Uranyl adsorption to the silica surface was studied by second harmonic generation (SHG). Resonantly enhanced SHG was used to measure an in situ electronic spectrum of adsorbed uranyl species at both pH 7 and pH 4, and in the presence of aqueous carbonate. By monitoring the SHG response, adsorption isotherms revealed that the adsorption free energy for U(VI) at the silica/water interface increased from �42.7(3) kJmol-1 at pH 7 to �32.5(3) kJmol-1 at pH 4. By using the non-resonant ?(3)technique, surface charge densities of adsorbed uranyl species were determined to be 0.0069(7) Cm-2 at pH 7 and 0.0031(5) Cm-2 at pH 4. When these values are referenced to the initial charge density of the interface, results indicate a bidentate mode of binding at pH 7 and a mondentate mode of binding at pH 4. Free energy vs. interfacial potential analysis revealed that neutral and monovalent cationic uranyl species are surface active in both aqueous pHs. Using these same methodologies, this work is now applied separately to the muscovite (mica) and Fe2O3/water interface, which is discussed.

Uranyl adsorption and speciation at the mineral/water interface studied by second harmonic generation

243rd National Meeting (2012)

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