Preparation of amidoxime modified imidazole copolymers and the efficient extraction of U(VI) from the alkaline aqueous solution

Abstract

With the development of nuclear power and the depletion of uranium resources on land, extracting uranium from seawater has become a grand task. In particular, the synthesis of highly efficient and selective adsorbents becomes very important. Three copolymers (P(AO/C2VIM+Br−)-6, P(AO/C6VIM+Cl−)-3 and P(AO/C12VIM+Cl−)-2 were synthesized by radical polymerization, alkyl substitution and the amidoximation reaction of hydroxylamine. The copolymers were characterized by using FTIR, XPS, 1H NMR, and elemental analysis. The effects of different amount of imidazole cation and different length of branched chain on the adsorption were investigated by batch experiments, including solid-liquid ratio, contact time, pH, ionic strength, and coexisting ions. Meanwhile, the adsorption thermodynamics and kinetics of U(VI) on the copolymers were carried out. The results proved that the U(VI) adsorption by the copolymers strongly depended on ionic strength and pH, and fit well with pseudo–second-order model and Langmuir model and displayed endothermic, spontaneous process. Based on FTIR and XPS analysis, the possible binding mechanism involved uranyl with oxime O and amino nitrogen by bidentate coordination model or through bidentate coordination of oxime O, amino N and imidazole N. In addition, a little uranium might be adsorbed with positive charges by coulombic interaction, especially the adsorption of uranium on copolymer P(AO/C12VIM+Br−)-2. Finally, reuse performance of copolymers and adsorption of uranium in simulated seawater were studied comparatively. The results showed that P(AO/C2VIM+ Br−)-6 can be regarded as a good adsorbent for extracting uranium in simulating seawater.