An electrochemical study of copper cementation of gold(I) thiosulfate

In the present study, copper cementation was evaluated as a method for the recovery of gold from thiosulfate leach solutions. It was found that it is possible to achieve appreciable cementation rates of gold onto a copper substrate. The presence of 0.4 M ammonia had a positive effect on cementation, shifting the reaction from the chemical reaction control regime to the diffusion control regime. This effect is explained by the shift in the anodic reaction, copper oxidation, as ammonia was added. Electrochemical studies of the cathodic reaction, gold deposition, were also carried out. It was found that a high overpotential is required to deposit gold onto a gold substrate. However, the presence of copper, either as metallic copper or as Cu(I) thiosulfate, dramatically enhances the gold deposition half reaction. Without this enhancement, the cementation reaction would occur at a very low rate.