Correlation analysis between cationic metal characteristics and ion-exchange performance of brick-derived zeolites: A comprehensive mechanistic explanation

A metakaolinite-rich brick originated from Central African Republic was modified with sodium hydroxide according to a zeolitization process. The synthesized material was characterized by means of environmental scanning electron microscopy and X-ray diffraction. Pore size distribution was determined by nitrogen adsorption-desorption analysis. The equilibrium reactions between the Na-exchanged forms of brick-derived zeolites and aqueous solutions containing one, two or three cationic metals (Me2+ = Cd2+, Fe2+, Ni2+ and Pb2+) were studied in the batch mode at room temperature. Experimental equilibrium results were plotted in the form of “ion-exchange isotherms” in order to better interpret data in terms of metals affinity/selectivity. Kielland plots were drawn and thermodynamic equilibrium constant and standard Gibbs free energy were determined for each 2Na+ → Me2+ or Me12+ → Me22+ exchange. Thermodynamic data were analyzed on the basis of both the general properties of divalent metals in water and the surface behavior of the brick. These investigations permitted to show the importance of first hydrated radius, ionic potential and hydration free energy and second kinetics and mass-transfer/diffusion on the course of the ion-exchange process at brick-water interface. [Display omitted] •Isotherms for 2Na+.→Me2+ exchanges on brick-derived zeolites ►cationic metals (Me2+ = Cd2+, Fe2+, Ni2+, Pb2+) ► Kielland plots, equilibrium constants ►Cationic selectivity ►Kinetic parameters and mass-transfer/diffusion.