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Selenite Adsorption Mechanisms on Pure and Coated Montmorillonite: An EXAFS and XANES Spectroscopic Study

Dep. of Soil Science, Univ. of Saskatchewan, 51 Campus Dr., Saskatoon SK S7N 5A8 Canada

View larger version (22K): [in a new window]   Fig. 1. Se K-Edge EXAFS results for aqueous selenite solutions. Solid lines denote the raw data, and open squares are the fit to theoretical standards.

View larger version (31K): [in a new window]   Fig. 2. Se K-Edge EXAFS results for selenite adsorbed on a range of sorbents at pH 4.5 and 0.01 M I. Solid lines denote the raw data, and open squares are the fit to theoretical standards. Arrows denote spectral features consistent with Se-Al backscattering due to inner-sphere complexation.

View larger version (13K): [in a new window]   Fig. 3. Relationship between protonation state, molecular symmetry, and bond delocalization for selenite species.

View larger version (18K): [in a new window]   Figure 4. (a) XANES spectra of H2SeO3, HSeO3–, and SeO32– (b) 12.665 to 12.69 keV energy range expanded to more clearly show differences in the near edge spectra.

View larger version (23K): [in a new window]   Fig. 5. Linear combination XANES fits of aqueous samples where more than one selenite protonation state is present. LC-XANES predicted distributions are within 0.5% of actual speciation values, and the estimated error of the LC-XANES fitting was 3%.

View larger version (22K): [in a new window]   Fig. 6. (a):Se K-Edge XANES spectra of selenite sorbed onto Mt, HYA,HAS, HYA-Mt, and HAS-Mt samples. HSeO3 and H2SeO3 solutions are included for comparison. (b) 12.665 to 12.69 keV energy range expanded to more clearly show differences in the near edge spectra for HAS, HYA, HYA-Mt, and Mt samples.

View larger version (11K): [in a new window]   Fig. 7. Selenite adsorption mechanisms for pH 4.5 samples consistent with EXAFS and XANES spectroscopy.

View larger version (22K): [in a new window]   Fig. 8. Linear combination XANES fits of selenite on HYA and HAS coated montmorillonite. Estimated error for the fitting is ± 5%.