Uranium(VI) complexation with inorganic ligands under elevated temperatures (25-70 °C).
For the safety assessment of high-level nuclear waste repositories in deep geological formations, a sound understanding of the migration behavior of mobilized radionuclides from the spent nuclear fuel is required. In recent decades, the solution chemistry of actinides, including hydrolysis and complexation with organic- and inorganic ligands, as well as the interactions of actinides at interfaces present in the geo- and biosphere have been intensely investigated. The vast majority of these investigations have been conducted at ambient conditions, implying that information on radionuclide sorption and speciation mechanisms is limited to temperatures around 25 °C. It is estimated that maximum temperatures in the near field of a SNF repository could reach 100 °C, depending on the waste form and host rock under consideration. Under these conditions, water properties such as the density, dielectric constant, viscosity and ion product are different from room temperature conditions, which may influence the speciation of metal ions in solution and their uptake on solid surfaces.
Thus, in the present thesis U(VI) complexation with common inorganic ligands present in the environment, i.e. silicates and carbonates, is investigated in the temperature regime between 25-70 °C. The thesis focuses on the determination of complex stability constants and thermodynamic parameters for the formed U(VI)-silicate and U(VI)-carbonate species. A combination of modern spectroscopic techniques such as TRLFS/UV-Vis, Si-NMR and ITC will be applied in the temperature-dependent studies.
This work is part of the BMBF-funded ThermAc project.