THE CYANIDE PROCESS

(PART 1)

(1) The reactions which occur between cyanogen and some of the elements are not fully understood, and until they are determined it will be impracticable to treat some ores. See Art. 3.

(2) Fine gold, free from enclosing material. See Art. 4. (3) With silver chloride the action is more energetic than with gold. See Art. 5.

(4) Copper and antimony sulphides, sulphates of base metals, etc. See Art. 6.

(5) Agitation; introduction into the solution of oxygen; or chemicals to either supply or take the place of oxygen. The latter are the halogens iodine, bromine, and chlorine. See Art. 9.

(6) Upon oxygen and strength of the solution. Without oxygen present gold will not be dissolved, no matter how strong the solution. See Art. 11.

(7) (a) Ferric oxide seems to have no effect upon cya

nide solutions.

(b) Ferrous sulphate destroys potassium cyanide and forms potassium sulphate, which is also injurious. See Art. 13.

(8) The loss of cyanide can be decreased by lessening the strength of the leaching solution. Some metallic oxides are

attacked by a strong solution of potassic cyanide, while with a weak solution they are but slightly affected. Also roasting decreases loss in some instances. See Art. 15.

(9) The gold is encased by the pyrite and it cannot be reached by the solution as readily as if the ore were porous. (10) Finely pulverized ore mixed with water. Art. 24.

See

(11) Fine crushing, agitation, and mixing with sand. See Art. 25.

(12) See Art. 29.

(13) In this country, 6.535 grams of silver nitrate to the liter of distilled water are used. The quantity of cyanide solution usually taken is 10 c. c., and each c. c. of the silver solution used represents 1 pound potassium cyanide to the ton of solution. See Art. 32.

(16) By experiment and assay of the ore before and after percolation; or by assaying the gold solution to ascertain the gold in it and subtracting this result from the assay of the ore before leaching. See Art. 43.

(17) This process being experimental, the reader is referred to Art. 49.

THE CYANIDE PROCESS

(PART 2)

(1) (a) Slimes pack and prevent the solution from circulating freely. See Art. 2.

(b) They are gotten rid of by washing them off the ore and then settling them in special tanks or ponds. See Art. 3.

(2) When a weak solution precedes a strong solution, it has for its object the destruction of those chemical compounds that would destroy the strong solution. See Art. 7.

(3) Solutions that are less than half the strength of the standard solution are sent to the weak gold-solution tank, but when they are more than half the strength of the standard solution, they are sent to the strong gold-solution tank. See Art. 8.

(4) The weak cyanide solution is usually about one-third the standard solution, but it may be more or less than onethird to suit conditions. See Art. 9.

(5) The solution would be divided by 10; hence, 60 cents is the answer. See Art. 12.

(6) KCN is added to sump solutions to standardize them as follows: Stock solution of a certain strength KCN is added to the sump solution; or weighed lumps of cyanide of potassium are allowed to hang in baskets in the sump solution and dissolve. The baskets may sometimes be placed under the pipe discharging from the sump into the storage tank. See Art. 14.

N. M. III.-34

(7) 12.23 tons. Ans. See Art. 15. (8) 10.278 lb. Ans. See Art. 16.

(9) The alkali metal zinc precipitates goid from a cyanideof-potassium solution. Consequently, potassium cyanide cannot dissolve gold so long as zinc is present. See Art. 17.

(10) (a) The color of precipitated gold is almost blackbrown when precipitation is going on properly, otherwise it takes various shades of dull gray.

(b) Zinc, acid, and some base-metal salts.

(11) (a) When copper occurs in the zinc boxes in weakgold solutions it is deposited.

(b) Weak solutions containing copper and gold can have their gold deposited and the copper retained in solution by adding potassium cyanide to the solutions to strengthen them. See Arts. 19, 20, and 21.

(12) The object of treating gold precipitates with sulphuric acid is to dissolve out the zinc and other impurities. The sulphate of zinc formed is washed off. The clean filtrates are agitated, drained, dried, and roasted with niter. Next they are fluxed and melted into bullion. See Arts. 26 and 27.

(13) The bullion obtained by the first smelting is impure, consequently, a further refining at a low temperature is sometimes considered advisable. See Art. 34.

(14) Cathodes should be of a thin sheet metal, dense in character, but such that the gold will adhere to it, and not drop off after deposition. The anodes should be of a substance not easily disintegrated or readily dissolved by the solution. See Arts. 36 and 37.

(15) (a) Zinc fume is the volatile substance that escapes when zinc is smelted and is afterwards condensed as "blue powder."

(b) Zinc fume is sifted into the solution as explained in Art. 69.

(16) Charcoal will precipitate gold from cyanide solutions. Professor Christy says, "The claims made by Mr. Johnson cannot be substantiated under circumstances more favorable than could ever occur in actual practice." Further, he finds precipitation quick at first, then slow, and that free HCN hinders precipitation, while other acids rather assist it; at least to some limited extent. To extract the gold from charcoal is expensive and tedious; consequently, the process has never found favor. See Arts. 41-45.

(17) The original idea involved in the pneumatic cyanide process was to furnish agitation, to hasten the leaching, but it was found that it also furnished oxygen as a corollary. See Art. 62.

(18) The Pelatan-Clerici process had for its object agitation and electrical precipitation. This would permit the treatment of slimes and coarser ore at the same time, also precipitate gold, and avoid long, tedious leaching operations. The cathode, being a bath of mercury, would catch coarse gold and retain it independent of the cyanide solution, which acts very slowly on coarse gold. See Arts. 57-61.

(19) Roasted in some instances, especially sulphurets. See Cripple Creek ore treatment in Art. 73.