Speaker
Description
Technetium 99 is a long-lived fission product whose environmental mobility is controlled by redox transformations between the highly soluble Tc(VII)O4− anion and low valent Tc(IV) species that exhibit strong sorption or precipitation behavior. Understanding the formation, stability, and interconversion of these species in complex aqueous environments is essential for reliable safety assessments of nuclear waste repositories, particularly under carbonate-rich or alkaline conditions representative of cementitious systems.
This work applies controlled potential electrochemistry, coupled with in situ UV vis, 99Tc nuclear magnetic resonance (NMR), and infrared spectroscopy (IR), to investigate Tc(VII) reduction pathways and ligand-dependent stabilization of low valent technetium species. Building on earlier carbonate studies, where carbonate was found to stabilize even lower Tc oxidation states.1 We systematically explore Tc(VII) reduction across a wide range of parameters. This includes carbonate concentrations, pH values, and Tc loadings. Distinct Tc(IV) and Tc(III) carbonate complexes are generated at defined potentials and identified by characteristic UV vis absorption bands. Newly observed 99Tc NMR resonances provide direct structural and electronic insight into these species, enabling refined mechanistic assignments for carbonate-mediated redox processes.
In addition, Tc(VII) reduction in strongly alkaline gluconate media is investigated by electrochemical methods to probe ligand-stabilized low valent Tc species relevant to organic-rich cement porewaters, since previous experiments have demonstrated the presence of low-valent gluconate complexes.2,3 Complementary background measurements in gluconate-only solutions allow unambiguous attribution of Tc-specific spectral features. These experiments establish a robust spectroelectrochemical baseline for identifying transient intermediates and quantifying their formation as a function of applied potential and ligand environment. These results will improve predictions of Tc mobility under repository-relevant conditions and support the development of more reliable long-term safety assessments for nuclear waste management.
Acknowledgements:
The authors acknowledge the German Federal Ministry of Research, Technology and Space and the German Federal Ministry for the Environment, Climate Action, Nature Conservation and Nuclear Safety for funding the NukSiFutur young investigator group TecRad (02NUK072) and the RULET project (02E12224B).
References:
1 Paquette, J. and Lawrence, W. E. Canadian Journal of Chemistry 63.9 (1985): 2369-2373.
2 Dardenne, K., et al. Inorganic Chemistry 60.16 (2021): 12285-12298.
3 Polly, R., et al. Inorganic Chemistry 64.11 (2025): 5412-5423.