Basic Research On Preparation Of Zinc Sulfate From Secondary Zinc Oxide

Secondary zinc oxide is a valuable secondary resource including zinc,lead,iron and bismuth.With the increasing shortage of resources and the stricter environmental protection requirements,the comprehensive utilization of secondary zinc oxide has become an urgent problem.In this paper,the utilization of secondary zinc oxide which was recovered by the fire volatilization process from the zinc bearing dust sludge in an iron and steel company was studied.The recovery of zinc from the secondary zinc oxide and the preparation of zinc sulfate were investigated using the hydrometallurgy technology.At the same time,the recovery of bismuth from the zinc leaching residue was also explored.The Avrami equation was employed to investigate the zinc leaching kinetic during the sulfuric acid leaching process.Zinc sulfate was prepared by the technology of sulfuric acid leaching,impurity removal and evaporation crystallization process.The results show that the content of99.09%zinc sulfate heptahydrate was prepared under the leaching conditions of leaching with sulfuric acid concentration of 22.42%,liquid-solid ratio of 2.5:1,stirring speed of 300 r/min,and leaching at 60?for 20 min,and the impurity removal conditions of using 0.474%H₂O₂ at 60?for 5 min,and the crystallization conditions of crystaling at 30?for 60 min.The technology of hydrochloric acid leaching and iron powder replacement reduction was carried out to recover bismuth form the zinc leaching residue.The results show that the bismuth concentrate,assaying 20.33%Bi with 46.57%bismuth recovery was obtained under the leaching conditions of leaching with 36%hydrochloric acid,and liquid-solid ratio of 2:1 and leaching at 60?for 20 min,and the replacement reduction conditions of adding iron powder with 20 times of bismuth,reduction at 70?for 3 h.In addition,the leaching residue with 47.10%Pb and 26.74%Fe was achieved,which can be used as a raw material to recover lead using the pyrometallurgical process.The morphological characteristics of the sulfuric acid leaching residue and zinc sulfate products were analyzed.The results show that the soot particles of secondary zinc oxide treated by acid leaching presented the obvious corrosion marks with the regular spherical shapes.The crystal morphology presented the regular particle which looks like the wheat grains.The leaching process of zinc hypoxide sulfuric acid leaching can be described by the Avrami equation.The apparent activation energy during the leaching process is 5.18 kJ/mol,and the apparent reaction order is 0.547 and the macroscopic reaction kinetics equation of zinc sulphate leaching is shown below.-ln(1-x)=11.269exp(-((5.18×10³)/KT))C_A^0.547t^0.235.