Study On Iron Removal From Hematite Process Of High - Iron Sphalerite

With the increasing exhaustion of high-quality zinc ore resources, more and more attention has been paid to the exploitation and utilization of high iron sphalerite resources that are widespread in China. The technique of hot-leaching hematite process for treating high iron sphalerite will obtain a better parameter than the conventional zinc hydrometallurgical process. At the basis of zinc sulfate solution bearing high iron, the present paper mainly focused on the research of hematite process which is applied to treat leaching liquor of high iron sphalerite. Listed below are the main results.(1) The iron-removal experiments by hematite process have been carried out relating to ferrous sulfate solution. The effects of ferrous and zinc sulfate concentration, temperature and time on iron removal efficiency were investigated. Various analysis methods were performed to present the physicochemical property of hematite residues. The results show that iron removal efficiency decreases with the increase concentration of FeSO4 and increases with increase of reaction temperatures, time and concentration of ZnSO4. Fe content of precipitate (>60%) increases with increase of temperatures, S content of precipitate (<1%) decreases with increase of temperatures. The slag rate of this process is approximately 80%-95% according to theoretical values. In order to obtain a high iron removal efficiency (>90%) and to acquire a solution with low ferrous concentration, the materials which contain ferrous ion concentration of 25 g/L,30 g/L and 35 g/L were suitable to perform at the temperatures of 170℃,185℃,200 ℃, respectively.(2) Based on the relative data from the previous study, hematite process has been adopted to treat the leaching liquor of high iron sphalerite. The effects of temperature, seed addition, time, oxygen partial pressure, zinc sulfate concentration and magnesium sulfate concentration on iron precipitation were investigated. The optimum conditons can be obtain based on the practical operation, the iron removal efficiency is larger than 95% at temperature of 190℃, seed addition of 20 g/L, time of 3 h and oxygen partial pressure of 0.3 MPa, zinc ion concentration lower than 100g/L, magnesium ion lower than 10g/L. Iron content of precipitate is larger than 50% and purified solution contains Fe below 2.5 g/L.(3) There is only one phase, called hematite, has been detected in the residues produced by hematite process using the ferrous sulfate solution. The phase in the iron slag does not change by increasing reaction temperatures, time and initial ferrous sulfate concentration. While the physicochemical properties of precipitates have a closed relationship with reaction temperature and concentration of initial ferrous sulfate. A well dispersed state, clear interface and growth stability of particles could be produced by increasing reaction temperature but it will decrease the particles size and increase the specific surface area of the hematite. Smaller size particles and grater specific surface area of the hematite residuals could be produced by increasing the initial ferrous sulfate concentration.(4) The metastable crystalline phases such as jarosite and goethite would be produced escapable during the hematite process for treating the leaching liquor of high iron sphalerite. A large proportion of Na- jarosite and a part of K-jarosite could be converted by increasing reaction temperature. To increase the concentration of sulfate is help to realize the conversion from goethite to hematite and lower the S content in the precipitate; to increase the addition of seed is help to improve the quality of hematite crystals. Increasing the concentration of sulfate would lower the particles size of the residual and increase the specific surface area of the hematite.(5) Under the optimum conditons, the environmentally friendly slag which contains less harmful elements could be produced by hematite process for treating the leaching liquor of high iron sphalerite. The distribution of impurities during the hematite process was that more than 95% of K and Ca and 50%-60% of Na, F, Ni and 37% of In co-precipitate with hematite, less than 1% of Zn, Mg, Mn and Cl remains in the residues. Zn exists in hematite as ZnSO4, low levels of Mg in the precipitates present as tiny liquid inclusions in the hematite particles. The sulfur in the precipitate mainly contributed by three parts:formed jarosite, un-dissolved sulfate and the sulfur absorbed on the surface of hematite.