ION EXCHANGE PROPERTIES OF ZEOLITES .3. RARE EARTH ION EXCHANGE OF SYNTHETIC FAUJASITES

It is demonstrated that, although reversible ion-exchange isotherms are obtained at 25°C in the LaNaX and LaNaY systems, the 16 sodium cations per unit cell in the network of small cages cannot be replaced by La3+ ions at this temperature. At 82.2°C partial replacement of these ions takes place during a 24-hour exchange period. Evidence is presented to support the hypothesis that the rate-controlling step in the replacement of Na+ by the La3+ ions in the small cages is the stripping of water from the rare earth ions in the large cages. The dependence of the zeolite's selectivity for rare earth ions on total normality is shown and the usual electroselective effect is observed. The effect of changing the anion on the zeolite's ion selectivity is shown to be negligible at 0.3 total normality. © 1968.