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Uranyl Surface Complexes Formed on Subsurface Media from DOE Facilities

^a Dep. of Geological and Environmental Sciences, Stanford Univ., Stanford, CA 94305-2115
^b Dep. of Civil Engineering, 208 Harbert Engineering Center, Auburn Univ., Auburn, AL 36849-5337
^c Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6038

View larger version (31K): [in a new window]   Fig. 1. X-ray absorption near-edge structure spectra of Oak Ridge (OR), Savannah River (SR), and Hanford (HF) media, compared with the spectra of UO2 and UO2(NO3)2 · H2O. E0 = energy of the U LIII edge.

View larger version (40K): [in a new window]   Fig. 2. First-derivative x-ray absorption near-edge structure spectra of Oak Ridge (OR), Savannah River (SR), and Hanford (HF) media, compared with standards. E0 = energy of the U LIII edge.

View larger version (38K): [in a new window]   Fig. 3. (A) The k2-weighted (k) U-LIII extended x-ray adsorption fine structure spectroscopy (EXAFS) spectra and (B) uncorrected radial structure functions for Hanford (HF), Savannah River (SR), and Oak Ridge (OR) subsurface media reacted with U. The experimental data (solid lines) are fit (dotted lines) using the parameters described in Table 3. FT = fourier transform; R = bond length.

View larger version (29K): [in a new window]   Fig. 4. Deconvolution of the k2(k) spectra (A) and radial structure functions for OR4. All samples exhibit similar coordination to oxygen. Three U-O distances and a U-P backscatter are required to fit (dotted lines) the experimental spectra (solid lines). A U-C shell is also shown that is only statistically significant for HF1. FT = Fourier transform; R = bond length.

View larger version (47K): [in a new window]   Fig. 5. Third-shell (centered at 3.1 Å) Fourier-filtered extended x-ray adsorption fine structure spectra of OR1. A U-P shell is required for fitting. A U-Fe contribution with the U-P shell does improve the fit. Table 4 summarizes the fitting parameters.

View larger version (51K): [in a new window]   Fig. 6. A model structure for U sorbed (A) to Savannah River and Oak Ridge, and (B) to HF subsurface media, showing the formation of an inner-sphere ternary complex containing carbonate for the HF media and phosphate for the OR and SR media. The (110) face of goethite is used to illustrate the inner-sphere complex; outer-sphere complexes are not depicted.