title: Uranium Redox Transformations after U(VI) Coprecipitation with Magnetite Nanoparticles.
abstract: Uranium redox states and speciation in magnetite nanoparticles coprecipitated with U(VI) for uranium loadings varying from 1000 to 10 000 ppm are investigated by X-ray absorption spectroscopy (XAS). It is demonstrated that the U M4high energy resolution X-ray absorption near edge structure (HR-XANES) method is capable to clearly characterize U(IV), U(V), and U(VI) existing simultaneously in the same sample. The contributions of the three different uranium redox states are quantified with the iterative transformation factor analysis (ITFA) method. U L3XAS and transmission electron microscopy (TEM) reveal that initially sorbed U(VI) species recrystallize to nonstoichiometric UO2+xnanoparticles within 147 days when stored under anoxic conditions. These U(IV) species oxidize again when exposed to air. U M4HR-XANES data demonstrate strong contribution of U(V) at day 10 and that U(V) remains stable over 142 days under ambient conditions as shown for magnetite nanoparticles containing 1000 ppm U. U L3XAS indicates that this U(V) species is protected from oxidation likely incorporated into octahedral magnetite sites. XAS results are supported by density functional theory (DFT) calculations. Further characterization of the samples include powder X-ray diffraction (pXRD), scanning electron microscopy (SEM) and Fe 2p X-ray photoelectron spectroscopy (XPS).
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Ivan
authors.initials: I
authors.lastname: Pidchenko
authors.affiliation: European Synchrotron Radiation Facility (ESRF) , CS40220, 38043 Grenoble Cedex 9, France.|Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology , P.O. Box 510119, D-01314 Dresden, Germany.
authors.forename: Kristina O
authors.initials: KO
authors.lastname: Kvashnina
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Tadahiro
authors.initials: T
authors.lastname: Yokosawa
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Finck
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Bahl
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Dieter
authors.initials: D
authors.lastname: Schild
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Polly
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Elke
authors.initials: E
authors.lastname: Bohnert
authors.affiliation: Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology , P.O. Box 510119, D-01314 Dresden, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Rossberg
authors.affiliation: Karlsruhe Institute of Technology, Institute for Photon Science and Synchrotron Radiation (IPS) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Göttlicher
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Kathy
authors.initials: K
authors.lastname: Dardenne
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Rothe
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Schäfer
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Horst
authors.initials: H
authors.lastname: Geckeis
authors.affiliation: Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal (INE) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors.forename: Tonya
authors.identifier: 0000-0002-3117-7701
authors.initials: T
authors.lastname: Vitova
mesh_terms: D058185:Magnetite Nanoparticles; D010084:Oxidation-Reduction; D056951:Photoelectron Spectroscopy; D014501:Uranium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D058185:Magnetite Nanoparticles; D014501:Uranium