Local fruit peel biosorbents for lead(II) and cadmium(II) ion removal from waste aqueous solution: A kinetic and equilibrium study

Abstract

Heavy metals are serious causes of water pollution affecting both living organisms and human life. This research focuses on the removal of Pb(II) and Cd(II) ions from waste aqueous solution through adsorption process using natural biosorbents chemically modified from three local fruit peels comprising dragon fruit peel (DFP), rambutan peel (RP), and passion fruit peel (PFP). Their surface morphologies and functional groups were consecutively determined using scanning electron microscope and Fourier transform infrared spectrometer. Concentrations of the adsorbed metal ions were quantified using atomic absorption spectrometer. Adsorption experiments were carried out with varying adsorbent dosages, pH values, contact time, and initial lead(II) and cadmium(II) concentrations. An adsorbent dosage of 0.25 g, a pH of 4, a contact time of 180 min, and an initial concentration of 100 mg/L were found to be the optimal set of conditions for biosorption of Pb(II) and Cd(II) ions. The chemically modified groups showed the highest percentages of Pb(II) and Cd(II) removal at 97.867% and 97.100% for RP, respectively. The adsorption proceeded according to the pseudo-second-order kinetic model. The adsorption data were consistent with the Langmuir and Freundlich isotherm models, but the Langmuir model provided the best fit. The Langmuir monolayer adsorption capacity values of biosorbents were determined to be 97.087 mg(Pb2+)/g, 114.943 mg(Pb2+)/g, 103.093 mg(Pb2+)/g, and 86.207 mg(Cd2+)/g, 102.041 mg(Cd2+)/g, 89.286 mg(Cd2+)/g for DFP, RP, and PFP, respectively. The results indicate that these biosorbents could be able to efficiently remove Pb(II) and Cd(II) and serve as economic and promising adsorbents for heavy metal removal from contaminated wastewater.