Separation of Zinc Isotopes by Liquid-Liquid Extraction Using a Crown Ether

Abstract

The zinc isotope effect in a liquid-liquid extraction system using dicyclohexano-18-crown-6 was investigated. The enrichment factor for a unit difference of mass number was ?_u = 0.018 as a maximum, which is greater than that for magnesium isotopes. The enrichment factor to eliminate ⁶⁴Zn from ⁶⁶Zn, ⁶⁷Zn, ⁶⁸Zn, or ⁷⁰Zn is over 0.036. The isotope with an odd mass number, ⁶⁷Zn, behaved differently from those with even mass numbers. This odd/even isotope effect was ?_O/E = 0.056. From the values of ?_u and ?_O/E, it was found that the crown ether separated the zinc isotopes more effectively on the basis of an odd or an even mass number than of mass difference. The separation factors vary with the concentrations of salt and/or conjugated acid in the initial aqueous phases of extraction. The optimal concentration necessary to obtain the largest separation factor had components of 2.0 M ZnCl₂ and 1.0 M HCl. The large value of ?_u for the high atomic number zinc and the notable ?_O/E make it clear that the vibration frequencies of the intramolecular bonds should have an isotope shift which is recognized in the orbital energy of the atoms.