title: XANES evidence for rapid arsenic(III) oxidation at magnetite and ferrihydrite surfaces by dissolved O(2) via Fe(2+)-mediated reactions.
abstract: To reduce the adverse effects of arsenic on humans, various technologies are used to remove arsenic from groundwater, most relying on As adsorption on Fe-(oxyhydr)oxides and concomitant oxidation of As(III) by dissolved O(2). This reaction can be catalyzed by microbial activity or by strongly oxidizing radical species known to form upon oxidation of Fe(II) by dissolved O(2). Such catalyzed oxidation reactions have been invoked to explain the enhanced kinetics of As(III) oxidation in aerated water, in the presence of zerovalent iron or dissolved Fe(II). In the present study, we used arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy to investigate the role of Fe(II) in the oxidation of As(III) at the surface of magnetite and ferrihydrite under oxygenated conditions. Our results show rapid oxidation of As(III) to As(V) upon sorption onto magnetite under oxic conditions at neutral pH. Moreover, under similar oxic conditions, As(III) oxidized upon sorption onto ferrihydrite only after addition of Fe(II)(aq) within the investigated time frame of 24 h. These results confirm that Fe(II) is able to catalyze As(III) oxidation in the presence of dissolved O(2) and suggest that oxidation of As(III) upon sorption on magnetite under oxic conditions can be explained by an Fe(2+)-mediated Fenton-like reactions. Thus, the present study shows that magnetite might be an efficient alternative to the current use of oxidants and Fe(II) to remove As from aerated water. In addition, this study emphasizes that special care is needed to preserve arsenic oxidation state during laboratory sorption experiments as well as in collecting As-bearing samples from natural environments.
authors.affiliation: Institut de Mineralogie et de Physique des Milieux Condenses (IMPMC), UMR 7590, CNRS - Universite Paris-6 Pierre & Marie Curie (UPMC) - Universite Paris-7 Diderot (UPD) - IPGP - IRD, 140, rue de Lourmel, Paris, France. georges.ona-nguema@impmc.upmc.fr
authors.forename: Georges
authors.initials: G
authors.lastname: Ona-Nguema
authors.forename: Guillaume
authors.initials: G
authors.lastname: Morin
authors.forename: Yuheng
authors.initials: Y
authors.lastname: Wang
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Foster
authors.forename: Farid
authors.initials: F
authors.lastname: Juillot
authors.forename: Georges
authors.initials: G
authors.lastname: Calas
authors.forename: Gordon E
authors.initials: GE
authors.lastname: Brown
mesh_terms: D001151:Arsenic / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry*; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry; D018508:Water Purification / Q000379:methods; D056928:X-Ray Absorption Spectroscopy / Q000379:methods*
chemical_list: D005290:Ferric Compounds; D014874:Water Pollutants, Chemical; C092844:ferric oxyhydroxide; D007501:Iron; D001151:Arsenic; D010100:Oxygen; D052203:Ferrosoferric Oxide