The role of glycine in the ammonium thiocyanate leaching of gold

Thiocyanate leaching is an efficient and environmentally friendly method to extract gold due to fast leaching speed, excellent reaction selectivity and slight environmental risks, but thiocyanate is easily oxidized to decompose by oxidant in the leaching process, resulting in large consumption of leaching agent. In this work, synergistic leaching experiments were carried out with a mixed reagent system of ammonium thiocyanate and glycine for exploring the role of glycine in thiocyanate leaching. And the theoretical mechanism of glycine in thiocyanate leaching was also investigated. The results showed that as glycine was added into the thiocyanate leaching solution, the decomposition reaction of thiocyanate would be lessened, resulting in lower ammonium thiocyanate consumption. Meanwhile, owing to its characteristic of gold dissolution, glycine can be used as an additional leaching agent to increase the gold leaching ratio. Optimized gold-extraction efficiency (93.15%) of gold-bearing flotation concentrate was achieved under the following conditions: a concentration of thiocyanate, glycine and oxidant Fe3+ at 0.6 mol/dm(3), 5 g/dm(3) and 0.05 mol/dm(3), respectively; stirring speed at 600 rpm; pH at 2; temperature at 298 K; leaching time of 3 h and a liquid-solid ratio of 4:1.