Unveiling the Role of the Soil Matrix in Trichloroethylene Degradation by Ball-Milled Sulfidated Microscale Zero-Valent Iron

Abstract

Ball-milled sulfidated microscale zerovalent iron (S-mZVI^bm) is highly effective in degrading trichloroethylene (TCE) in anoxic water. This study investigated its performance and soil-mediated regulation in a soil-water mixed system (SWMS) using two natural soils. The results show that soil addition markedly enhanced the reactivity of S-mZVI^bm. Compared with the aqueous system, the degradation rate constant of TCE (k_TCE) exhibited a 6.0–8.4-fold increase at a soil-to-water ratio (S/W) of 0.5 to 2.0, while H₂ production concurrently increased 210%–450%. This activation was accompanied by a decrease in apparent electron efficiency from 74.3% in water to 15.9%–27.6% in SWMS. S-mZVI^bm retained higher reactivity in SWMS than in water across pH 6–10, with a maximum k_TCE of 0.26 h^–1 at pH 8.0. SEM, XPS, and component-specific experiments indicated that soil-mediated surface restructuring and Fe(II) redistribution-induced depassivation increased the accessibility of Fe⁰-rich domains, whereas organic matter and Ca/Mg-bearing phases imposed inhibitory effects. Sulfidation suppressed H₂ evolution and reduced soil-specific variability under multicontaminant conditions involving TCE, carbon tetrachloride, nitrobenzene, and perchloroethylene. These results identify soil as an active regulator of Fe⁰ accessibility and electron allocation rather than a passive reaction medium, providing a mechanistic basis for site-specific S-mZVI^bm remediation.