The electrochemical catalytic role of Pb2+ in thiosulfate gold oxidation process

Abstract

The catalytic effect of Pb2+ adsorption on gold surface in gold thiosulfate leaching was investigated by electrochemical methods. Open circuit potential (OCP), cyclic voltammetry (CV) and polarization tests showed that 50 and 100 mg/L Pb2+ addition to thiosulfate solution increased the OCP from −0.136 V to −0.110 and −0.105 V, respectively, due to adsorbed Pb on the gold surface. The Pb2+ addition also increased corrosion rate of gold as well as the anodic current densities. Chronoamperometry was used to determine the interaction between Pb2+ and Au during the anodic polarization at −0.1, 0.0, and +0.1 V. A concentration of 100 mg/L Pb2+ accelerated the gold oxidation rate relative to the Pb2+-free condition, particularly at higher anodic potentials, which resulted in higher dissolved gold concentrations (from near 0 to 2 mg/L). Analysis of the electrode surface with scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy showed that gold oxidation in the thiosulfate solution in the presence of 100 mg/L Pb2+ follows a two-step process: (1) formation of an AuPb2 layer on the gold surface, which improved gold oxidation by inhibiting gold surface passivation; and (2) dissolution of the AuPb2 layer assisted by the applied anodic potential. Addition of 50 and 100 mg/L Pb2+ clearly improved gold oxidation kinetics and efficiency during thiosulfate gold leaching.