Sorption and Speciation of Uranium on Silica Colloids

Abstract

Sorption behavior of uranium onto silica colloids is studied to derive surface complexation data. Several spectroscopic and structural methods, i.e., Time-resolved Laser-induced Fluorescence (TRLIF), X-ray Absorption Fine Structure (XAFS), and Small-angle X-ray Scattering (SAXS) are employed for characterization of colloid suspensions and surface-sorbed species. TRLIF and EXAFS allowed identification of two principal uranium species on the silica surfacebidentate coordinated uranyl complexes of the following stoichiometries (SiO) 2 UO 2 and (SiO) 2 UO 2 OH À . No polynuclear species or surface precipitates are formed as shown by EXAFS and SAXS examination of suspensions at various silica/uranium ratios. However, when uranium coverage of the silica surface exceeds 7%, the colloid stability as determined by electrophoretic mobility increases. Potentially, this could affect colloid-facilitated transport.

Distribution, behavior, and erosion of uranium in vineyard soils

“…Greater sorption of U to particles has been observed to finer fractions and clays, as well as in greater presence of Fe (Kumar et al 2015). In addition, sorption of U to silica colloids results in the formation of various complexes (Batuk et al 2011). Furthermore, sorption of U to soil organic matter (e.g., humic acids) is dependent on pH, increasing when lower than 6 but forming soluble uranylhumate complexes above 6 (Pompe et al 1999).…”

Rates and mechanisms of uranyl oxyhydroxide mineral dissolution

“…6D) (the amount of U sorption on quartz was too low in high carbonate BPW columns to collect EXAFS spectra). The optimum shell-by-shell fit (Table 4) was obtained by grouping U-O eq shells at distances similar to those reported in the literature for sorbed aqueous uranyl on silica (R = 2.28 and 2.48 Å ) (Sylwester et al, 2000;Batuk et al, 2011) and varying N with r 2 fixed on average values determined from fits to crystalline reference compounds. This EXAFS model informed the stoichiometry chosen for the two uranyl surface complexation reactions and estimation of their sorption constants in RT simulations (Section S5 and Table S4 in SI).…”

“…f Interatomic distances (R) and N for U(VI) sorbed on quartz were based on EXAFS fit results reported in Sylwester et al (2000) and Batuk et al (2011) for sorbed aqueous uranyl on silica and silica colloids in pH 6.46 and 6.5 experiments, respectively. VF optimization model was applied (Fig.…”

Particulate Phases Possibly Conveyed from Nuclear Waste Repositories by Groundwater

“…By using the surface complexation model, several investigators have modeled the radionuclides adsorption on the surface of the colloidal particles to form pseudo-colloids. For instance Batuk et al (2011) interpreted in this way the sorption behavior and speciation of U on silica colloids, Degueldre & Bolek (2009) modeled plutonium adsorption on hydrous metal oxide solids, Del Nero et al (2004) interpreted Np(V) sorption on amorphous Al and Fe silicates, and uranyl ions on Al-hydroxide (Froideval et al, 2006). Sorption of Np(V), Pu(V), and Pu(IV) on colloids of Fe(III) oxides and hydrous oxides and MnO 2 was studied over wide ranges of solution pH and ionic strength by Khasanova et al (2007).…”