GEOCHEMICAL FEATURES OF ADSORPTION OF TRITIUM FROM WATER SOLUTIONS BY CLINOPTILOLITE
Keywords:
clinoptilolite, mineral adsorbent, tritium, tritiated water, thermal processing, fractionation of hydrogen isotopes.Abstract
To study the mechanism of tritium extraction from aqueous solutions of the zeolite, two similar in composition closed stationary experimental systems based on clinoptilolite from the Sokirnytsky deposit (Ukraine) were created. In the first experiment, unchanged natural clinoptilolite was used; in the second, the mineral was thermally treated at 110 °C. The duration of the experiments was about 10 months. Measurements of the specific activity of tritium in the aqueous residue and in the mineral medium made it possible to determine the redistribution of tritium between the solid and liquid phases, as well as between the various structural positions in clinoptilolite. The adsorbed moisture present in the mineral during the interaction of the mineral and aqueous phases initially leads to a partial decrease in the concentration of the tritium indicator in the “HTO”. In the future, this moisture provides the possibility of transit penetration of HTO molecules into clinoptilolite channels due to diffuse molecular exchange of HTO ↔ H2O between the water and mineral phases. Heat treatment reduces the possibility of partial dilution of tritiated water, which interacts with the mineral. Thermal activation of adsorption centers in the mineral mass provides more efficient removal of tritium from the aqueous phase. After heat treatment, the pore space and the surface of the mineral particles are freed from the adsorbed water present in the mineral, and their surface is thermally activated. This leads to a relatively more intensive surface adsorption, where up to 68.5% of tritium absorbed by the mineral accumulates. The interaction of tritiated water with thermally activated surface of mineral particles was accompanied by dynamic adsorption-desorption processes, electrokinetic phenomena in the surface electric layer, which caused the fractionation of hydrogen isotopes with a coefficient α = 1.17. The presence in a heat-treated clinoptilolite of the partial filling of the coordination spheres of alkaline cations, which is similar to the original mineral, made it possible to fractionate hydrogen isotopes in the mineral channels with a coefficient α = 1.16. The heat treatment of clinoptilolite changed the ratio of hydrogen isotopes to hydroxyl groups, where the fractionation coefficient α increased accordingly to 1.06.
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