Evaluating the adsorptive capacity of montmorillonitic and calcareous clays on the removal of several heavy metals in aqueous systems

The present work aimed to achieve mineralogical and spectroscopic characterization of the Late Cretaceous clays of Aleg formation (Coniacian-Lower Campanian system), Tunisia, for the removal of several toxic metals in aqueous system. The collected clay samples were first characterized by different techniques including X-ray fluorescence (XRF), thermal analysis (TG/TDA), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). Results showed that the natural clay samples are mainly composed of silica, alumina, iron, calcium and magnesium oxides. The sorbents are mainly mesoporous materials with modest specific surface area of <71 m2/g. Then, the possible use of the studied clay samples as adsorbents for the removal of Pb(II), Cd(II), Cu(II) and Zn(II) from aqueous solutions was evaluated. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherm models were used to simulate the equilibrium data. The maximum adsorption capacity varied between 6.78 and 131.58 mg/g, showing much higher removal efficiency than the relevant previous studies. Langmuir isotherms showed the best fitting to the experimental data. Among the studied clay samples, the amount of calcium carbonates was the most influencing parameter for heavy metal removal. The results suggest that the studied clay samples can be effectively used for the treatment of contaminated wastewaters.

► Tunisian natural adsorbents have high adsorptive capacities for heavy metals.
► Impurities influenced the removal capacity especially carbonates minerals.
► The removal kinetics was governed by the pseudo-second-order model.
► The experimental data fitted to Langmuir model better than Freundlich and D–R models.
► The studied material achieved better removal efficiency than other natural adsorbents.