Sorption of 90Sr and 137Cs on Clays used in the Construction of Safety Barriers in Radioactive Waste Storage Facilities
The aim of the work was to study the sorption capacity of samples of natural clays with respect to 90Sr and 137Cs to assess the possibility of their use as components of protective barriers at radioactive waste isolation plants. The objects of study were bentonite clays of the Zyryanskoye deposit (Ural) and Desyaty Khutor deposit (Republic of Khakassia) as well as the refractory clay of the Kampanovskoye deposit (Krasnoyarsk Territory).
The sorption capacity of clays by the ionexchange mechanism is characterized by the value of the cation exchange capacity (CEC). In sorption experiments, for all the studied clays, a high degree of extraction of strontium and cesium radionuclides from aqueous solutions was observed. It was shown that the sorption of 90Sr was affected by the montmorillonite content in the samples: bentonite clays absorb up to 98–99% of the initial radionuclide content in the solution, whereas about 80% of strontium is sorbed by the refractory clay. Cesium is almost completely sorbed by the studied samples: the degree of sorption is more than 99%. As a consequence, the highest value of the distribution coefficient was obtained for the sample from the Kampanovskoye deposit (Kd = 5,0⋅103 cm3/g). The methods for fixing the sorbed radionuclides on clay samples were determined by the selective desorption method according to the modified Tessier method. It has been demonstrated that strontium ions are more mobile than caesium ions, up to 97% of which is retained by clays.
Based on the experimental data, it can be concluded that it is possible to use bentonite clays of the Zyryanskoye deposit and Desyaty Khutor deposit as well as refractory clays of the Kampanovskoye deposit as components of protective barriers at radioactive waste isolation plants.
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