Eco-friendly and economical gold extraction by nickel catalyzed ammoniacal thiosulfate leaching-resin adsorption recovery

Nickel catalyzed ammoniacal thiosulfate leaching-resin adsorption recovery, an environmentally friendly and cost-effective process, was developed to extract gold from a gold concentrate calcine. The catalytic mechanism was presented based on thermodynamic analysis that NH3 catalyzed the anodic dissolution of gold, and Ni3O4 catalyzed the cathodic reduction of O2. The leaching result indicates that thiosulfate consumption reduced considerably under nickel-ammonia catalysis, whilst gold leaching percentage was comparable with that under conventional copper-ammonia catalysis. The kinetics study demonstrates that the reaction orders of initial nickel (II), ammonia and thiosulfate concentrations were separately 0.21, 0.37 and 0.28. The apparent activation energy calculation shows that the catalytic efficiencies of nickel-ammonia and copper-ammonia were close, and gold leaching with nickel-ammonia catalysis was possibly diffusion controlled that was supported by the XPS analysis result. For the gold recovery from its actual leach solution by ion-exchange resin, the resin and desorbent dosages were less, and loaded gold could be desorbed by a simple one-step desorption process because nickel did not co-adsorb with gold on resin surface. Besides, gold leaching percentage only declined 1.8% after the leach solution was recycled five times, and thiosulfate consumption decreased 5.8 kg/t-calcine.