title: Uranium Isotope Fractionation during Adsorption, (Co)precipitation, and Biotic Reduction.
abstract: Uranium contamination of surface environments is a problem associated with both U-ore extraction/processing and situations in which groundwater comes into contact with geological formations high in uranium. Apart from the environmental concerns about U contamination, its accumulation and isotope composition have been used in marine sediments as a paleoproxy of the Earth's oxygenation history. Understanding U isotope geochemistry is then essential either to develop sustainable remediation procedures as well as for use in paleotracer applications. We report on parameters controlling U immobilization and U isotope fractionation by adsorption onto Mn/Fe oxides, precipitation with phosphate, and biotic reduction. The light U isotope (235U) is preferentially adsorbed on Mn/Fe oxides in an oxic system. When adsorbed onto Mn/Fe oxides, dissolved organic carbon and carbonate are the most efficient ligands limiting U binding resulting in slight differences in U isotope composition (δ238U = 0.22 ± 0.06‰) compared to the DOC/DIC-free configuration (δ238U = 0.39 ± 0.04‰). Uranium precipitation with phosphate does not induce isotope fractionation. In contrast, during U biotic reduction, the heavy U isotope (238U) is accumulated in reduced species (δ238U up to -1‰). The different trends of U isotope fractionation in oxic and anoxic environments makes its isotope composition a useful tracer for both environmental and paleogeochemical applications.
authors: School of the Environment and ‡Water Quality Center, Trent University , 1600 West Bank Drive, Peterborough, Ontario, Canada K9L 0G2.
authors: Duc Huy
authors: DH
authors: Dang
authors: School of the Environment and ‡Water Quality Center, Trent University , 1600 West Bank Drive, Peterborough, Ontario, Canada K9L 0G2.
authors: Breda
authors: B
authors: Novotnik
authors: School of the Environment and ‡Water Quality Center, Trent University , 1600 West Bank Drive, Peterborough, Ontario, Canada K9L 0G2.
authors: Wei
authors: W
authors: Wang
authors: School of the Environment and ‡Water Quality Center, Trent University , 1600 West Bank Drive, Peterborough, Ontario, Canada K9L 0G2.
authors: R Bastian
authors: RB
authors: Georg
authors: School of the Environment and ‡Water Quality Center, Trent University , 1600 West Bank Drive, Peterborough, Ontario, Canada K9L 0G2.
authors: R Douglas
authors: RD
authors: Evans
mesh_terms: D000327:Adsorption; D005591:Chemical Fractionation; D019015:Geologic Sediments / Q000737:chemistry; D060587:Groundwater; D007554:Isotopes; D014501:Uranium / Q000737:chemistry*
chemical_list: D007554:Isotopes; D014501:Uranium