Enhanced elimination of V5+ in wastewater using zero-valent iron activated by ball milling: The overlooked crucial roles of energy input and sodium chloride

The ball-milling technology, a highly efficient and cost-effective method, had excellent application prospects for overcoming passivation issues of normal zero-valent iron (ZVI) to enhance the decontamination efficiency. In this work, we investigated the effects and mechanisms of pH, process control agents (PCA), and main process parameters on the removal of V5+ using ball-milled zero-valent iron (ZVIbm). The results showed that ZVI was successfully activated due to mechanochemical action. The enhanced proton conductivity of ZVIbm leaded to the rapid production of more Fe2+, thereby resulting in an order of magnitude higher elimination of V5+ by ZVIbm than by ZVI under near-neutral conditions. In addition, the introduction of NaCl in the ball milling process could not only effectively alleviate the agglomeration phenomenon of ZVIbm, but also effectively enhance its activity. Unexpectedly, due to over-compaction and small size effects, excessive energy input weakened the reactivity of ZVIbm on V5+ elimination. Various characterization results confirmed that the removal of V5+ by ZVIbm was dominated by reduction and supplemented by adsorption. This work updated the basic understanding of the critical effects of process parameters and NaCl on ZVIbm in the remediation of vanadium-containing wastewater.