Adsorption of hexavalent chromium on a lignin-based resin: Equilibrium, thermodynamics, and kinetics

Abstract

A novel lignin-based resin (LBR), prepared by condensation polymerization of sodium lignosulfonate with glucose under acidic conditions, was used as an adsorbent for sorption of Cr(VI). The effects of varying experimental parameters (such as pH, initial metal ion concentration, LBR dose, contact time, and temperature) on the adsorption process were studied by batch adsorption experiments. The surface properties change during adsorption of Cr(VI) was characterized by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis. Isotherm modeling studies demonstrated that the Freundlich isotherm model gave a better fit to the experimental data, and the maximum adsorption capacity was 57.681mgg−1. The calculated thermodynamic parameters of the sorption (ΔG, ΔH and ΔS) showed that the adsorption of Cr(VI) on LBR is spontaneous and endothermic under the conditions employed. The experimental data was also tested by both pseudo-first-order kinetic and pseudo-second-order kinetic models. The adsorption process is well described by the pseudo-second-order kinetic model. A three-step removal mechanism of Cr(VI) by LBR was proposed, including: electrostatic attraction of acid chromate ion by protonated LBR, reduction of Cr(VI) to Cr(III) and bond formation of Cr(III) with the oxygen-containing functional groups.