title: Enhanced and stabilized arsenic retention in microcosms through the microbial oxidation of ferrous iron by nitrate.
abstract: Magnetite strongly retains As, and is relatively stable under Fe(III)-reducing conditions common in aquifers that release As. Here, laboratory microcosm experiments were conducted to investigate a potential As remediation method involving magnetite formation, using groundwater and sediments from the Vineland Superfund site. The microcosms were amended with various combinations of nitrate, Fe(II) (aq) (as ferrous sulfate) and lactate, and were incubated for more than 5 weeks. In the microcosms enriched with 10 mM nitrate and 5 mM Fe(II) (aq), black magnetic particles were produced, and As removal from solution was observed even under sustained Fe(III) reduction stimulated by the addition of 10 mM lactate. The enhanced As retention was mainly attributed to co-precipitation within magnetite and adsorption on a mixture of magnetite and ferrihydrite. Sequential chemical extraction, X-ray absorption spectroscopy and magnetic susceptibility measurements showed that these minerals formed at pH 6-7 following nitrate-Fe(II) addition, and As-bearing magnetite was stable under reducing conditions. Scanning electron microscopy and X-ray diffraction indicated that nano-particulate magnetite was produced as coatings on fine sediments, and no aging effect was detected on morphology over the course of incubation. These results suggest that a magnetite based strategy may be a long-term remedial option for As-contaminated aquifers.
authors.affiliation: Department of Earth and Environmental Sciences, Columbia University, Mail Code 5505, New York, NY, 10027, USA; Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY, 10964, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Sun
authors.affiliation: Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY, 10964, USA.
authors.forename: Steven N
authors.initials: SN
authors.lastname: Chillrud
authors.affiliation: Department of Environmental Sciences, Barnard College, 3009 Broadway, New York, NY, 10027, USA.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Mailloux
authors.affiliation: Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY, 10964, USA; Department of Environmental Sciences, Barnard College, 3009 Broadway, New York, NY, 10027, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Stute
authors.affiliation: Department of Geology and Environmental Earth Science, Miami University, Oxford, OH, 45056, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Singh
authors.affiliation: Department of Geology and Environmental Earth Science, Miami University, Oxford, OH, 45056, USA.
authors.forename: Hailiang
authors.initials: H
authors.lastname: Dong
authors.affiliation: Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY, 10964, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Lepre
authors.affiliation: Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, NY, 10964, USA. Electronic address: bostick@ldeo.columbia.edu.
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Bostick
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000032:analysis* / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry; D009566:Nitrates / Q000737:chemistry*; D010084:Oxidation-Reduction; D012996:Solutions; D014873:Water Pollutants / Q000032:analysis* / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D005296:Ferrous Compounds; D009566:Nitrates; D012996:Solutions; D014873:Water Pollutants; C020748:ferrous sulfate; C092844:ferric oxyhydroxide; D001151:Arsenic; D052203:Ferrosoferric Oxide
keywords: Arsenic concentration; Immobilization; Iron minerals; Magnetite; Microcosm experiment; Redox transformation