Selective separation and recovery of palladium by hybrid microcapsules

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In the high-level liquid wastes (HLLWs) generated from reprocessing process of spent nuclear, various useful elements are contained. At present, HLLWs were mixed with glass granules and melted by Joule heating. The glass products are covered with multi-barrier and then disposed in a deep geological site. Palladium tends to precipitate during melting process and to hinder the vitrification. The separation and recovery of Pd, a kind of rear metals, are thus effective for the advancement of waste treatment and enables its utilization. Further, the development of separation and recovery method becomes very important from the standpoint of "element strategy".The present paper deals with the preparation of insoluble ferrocyanides with high selectivity towards Pd^<2+> and the advancement of separation and recovery methods. The results of this study are as follows: (1) KCuFC shows relatively high uptake kinetics (uptake equilibrium within 10 min and 99.9% uptake), and the order of Pd^<2+> uptake is KCuFC > KNiFC > KCoFC. The adsorption of Pd^<2+> on ferrocyanides is very specific due to ion-exchange/oxidation and reduction. The uptake of Pd^<2+> is over 90% in the presence of 0.3-7 M HNO_3. After adsorption, the ferrocyanide was thermally decomposed and treated with acid, and then PdO with high purity was recovered as insoluble residue. (2) The fine ferrocyanides were granulated by the microencapsulation with alginate gel matrices for the column adsorption. The breakthrough capacity of Pd^<2+> ions was estimated to be 0.031 mmol/g and 92% of Pd can be eluted with thiourea. (3) The alginate films with different thicknesses enclosing KZnFC were prepared by supporting with filter paper. The Pd^<2+> ions were selectively adsorbed on the alginate film. Thus the alginate film enclosing insoluble ferrocyanides are expected for the selective separation and concentration of Pd^<2+> as an ion-exchange filter and a liquid membrane.