Photoreduction of ⁹⁹Tc Pertechnetate by Nanometer-Sized Metal Oxides: New Strategies for Formation and Sequestration of Low-Valent Technetium

Journal Article · Wed Nov 23 00:00:00 EST 2011 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja2060929· OSTI ID:1082198

Burton-Pye, Benjamin P. ^[1]; Radivojevic, Ivana ^[1]; McGregor, Donna ^[2]; Mbomekalle, Israel M. ^[1]; Lukens, Wayne W. ^[3]; Francesconi, Lynn C. ^[2]

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1. Hunter College of the City Univ. of New York, NY (United States)
2. Hunter College of the City Univ. of New York, NY (United States). Graduate Center
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Technetium-99 (⁹⁹Tc)(β^-_max: 293.7 keV; t_1/2: 2.1 x 10⁵ years) is a byproduct of uranium-235 fission and comprises a large component of radioactive waste. Under aerobic conditions and in a neutral- basic environment, the pertechnetate anion (⁹⁹TcO₄^-) is stable. ⁹⁹TcO₄^- is very soluble, migrates easily through the environment and does not sorb well onto mineral surfaces, soils or sediments. This study moves forward a new strategy for the reduction of TcO₄^- and chemical incorporation of the reduced ⁹⁹Tc into a metal oxide material. This strategy employs a single material, a polyoxometalate (POM), α_2-[P₂W₁₇O₆₁]^10-, that can be photoactivated in the presence of 2-propanol to transfer electrons to TcO₄^- and incorporate the reduced ⁹⁹Tc covalently into the α₂^- framework to form the Tc^VO species, Tc^VO(α_2-P₂W₁₇O₆₁)^7-. This occurs via the formation of an intermediate species that slowly converts to Tc^VO(α_2-P₂W₁₇O₆₁)^7-. EXAFS and XANES analysis and preliminary EPR analysis, suggests that the intermediate consists of a Tc(IV) α₂- species where the ⁹⁹Tc is likely bound to only 2 of the 4 W-O oxygen atoms in the α_2-[P₂W₁₇O₆₁]^10- defect. This intermediate then oxidizes and converts to the ⁹⁹Tc^VO(α_2-P₂W₁₇O₆₁)^7- product. The reduction and incorporation of ⁹⁹TcO^4- was accomplished in a ''one pot'' reaction using both sunlight and UV irradiation, and monitored as a function of time using multinuclear NMR and radio TLC. The process was further probed by the ''step-wise'' generation of reduced α_2-P₂W₁₇O₆₁^12- through bulk electrolysis followed by the addition of TcO₄^-. The reduction and incorporation of ReO₄^-, as a non-radioactive surrogate for ⁹⁹Tc, does not proceed through the intermediate species, and Re^VO is incorporated quickly into the α_2-[P₂W₁₇O₆₁]_10- defect. These observations are consistent with the periodic trends of ⁹⁹Tc and Re. Specifically, ⁹⁹Tc is more easily reduced compared to Re. In addition to serving as models for metal oxides, POMs may also provide a suitable platform to study the molecular level dynamics and mechanisms of the reduction and incorporation of Tc into a material.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Div.
• Sponsoring Organization: USDOE
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 1082198
• Report Number(s): LBNL-5408E
• Journal Information: Journal of the American Chemical Society, Vol. 133, Issue 46; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English

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