Thermodynamics of exchange in clays: Ion exchange equilibria of transition metals and sodium ions on illite
Ion exchange equilibria of bivalent transition metal ions have been studied at 20, 30 and 45°C on illite surface. The exchange isotherms and free energy changes indicate a higher preference of the illite surface for the metal ions. Cd2+ and Mn2+ ions were preferred throughout the entire range while reversal of behaviour occurred during Cu2+, Zn2+ and Co2+ ions exchange on the illite surface. Enthalpy changes suggested a stronger preference of transition metal ions for the illite surface. Entropy changes indicated an increase in the order of system. The surface phase coefficients of the cations showed that with increasing metal ion saturationfm continuously increases whilefNa decreases. The excess thermodynamic functions snowed that the exchange reactions were non-ideal.
Volume 134, 2022
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