advantage of. There is probably one very serious objection to the addition of bromo cyanide to the mill scheme as at present carried out and that is the alkalin- ity of solutions due to the lime added. As pointed out, alkalies destroy bromo cyanogen, probably without the formation of cy- anogen, and it is very likely lhat the alkaline earth hydrates will do the same. It may be possible that if the battery solution entering the batteries carries but very little protective alkalinity and the amount of lime added with the ore be cut down as low as possible, something might still be accomplished with the bromo cyanogen. This is a matter of experiment. In West Australia * at Kal- goorlie, lime is added after the agitation of the pulp with cyan- ide and bromo cyanogen solution, but as the solutions are re- * The Diehl process, by H. Knutzen, Trans. Ins. M. and Met. June 19, 1902. 38 used must contain some lime when used with the bromo cyano- gen. The next place where an addition of bromo cyanide can be made is during the first addition of barren solution to the slimes. It could be added in amount so that the resultant solution in the slimes vat will contain from o.oi to 0.02 percent bromo cyanogen. If desirable another addition of bromo cyanogen solution may be made at a subsequent addition of barren solution. The constant addition of bromo cyanogen to the battery so- lution would, however, require considerable bromo cyanogen per day and unless a rather marked increase of extraction, due to its addition, could be noticed, would hardly be profitable. For example, in a plant crushing 125 tons of ore per day using 4 tons of a 2 pound battery solution, per ton of ore, the amount of bromo cyanogen required would be 120 pounds, in order to get 0.01 per cent of bromo cyanogen in the battery. This would cost $66 exclusive of an increased consumption of potassium cyanide due to the addition of bromo cyanogen. On $8 ore, therefore, in order to make the addition of bromo cyanogen profitable, an increase of at least 7 per cent must be shown in the extraction, due to the addition of the bromo cyano- gen to the battery alone. The question would have to be worked out on a working scale in the mills themselves, and the cost of the experiment would not be very great, as experiments go. .39 The Crushing in Cyanide Solution Process as Carried on in ihe Black Hills of South Dakota. by Charles H. Fulton. INTRODUCTORY.— The crushingin cyanide solution pro- cess was first introduced into the Black Hills at the old Dakota plant at. Central City by Mr. John Hinton. The method origin- ated in New Zealand, being first used by F. R. -W. Daw in 1897, at the Crowns mine. In the Black Hills it has become practi- cally the established method for the denser siliceous ores, there being at present five plants in operation using this method, with several more of the same kind projected. The dry crushing process still holds its own on the more porous and open sili- ceous ores and there are also plants in operation which do fine dry crushing, on dense siliceous ores. The mills em- ploying the crushing in cyanide solution process are the Horse- shoe mill, 120 stamps, 60 in operation; the Dakota mill, 30 stamps; the Maitland mill, 40 stamps; the Hidden Fortune mill, 60 stamps, and the Lundborg, Dorr & Wi’ on mill, a six foot Monadnock Roller mill. THE NATURE OF THE ORES TRY A TED . — For in- formation on this subject reference is made t } the foregoing paper. GENERAL TEA TURES OF THE PRQCESS. The process comprises the following operations: 1. The crushing of the ores, generally by stamps, in a cyanide solution ranging from 1.3 to 2.2 pounds of cyanide per ton, and carrying a protective alkalinity, equivalent to 1 to 1.5 pounds of sodium hydrate per ton. 2. The separation of the sands from the slimes by means of cone classifiers. 3. The treatment of the sands by percolation. 4. The treatment of the slimes by agitation and decantation. 5. The precipitation of the values by means of zinc thread. The process is applicable to the dense siliceous ores that re- quire a comparatively fine crushing, and which contain but a small quantity of cyanide consuming compounds. For ores that 40 without previous alkaline treatment destroy much cyanide the process is not applicable. As a matter of fact it may be stated that the cyanide consumption in this method is higher than in dry crushing. The cyanide consumption in the wet crushing mills of the district varies from 0.75 to 1.50 pounds per ton of ore treated. At a typical dry crushing plant, the Imperial mill at Deadwood, milling the same class of ore, the consump- tion is 0.4 pound per ton. At the other dry crushing plants of the district it ranges from 0.4 to 0.75 oound per ton. The in- creased consumption of cyanide is a defect inherent in the pro- cess for several reasons. 