Novel EDTA-chitosan/alginate porous composite beads for the removal of Pb(ii) and methylene blue from aqueous solutions†

Abstract

Wastewater containing heavy metals and organic dye pollutants discharged into receiving waters poses a serious environmental concern. Herein, a novel EDTA-chitosan/alginate porous composite bead adsorbent (EC–AB) was reported for the simultaneous removal of lead (Pb(II)) and methyl blue (MB) complexes from wastewater. Characterization results showed that EC–AB contained plenty of oxygen/nitrogen functional groups. The effect of CaCO₃ addition, pH of the initial solution, contact time, initial pollutant concentration, and ionic strength on EC–AB pollutant removal performance and the adsorption mechanism were systematically analyzed. These findings indicated that EC–AB exhibited high removal efficiency over a wide pH range and at high ionic strength. The maximum adsorption capacities of EC–AB for Pb(II) and MB were 504.11 mg g⁻¹ and 660.76 mg g⁻¹, respectively, at 298 K. Adsorption kinetics and isotherm studies indicated that the adsorption well fitted the pseudo-second-order kinetic model and the Langmuir isotherm. A possible adsorption mechanism involving electrostatic attraction, chelation, ion exchange, H-bonding and synergistic effects was proposed. Moreover, EC–AB showed superior stability and reusability, with removal efficiencies of 76.64% for Pb(II) and 80.29% for MB after five continuous adsorption–desorption cycles for treating complex wastewater. In summary, this work provides a beneficial strategy for designing high-performance adsorbents for the treatment of wastewater.