The factors affecting the leaching rate of gold during cyanidation are: the concentration of cyanide and oxygen, the pH value of the slurry, the raw material properties of the gold mineral, the leaching temperature, the slime content, the pulp concentration and the leaching time.
The cyanide concentration during leaching is generally 0.03% to 0.08%, and the dissolution rate of gold rises linearly to the maximum with increasing cyanide concentration. Then slowly rise, when the cyanide concentration reaches 0.15%, the dissolution rate of gold is independent of cyanide, or even decreased (due to cyanide hydrolysis).
The dissolution rate of gold increases with increasing oxygen concentration, and the dissolution of gold can be enhanced by an oxygen-rich solution or high-pressure aeration oxidation.
Ability to dissolve gold and silver cyanide as reagent: ammonium hydroxide> calcium cyanide> sodium> hydroxide. The price of potassium cyanide is the most expensive. Most of the current use of sodium cyanide, the consumption of cyanide depends on the nature of the material and the operating factors, often 20 to 200 times the theoretical amount.
The nature of the material affects the leaching rate of gold. Although cyanidation is the main method of extracting gold, gold-bearing ore, but some material not directly employed cyanidation process, if the copper in the ore, arsenic, antimony, bismuth, sulfur, phosphorus, magnetic iron ore, iron ore and other one hundred When the content of the component is high, the cyanide consumption or the oxygen in the slurry is greatly increased, and the gold leaching rate is lowered. When the ore contains high carbon, the carbon will adsorb the dissolved gold and lose with the tailings. The pre-oxidation roasting or flotation method can remove the harmful impurities.
The hydrolysis of cyanide is:
KCN+H 2 Oâ†â†’KOH+HCN↑
Therefore, toxic HCN is volatilized; lime is added to weaken the cyanide hydrolysis, and the above reaction proceeds to the left to reduce the chemical loss of cyanide. Lime also neutralizes the action of acid substances, and can precipitate harmful ions in the slurry, so that the dissolution of gold is in the best condition, and lime is commonly used as a protective base. The amount of lime added is such that the pH of the slurry reaches 11 to 12, and the pH of the slurry is too high, which is unfavorable for the dissolution of gold.
The size of the gold particles mainly affects the cyanide time, and the dissolution rate of the coarse gold particles (>74 microns) is slow. Therefore, it is reasonable to pre-recover coarse gold by amalgamation , re-election or flotation before cyanidation. The dissociation of fine gold particles from the monomer during the grinding process is still an important factor in increasing the leaching rate of gold.
The mineral content and slurry concentration during cyanide directly affect the diffusion rate of the components. The concentration of pulp should be less than 30% to 33%. The concentration of slurry should be less than 22% to 25%, but the concentration should not be too low, otherwise the consumption of cyanide will increase.
The cyanide time varies depending on the nature of the material, the cyanidation method and the cyanide conditions. Usually stirred cyanide leaching often greater than 24 hours, sometimes up to 40 hours, 72 hours required when cyanide gold telluride, diafiltration cyanide leaching takes more than 5 days.
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