Speciation of technetium(IV) chloride under gamma irradiation
Résumé
Speciation of Tc in aqueous solution is a complex phenomenon because several parameters intervene simultaneously. We show under gamma radiations, it is completely modified. At pH 8.5 TcO$_2$ is oxidized to Tc(VII) with a yield of 1.38×10$^^{−7}$ mol J${−1}$. At pH 1.5, it was demonstrated that Tc is present as hydroxylated species Tc$_nO_y^{(4n-2y)+}$ (L. Vichot, M. Fattahi, M. Musikas: Radiochim. Acta 91, 263 (2003)). Its oxidation leads also to Tc(VII) with an experimental yield of 1.45×10$^{−7}$ mol J$^{−1}. In more acidic solutions, results are consistent with hydrolysis and oxidation of Tc(IV) to Tc(V). As for colloidal solutions of Tc(IV) or TcO$_2$, they give Tc(VII) whereas solutions of TcCl$_6^{2-}$ at pH 0.5 and 1.5 do not lead directly to Tc(VII). Reduced states of Tc are very sensitive to radiation. Hydrolysis as well as polymerisation of Tc are accelerated. Furthermore the radiolytic processes are pH dependent.