Purification of high-performance vanadium electrolyte from Al-containing solutions via NH ₄ Al(SO ₄ ) ₂ ·12H ₂ O crystallization and saponified P204 (D2EHPA) extraction

Traditional vanadium electrolyte production faces challenges of complex processes, high costs, and inefficient impurity removal. This study developed an integrated crystallization-solvent extraction method to directly produce high-performance electrolyte from high-aluminum vanadium shale leachate (Al: 21.2 g/L, V: 54.2 g/L). Through ammonium alum crystallization under optimal conditions (NH 4 + /Al 3 + =1:1, 5°C, 6 h), 51.67% aluminum was removed with <1% vanadium loss. Subsequent five-stage countercurrent extraction achieved 96.04% vanadium recovery, while four-stage stripping produced a 2.0 mol/L V electrolyte. The obtained electrolyte exhibited excellent properties: viscosity of 5.00 mm 2 /s, conductivity of 253.7 mS/cm, and electrochemical performance comparable to commercial standards. Battery tests demonstrated outstanding stability with average coulombic efficiency of 87.86%, voltage efficiency of 93.00%, and energy efficiency of 81.70% over 80 cycles at 40 mA/cm 2 . This short process offers strong potential for industrial application in vanadium redox flow batteries.