Study of the Effect of Various Parameters on the Adsorption of Heavy Metals by Bentonite-Polypyrrole Composite

In this research, the adsorption of heavy metals (Chromium and Lead) in aqueous solutions was investigated using a Bentonite-Polypyrrole composite. The composite was synthesized via in situ polymerization of pyrrole in the presence of bentonite (40%). Tests were conducted under various conditions to study the influence of different parameters (pH, initial concentration, contact time, competing ions, Zeta potential, organic matter) on the adsorption process. Langmuir and Freundlich's isothermal models were applied to assess the equilibrium data The kinetics of adsorption were determined using the Lagergren pseudo-second-order model. The characterization of the composite was tested by Scanning Electron Microscopy (SEM), Fourier Transform InfraRed (FT-IR) spectroscopy, and X-Ray Diffraction (XRD), and the results show intercalation of polypyrrole in the bentonite layers. The best results were obtained for a contact time of 60 minutes, an initial concentration of 10 mg/L, pH 2 for chromium, and pH 5 for lead. The presence of humic acids can modify the surface characteristics of the composite and affect the adsorption capacity. The measurements of the electrokinetic potential show that the zeta potential of the composite after adsorption of the metal cations is greater than that of the corresponding composite. The presence of organic matter regularly decreases the maximum exchange capacity with respect to metal cations. The Langmuir and Freundlich isotherm indicated a high affinity of Bentonite-Polypyrrole composite for chromium (VI) and lead (II) ions.