Arsenic, a pollutant often found in groundwater, affects drinking water of over 100 million people around the world. Iron-based technologies, including zero-valent iron (ZVI) technology, are one of the most effective methods for removing arsenic from water. Removal of As by ZVI was often attributed to surface adsorption and co-precipitation onto iron oxides, products of ZVI corrosion reaction upon its deployment. In this study, we investigate the fate and evolution of As(III) through its removal by the Activated Iron Media (AIM), an engineered ZVI-based media consisted of a mixture of ZVI powder, a reactive surface FeOx coating, and a discrete FeOx phase. The engineered FeOx of the AIM features mixed Fe(II)/Fe(III) crystalline with an inverse spinel structure that develops from a meta-stable, Fe(II)-rich green rust structure evolving towards a Fe3O4-like structure. The effectiveness of AIM as media was compared with virgin ZVI, magnetite, alone or mixed under different conditions for arsenite removal. Composition and structure of FeOx, O2, and labile Fe2+ are identified as the key factors that determine the media reactivity. In particular, we discovered that the AIM system with a O2 and Fe2+ supply achieves best As removal, decreasing 50 mg/L As to below 1 ug/L within 30 min. In the AIM system operated under oxic condition (with O2), Ar(III) was found to be partially oxidized to As(V), which can be more readily immobilized by FeOx. Under O2 free environments, the immobilized As(V) within the AIM is gradually reduced to As(III) and then As(0) over time. Control tests with AIM+O2 reveal that interaction of O2 with AIM could generate a substantial amount of hydroxyl radicals, which is likely responsible for the oxidation of Arsenite to Arsenate, thus greatly accelerate As removal by the media. The presence of ZVI and the availability of labile Fe(II) may be essential in facilitating the production of hydroxyl radical by maintaining the favorable properties of the FeOx such as high electron conductivity, Fe(II)-rich nonstoichiometric and flexible structure, and thus sustaining its unique reactivities.

Arsenic(III) removal by the activated iron media system facilitated by O2-initiated advanced oxidation reaction

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.