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Title: Structure and Thermochemistry of Perrhenate Sodalite and Mixed Guest Perrhenate/Pertechnetate Sodalite

Here we report that treatment and immobilization of technetium-99 ( 99Tc) 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[AlSiO 4]6(ReO 4) 2, and the structure of a mixed guest perrhenate/pertechnetate sodalite, Na 8[AlSiO 4] 6(ReO 4) 2-x(TcO 4) x. Perrhenate was used as a chemical analogue for pertechnetate. Bulk analyses of each solid confirm a cubic sodalite-type structure (P$$\overline{43}$$n, 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 ReO 4 anions are distributed in a periodic array in the sample, nanoscale clustering is not observed, and the ReO 4 – anion occupies the center of the sodalite β-cage in Na8[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 99Tc present in reprocessed nuclear waste streams and contaminated subsurface environments.
Authors:
ORCiD logo [1] ;  [2] ;  [3] ; ORCiD logo [4] ;  [2] ;  [5] ;  [6] ;  [1] ;  [6] ;  [1] ;  [3] ; ORCiD logo [2]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of California, Davis, CA (United States)
  3. Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)
  4. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  5. Princeton Univ., NJ (United States)
  6. Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Environmental Science and Technology
Additional Journal Information:
Journal Volume: 51; Journal Issue: 2; Journal ID: ISSN 0013-936X
Publisher:
American Chemical Society (ACS)
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source (SNS)
Sponsoring Org:
USDOE Office of Environmental Management (EM); USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; perrhenate sodalite; pertechnetate sodalite; scanning transmission electron microscopy; ultra STEM; x-ray absorption spectroscopy; extended x-ray absorption spectroscopy
OSTI Identifier:
1340434