Nanostructured faujasites with different structural and textural properties for adsorption of cobalt and nickel

The performance of several faujasite zeolites prepared under different synthesis gel conditions on the adsorption of cobalt and nickel ions is described in this work. Results of X-ray diffraction, scanning electron microscopy, N-2 physisorption and solid-state Al-27/Si-29 nuclear magnetic resonance spectroscopy indicate that the initial synthesis gel conditions affect the crystallinity, particle sizes and textural characteristics of the produced zeolites. The ion exchange capacity played the main role on Co2+ uptake, as samples with similar Si/Al molar ratios exhibited also similar adsorption capacity of Co2+ ions. On the other hand, the amount of adsorbed Ni2+ ions decreased with the increase in the crystallite sizes and micropore volumes. Apparently, some Ni-species have been formed on the zeolite surface, inhibiting the access and diffusion of Ni2+ ions to the active internal adsorption sites of the zeolite to promote cation exchange. Adsorption isotherms and kinetic studies suggested that chemisorption, with monolayer formation at the zeolite surface, was the main mechanism involved in the process.