Chromium removal with cross-linked chitosan adsorption and base-precipitation combination

A novel technique for a complete removal of both Cr(VI) and Cr(III) ions, namely cross-linked chitosan (CCTS) adsorption and base-precipitation combination, was studied in this work in great detail. The optimum conditions for Cr(VI) adsorption onto CCTS were determined as a function of pH, CCTS dosage and contact time, while Cr(III) precipitation was investigated as a function of pH value. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were applied to describe the Cr(VI) adsorption isotherm on CCTS. The Langmuir model agreed much better with experimental data than the Freundlich and D–R by a correlation coefficient (R²) of 0.994. The capacity and ΔG^o of CCTS for Cr(VI) were 70.4 mg/g and −26.6 kJ/mol respectively, indicating the feasible and spontaneous nature of the Cr(VI) sorption process. This combined technique was applied for real wastewater treatment from the electroplating industry and obtained a one-off retention in solution not more than 0.5 mg/L for both Cr(VI) and Cr total. These results meet the Chinese standards for effluent discharge.