New insights into the mechanism of pyrite oxidation in copper(II)- ammonia-thiosulfate gold leaching system: An Electrochemical, AFM, Raman spectroscopy and XPS investigation

The nontoxicity, low cost, and environmental friendliness of the Cu2+-NH3-S2O32- gold leaching system make it a viable alternative to cyanide-based systems. However, the strong influence of certain sulphide minerals (e.g., pyrite) on the performance of the former system complicates its compositional regulation. Herein, the mechanism of electrochemical pyrite oxidation in the Cu2+-NH3-S2O32- system is probed by electrochemical techniques combined with surface analysis techniques. The results indicate that the anodic oxidation of pyrite can be assigned to active, passive, or transpassive regions, depending on the applied potential, with high potentials accelerating the reactions on the pyrite surface. Thiosulphate concentration is shown to influence the surface properties and the rate of surface reactions of pyrite. AFM images indicated that the morphological changes on the pyrite electrode surface became much rougher with increasing potential. Moreover, Raman spectroscopy and XPS provided strong evidence for the analysis of the surface species of pyrite surface oxidation. Our work will further explain and provide a mechanism for the oxidation of pyrite in the Cu2+-NH3-S2O32- system. More importantly, this study is expected to be able to provide a theoretical basis for guiding the regulation and control of gold leaching reagent in the Cu2+-NH3-S2O32- system.