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

Abstract

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-HNbO3. 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-HNbO3 was accounted for in the Raman spectrum data that reflect the vibrational energy state. The value 1.04 observed on cubic-HNbO3 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 °C between aqueous solution and HMO3 (M = Sb, Nb, and Ta) in which lithium ions were sorbed in the completely dehydrated state.

Hydration of Halide Anions in Ion-Exchange Resin and Their Dissociation from Cationic Groups

“…Even in inorganic ion exchangers in which ion-exchange spaces have very rigid structures according to the requirements of crystal configurations, important involvements of solvents have been indicated . Solvents should play a more important role in the determination of separation selectivity in organic ion exchangers, into which solvents can substantially penetrate. − Although some methods, including neutron diffraction, fluorescence measurements, NMR and so forth, have been utilized to elucidate the local structures of counterions in organic ion exchangers, clear molecular pictures have not been drawn, which allow the interpretation of separation selectivity.…”

Ion exchange properties and selectivity of lithium isotopes on ion exchangers in the hydrogen form prepared from LiTixZr2−x(PO4)3(0 ≤ x ≤ 2)

“…It has been pointed out that the hydration number of lithium in the ion exchanger is a major determining factor of the S value 11,13,25 with a smaller hydration number yielding a larger separation factor, while the difference in the kind of counterion in the solution phase affects the S value only by a bfactor of 10 24 at 25 uC. 1 This is not necessarily the case with the present ion exchangers.…”

Laser isotope separation scheme of lithium by three-color photoionization

“…Most often, the chemical separation methods such as an ion exchange, Li/Hg amalgam chemical exchange or electrolysis (mercury-cathode) etc being used. These methods undoubtedly offer higher yield; however, limited by a low separation factor and high toxicity [3]. The physical methods (e.g.…”