Selective leaching of silver-rich residue in NH4SCN solution under oxygen pressure

An oxidative pressure leaching process to extract silver from the silver-rich residue of demanganized silver–manganese sulfide concentrate with ammonium thiocyanate solution was investigated in this paper. The effects of several factors: temperature, leaching time, oxygen pressure, Fe3+ concentration, lignin concentration, and initial pH of the leaching reagent, on the extraction percentages of silver were studied. The following optimized leaching conditions were obtained: Fe3+ concentration 4.2 g/L, lignin concentration 0.6 g/L, NH4SCN concentration 1.5 M, initial pH value 1.8, and oxygen pressure 1.4 MPa at 120 °C for 3 h. Under these optimized conditions, the average extraction percentage of silver was about 88% and 6.5% of NH4SCN was lost after four cycles. The ammonium thiocyanate method has advantages over the conventional cyanidation method and chlorination method, with a higher efficiency, lower toxicity and better selectivity and stability.

Graphical abstractThis is the flowsheet for the selective leaching of silver from the silver-rich residue. In this paper we proposed an oxidative pressure leaching process to extract silver from the silver-rich residue of the demanganized silver–manganese sulfide concentrate with ammonium thiocyanate solution. This method has advantages over the conventional cyanidation method and chlorination method, with a higher efficiency, lower toxicity and better selectivity and stability.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights▶ We proposed an oxidative pressure leaching process to extract silver from the silver-rich residue of the demanganized silver-manganese sulfide concentrate with ammonium thiocyanate solution. ▶ Under the optimum conditions, the average extraction percentage of silver was about 88%. ▶ This leaching reagent has some advantages, such as higher efficiency, lower toxicity and better selectivity and stability.