The study of the kinetics of gold leaching in the ammonium thiosulfate in the presence of copper

The kinetics of gold leaching in ammonium thiosulfate solution in the presence of copper have been studied by electrochemical polarization and direct rotating disk leaching methods. The effects of pH, temperature, rotating velocity and the concentrations of different reagents on the gold leaching rate have been investigated. It was found that the anodic oxidation of gold in ammonium thiosulfate solution is complex. Ammonia, thiosulfate and copper species all affect the anodic process. The anodic process is under surface reaction control. The above species plus oxygen are involved in the cathodic process. The role of copper species are facilitating oxygen reduction through the Cu(S₂₃)₃⁵⁻/Cu(NH₃)₄²⁺ couple. The gold leaching rate in ammonium thiosulfate in the presence of copper species is mainly controlled by the cathodic process, which is under diffusion or mixed kinetics control. The results of the rotating gold disk leaching study are consistent with those from the electrochemical study. The gold leaching process in ammonium thiosulfate solution is under diffusion or mixed kinetics control. The gold leaching rate can be correlated with different parameters as follows. The application of this rate equation is limited to the range of conditions used in this study.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat