Study of Cesium and Strontium sorption in Brazilian clays for their use as a barrier in repositories of radioactive wastes

Wastes in general should be properly treated and stored. Then the radioactive wastes also require suitable and safe management beginning in their generation until the storage in repository. The main purpose of the radioactive waste management is to preserve the human beings and the environment. The objective of this research was to characterize some Brazilian clays in order to evaluate the viability of their use in the backfill layer, one of the radioactive waste repository barriers. The main function of this barrier is to contribute in the delay of the radionuclides movement, and to prevent their release into the environment. Four clays provided by national suppliers were selected for the research: Ca-Montmorillonite (Dol 01), Na-Montmorillonite (Dol 02), Kaolinite (Ind 01) and Vermiculite (Ubm 04). Their physical, chemical and mineralogical characteristics were determined, and also their sorption potential of Cesium and Strontium cations. It was confirmed through these results a direct relationship among their specific surface (SS), the capacity of cationic exchange (CCE) and pH. The CCE results followed this increasing order: Ind 01, Dol 01, and Dol 02. In accordance with the models of Freundlich (KJ) and Langmuir (M), the clays Dol 01 and Dol 02 were the best sorbers of Sr2+. The Ind 01 and Ubm 04 were the best ones in the case of Cs+. The Gibbs free energy change (ΔG deg) was calculated for the sorption reactions between the clays and the cations, and it was negative for all clays, confirming the sorption reaction spontaneity. (author)