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

doi:https://doi.org/10.1063/1.2644465

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

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Abstract

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)O4-] 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•nH2O(s)]. We have been studying the kinetics and solid products resulting from abiotic reduction of Tc(VII)O4- 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)O4- with surface-complexed Fe(II). These co-precipitates greatly slow themore »« less

Authors:: Heald, Steve M; Zachara, John M; Jeon, Byong Hun; McKinley, James P; Kukkadapu, Ravi K; Moore, Dean A

Publication Date:: 2007-07-05

Research Org.:: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)

Sponsoring Org.:: USDOE

OSTI Identifier:: 914680

Report Number(s):: PNNL-SA-50815
4594; KP1302000; TRN: US0803360

DOE Contract Number:: AC05-76RL01830

Resource Type:: Conference

Resource Relation:: Conference: X-RAY Absorption Fine Structure - XAFS13: 13th International Conference. AIP Conference Proceedings, 882:173-175

Country of Publication:: United States

Language:: English

Subject:: 12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES; ABSORPTION; CHEMICAL STATE; FINE STRUCTURE; FISSION PRODUCTS; OXIDE MINERALS; OXIDES; RADIOACTIVE WASTES; TECHNETIUM; XAFS; Technetium; iron oxides; Environmental Molecular Sciences Laboratory

Citation Formats


                    Heald, Steve M, Zachara, John M, Jeon, Byong Hun, McKinley, James P, Kukkadapu, Ravi K, and Moore, Dean A. XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-precipitates.  United States: N. p., 2007. 
        Web.  doi:10.1063/1.2644465.

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                    Heald, Steve M, Zachara, John M, Jeon, Byong Hun, McKinley, James P, Kukkadapu, Ravi K, & Moore, Dean A. XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-precipitates.  United States.  https://doi.org/10.1063/1.2644465

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                    Heald, Steve M, Zachara, John M, Jeon, Byong Hun, McKinley, James P, Kukkadapu, Ravi K, and Moore, Dean A. Thu .  
        "XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-precipitates".  United States.  https://doi.org/10.1063/1.2644465.

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@article{osti_914680,

  title        = {XAFS Study of the Chemical and Structural States of Technetium in Fe(III) Oxide Co-precipitates},

  author       = {Heald, Steve M and Zachara, John M and Jeon, Byong Hun and McKinley, James P and Kukkadapu, Ravi K and Moore, Dean A},

  abstractNote = {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)O4-] 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•nH2O(s)]. We have been studying the kinetics and solid products resulting from abiotic reduction of Tc(VII)O4- 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)O4- with surface-complexed Fe(II). These co-precipitates greatly slow the oxidation rate of Tc(IV) relative to amorphous Tc(IV)O2•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.},

  doi          = {10.1063/1.2644465},

  url          = {https://www.osti.gov/biblio/914680},
  journal      = {},
number       = ,

  volume       = ,

  place        = {United States},

  year         = {2007},

  month        = {7}

}

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

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