U(VI) sorption onto environmental relevant minerals: vibrational spectroscopy and complementary tools


U(VI) sorption onto environmental relevant minerals: vibrational spectroscopy and complementary tools

Müller, K.; Foerstendorf, H.; Krepelova, A.; Baumann, N.; Brendler, V.

The sorption onto minerals along groundwater flow paths is an important mechanism determining the migration behaviour of uranium(VI) in the natural environment. The U(VI) surface complexation on several mineral phases was studied applying different spectroscopic methods. Using ATR-FTIR spectroscopy an in-situ investigation of U(VI) sorption onto kaolinite and titanium dioxide was performed at a micromolar concentration range. Thin mineral films are deposited on the surface of the crystal of an ATR flow cell. When U(VI) passes through the cell, characteristic absorption changes are observed representing sorption processes of U(VI) on the mineral surfaces. From the spectra the formed sorption complexes can be deduced.
The characteristic asymmetric stretching vibration of the uranyl ion is red-shifted by 40 cm–1 upon surface complexation of the UO22+ ion on kaolinite probably indicating strong sorption due to inner-sphere surface complexation. In homology, red shifts were also observed in the IR spectra of the titanium dioxide system, but the extent of the frequency shifts differs among different TiO2 samples.
In order to gain more information of the U(VI) complexes formed on the kaolinite surface, time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied [1]. Two U(VI) surface species, differing in the amount of water molecules in their coordination environment, could be identified. For the U(VI)-TiO2 system significant different spectroscopic response was observed for anatase and rutile. TRLFS investigations of anatase suspensions were hampered by strong quenching effects of the mineral phase. In contrast, the measurements of U(VI) in the rutile suspensions yield reasonable results.
A third spectroscopic method used for the characterization of the formed U(VI) complexes on surfaces of kaolinite and ferrihydrite is extended X-ray absorption fine structure (EXAFS) [2].
The obtained spectroscopic results serve as a data base for the development and the parameterization of models describing surface complexation phenomena.

1. Krepelova, A.; Brendler, V.; Sachs, S.; Baumann, N.; Bernhard, G. Environmental Science & Technol-ogy 2007, 41, (17), 6142-6147.
2. Reich, T.; Moll, H.; Arnold, T.; Denecke, M. A.; Hennig, C.; Geipel, G.; Bernhard, G.; Nitsche, H.; Allen, P. G.; Bucher, J. J.; Edelstein, N. M.; Shuh, D. K., Journal of Electron Spectroscopy and Related Phe-nomena 1998, 96, (1-3), 237-243.

  • Lecture (others)
    Seminar at National Commission of Atomic Energy (CNEA) of Argentina, 21.04.2008, San Martin, Argentina

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Publ.-Id: 11070