Effect of alkali treatment on the removal of Co(II) ions by Leucaena leucephala biomass

Abstract

In this study, raw Leucaena leucephala (Raw-LL) and its chemically treated NaOH counterparts (LL-NaOH) were used as low-cost biosorbents to remove Cobalt (II) from the aqueous solution. The biosorbents were characterized by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), thermal gravimetric analysis (TGA), and X-ray diffraction (XRD), while the point of zero-charge (pHPZC) was also measured. Co(II) removal by Raw-LL and LL-NaOH was studied using batch experiments after optimizing various factors, namely the initial solution pH, contact time, initial Co(II) concentration, dosage of biosorbents, and temperature. The derived results from the characterization revealed changes in the biosorbent’s surface chemistry that positively impacted Co(II) removal. In addition, the sorption capacity of Co(II) on Raw-LL and LL-NaOH showed dependence on all investigated parameters. The kinetic data were fitted to pseudo-first and pseudo-second-order kinetic models, and the isotherm data were analyzed by Langmuir and Freundlich models. The biosorption of Co(II) on Raw-LL and LL-NaOH followed pseudo-second-order kinetic (R2 > 0.999) and Langmuir isotherm model (R2 > 0.995). Based on the Langmuir isotherm, the maximum biosorption capacity was 9.4 (Raw-LL) and 25.4 mg/g (LL-NaOH), values considered high for biomass-derived materials without activation/carbonization at elevated temperatures.