Iron modified chitosan/coconut shell activated carbon composite beads for Cr(VI) removal from aqueous solution.

Iron modified chitosan/coconut shell activated carbon (Fe/CSCC) composite bead is synthesized to remove Cr(VI) and is characterized to reveal the influencing factors and reaction mechanism. Results show that the adsorption capacity (Qe) of Cr(VI) increases with the increase of iron loading, contact time (t), Cr(VI) initial concentration (C0), and temperature (T), but decreases with the increase of pH, and mass and volume ratio (m/v). After 0.1 mol FeCl3 modification, the removal efficiency of Cr(VI) by Fe/CSCC reaches as high as 97.25 % at pH = 3, m/v = 1.0 g/L, t = 2880 min, C0 = 25 mg/L, and T = 25 °C. The coexisting ions of SO42-, HPO4-, and Ca2+ lead to the decrease of Qe by 7.82, 5.05, and 5.50 mg/g, respectively, and the inhibition effect increases with their increasing concentrations. Fe/CSCC adsorption for Cr(VI) is an endothermic spontaneous process, and a chemical and monolayer adsorption, which is better fitted to a pseudo-second-order kinetic. The fitted maximum Qe is 64.49 mg/g by using the Langmuir model. Moreover, after five cycles of regeneration, the Qe value only drops about 3.46 mg/g. Characterization analysis of BET, XRD, FTIR, XPS, and SEM-EDS indicates that Cr(VI) is mainly adsorbed by Fe/CSCC through electrostatic attraction and complexation, which is related to the -COOH and - NH2 groups, and Fe - O groups, respectively.