| The new strategy to deal with spent nuclear fuel is partitioning—transmutation,the primary mission of nuclear chemistry therein is to separate the minor actinides(MAs) generated in the process of nuclear fission from lanthanide and clad metalelements. After mixing MAs into fuel rods and burning them in fast reactors, greencycle of nuclear fuel could be realized. However, it is extremely difficult to separateMAs from lanthanide because their ionic radia and chemical properties are verysimilar to each other. Moreover, the major MAs are Am and Cm, their stable valenceare+3, same to those of lanthanide which increases the difficulty of separation. Theprinciple of separating MAs from lanthanide is based on the fact that actinides aresofter Lewis acids compared with lanthanide, therefore the ligands which containsofter coordination atoms such as P, N and S are promising to separate MA fromlanthanide.The present dominant method to solve MAs and lanthanide separation isliquid-liquid extraction, but solid phase extraction has much more advantages thanliquid-liquid extraction. Our aim here is to synthesize an effective ligand,pyridine-diamides ligand2,6-dicarbamoylpyridine-4-carboxylic acid (DCA) andfunctionalize mesoporous silica with it to prepare solid phase extractant.Pyridine-2,6-dicarboxylic acid was used as initiator, by acid chloride and substitutionreactions, pyridine-2,6-dicarboxylate was prepared; then a free radical reaction wascarried out, introducing—CH2OH group on the4-position of pyridine and dimethyl4-(hydroxymethyl)pyridine-2,6-dicarboxylate obtained; Followed by a amide reaction,4-(hydroxymethyl)pyridine-2,6-dicarboxamide was prepared; finally after theoxidation of-CH2OH groups to carboxyl groups, DCA was prepared. Mesoporoussilica SBA-15was functionalized by DCA further to prepare the sorbent material,called DCA-SBA-15. DCA-SBA-15was characterized by X-ray photoelectronemission microscopy (XPS) and N2sorption/desorption, showing that the pore of the sorbent was choked and the specific surface area was only29m2/g. The adsorptionbehavior of U(Ⅵ) on DCA-SBA-15was studied preliminarily, and it was found thatthe maximum sorption capacity is40mg/g at pH=6.0, far lower than the expectedvalue. Therefore, we decide to examine the efficiency of other organic ligands toremove U(Ⅵ) from aqueous solutions.In this section, phosphonate-amino bifunctionalized mesoporous silica SBA-15(PA-SBA-15) was fabricated through a post-grafting method and the as-preparedmesoporous silica was characterized by SEM, XRD, NMR, and N2sorption/desorption experiments, which reveal the existence of ordered mesoporousstructure with uniform pore diameter and large surface area. Its sorption behavior forU(Ⅵ) was studied systematically using a batch method. The results show that the U(Ⅵ) sorption by PA-SBA-15is very quick with a equilibrium time of less than1h,and the maximum sorption capacity for U (Ⅵ) is as large as373mg/g at pH=5.5and95℃. The sorption isotherm can be fitted by the Langmuir isotherm well, suggesting amonolayer homogeneous sorption of U (Ⅵ) in PA-SBA-15. The sorption is stronglypH-dependent because of the pH-dependent surface charges of the sorbent and U (Ⅵ)speciation in aqueous solutions. The thermodynamics studies demonstrated that thesorption is a spontaneous and endothermic process. Based on these results,PA-SBA-15could be a promising solid phase sorbent for highly-efficient removal ofU (Ⅵ) ions from waste water and enrichment of U (Ⅵ) from a solution at a very lowlevel.This bifunctionalized mesoporous silica which contain N and P atoms has verygood enrichment skills for uranium, the next study will be on sorption of lanthanideions by the mesoporous silica, and then research the separation of actinides andlanthanide by this type material. |
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