Gold cementation from ammonium thiosulfate solution by zinc, copper and aluminium powders

Gold cementation test A as 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/1 NH4OH, 0.01-0.05 mol/1 CUSO4 * 5H(2)O, 0.2-0.4 mol/1 (NH4)(2)S2O3 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/1 NH4OH, 0.01 mol/1 CuSO4 * 5H(2)O and 0.4 mol/1 (NH4)(2)S2O3 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.