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

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• 作者：Radu Custelcean ; Frederick V. Sloop ; Jr. ; Arbin Rajbanshi ; Shun Wan ; Bruce A. Moyer
• 刊名：Crystal Growth & Design
• 出版年：2015
• 出版时间：January 7, 2015
• 年：2015
• 卷：15
• 期：1
• 页码：517-522
• 全文大小：304K
• ISSN：1528-7505

文摘

The thermodynamics and kinetics of crystallization of sodium sulfate with a tripodal tris-urea receptor (L1) from aqueous alkaline solutions have been measured in the 15鈥?5 掳C temperature range for a fundamental understanding of the elementary steps involved in this sulfate separation method. The use of radiolabeled Na₂³⁵SO₄ provided a practical way to monitor the sulfate concentration in solution by 尾 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. This corresponds to 77鈥?1% 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 掳C, corresponding to an activation energy of 14.1 kcal/mol. At the highest measured temperature of 55 掳C, 63% and 75% of sulfate was removed from solution within 8 and 24 h, respectively. These results indicate the capsule crystallization method is a viable approach to sulfate separation from nuclear wastes.