| Vanadium,an important strategic metal resource,has excellent materialized properties and special performance,and is widely used in metallurgy,aerospace,chemical industry,new energy and other fields.Vanadium products are in huge market demand.Vanadium titanium magnetite is an important vanadium resource in China,but the vanadium slag components vary in different regions and different enterprises due to the differences in vanadium resources and vanadium extraction process.The chemical composition of vanadium slag significantly impacts the phase,element distribution and roasting process,while vanadium slag phase structure,the form of vanadium in clinker,the generation of vanadate,and the formation of high melting point calcium silicate may affect the level of vanadium conversion rate in production.Based on this,the composition and microstructure of seven different vanadium slag,the vanadium slags with different chromium contents,and the vanadium slags with different calcium contents were characterized by X-ray diffraction(XRD)and scanning electron microscope(SEM)to master the change of multicomponent’s existed form and phase changing laws.Then the experiment of calcification roasting-acid leaching was carried out to clarify the migration rules of different components.The main conclusions are obtained as follows:According to the analysis,the seven vanadium slags with different components were composed of spinel,olivine,and pyroxene.Vanadium and chromium exist in the form of(Mn,Fe)(Cr,V)2O4,the strongest diffraction peak of spinel in vanadium slags with high chromium content migrated to a higher angle.There were fewer and weaker spinel phase diffraction peaks in high-calcium and high-phosphorus vanadium slag(HCPVS),while olivine and pyroxene peaks were stronger.The spinel phase in vanadium slags were irregular block structure with silicate surrounded.Whereas the spinel phase was highly dispersed in HCPVS,and the spinel distribution is relatively scattered,with no obvious bulk structure.After calcification roasting,vanadium spinel was completely decomposed,most of the iron were oxidized to Fe2O3,chromium existed as(Fe0.6Cr0.4)2O3 solid solution.Low-valence vanadium was oxidized and reacted with CaO to form calcium vanadate(Ca2V2O7 and Ca3V2O8),almost all titanium were combined to form Fe2TiO5.The olivine phase was completely decomposed,while the pyroxene phase not.Abundant dicalcium silicate was produced in HCPVS as the high content of calcium and silicon.After acid leaching,V leaching rates were greater than 85%except Desheng vanadium slag(DSVS)and HCPVS,moreover,V leaching rate for calcification roasting was lower than direct roasting in HCPVS.Cr leaching rates were less than 5%.In addition to HCPVS and DSVS,Si leaching rates were less than 3%.Mn leaching rates in partial vanadium slags were higher than 15%.Both Ti and Fe leaching rates were below 0.3%and 0.1%,respectively.According to the analysis of vanadium slags with different Cr2O3 contents,vanadium and chromium always existed as(Mn,Fe)(Cr,V)2O4.The strongest diffraction peak of spinel migrated to a higher angle as the Cr2O3 contents increased.When the Cr2O3 content was low,chromium and vanadium were mainly distributed inside the spinel,while titanium was outside.As Cr2O3 content increases,chromium and vanadium decentralization and titanium marginalization differences decreased,and the average size of spinel gradually decreased and was more uniform.After calcification roasting,vanadium was oxidized and reacted with CaO to form Ca2V2O7,and partial vanadium reacted with manganese to generate manganese vanadate.Almost all chromium turned into an acid-insoluble(Fe0.6Cr0.4)2O3 solid solution.After acid leaching,V leaching rate gradually decreased with increased Cr2O3 content.Cr leaching rate exceeded 2%,up to 3.71%,but it was less than 1%after increasing the roasting temperature and heating rate.As Cr2O3 content increases,Si leaching rate was gradually increased but not exceeding 2%,Mn leaching rate rose first and decreased subsequently,but both titanium and iron conversely.According to the analysis of vanadium slags with different CaO contents,vanadium and chromium always existed as(Mn,Fe)(Cr,V)2O4,no changes as the CaO content increased.As the CaO content in vanadium slags rose,the olivine phase Fe2SiO4 gradually changed to Ca2SiO4.When the CaO content was low,titanium exists mainly in titanium iron spinel.When the CaO content rose to 9.7%,part of Ti began to transfer from spinel to CaTiO3,and the higher the calcium content was,the more CaTiO3 generated.The shape of spinel was polygonal and then the average size of spinel gradually increased as the CaO content gradually increases.When the calcium content rose to 13.7%,the spinel shape became irregular,and the silicate was gradually complicated.V was produced as Ca2V2O7 for lower CaO contents in vanadium slags after calcification roasting.As the calcium content rose to 3.7%,Ca3V2O8 gradually generated.The CaO content increased continually,the Ca3V2O8 increased as well.After acid leaching,the highest V leaching rate was 87.52%when the CaO content was 2.7%.As CaO content increased further,the V leaching rate decreased slightly.Cr leaching rates were relatively high at the range of 7.81%-13.02%,but it was less than 1%after increasing the roasting temperature and heating rate. |
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