The leaching of gold in cyanide solutions in the presence of impurities. II. The effect of silver

In the present study, a rotating electrochemical quartz crystal microbalance was used to investigate the effect of silver on the leaching of gold in aerated alkaline cyanide solutions. It was found that trace amounts of silver in the solid phase significantly enhances the leaching rate, and it is believed that the role of silver is to disrupt the film of AuCN which exists on the gold surface. In the presence of silver, the rate-determining step is the mass transfer of reactants, with the rate being limited by cyanide diffusion at low cyanide concentrations, and oxygen diffusion (jointly) at high cyanide concentrations. Such a result is similar to the pioneering results of Kudryk and Kellogg [J. Met., 6, 541 (1954)], suggesting that their work was carried out using silver contaminated gold. Complementary electrochemical studies showed that the oxidation of gold containing 1% silver was cyanide diffusion controlled at relatively low overpotentials, suggesting that surface films do not hinder the oxidation of gold /silver alloys in the same way in which they block the oxidation of pure gold.