title: Transport of U(VI) through sediments amended with phosphate to induce in situ uranium immobilization.
abstract: Phosphate amendments can be added to U(VI)-contaminated subsurface environments to promote in situ remediation. The primary objective of this study was to evaluate the impacts of phosphate addition on the transport of U(VI) through contaminated sediments. In batch experiments using sediments (<2 mm size fraction) from a site in Rifle, Colorado, U(VI) only weakly adsorbed due to the dominance of the aqueous speciation by Ca-U(VI)-carbonate complexes. Column experiments with these sediments were performed with flow rates that correspond to a groundwater velocity of 1.1 m/day. In the absence of phosphate, the sediments took up 1.68-1.98 μg U/g of sediments when the synthetic groundwater influent contained 4 μM U(VI). When U(VI)-free influents were then introduced with and without phosphate, substantially more uranium was retained within the column when phosphate was present in the influent. Sequential extractions of sediments from the columns revealed that uranium was uniformly distributed along the length of the columns and was primarily in forms that could be extracted by ion exchange and contact with a weak acid. Laser induced fluorescence spectroscopy (LIFS) analysis along with sequential extraction results suggest adsorption as the dominant uranium uptake mechanism. The response of dissolved uranium concentrations to stopped-flow events and the comparison of experimental data with simulations from a simple reactive transport model indicated that uranium adsorption to and desorption from the sediments was not always at local equilibrium.
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA.
authors.forename: Vrajesh S
authors.initials: VS
authors.lastname: Mehta
authors.affiliation: Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA.
authors.forename: Fabien
authors.initials: F
authors.lastname: Maillot
authors.affiliation: Department of Fundamental and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA 99352, USA.
authors.forename: Zheming
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA.
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Catalano
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, MO 63130, USA. Electronic address: giammar@wustl.edu.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Giammar
mesh_terms: D000327:Adsorption; D061249:Batch Cell Culture Techniques; D001965:Bromides / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry*; D007834:Lasers; D010710:Phosphates / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D014501:Uranium / Q000737:chemistry*
chemical_list: D001965:Bromides; D010710:Phosphates; D014501:Uranium
keywords: CXTFIT; In situ immobilization; Phosphate; Reactive transport; Sequential extractions; Uranium