title: Reactivity of Uranium and Ferrous Iron with Natural Iron Oxyhydroxides.
abstract: Determining key reaction pathways involving uranium and iron oxyhydroxides under oxic and anoxic conditions is essential for understanding uranium mobility as well as other iron oxyhydroxide mediated processes, particularly near redox boundaries where redox conditions change rapidly in time and space. Here we examine the reactivity of a ferrihydrite-rich sediment from a surface seep adjacent to a redox boundary at the Rifle, Colorado field site. Iron(II)-sediment incubation experiments indicate that the natural ferrihydrite fraction of the sediment is not susceptible to reductive transformation under conditions that trigger significant mineralogical transformations of synthetic ferrihydrite. No measurable Fe(II)-promoted transformation was observed when the Rifle sediment was exposed to 30 mM Fe(II) for up to 2 weeks. Incubation of the Rifle sediment with 3 mM Fe(II) and 0.2 mM U(VI) for 15 days shows no measurable incorporation of U(VI) into the mineral structure or reduction of U(VI) to U(IV). Results indicate a significantly decreased reactivity of naturally occurring Fe oxyhydroxides as compared to synthetic minerals, likely due to the association of impurities (e.g., Si, organic matter), with implications for the mobility and bioavailability of uranium and other associated species in field environments.
authors.affiliation: Chemical and Biological Engineering, Montana State University , Bozeman, Montana 59717, United States.
authors.forename: Brandy D
authors.initials: BD
authors.lastname: Stewart
authors.affiliation: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, California 94720, United States.
authors.forename: A Cristina
authors.initials: AC
authors.lastname: Cismasu
authors.affiliation: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, California 94720, United States.
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Williams
authors.affiliation: Chemical and Biological Engineering, Montana State University , Bozeman, Montana 59717, United States.
authors.forename: Brent M
authors.initials: BM
authors.lastname: Peyton
authors.affiliation: Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, California 94720, United States.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Nico
mesh_terms: D000327:Adsorption; D003120:Colorado; D005290:Ferric Compounds / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; C021024:ferric hydroxide; D014501:Uranium; C092844:ferric oxyhydroxide; D007501:Iron