title: Speciation of uranium in sediments before and after in situ biostimulation.
abstract: The success of sequestration-based remediation strategies will depend on detailed information, including the predominant U species present as sources before biostimulation and the products produced during and after in situ biostimulation. We used X-ray absorption spectroscopy to determine the valence state and chemical speciation of U in sediment samples collected at a variety of depths through the contaminant plume at the Field Research Center at Oak Ridge, TN, before and after approximately 400 days of in situ biostimulation, as well as in duplicate bioreduced sediments after 363 days of resting conditions. The results indicate that U(VI) in subsurface sediments was partially reduced to 10-40% U(IV) during biostimulation. After biostimulation, U was no longer bound to carbon ligands and was adsorbed to Fe/Mn minerals. Reduction of U(VI) to U(IV) continued in sediment samples stored under anaerobic condition at < 4 degrees C for 12 months, with the fraction of U(IV) in sediments more than doubling and U concentrations in the aqueous phase decreasing from 0.5-0.74 to < 0.1 microM. A shift of uranyl species from uranyl bound to phosphorus ligands to uranyl bound to carbon ligands and the formation of nanoparticulate uraninite occurred in the sediment samples during storage.
authors.affiliation: Biosciences Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439-4843, USA. skelly@anl.gov
authors.forename: Shelly D
authors.initials: SD
authors.lastname: Kelly
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Kemner
authors.forename: Jack
authors.initials: J
authors.lastname: Carley
authors.forename: Craig
authors.initials: C
authors.lastname: Criddle
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Jardine
authors.forename: Terence L
authors.initials: TL
authors.lastname: Marsh
authors.forename: Debra
authors.initials: D
authors.lastname: Phillips
authors.forename: David
authors.initials: D
authors.lastname: Watson
authors.forename: Wei-Min
authors.initials: WM
authors.lastname: Wu
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry*; D013057:Spectrum Analysis; D014501:Uranium / Q000032:analysis / Q000145:classification*; D014965:X-Rays
chemical_list: D014501:Uranium