Pre-oxidized zerovalent iron creates reactive Fe(II) species for continuous self-driven depassivation: Implications for contaminant removal

Exogenous ferrous ion dosing allows depassivation of aged zerovalent iron (ZVI) for industrial wastewater treatment, while sustaining the persistent existence of Fe(II) species for continuous depassivation throughout decontamination remains challenging. To tackle this dilemma, pre-oxidized microscale ZVI (poZVI bm ) is proposed via ball milling with peroxydisulfate (PDS) solids, for tailoring an “continuous self-driven depassivation” scenario with Fe 0 /Fe(II) symbiosis. The poZVI bm exhibits a 4.4 ∼ 19.0 times higher equilibrated adsorption capacity for hexavalent chromium (Cr(VI)) than the referenced ball milled ZVI (ZVI bm ) and other benchmarked mZVI composites (e.g. oxalated ZVI bm , sulfidized ZVI bm , and nanoscale ZVI), following a chemisorption-reduction process. It also demonstrates a 4.5 ∼ 18.7 folds faster surface area-normalized removal rate for nitrobenzene (NB) than all these counterparts, mediated by reductive transformation. Cr(VI) removal and NB reduction depend on the dissolved and surface-sorbed Fe(II), respectively, which can be optimized by regulating pre-oxidation degree of poZVI bm . The “continuous self-driven depassivation” of poZVI bm starts with the local microenvironment acidification due to the adsorption of abundant dissolvable Fe(II) over surface-located Fe(III), which drives continuous dissolution of Fe 0 core to create more reactive Fe(II), and therefore repeats the above procedure. Owing to wide pH adaptability (pH 3 ∼ 9) and impressive corrosion behavior of poZVI bm , these findings inspire the intimate integration of Fe 0 /Fe(II) component for high-efficient remediation of multicomponent industrial wastewater.