Study On Microemulsion Extraction Of Vanadium For Preparation Of High-purity Vanadium Products

As an industrial vitamin,vanadium(V)is an important strategic resource,which is widely used in fields including metallurgy,aerospace,nuclear industry,chemical catalysis,energy storage,medical treatment.At present,the utilization of vanadium resource suffers from the problems of low recovery rate,serious environmental pollution and low added value of products.Targeting at these problems,microemulsion extraction method of vanadium has been established in this paper,based on which vanadium is recovered from APV-precipitated waste water and its sludges to improve the recovery efficiency of vanadium resources and reduce environmental hazards;the microemulsion extraction method of vanadium has also been utilized to prepare high-purity vanadium products directly from intermediate materials during vanadium extraction process to enhance the added value of products.Thus,promotion in the value-added utilization of vanadium resources in China can be expected.Firstly,the microemulsion system of trioctyl methyl ammonium chloride/isoamyl alcohol/n-heptane/Na Cl was established,with trioctyl methyl ammonium chloride(MTA)as the surfactant to form microemulsion in n-heptane and isoamyl alcohol as the cosurfactant.The microemulsion extraction conditions for V were optimized.The highest extraction efficiency of vanadium reached was 99.90%at p H 3 of feed solution with the extractant concentration of 73.35 mmol·L^-1,phase ratio of 4,and extraction time of 2 min at 25°C.By combination of ab initio molecular dynamics(AIMD)simulations and experimental characterization methods,it is revealed that the V-O octahedral coordinated H₂V₁₀O₂₈^4-ion can transform into V-O tetrahedral coordinated V₁₀O₂₆^2-ion with the inducing of MTA⁺cation,which indicates the high affinity and selectivity of MTA⁺for H₂V₁₀O₂₈^4-ion.Then the method for separating V(V)and Cr(VI)by microemulsion extraction was established.For the mixture solution of V(V)and Cr(VI),the pretreatment of"reduction-selective oxidation"was adopted to selectively transform Cr(VI)into Cr³⁺cation to realize the charge difference between V and Cr ions in order to facilitate the subsequent selective extraction of V by microemulsion.Under the optimum conditions,the extraction efficiency of V was 98.45%and that of Cr is 4.44%,which indicates the efficient separation of V(V)and Cr(VI).Based on the established separation method of V(V)and Cr(VI),the detoxification and resource utilization of APV-precipitated waste water and its sludge(V-Cr-bearing reducing slag and chromium sludge)was realized.From APV-precipitated waste water,96.29%of V and 95.56%of Cr were recovered as V₂O₅ and Cr₂O₃ respectively.In the V-Cr-bearing reducing slag,93.04%Si,96.32%V and 92.68%Cr were recovered respectively.From the chromium sludge,92.58%of Si,95.53%of V,98.25%of Fe and 92.68%of Cr were recovered as valuable products respectively.Furthermore,the method for separating V(V)and P in solution was established by microemulsion extraction.The extractant cations MTA⁺extract vanadate anions based on the affinity difference of extractant molecule MTA⁺to vanadate anions and phosphate anions,resulting in the success in solving the difficulty in V(V)and P separation in acidic solution.Under the optimum conditions,the extraction efficiencies of V and P were 99.9%and 5.5%,respectively.With the vanadium-containing leaching liquor originated from high-P vanadium slag as the raw material,the V₂O₅ product with high purity of 99.7%was obtained by the established microemulsion-based separation method.The V recovery for the whole process is as high as 87.3%.In order to meet the demand of vanadium redox flow battery for high purity VOSO₄,the microemulsion extraction-reductive stripping preparation method was established.Using the simulated vanadium-containing solution as raw material and the sulfuric/sulfurous acid mixture solution as stripping solution,the stripping efficiency of V is 99.43%.The reductive stripping principle of V(V)in loaded microemulsion was simultaneously revealed;V(V)was firstly reduced to V(IV)and then combined with SO₄^2-to transfer into the aqueous phase.From the industrial leaching liquor originated from calcification roasting/acid leaching process,the high-purity VOSO₄ solution was successfully prepared by the proposed microemulsion extraction-reductive stripping method.The product components meet the national standard requirements while its electrochemical performance was excellent.The total product yield is as high as87.50%.In order to meet the requirements of vanadium battery and aerospace grade alloy for high-purity V₂O₅,an efficient preparation method of high-purity V₂O₅ was established via microemulsion extraction.According to the characteristics of high vanadium content and low chromium content in industrial leaching liquor originated from the sodium roasting/water leaching process,the high-purity V₂O₅ was prepared by the route of calcification precipitation for chromium separation?alkaline leaching for re-dissolution of vanadium?microemulsion extraction?alkaline stripping?Precipita-tion?calcination.Under the optimum conditions,the precipitation efficiency of V was as high as 99.45%while that of Cr was only 1.52%during the calcification precipitation step.The re-dissolution ratio of V from the calcium vanadate precipitation could reach99.24%.During microemulsion extraction step,the extraction efficiency of V was up to99.91%.Finally,the obtained V₂O₅ had the purity of 99.92%and its yield was 95.68%.To sum up,the mechanism of transformation of H₂V₁₀O₂₈^4-ion by the inducing of MTA⁺cation is elucidated in this paper,based on which the microemulsion extraction method of vanadium was established with high extraction capacity and high extraction efficiency.Applying the established microemulsion extraction method,the problem of harmless resource utilization of APV-precipitated waste water and its sludges has been solved,and the highly efficient preparation principle of high purity VOSO₄ solution and high purity V₂O₅ was proposed in short processes.This work has laid a theoretical and technical foundation for the value-added utilization of vanadium resources in China.