Utilization of Passion Fruit Skin By-Product as Lead(II) Ion Biosorbent

In this study, residues of passion fruit skin were examined as biosorbent materials, evaluating their capacity to adsorb lead(II) ions in in natura skin (SK-N) and two modified skins, with NaOH (SK-S) and with NaOH and citric acid (SK-SCA). The biomass characterization was done through Fourier transform infrared spectroscopy which confirmed the chemical modification by a peak at 1,730 cm(-1). Also, scanning electron microscopy analyses were done, where the increase of residue roughness was observed after the modification. And finally, the values of point of zero charge were determined and were lower than 5.5 for all residues. In the experiments of adsorption in function of pH, it was verified that after pH4, the adsorbed amount was practically constant. Regarding the necessary time to reach equilibrium, the value that was found was approximately 170 min, and kinetics followed the behavior described by the pseudo-second-order equation. The maximum adsorption capacity was 204 mgg(-1) for the SK-SCA biomass. The residues followed Langmuir adsorption model. Through thermodynamic parameters, it was verified that adsorption occurs spontaneously due to the negative values of Gibbs' energy. Moreover, desorption studies showed that adsorbed ions may be recovered in two cycles. Thus, due to the high adsorption capacity of lead ions, passion fruit skin can be utilized in filters to retain this metal in the future.