Optimization of batch and packed-bed column Cr(vi) adsorption of an amine-rich chitosan/polyethyleneimine composite: application in electroplating wastewater treatment†

Toxic oxyanions of Cr(VI) can be potentially removed by adsorbents with positively charged surfaces. In this study, we synthesized a stable and insoluble amine-rich polymer composite (CS–PEI–GLA) by crosslinking polyethyleneimine (PEI), a soluble amine-rich synthetic polymer, and chitosan (CS) with glutaraldehyde (GLA). The positively charged amine groups were the main adsorption sites. The batch investigation demonstrated that the adsorbent was able to remove ≥90% of chromium at pH ranging from 2 to 8. Due to deprotonation of the amine groups, chromium removal decreased at higher pH values. The adsorption was fast and reached equilibrium after 45 min. The maximum adsorption capacity was 500 mg g⁻¹ according to the Langmuir isotherm and did not decrease in the presence of monovalent anions. In the column study, the adsorption capacity was the highest when the flow rate was the lowest (5 mL min⁻¹), influent concentration was medium (225 mg L⁻¹), and the bed height was the shortest (3.5 cm). NaOH was the best recovery reagent with recovery of 67% in batch and 31% in the column. The CS–PEI–GLA composite was able to remove 97.1 ± 0.1% chromium in batch and treat 750 mL of electroplating wastewater with a 3.5 cm packed-bed column.