Comparative study of the U(VI) complexation onto γ-Al₂O₃ by ATR FT-IR and EXAFS spectroscopy

Aluminates, representing an essential component of clay minerals, play a decisive role in regulating the mobility of contaminants in rock and soil formations, in particular due to their tendency to form coatings on mineral surfaces [1].
In this work, U(VI) sorption on γ-Al₂O₃ is comparatively investigated using in situ vibrational and X-ray absorption spectroscopy. The focus was set to micromolar U(VI) concentrations and a variety of environmentally relevant sorption parameters in order to resolve discrepancies reported earlier [2-4].
Time-resolved (TR) IR spectroscopic sorption experiments at the alumina-water interface evidence the formation of three different species as a function of surface loading (c.f. Fig.): a monomeric carbonate complex, an oligomeric surface complex and a surface precipitate. These results are confirmed by IR experiments performed at different flow rates, pH values, ionic strengths, U(VI) concentrations, and in inert gas atmosphere. Results of EXAFS experiments of batch samples are consistent to these findings.
[1] Guillaumont, R. (1994) Radiochimica Acta 66-7, 231-242. [2] Catalano, J. G. et al. (2005) Geochim. Cosmochim. Acta 69, 3555-3572. [3] Moskaleva, L.V. et al. (2006) Langmuir 22, 2141-2145. [4] Sylwester, E. R. et al. (2000) Geochim. Cosmochim. Acta 64, 2431-2438.