Kinetic studies of gold leaching from a gold concentrate calcine by thiosulfate with cobalt-ammonia catalysis and gold recovery by resin adsorption from its pregnant solution

The leaching of gold from a gold concentrate calcine using a novel thiosulfate leaching method that utilizes cobalt-ammonia complex as the oxidant in place of the traditional copper-ammonia catalysis was investigated. The result shows that the thiosulfate consumption can be evidently reduced without the impact on the gold extraction. The leaching kinetics of gold in thiosulfate solution with cobalt-ammonia catalysis has been studied. It was found that the reaction orders with respect to ammonia, cobalt and thiosulfate concentrations are 0.42, 0.20 and 0.34, respectively. The optimal pH value for gold leaching is 10.0, and gold can be effectively extracted at ambient temperature. The apparent activation energy is determined to be 5.68 kJ/mol, and this indicates that the gold leaching in the Co-NH3-S2O32- system is likely to be controlled by the diffusion of reactants and products through a solid layer. The XPS analysis results strongly support this hypothesis. The apparent activation energies of gold leaching in the thiosulfate-only and Cu-NH3-S2O32- systems are 30.9 kJ/mol and 8.01 kJ/mol, respectively. It can be concluded that the cobalt-ammonia catalysis for thiosulfate leaching of gold has higher catalytic efficiency than copper-ammonia catalysis. The tests for gold recovery from the pregnant solution of the Co-NH3-S2O32- system by resin adsorption were implemented, and the results demonstrated that the competitive adsorption of cobalt with gold did not occur owing to the weak affinity of the strong base anion resin for cobalt complex ions. Therefore, the elution of gold on loaded resin only needs to perform a simple one-stage process instead of the complex two-stage elution process for the Cu-NH3-S2O32- system, which will be contribute to reduce the cost of gold recovery from the pregnant solution.