<Original Papers>On Dissolution of Gold in Cyanide Solutions. (VII) : The Effect of Impurities Contaminating the Cyanide Solution on the Rates of Dissolution of Gold and Silver in the Cyanidation Tests for Gold Ores

The cyanidation tests were undertaken with the aim of examining the effect of the following salts influencing the extraction of gold and silver from ores by means of a miniature Pachuca tank. (I) Additional amount of xanthate, (II) sodium sulfide, (III) potassium ferrocyanide, (IV) potassium zincocyanide, (V) double cyanide of copper and potassium, (VI) potassium thiocyanate, (VII) of potassium sulfate, (VIII) simultaneous addition of some impurities above-mentioned. The ores used were from T, S and O mines. As they consisted principally of silica with small amount of sulfides, the degree of contamination in solution caused by the cyanidation of these ores alone was very small. The tests were thus made by adding intentionally individual impurities mentioned above to cyanide solutions. These tests were made under the following conditions : (1) Pulp agitated for 6hrs. (2) 50 or 100 grams of ore and 500 cc of solution used. (3) Constant cyanide strength of 0.086 per cent KCN used in all tests. The following results are thereby obtained. (1) Xanthate decreases considerably the dissolution rates of gold and silver, in both cases of cyanidation after stirring ores in dilute xanthate solution, filtering, and then washing, and of cyanidation in coexistence with xanthate ions in solution after pre-conditioning. On the other hand, it decreases slightly in the case of cyanidation in coexistence with xanthateions without pre-conditioning. (2) The existence of sodium sulfide is fatal to the dissolution of gold and silver and this coincides nearly with the result of the fundamental experiment of the author (see the fifthreport). The further addition of lead acetate to this solution removes the fatal action of sodium sulfide, but its amount in excess causes again a retarding action probably due to the passive state introduced on the surface of sold and silver. (3) The addition of potassium ferrocyanide has little effect on the dissolution and in the case of O ore it quickens in some degree the dissolution, most coinciding with the result of the fundamental experiment. (4) Potassium zincocyanide has also little effect on the dissolution rates of gold and silver. The addition of free alkali to the solution containing potassium zincocyanide alone cause the yield of potassium cyanide, resulting in the dissolution of gold and silver. (5) The double cyanide of copper and potassium has little effect on the dissolution rate of gold in the case of T and S ores, while it retards remarkably the dissolution of gold and silver in the case of O ore. (6) Both potassium thiocyanate and sulfate have no effect on the dissolution which nearly coincides with the results of the fundamental experiments. (7) Some experiments, in the case of simultaneous addition of above-mentioned impurities except xanthate and sodium sulfide, show that the dissolution of gold and silver is retarded not greatly in spite of great contamination, and that lead acetate, prior to all other coexistent impurities, exerts the effect characteristic of it