Leaching of gold and copper minerals in cyanide deficient copper solutions

The concept of leaching copper–gold ores using leach solutions which contain Cu(CN)32− was investigated. Gold leaching occurs in air saturated Cu(CN)32− solutions at a much slower rate than in free cyanide solutions. A similar gold leach rate is observed when copper is alloyed with the gold. The dissolution of several common copper minerals in Cu(CN)32− also occurs at significantly slower rates, and in some cases not at all. This has the advantage of reducing copper dissolution and hence cyanide consumption. When leaching chalcocite (Cu2S) in free cyanide solution, the dissolved sulfide ions significantly hinder gold leaching. However, when leaching chalcocite in Cu(CN)32− solutions, little sulfide was dissolved and gold leaching was found to be more rapid than for the free cyanide solution. Preliminary test work with gold ore samples containing CuO indicated that the initial kinetics of gold dissolution in air saturated Cu(CN)32− solutions were comparable to free cyanide. However, some gold was not leached when the leaching of the copper minerals was incomplete.