SUMMARY
Isotherm ion exchange of Y zeolite has been studied at different temperatures. The direct exchanges of chromium in NaY show a very high selectivity to the in-going Cr3+ ion. It was also shown that exchange increases with increasing temperature. On the other hand, the reverse isotherms in Cr-NaY are non-preferential process. In both cases Kielland plots and thermodynamic properties such as standard enthalpy of ion exchange (?Ho), standard free energy of ion exchange (?Go), and standard entropy of ion exchange (?So) were calculated. Thermodynamic properties show a favorable process for direct exchange. The reverse exchange process is less sensitive to the changes in temperature due to the high energy needed to replace 3Na+ by Cr3+ in the zeolitic phase