Influence of biomass feedstocks on magnetic biochar preparation for efficient Pb(II) removal

Biomass feedstocks have different physicochemical properties owing to their composition, morphology, functional groups, and surface chemistry, leading to considerable differences in the adsorption capacity of their biochars. However, few studies have focused on selecting appropriate biomass feedstocks for the adsorption of Pb(II) and other potentially toxic elements from wastewater. In addition, the effect of magnetic modification on various biomass feedstocks remains unclear. In this study, three types of biomass feedstocks, including fir wood, bamboo wood, and rice straw, were used to prepare biochars (BFW, BBW, and BRS) and magnetic biochars (MagFW, MagBW, and MagRS). Results showed that the Langmuir adsorption capacity of BRS reached 153 mg/g for Pb(II), which was approximately 2.8 and 1.9 times that of BFW and BBW, respectively. The higher Pb(II) adsorption of BRS primarily resulted from its rich mineral content, relatively high pH, and abundant oxygen-containing functional groups, which strengthened the release of alkali/alkaline earth metal cations, precipitation of (hydro)cerussite, ion exchange with H+, and complexation by hydroxyl and carboxyl groups. Magnetic modification changed mainly the surface charge, pH, and surface functional groups of various biochars, thus improving their Pb(II) adsorption capacity through electrostatic attraction, ion exchange, and complexation. Specifically, MagFW (308 mg/g) and MagBW (284 mg/g) demonstrated a more pronounced increase in Pb(II) adsorption capacity than MagRS (297 mg/g), because of the enhanced mineral precipitation and complexation with the FeO band. Results from this study suggest that the application of biochar may be a feasible, effective, and eco-friendly strategy for removing Pb(II) from wastewater.