Effect of sulfides on gold dissolution in ammoniacal thiosulfate medium

To understand how various sulfide minerals affect the dissolution behavior of gold in the ammoniacal thiosulfate leaching system, an extensive study has been carried out on gold leaching in the presence of sulfides using pure gold plates. Special emphasis has been placed on gold leaching in association with sulfide dissolution, thiosulfate decomposition, and dissolved oxygen depletion in leach solutions. The results demonstrated that the leaching behavior of gold depended strongly on the solubilities of the sulfides, the thiosulfate decomposition, and the oxygen concentration in slurries. Gold dissolution was enhanced or diminished, depending on the sulfide types and the sulfide concentrations in slurries. An increase in the stirring speed accelerated the gold dissolution rates due to the improved mass transfer occurring in the gold leaching process and the increased dissolved oxygen content in leach solutions. The addition of sulfate in the sulfide slurries increased the gold leaching rates because of the depression of the sulfide dissolution in the leaching systems. Topological studies by scanning electron microscopy (SEM) demonstrated that the existence of passivating layers at the leached gold surfaces could result in the retardation of gold dissolution in the presence of sulfide minerals.