Mechanism Of Multiple Impurities Separation And Regulation During Vanadium Extraction From Shale

With the application area of vanadium continuous expanding,especially the development of all-vanadium redox flow batteries and vanadium-aluminium alloy,the requirements for the purity of vanadium product is becoming more and more stricter such as V₂O₅ content higher than 99.9%.This rigorous requirements make it difficult to extract high purity vanadium product from many vanadium containing resources such as vanadium titanium magnetite due to its high content of Fe and Al in raw ore.Vanadium-bearing shale is an advantageous vanadium resources in China because of its big ore reserves and wide distribution and is an important resource to obtain such high purity vanadium product.Vanadium extraction from vanadium-bearing shale based on acid leaching is widely used in research and production applications due to its advantage of high recovery efficiency and good adaptability to raw ores.However,the long-term problem that cannot be resolved in this process is a variety of harmful impurity ion dissolution into leaching solution along with vanadium in strongly acidic conditions which not only makes it difficult for subsequent solvent extraction or ion-exchange,also bring adverse effects to obtain high purity vanadium.This problem has become one of the main research focus in this area.Therefore,it is essential.to examine the leaching behavior of vanadium and impurities and the separation of vanadium and impurities in vanadium enrichment and purification process as well as propose appropriate control measures of impurities separation on preparation of high purity vanadium product.Based on roasting-acid leaching process of vanadium extraction,this paper examined the occurrence of vanadium and impurities in vanadium-bearing shale and investigated the separation behavior of vanadium and impurities during leaching and preconcentration process and discussed the effect of impurities on vanadium purity.Then a deeply impurity remove process was proposed to prepare high purity vanadium product.Main research content and the conclusions are as follows:（1）V mostly exists in mica and a little exists as free oxide;Si,Al,Mg,K,Na,Ca,P and Fe exists in mica,feldspar,kaolinite,calcite,apatite and pyrite respectively.After roasting,apart from the occurrence of Fe changed into hematite and occurrence of Ca changed into anhydrite,the occurrence of other elements has not been changed.The coexistence relationships of V and impurities determined the separation of vanadium and impurities during leaching is very difficult.（2）Leaching thermodynamic studies showed the minerals dissolved in sulfuric acid differed in Gibbs free energy change of the reaction,but this difference is small.Leaching kinetics analysis shows that V,Al,K,Mg,Fe,Na leaching process is controlled by solid membrane diffusion,and leaching apparent activation energy of these elements differs in45⁷0KJ/mol range,the similarity of leaching kinetics of these elements result in the difficult of impurities removal in the vanadium leaching process.（3）It is identified that Al,Fe,P,and Si are the most important factor affecting the purity of V2O5 product.While Al,and P change the course of crystallization of ammonium-polymer-vanadate（APV）and induces Na⁺in solution precipitated into vanadium product.Fe and Si can generate corresponding precipitation as NH4Fe3（SO4）2（OH）6 and silicon gel during vanadium precipitation process and finally affect V₂O₅ purity.（4）MgSO4 was used as impurity removal reagent for P and Si in alkaline conditions while make the concentration of Fe and Al in vanadium rich solution further reduced.When the vanadium rich solution was generated by solvent extraction with P204 the impurities removal route is crude vanadium product precipitation-crude vanadium dissolved in alkaline solution-impurities removal by MgSO₄-acidic precipitation of ammonium-polymer-vanadate-calcination,then high purity vanadium product can obtained.