title: Uranium Isotopic Fractionation Induced by U(VI) Adsorption onto Common Aquifer Minerals.
abstract: Uranium groundwater contamination due to U mining and processing affects numerous sites globally. Bioreduction of soluble, mobile U(VI) to U(IV)-bearing solids is potentially a very effective remediation strategy. Uranium isotopes (238U/235U) have been utilized to track the progress of microbial reduction, with laboratory and field studies finding a ∼1‰ isotopic fractionation, with the U(IV) product enriched in238U. However, the isotopic fractionation produced by adsorption may complicate the use of238U/235U to trace microbial reduction. A previous study found that adsorption of U(VI) onto Mn oxides produced a -0.2‰ fractionation with the adsorbed U(VI) depleted in238U. In this study, adsorption to quartz, goethite, birnessite, illite, and aquifer sediments induced an average isotopic fractionation of -0.15‰ with the adsorbed U(VI) isotopically lighter than coexisting aqueous U(VI). In bicarbonate-bearing matrices, the fractionation depended little on the nature of the sorbent, with only birnessite producing an atypically large fractionation. In the case of solutions with ionic strengths much lower than those of typical groundwater, less isotopic fractionation was produced than U(VI) solutions with greater ionic strength. Studies using U isotope data to assess U(VI) reduction must consider adsorption as a lesser, but significant isotope fractionation process.
authors.affiliation: Department of Geology, University of Illinois at Urbana-Champaign , 156 Computing Applications Building, 605 E. Springfield Avenue, Champaign, Illinois 61820, United States.
authors.forename: N E
authors.initials: NE
authors.lastname: Jemison
authors.affiliation: Department of Geology, University of Illinois at Urbana-Champaign , 156 Computing Applications Building, 605 E. Springfield Avenue, Champaign, Illinois 61820, United States.
authors.forename: T M
authors.initials: TM
authors.lastname: Johnson
authors.affiliation: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University , 104 CEOAS Administration Building, 101 26th Street, Corvallis, Oregon 97322, United States.
authors.forename: A E
authors.initials: AE
authors.lastname: Shiel
authors.affiliation: Department of Geology, University of Illinois at Urbana-Champaign , 156 Computing Applications Building, 605 E. Springfield Avenue, Champaign, Illinois 61820, United States.
authors.forename: C C
authors.initials: CC
authors.lastname: Lundstrom
mesh_terms: D000327:Adsorption; D019015:Geologic Sediments; D060587:Groundwater; D008903:Minerals; D014501:Uranium; D014875:Water Pollutants, Radioactive
chemical_list: D008903:Minerals; D014875:Water Pollutants, Radioactive; D014501:Uranium