Adsorption of Pb²⁺ from aqueous solutions using Fe–Mn binary oxides-loaded biochar: kinetics, isotherm and thermodynamic studies

Abstract

This study evaluated the removal of Pb²⁺ in aqueous solution using Fe-Mn binary oxides-loaded biochar (BFMs). The characteristics of BFM were obtained using a scanning electron microscopy, an energy dispersive spectrometer (EDS), Brunauer-Emmett-Teller, a X-ray diffraction (XRD), and a X-ray photoelectron spectroscopy (XPS). The effects of pH, adsorbent dose, contact time, initial Pb²⁺ concentration, and temperature in the batch sorption experiments were investigated. Adsorption was evaluated by adsorption kinetics, isotherm models, and thermodynamics. With the initial Pb²⁺ concentration of 200 mg/L, pH 4, and 298.15 K, the optimum adsorption of BFM was obtained at a reaction time of 300 min, adsorbent dose of 2 g/L, and maximum adsorption capacity of 113.715 mg/g. Furthermore, the kinetics was best fitted to the pseudo-second-order model, whereas the adsorption equilibrium was best described by the Langmuir isotherm model. This result indicated that Pb²⁺ was adsorbed onto BFM by chemical interactions through the monolayer. The adsorption was spontaneous (ΔG < 0) and endothermic (ΔH > 0).