Speciation of technetium(IV) chloride under gamma irradiation

Abstract

Technetium speciation / Gamma radiolysis / Technetium one-electron oxidation / Radioactive waste disposalSummary. 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 n O 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.

Behavior of Heptavalent Technetium in Sulfuric Acid under α-Irradiation: Structural Determination of Technetium Sulfate Complexes by X-ray Absorption Spectroscopy and First Principles Calculations

“…1 Previous studies investigated the effect of γ-radiolysis on the speciation of Tc in hydrochloric and sulfuric acids. 2,3 In dilute sulfuric acid, it was shown that Tc(IV) colloids were formed under irradiation by X-rays of pertechnetate solutions. 4,5 Under α-irradiation, the formation of colloidal species has never been reported.…”

“…Although many studies have been performed under γ-irradiation, the effect of α-irradiation on the behavior of Tc species in acidic media has been less studied . Previous studies investigated the effect of γ-radiolysis on the speciation of Tc in hydrochloric and sulfuric acids. , In dilute sulfuric acid, it was shown that Tc(IV) colloids were formed under irradiation by X-rays of pertechnetate solutions. , Under α-irradiation, the formation of colloidal species has never been reported. Even though α-radiolysis of dilute sulfuric acid solutions was studied, , no data have been reported at high concentration of H 2 SO 4 .…”