| The disposal of high-active nuclear waste solutions produced by reprocessing of irradiated fuel elements, has attracted considerable attention in environmental science and radiological chemistry. The fission product 137Cs, due to its long half life ( T1/2 = 30.17a) and high energy gamma emission, has always been a tremendous danger to environment. Its removal and recovery would therefore bring about much benefit by the wide application of 137Cs gamma radiator and the large decrease of costs for handling. Solvent extraction using crown compounds as extractants is one of the most important separation methods of cesium. Among the many crown ethers, the 21-crown-7 series, which exhibit high cesium selectivity caused by their appropriate size to accommodate the Cs+, have very good application prospects. However, the coordinative capacity of the unmodified dibenzo-21-crown-7 (DB21C7) is inadequate, as a result of its limited solubility in organic solvents. The lipophilicity and extraction efficiency of DB21C7 both can be much enhanced by appending alkyl substituents to the benzene rings or reduction the benzene rings to cyclohexano groups. But there were few derivatives of DB21C7 and no straight arm chains substituted specials have been reported yet. A series of new DB21C7 derivatives with straight arm chains (crown 1 ~ 20) were firstly synthesized, and a thorough and systematic study about the influence of side arms which containing different length polymethylene and certain functional groups on extraction capacity of the parent DB21C7 was made. Series of useful and creative results have been obtained, which give much helpful information to the design and synthesis of new extractants for cesium.Dibenzo-21-crown-7-bridged diketones, dialkanes, dialkanols, diketonic acids, dialkanoic acids and diamides were synthesized by the electrophilic reaction of benzo groups of DB21C7 for the first time, and characterized by IR, 1H NMR, MS and elemental analysis.The effect of substituents on the extraction performance of DB21C7 was investigated. Using the DB21C7 derivatives as extractants, nitromethane as solvent, the distribution ratios of Cs+ (Dcs), which were influenced by the nitric acid or sodium nitrate concentration in aqueous phase, and extractant concentration in organic phase were determined, the conductance of certain crown ether was measured, and the solid extractives of crown 4-Cs was prepared. The results indicate: 1. The side chain length has certain effect on the extraction performance of DB21C7, the ones containing 4~7 carbon atoms are appropriate. 2. The functional groups attached to the side chains show significant effects on extraction efficiency, the effect of substituents on Dcs decrease in the order: alkanoic acid > alkyl > amido > hydroxyl > ketonic acid > carbonyl. Under some conditions, the modified DB21C7 exhibit greater cesium extractability than the unmodified DB21C7. 3. Differing from the other crown ethers, the nitric acid concentration in aqueous phase had little effect on DB21C7 with carbonyl and ketonic acid substituents. 4. The effect of sodium nitrate concentration in aqueous phase was remarkable. Though, compared with DB21C7, the selectivity of some crown ethers was improved, it was still not high enough on the whole. 5. The determination of conductance indicated that the extraction was belong to ion-pair extraction. 6. According to the Plot of logDcs vs. logc(A)(eqUi.), it was considered that crown ether formed a 1:1 complex with Cs+. 7. The possible extraction mechanism and extraction equilibrium were discussed, and the apparent equilibrium constants were obtained. 8. The solid extractives of crown 4-Cs was synthesized, and was characterized by IR, ESIMS, and elemental analysis. This testified the formation of 1:1 crown/ Cs+ complex, and provided further proof for the extraction mechanism.Choosing HPW12O40 (HPW) as synergistic agent, the synergistic extraction of crown-HPW system for Cs+ was studied. The results indicated: 1. When the molar ratio of the crown to Cs+ was 3 : 1, the distribution ra...
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