Simultaneous removal of Cu2+ and Pb2+ ions by unmodified apple pomace: Isotherms, kinetics and implications for scale-up

Abstract

Heavy metal contamination of water resources poses significant environmental and public health risks, particularly from toxic metals such as Cu 2+ and Pb 2+ . This study investigates the simultaneous removal of Cu 2+ and Pb 2+ from wastewater using apple pomace, a by-product of apple juice production that is often discarded, leading to secondary pollution. Isotherm studies were conducted for the binary solute system of Cu 2+ and Pb 2+ , with one metal fixed at 50 mg L −1 and the other varying from 10 to 50 mg L −1 to characterize adsorption equilibria. The Dubinin-Radushkevich (D-R) isotherm model provided the best fit for Pb 2+ (R 2 = 0.97), while the Freundlich isotherm gave the best fit (R 2 = 0.87) for Cu 2+ . Maximum experimental adsorption capacities under competitive conditions were 3.45 mg g −1 for Cu 2+ and 3.98 mg g −1 for Pb 2+ . Although the adsorption capacities were lower than those reported for chemically modified apple pomace, the elimination of pre-treatment costs and secondary waste generation enhances the practical feasibility. Kinetic studies were conducted at identical concentrations (50 mg L −1 each) and analysed using nonlinear models. The Elovich model provided the best fit for Cu 2+ (R 2 = 0.96), while the intraparticle diffusion model best described the Pb 2+ kinetics (R 2 = 0.93). Notably, Pb 2+ exhibited preferential adsorption over Cu 2+ , which is consistent with its higher affinity for oxygen-containing functional groups. The findings underscore apple pomace as a promising adsorbent for the simultaneous removal of Cu 2+ and Pb 2+ , providing a basis for further optimization and scale-up investigations. • Unmodified apple pomace efficiently removed Cu 2+ and Pb 2+ from binary solutions. • Pb 2+ shows higher affinity and preferential adsorption over Cu 2+ . • The Dubinin-Radushkevich (D-R) and Freundlich isotherm models best describe the adsorption of Pb 2+ and Cu 2+ , respectively. • The Elovich and intraparticle diffusion models best represent adsorption kinetics. • Ion exchange and complexation with oxygen-rich functional groups govern the adsorption mechanism.