Thiosulphate Leaching of Gold/Silver from a Copper-Bearing Pyritic Gold Concentrate

There are increasingly stricter environmental regulations imposed for use of cyanide leaching for the extraction of gold from ores. Alternative lixiviants to cyanide, preferably with low toxicity, have been extensively studied. Thiosulphate has emerged as one of the most suitable alternative leaching agents in place of cyanide due to its low toxicity and technical attributes such as fast leaching kinetics and high gold extractions from carbonaceous ores in particular. This study investigates the extraction of gold and silver from a copper-bearing pyritic gold concentrate, characterized by 62 g/t Au, 110 g/t Ag, and 0.3% Cu, using thiosulphate solutions. The concentrate comprises predominantly quartz and pyrite, along with minor minerals including sphalerite and galena. Previous studies indicated poor response to cyanide leaching. The effects of ammonia, thiosulphate, and copper concentrations on gold and silver extraction were examined over 8 hours. Results showed that increasing ammonia and thiosulphate concentrations significantly improved gold leaching, while high copper levels had detrimental effects, especially at lower thiosulphate concentrations. Complete gold extraction was achievable under optimal conditions, whereas silver extractions remained consistently low. These findings demonstrate that thiosulphate leaching could effectively extract gold from copper-bearing pyritic gold concentrates.