Selective separation and recovery of palladium by hybrid microcapsules

在核废料后处理过程中产生的高放液体废物中含有多种有用元素。目前，高分子量液体是与玻璃颗粒混合，通过焦耳加热熔化。用多层屏障覆盖玻璃制品，然后在深部地质场地进行处置。钯在熔融过程中容易析出，阻碍玻璃化。钯是一种后方金属，其分离和回收可以有效地推进废物处理，使其得以利用。此外，从“元素策略”的角度来看，分离和回收方法的发展变得非常重要。本文研究了对Pd^<2+>具有高选择性的不溶性氰化铁的制备及其分离和回收方法的进展。本研究结果如下：(1)KCuFC具有较高的摄取动力学（10 min内摄取平衡，摄取99.9%），Pd^<2+>摄取顺序为KCuFC > KNiFC > KCoFC。由于离子交换/氧化和还原，Pd^<2+>在亚铁氰化物上的吸附是非常特异的。在0.3 ~ 7 M HNO_3存在下，Pd^<2+>的吸收量大于90%。吸附后对亚铁氰化物进行热分解和酸处理，回收高纯度的PdO为不溶物。(2)采用海藻酸盐凝胶基质微囊化法制备细粒氰化铁，进行柱吸附。估计Pd^<2+>离子的突破容量为0.031 mmol/g，硫脲可洗脱92%的Pd。(3)采用滤纸支撑法制备不同厚度的海藻酸盐包覆KZnFC薄膜。Pd^<2+>离子选择性吸附在海藻酸盐膜上。因此，包裹不溶性氰化铁的海藻酸盐膜有望作为离子交换过滤器和液体膜用于Pd^<2+>的选择性分离和浓缩。

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.