XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-Precipitates

Journal Article · Fri Feb 02 04:00:00 EST 2007 · AIP Conference Proceedings

DOI:https://doi.org/10.1063/1.2644465· OSTI ID:21054585

Heald, Steve M; Zachara, John M; Jeon, Byong-Hun; McKinley, James P; Kukkadapu, Ravi; Moore, Dean ^[1]

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1. 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, Journal Name: AIP Conference Proceedings Journal Issue: 1 Vol. 882; ISSN APCPCS; ISSN 0094-243X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
CHEMICAL STATE
CONTAMINATION
DIMERS
ENVIRONMENT
FINE STRUCTURE
FISSION PRODUCTS
GEOCHEMISTRY
GOETHITE
HALF-LIFE
IRON OXIDES
OXIDATION
PERTECHNETATES
PRECIPITATION
REDUCTION
TECHNETIUM 99
VALENCE
X-RAY SPECTRA
X-RAY SPECTROSCOPY