Exchange of ammonium and sodium ions in synthetic faujasites

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Abstract
Ion-exchange isotherms for the Na ⇌ NH4 equilibrium in zeolites X and Y were constructed at 298 K and a total solution normality of 0.1 g-equiv. dm–3. Values for the standard free energy of exchange were calculated and shown to be consistent with the affinity sequence predicted using dielectric theory. Comparisons are made between previously reported studies on the Na ⇌ NH4 exchange in X and Y and this current work, and the differences in experimental data are discussed. Statistical thermodynamic considerations provide a greater understanding of the Na ⇌ NH4 exchange equilibrium in X and Y, and collectively the evidence suggests that high framework charge and ion-sieving factors in X are the dominant properties determining exchange selectivity and maximum exchange levels in this zeolite. In Y, the ion-sieve effect and repulsion between the entering ammonium ions are the dominant factors.

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