Removal of Cr (VI) by crosslinked chitosan adsorbent prepared using simulated copper-containing wastewater

A chitosan (CS) hydrogel bead cross-linked by Cu²⁺ with a macroscopic spheral shape (designated as CS-Cu-B) was synthesized using simulated copper-containing wastewater without additional crosslinking agents. The optimal conditions for CS-Cu-B formation were identified as 1500 mg/L of Cu²⁺ concentration, pH 5.4 and 50 °C under which CS-Cu-B was further utilized as an adsorbent for Cr(VI). The adjacent chitosan chains were crosslinked by coordination between positive-charged Cu²⁺ ions and the amino and hydroxyl groups of chitosan. This enhanced the surface charge and increased the specific surface area of CS-Cu-B, thereby augmenting its Cr(VI) adsorption capacity. The effect of adsorbent dosage, pH of Cr(VI) solution, and presence of coexisting ions on Cr(VI) adsorption was investigated. Detailed analyses of the adsorption kinetics, isotherms and thermodynamics of Cr(VI) on CS-Cu-B were also conducted. CS-Cu-B demonstrated a maximum Cr(VI) adsorption capacity of 90.76 mg/g at pH 4.0 and exhibited excellent reusability, retaining 87.90 % of its adsorption capacity after five adsorption-desorption cycles. Both experimental characterizations and DFT calculation elucidated that the electrostatic attraction adsorption is the main driving force for the adsorption of CS-Cu-B on Cr(VI). A consecutive preparation-adsorption strategy using simulated copper-electroplating wastewater was proposed to facilitate the recycling of heavy metals.