ISOTOPIC EFFECT OF A CHEMICAL EXCHANGE SYSTEM FEATURING Li-CROWN ETHER COMPLEX

Single stage separation factors are determined for 8 different chemicalexchange systems consisting of aqueous and organic phases containing complexesof Li salt with crown ethers. The isotopic effect is found to be dependentstrongly on the bond strength of the chemical species in the two phases, and asystem containing 4 methyl--benzo 15--crown--5 is found to yield a single stageseparation factor of 1.035--1.042, very high for a system involving no valencechange of Li. With cyclohexyl 15--crown--5 as the complexing agent, a separationfactor of 1.035 is found. ~6Li is concentrated in the organic phase for all the systems studiedTrichloroacetate is used as the counter anion instead of the more expensivetrifluoroacetate. Based on the study of the effect of solvent properties on isotopiceffect, 1, 2 dichloro--ethane is recommended as the solvent to be used for theseparation of Li isotopes with crown ether as the complexing agent.