Leaching of Gold with Copper-citrate-thiosulfate Solutions

The use of citrate as an alternative reagent to ammonia in thiosulfate solutions offers an environmentally friendly, nontoxic, and cost-effective leaching method for gold extraction from ore/concentrate. In this work, the behavior of gold disc with copper-citrate-thiosulfate solutions has been investigated to identify the leaching mechanism of gold in the complex system of citrate-thiosulfate. The experimental parameters include rotating speed of gold disc, temperature, solution pH, and composition of lixiviant. The addition of copper and citrate in thiosulfate solutions can accelerate gold dissolution rate by about an order of magnitude. For the copper-citrate-thiosulfate system, thiosulfate ion works as the complexing agent for aurous ion, and it is extremely critical to the gold leaching process. The results of kinetic analysis of the leaching data indicate a chemical reaction-controlled process under the experimental conditions, giving an activation energy of 49.74 kJ/mol. The reaction orders of gold leaching with respect to copper, citrate, and thiosulfate concentration in copper-citrate-thiosulfate solutions are 0.95, −1.49, and 1.18, respectively. An acceptable gold leaching rate of 0.18 to 0.27 μmol·m−2·s−1 could be obtained under the conditions of above 0.1 mol/L copper and thiosulfate concentrations.