Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

The determination and verification of thermodynamic and kinetic parameters of complexation, redox and sorption processes will improve the safety assessment of nuclear waste disposal sites. Sorption processes of U(VI) on mineral surface were traditionally investigated as a function of different reaction parameters (pH, I, T, Eh, c, atm., gs) by employing batch sorption experiments and surface complexation modeling (SCM). In the last decades, the batch sorption experiments were additionally investigated by the application of different spectroscopic techniques (TRLFS, EXAFS, ATR FT-IR). Especially the in situ ATR FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes by the formation of the U(VI) surface complexes. The main objective of this study is to demonstrate the possibility of laser fluorescence spectroscopy for in situ monitoring and characterization of U(VI) sorption reactions. Therefore we investigated the sorption of an aqueous solution of U(VI) onto SiO2. In analogy to the in situ ATR FT-IR measurements, three subprocesses (conditioning, sorption, flushing) are performed in in situ laser fluorescence experiments, as shown in Fig. 1. The resulting fluorescence spectra showed significantly different fluorescence characteristics between the aquoues U(VI) and the sorbed U(VI) species. These preliminary results show that the application of the in situ laser fluorescence spectroscopy is a new alternative technique for identification and characterization of U(VI) complexes at mineral-water interfaces on a molecular level. Furthermore, the time-resolution in the sub-minute range allows kinetic studies of the surface reactions.