Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The migration behavior of heavy metal contaminants like actinyl ions (U, Np) is mainly controlled by sorption processes at water-mineral interfaces. Hence, the investigation of the interactions of actinides with metal oxides such as Al(OH)3, Fe(OOH)x, TiO2, or SiO2, serving as model phases for more complex, naturally occurring minerals in aqueous solution, becomes essential for the safety assessment in the near and far field of nuclear repositories. In this study, gibbsite is used as a mineral model system because it the most common crystalline aluminum hydroxide and an ubiquitous weathering product of aluminosilicate minerals.
Spectroscopic data of surface complexes of uranium(VI) on gibbsite were obtained by in-situ Attenuated total reflection Fourier-transform (ATR FT-IR) and X-ray absorption spectroscopy.
The formation of a monomeric binary inner-sphere surface complex is derived from vibrational spectroscopic and EXAFS data irrespective of the prevailing atmospheric condition and surface loading. In addition, from infrared spectra it was found that U(VI) surface precipitation occurs at a micromolar concentration level after a relatively short contact time in an inert gas atmosphere. However, this is circumvented by lowering the initial U(VI) concentration or in the presence of atmospheric CO2 due to the formation of ternary uranyl carbonato surface complexes. The ternary complex was identified as a dimeric inner-sphere uranyl surface species containing a bidentately coordinated carbonate ligand.
Furthermore, DFT calculations were done to determine the structure and IR spectra of the aqueous dimeric uranyl-carbonate-hydroxo complex.