Amorphous MnO₂ Modified Biochar Derived from Aerobically Composted Swine Manure for Adsorption of Pb(II) and Cd(II)

This study reports creative preparation of MnO2-biochar (MBR) via MnO2 modification of biochar (BR) derived from aerobically composted swine manure. SEM coupled with EDX analyzer, TEM, XRD, BET, and FT-IR were employed to examine the surface properties and pore structures of MBR and BR. Adsorption experiments of Pb(II) and Cd(II) including isotherms, kinetics, and thermodynamics as well as the influence of pH on zeta-potential were also investigated. The results indicated that MBR showed rougher and larger surface area and pore volume than BR. In batch adsorption, MBR showed superior adsorption performance (maximum capacity for Pb 268.0 mg/g and Cd 45.8 mg/g) to BR (Pb 127.75 and Cd 14.41 mg/g). The adsorption process was pH-dependent, and the removal efficiency reached its maximum at 0.2 g/L dosage of MBR, after which it declined. Finally, X-ray photoelectron spectrometer (XPS) studies indicated the oxidative Mn4+ on MBR, and suggested that apart from electrostatic attachment, specific adsorption (i.e., Pb/Cd–O or hydroxyl binding) and ion exchange were the removal mechanisms of metal ions. Therefore, this modification method toward BR was promising for wastewater treatment of heavy metal pollution.