Thiosulfate Leaching of Gold in the Presence of Thiourea

Thiosulfate as an alternative lixiviant for gold has garnered significant interest due to rising environmental concerns associated with cyanide usage. This study investigates the catalytic role of Cu(II) and the stabilizing effect of ammonia in enhancing gold leaching in alkaline thiosulfate solutions. However, it was noted that Cu(II) also accelerated the oxidative degradation of thiosulfate, making the process less economical compared to cyanide leaching. To address this, we explored the potential of additives, particularly thiourea, in boosting gold dissolution while minimizing reagent consumption. Electrochemical assays with a rotating gold disc revealed that the oxidation of gold was markedly elevated in ammoniacal thiosulfate solutions with thiourea additions, achieving optimal results at concentrations up to 7.2 mM. Although thiourea significantly enhanced gold extraction under low reagent levels, excessive thiourea proved detrimental, inhibiting further leaching. Additionally, experimental results via X-ray Photoelectron Spectroscopy (XPS) suggest that thiourea decomposes into sulfide and interacts to form gold sulfide species on the surface. Therefore, thiourea functions as a favorable additive, promoting effective thiosulfate leaching of gold from sulfide ores at minimal reagent concentrations.