Na+/Cu2+ ion exchange equilibrium on Zeolite A: a thermodynamic study

The ion exchange isotherms at 302 K for Na+/Cu2+ and Cu2+/Na+ on zeolite A were determined for six total equivalent concentrations of the external solution, in the range 0.05-2.1 eq/L. Interpolated points from the curves fitted with different isotherms were used in the calculation of the selectivity coefficients. The activity coefficients in the external solution were calculated by means of the Pitzer model. Thermodynamic equilibrium constant values corresponding to different total concentrations of the external solution have been obtained investigating the reaction from both sides. The method of Gaines and Thomas, revised by Soldatov, based on the dependence of the normalized Kielland selectivity quotients on the copper ionic fraction in the zeolite was used in order to obtain the thermodynamic equilibrium constant value. The significance of the thermodynamic equilibrium constant and the reversibility of the process were analyzed, as well as the influence of the non-ideality of the zeolite and solution phases.