1. Agitation of the ore with cyanide solution in the battery causes extra consumption. 2. Although the battery cyanide solution carries a protective alkalinity (alka- linity above that due to cyanide and cyanogen compounds) of from 1 to 1.5 pounds per ton, this does not by any means com- pletely protect the cyanide from destruction by cyanicides. The reaction between cyanicides and cyanide and alkaline earth hy- drates and caustic alkalies probably takes place in part at least simultaneously. It has been recognized by metallurgists that with many ores it is essential to apply a comparatively highly alkaline solution low in cyanide to the ores before the stronger cyanide solutions are employed, for the alkalinity carried in the strong cyanide solution would be ineffective in preventing a considerable consumption. 3. There is also an increase in the consumption due to the discharge' of considerable cyanide in the moisture go- ing out with the slimes tailings. This might be called a mechan- ical consumption. This consumption alone amounts to from 0.3 to 0.6 pounds per ton of ore treated. The mechanical consump- tion of dry crushing plants is but an insignificant factor. At the present time it is difficult to make a comparison as regards the relative merits of the process under discussion and the dry crushing process. There is probably, on the whole, little difference between the two processes as regards cost although the wet crushing mills probably have a slight advantage in this respect, in spite of the slimes treatment and the higher consump- tion of chemicals. The wet crushing plants, of course, have an advantage in that they do not suffer from the dust nuisance. However, the hope that the wet crushing plants, on account of the great fineness of crushing that could be carried on, would be able to treat the blue ores in the raw state successfully, has not been verified and it is probable that for this class of ores roast- ing will finally have to be resorted to. In this case, of course, 4i dry crushing will have all the advantage. Some of the mines of the district furnish but little blue ore, while others have a great deal in their reserves. For the first type the crushing in cyanide solution method is, without doubt, a permanent institution. THE CRUSHING OF THE ORES —The ores are rough crushed generally by Gates crushers and in one instance, at the Maitland mill, by a Blake crusher. The crushed ore will pass a i. 5 to 2 inch ring and is fed to the stamps by Challenge feeds. Stamps with one exception are used for the fine crushing of the ore. The Lundberg, Dorr & Wilson mill employs a 6 foot Monadnock roller mill fer the fine crushing, a set of rolls being placed between the Gates crusher and the roller mill, in order to get the proper sized feed of ore. The following table gives the details cf the stamps at four of the mills. Details of the Stamp Mills. Name of Mill Weight of Stain . X o ? T3 gj 5’ Height of Drop Indies. Depth of Discharge, In. sg i_.SI Ss- S O cr x 2 cT a 3. r- < '33 (t 0 “ y,_ P Screen Used Amount of Solution per Ton of Ore. Capacity per Stamp in tons per 24 hrs. Type of Mortar. Hidden Fortune* 1 120 9 X ' 7 8 16 24 mesh. *6 wire 5 4 Double issue rear blocked up. Maitland QIO 97 88 7 to 8 8 6 x 3 26 y 13 mesh 26 wire. 4 to 5. 3-5t04 Single i sue. Dakota. 950 9 *5 10 by 4 mesh, 20 w re. 5 r 4 Single issue. Dakota 950 88 8 : 7 22 Same, 5 Double issue rear blocked up. Horseshoe IOOO 9o 8 5 to 18 i4 by 7 mesh, 21 wire 6 4-5t°5 Double issue rear blocked up. *Crushing in very dilute cyanide solution and amalgamating with inside plate and over tables. Some of the earlier mills installed double issue mortars with the idea of getting an increased stamp duty, but it was soon found that the amount of solution required in crushing was so great that the mills were unable to handle it economically and the rear discharges were closed by wooden frames. It will be seen from the table that the depth of issue and the width of the mor- tar at the discharge level vary considerably at the different mills. The weight of stamp has not so great a variation. As the stamps used are for crushing purposes only at all of 42 the mills with the exception of the Hidden Fortune, it would seem that in general a narrow box, a shallow discharge and a heavy stamp, up to noo to 1200 pounds would give the greatest capacity and most economical