title: Uranyl adsorption at the muscovite (mica)/water interface studied by second harmonic generation.
abstract: Uranyl adsorption at the muscovite (mica)/water interface was studied by second harmonic generation (SHG). Using the nonresonant χ(3) technique and the Gouy-Chapman model, the initial surface charge density of the mica surface was determined to be -0.022(1) C/m(2) at pH 6 and in the presence of dissolved carbonate. Under these same conditions, uranyl adsorption isotherms collected using nonresonant χ(3) experiments and resonantly enhanced SHG experiments that probe the ligand-to-metal charge transfer bands of the uranyl cation yielded a uranyl binding constant of 3(1) × 10(7) M(-1), corresponding to a Gibbs free energy of adsorption of -52.6(8) kJ/mol, and a maximum surface charge density at monolayer uranyl coverage of 0.028(3) C/m(2). These results suggest favorable adsorption of uranyl ions to the mica interface through strong ion-dipole or hydrogen interactions, with a 1:1 uranyl ion to surface site ratio that is indicative of monovalent cations ((UO(2))(3)(OH)(5)(+), (UO(2))(4)(OH)(7)(+), UO(2)OH(+), UO(2)Cl(+), UO(2)(CH(3)COO(-))(+)) binding at the interface, in addition to neutral uranyl species (UO(2)(OH)(2) and UO(2)CO(3)). This work provides benchmark measurements to be used in the improvement of contaminant transport modeling.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Saslow Gomez
authors.forename: David S
authors.initials: DS
authors.lastname: Jordan
authors.forename: Julianne M
authors.initials: JM
authors.lastname: Troiano
authors.forename: Franz M
authors.initials: FM
authors.lastname: Geiger
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry*; D002414:Cations, Monovalent; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D013499:Surface Properties; D017974:Uranium Compounds / Q000737:chemistry*; D014875:Water Pollutants, Radioactive / Q000737:chemistry*
chemical_list: D000538:Aluminum Silicates; D002414:Cations, Monovalent; D017974:Uranium Compounds; D014875:Water Pollutants, Radioactive; C517971:muscovite