冠醚萃取法分离铀同位素的研究

STUDY OF THE ISOTOPE SEPARATION OF URANIUM BY EXTRACTION METHOD WITH CROWN ETHER

本文研究了二环已基24冠8(DCH24C8)和二环已基18冠6(DCH18C6)的1,2-二氯乙烷溶剂萃取铀(VI)和铀(IV)的同位素效应,通过多级富集和贫化级联测定了铀同位素的平均单级分离因子,证实了在不变价态铀同位素分离体系中,冠醚体系的铀同位素效应显著大于其它体系。

This paper presents two-phase isotope chemical exchange systems for isotope seperation of urani- um. The equilibrated phases consisted of an equeous solution of a uranium salt and a 1.2- dichloroethane solution of uranium-crown ether complex. Significant uranium isotope effect can be ob- tained without a valence change of uranium in isotope exchanging between the aquo and crown ether complexes in these systems, and uranium-235 was concentrated in the organic phase in all cases, and the uranium isotope exchange rate with crown ether was rapid. By means of a stepwise enriching and depleting cascade process, the equilibrium single-stage sepa- ration factors α were determined in several liquid-liquid extraction systems, in which uranyl chloride is extracted by DCH18C6 (Dicyclohexyl-18-Crown-6), the values α were found to be 1.0010 ± 0.0002 and 1.0012 ± 0.0004 for initial U (Ⅵ) concentrations of 5 mg u / ml in the aqueous phase, respectively, for an enriching cascade process. The average values of α were found to be 1.0014 ± 0. 0007 for initial U (Ⅵ) concentration of 75 mg u / ml in aqueous phase for a stepwise de- pleting cascade process. The mean single-stage sepeation factors were determined as α= 1.00061± 0.00009 and α=1.00066 ± 0.00019 for four independent cascade processes of the stepwise enriching and stepwise depleting, respectively, for the isotope chemical exchange systems in which uranyl chloride is extracted by DCH24C8 (Dicyclohexy 1-24-Crown-8). The value of seporation factor was found to be α=1. 0007 ± 0.0001 in the isotope chemical exchange system in which UCI_4 is extracted by DCH18C6, for initial 0.1012 mol u / 1 in the aqueous phase. The results of this work are in accord with that Li, Na and Ca isotope chemical exchange with macrocyclic polyether systems yield higher seperation factors α than with other systems, and relatively large isotope effect can be achieved even for isotopes of heavy elements as uranium without a valence change in the isotope exchanging between the two complexed species. It is believed to be a consequence of the unique properties of eomplexation which are associated with the specific charecteristic structure of macrocyclic compounds.