Using Nickel as a Catalyst in Ammonium Thiosulfate Leaching for Gold Extraction

Abstract

The use of copper as a catalyst for gold leaching in ammonium thiosulfate solution might cause the high consumption of thiosulfate. Also, the high copper consumption is resulted in the zinc precipitation process for recovering the gold from the pregnant solution. In this investigation, nickel was used as a catalyst to minimize the reagent consumption. On a 100 mass%-75 μm of silicate type gold ore containing 16 g/t Au and 0.2 mass% of Fe and C, the nickel catalyzed ammonium thiosulfate solution could extract 95% of gold with the 1.2 kg/t-ore of ammonium thiosulfate consumption in 24 hours at the most favorable reagent combination of 0.0001 mol/dm³ NiSO₄, 0.05 mol/dm³ (NH₄)₂S₂O₃ and 0.5 mol/dm³ NH₄OH at pH9.5, while the standard cyanidation at 0.02 mol/dm³ (1.0 g/dm³) NaCN consumed around 1.5 kg/t-ore NaCN. In the concentration range of 0.0001∼0.005 mol/dm³ Ni²⁺, the ammonium thiosulfate consumption was 1∼5 kg/t-ore, while the ammonium thiosulfate consumption of copper catalyzed lixiviant was greatly increased from 3 kg/t-ore to 21 kg/t-ore as the increase of Cu²⁺ concentration from 0.0001 mol/dm³ to 0.001 mol/dm³. The feasibility of recycling barren solution was confirmed with zinc precipitation at nearly 100% of gold recovery. Nickel consumption on the cementation process was less than 50%. For extracting gold from the copper bearing sulfide ore, a higher ammonia and thiosulfate concentrations were required with 0.0001 mol/dm³ of Ni²⁺. The ammonium thiuosulfate consumption with nickel as catalyst on the copper bearing sulfide ore was about 1∼5 kg/t-ore less than that using copper as catalyst.