Recovery Sulphur From Zinc Concentrate Of Pressure Acid Leaching Residue

Zinc resources are very rich in Yunnan, where zinc resources are proved reserves of more than 20 million tons, including iron sphalerite accounts for about a third of the zinc resources. Yunnan metallurgy enterprise uses the pressure acid leaching technology to treat such ZnS concentrate. Not only is zinc leaching rate high, but also sulfur is fixed to the slag in the elemental sulfur. With a large quantity of high-sulfur residue produced, it is desirable to recover sulfur from this residue, so that it is economically advantageous, and reduces environmental pollution.This article mainly aims at recovery of sulfur from pressure acid leaching residue of ZnS concentrate using ammonium sulfide method, including that the element sulphur leaching process, thermal decomposition process of leaching mother liquor and regeneration of ammonium sulfide recycling process. The results are as follows:Firstly, by single factor experiment of leaching process, this paper probed ammonium sulfide concentrate, leaching time, liquid-solid ratio, leaching temperature on the influence of sulfur leaching rate. Based on single factor experiment, the leaching process conditions were optimized using response surface methodology based on the central composite design. Effects of three leaching variables:liquid/solid ratio (χ1), leaching time (χ2) and ammonium sulfide concentration (χ3) on the sulfur leaching rate were investigated. For the response of sulfur leaching rate, the quadratic model was selected, as suggested by the software. The model is expressed by following equation: Y= 94.93+15.93χ1-0.12χ2χ3-13.86χ12-7.67χ22-5.02χ32Among the equation, the factors X1, X2, X3, X12, X22 and X32 of the influence of sulfur leaching rate is significant. The optimum conditions for leaching elemental sulfur from pressure acid leaching residue of zinc concentrate were obtained by using ammonium sulfide concentration of 2.5 mol/L, leaching liquid-solid ratio of 6.5:1 and leaching time of 7 min. Under the optimum experimental conditions, the sulfur leaching rate is more than 98%. The residue was analysised by XRD before and after leaching. After comparison, S0 diffraction peak of residue has disappeared after leaching. The experimental results obtained agreed satisfactorily with the model predictions, with a correlation coefficient (R2) of 0.99. Response surface method can well ammonium leaching of sulfide element sulphur regression analysis of the process and parameter optimization.Secondly, single factor experiments of thermal decomposition process was carried out to explore effects on sulfur exhalation rate, and the leaching process conditions were optimized using response surface methodology based on the central composite design. Effects of three variables:thermal decomposition temperature (χ1), holding time (χ2) and condensed water velocity (χ3) on the sulfur exhalation rate were investigated. The model is expressed by following equation: Y= 94.93+15.93χ1-0.12χ2χ3-13.86χ12-7.67χ22-5.02χ32The experimental results obtained agreed satisfactorily with the model predictions, with a correlation coefficient (R2) of 0.95. The optimum conditions for thermal decomposition were obtained by using thermal decomposition temperature 92℃heat preservation, holding time 38 min, condensed water velocity 776 ml/min. Under the optimum experimental conditions, sulfur exhalation rate was more than 98%.Thirdly, comprehensive conditions experiment showed that in the comprehensive optimized conditions, the sulfur recovery rate was 96% above and the products were accord with national industrial sulfur level standard. The enrichment rate of valuable metal of Fe, Zn, Pb and Cu was 3.5,4.2,3.2 and 4.2 in leaching residue. Through the enlargement exploration experiment of 20 kg pressure acid leaching residue of ZnS concentrate, the experimental results and test were basically the same. The sulfur recovery rate was about 94%, and the produnts conforms to the national industry standard sulfur product.Finally, in the regeneration of ammonium sulfide recycling experiment, when concentration of the new liquid of ammonium sulfide solution and regeneration of ammonium sulfide was the same, the effect of extracting sulfur was also the same. The average recovery of ammonium sulfide was 90%. Their recycling greatly reduced the cost.