title: Rapid Mobilization of Noncrystalline U(IV) Coupled with FeS Oxidation.
abstract: The reactivity of disordered, noncrystalline U(IV) species remains poorly characterized despite their prevalence in biostimulated sediments. Because of the lack of crystalline structure, noncrystalline U(IV) may be susceptible to oxidative mobilization under oxic conditions. The present study investigated the mechanism and rate of oxidation of biogenic noncrystalline U(IV) by dissolved oxygen (DO) in the presence of mackinawite (FeS). Previously recognized as an effective reductant and oxygen scavenger, nanoparticulate FeS was evaluated for its role in influencing U release in a flow-through system as a function of pH and carbonate concentration. The results demonstrated that noncrystalline U(IV) was more susceptible to oxidation than uraninite (UO2) in the presence of dissolved carbonate. A rapid release of U occurred immediately after FeS addition without exhibiting a temporary inhibition stage, as was observed during the oxidation of UO2, although FeS still kept DO levels low. X-ray photoelectron spectroscopy (XPS) characterized a transient surface Fe(III) species during the initial FeS oxidation, which was likely responsible for oxidizing noncrystalline U(IV) in addition to oxygen. In the absence of carbonate, however, the release of dissolved U was significantly hindered as a result of U adsorption by FeS oxidation products. This study illustrates the strong interactions between iron sulfide and U(IV) species during redox transformation and implies the lability of biogenic noncrystalline U(IV) species in the subsurface environment when subjected to redox cycling events.
authors.affiliation: Civil and Environmental Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Yuqiang
authors.initials: Y
authors.lastname: Bi
authors.affiliation: Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Malgorzata
authors.initials: M
authors.lastname: Stylo
authors.affiliation: Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne , CH-1015 Lausanne, Switzerland.
authors.forename: Rizlan
authors.initials: R
authors.lastname: Bernier-Latmani
authors.affiliation: Civil and Environmental Engineering, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Kim F
authors.initials: KF
authors.lastname: Hayes
mesh_terms: D000327:Adsorption; D002254:Carbonates / Q000737:chemistry; D004785:Environmental Pollutants / Q000737:chemistry; D005296:Ferrous Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D010100:Oxygen / Q000737:chemistry; D056951:Photoelectron Spectroscopy; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D002254:Carbonates; D004785:Environmental Pollutants; D005296:Ferrous Compounds; D014501:Uranium; D010100:Oxygen; C022597:ferrous sulfide