Benedicte Prelot1 Pierre Gras1 UtDong Thach1 Delhia Alby1 Peter Hesemann1 Fabrice Salles1 Clarence Charnay1 Jerzy Zajac1

1, ICG Montpellier, Montpellier, , France

During the past years, concerns over nuclear plant securities increased following several major crises. Decontamination of radionuclides is one of the main countermeasures to be applied during the initial stage of the response to a severe nuclear emergency. They are mainly based on sorption processes using specific materials. In the present study, complete thermodynamic approach, combining sorption isotherms and calorimetric measurements have been developed on nanostructured solids such as zeolites, mesoporous zeolites, layered materials, or innovative hybrid silicas.
Synthetic zeolites such as Linde-Type A (LTA) 4A are particularly efficient for cesium and strontium decontamination. The determination of the exchange capacity and the displacement enthalpy measured with Isotherm Titration Calorimetry (ITC) has shown that sorption is endothermic for Sr whereas it is exothermic for Cs. The structure evolution of materials during cation adsorption has been studied to determine the various cation sites and their occupation. The enthalpy could be linked to cation diffusion and hydration shell.
In the case of mesoporous LTA zeolite prepared with various amount of structuring agent, sorption capacity and kinetics are not strictly ascribed to the degree of mesoporosity. Nevertheless, the heat effect is first exothermic for the first exchanged Strontium, and becomes endothermic when the surface coverage increases, illustrating the changes in the various contributions of the heat effects (adsorption of strontium, desorption of sodium, and dehydration-hydration properties of these ions). Moreover, the curves are shifted towards lower surface coverage when the amount of structuring agent increases, demonstrating the influence of the mesoporosity on the exchange and dehydration mechanisms.
Nanoflower-like manganate nanostructures were synthesized. The lamellar structure of such materials is considered to strongly influence the retention performance. These materials exhibit high sorption capacity of Strontium from ultrapure water or multi-component aqueous solutions. Nevertheless, in the presence of calcium, competition between the various species is observed, which was correlated with the displacement enthalpy of the various species. In some cases, molecular simulations were performed to rationalize the retention process.
Concerning anions, the sorption of iodide has been studied for hybrid ionosilicas prepared with tetrasylilated ammonium precursor and CTAB as structuring agent. Thanks to ITC measurements, it has been possible to evidence the high radiolytic stability of these original and innovative materials. No morphological, textural and chemical modifications of the material were detected upon electron irradiation, and their performances are similar.
In all cases, complementary information was obtained from the combination of original materials and detailed thermodynamic study of the sorption processes, and especially from ITC measurements.