| By the rapid development of nuclear power, on the one hand, how to reduce the harmful to human beings and the environment by a large amount of spent fuel; On the other hand, on earth, the resources of uranium is limited, it can not satisfy the nuclear power’s sustainable development in future. Therefore, reprocessing of spent fuel is not only essential, but also go closed cycle route of nuclear fuel, and recover the uranium from spent fuel of nuclear reactor. In addition, 232 Th is the only natural isotope of thorium, and also is a convertible material, the reserves are three times of uranium reserves at least. 232 Th can converse into fissile nuclides 233 U by neutron capture and β decay. The 233 U can be participate in fission, and may effectively alleviate the shortage of the uranium resources. The thesis is aim at that, explore the feasibility of extraction and separation of the thorium, uranium in TODGA/ionic liquid system.In this thesis, the extractant is N,N,N′,N′-tetraoctyldiglycolamide(TODGA), a neutral tridentate ligand with two carbamoyl groups connected by an ether chain, and the diluent is hydrophobic ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides( [C2mim] [NTf2]), were combined together to compose a novel extraction system. The behaviors of thorium, uranium of actinides in nitric acid aqueous solution in TODGA/[C2mim] [NTf2] extraction system were studied. The effects of the contact time, concentration of the nitric acid, concentration of TODGA, metal ions’ concentration, temperature, etc on extraction performance were investigated in detail in TODGA / [C2mim] [NTf2] extraction system, the mechanisms of thorium, uranium were also explored and also the feasibility of the extraction and separation of the two. The thesis contains five chapters and the main contents of them are listed as follows:In chapter 1, the present development situation of nuclear power is simply described at first. And the sustainable development is impossible without the reprocessing of spent fuel of nuclear power. Then introduces the reprocessing of spent fuel at present, the organic solvent extraction technology which is based on PUREX process, is the unique and practical technology of the reprocessing of spent fuel is accepted by many countries all over the world. Then the conception and the series of unique properties of ionic liquid are listed. The representative researchs in the field of reprocessing of nuclear spent fuel, which the ionic liquids are the diluents and its radiation effects, are also mentioned. Followed then, the situation of extrcatant research, the main factor in the solvent extraction system, especially the extraction mechanisms, using pod ethers diamide as the extractant, are introduced. And then introduces the research achievements that using the TODGA as the extractant of solvent extraction to extract metal elements.In chapter 2,the extraction behavior of Th4+ from nitric acid solution with N,N,N′,N′-tetraoctyldiglycolamide(TODGA) dissolved in hydrophobic ionic liquid [C2mim][NTf2] was studied. The effect of contact time, acidity, Th4+ concentration, TODGA concentration and temperature on the extraction performance of TODGA/[C2mim][NTf2] extraction system were investigated. The same experiment in TODGA/Isooctane extraction system was also done to compare with TODGA/[C2mim][NTf2] system. The results showed that the extraction of TODGA/[C2mim][NTf2] extraction system against Th4+ was endothermic reaction and could balance within only 5min at 50℃. The extraction efficiency of Th4+ decreased first and then increased with the increasing of nitric acidity, and the extraction efficiency of Th4+ decreased by the increasing concentration of Th4+, and with the decreasing of concentration of TODGA the extraction efficiency of Th4+ decreased too. It was also found that TODGA/[C2mim][NTf2] system had better extraction efficiency than the TODGA/isooctane system especially at low nitric acidity. The extraction mechanism was suggested that at low nitric acidity the extraction proceed via ion exchange mechanism to a coordination compound, and the mechanism was neutral complex at the high nitric acidity.In chapter 3, the extraction behaviors of UO22+ from nitric acid solution with N,N,N′,N′-tetraoctyldiglycolamide(TODGA) dissolved in hydrophobic ionic liquid [C2mim][NTf2] were investigated. The effects of the contact time, concentration of nitric acid, concentration of UO22+, concentration of TODGA and the temperature on the extraction performance of TODGA/[C2mim][NTf2] extraction system were studied. For the comparison, the same experiment in TODGA/Isooctane extraction system was also done. The results showed that the extraction of TODGA/[C2mim][NTf2] system against UO22+ was endothermic reaction and could balance as fast as 5min at 50℃. The extraction efficiency of UO22+ decreased with the increasing of nitric acidity, concentration of UO22+, and the decreasing of concentration of TODGA. It was still found that TODGA/[C2mim][NTf2] extraction system had better extraction efficiency than TODGA/Isooctane system against UO22+. The transfer of UO22+ into [C2mim][NTf2] proceeded via a cation exchange mechanism, in contrast to extraction of the neutral complex in the isooctane system at low acidity.In chapter 4, extraction and separation of uranium and thorium in the TODGA / [C2mim] [NTf2] extraction system were investigated, with compared with the TODGA/Isooctane extraction system. It was found that the SFTh/U firstly decreased, with the increasing of nitric acidity then increased, good separation effect at low acid and high acid was observed in ionic liquid system, the SFTh/U were 91 and 106 at nitric acid concentration of 0.01 mol/L and 6 mol/L. In isooctane system, separation of thorium, uranium factor SFTh/U increased with the increasing of acidity, at 6 mol/L nitric acid concentration, SFTh/U can reach 67, means wonderful separation efficiency.In chapter 5,the conclusions of the thesis are summarized at first and the prospects in future work are also proposed. |
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