Preparation Of High Purity V₂O₅ By Microemulsion Extraction

Vanadium is considered as an industrial vitamin,which is widely used in aerospace,metallurgy,chemical industry and other fields.In China,the main source of vanadium is vanadium titanomagnetite,and about 88%of vanadium is extracted from vanadium titanomagnetite.At present,the traditional method of extracting vanadium from vanadium titanomagnetite is smelting vanadium titanomagnetite in blast furnace to obtain molten iron and then oxidizing the molten iron in converter to obtain semi-steel and vanadium slag.The obtained vanadium slag is used as raw material to extract vanadium via the roasting-leaching process in order to obtain vanadium-containing leachate.By ammonium salt precipitation,the ammonium polyoxovanadate is obtained from the vanadium-containing leachate,which is filtrated and calcinated to obtain the final product of vanadium pentoxide（V₂O₅）.However,the V₂O₅ produced by this process has high impurities,which can not meet the higher and higher demand of current industrial application.Therefore,in order to obtain V₂O₅with higher purity,the current industrial production method is to dissolve,precipitate and calcine the crude V₂O₅ repeatedly for impurity removal.However,this preparation process of high-purity V₂O₅ has long process,low production efficiency,low product yield,large discharge of waste water,which is conflict to the green and sustainable development.Therefore,it is urgent to establish an efficient preparation method of high purity V₂O₅.In this paper,the preparation method of high-purity V₂O₅ by microemulsion extraction was established,using the industrial vanadium-containing leachate from the sodium roasting-water leaching process of vanadium slag as raw material.Focusing on the technical route of"separation of vanadium and chromium by calcification precipitation→calcium vanadate re-dissolution→microemulsion extraction→alkaline stripping→precipitation→calcination",calcium vanadates were firstly obtained by selective calcification precipitation to separate vanadium and chromium.Then vanadium in calcium vanadate was re-dissolved into aqueous solution with sodium bicarbonate solution as dissolution agent,following which vanadium in dissolution solution was extracted by microemulsion.From the loaded microemulsion,vanadium was stripped with sodium hydroxide solution and prepared into high-purity V₂O₅ product by ammonium salt precipitation and calcination.The optimal conditions of separating vanadium and chromium by calcified precipitation and dissolving calcium vanadate by sodium bicarbonate were investigated,and the kinetics of dissolution process was analyzed.The optimal conditions of microemulsion extraction and stripping process were studied,together with the recycling performance of microemulsion.Finally,the high-purity V₂O₅ product was obtained and charaterized.The major research results of this paper are as follows:（1）The calcification precipitation method of vanadium and chromium in industrial vanadium leachate was established.Calcification precipitation was carried out by adding polyvinyl fluoride beads and dropping addition of calcium salts.The results showed that in the Ca/V molar ratio of 1.8,reaction temperature of 55℃and reaction time of 60 min,the precipitation rate of vanadium was 99.45%while that of chromium was 1.46%,indicating the efficiency separation of vanadium and chromium.（2）The method of re-dissolving calcium vanadate was established.With calcium vanadate as raw material and Na HCO₃ solution as dissolution agent,the influencing factors of the dissolution process were optimized.The results showed that in the molar ratio of Na HCO₃/V of 2.75,the solid-liquid ratio of 1:5,the dissolution temperature of55℃and the dissolution time of 50 min,the dissolution rate of vanadium in calcium vanadate can reach 99.24%.（3）The re-dissolution process of calcium vanadate followed the particle"shrinking unreacted core"model,but it was divided into two stages.In the short period of 0-10 min,the dissolution rate was mainly controlled by the diffusion of solid product layer;In the long period of 10-50 min,the dissolution process was controlled by the diffusion of solid product layer and chemical reaction.（4）The optimal microemulsion extraction conditions were explored and the microemulsion extraction method of vanadium was established.The results showed that with the concentration of extractant Aliquat 336 of 20%,the aqueous-to-organic phase ratio（A/O）of 1,the extraction time of 2 min and the extraction temperature of25℃,the extraction rate of vanadium reached the highest value of 99.97%.When the concentration of stripping agent was 1 mol/L Na OH+4 mol/L Na Cl,the stripping ratio A/O of 1,the reaction temperature of 25℃and the stripping time of 2 min,the stripping rate of vanadium was as high as 99.0%.The microemulsion exhibited good circulation performance.The purity of V₂O₅ finally obtained was 99.92%,and the yield during the whole process was 96.70%.Compared with the existing preparation technology of high-purity V₂O₅,the preparation method by microemulsion extraction established in this paper significantly improves the production efficiency and product yield.The method has solved the difficulty in high-efficiency and short-process preparation of high-purity V₂O₅,which theoretically breaks through the technical bottleneck for key raw material production which restricts the popularization and application of vanadium redox flow batteries and the development of aerospace grade titanium alloy,leading to the significant promotion in the high-value utilization of vanadium resources in China.