Minor chromium passivation of S-ZVI enhanced the long-term dechlorination performance of trichlorethylene: Effects of corrosion and passivation on the reactivity and selectivity.

The corrosion and surface passivation of sulfidized zero-valent iron (S-ZVI) by common groundwater ions and contaminants are considered to be the most challenging aspects in the application of S-ZVI for remediation of chlorinated contaminants. This study investigated the impacts of corrosive chloride (Cl-) and passivation of hexavalent chromium (Cr(VI)) on the long-term reactivity, selectivity, corrosion behavior, and physicochemical properties during the 60-day aging process of S-ZVI. Although the co-existing of Cl- promoted the initial reactivity of S-ZVI, the rapid consumption of Fe° content shortened the reactive lifetime owing to the insufficient electron capacity. Severe passivation by Cr(VI) (30 mg L-1) preserved the Fe° content but significantly interfered with the reductive sulfur species, resulting in an increase in electron transfer resistance. In comparison, minor passivated S-ZVI (5.0 mg L-1 Cr(VI)) inhibited the hydrogen evolution while concurrently mitigating the further oxidation of the reductive iron and sulfur species, which significantly enhanced the long-term reactivity and selectivity of S-ZVI. Furthermore, the enhancement effect of minor passivation could be detected in the aging processes of one-step, two-step, and mechanochemically synthesized S-ZVI particles with different S/Fe ratios and precursors, which further verified the advantages of minor passivation. This observation is inspirable for the development of innovative strategies for environmental remediation by S-ZVI-based materials.