Structural analysis of sorption processes of U(VI) and Np(V) onto water mineral interfaces
The migration behavior of heavy metal contaminants like actinyl ions (UO22+, NpO2+) in ground water aquifers is mainly controlled by sorption processes at water-mineral interfaces. Hence, the investigation of the interactions of actinides with metal oxides, 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. Among the different solid phases, namely Fe(OOH)x, TiO2, or SiO2, aluminum oxide and hydroxides are of particular interest because they represent main components in clays and clay minerals which, in turn, are considered as appropriate host rock materials for nuclear waste repositories.
Moreover, beneath the mineralogical aspects, the migration behavior of uranium is in the focus of environmental research, because it has become a widespread contaminant for human population in the past due to mining activities, spent fuel reprocessing, nuclear weapon tests and fall out of nuclear power plants. Considering of the radioactive decay of 241Am (half life of 432.7 years), the isotope 237Np will become a major contributor to the radiation inventory of nuclear waste repositories in the long term scale.
In this work the interactions of uranium(VI) and neptunium(V) at mineral model systems relevant in the near and far field of nuclear repositories are investigated in aqueous solution. The work focuses on the impact of selected anions on the sorption processes of U or Np. The ternary systems are investigated by a combined approach using ATR FT-IR spectroscopy and quantum chemical calculations providing molecular structural information of the sorption complexes. Further techniques such as EXAFS, TRLF and Raman spectroscopy will provide complementary information.
- Katharina Gückel, André Rossberg, Vinzenz Brendler, Harald Foerstendorf: "Binary and ternary surface complexes of U(VI) on the gibbsite/water interface studied by vibrational and EXAFS spectroscopy", Chemical Geology, 2012, 326-327, pp. 27–35.