Adsorption of metal ions by microwave assisted grafting of cross-linked chitosan beads. Equilibrium, isotherm, thermodynamic and desorption studies

Chemical modification of chitosan has become increasingly essential due to chitosan versatility that enables the material to be easily modified in a way of increasing its properties in adsorption processes. In this investigation, chitosan solution was cross-linked with glutaraldehyde the cross-linked solution was used in producing the beads and thereafter grafted with ethylene acrylic acid. The chemical functionalities of the beads were obtained by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), X-ray diffraction (XRD) and Thermogravimetric analysis (TGA). Adsorption of Pb2+, Cu2+, Ni2+, Zn2+, Cr6+ and Cd2+ ions from single component aqueous mixture by grafted cross-linked chitosan beads (GXXB) was studied as a function of pH, temperature, initial concentration, contact time, agitation speed and ionic strength. Equilibrium data was obtained from the adsorption experiment, the data were applied in isotherm, thermodynamics and kinetic studies. The Langmuir, Temkin and Dubinin-kaganer-Radushkevich (DKR) model were successful in describing the isotherm data for the considered metal ions while the Freundlich model was not efficient in describing the experimental data. Pseudo-second order and intra-particle model described the kinetic data quite well. Thermodynamic parameters such as Gibb's free energy change (G(o)), enthalpy change (H-o) and entropy change (S-o) were calculated and the results showed the adsorption of Pb2+, Cu2+, Ni2+, Zn2+, Cr6+ and Cd2+ ions onto GXXB is spontaneous and endothermic in nature. Regeneration of the used adsorbent was effective for the studied metal ions.