Perchloroethene and Chromium Removal from Humic Acid-Containing Groundwater by Zero-Valent Iron Systems

In zero-valent iron (Fe⁰) treatment systems, the co-presence of humic acid and divalent cations was found to impose combined effects that differ from corresponding individual effects. This study investigated the reactions of Fe⁰ with humic acid-containing solutions in batch experiments using HPSEC, TEM, FTIR, and XPS analyses. The formation of soluble iron-humate complexes in monovalent cation solution suppressed iron precipitation on Fe⁰ surfaces, probably hindering contaminant removal by adsorption and co-precipitation. By contrast, the majority of humic acid formed large aggregates with metal hydrolyzed species in divalent cation solutions, which slightly reduced the removal rates of perchloroethene and chromium by blocking or out-competing the reactive sites for reduction.