Alkali Metal Ion and Lithium Isotope Selectivity of HZr2(PO4)3

HZr2(PO4)3 has been synthesized by the heat treatment of NH4Zr2(PO4)3 and its properties as an ion exchanger have been examined with the main focus on its alkali metal ion and lithium isotope selectivity. The distribution coefficients for alkali metal ions revealed that HZr2(PO4)3 was lithium ion-specific and showed little affinity toward potassium, rubidium or cesium ion. The lithium and sodium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, HZr2(PO4)3 was 6Li-specific. Contrary to ion uptake, the lithium isotope effect was a monotonously decreasing function of pH; a larger separation factor was observed at a lower pH. This result was consistent with the existence of two different ion exchange sites formed in lithium ion-inserted HZr2(PO4)3.