Recovery of gold from refractory gold ores: Effect of pyrite on the stability of the thiourea leaching system

The extraction of gold from refractory gold ores (RGOs) without side reactions is an extremely promising endeavor. However, most RGOs contain large amounts of sulfide, such as pyrite. Thus, investigation of the influence of sulfide on the gold leaching process is important to maximize the utilization of RGOs. In this work, the effects of pyrite on the stability of the thiourea system were systematically investigated under different conditions. Results showed that the decomposition rate of thiourea was accelerated sharply in the presence of pyrite. The effect of pyrite on gold recovery in thiourea leaching systems was then confirmed via a series of experiments. The decomposition efficiency of thiourea decreased by 40% and the recovery efficiency of gold increased by 56% after the removal of sulfide by roasting. Under optimal conditions, the efficiency of the gold recovery system increased to 83.69% and only 57.92% of thiourea decomposition was observed. The high consumption of thiourea by the leaching system may be attributed to not only adsorption by mineral particles but also catalytic decomposition by some impurities in the ores, such as pyrite and soluble ferric oxide.