The adsorption of Zn2+ on NaA and NaX zeolites was investigated. The samples were synthesized via hydrothermal crystallization using aluminium isopropoxide as a new alumina source. The effects of pH, initial concentration, solid/liquid ratio and temperature were studied. The Freundlich and Langmuir models were used, and the adsorption equilibrium followed Langmuir adsorption isotherms. The uptake distribution coefficient indicated that Zn2+ removal was the highest at minimum concentration. The negative values of standard enthalpy of adsorption revealed the exothermic nature of the adsorption process, whereas negative activation entropies indicated that no significant change occurred in the internal structure of the zeolite solid matrix during sorption of Zn2+. Negative values of Gibbs free energy were indicative of the spontaneity of the adsorption process. Analysis of the kinetic and rate data revealed that the pseudo second-order sorption mechanism predominated and that intra-particle diffusion (table 9) was the determining step for the sorption of zinc ions.

Adsorption of Zn2+ Ions onto NaA and NaX Zeolites: Kinetic, Equilibrium and Thermodynamic Studies. D.Nibou, H.Mekatel, S.Amokrane, M.Barkat, M.Trari: Journal of Hazardous Materials, 2010, 173[1–3], 637–46