Sorption of radionuclides on glauconite of the Neogene

A safe disposal of radioactive waste requires that the long-term dispersion of the radionuclides (RN) from the waste to the environment is minimal. The assessment of RN dispersal requires a thorough understanding of the processes and mechanisms controlling the radionuclide transport around these barriers. In this PhD we investigated the sorption of two medium-lived radionuclides, i.e. caesium-137 (137Cs) and strontium-90 (90Sr) on glauconite sands of the Paleogene and Neogene formations (Fm) in Belgium. It was found that glauconite sands have surprisingly high 137Cs sorption for a sand, close to values measured on Boom Clay. However, the natural occurrence of glauconite in large grains is decreasing the accessibility of the sorption sites and reaching sorption equilibrium takes about 1 month. Variations among the sands can be explained by the glauconite content and the cation exchange capacity (CEC). A characterisation and optimisation of a three-site sorption model for glauconite suggests that the glauconite sands have highly selective sites that bind 137Cs+ with similar properties as in illite. The model allows the prediction of 137Cs sorption based on basic glauconite sand characteristics (e.g. the CEC). Column experiments prove that Cs sorption on highly permeable glauconite sands is sufficiently fast to delay breakthrough in realistic flow rates. Adsorption of 90Sr2+ is suitably high and the sorption strength is in line with that of other geological barriers when judged from the CEC. An accelerate weathering study revealed that glauconite sand is not highly sensitive to weathering under the experimental conditions and that the effects on the 137Cs sorption are marginal. In conclusion, glauconite sands can exhibit strong sorption potential for 137Cs and 90Sr and can thereby can act as an additional sorption sink for 137Cs and 90Sr.