Adsorption of Pb2+ by Alkali-Treated Citrus limetta Peels

The biomass Citrus limetta fruit peels was subjected to Pb2+ adsorption from aqueous PbNO3 solutions of different concentrations. Pretreatment of the biomass using cold alkali enhanced the adsorption by 87% even after considering the percentage weight loss. The biomass was characterized by scanning electron microscopy (SEM), electrokinetic analysis, and FT-IR spectroscopy. The equilibrium sorption capacity was observed to be 630 mg/g and the adsorption obeyed the Langmuir, Dubinin-Radushkevich (D-R), and ion-exchange models. The optimum pH and biomass concentration for maximum adsorption capacity were observed to be 4.5 and 0.1 g/L, respectively. Almost 80% sorption takes place within the first 15 min. The role of carboxylic and other functional groups was revealed to be ion exchange with a 1:2 stoichiometry between Pb2+ and carboxylic groups.