Study On Reduction Roasting Of Zinc Calcine And Selective Leaching

In conventional zinc hydrometallurgical process of oxidizing roasting-leaching-purification-electrowinning, zinc ferrite is unavoidably produced during the process of roasting zinc sulfide concentrate and hard to be dissolved in low acid leaching. A large amount of leaching sludge is not only a loss of resource but also a harm to environment. Zinc calcine is used as the research material in this study. Zinc ferrite is decomposed into zinc oxide and iron oxides by reduction roasting. High leaching ratio of zinc and low leaching ratio of iron in low acidity leaching is achieved for the separation of zinc and iron.XRD, SEM-EDX and LPSA are used to investigate the properties and mineralogical characteristics in the experiment. The parameters of reducing roasting for extraction of iron and zinc in acid leaching are systematically studied. The results demonstrate that the reduction function of charcoal is much better than that of CO and cause the iron be reduced so deeply that hardly to be retrieved by magnetic methods; The highest leaching rate of zinc reaches over93%under low leaching rate of iron after roasted at800℃for2h. The parameters of acid leaching and alkali leaching are systematically investigated and the results show that the acidity and temperature of leaching are main factors for the leaching rate of zinc and iron. The leaching rate of zinc reaches over95%and iron leaching rate below30%at30℃, leaching acidity of110g/L, liquid to solid ratio of7, stirring speed of200-400r/min for1h. The leaching rates of zinc and iron are consistent with the roasting time in low-high-low step. This indicates that the chemical reactions happened in the way of decomposing-combining-decomposing. The leaching rate of zinc is improved about10%under leaching rate of iron below5%after roasted and leached in alkaline conditions. The kinetic of zinc and iron of acid leaching has been studied and kinetic equations of iron and zinc are respectively described as follows:1-(1-a)1/3=311.76×exp(-210980/RT)t 1-3(1-a)2/3+2(1-a)=76.96×exp(-8763/RT)tThe results show that the acid leaching process of zinc and iron are controlled by diffusion procedures and surface reaction. Thus, the leaching rate of zinc can be improved by increasing leaching acid and decreasing the grain size of ore; the leaching rate of iron can be inhubited by decreasing leaching temperature.