Equilibrium, kinetic and thermodynamic studies of adsorption of Cd(II) from aqueous solution onto HACC–bentonite

A novel adsorbent was prepared using bentonite modified with N-2-hydroxypropyl trimethyl ammonium chloride chitosan (HACC), which was named as HACC–bentonite. It was characterized by Fourier-transform infrared spectroscopy (FTIR), X-Ray Diffractomer (XRD) and Scanning electron microscopy (SEM). Cadmium is one of the toxic metals and has received a great deal of attention. The adsorption of Cd(II) onto HACC–bentonite was examined in aqueous solution with respect to the pH, adsorbent dosage, contact time, temperature and initial concentration. Langmuir, Freundlich and Temkin isotherms were employed to describe adsorption equilibrium. The maximum amount of Cd(II) adsorbed (qm), as evaluated by Langmuir isotherm, was 22.23 mg per gram of HACC–bentonite at pH 7 0 or so and 20 °C. The Lagergren-first-order and pseudo-second-order models were used to describe the kinetic data. The experimental data fitted well the pseudo-second-order kinetics. Furthermore, thermodynamic parameters, free energy (ΔG0), enthalpy (ΔH0) and entropy (ΔS0) of adsorption were also calculated. These parameters showed that the adsorption of Cd(II) onto HACC–bentonite was feasible, spontaneous and an endothermic process in nature. The change of adsorption enthalpy indicated that the adsorption of Cd(II) onto HACC–bentonite may be carried out via cat-ion exchange.

► A novel adsorbent was prepared by modifying bentonite with HACC. ► The maximum amount of Cd(II) adsorbed (qm) was 22.23 mg/g at pH 7 or so and 20 °C. ► The experimental data fitted the pseudo-second-order kinetics well. ► This adsorption was a feasible, spontaneous and endothermic process. ► It was carried out via cat-ion exchange.