Thiocyanate hydrometallurgy for the recovery of gold.: Part II: The leaching kinetics

Acid thiocyanate leaching of gold was investigated in the presence of ferric sulfate as an oxidant. According to leaching kinetic studies the initial rate of gold leaching is slow, and not significantly dependent on thiocyanate (0.05–0.2 M) and ferric (0.1–1.0 g/L) concentrations. Ferrous and cupric ions had no effect on leaching kinetics under the conditions studied. In contrast, silver (I) and copper (I) ions significantly impeded the rate of gold leaching. The electrochemical experiments (linear sweep voltammetry and chronoamperometry) indicated that the anodic reaction for gold leaching in acid thiocyanate solutions is the limiting step for the leaching process. Gold dissolution and thiocyanate oxidation participate simultaneously in the anodic process. The addition of thiourea noticeably enhanced the rate of gold leaching. Fourier transform infrared spectroscopy (FTIR) studies demonstrated that thiocyanate and its complexes with the metal ions involved in the leaching systems (Fe (III), Cu (II), Cu (I) and Ag (I)) had very weak adsorption properties at the gold surface.