Raw leaves and leaf residues from the extraction of essential oils as biosorbents for metal removal

Abstract The present study evaluates the use of raw leaves and leaf residues (citronella, lemongrass, palmarosa and eucalyptus) from extraction process of essential oils as biosorbents of Cd 2+ , Pb 2+ , and Ni 2+ from an aqueous solution. The eucalyptus leaf residue (ELR) was selected as the best biosorbent for the removal of metals. The Langmuir model fitted the experimental equilibrium data very well. The maximum biosorption capacity of the raw ELR, for Cd 2+ , Pb 2+ , and Ni 2+ , in a single metal system, was 0.135 ± 0.005 (⁓ 15 mg g −1 ), 0.216 ± 0.007 (⁓ 45 mg g −1 ) and 0.0910 ± 0.0002 (⁓ 5 mg g −1 ) mmol/g at pH 3.8, respectively. However, the biosorption equilibrium using the Pb 2+ /Cd 2+ /Ni 2+ mixture revealed that there is competitiveness between the metal ions to the active sites. The basic treatment in the biomass improved the metal removal capacity. The biosorption behavior in the batch system was modeled using a mass transfer kinetic model, considering that the biosorption rate is controlled by a Linear Driving Force model (LDF). The experiments in batch mode desorption were efficient using a 0.1 mol L −1 HNO 3 . Metals removal efficiency maintains a certain level after three regeneration cycles. The biosorption capacities obtained in the fixed bed column experiments were lower than those obtained in a single closed system. An LDF model was able to predict biosorption by ELR in the fixed bed successfully.