Study On Vanadium Migration Process Of Mica-type Black Shale In Fluoride-containing Acid Leaching

Vanadium-bearing black shale is a unique vanadium resource in China.With the increasing demand for vanadium in China,the development of technology and theory of extracting vanadium from black shale have been widely concerned.The fluoride-containing acid leaching technology has become one of the mainstream vanadium extraction technologies for its simple process,low energy consumption and high vanadium leaching rate.There is a great difference in the dissolving process of different mineral structural units.Thus,the accurate occupation of vanadium in the mineral lattice is very important to study its release process.Extracting vanadium from black shale is aimed at releasing vanadium from the mineral lattice structure to the solution environment.However,the effects of various parameters in fluoride-containing acid leaching process is not clear,especially the promoting effect of acid and fluorine-containing leaching agent.In addition,the black shale with different mica types has different leaching behavior in the actual production process,and the microscopic explanation of this phenomenon also needs to be further clarified.To improve the theoretical system of extracting vanadium from shale,it is necessary to clarify the valence change of vanadium in the release process and the state transition process of vanadium in fluorine-containing solution.Based on the experimental research,this study uses the quantum chemical simulation method to clarify the accurate location of vanadium in the mineral lattice,the influencing mechanism of parameters on fluorine-containing acid leaching process,the destruction process of target mineral structure,the different leaching characteristics of mica-type black shale,the process of atomic migration and coordination state transition of vanadium in fluorine-containing system.The essential process of extracting vanadium from mica-type black shale on fluorine-containing acid leaching was studied,and obtains the following conclusions.Phase analysis and leaching test of black shale show that vanadium is mainly distributed in mica structure.Vanadium substitution in mica octahedron has the lower substitution energy and structural distortion than that in feldspar and quartz.The optimal location of vanadium was determined from the atomic level.Moreover,the valence bond properties of vanadium-containing mica shows that the V-O bond is an ionic bond with certain covalency.The key of extracting vanadium is to break the V-O bonds in octahedron during leaching.The numerical model of fluorine-containing acid leaching of vanadium from black shale shows that leaching temperature,calcium fluoride content and sulfuric acid concentration have significant effects on the leaching rate of vanadium,and there are interactions between them.The content and activity of hydrogen and fluorine ions is the key to the vanadium extraction from shale and the basis of process improvement and parameter selection.The simulation process of the interface reaction of tetrahedron and octahedron of mica further reveals the synergistic destructive effect of hydrogen and fluorine ions.Hydrogen ions release potassium ions and promote the destruction of oxygen skeleton of mica through the formation and removal of structural hydroxyl groups,and the exposure of the positively charged central atom provide a defect site for the coordination of fluoride ions.Fluoride ions mainly coordinate with and dissolve the central atom of polyhedron to achieve its complete destruction.At the same time,by comparing the interfacial reaction process of sulfate and hydrogen sulfate ions,it is revealed that fluoride ions are more likely to combine with the central atom due to smaller ion radius and stronger electronegativity,thus strengthening the migration dissolution of vanadium.The release of vanadium from mica structure in fluorine-containing system can be divided into three stages:the release of potassium ions between layers?destruction of the tetrahedral layer of mica?destruction of the octahedral layer of mica.The removal of structural oxygen atoms is the limiting step of the dissolution of mica.The difference of the destruction process of mica is mainly reflected in octahedral structure.The reaction energy barrier and the relative potential energy of the octahedral structure of phlogopite are lower than those of muscovite.Meanwhile,vanadium in phlogopite is more easily combined with fluoride ion to be released than in muscovite.This study explains the reasons why two kinds of mica-type black shale have different leaching characteristics of vanadium from the perspective of mineral structure.During the release of vanadium from mica octahedron,the valence state of vanadium rises with the increasing number of fluoride ions.It is proved that the fluorine-containing acid leaching of vanadium from black shale is also an oxidation conversion process.The possible coordination reaction process after the release of vanadium atom into fluorine-containing solution is explored preliminarily:V?IV?(VO²⁺?VOF⁺?VOF₂?VOF₃^-?VF₃?OH??VF₃?H₂O?⁺?VF₃⁺?VF₄?VF₅^-),V?V??VO₂⁺?VO₂F?VO₂F₂^-?VOF₂?OH??VOF₂?H₂O?⁺?VOF₂⁺?VOF₃?VOF₄^-?VF₄?OH??VF₄?H₂O?⁺?VF₄⁺?VF₅?VF₆^-?.The state transformation process of vanadium in mineral and solution during the fluorine-containing acid leaching process reveal that the essence of vanadium migration is the breaking of V-O bonds and the formation of V-F bonds.