The structure of uranium (VI) sorption complexes on silica, alumina, and montmorillonite

Uranium speciation and stability after reductive immobilization in aquifer sediments

“…As shown in the reference biogenic uraninite spectrum, a prominent FT U-U shell at 3.86 Å ) is not found in these sediments. is inconsistent with bidentate coordination of U(IV) to silicate surfaces where a coordination number of 1 would be expected (Sylwester et al, 2000). Coffinite (USiO 4 ) can be ruled out as a significant phase; it should exhibit 4 U atomic neighbors at 3.83 Å (not observed).…”

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.…”

Distribution coefficients for the sorption of Th, U, Np, Pu, and Am on Opalinus Clay

“…However, up to now no sorption data for americium and plutonium on OPA have been published. More sorption studies have been reported for the uptake of actinides by pure clay minerals, that are the main constituents of OPA (e. g., montmorillonite [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], illite [32][33][34][35][36][37][38][39][40], kaolinite [31,[41][42][43][44][45][46][47][48][49][50][51] , the cation exchange capacity was equal to 10 ± 4 meq/100 g for both powders [9,11]. The mineral composition and the content of the trace elements of the used OPA measured by X-ray fluorescence analysis are given elsewhere [11].…”