title: U(VI) adsorption on aquifer sediments at the Hanford Site.
abstract: Aquifer sediments collected via split-spoon sampling in two new groundwater wells in the 200-UP-1 operable unit at the Hanford Site were characterized and showed typical Ringold Unit E Formation properties dominated by gravel and sand. High iron-oxide content in Fe oxide/clay coatings caused the highest U(VI) adsorption as quantified by batch K(d) values, indicating iron oxides are the key solid adsorbent in the 200-UP-1 sediments that affect U(VI) fate and mobility. Even though U(VI) adsorption on the gravel-sized fraction of the sediments is considered to be negligible, careful characterization should be conducted to determine U(VI) adsorption on gravel, because of presence of Fe oxides coatings and diffusion-controlled adsorption into the gravel particles' interior surfaces. A linear adsorption isotherm was observed up to 10(-6) M (238 microg/L) of total U(VI) concentration in batch U(VI) adsorption tests with varying total U(VI) concentrations in spiked groundwater. U(VI) adsorption decreased with increasing concentrations of dissolved carbonate, because strong anionic aqueous uranium-carbonate complexes formed at high pH and high alkalinity conditions. Noticeable uranium desorption hysteresis was observed in a flow-through column experiment, suggesting that desorption K(d) values for aged uranium-contaminated sediments at the Hanford Site can be larger than adsorption K(d) values determined in short-term laboratory experiments and slow uranium release from contaminated sediments into the groundwater is expected.
authors.affiliation: Pacific Northwest National Laboratory, PO Box 999, MS P7-22, Richland, WA 99354, USA. wooyong.um@pnl.gov
authors.forename: Wooyong
authors.initials: W
authors.lastname: Um
authors.forename: R Jeffrey
authors.initials: RJ
authors.lastname: Serne
authors.forename: Christopher F
authors.initials: CF
authors.lastname: Brown
authors.forename: George V
authors.initials: GV
authors.lastname: Last
mesh_terms: D000327:Adsorption; D052918:Environmental Restoration and Remediation; D005290:Ferric Compounds / Q000737:chemistry; D019015:Geologic Sediments; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D012822:Silicon Dioxide; D012990:Soil Pollutants, Radioactive; D013997:Time Factors; D014501:Uranium / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014875:Water Pollutants, Radioactive; D018508:Water Purification / Q000379:methods*; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; D012990:Soil Pollutants, Radioactive; D014875:Water Pollutants, Radioactive; D014867:Water; C000499:ferric oxide; D014501:Uranium; D012822:Silicon Dioxide