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Hana Vinšová, Petr Večerník, Věra Jedináková-Křížová

Sorption characteristics of ⁹⁹Tc onto bentonite material with different additives under anaerobic conditions

Keywords: Sorption, Technetium, Bentonite, Glove box conditions, Deep repository

The radionuclide ⁹⁹Tc is one of the fission products of spent nuclear fuel. The chemical forms of this element depend primarily on the pH and E_h of the environment. The aim of this study was to describe the sorption of the pertechnetate anion onto bentonite under anaerobic conditions, which accurately simulate the environment of a deep repository. Several additives were tested to determine whether they increase the retention of ⁹⁹Tc on this material — Fe, FeS, Fe₃O₄ and activated carbon.
It was found that it is very difficult to create the same conditions present in the deep repository in the laboratory, which is why the reduction of the pertechnetate anion to its lower oxidation state (Tc(IV)) was not achieved. The retention of the pertechnate anion on bentonite is very low (K_D ∼1 mL/g), the uptake of the pertechnetate anion onto bentonite was achieved by the addition of suitable additives to the bentonite mixtures e.g. activated carbon, Fe and FeS (K_D ∼102–103 mL/g). Various chemical forms of technetium were obtained in the solution, dependant on the various reaction mechanisms of the pertechnetate anion. Fe and FeS enabled the reduction of the pertechnetate anion to its lower oxidation state in the form of insoluble TcO(OH)₂ or TcO₂·n H₂O, physical sorption is the dominant mechanism with activated carbon.

Radiochimica Acta, Oldenbourg Wissenschaftsverlag

Print ISSN: 0033-8230
Volume: 94, 08/2006
Pages: 435 - 440

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