Adsorptive removal of Pb 2+, Co 2+ and Ni 2+ by hydroxyapatite/chitosan composite from aqueous solution

Abstract

In the present work hydroxyapatite/chitosan (HApC) composite was synthesized by precipitation method and was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) crystallography and scanning electron microscopy (SEM). The HApC composite was tested for the adsorption of lead, cobalt and nickel from aqueous solution and compared its removal capacity with hydroxyapatite (HAp). Effect of various physico-chemical parameters such as pH, adsorbent dose, contact time, initial metal ion concentration and temperature on adsorption of metal ions onto HApC composite was investigated. The adsorption process followed pseudo-second order kinetics and intra-particle diffusion model. Equilibrium data were fitted well in the Langmuir and Freundlich isotherm models. The negative values of Gibb's free energy change (Δ G°) showed that the adsorption process was feasible and spontaneous in nature. The positive values of enthalpy change (Δ H°) indicated that the process was endothermic. The positive values of entropy change (Δ S°) showed increased randomness at the solid/solution interface.