Liquid-Phase Oxidation of Commercial V2O5 for High-Purity Product Enabled by Oxygen Microbubbles

Driven by the rapid advancements in vanadium redox flow batteries (VRFB) and global policies supporting carbon emission reduction, the market demand for high-purity vanadium pentoxide (V2O5) has been steadily increasing. However, the coexistence of complex impurities and multivalent vanadium in commercial V2O5 (98wt%) makes it unsuitable as a key raw material for the stringent requirements of VRFBs. Herein, an alkaline liquid-phase oxidation system was developed, which utilizes oxygen microbubbles as the oxidizing medium to enable efficient oxidation and removal of impurities. This system achieved low-valence vanadium oxidation rate of 95.56wt%, concurrently maintained a 99.82wt% total vanadium recovery, and enhanced the final V2O5 product purity from 98wt% to 99.83wt%. Mechanistic studies revealed that in the presence of oxygen microbubbles, the partially dissolved V4+ and V5+ ions form a Fenton-like redox couple and generates a significant quantity of reactive oxygen species (ROS) including singlet oxygen (1O2), hydroxyl radical (·OH), and superoxide anion (·O2-), which in turn promote the subsequent oxidation of refractory tetravalent vanadium species. Quenching experiments further confirmed that the contributions of 1O2, ·OH, and ·O2- to the vanadium oxidation process were 78.00wt%, 7.25wt%, and 5.03wt%, respectively, where the 1O2 identified as the dominant active species. As a result, the final V2O5 product preparation through conventional purification and crystallization process exhibited remarkably low incorporation of key impurities, with Al content lower than 0.09wt% and Si content lower than 0.2wt%. This study proposes a novel deep liquid-phase oxidation strategy for low-valence vanadium based on oxygen microbubbles, offering a viable industrial pathway for the green and efficient production of high-purity V2O5 with both economic and environmental benefits.