Preparation of magnetic kaolin embedded chitosan beads for efficient removal of hexavalent chromium from aqueous solution

Abstract

The removal of toxic hexavalent chromium (Cr(VI)) ions is highly demanded. Herein, the magnetic kaolin embedded chitosan (MKCS) beads with different mass ratios of MK/CS were prepared by a simple pH-precipitation method and applied for the removal of Cr(Ⅵ) ions from aqueous solution. Factors influencing the removal of Cr(Ⅵ) ions such as solution pH, adsorbent dosage and contact time were investigated systematically by batch experiments. The results showed that MK0.2CS beads (the mass ratio of MK to CS equals 0.2) can remove more than 92% and 72% of Cr(Ⅵ) respectively with the initial concentrations of 40 and 60 mg/L. And the MK0.2CS beads showed an adsorption capacity of 144.0 mg/g with the initial Cr(VI) concentration of 300 mg/L at 25 °C. The adsorption data is fitted well with the pseudo-first-order kinetic model, indicating that the adsorption is a physical process. The adsorption isotherm study and thermodynamic study revealed a multilayer and exothermic adsorption, respectively. After Cr(Ⅵ) uptake, the adsorbent was well-regenerated by 1 M NaOH, and the results showed that the MKCS beads can be reused successfully in repeated adsorption-desorption cycles. The MKCS beads were thoroughly characterized before and after Cr(VI) adsorption. XPS analysis revealed that the adsorption of Cr(Ⅵ) on MKCS beads could be attributed to electrostatic interaction. The results suggested that the MKCS beads can be considered as an effective and promising adsorbent for wastewater treatment.