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Environmentally friendly extraction of gold from refractory concentrate using a copper – ethylenediamine – thiosulfate solution

Wang, Qiang, Hu, Xianzhi, Zi, Futing, Yang, Peng, Chen, Yunlong, Chen, Shuliang
Journal of cleaner production 2019 v.214 pp. 860-872
ammonia, copper, cyanides, ethylenediamines, gold, leaching, mixing, pH, response surface methodology, roasting, temperature, thiosulfates, toxicity
The growing environmental concerns associated with the use of cyanides and their toxicity have led to the prohibition of cyanidation-based gold leaching in many countries, necessitating the search for other extraction methods. Herein, we show that thiosulfate leaching presents an alternative green way of gold extraction from S- and As-rich refractory gold concentrates, revealing the importance of oxidative ore pretreatment. Prior to leaching, samples were oxidized by roasting, with the optimum roasting temperature (642 °C) and time (240 min) determined using the response surface method. Subsequently, the roasted residues were subjected to cyanidation, copper – ammonia – thiosulfate system, and copper – ethylenediamine – thiosulfate system treatment. As a result, 18-h cyanidation achieved a gold extraction efficiency of 80.6%, with the consumption of NaCN equaling 1.05 kg/t, whereas the corresponding values for 1.5 h copper – ammonia – thiosulfate treatment equaled 63.0% and 11.3 kg/t. Importantly, 4 h copper – ethylenediamine – thiosulfate system treatment (5 mM copper ion, 10 mM ethylenediamine, 0.1 M thiosulfate, pH = 8–11, liquid-to-solid ratio = 3, stirring speed = 250 rpm) achieved a gold extraction efficiency of 80.3%, with the corresponding thiosulfate consumption equaling only 4.14 kg/t. Thus, copper – ethylenediamine – thiosulfate leaching proved to be an efficient, environmentally friendly, and low-cost method, being well-suited for gold extraction from roasted residues.