results. However, the retaining of the ore in the mortar for a certain length of time in order to agitate thoroughly with cyanide solution is desirable. At most of the mills from 50 to 53 per cent of the values of the ore are extracted in the batteries and the classifying cones. Stamps for this type of crushing should attain a capacity of 5 tons and over per stamp, and in the later designs of mills to be built this has been provided for. At some of the mills the ore is very hard which in part accounts for the rather low capacities. The screens used also vary consider ibly at the different mills, ranging from 26 mesh, 26 wire, to 10 mesh, 20 wire. This is necessitated by the requirements of the individual ores which, while having the same general characteristics, differ somewhat in the fineness of crushing required. Recently several of the mills have installed wire cloth screens in which the opening is rectangular, instead of square, tne lo*:g dimension in these screens being from 2 to 2.5 times that of the short dimension. Screens of this type give somewhat greater capacity and do not choke so readily as screens wnh a square mesh. The denser siliceous ores require a comparatively fine cruh- ing, but if the crushing is carried beyond a certain fineness noth- ing is gained in extraction and trouble is encountered in the pro- duction of an excessive amount of slimes which are difficult to handle in the mill. It has been demonstrated that if the ore is crushed so that the great bulk of it is not co imer th in 30 mesh (0.0195 inches) and not finer than 60 mesh, (0.0075 inches,) the economic extraction is obtained. Material finer than 60 mesh yields but v^ry little higher extraction than that between 30 and 60 mesh. The 5 per cent greater extraction obtained in the mills on the slimes, although the recovery is the same as on the sands, is for the greater part due to the agitation obtained in the treat- ment. If the size of the ore particles however is coarser than 30 mesh the extraction on most of the ores is materially decreased. The following table shows the nature of the mill product made at some of the mills: Mechanical Analyses of Mill Products. t Name of Mill. Mesh of Screen Dakota Samps. Screen 10 by 4 mesh 20 wire. Lundborg, Dorr & Wilson Mon- adnock Roller Mill, Screen 18 Mesh, 0.046 i space Imperial, R 11 s. Screen r6 mesh, 21 wire. plus 20 12,7 1 ercent. 1.0 per cent. 3.0 per cent. •xl plus Mo 18.0 { er cent 0 n D rf plus 40 22.0 pe" cent. 10 0 per cent. 17 0 1 er c nt. 'K n> 0 plus 60 xo 0 per cent. t6.o per cent. 5 (K ; lus 80 14.8 per cent. 5.0 per cent. 0 cn plus IOO 6.0 per cent. 10.0 per cen* . 5.0 p r cent. 3 ( * minus too 36.0 per cent. plus 150 14.8 per cent. minus 150 29.8 per cent. plus 200 19 0 per cent. minus 200 N 50.0 per cent. The Dakota mill uses the coarsest screens of any of the mills and gets a product about 20 per cent of which is coarser than 30 mesh, a rather high percentage, but in view of the very low tenor of the ores treated, and their shaly nature, this crush- ing is the most economic that could be practiced. The other mills use finer screens and their mill product approaches closely to that of the Monadnock mill quoted in the above table. One mill, the Hidden Fortune, crushes some cement ore which con- tains a considerable coarse free gold. This mill has adapted the crushing in cyanide solution process in conjunction with amalgamation inside and outside of the mortar. A very weak cyanide solution, 1.5 pounds per ton, is used with success as a battery solution, no difficulty being experienced to get good amalgamation. The plates need somewhat more frequent dressing owing to the hardening action of the cyanide on the 44 amalgam.* It is also very probable that the plates will have to | be more frequently renewed owing to the solvent action of the cyanide. WEARING PARTS OF THE STAMP MILLS— Most of the mills have adopted chrome steel for shoes and in part for dies as giving the most satisfaction and being the most economical. Table III, compares the different materials that have been used. The Cost of Shoes and Dies of Different Material. Note . Shoes weigh 180 pounds and dies 120 to 140 pounds. Laid down at Terry, S. D., chrome steel costs 5.83c per pound, | Wilson forged steel, 5.72c per pound, and cast iron, 3.5c per j ponnd. Name of Mill. Name of Part. Material Tons of Ore Crushed. No.of Days Used. Cost per Ton of Ore Cm hed. Maitland Shoe Chrome steel 250 90-95 4.9c - Cast iron 105 35-4 • 4.05c “ Die Cast iron 105 40 3.28c “ Wilso.i forged steel 280 105 3.06c Horseshoe Shoe Chrome Steel 336 84 3.I2C - “ Cast iron 104 26 6 15 