Production of vanadyl sulfate electrolyte from stone coal acidic leaching solution using mediation solvent extraction-complex reductive stripping method

In this study, a new method for vanadium extraction and separation from acidic stone coal leaching solution was proposed. With the addition of H2O2 in the solution, the positive vanadium VO2+ ion in the solution was converted into anionic di-peroxo vanadium VO(O2)2- ion. Using methyl tri-octyl ammonium chloride (N263) + n-octanol + sulfonated kerosene as extractant, vanadium was fully separated from Fe (III) and other metal impurities during the extraction process. Under the conditions of 10 % N263, 10 % n-octanol, reaction time 10 min, and O/A ratio 1:1, 99 % of vanadium was extracted into the organic phase. After extraction, an organic phase containing V and Mo was obtained. Due to low solubility of V (V) in acidic solution, oxalic acid was mixed with sulfuric acid solution and employed as complex-stripping solution. It was found that oxalate ion formed a complex with V (V), which could break the solubility barrier of V (V) in acidic solution, realizing the direct stripping of V (V). The effect of oxalic acid amount and temperature on the stripping process were investigated, the results showed that increase in oxalic acid amount and reaction temperature favored vanadium stripping. Under conditions of 25 % H2SO4, oxalic acid concentration of 1 g/L, 80 °C temperature, reaction time 50 min, and O/A ratio of 6:1, 99.7 % of vanadium was stripped into the aqueous solution. The vanadyl sulfate product obtained was compared with standard vanadium electrolyte, and it was found that vanadyl sulfate obtained by this method meets the requirements of vanadium electrolyte relevant standards. This paper proposed a new process for high purity vanadyl sulfate production from acidic stone coal leaching solution, which could provide a reference for Vanadium Redox Flow Batteries (VRFB) industry.