Study On Recovery Of Silver From Zinc Sulfide Concentrate By Pressure Leaching Of Indium And Slag

By leaching zinc sulfide concentrate under high pressure leaching, the majority of indium entered into leaching solution and silver mainly stayed in leaching residue. In oreder to improve the utilization ratio of resources and meet the need of non-ferrous metallurgy development, the feasibility of this project was established after analyzing the principles, thermodynamics and kinetics of zinc sulfide concentrate high pressure leaching and thiourea leaching silver. Meanwhile, the leaching of indium from zinc sulfide concentrate under high pressure and use of thiourea leaching silver from zinc leaching residue were studied.In the experiments of zinc sulfide concentrate high pressure leaching, the effects of leaching temperature, leaching time, sulfuric acid concentration, oxygen partial pressure, particle size and ratio of solid to liquid on the Indium leaching rate were examined. The results showed that the indium leaching rate can reach more than 78% and the rate of silver entering leaching residue is over 98% under the optimum conditions including leaching temperature of 150 ℃, leaching time of 90 min, sulfuric acid concentration of 152 g/L, oxygen partial pressure of 1.2 MPa, particle size of 45 μm and ratio of solid to liquid 5 mL/g.In the experiments of thiourea leaching silver from zinc leaching residue, the influents of leaching time, thiourea concentration, ratio of solid to liquid, Fe3+ concentration and leaching temperature on the silver leaching rate were investigated. The results illustrated that under the optimum conditions including leaching time of 5 h, thiourea concentration of 40 g/L, ratio of solid to liquid 8 mL/g, Fe3+ concentration of 0 g/L and leaching temperature of 60 ℃, the silver leaching rate can reach more than 88%.In the optimization experiments of thiourea leaching silver through response surface methodology, the effects of leaching time, thiourea concentration, ratio of solid to liquid and the interaction among them on the silver leaching rate was studied and the multiple regression equation of fitting model was established. The results indicated that the model is significant and the influents of leaching time and ratio of solid to liquid are significant as well as the interaction among these three factors. The optimum conditions after optimization included leaching time of 6 h, thiourea concentration of 50 g/L and ratio of solid to liquid 10 mL/g. With this conditions, the predicted value of silver leaching rate can achieve 92.15%. In order to verify the accuracy of the predicted value, the experiments under the optimum conditions was accomplished and the actual value of silver leaching rate was 91.40%. The difference between the predicted value and the actual value was 0.75 and the relative error was 0.81%. This result means the predicted value is coincided with the actual value.