Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation
Synthesized goethite was successfully used with addition of Fe(II) to sequester Tc present in both deionized water and simulated off-gas scrubber waste solutions. Pertechnetate concentration in solution decreased immediately when the pH was raised above 7 by addition of sodium hydroxide. Removal of Tc(VII) from solution occurred most likely as a result of heterogeneous surface-catalyzed reduction to Tc(IV) and subsequent co-precipitation onto the goethite. The final Tc-bearing solid was identified as goethite-dominated Fe(III)-(oxy)hydroxide based on XRD analysis, confirming the widespread observation of its characteristic acicular habit by TEM/SEM images. Analysis of the solid precipitate by XAFS showed that the dominant oxidation state of Tc was Tc(IV) and was in octahedral coordination with Tc-O, Fe-O, and Tc-Fe bond distances that are consistent with direct substitution of Tc for Fe in the goethite structure. In some experiments the final Tc-goethite product was subsequently armored with additional layers of freshly precipitated goethite. Successful incorporation of Tc(IV) within the goethite mineral lattice and subsequent goethite armoring can limit re-oxidation of Tc(IV) and its subsequent release from Tc-goethite waste forms, even when the final product is placed in oxidizing environments that typify shallow waste burial facilities.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1018142
- Report Number(s):
- PNNL-SA-72463; ESTHAG; 35405; EY7144147; TRN: US1103268
- Journal Information:
- Environmental Science & Technology, 45(11):4904-4913, Vol. 45, Issue 11; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GOETHITE
LIQUID WASTES
PERTECHNETATES
REMOVAL
SCRUBBERS
SODIUM HYDROXIDES
VALENCE
WASTE FORMS
WATER
X-RAY DIFFRACTION
Technetium
secondary wastes
Hanford Site
Goethite
Coprecipitation
Environmental Molecular Sciences Laboratory