Mechanism of electrochemical oxidation of gold surfaces in a novel cobalt (II)-glycine-thiosulfate leaching system: An electrochemical experiments and DFT study

The thiosulfate gold leaching system is a promising alternative to cyanide gold leaching because of its low cost, environmental friendliness, and selectivity for gold ore. However, in the traditional thiosulfate leaching gold system, copper(II)-ammonia-thiosulfate (Cu2 + -NH 3 -S 2 O 3 2- ), copper ions increase the consumption of thiosulfate, and excessive ammonia causes water eutrophication and other problems. Therefore, this paper investigated the redox mechanism of gold electrodes in the cobalt(II)-glycine-thiosulfate (Co2+-Gly-S2O32-) composite system by electrochemical techniques. The reaction on the surface of the gold electrode was inferred by CV, and the anodic oxidation of the gold electrode was studied by LSV, i-t, and thermodynamic and kinetic parameters obtained from Tafel plots and kinetic parameters obtained from EIS. Finally, the products on the surface of the gold electrode were analyzed by SEM, AFM, FT-IR, and XPS. In addition, the oxidation mechanism was discussed by quantum chemical calculation using DFT method. The results show that thiosulfate concentration does not alter the oxidation mechanism but affects the kinetic process. High concentration of thiosulfate favors the oxidation tendency of gold, therefore, the concentration of thiosulfate should not be too low. In addition, when additional driving force (high potential) is provided will favor the oxidation of S0 and reduce the hindrance to the oxidation of the gold surface. Meanwhile, we also obtained a model of the electrochemical oxidation mechanism of the gold surface.