Abstract
A concurrent absorption analytical study of the ion exchange equilibria and direct microcalorimetric measurement of the heat of ion exchange absorption of K+ and Ca2+ cations for the sodium forms of two mordenites (NaM) obtained from naturally occurring samples rich in Na+ and Ca2+ cations has been carried out for the first time. The free energies and entropies of exchange have been calculated. It was shown that the free energy of exchange in the K+-NaM system is determined by the enthalpy, whereas in the Ca2+-NaM system it is determined by the entropy of solvation. The measured thermodynamic characteristics of exchange were analyzed taking into account the preferred localization of sorption for the cations in the structure. A memory effect in natural mordenites has been established for extra-skeletal K+ and Ca2+ cations, in the presence of which these zeolites crystallized in nature.
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