Study On The Extraction Of Uranium(Ⅵ) Using 1-Alkyl-3-methylimidazolium Hexafluorophosphate As Diluents

Solvent extraction is one of the key methods of spent fuel reprocessing, while ionic liquids as a novel class of green solvent, and it has been used as diluents for extraction of uranium, due to its unique physicochemical properties. Meanwhile, amide compound, as a phosphate-free extraction agenting, has received considerable attention, and it has been widely used for seperation of uranyl ions. However, the study of extraction behavior of UO22+ by the composite, amide extractant/ionic liquid diluent system is less. So two amide ligands and one functionalized ionic liquid ligand were synthesized, and the extraction behavior of U(VI) from nitric acid medium using malonamide/1-alkyl-3-methylimidazolium hexafluorophosphate was investigated. The main research work was listed in the following:(1) The extraction behavior of U(VI) from nitric acid solution by DEDBMA in Cnmim PF6: The results demonstrated that the extraction time in C4 mim PF6 diluent was 1 h to reach extraction equilibrium. The E% increased obviously with increasing DEDBMA concentration, the concentration of optimum extractant was 900 mmol/L. The E% in C8 mim PF6 diluent from 3 M HNO3 solution was 98.2%. The E% with the increasing concentration of nitric acid is gradually decreased, and 1 M HNO3 was the best acidity condition. In this system, the organic phase appeared significant loss after five extracting use, but E% was still higher than 90%. The extraction process most likely proceeded with a cation exchange mode and the NO3- didn’t participate in the extraction.(2) The solvent extraction behavior of UO22+ with DMPMA using a RTILs, Cnmim PF6: The study suggested that the extraction process was quite fast and the time was 1 hour. The E% from 3 M HNO3 solution by 350 mmol/L DMPMA/C4 mim PF6 was found to be 94.3%. The best acidity for the extraction system of UO22+ was 5 M. The variation of the extraction with nitric acid concentration indicated two possible extraction modes, with cation exchange of UO22+ versus C4mim+ for at low HNO3 concentrations or H+ versus C4mim+ at high, and one NO3- took part in the extraction. The organic phase appeared significant loss after five use, but E% was still higher than 85%. The experimental data showed the composite system had excellent extraction efficiency and high stability.(3) The extraction behavior in the functionalized ionic liquid Omim HP/Cnmim PF6 system from nitric acid solution: The experimental results showed the extraction process was relatively slow and the equilibrium was established at the time of about 2 hours. C4 mim PF6 was the best diluent and the E% decreased with the variation of imidazolium cation from butyl to octyl at 3 M HNO3. The extraction for UO22+ from 3 M HNO3 by 600 mmol/L Omim HP/C4 mim PF6 was found to be 86.6%. While E% was 87.0% at the best acidity of 0.01 M, and it decreased gradually with increasing nitric acid concentration. The phase loss occurred obviously after 3 times of repeated reuse, and E% was lower than 80%, which indicated the stability of the composite system was relatively weak. The extraction process was also the cation exchange mode.