Radiopolarography of technetium(VII) in acidic medium

Grassi, Joaquín; Rogelet, P.; Devynck, Jacques; Trémillon, B.

doi:10.1016/s0022-0728(78)80345-3

Cited by 14 publications

(1 citation statement)

References 13 publications

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“…Technetium-99 is a β-emitting fission product highly relevant in the safety assessment of repositories for radioactive waste disposal due to its significant inventory in spent nuclear fuel, long half-life (t 1/2 ∼ 2.1 × 10 5 a) and redox-sensitive chemical behaviour. Although several oxidation states of Tc are reported in the literature (from 0 to +VII), [1][2][3][4][5] Tc(VII) and Tc(IV) are the prevailing redox states in the absence of any complexing ligand other than water under non reducing and reducing conditions, respectively. Tc(VII) is the most stable oxidation state of Tc in suboxic/oxidising environments, it is found as the highly mobile TcO 4 − anion over the entire pH range and shows very high solubility and weak sorption properties.…”

Section: Introductionmentioning

confidence: 99%

Systematic XAS study on the reduction and uptake of Tc by magnetite and mackinawite

Yalçıntaş

Scheinost²,

Gaona

et al. 2016

Dalton Trans.

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The mechanisms for the reduction and uptake of Tc by magnetite (FeO) and mackinawite (FeS) are investigated using X-ray absorption spectroscopy (XANES and EXAFS), in combination with thermodynamic calculations of the Tc/Fe systems and accurate characterization of the solution properties (pH, pe, [Tc]). Batch sorption experiments were performed under strictly anoxic conditions using freshly prepared magnetite and mackinawite in 0.1 M NaCl solutions with varying initial Tc(vii) concentrations (2 × 10 and 2 × 10 M) and Tc loadings (400-900 ppm). XANES confirms the complete reduction of Tc(vii) to Tc(iv) in all investigated systems, as predicted from experimental (pH + pe) measurements and thermodynamic calculations. Two Tc endmember species are identified by EXAFS in the magnetite system, Tc substituting for Fe in the magnetite structure and Tc-Tc dimers sorbed to the magnetite {111} faces through a triple bond. The sorption endmember is favoured at higher [Tc], whereas incorporation prevails at low [Tc] and less alkaline pH conditions. The key role of pH in the uptake mechanism is interpreted in terms of magnetite solubility, with higher [Fe] and greater recrystallization rates occurring at lower pH values. A TcS-like phase is predominant in all investigated mackinawite systems, although the contribution of up to 20% of TcO·xHO(s) (likely as surface precipitate) is observed for the highest investigated loadings (900 ppm). These results provide key inputs for an accurate mechanistic interpretation of the Tc uptake by magnetite and mackinawite, so far controversially discussed in the literature, and represent a highly relevant contribution to the investigation of Tc retention processes in the context of nuclear waste disposal.

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