Synergistic Leaching Mechanism And Process Of Wet Zinc Smelting Leaching Slag And High Iron Zinc Concentrate

Marmatite is a vital resource of zinc,which exists extensively in China.However,the high-iron sphalerite extracted from zinc deposit by flotation is refractory.Millions of tons of zinc residue are released from smelting plants in China every year.The traditional technology for the zinc residue processing is defective due to serious pollution and low metal recovery.It is thus important to develop new methods of zinc hydrometallurgy process for the high-iron sphalerite and the zinc residue to expand raw material sources of zinc smelting and improve the zinc process in our country.In order to recover valuable metals efficiently from the high-iron sphalerite and the zinc residue,our group designed a new technological process,which was "simultaneous leaching of high-iron sphalerite and zinc residue—copper cementation—solvent extraction of indium—hematite precipitation".The key tache in this process is the "simultaneous leaching".This dissertation started with the thermodynamic properties of high-iron sphalerite and zinc residue,continued to focus on the mutual conversion and transmission of Fe3+/Fe2+ and S0/S2-,and discussed the basic theory and adjust technology for the simultaneous leaching of high-iron The main research work and results were as follows:(1)The analysis of technological mineralogy on the high-iron sphalerite and the zinc residue were carried out by means of chemical composition,chemical phase composition,XRD and SEM-EDS.Though the high-iron sphalerite had high proportion of iron and indium,the content of zinc in the high-iron sphalerite was low.The major phases in the high-iron sphalerite were sphalerite and marmatite.Its chemical phase analysis showed that more than 95%of zinc was present in sulphide.The content of iron and indium in zinc residue was high.The major zinc-bearing phases in the zinc residue included zinc ferrite(69%)and zinc silicate(15%).(2)The thermodynamic properties of high-iron sphalerite and zinc residue were studied.The thermodynamic stable region of zinc ferrite got smaller as pH and redox potential decreasing in sulfuric acid solution.By dissolving zinc ferrite,Fe3+ was released.The redox potential rose and the H+ activity coefficient dropped with increasing in Fe3+ concentration.Thus,the Fe3+decelerated the dissolution of zinc ferrite.The thermodynamic stable region of sphalerite became smaller as pH decreasing or redox potential increasing in ferric sulfate solution.The reactivity of sphalerite grew along with more iron content.In the zinc ferrite-high-iron sphalerite simultaneous leaching system,the Fe3+ was released by dissolving the zinc ferrite and was converted into Fe2+ by the high-iron sphalerite.Reduction of Fe3+ and dissolution of the high-iron sphalerite could take place at the same time.(3)In zinc ferrite-sphalerite simultaneous leaching system,the dissolution rate of zinc ferrite had a positive correlation with temperature,H2SO4 concentration and amount of sphalerite;the dissolution rate of sphalerite had a positive correlation with the temperature,H2SO4 concentration and amount of zinc ferrite.The dissolution rates of zinc ferrite and sphalerite increased with the decreasing of particle size of grain.The dissolution of zinc ferrite process followed a grain model with chemical reaction as the main rate-controlling step.The relationship between dissolution rate of zinc ferrite and amount of sphalerite was:kr×10-2＝1.45×10-2×η+1.35×10-2The kinetic mechanism of simultaneous leaching process was investigated for zinc ferrite-sphalerite system.The leaching process was found to be most adequately described by the core-shrinking model.Initially,the leaching rate of zinc was controlled by the chemical reaction at the surface of the grains.The activation energy of the chemical controlled step was 51.44kJ/mol.The reaction order with respect to sulfuric acid was approximately 0.52.Then,the leaching rate was controlled by the diffusion of the reagents or products through the elemental sulphur layer.(4)In the zinc residue-high-iron sphalerite simultaneous leaching system,the leaching process was found to be best described by the core-shrinking model.Initially,the leaching rate of zinc and iron were controlled by the chemical reaction at the surface of grains.The activation energy of the chemical controlled step for zinc and iron were 55.11kJ/mol and 43.42kJ/mol,respectively.The reaction order with respect to sulfuric acid for zinc and iron were approximately 1.14 and 1.12,respectively.Then,the leaching rate was controlled by the diffusion of the reagents or products through the elemental sulphur layer.(5)It was found that leaching of zinc residue in the presence of high-iron sphalerit was a viable method that could effectively extract zinc、iron、indium and convert Fe3+ into Fe2+ at the same time.In the simultaneous leaching process,the dissolution rate of zinc ferrite was higher than high-iron sphalerite.After the leaching,the zinc residue was completely dissolved,whereas a small amount of the high-iron sphalerite did not dissolve.The simultaneous leaching residue was examined by XRD and SEM-EDS that a sulphur layer was formed around the residue.The dissolution of the high-iron sphalerite was the key factor in the simultaneous leaching process.By(In?)the optimum conditions,the extraction of zinc,iron,indium,copper was above 96%、96%、95%、97%,respectively,by reflux leaching tests using two stages.The concentration of Fe3+ and sulfuric acid was about 3g/L and 30g/L,respectively.After Fe3+ reduction,it is effortless to separate zinc and iron and to recover valuable metals from leach solution.