Gold Cementation from Ammonium Thiosulfate Solution by Zinc, Copper and Aluminium Powders

Abstract

Gold cementation test was conducted without de-aeration by using zinc, copper and aluminium powders from an ammonium thiosulfate solution contained 8 mg/l Au. The amount of metal powder was varied in the range of 30–450 Metal/Gold mass ratio. The solution composition was 1–5 mol/l NH₄OH, 0.01–0.05 mol/l CuSO₄∗5H₂O, 0.2–0.4 mol/l (NH₄)₂S₂O₃ and pH 9.5–10.5. The results indicated that the gold was effectively recovered from a solution of lower ammonia and copper concentrations and higher thiosulfate concentration. The optimum reagent composition for the gold cementation from the ammonium thiosulfate solution was founded to be 1 mol/l NH₄OH, 0.01 mol/l CuSO₄∗5H₂O and 0.4 mol/l (NH₄)₂S₂O₃ at pH 9.5. 100% of gold was recovered by zinc and aluminium powders at a Metal/Gold mass ratio of 30. Copper powder recovered 93% of gold at a Metal/Gold mass ratio of 50. Zinc might re-generate thiosulfate concentration and precipitate most of copper in the solution. Aluminium precipitation might recover gold with less amount of copper deposition and some thiosulfate reduction. Copper precipitation reduced a small amount of thiosulfate concentration and greatly increased copper concentration. Ammonia concentration stayed constant during cementation process.