Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume 51, Issue 2, Pages 997-1006Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.6b01879
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Funding
- U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES) [DE-AC02-98CH10886]
- DOE, Office of Science, BES [DE-AC02-76SF00515]
- DOE Office of Science by ANL [DE-AC02-06CH11357]
- Lawrence Berkeley National Laboratory [DE-AC02-05CH11231]
- Scientific User Facilities Division, BES, DOE
- DOE [DE-AC05-00OR22725]
- Subsurface Biogeochemical Research Program under the US Department of Energy (DOE) Office of Biological and Environmental Research, Climate and Environmental Sciences Division
- Heavy Element Chemistry Program under the Office of Basic Energy Sciences (BES) Chemical Sciences, Biosciences and Geosciences Divisions
- Tank Waste Management Technology Development Program under the Office of Environmental Management
- U.S. Department of Energy [DE-AC05-00OR22725]
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Treatment and immobilization of technetium-99 (Tc-99) contained in reprocessed nuclear waste and present in contaminated subsurface systems represents a major environmental challenge. One potential approach to managing this highly mobile and long-lived radionuclide is immobilization into micro- and meso-porous crystalline solids, specifically sodalite. We synthesized and characterized the structure of perrhenate sodalite, Na-8[AlSiO4](6)(ReO4)(2), and the structure of a mixed guest perrhenate/pertechnetate sodalite, Na-8[AlSiO4](6)(ReO4)(2-x)(TcO4)(x). Perrhenate was used as a chemical analogue for pertechnetate. Bulk analyses of each solid confirm a cubic sodalite-type structure (P (4) over bar 3n, No. 218 space group) with rhenium and technetium in the 7+ oxidation state. High-resolution nanometer scale characterization measurements provide first-of-a-kind evidence that the ReO4- anions are distributed in a periodic array in the sample, nanoscale clustering is not observed, and the ReO4- anion occupies the center of the sodalite beta-cage in Na-8[AlSiO4](6)(ReO4)(2). We also demonstrate, for the first time, that the TcO4- anion can be incorporated into the sodalite structure. Lastly, thermochemistry measurements for the perrhenate sodalite were used to estimate the thermochemistry of pertechnetate sodalite based on a relationship between ionic potential and the enthalpy and Gibbs free energy of formation for previously measured oxyanion-bearing feldspathoid phases. The results collected in this study suggest that micro- and mesoporous crystalline solids maybe viable candidates for the treatment and immobilization of Tc-99 present in reprocessed nuclear waste streams and contaminated subsurface environments.
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