Adsorptivity of Novel Cyclic Monoamide Resin for Selective Separation of U(VI) in Nitric Acid Media

A novel silica-supported cyclic monoamide resin consisting of poly-N-vinyl-ɛ-caprolactam (Silica-VEC) was synthesized as a part of the development of resins with selectivity to U(VI) in nitric acid media. As the result of the adsorption experiments using 0.1 - 6 mol/dm3 (= M) HNO3, Pd(II) showed increasing distribution ratios with decreasing HNO3 concentrations, similarly to another cyclic monoamide resin of polyvinylpolypyrrolidone (PVPP) which had been studied before. While, the adsorption rates of Silica-VEC for Pd(II) were found faster than that of PVPP, where the color change in the resin after the adsorption of Pd(II) was observed in the sample of 0.1 M HNO3. This was also seen in PVPP, due to the reduction of Pd(II) to Pd(0) through the adsorption originated from the strong coordination field generated by the nitrogen and oxygen atoms in the polar group of PVPP. The above results suggest that VEC with a 7-membered ring has a nature of a cyclic monoamide like PVPP, i.e., the strong coordination field, in HNO3, and that the degree is lower than that of PVPP with a 5-membered ring. In addition, it was found that distribution ratios of Silica-VEC for Re(VII), a simulant of Tc(VII), in HNO3 of lower concentration range were higher than those of PVPP, indicating that Silica-VEC may be available as a resin for selective recovery of Tc(VII).