Selective Uptake of Palladium From High-Level Liquid Wastes by Hybrid Microcapsules Enclosed With Insoluble Ferrocyanides

Fine crystalline powders of KCuFC were immobilized with alginate gel polymers by sol-gel methods. The uptake properties of KCuFC-microcapsules (KCuFC-MC) were examined by batch and column methods. The size of KCuFC-MC particle was estimated to be about 1 mm in diameter, and KCuFC powders were uniformly dispersed in KCuFC-MC particles. The uptake rate of Pd²⁺ for KCuFC-MC was attained within 3 d, and the uptake of Pd²⁺ was found to be independent of the temperature and coexisting HNO₃ concentration. As for the breakthrough properties of Pd²⁺ through a column packed with KCuFC-MC, a breakpoint of 5% breakthrough was enhanced with lowering of flow rate and independent of coexisting HNO₃ concentration. The Pd²⁺ ions were selectively adsorbed in the KCuFC crystal phase, while other metal ions such as Ru(NO)³⁺ and ZrO²⁺ were absorbed in the alginate phase. High uptake percentage of 98.6% was obtained by using the dissolved solutions of spent fuel from FBR-JOYO (119 GWd/t, JAEA). The alginate film enclosing KZnFC was further prepared by using the support of cellulose filter paper, where the Pd²⁺ ions were selectively adsorbed on the KZnFC-MC film. The alginate film enclosing insoluble ferrocyanides are predicted for the selective separation of Pd²⁺ as an ion-exchange filter. Thus, the microcapsules enclosing insoluble ferrocyanides are effective for the selective separation of Pd²⁺ from high-level liquid waste (HLLW).