Characterization and adsorption properties of rectorite/sludge-derived biochar composites for Pb(II) removal

Clay-based adsorbent materials are widely used to remove heavy metal ions from water. In this study, we have fabricated a novel composite material, consisting of rectorite and sludge-derived biochar (REC/SDBC), and characterized its effectiveness in removing lead from water. Our SEM images show that the REC is evenly dispersed on the surface of the SDBC. The composites have a mesoporous structure, and its BET surface is (16.5 m2/g) comparable with that of SDBC but larger than that of REC. We found that the maximum adsorption capacity for Pb(II) was 26.89 mg g-1 for REC/SDBC composites with a REC:SDBC ratio of 3:1, which was achieved within 120 min. This is higher than the adsorption capacities of REC (19.81 mg g-1) and SDBC (23.15 mg g-1) alone. Furthermore, we observed that the adsorption capacity was greater at pH 5.0 compared to other pH values. Our results also indicate that the pseudo-second-order model and the Langmuir isotherm model provide good fits for the rates and isotherms of Pb(II) adsorption onto REC/SDBC composites. The adsorption kinetic constant and the Langmuir adsorption constant were calculated to be 0.0065 g mg-1 min-1 and 0.319 L mg-1, respectively. X-ray photoelectron spectroscopy analysis confirmed that the reaction mechanism is mainly dominated by chemisorption, involving cationic exchange, surface complexation, and surface precipitation. The high adsorption capacity, combined with the cost-effectiveness and environmental-friendly nature of REC/SDBC composites, make them promising candidates for removing heavy metallic elements from wastewater.