title: In Situ Magnetite Formation and Long-Term Arsenic Immobilization under Advective Flow Conditions.
abstract: In situ precipitation of magnetite and other minerals potentially sequesters dissolved arsenic (As) in contaminated aquifers. This study examines As retention and transport in aquifer sediments using a multistage column experiment in which magnetite and other minerals formed from added nitrate and ferrous iron (Fe). Sediments were collected from the Dover Municipal Landfill Superfund site. Prior to nitrate-Fe(II) addition, As was not effectively retained within the sediments in the column. The combination of nitrate (10 mM) and Fe(II) (4 mM), resulted in mineral precipitation and rapidly decreased effluent As concentrations to <10 μg L(-1). Mineralogical analyses of sectioned replicate columns using sequential extractions, magnetic susceptibility and X-ray absorption spectroscopy indicate that magnetite and ferrihydrite formed in the column following nitrate-Fe(II) addition. This magnetite persisted in the column even as conditions became reducing, whereas ferrihydrite was transformed to more stable Fe oxides. This magnetite incorporated As into its structure during precipitation and subsequently adsorbed As. Adsorption to the minerals kept effluent As concentrations <10 μg L(-1) for more than 100 pore volumes despite considerable Fe reduction. The results indicate that it should be feasible to produce an in situ reactive filter by nitrate-Fe(II) injection.
authors.affiliation: Department of Earth and Environmental Sciences, Columbia University , Mail Code 5505, New York, New York 10027, United States.|Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, New York 10964, United States.
authors.forename: Jing
authors.initials: J
authors.lastname: Sun
authors.affiliation: Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, New York 10964, United States.
authors.forename: Steven N
authors.initials: SN
authors.lastname: Chillrud
authors.affiliation: Department of Environmental Sciences, Barnard College , 3009 Broadway, New York, New York 10027, United States.
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Mailloux
authors.affiliation: Lamont-Doherty Earth Observatory, PO Box 1000, 61 Route 9W, Palisades, New York 10964, United States.
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Bostick
mesh_terms: D001151:Arsenic; D052203:Ferrosoferric Oxide; D060587:Groundwater / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D056928:X-Ray Absorption Spectroscopy
chemical_list: D007501:Iron; D001151:Arsenic; D052203:Ferrosoferric Oxide