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Title: Sodium Sulfate Separation from Aqueous Alkaline Solutions via Crystalline Urea-Functionalized Capsules: Thermodynamics and Kinetics of Crystallization

We measured the thermodynamics and kinetics of crystallization of sodium sulfate with a tripodal tris-urea receptor (L1) from aqueous alkaline solutions in the 15 55 C temperature range, with the goal of identifying the optimal conditions for efficient and quick sulfate removal from nuclear wastes. The use of radiolabeled Na235SO4 provided a practical way to monitor the sulfate concentration in solution by liquid scintillation counting. Our results are consistent with a two-step crystallization mechanism, involving relatively quick dissolution of crystalline L1 followed by the rate-limiting crystallization of the Na2SO4(L1)2(H2O)4 capsules. We found that temperature exerted relatively little influence over the equilibrium sulfate concentration, which ranged between 0.004 and 0.011 M. Moreover, this corresponds to 77 91% removal of sulfate from a solution containing 0.0475 M initial sulfate concentration, as found in a typical Hanford waste tank. The apparent pseudo-first-order rate constant for sulfate removal increased 20-fold from 15 to 55 C, corresponding to an activation energy of 14.1 kcal/mol. At the highest measured temperature of 55 C, 63% and 75% of sulfate was removed from solution within 8 h and 24 h, respectively.
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
1185753
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Crystal Growth and Design
Additional Journal Information:
Journal Volume: 15; Journal Issue: 1; Journal ID: ISSN 1528-7483
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Environmental Management (EM)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY