Preparation and characterization of manganese‐containing biochars and their lead ion adsorption mechanism

Abstract

AbstractHeavy metal pollution causes severely adverse impacts on human and ecosystem health. Adsorption is one of the most effective technologies used in the removal of heavy metal ions from contaminated water. However, its widespread applications are limited, owing to its high cost and low adsorbent selectivity. In this study, modified manganese‐containing biochars were synthesized to improve their Pb2+ adsorption ability. Fraxinus mandshurica sawdust samples were impregnated with pure water as well as KMnO4 and MnSO4 aqueous solutions (FM‐BC, FM‐M7BC, and FM‐M2BC, respectively) for 24 hours at 25°C and pyrolyzed at 400°C. The resulting biochars were characterized using x‐ray diffraction (XRD), scanning electron microscopy (SEM), energy‐dispersive x‐ray analyses (EDX), Fourier‐transform infrared spectroscopy (FTIR), N2 adsorption‐desorption isotherms, and Boehm titration. Batch adsorption experiments revealed the kinetics and magnitude of Pb2+ adsorption onto the biochars. The Pb2+ adsorption capacity of FM‐M7BC (156.25 mg · g−1) was significantly higher than those of FM‐M2BC (25.35 mg · g−1) and FM‐BC (11.99 mg · g−1), and based on FTIR and Boehm titration results before and after Pb2+ adsorption, an adsorption mechanism was proposed. FM‐M7BC showed the highest adsorption enhancement owing to the strong affinity of MnCO3 particles and O‐containing groups for Pb2+. Additionally, the influence of the different oxidation states of manganese (Mn(VII), and Mn(II)) in the manganese components on the Pb2+ adsorption performance of the biochars was extremely strong. FM‐M7BC was an effective adsorbent for removing Pb2+.