The speciation of U(VI) in aqueous solution and sorbed onto TiO2 studied by in situ vibrational spectroscopy

The migration behavior of uranium in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) at the TiO2-water interface has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.