Study On The Phase Transformation Of Iron Vitriol Slag And The Leaching Behavior Of Valuable Metals

In order to achieve the high-efficiency separation of zinc and iron in the process of zinc hydrometallurgy,many zinc hydrometallurgy enterprises in China have adopted the hot acid leaching jarosite process to remove iron,this process produces about 0.5t of jarosite residues for every 1t of electric zinc production.According to statistics,the annual output of jarosite residues in China is up to 1 million tons.In addition to a certain amount of valuable metals such as zinc,indium and copper,jarosite residues also contains toxic elements such as lead,cadmium and arsenic,which will cause pollution of groundwater and environment and waste of metal resources under natural conditions.The existing processes and treatment methods can only partially realize the recovery of valuable metals in jarosite residues or the recycling of iron,and the treatment process is lengthy and prone to secondary pollution.In this paper,by using the unique technical advantages of hydrothermal metallurgy,the hydrothermal phase transformation of jarosite and the leaching behavior of valuable metals were studied.At the same time,the utilization of iron resources and the enrichment and extraction of valuable metals were realized.The main research contents and conclusions are as follows:?1?The potential p H diagram of Zn-Fe-S-H₂O system under hydrothermal condition was drawn,and the dominant region of Fe₂O₃ under high temperature hydrothermal condition was determined,the conclusion is as follows:Fe₂O₃ can be formed by the transformation of jarosite phase under high temperature hydrothermal condition,Zn Fe₂O₄ will decompose under hydrothermal condition,and the valuable metal Zn will be enriched in the transformation liquid.The simulation results of geometry optimization and energy calculation in material Studio software show that the stability of four kinds of jarosite is in the order of:Pb-jarosite>K-jarosite>Na-jarosite>NH₄-jarosite.That is to say,NH₄-jarosite is most likely to decompose and transform under hydrothermal conditions,and Pb-jarosite is the most stable.The crystal model shows that In can replace Zn in the zinc ferrite lattice or Fe in the jarosite phase lattice by the way of isomorphism,and it is easier to replace Fe in jarosite phase lattice.?2?The experimental results of hydrothermal phase transformation of jarosite residues show that:Under hydrothermal condition,the phase of jarosite can be transformed into Fe₂O₃,and Zn Fe₂O₄,another phase containing iron in the residues,can be decomposed.After hydrothermal treatment,the hematite residues with Fe₂O₃content of 68%can be obtained,and the Fe content in the residues can reach 48%.When the temperature is increased from 160?to 240?,the transformation rate of jarosite phase is increased from 32%to 97%.The transformation rate of jarosite phase can reach 94%after reacting at 220?for one hour.When the acidity is higher than15g/L,the transformation rate of jarosite phase will be inhibited.The particle size of the formed hematite residues is small,and there is the phenomenon of back dissolution of hematite during the cooling process.Increasing the cooling rate can effectively prevent the back dissolution of hematite.?3?The valuable metal Zn in the jarosite residues mainly exists in the form of Zn Fe₂O₄.When the temperature rises from 160?to 220?,the leaching rate of Zn rises from 9%to 87%.And the transformation reaction of jarosite phase will precede the decomposition reaction of Zn Fe₂O₄ phase under hydrothermal condition,and the leaching rate of Zn can reach 89%within 5h.In the range of 5:1m L/g?20:1m L/g,increasing the liquid-solid ratio can increase the leaching rate of the Zn from 49%to94%,when the liquid-solid ratio increases to 30:1m L/g,the leaching rate of the Zn will decrease to 61%;in the range of 0.01g/L?15g/L,the leaching rate of the Zn will remain at about 90%,when the acidity reaches 20g/L,the leaching rate of Zn will decrease to 18%.?4?The jarosite slag used in this experiment contains indium 149g/t,among which In₂?SO₄?₃ and In₂O₃ are 2g/t and 10g/t respectively,and the remaining 137g/t is jarosite containing indium and zinc ferrite containing indium.Under the condition of180?and initial acidity of 40g/L,the indium leaching rate is 29%.The indium mainly comes from zinc ferrite containing indium.After hydrothermal treatment,the indium in the zinc ferrite containing indium will be leached out of the conversion solution,and continue to react with Pb SO₄ to form indium lead jarosite.Under the condition of 220?and initial acidity of 0g/L,the indium leaching rate is 20%.At this time,the jarosite containing indium will be transformed into In₂O₃ after hydrothermal treatment.