An electrochemical study of the dissolution behavior of gold in a novel glycine-thiosulfate system

Abstract

Ammonia-free thiosulfate systems are known for their non-toxicity, low reagent consumption, and excellent leaching efficiency in gold extraction studies. This study proposes a novel and environmentally friendly glycine-thiosulfate system and comprehensively investigates the dissolution behavior of gold through the application of electrochemical methods. Electrochemical quartz crystal microbalance (EQCM) has demonstrated that the anodic dissolution of gold is predominantly influenced by the forms of copper(II)-glycine complexes as catalysts, and the presence of Cu(C2H4NO2)3− complex in strong alkaline has enhanced dissolution rate of gold, in contrast to Cu(C2H4NO2)20 complex in near-nurture condition. Such excellent catalytic capability of the Cu(C2H4NO2)3− complex for gold dissolution can be attributed to the lowest corrosion potential, slighter passivation behavior, and rapid electron transfer from the analysis of corrosion electrochemistry (OCP, PDP, and EIS) and advanced spectrum technologies (LA-ICP-MS and XPS). The dissolution of gold in the novel glycine-thiosulfate system undergoes a typical ligand exchange process (Au+→Au(C2H4NO2)2−→Au(S2O3)23−), and the formation of passivation species on the gold surface is predominantly formed by Au(I)-glycine coordination, rather than the sulfur-containing products from thiosulfate decomposition. Based on these results, the proposed two electrochemical reaction mechanisms will contribute to the optimization of leaching conditions in the novel glycine-thiosulfate system.