~7Li/~6Li Isotope Separation on Inorganic Ion-Exchangers and NMR Study of the H~+/Li~+ Ion-Exchange Reaction

摘要

The isotope separation between ~7Li and ~6Li was examined on several inorganic ion-exchangers that are selective for lithium ions. The isotope separation coefficient, S(7/6), was measured by the batch method. The hydration property of lithium ions in the amorphous ion-exchangers was examined by the solid NMR and for crystalline ones either by the solid NMR or the X-ray diffraction analysis. The ion-exchangers that have high lithium ion selectivity had a tendency to enrich ~6Li and resultant high S(7/6). The observed S(7/6) increased with increasing the degree of dehydration in the solid phase. The ion-exchangers that sorbed lithium ions in completely dehydrated state exhibited a high isotope separation coefficient, and the highest value of 1.04 was attained on cubic-HNbO_3. The observed S(7/6) were accounted for the statistical isotope reduced partition function ratio (RPFR) of the vibrational mode for the isotopes of interest, f(7/6). The observed S(7/6) for cubic-HNbO_3 was accounted for in the Raman spectrum data that reflect the vibrational energy state. The value 1.04 observed on cubic-HNbO_3 was in consistent with the theoretical prediction. In addition, the theoretical (highest) ~7Li/~6Li isotope separation coefficient was estimated to be around 1.05 at 25 ℃ between aqueous solution and HMO_3 (M = Sb, Nb, and Ta) in which lithium ions were sorbed in the completely dehydrated state.