The Sorption of Eu(III) on Opalinus Clay at elevated Temperatures and in Presence of Organics

Presently, argillaceous rock formations are under investigation as potential host rocks for nuclear waste repositories. In addition to the diffusion the sorption of radionuclides on mineral phases is an important physicochemical process in a nuclear waste repository in the case of a water inleakage. Concerning the required long-term safety and risk assessment of the storage of high-level radioactive waste the understanding of these processes is essential. The investigations concentrated on the sorption of Eu(III) on OPA under realistic OPA pore water conditions (medium: pH 7.6; ionic strength 0.4 mol•L-1; presence of chloride, sulfate, carbonate) up to 50°C. In addition to the temperature dependent investigations the influence of tartrate and citrate (representatives of NOM) on the Eu(III) sorption was studied.
The sorption is characterized by a very strong binding of Eu(III) to the clay surface and a significant temperature dependency. With rising temperature the Rd value rises, showing that the Eu(III) sorption increases. In the presence of tartrate or citrate the Eu(III) sorption decreases with rising ligand concentration.