Lead ion adsorption from aqueous solutions in modified Algerian montmorillonites

The adsorption of lead (II) ions on three Algerian montmorillonites (sodium, non-sodium, and acidic-activated) was studied. Transmission electron microscopy coupled with energy dispersive X-ray analysis, X-ray fluorescence and physical adsorption of gases were used to characterize the clays. This characterization has shown than the activation with acid increases the surface area as a consequence of the rupture of the laminar structure. The effect of the pH in the lead adsorption capacity was analyzed. The results show that adsorption is strongly depended on the pH. At low pH values, the mechanism that governs the adsorption behavior of clays is the competition of the metal ions with protons. Between pH 2 and 6, the main mechanism is an ion exchange process. The kinetics of the adsorption is tested with respect to pseudo-first-order and second-order models. The adsorption process, gives a better fit with the Langmuir isotherm, being the monolayer capacity ranging between 18.2 and 24.4?mg?g^?1. The adsorption of lead decreased in the order Acidic-M₂?>?M₂?>?M₁. Thermodynamic parameters such as ??H, ??S, and ??G were calculated. The adsorption process was found to be endothermic and spontaneous. The enthalpy change for Pb(II) by M₁ adsorption has been estimated as 60?kJ?mol^?1, indicating that the adsorption of Pb(II) by all montmorillonites used corresponds to a physical reaction. The adsorption capacity of washed Acidic-M₂ was very high compared to M₂ and M₁.