| The vanadium-bearing slag containing several valuable elements such as V,Cr,Ti,Fe,Mn is produced from vanadium-titanium magnetite by blast furnace smelting and vanadium-extraction process in converter.The main crystalline phases of this slag are vuorelainenite((Mn,Fe)(V,Cr)2O4),titanomagnetite(Fe2.5Ti0.5O4)and fayalite,manganoan((Fe,Mn)2SiO4).Meanwhile,this slag exhibits a typical encompassed structure.The existing processes proposed are mainly focused on the vanadium and chromium extraction by oxidation roasting method,and have achieved fruitful industrial application,but other elements are less used.Meanwhile,the high-valence oxides of V and Cr are toxic substances and have the potential for environmental pollution.Thus,we propose to use selective chlorination method to separate various valuable elements(V,Cr,Ti,Fe and Mn)and then fabricate new value-added products.According to the existence form and value of valuable metal elements(Fe,Mn,V,Cr and Ti)in vanadium slag,NH4Cl was selected to chlorinate vanadium slag.Thermodynamic calculations shows that the iron and manganese in vanadium slag could be chlorinated by hydrogen chloride,but the V,Cr and Ti could not be chlorinated in the temperature range from 0 to 1000 ℃.Selective chlorinated extraction of vanadium slag could be achieved.The effects of reaction temperature,reaction time,flux NaCl and mass ratio of NH4Cl-vanadium slag on the chlorination ratio of iron and manganese were investigated.Under optimal chlorination conditions,the chlorination ratio of iron and manganese were 72%and 95%,respectively.The solid chlorinating agent NH4CI starts to decompose above 230 ℃and recombines below 112 ℃.With this advantage,excessive NH4CI in the experiment achieved secondary utilization.More importantly,the chlorinating agent NH4Cl could be recycled by selective chlorination and Mn-Zn ferrite process.Meanwhile,the enrichment ratio of V,Cr and Ti was obtained as 48%.In addition,AICl3 was selected to chlorinate vanadium slag.Based on the thermodynamic calculations in the temperature range from 0 to 1000 ℃,the valuable elements(Fe,Mn,V,Cr and Ti)in vanadium slag could be chlorinated by AICl3.Due to the strong volatility of AlCl3,the volatilization of AICl3 was effectively reduced by designing different molten salt NaCl-KCl-AlCl3 composition.The effects of reaction temperature,reaction time,mass ratio of AlCl3/slag and mass ratio of salt/AlCl3 on the chlorination ratio of valuable elements were investigated.Under optimal chlorination conditions,the chlorination ratio of iron,vanadium,chromium and manganese were 90.3%,76.5%,81.9%and 97.3%.The volatilization ratio of titanium was 79.9%.The results of kinetic study indicate that the rate-control step of iron and manganese chlorination process were the solid product layer diffusion control;the rate-control step of vanadium and chromium chlorination process were the surface chemical reaction.The iron and manganese in vanadium slag after NH4Cl chlorination were present in the form of FeCl2 and MnCl2 in the molten salt.Using this as a raw material,the preparation of Mn-Zn ferrite and preparation of alloys by electrolytic separation were studied to achieve high value utilization.In the process of synthesizing Mn-Zn ferrite,the effects of pH,temperature and Mn/Zn molar ratio on the phase and properties of Mn-Zn ferrite were investigated.Under the optimal conditions,a Mn0.8Zn0.2Fe2O4 of high saturation magnetization(Ms=68.6 emu/g)and low coeercivity(Hc=3.3 Oe)was successfully synthesized,which was superior to the ferrite materials synthesized from pure materials and secondary resources in the literature.In the process of preparing FeMn alloy by molten salt electrolysis,the electrochemical behaviors of FeCl2,MnCl2 and FeCl2-MnCl2 in molten salt NaCl-KCl were investigated.Meanwhile,the effects of electrolytic voltage on the separation ratio of samples were studied.Under the optimal conditions,the Mn/Fe mass ratio of iron-rich phase and manganese-rich phase of the deposited products were 0.0625 and 36.4,respectively.Mn/Fe mass ratio of magnetic concentrate and nonmagnetic material obtained by magnetic separation process were 0.08 and 28.41,respectively.Apparently,the molten salt electrolysis method on separation ratio of Mn and Fe was better than magnetic separation.The vanadium and chromium in vanadium slag after AlCl3 chlorination were present in the form of VCl3 and CrCl3 in molten salt.Therefore,the electrochemical behavior and electrodeposition of VCl3,CrCl3 and VCl3-CrCl3 in molten salt were investigated.Meanwhile,the effects of different VCl3/CrCl3 mass ratio on the electrodeposition products were investigated.Under the optimal conditions,the mass percentages of V,Cr and O in the product obtained by electrodepostion were 3.71%,94.28 and 2.01%in the NaCl-KCl-CrCl3-VCl3 molten salt system.Finally,the vanadium slag was chlorinated by AlCl3 and the electrolysis process of mult-molten salt system containing FeCl2,FeCl3,MnCl2,VCl3 and CrCl3 were investigated.The effects of different factors on electrodeposited products were also investigated.The results indicated that the content of impurities Al2O3 in the electrodeposited products reduced with increasing the temperature and decreasing the sample/salt rato.The electrodeposited product was Fe-V-Cr alloy at 2.3V.The element Mn appeared in the electrodeposited product at 3V and Fe-V-Cr-Mn alloy was obtained and exhibited a dispersed cubic particles morphology.Valuable metal elements in vanadium slag were separated by selective chlorination.Meanwhile,based on the characteristics and value of the elements,we explored the application process of high value of valuable elements.This new process provides a new exploration and attempts for the efficient use of valuable elements in vanadium slag. |
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