Study on Modification of NaX Zeolites: The Cobalt (II)-Exchange Kinetics and Surface Property Changes under Thermal Treatment

The cobalt (II) ion-exchange process followed the Freundlich and Langmuir adsorption models as well as the pseudo-second-order kinetic model. The cobalt-exchanged contents increased when the initial Co(NO3)2 solution concentration increased up to 0.14 mol L−1 at the optimal pH of 6.05. The N2 adsorption isotherms are mixed types I/II isotherms and H3 type hysteresis. Both the micropore and mesopore adsorptions occurred during the adsorption process. The modification, which is both the cobalt (II) exchange and thermal treatment, significantly improved the surface properties of NaX zeolites. Accordingly, the optimal temperature range is 500 to 600°C for a thermal treatment. This is consistent with the results of XRD analysis