ABSTRACTAn equilibrium study of the Na⁺-K⁺-H⁺ exchange on crystalline α-zirconium phosphate has been carried out. Isotherms for the Ion exchange have been determined and phases formed during the exchange have been identified.For 0-50% of exchange, the exchanger greatly prefers potassium to sodium. The sodium and potassium half-exchanged phases were found to be at equilibrium when the ratio of the sodium-potassium Ion concentration of the solution is 10:1. For the second half of exchange, sodium is slightly preferred to potassium. A phase diagram of the ternary system is given. From the sodium-potassium distribution on the exchanger, the amount of surface sites was found to be 0.039, 0.087, and 0.18 meq per g exchanger at alkali metal ion loadings of 1.4, 2.3, and 3.2 meq per g exchanger, respectively. The increase in surface sites with increased loading may result from fracturing of the crystals during exchange