title: Trivalent Actinide Uptake by Iron (Hydr)oxides.
abstract: The retention of Am(III) by coprecipitation with or adsorption onto preformed magnetite was investigated by X-ray diffraction (XRD), solution chemistry, and X-ray absorption spectroscopy (XAS). In the coprecipitation experiment, XAS data indicated the presence of seven O atoms at 2.44(1) Å, and can be explained by an Am incorporation at Fe structural sites at the magnetite surface. Next-nearest Fe were detected at distances suggesting that Am and Fe polyhedra share corners in geometries ranging from bent to close to linear Am-O-Fe bonds. After aging for two years, the coordination number and the distance to the first O shell significantly decreased, and atomic shells were detected at higher distances. These data suggest a structural reorganization and an increase in structural order around sorbed Am. Upon contact with preformed Fe3O4, Am(III) forms surface complexes with cosorbed Fe at the surface of magnetite, a possible consequence of the high concentration of dissolved Fe. In a separate experiment, chloride green rust (GR) was synthesized in the presence of Am(III), and subsequently converted to Fe(OH)2(s) intermixed with magnetite. XAS data indicated that the actinide is successively located first at octahedral brucite-like sites in the GR precursor, then in Fe(OH)2(s), an environment markedly distinct from that of Am(III) in Fe3O4. The findings indicate that the magnetite formation pathway dictates the magnitude of Am(III) incorporation within this solid.
authors: Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT) , P.O. Box 3640, D-76021 Karlsruhe, Germany.
authors: Nicolas
authors: N
authors: Finck
authors: Nano-Science Center, Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen, Denmark.
authors: Sorin
authors: S
authors: Nedel
authors: Nano-Science Center, Department of Chemistry, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen, Denmark.
authors: Knud
authors: K
authors: Dideriksen
authors: CEA, DEN/DPC/SEARS/LISL, Building 391, F-91191 Gif-sur-Yvette, France.
authors: Michel L
authors: ML
authors: Schlegel
mesh_terms: D008671:Actinoid Series Elements; D007501:Iron / Q000737:chemistry*; D010087:Oxides / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D008671:Actinoid Series Elements; D010087:Oxides; D007501:Iron