Adsorption of copper(II) ions by a chitosan-oxalate complex biosorbent

Oxalic acid, an effective metal-chelating ligand, is abundant in natural resources. In this study, a chitosan-oxalate complex biosorbent (COCB) was prepared by an iontropic cross-linking method. The COCB beads were characterized by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The XRD analysis shows that Cu(II) ions can form complexes with chitosan and oxalate. Adsorption of Cu(II) ions onto COCB beads was pH-dependent. The isothermal adsorption data fitted well to Langmuir equation with the maximum adsorption capacities of 227.27 mg/g for porous COCB beads and 175.44 mg/g for non-porous COCB beads at pH 5.0. The adsorption kinetics described by the pseudo-second-order diffusion models, suggesting that the rate-limiting step in adsorption was chemical sorption. Thermodynamic parameters (ΔG° < 0 and ΔH° > 0) indicated a spontaneous and endothermic adsorption process. The COCB bioadsorbent exhibited fast adsorption rate and high adsorption capacity for Cu(II) uptake.