Synergistical thiourea and thiosulfate leaching gold from a gold concentrate calcine with copper-ammonia catalysis

Thiosulfate leaching is a non-toxic and eco-friendly alternative method to cyanidation. However, thiosulfate leaching was used to leach gold from the gold concentrate calcine, and gold extraction effect was poor. To achieve effective leaching of gold, thiourea was added to facilitate gold extraction. This research not only investigated the leaching conditions and leaching kinetics but also discussed the potential reason and reaction mechanism of thiourea improving gold extraction. Gold extraction efficiency within 2 h was close to that of cyanidation (24 h) under the conditions: 0.2 mol/L thiosulfate, 0.12 mol/L thiourea, 5 mmol/L copper ion, 0.6 mol/L ammonia, 3 of liquid to solid ratio, and 308 K of leaching temperature. The gold in the leached solution was effectively recovered by the resin. According to the mechanism analysis, the gold in the leached solution existed in the form of gold(I) thiourea complex and gold(I) thiosulfate complex. The reason responsible for improving gold extraction efficiency lied in that inhibited the form of passivation layer and synergistically leached gold, and rapid leaching speed may be due to synergistical leaching. Thiourea is added in the thiosulfate leaching process, and offers a feasible, efficient, and fast leaching method for green development of the hydrometallurgy industry.