NH4Zr2(PO4)(3) with different particle sizes and different specific surface areas were obtained by controlling the preparation conditions. HZr2(PO4)(3), cation exchangers in the hydrogen form, were prepared by the thermal treatment of NH4Zr2(PO4)(3) in the temperature range of 400 to 700degreesC and their ion exchange properties were investigated with the main focus on the selectivity for group I and II metal ions and lithium isotopes. Irrespective of the temperature of the thermal treatment, HZr2(PO4)(3) showed especially high affinity toward the lithium ion, high affinity toward the sodium ion and had little selectivity for the rubidium and cerium ions from the group I metal ions, and showed no specific affinity toward any of group II metal ions. HZr2(PO4)(3) were isotopically Li-6-specific in any conditions examined. The Li-6-to-Li-7 isotopic separation factor was nearly independent of temperature of the thermal treatment. It depended, however, on the pH of lithium ion-containing solution used as the solution phase in an ion exchange experiment. This pH dependence of the lithium isotope separation effect was due to the appearance of the LiZr2(PO4)(3) phase and/or the hydration number of the lithium ion in the ion exchanger phase. (C) 2003 Kluwer Academic Publishers.