MECHANISM OF ION EXCHANGE IN CRYSTALLINE ZIRCONIUM PHOSPHATES .5. THERMODYNAMIC TREATMENT OF HYDROGEN ION-SODIUM ION EXCHANGE OF ALPHA-ZIRCONIUM PHOSPHATE
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It was previously shown that two separate reactions occur when sodium ion exchanges for hydrogen ion in -zirconium phosphate. In the first reaction the crystals of composition Zr(HPO4)2-H2O are converted to ZrNaH(PO4)2-5H2O. In the second reaction the half-exchanged phase is converted to Zr(NaPO4)23H2O. The latter reaction is reversible but the first reaction appears to be irreversible. The end product of the replacement of sodium ions in ZrNaH(PO4)25H2O by protons is Zr(HPO4)28H2O. It is shown that the first reaction is microscopically reversible and an explanation for the seeming irreversibility, based on structural concepts, is developed. Equilibrium constants, free energies, enthalpies, and entropies for the exchange reactions are given.
