title: Effect of Mn(II) on the structure and reactivity of biogenic uraninite.
abstract: The efficacy of a site remediation strategy involving the stimulaton of microbial U(VI) reduction hinges in part upon the long-term stability of the product, biogenic uraninite, toward environmental oxidants. Geological sedimentary uraninites (nominal formula UO2) reportedly contain abundant cation impurities that enhance their resistance to oxidation. By analogy, incorporation of common groundwater solutes into biogenic uraninite could also impart stability-enhancing properties. Mn(II) is a common groundwater cation, which has a favorable ionic radiusfor substitution reactions. The structure and reactivity of Mn(II)-reacted biogenic uraninite are investigated in this study. Up to 4.4 weight percent Mn(II) was found to be structurally bound in biogenic uraninite. This Mn(II) incorporation was associated with decreasing uraninite particle size and structural order. Importantly, the equilibrium solubility of Mn-reacted uraninite was halved relative to unreacted uraninite, demonstrating changes in thermodynamic properties, while the dissolution rate was up to 38-fold lower than that of unreacted biogenic uraninite. We conclude that structuralincorporation of Mn(II) into uraninite has an important stabilizing effect leading to the prediction that other groundwater solutes may similarly stabilize biogenic uraninite.
authors.affiliation: Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne, Lausanne, CH 1015, Switzerland.
authors.forename: Harish
authors.initials: H
authors.lastname: Veeramani
authors.forename: Eleanor J
authors.initials: EJ
authors.lastname: Schofield
authors.forename: Jonathan O
authors.initials: JO
authors.lastname: Sharp
authors.forename: Elena I
authors.initials: EI
authors.lastname: Suvorova
authors.forename: Kai-Uwe
authors.initials: KU
authors.lastname: Ulrich
authors.forename: Apurva
authors.initials: A
authors.lastname: Mehta
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Giammar
authors.forename: John R
authors.initials: JR
authors.lastname: Bargar
authors.forename: Rizlan
authors.initials: R
authors.lastname: Bernier-Latmanit
mesh_terms: D001665:Binding Sites; D001673:Biodegradation, Environmental; D005583:Fourier Analysis; D005618:Fresh Water / Q000737:chemistry; D017895:Manganese Compounds / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D012995:Solubility; D013057:Spectrum Analysis; D013816:Thermodynamics; D017974:Uranium Compounds / Q000032:analysis / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000032:analysis / Q000737:chemistry*
chemical_list: D017895:Manganese Compounds; D017974:Uranium Compounds; D014875:Water Pollutants, Radioactive; C012597:uranium dioxide