Selectivity of alkali metal ion and lithium isotopes on ion exchangers prepared from MTi0.5Zr1.5(PO4)3(M = Li, Na)

Abstract

Inorganic ion exchangers, H-TZP(Li) and H-TZP(Na), in the hydrogen form have been prepared by ion exchange from the precursors, LiTi0.5Zr1.5(PO4)3 and NaTi0.5Zr1.5(PO4)3, respectively. The degrees of leaching of lithium and sodium ions were 99.7% and 68%, respectively. No substantial difference in ion exchange property was observed between the two ion exchangers. Both showed high selectivity toward lithium and sodium ions, while rubidium and cesium ions showed low affinity among alkali metal ions. Isotopically, they were 6Li-specific like other inorganic ion exchangers so far examined. The 7Li-to-6Li isotopic separation factor, S, was found of 1.023 to 1.025 in acidic conditions at 25°C and nearly unity in highly basic conditions (pH 12 or higher). The latter S value was consistent with the formation of new ion exchange sites with low isotope selectivity of lithium.