title: Arsenic(III) and arsenic(V) speciation during transformation of lepidocrocite to magnetite.
abstract: Bioreduction of As(V) and As-bearing iron oxides is considered to be one of the key processes leading to arsenic pollution in groundwaters in South and Southeast Asia. Recent laboratory studies with simple aqueous media showed that secondary Fe(II)-bearing phases (e.g., magnetite and green rust), which commonly precipitate during bioreduction of iron oxides, captured arsenic species. The aim of the present study was to follow arsenic speciation during the abiotic Fe(II)-induced transformation of As(III)- and As(V)-doped lepidocrocite to magnetite, and to evaluate the influence of arsenic on the transformation kinetics and pathway. We found green rust formation is an intermediate phase in the transformation. Both As(III) and As(V) slowed the transformation, with the effect being greater for As(III) than for As(V). Prior to the formation of magnetite, As(III) adsorbed on both lepidocrocite and green rust, whereas As(V) associated exclusively with green rust, When magnetite precipitated, As(III) formed surface complexes on magnetite nanoparticles and As(V) is thought to have been incorporated into the magnetite structure. These processes dramatically lowered the availability of As in the anoxic systems studied. These results provide insights into the behavior of arsenic during magnetite precipitation in reducing environments. We also found that As(V) removal from solution was higher than As(III) removal following magnetite formation, which suggests that conversion of As(III) to As(V) is preferred when using As-magnetite precipitation to treat As-contaminated groundwaters.
authors.affiliation: Université Pierre et Marie Curie (UPMC Paris 6) - Centre National de la Recherche Scientifique (CNRS), Institut de Minéralogie et de Physique des Milieux Condensés (CNRS-UPMC UMR 7590), Campus Jussieu, 4 place Jussieu, 75005, Paris, France.
authors.forename: Yuheng
authors.initials: Y
authors.lastname: Wang
authors.forename: Guillaume
authors.initials: G
authors.lastname: Morin
authors.forename: Georges
authors.initials: G
authors.lastname: Ona-Nguema
authors.forename: Gordon E
authors.initials: GE
authors.lastname: Brown
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000737:chemistry* / Q000145:classification; D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D060587:Groundwater / Q000737:chemistry; D007700:Kinetics; D058185:Magnetite Nanoparticles; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; D014874:Water Pollutants, Chemical; C000499:ferric oxide; D001151:Arsenic; D052203:Ferrosoferric Oxide