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

Journal Article · Thu Dec 04 00:00:00 EST 2014 · Crystal Growth and Design

DOI:https://doi.org/10.1021/cg501656s· OSTI ID:1185753

Custelcean, Radu ^[1]; Sloop, Frederick V. ^[1]; Rajbanshi, Arbin ^[1]; Wan, Shun ^[1]; Moyer, Bruce A. ^[1]

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1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

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.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Environmental Management (EM)
• Grant/Contract Number: AC05-00OR22725
• OSTI ID: 1185753
• Journal Information: Crystal Growth and Design, Vol. 15, Issue 1; ISSN 1528-7483
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY