Development of a novel cobalt-glycine catalyzed thiosulfate system by DFT calculation for eco-friendly and efficient gold extraction

Abstract

In this study, a novel thiosulfate leaching system, cobalt-glycine catalyzed system, was proposed. DFT calculations suggest that the coordination ability of organic ligands with metal ions conforms to the order: glycine > oxalic acid > citric acid > acetylacetone, and the reactivity and adsorption capacity of complexes on gold surface follow the order: cobalt-glycine > nickel-glycine > iron-glycine > copper-glycine > copper-ammonia. Cobalt-glycine complex is more likely to gain electrons from the gold surface and promote gold dissolution than copper-ammonia complex. During gold leaching, glycine catalyzes the coordination of Au+ with S2O32− and stabilizes cobalt ions under alkaline conditions, and Co(gly)x(2−x) catalyzes the reduction of O2. The gold leaching percentage and thiosulfate consumption of cobalt-glycine system are 94.85 % and 17.38 kg/t-ore, it has higher gold leaching percentage and lower thiosulfate consumption than copper-ammonia system. 99.27 % of gold in the leaching solution of cobalt-glycine system is adsorbed on resin, which could be recovered by one-step desorption because cobalt is hardly adsorbed on resin. However, copper in the leaching solution of copper-ammonia system competes with gold for adsorption on resin, so the gold adsorption percentage is low at 95.36 % and two-step desorption are required to separate copper and gold. The novel cobalt-glycine system is more environmentally friendly, simplified and efficient than traditional copper-ammonia system.