A novel manganese-oxide/biochar composite for efficient removal of lead(II) from aqueous solutions

Biochar (BC) derived from pyrolysis of plant biomass can be used as an inexpensive adsorbent for removal of aqueous heavy metals. In the present study, amorphous hydrous manganese oxide was loaded onto BC to fabricate a novel manganese-oxide/biochar (Mn/BC) composite for further enhancing lead(II) removal by sorption from water. Mn/BC was characterized by X-ray diffraction, scanning electron microscope, and specific surface area analysis. After impregnation with 3.65 % Mn, BC raised the removal efficiency of lead(II) from 6.4 to 98.9 % at pH 5.00. This improvement is attributed to the increase in surface hydroxyls and the decrease in pH_PZC (pH at the point of zero charge) of carbon. The maximum monolayer adsorption of lead(II) on Mn/BC at 298 K was five times that on BC. The smaller pseudo-second-order rate constant of Mn/BC compared with that of BC indicated that the sorption rate of Mn/BC is faster than that of BC. The calculated thermodynamic parameters implied that the sorption of lead(II) is a spontaneous and endothermic process. The results suggest that Mn/BC composite is a promising adsorbent for the efficient removal of lead( II) from water.