Study On Leaching Process And Mechanism Of High Indium High Iron Sphalerite

With the exhaustion of mineral resources, the using of sphalerite containing high iron and indium becomes frequent. Although the oxygen pressure acid leaching process is mature, the mechanism of leaching process and metallurgical behavior of metal elements are unclear. In this paper, the mechanisms of pressure leaching of sphalerite are studied through drawing related potential-pH diagrams, conducting experiments and analyzing electrochemical behavior of sphalerite.Using the related thermodynamic software, the potential-pH figure of Zn-Fe-S-H2O system with different concentration of iron ion, Ag-S-H2O system, Cu-S-H2O system, Cu-Fe-S-H2O system, Pb-S-H2O system are drawed under temperature of 150 ℃ and oxygen pressure of 1.0 MPa. The results showed that, with the increasing of iron ion concentration, the stable area of Fe2+ and Fe3+ decreases, the stable area of Fe2O3 increases gradually. Because E(Fe3+/Fe2+) line is lower than oxygen lines and higher than E(ZnS/S) line, ZnS can be catalyzed oxidation by Fe3+. Ag2S, CuFeS2 and PbS generate elemental sulfur under the condition of oxygen pressure acid leaching process, and the silver, lead exist in the slag phase in the form of AgSO4 and PbSO4 E(CuFeS2/S) line is lower than E(Fe3+/Fe2+) line, so CuFeS2 can be catalyzed oxidation by Fe3+ into Cu2+.The optimum parameters of acid leaching under pressure of sphalerite containing high iron and indium were studied. The factors of leaching temperature, sulfuric acid concentration, liquid-solid ratio and oxygen pressure were researched in detail on the leaching rates of zinc, indium and iron. The results showed that the optimum parameters are put forward, leaching temperature of 150～160℃, sulfuric acid concentration of 150～155 g/L, liquid-solid ratio of 5 : 1, oxygen pressure of 1.0 MPa, leaching time of 90 min, mass fraction of dispersant of 0.4%, grain diameter of-45 μm. As a result, the zinc and indium leaching rates are up to 98% and 80% respectively, while iron leaching rate is 9%, iron content in leaching solution is less than 2 g/L. Iron in slag phase is mainly in form of goethite by XPS detection.The electrochemical behavior of sphalerite and pure ZnS showed that ZnS is oxidized into znic ion and elemental sulfur in the process of anodic polarization. The elemental sulfur adsorb on the electrode to hinder the further oxidation of ZnS. Increasing concentration of sulfuric acid and trivalent iron ion concentration can promote ZnS oxidation process, but the mechanism is different. The increase of sulfuric acid concentration promote the solution conductivity to accelerate the rate of ZnS oxidation. While ZnS can be oxidized directly by the trivalent iron ion because of its strong oxidation to accelerate the rate of ZnS oxidation. Sphalerite oxidation process is complex and multiple oxidation reactions are occured. The mechanism of increasing the concentration of sulfuric acid to promote sphalerite oxidation process is the same with the mechanism of ferric iron ions to promote ZnS oxidation process. The reason is that elemental iron dissolve priorly to generate the ferric iron, the ferric iron can oxidize ZnS directly.