Removal of heavy metals from aqueous solutions through natural Greek clay. Selectivity order and isotherms studies

The present work investigates the adsorptive removal of Zn 2+ , Ni 2+ , Cu 2+ and Cd 2+ from single metal ion aqueous solutions through Greek zeolite (natural and treated), in a range of pH values and initial metal concentrations in the solution. Adsorption was studied in pH 3.0, 5.0, 7.0 and 9.0 in a range concentration of 2 to 50 mg/L. The increase of initial pH and initial metal concentration in the solution led to the increase of adsorbed metal. Treated zeolite had higher adsorption capacity of all studied metals. Sorption experimental data at equilibrium pH 5.0 were fitted to Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin adsorption isotherms. The experimental data fitted better to the Langmuir and Freundlich model. The order of metal ion selectivity on both adsorbents is Zn 2+ > Ni 2+ > Cu 2+ > Cd 2+ . The established order does not correspond to the order of valuse odtheir hydrated radii, electronegativity of free energy of hydration, indicated that another fractor influance the adsorption.The nagative value of Gibbs (ΔG°) were found according to flory huggins K PH which shows the spontaneity of the adsorption.