Micromechanism Study of Strengthening Effect of Copper on Gold Thiosulfate Leaching

To study the effect of copper on gold thiosulfate leaching, the gold dissolution of three different sample powders (gold, gold/copper, and gold/copper oxide) in a solution of 5 mM Cu²⁺, 0.4 M ammonia, and 0.1 M thiosulfate was studied. Scanning electron microscopy analysis showed no sulfur passivation on the gold surface, and there were more prominent corrosion pits on the gold surfaces of samples that were ground with copper or copper oxide. The Evans diagrams showed that copper and copper oxide can promote both the anode and cathode processes of gold dissolution. Based on first principle simulations, copper and copper oxide exhibited the ability to disrupt the stability of gold surface atoms and cause different degrees of relaxation. Both copper and copper oxide reduce the d-band center of the gold surface atoms and the adsorption between gold and thiosulfate. In addition, the bond length of the S-S bond of thiosulfate adsorbed onto the gold surface was longer when copper or copper oxide were not present. According to the change in the potential surface energy, the energy barriers for gold atom dissolution from gold, gold/copper, and gold/copper oxide surfaces were 1.79, 0.72, and 1.01 eV, respectively.