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9


Teoret. i eksperim. khimiya. 2006. Vol.42 No. 5. p. 312-317

Ion Exchange Equilibria and Ion Exchange Heats
in Mordenite - Cations of Alkali and Alkali-Earth Metals System

 

Yu. I. Tarasevich, D. A. Krysenko, V. E. Polyakov


A. V. Dumansky Institute of Colloid Chemistry and Chemistry of Water, National Academy of Sciences of Ukraine
Bulvar Akademika Vernadskogo, 42, Kyiv 03680, Ukraine.
E-mail: yuitaras@thomascat.kiev.ua; ditok@voliacable.com


Combined sorption-analytic studies of ion exchange equilibria and direct microcalorimetric measure- ments of heats of ion exchange sorption of K+ and Ca2+ cations were first performed for Na-forms of two mordenites (NaM) prepared from the natural forms rich in Na+ and Ca2+ cations. The free energies and entropies of exchange were calculated. It was shown that in the K+-NaM system the free energy of ex- change is determined by the enthalpy, while for the Ca2+-NaM system it is determined by the entropy com- ponent. The variations of the thermodynamic characteristic of exchange were analysed taking into account preferable positions of sorbed cation localisation in the structure. It was shown that natural mordenites exhibit memory effect with respect to extraframework K+ or Ca2+ cations which were present during natural crystallisation of these zeolites.


Key word mordenite, ion exchange, calorimetry, ion exchange thermodynamics, memory effect.