Enhancing adsorption of Pb (II) and Cu (II) ions onto chitosan using tri-sodium citrate and epichlorohydrin as cross-linkers

Abstract

In this study, tri-sodium citrate (CA), a chelating agent of low-cost and non-toxicity, was used together with epichlorohydrin (ECH) to cross-link chitosan (CTS) for enhancing the adsorption of Pb (II) and Cu (II) ions onto CTS. The chemical structure changes of the cross-linked CTS and metal ions-loaded absorbent were confirmed by thermogravimetric analysis, FTIR spectroscopy and X-ray diffraction. The effects of these factors, such as pH, temperature, contact time, and initial concentration of metal ions on the adsorption of Pb (II) and Cu (II) ions onto CTS–CA–ECH beads were investigated. The adsorption kinetics was evaluated utilizing pseudo-first-order and pseudo-second-order (PSO) models, the results indicated that the adsorption process fit well with the PSO kinetic model. Meanwhile, adsorption equilibrium isotherms were examined by Langmuir and Freundlich models, the results showed that the experimental data agreed well with Langmuir models and the maximum adsorption capacities were 121.95 and 151.52 mg g−1 for Pb (II) and Cu (II) ions, respectively. Furthermore, desorption and regeneration tests indicated that ethylenediamine tetra-acetic acid could effectively regenerate the metal ions loaded CTS–CA–ECH beads, suggesting that the currently prepared adsorbent possessed an excellent reusability for the adsorption of Pb (II) and Cu (II) ions.