title: Confocal micrometer-scale X-ray fluorescence and X-ray absorption fine structure studies of uranium speciation in a tertiary sediment from a waste disposal natural analogue site.
abstract: Investigations by micrometer-scale X-ray fluorescence and X-ray absorption fine structure (micro-XRF and micro-XAFS) recorded in a confocal geometry on a bore core section of a uranium-rich tertiary sediment are performed in order to assess mechanisms leading to immobilization of the uranium during diagenesis. Results show uranium to be present as a tetravalent phosphate and that U(IV) is associated with As(V). Arsenic present is either As(V) or As(O); we found no evidence for As(III). The As(O) is observed to be intimately associated with the surface of Fe(II) nodules and likely arsenopyrite. A hypothesis for the mechanism of uranium immobilization is proposed, where arsenopyrite acted as reductant of groundwater-dissolved U(VI), leading to precipitation of less soluble U(IV) and thereby forming As(V).
authors.affiliation: Institut für Nukleare Entsorgung, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany. melissa@ine.fzk.de
authors.forename: Melissa A
authors.initials: MA
authors.lastname: Denecke
authors.forename: Koen
authors.initials: K
authors.lastname: Janssens
authors.forename: Kristof
authors.initials: K
authors.lastname: Proost
authors.forename: Jörg
authors.initials: J
authors.lastname: Rothe
authors.forename: Ulrich
authors.initials: U
authors.lastname: Noseck
mesh_terms: D015502:Absorptiometry, Photon / Q000379:methods; D001152:Arsenicals / Q000032:analysis* / Q000737:chemistry; D018153:Czech Republic; D019015:Geologic Sediments / Q000032:analysis*; D008956:Models, Chemical; D011850:Radioactive Waste / Q000032:analysis*; D012990:Soil Pollutants, Radioactive / Q000032:analysis*; D013052:Spectrometry, X-Ray Emission / Q000379:methods; D017974:Uranium Compounds / Q000032:analysis* / Q000737:chemistry
chemical_list: D001152:Arsenicals; D011850:Radioactive Waste; D012990:Soil Pollutants, Radioactive; D017974:Uranium Compounds