Investigating the mechanisms of biochar’s removal of lead from solution

The objective of this study was to investigate the relationship between Pb2+ adsorption and physicochemical properties of biochars produced at different pyrolytic temperatures. Ten biochars were prepared from peanut shell (PS) and Chinese medicine material residue (MR) at 300–600 °C. Adsorption kinetics and isotherms were determined, and the untreated and Pb2+-loaded biochars were analyzed by FTIR, SEM–EDX and XRD. Functional groups complexation, Pb2+–π interaction and precipitation with minerals jointly contributed to Pb2+ adsorption on these biochars. New mineral precipitates (e.g., Pb2(SO4)O and Pb4(CO3)2(SO4)(OH)2) formed during Pb2+ sorption. For high-temperature biochars (⩾500 °C), Pb2+ sorption via complexation reduced, but the contribution of Pb2+–π interaction was enhanced. Dramatic reduction of Pb2+ sorption on demineralized biochars indicated the dominant role of minerals. These results are useful for screening effective biochars as engineered sorbents to remove or immobilize Pb2+ in polluted water and soil.