Treatment Of Zinc Leaching Residue Based On The Selective Reduction Of Zinc Ferrite

The generation of zinc ferrite makes it difficult to separate zinc and iron in zinc smelting industry. Large numbers of zinc leaching residueproduced lead to environmental and resources problems. In this study, a selective reduction roasting process is proposed to transform zinc ferrite into ZnO and Fe3O4in the atmosphere mixing with CO and CO2. Zinc and iron can be recovered by acid leaching and magnetic separation, respectively.Predominance area of Zn-Fe-C-O shows that reduction atmosphere is the key factors on the selective decomposition. The relationship between roasting conditions and zinc ferrite decomposition was conducted by weight loss and phase composition. Roasting temperature and CO concentration have a positive effecton the decomposition of zinc ferrite. Therefore the temperature should be higher than700℃and the concentration of CO should be higher than6%to get high decomposition velocity. Moreover, CO2was an effective additive to restrain the over-reduction of zinc ferrite and the ratioof CO/(CO+CO2) at30%was appropriate. However, the weight loss was less than theoretical value (2.21%) and the content of zinc oxide reached to76.4%when the decomposition stoped. SEM-EDS indicated the ion migration progress during the decomposition of ZnFe2O4:iron ions migratedto the core while zinc ions spreaded to the surface. The product of ZnO layer restrained the diffusion of reducing gases, which limited the decomposition of ZnFe2O4.XRD and XPS results showed that the decomposition of ZnFe2O4divided into four stages:1) ZnFe2O4decomposedto ZnO and Fe3O4;2) Fe3O4reduced to Fe1-xO;3) The reaction between Fe1-xO and ZnO generated Fe0.85-xZnxO solid solution;4) Fe0.85-xZnxO converted to FeO and ZnO. The decomposition of zinc ferrite was a continuous process and the first stage was the objective to realize the separation of zinc and iron.The effects of roasting conditions on the reduction of zinc leaching residue were investigated and the optimum conditions was obtained as follows:roasted at750℃for90min with8%CO and the ratio of CO/(CO+CO2) at30%. Under the roasting condition, the rate of soluble zinc reached to58.57%. The roasted residue leached at35℃for60min with90g/L sulfuric acid and liquid to solid ratioat10:1. Under the leaching conditions,61.38%of zinc was recovered. After magnetic separation with magnetic intensity at1160G for20min,80.9%recovery of iron was achieved. The specific magnetic induction increased from2.40emu/g to50.82emu/g due to the formation of Fe3O4.This novel method not only realized the simultaneous recovery of zinc and iron but also solved the environmental problem caused by the storage of zinc leaching residue.