Influence of temperature pre-treatment and high-molar saline solutions on the adsorption capacity of organo-clay minerals

Abstract

Clays play an important role in the design of HLW repositories. Serving as a buffer material between waste container and host rock, clays provide mechanical stability and radionuclide retardation due to advantageous hydrological and chemical properties. A crucial limitation, however, results from the fact that the affinity of natural clays for anionic species is very low. Modification of the clays with certain organic cations results in organo-clays, which have already proved high adsorption capacities for anions under laboratory conditions. In order to test the adsorption performance under various near-field conditions of a waste repository, experiments on the retention of radioiodide by different organo-clays were carried out under the influence of elevated temperatures and high-molar saline solutions. The results show that most of the investigated organo-clays exhibit stable structures and adsorption performances under the tested near-field conditions. Iodide adsorption remains at high levels in the temperature range under consideration for radioactive waste repositories. Adsorption reductions above 160 °C can be explained by both, losses of organo-cations and decreases of basal spacings. Under the impact of high-molar saline solutions, the organo-clays were able to adsorb considerable amounts of iodide in spite of extremely high concentrations of competing anions in the applied solutions.