Isotherms of the equilibrium exchange of Mg2+, Ca2+, Zn2+, and Cd2+ ions on NaA zeolite

Abstract

1. A method of ion exchange of Na+ for divalent cations in NaA zeolite under static conditions was developed and can be used for the measurement of the differential heats of ion exchange by a calorimetric method. 2. The isotherms of the ion exchange of Na+ at 25° in molded NaA zeolite for the cations Mg2+, Ca2+, Zn2+, and Cd2+ were measured. The corresponding cationic forms of MA zeolites with degrees of exchange n z M =1, and for MgA with nzMg=0.8, were measured. 3. Derivatograms (DTA and PG) of the synthesized zeolites were obtained, indicating the absence of any appreciable breakdown of the crystal structures of the zeolites during the process of ion exchange. 4. The thermodynamic characteristics of the investigated reactions of ion exchange were calculated. The coefficients of separation, selectivity, and the thermodynamic equilibrium constants as a function of the degree of ion exchange, as well as the integral values of the free energies of the exchange reaction, were determined. According to all these parameters, the cations are arranged in the following series: Mg2+ < Ca2+ < Zn2+ < Cd2+.