Study on electrochemistry and gold leaching in cobalt-ammonia-thiourea synergistic gold leaching system

Abstract To address the highly toxic defect of traditional cyanide gold leaching and the technical bottlenecks of the single thiourea gold leaching system, this study employed the [Co(NH 3 ) 6 ] 3+ /[Co(NH 3 ) 6 ] 2+ redox couple as a new-type oxidant, and conducted research focusing on the electrochemical characteristics and gold leaching process of the cobalt-ammonia-thiourea synergistic gold leaching system. Firstly, electrochemical techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were used for systematic analysis of the gold leaching system. Then, actual leaching experiments were carried out with a gold ore from Laos as the research object to explore the microscopic action mechanism and macroscopic process laws of the system. Electrochemical analysis showed that thiourea forms a new complex with cobalt ions, which changes the redox potential of cobalt ions. The oxidation peak at 0.265 V corresponds to the oxidation of thiourea to formamidine disulfide. Moreover, the increase in cobalt ion concentration can reduce the charge transfer resistance, accelerate the charge transfer on the electrode surface, and improve the reaction kinetic activity. The redox reaction of the system exhibits good reversibility. Leaching experiments indicated that pH, leaching time, thiourea concentration, and cobalt ion concentration have significant effects on the leaching efficiency. When the pH is 3, the leaching rate is stable and the thiourea consumption is relatively low; the reaction reaches equilibrium after 10 h of leaching; the optimal values are 0.1 M for thiourea concentration and 0.04 M for cobalt ion concentration. Under the optimal conditions (pH 3, thiourea 0.1 M, cobalt ion 0.04 M, liquid-solid ratio 4:1, stirring speed 300 rpm, leaching time 10 h), the average gold leaching rate reaches 80.10 %, and the average thiourea consumption rate is 14.60 kg/t. This study constructs a synergistic gold leaching system combining theory and practice, providing important support for the precise regulation and industrial application of non-cyanide gold leaching technology.