Substitution Recovery of Gold from Copper-Ethylenediamine-Thiosulfate Leaching Solution with Copper Power

The substitution method of recovering gold from thiosulfate-ethylenediamine (en)-Cu²⁺ leaching solution using copper powder was studied. The effects of reaction time, stirring speed, pH, thiosulfate concentration, en/Cu²⁺ molar ratio, Cu/Au⁺ mass ratio, and temperature on gold recovery were systematically examined. The experimental results showed that reaction time, stirring speed, thiosulfate concentration, en/Cu²⁺ molar ratio, Cu/Au⁺ mass ratio, and temperature have a significant influence on the recovery rate of gold, whereas the pH has little effect. A high gold recovery rate of 95.38% was achieved in 0.2 mol/L thiosulfate at 40°C after 40 min with a stirring speed of 400 rpm, pH of 11, en/Cu²⁺ molar ratio of 6, and Cu/Au⁺ mass ratio of 150. A kinetic study revealed that the reduction of gold-thiosulfate complex ions (Au(S₂O₃) ₂ ^3- ) on the surface of copper powder follows a first-order kinetics model with an apparent activation energy of 39.82 kJ/mol.