title: Quantitative separation of monomeric U(IV) from UO2 in products of U(VI) reduction.
abstract: The reduction of soluble hexavalent uranium to tetravalent uranium can be catalyzed by bacteria and minerals. The end-product of this reduction is often the mineral uraninite, which was long assumed to be the only product of U(VI) reduction. However, recent studies report the formation of other species including an adsorbed U(IV) species, operationally referred to as monomeric U(IV). The discovery of monomeric U(IV) is important because the species is likely to be more labile and more susceptible to reoxidation than uraninite. Because there is a need to distinguish between these two U(IV) species, we propose here a wet chemical method of differentiating monomeric U(IV) from uraninite in environmental samples. To calibrate the method, U(IV) was extracted from known mixtures of uraninite and monomeric U(IV) and tested using X-ray absorption spectroscopy (XAS). Monomeric U(IV) was efficiently removed from biomass and Fe(II)-bearing phases by bicarbonate extraction, without affecting uraninite stability. After confirming that the method effectively separates monomeric U(IV) and uraninite, it is further evaluated for a system containing those reduced U species and adsorbed U(VI). The method provides a rapid complement, and in some cases alternative, to XAS analyses for quantifying monomeric U(IV), uraninite, and adsorbed U(VI) species in environmental samples.
authors.affiliation: Environmental Microbiology Laboratory, Ecole Polytechnique Fédérale de Lausanne, CH-1015, Switzerland.
authors.forename: Daniel S
authors.initials: DS
authors.lastname: Alessi
authors.forename: Benjamin
authors.initials: B
authors.lastname: Uster
authors.forename: Harish
authors.initials: H
authors.lastname: Veeramani
authors.forename: Elena I
authors.initials: EI
authors.lastname: Suvorova
authors.forename: Juan S
authors.initials: JS
authors.lastname: Lezama-Pacheco
authors.forename: Joanne E
authors.initials: JE
authors.lastname: Stubbs
authors.forename: John R
authors.initials: JR
authors.lastname: Bargar
authors.forename: Rizlan
authors.initials: R
authors.lastname: Bernier-Latmani
mesh_terms: D000327:Adsorption; D001639:Bicarbonates; D001673:Biodegradation, Environmental; D018533:Biomass; D052203:Ferrosoferric Oxide; D005296:Ferrous Compounds / Q000737:chemistry; D005583:Fourier Analysis; D019015:Geologic Sediments / Q000737:chemistry / Q000382:microbiology; D016014:Linear Models; D010084:Oxidation-Reduction; D010710:Phosphates / Q000737:chemistry; D020592:Shewanella / Q000378:metabolism / Q000648:ultrastructure; D014501:Uranium / Q000302:isolation & purification*; D017974:Uranium Compounds / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D001639:Bicarbonates; D005296:Ferrous Compounds; D010710:Phosphates; D017974:Uranium Compounds; D014501:Uranium; C518753:ferrous phosphate; C012597:uranium dioxide; D052203:Ferrosoferric Oxide