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Title: Perrhenate incorporation into binary mixed sodalites: The role of anion size and implications for technetium-99 sequestration

Perrhenate (ReO4-), as a TcO4- analogue, was incorporated into mixed-anion sodalites from binary solutions containing ReO4- and a competing anion Xn- (Cl-, CO32-, SO42-, MnO4-, or WO42-). For this study, our objective was to determine the extent of solid solution formation and the dependence of competing ion selectivity on ion size. Using equivalent aqueous concentrations of the anions (ReO4-/Xn- molar ratio = 1:1), we synthesized mixed-anion sodalites from zeolite and NaOH at 90 °C for 96 h. The resulting solids were characterized by bulk chemical analysis, powder X-ray diffraction, scanning electron microscopy, and X-ray absorption near edge structure (XANES) spectroscopy to determine crystal structure, chemical composition, morphology, and rhenium (Re) oxidation state. Rhenium in the solid phase occurred predominately as Re(VII)O4- in the sodalites, which have a primitive cubic pattern in the space group P43n. The refined unit-cell parameters of the mixed sodalites ranged from 8.88 to 9.15 Å and showed a linear dependence on the size and mole fraction of the incorporated anion(s). The ReO4- selectivity, represented by its distribution coefficient (Kd), increased in the following order: Cl- < NO3- < MnO4- and CO32- < SO42- < WO42- for the monovalent and divalent anions, respectively. The relationship between themore » ReO4- distribution coefficient and competing anion size was nonlinear. When the difference in ionic radius (DIR) between ReO4- and Xn - (n = 1 or 2) was greater than ~ 12%, then ReO4- incorporation into sodalite was insignificant. The results imply that anion size is the major factor that determines sodalite anion compositions. Given the similarity in chemical behavior and anion size, ReO4- serves as a suitable analogue for TcO4- under oxidizing conditions where both elements are expected to remain as oxyanions in the + 7 oxidation state.« less
 [1] ;  [1] ;  [2] ;  [3]
  1. Washington State Univ., Pullman, WA (United States). Department of Crop and Soil Sciences
  2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Environmental Sciences Division
Publication Date:
OSTI Identifier:
Grant/Contract Number:
AC05-00OR22725; PS02-09ER65075; AC02-05CH11231
Accepted Manuscript
Journal Name:
Chemical Geology
Additional Journal Information:
Journal Volume: 395; Journal ID: ISSN 0009-2541
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES Mixed-anion sodalites; Anion selectivity; Distribution coefficient; Perrhenate; Pertechnetate; technetium-99; Nuclear waste