One-step functionalization of chitosan using EDTA: Kinetics and isotherms modeling for multiple heavy metals adsorption and their mechanism

Potentially toxic heavy metals commonly exist in industrial wastewaters, presenting a critical global health threat to human health and environment, therefore, making their treatment is more challenging. In this study, an attractive polymer composite (CS-EDTA) adsorbent was developed by immobilization of ethylenediaminetetraacetic acid (EDTA) onto chitosan (CS) through cross-linking for the adsorptive removal of multiple heavy metals from industrial wastewater. The adsorption of heavy metals, i.e., Pb(II), Cd(II), and Cu(II) onto the developed composite was investigated by performing batch experiments with varying contact time and metal ion concentration in the mono-component system. The adsorption data fitted to the monolayer Langmuir isotherm; the maximum adsorption capacities were calculated as 370.37 ± 14.26, 243.90 ± 12.47, and 227.27 ± 15.33 mg g⁻¹ for Pb(II), Cd(II), and Cu(II), respectively. The kinetics of the adsorption followed the pseudo-second order (PSO) models, and obtained the rate constant values of 0.009 ± 0.0004, 0.001 ± 0.0001, and 0.0007 ± 0.0001 g mg⁻¹ min⁻¹ for Pb(II), Cd(II), and Cu(II), respectively. The adsorption of the heavy metals was attributed to the electrostatic interactions between the metals and different functional groups ([sbnd]OH, [sbnd]NH₂, and [sbnd]COOH) of the adsorbent and complexation with EDTA, which was confirmed by the elemental mapping, EDS and FT-IR techniques. The reusability of the polymer composite was also tested and obtained >92 % efficiency even after five consecutive adsorption-desorption cycles which clearly demonstrating the high stability of the adsorbent. Lastly, the developed polymer composite was applied for real industrial wastewater. Excellent removal efficiencies (>84 %) were obtained, which makes it a potential candidate for the removal of heavy metals from real industrial wastewater.