Equilibrium, kinetic, thermodynamic and desorption studies of cadmium and lead by polyaniline grafted cross-linked chitosan beads from aqueous solution

Abstract

Modification of chitosan beads by cross-linking and grafting was investigated in this work, in order to use the grafted beads in the removal of cadmium and lead from contaminated water. The beads were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) to provide evidence of successful cross-linking and grafting. Batch experiments were carried out as a function of adsorption parameters such as pH, initial concentration, contact time and adsorbent dosage. Equilibrium data were obtained from the adsorption experiment performed, the data were correlated with the Langmuir and Freundlich isotherm models. The maximum adsorption capacity for cadmium and lead ions at a temperature of 45°C from Langmuir model was found to be 145mg/g and 114mg/g respectively. Subsequently, thermodynamic parameters such as Gibb's free energy change (ΔGo), enthalpy change (ΔHo) and entropy change (ΔSo) were calculated and the results showed that the adsorption of cadmium and lead ions onto polyaniline grafted cross-linked chitosan beads (GXCS) is spontaneous and endothermic in nature. The pseudo-first-order and pseudo-second-order model were used in analyzing kinetic data for both metal ions. The data fit well with the pseudo-second-order model. Desorption of GXCS loaded with cadmium and lead ions was assessed for five consecutive adsorption/desorption cycle. However, among the eluents that was investigated 0.5M HCl was successfully used in desorbing the spent adsorbent and a percentage desorption of 98.94% and 97.50% was obtained for cadmium and lead ions respectively, at a desorption time of 3h.