Abstract
The beneficial effect of silver in gold leaching by oxygen in alkaline cyanide and thiosulfate media has been reported by previous researchers. This paper describes a preliminary study of a similar effect in thiosulfate leaching of gold by ammoniacal copper(II) at ambient temperature. Silver dissolves faster than gold in ammoniacal copper(II) thiosulfate solutions. The results based on gold colloids show that the addition of silver colloids or silver(I) nitrate has a beneficial effect on gold dissolution. The chemical controlled dissolution of gold by copper(II) is slower than the diffusion controlled dissolution of silver. The rate of dissolution of gold powder is also enhanced in the presence of silver(I) nitrate. The dissolution curves of gold colloids were analysed on the basis of a shrinking sphere kinetic model. Species distribution diagrams, electrode potential calculations, and gold and silver dissolution kinetics were used to shed more light on the surface reaction mechanism.