| Abstract: |
The safety case for radioactive waste repositories is, to a large extend based on the physical and chemical retention of radionuclides on clay minerals which are important constituents in both the man-made engineered barriers and in argillaceous host rock formations. The presence of carbonate, one of the most important inorganic ligands for lanthanide and actinide ions in groundwaters and clay porewaters, can have a significant influence on their sorption behaviour on clay minerals. The sorption of Eu(III) on Na-montmorillonite in the absence and the presence of carbonate was investigated in batch sorption experiments. In the presence of carbonate two sets of experimental conditions were investigated. Eu(III) sorption measurements were performed as a function of pH in equilibrium with atmospheric pCO2 (=10−3.5 bar) and at a variable pCO2 (=10−1.4 to 10−3.4 bar). The sorption data were modelled using the 2 site protolysis non-electrostatic surface complexation and cation exchange model. Both experimental data sets in the presence of carbon could be quantitatively modelled by including in the sorption model two additional surface complexation reactions on the strong sites forming ≡SSOEuCO30 and ≡SSOEuOHCO3− surface complexes. |