c “ “ Wilson forged steel 280 70 3.67c “ Die Chrome Stec -1 400 100 2.29 “ . .r.» , 120 3 o 4 08 Wilson f. rged ste 1 340 85 2.35 The Dakota mill also uses chrome steel shoes and is experi- menting with a cast iron die containing 20 per cent of chrome steel scrap, made at a local foundry, which costs 3.5c per pound laid down at the mill. Dies of this kind weigh 120 pounds and lasted 46 days, crushing 175 tons of ore and leave 14 pounds of scrap which is sold at 0.5c per pound, At the Lundborg, Dorr and Wilson mill at Terry a 6 foot Monadnock roller mill is used to crush in cyanide solution in * This same method is used, in part at one or two mills employing the Diehl Process at Kalgoorlie, Australia. See the Diehl Process, H. Knutzen, Trans. I. M. and M. June 1902, t •: Mortar Box for Crushing in Cyanide Solution. 45 place of stamps. This mill crushes about 70 to 90 tons of ore per da}', from 0.75 inch size through an 18 mesh screen, 0.046 inch space. The mill makes 32 revolutions per minute and has 19.5 square feet of screen area. A peculiar feature in the wear of this mill is that both the die ring and the roller tire cup on bearing, instead of the die cupping and tire crowning. This however does not seem to affect the efficiency of the crushing. The mill is giving satisfaction but no figures are as yet available to afford a comparison between it and the stamps on siliceous ore. It might be stated that the ores crushed at this mill are in part comparatively soft although some hard blue quartzite ores are also being crushed. The cyanide solution is introduced into the batteries at most of the mills, by two 1.5 inch pipes entering at the front of the battery between the first and second and the third and fourth stamps. Each pipe is controlled by an iron cock. At two of the mills a special form of mortar is used having a cast iron collecting launder bolted on at the front, and having a central discharge into the main launder collecting the sludge from all the batteries. This mortar is shown in the accompanying plate which also gives the form and dimensions of the mortar used at the Maitland mill. Generally all the screens are overhung with heavy canvas to avoid splash. THE SEPARATION OF THE SANDS FROM 1HE SLIMES BY MEANS OF CONE CLASSIFIERS — This is no v don? in the district almost entirely by means of simple sheet iron cones. These cones are the outer cones of or- dinary hydraulic classifiers, the inner cones having been re- moved. It may be stated at the outset that the problem of re- moving the sands from the slimes when crushing in cyanide so- lution with considerable lime is a more difficult problem than when crushing in water with practically no lime. The lime causes much trouble, first, by its coagulating effect on the slimes, causing them to settle with , the sands and coat sand par- ticles with slimes, and second, by causing the formation of an excessive amount of froth or foam, which is certainly a great nuisance about the mill. The plate accompanying this part of the paper shows the general arrangement of the classsi- fying cones. The batteries discharge their sludge by launder into a cen- tral sump from which it is raised to the cones. The raising 46 pump at three of the mills is the Frenier Spiral sand pump, and at one of the mills a centrifugal pump. For the raising of the battery sludge consisting of sands and slimes the Frenier pump is preferred to a centrifugal on account of less wear. For the transference of slimes and for their agitation a centrif- ugal pump is generally used. The usual size of the spiral sand pump employed is the 54 by 10 inches. These pumps are run at 19 to 20 revolutions per minute, raising the pulp 15 to 20 feet. Twenty feet is about the practical maximum lift of these pumps and for greater lifts they are placed in tandem. A pump of the above size will readily handle from 350 to 450 tons of sludge per day. The discharge of these sand pumps is intermittent so that at all of the mills a distributor box is used to steady the flow and give a uniform feed to the' cones. These distributing boxes have different forms at the various mills. At the Horseshoe mill a pyramidal box is used 4 by 4 feet in cross section at the top, the sides sloping at 60 degrees to meet at a point. The inverted pyramid is topped by a box 12 inches high through which the two 4 inch pipes from the sand pumps enter. About 12 inches from the bottom of the pyramid four three inch pipes emerge one at each side, which feed into four 50 inch cones. The distributor is placed centrally over the four cones and as low as possible so that the head under