Study On The Process Of Selective Leaching Of Zinc-containing Fumes From Steel Mills In Alkaline Ida^2--H₂O System

It is well known that China is a big country in producing refined steel.Dust produced by scrap smelting contains large amount of iron and zinc,which is regarded as one of the important secondary resources.Meanwhile,China is also a great consumer of zinc.With the increasing consumption of zinc mineral resources,the development and utilization of secondary resources becomes more important.Zinc-containing dust was recycled by beneficiation method in the past,which was proved have a bad effect on the normal operation of blast furnace.Currently,the common zinc extraction processes include wet zinc extraction process and pyrogenic process.The existing pyrogenic process is energy intensive and probably polluting.Among to the tradition wet zinc extraction process,acid leaching is the best mature technology,but this method is difficult to separate many impurity elements such as calcium,magnesium,iron,silicon and carbon from the leaching solution.And the iron element needs to increase the step of iron removal in the later stage,so the acid leaching method is gradually replaced.Therefore,improving the development process of extracting zinc from secondary zinc resources makes it more efficient and environmental protection will be very meaningful.Based on the research about extracting Zinc in alkaline solution with inorganic ligands,metal amino acid chelate was selected to deal with low grade zinc oxide ore by some groups.Zinc amino acid is a five-circle chelate formed by zinc ions and N atoms and carboxyl groups of electrons given in amino acids,which breaks the ligand limitation of ammonia removal and alkali leaching process in NH₃,Cl^-and OH^-.Therefore,iminodiacetic acid was selected as ligand to explore the new process of zinc-containing soot in steel plants on selective leaching.Thermodynamic behaviors of Zinc Oxide?ZnO?with alkaline iminodiacetate aqueous solution were studied.Species distribution diagrams of Ida^2-in the solution were obtained based on the coordination chemistry theory.Thermodynamics of Zn²⁺in the system of ZnO-Ida^2--H₂O were studied based on the double equilibrium theory.When the concentration of Ida^2-and PH value varied in ranges of 0.5².5 mol·L^-1 and6¹2,the equilibrium thermodynamic diagrams were applied to analyze the effects of Ida^2-concentration and pH value on the extraction of ZnO.In particular,the total Zinc concentration,Zinc type type and the distribution Ida^2-were studied,respectively.In addition,the calculation results were verified by experiments.The results show that the total zinc concentration remains stable when the pH value ranges from 7⁹ under a certain Ida^2-concentration with a relatively small error value.And when the Ida^2-concentration and pH value is 2 mol·L^-1 and 8 respectively,the error of zinc concentration between theory and experimental reaches the minimum value 1.07%.The raw materials used in the experimental study was obtained from the soot which was collected from the dust collection bag of blast furnace in Shagang LTD.The results revealed that the Ida^2-is selective which is easy to form stable complex with Zn²⁺.The temperature,concentration,liquid-solid ratio and pH value were shown to positively affect leaching results.When the liquid-solid ratio is 25:1,the concentration of Ida^2-is 3.5 mol·L^-1,stirring speed is 500 r·min^-1,the temperature reaches 140°C,the PH value is 7.5,the reaction time is 4 h and the pressure is 0.5MPa,the leaching performance is best.Under the best conditions,leaching rate of Zinc and Fe is stable with a high level of 94.18%including about 60%from ZnFeO₄solution,and the leaching rate of Fe can be controlled under 17.5%.The content of Ca and Mg in solution is about 7.7 mol·L^-11 and 24.5 mg·L^-1,respectively.In addition,under the best conditions,the content of Pb,Mn,Cr and Cu reaches in the leaching solution is about 77.375 mg·L^-1,7.421 mg·L^-1,9.567 mg·L^-1 and 5.861 mg·L^-1.