XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-Precipitates
- Pacific Northwest National Laboratory, Richland WA (United States)
XAFS has been used to study the chemical state and structural environment of technetium in Fe(III) oxide co-precipitates. 99Technetium is an abundant fission product which poses a significant environmental hazard due to its long half-life, abundance in nuclear wastes, and environmental mobility as the pertechnetate ion [Tc(VII)O{sub 4}{sup -}] under oxidizing conditions. Tetravalent Tc [Tc(IV)] is the stable valence state under reducing or anoxic conditions where its environmental mobility is significantly lowered by formation of a sparingly soluble, hydrated amorphous oxide precipitate [Tc(IV)O2{center_dot}nH2O(s)]. We have been studying the kinetics and solid products resulting from abiotic reduction of Tc(VII)O{sub 4}{sup -} by aqueous, adsorbed, and structural Fe(II) to provide insights on Tc migration in microaerophilic groundwaters. The reduction reaction yields Fe/Tc precipitates of variable structures that have not been previously studied. For the homogeneous reaction with aqueous Fe(II) at relatively high Tc:Fe concentrations, the predominant redox product is a solid containing Tc(IV) dimers attached in a bidentate edge-sharing configuration to FeO6 octahedra on the surface or unoccupied interior sites of a ferrihydrite-like precipitate. A similar ferrihydrite-type solid is formed on the surface of Fe oxide minerals such a hematite and goethite following the heterogeneous reaction of Tc(VII)O{sub 4}{sup -} with surface-complexed Fe(II). These co-precipitates greatly slow the oxidation rate of Tc(IV) relative to amorphous Tc(IV)O2{center_dot}nH2O(s), possibly allowing for the long term sequestration of 99Tc in stable (bio)geochemical mineral forms that may reduce the long term environmental risk of 99Tc subsurface contamination.
- OSTI ID:
- 21054585
- Journal Information:
- AIP Conference Proceedings, Vol. 882, Issue 1; Conference: XAFS13: 13. international conference on X-ray absorption fine structure, Stanford, CA (United States), 9-14 Jul 2006; Other Information: DOI: 10.1063/1.2644465; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
Similar Records
XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-precipitates
Reduction of Pertechnetate [Tc(VII)] by Aqueous Fe(II) and the Nature of Solid Phase Redox Products