Study On Deep Purification Of Shale-Rich Vanadium Solution By Saponification Extraction To Preparate The High-Capacity Vanadium Electrolyte

Driven by the"two-carbon"policy,all-vanadium flow batteries have attracted much attention and been widely used.Vanadium shale is a characteristic and superior vanadium containing resource in China.The vanadium-rich solution obtained from vanadium shale by direct acid leaching is characterized by high acid and impurity.Vanadium electrolyte can be prepared by multiple processes such as vanadium sedimentation,alkali solution and REDOX.Therefore,focusing on the development needs of new energy storage of the country,the application of large-scale energy storage of vanadium battery is promoted.In order to reduce the preparation cost of vanadium electrolyte,the actual vanadium-rich solution is used as raw material in this paper,and the technology of vanadium electrolyte preparation by extraction method in a short process is studied.The main research contents and conclusions are as follows:（1）The study on directly preparation of vanadium electrolyte by extraction of vanadium-rich solution from shale shows that P204 saponification can improve the equilibrium p H of extraction and realize effective extraction of high concentration vanadium and separation of vanadium impurities at low p H value,so it is selected as the extraction system for preparation of vanadium electrolyte.FT-IR analysis showed that the extraction of VO²⁺by saponified P204 was a cation exchange mechanism.High concentration vanadyl sulfate solution（ES₁）can be prepared by saponification P204extraction and stripping of sulfuric acid.However,ES₁ has some problems such as low conductivity,high viscosity,poor electrochemical activity and poor reversibility compared with standard electrolyte due to the influence of impurity ions.（2）The results show that ammonium sulfate is added to vanadium-rich solution before extraction.Under the condition that n（NH₄⁺）:n(Al³⁺)of 1:1,temperature of 5^oC,and time of 6 h,aluminum impurities are pre-removed in the form of ammonium alum crystallization,and the removal rate is 51.67%.Under the conditions of 60%saponification degree,initial p H of 1.0,30 vol%P204,phase ratio（O/A）of 3:1,extraction time of 8 min,the five-stage countercurrent extraction of vanadium reached 96.04%.The effective separation of vanadium from impurities aluminum and iron and the preparation of electrolyte can be achieved by four stage countercurrent extraction under the condition of 6:1,phase ratio（O/A）of 6:1 and 4 mol/L sulfuric acid for 20 min.（3）The performance test of the electrolyte and the economic analysis of the process show that the theoretical specific capacity of the prepared electrolyte（ES₂）with a concentration of 2.0 mol/L vanadium reaches 53.6Ah/L,which is 24.94%higher than that of the commercial electrolyte.Compared with standard electrolyte,it has good physicochemical properties,electrochemical activity and charging and discharging efficiency.Under the current density of 40 m A/cm² for 80 cycles,the average Coulomb efficiency,voltage efficiency and energy efficiency are 87.86%,93.00%and 81.70%,respectively.Compared with the traditional preparation process,the process can shorten the preparation period and reduce the preparation cost by 29.53%.