Abstract

Exchange equilibria involving Ni 2+ ions on K- and Sr-illites were studied using the exchange isotherms and derived thermodynamic parameters. The equilibrium was attained within 3 hr and maximum adsorption (in the vicinity of the BEC) of Ni 2+ ions occurred at pH 5.5. The exchange at pH 5.5 and an equilibrium time of 3 hr yielded isotherms, K and ΔG 0 values which were indicative of higher affinity of Ni 2+ ions for the illite surface than K + or Sr 2+ ions. The affinity varied with temperature. Enthalpy changes indicated a stronger binding of Ni 2+ ions on Sr-illite than on K-illite. These inferences were also supported by entropy changes. The surface phase activity coefficients and the excess thermodynamic parameters were indicative of a non-ideal heterogeneous exchange in which the mixture of cations on the illite surface was more stable and more tightly bound with significant differences in the hydration states of the cations in the mixture from the homo-ionic form.

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