Adsorptive removal of lead and cadmium ions from aqueous solutions by aluminium oxide modified onion skin wastes: Adsorbent characterization, equilibrium modelling and kinetic studies

Abstract

Aluminium oxide modified onion skin waste (Al2O3/OSW) was characterized and used for adsorption of metal ions (Pb2+ and Cd2+) in this study, and the relations between sorbent properties and metal ion sorption were investigated. The effects of adsorption process conditions on metal ion removal efficiency, including initial cation concentration, contact time, adsorbent dosage and pH, were examined. The obtained adsorption data were analyzed by various adsorption isotherm and kinetic models. It was found that the optimum values of the initial concentration, contact time, adsorbent dosage and pH were 10 mg/L, 120 min, 1.6 g/L and 6.0, respectively. At these optimum conditions, maximum removal percentages of Pb2+ and Cd2+ were 91.23 and 94.10%, respectively. The isotherm and kinetic studies showed a multilayer adsorbate-adsorbent system with the dominance of the chemisorption mechanism. The study concluded that onion skin waste is a viable, cheap and effective alternative for removing heavy metal ions from water/wastewater.