title: Adsorption of uranium(VI) to manganese oxides: X-ray absorption spectroscopy and surface complexation modeling.
abstract: The mobility of hexavalent uranium in soil and groundwater is strongly governed by adsorption to mineral surfaces. As strong naturally occurring adsorbents, manganese oxides may significantly influence the fate and transport of uranium. Models for U(VI) adsorption over a broad range of chemical conditions can improve predictive capabilities for uranium transport in the subsurface. This study integrated batch experiments of U(VI) adsorption to synthetic and biogenic MnO(2), surface complexation modeling, ζ-potential analysis, and molecular-scale characterization of adsorbed U(VI) with extended X-ray absorption fine structure (EXAFS) spectroscopy. The surface complexation model included inner-sphere monodentate and bidentate surface complexes and a ternary uranyl-carbonato surface complex, which was consistent with the EXAFS analysis. The model could successfully simulate adsorption results over a broad range of pH and dissolved inorganic carbon concentrations. U(VI) adsorption to synthetic δ-MnO(2) appears to be stronger than to biogenic MnO(2), and the differences in adsorption affinity and capacity are not associated with any substantial difference in U(VI) coordination.
authors.affiliation: Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA.
authors.forename: Zimeng
authors.initials: Z
authors.lastname: Wang
authors.forename: Sung-Woo
authors.initials: SW
authors.lastname: Lee
authors.forename: Jeffrey G
authors.initials: JG
authors.lastname: Catalano
authors.forename: Juan S
authors.initials: JS
authors.lastname: Lezama-Pacheco
authors.forename: John R
authors.initials: JR
authors.lastname: Bargar
authors.forename: Bradley M
authors.initials: BM
authors.lastname: Tebo
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Giammar
mesh_terms: D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D017895:Manganese Compounds / Q000737:chemistry*; D008956:Models, Chemical; D010087:Oxides / Q000737:chemistry*; D013499:Surface Properties; D014501:Uranium / Q000302:isolation & purification*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D017895:Manganese Compounds; D010087:Oxides; D014501:Uranium; C027424:manganese oxide