Signatures of technetium oxidation states: a new approach

Abstract

A first general strategy for the determination of Tc oxidation state by new approach involving X-ray absorption near edge spectroscopy (XANES) at the Tc L3 edge is shown. A comprehensive...

A Combined Study of Tc Redox Speciation in Complex Aqueous Systems: Wet-Chemistry, Tc K-/L3-Edge X-ray Absorption Fine Structure, and Ab Initio Calculations

“…The evaluation of Tc K-edge EXAFS data gives relevant insights into structural parameters such as the coordination number and Tc−O distances but does not allow derivation of conclusive chemical models for the Tc(IV)−gluconate complexes prevailing in the aqueous phase. As already hinted in the literature for Tc solid phases, 42,43 our work provides the first evidence on the high sensitivity of L 3 -edge XANES toward the molecular environment of Tc in aqueous samples. The coupling of this highly sensitive technique with ab initio methods represents a prominent tool for the accurate characterization of the molecular environment of Tc in the aqueous phase, thus underpinning the development of accurate chemical and thermodynamic models in real aqueous systems.…”

“…As shown below (Section ), attempts for DFT optimizations of the coordination polyhedron of sample B as a basis for ab initio calculations of the corresponding Tc L 3 -edge XANES spectra, as for now, have not been successful. Note that Bauters et al reported a remarkable range of the WL shape and crystal-field splitting for various Tc­(IV) complexes in their recent comprehensive Tc L 3 -edge XANES study of technetium oxidation state signatures depending on the ligand type and the coordination structure.…”

“…Note that the core–hole lifetime broadening at the Tc L 3 -level is only 1.91 eV compared to 4.91 eV at the K-level, enabling detection of subtle spectral differences between different oxidation states and bonding schemes. To the best of our knowledge, up to now (2021), the only publications covering XANES measurements at the Tc L 3 absorption edge were presented by Blanchard et al in 2014 and Bauters et al in 2020 . In the context of the former study, Tc-containing powder samples were embedded in epoxy resin and mounted in a windowless holder.…”

“…To the best of our knowledge, up to now (2021), the only publications covering XANES measurements at the Tc L 3 absorption edge were presented by Blanchard et al in 2014 42 and Bauters et al in 2020. 43 In the context of the former study, Tc-containing powder samples were embedded in epoxy resin and mounted in a windowless holder. Tc L 3 -edge spectra were collected at the Australian Synchrotron using the total electron yield (TEY) and total fluorescence yield (TFY) XAS detection modes with Tc samples held at UHV conditions.…”

Design and Application of Materials for Sequestration and Immobilization of 99Tc

“…Depending on the surrounding conditions (such as pH, ionic strength, co-localized complexing agents, and the redox potential of aqueous media), 99 Tc can exist in oxidation states ranging from I to VII in nuclear waste solutions. Various studies have revealed that the environmental mobility of 99 Tc is primarily governed by the tetra- (IV) and heptavalent (VII) oxidation states, while the other oxidation states require stabilizing ligands. − In oxic environments, 99 Tc persists as a soluble and highly mobile oxyanion pertechnetate (TcO 4 – , Tc­(VII)), which is also known for eluding targeted waste treatment technologies. Once released into the environment, TcO 4 – does not readily sorb to common near- and subsurface minerals such as ferric (Fe­(III)) minerals or clays, e.g., bentonite, due to its low negative charge. − However, if Tc­(VII) is reduced to more stable Tc­(IV) by a natural or synthetic reducing agent, sequestering and immobilizing 99 Tc becomes more favorable.…”