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 ( Q e ) of Cr(VI) increases with the increase of iron loading, contact time ( t ), Cr(VI) initial concentration ( C 0 ), and temperature ( T ), but decreases with the increase of pH, and mass and volume ratio ( m/v ). After 0.1 mol FeCl 3 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, C 0  = 25 mg/L, and T  = 25 °C. The coexisting ions of SO 4 2− , HPO 4 − , and Ca 2+ lead to the decrease of Q e 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 Q e is 64.49 mg/g by using the Langmuir model. Moreover, after five cycles of regeneration, the Q e 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 − NH 2 groups, and Fe − O groups, respectively.