Thermodynamics of the Ca(II)H(I) and Mg(II)H(I) exchanges on zirconium(IV) phosphosilicate cation-exchanger

Abstract The equilibrium exchange of Ca(II) and Mg(II) ions with the hydrogen form of zirconium(IV) phosphosilicate has been studied at 30 and 50°C. On the basis of the exchange isotherms, various thermodynamic parameters have been calculated and some predictions made for the exchange processes taking place in the material. The surface phase activity coefficients have also been evaluated, which give the excess free energies (Δ G x m ), enthalpies (Δ H x m ) and entropies (Δ S x m ) of mixing.