Sorption of aqueous methylene blue, cadmium and lead onto biochars derived from scrap papers

Biochars made from scrap newspaper and book paper (NPBx and BPBx, x represents pyrolysis temperature, ºC) were characterized and used to remove methylene blue (MB), cadmium(Cd(II)) and lead (Pb(II)) from water solution. BPBx had higher yield, C content, and ash content and lower Ca content than NPBx made at the same temperature. Calcite and pyrophyllite were main minerals in NPBx and BPBx, respectively. Biochars made at higher temperature had higher pHpzc values (6.9~11.0). The sorption kinetics of the three pollutants fit pseudo-second model well (R² = 0.991~0.999). NPB300 and NPB450 had the largest Langmuir sorption capacity of about 23 mg g^-1 for MB, while BPB600 had the capacity of 19.5 mg g^-1. NPB600 had the largest Langmuir sorption capacity of 13.8 mg g^-1 for Cd(II) and 451 mg g^-1 for Pb(II). Column sorption capacities were 13.2 mg g^-1 (NPB300) and 9.46 mg g^-1 (NPB450) for MB and 7.39 mg g^-1 (NPB600) for Cd(II). De-ashed BPBx had greater sorption capacity for MB than pristine BPBx. Deposition caused by reaction with CaCO₃ was the main reason for Pb(II) sorption by NPB600. Scrap newspaper biochars derived at high temperatures were efficient sorbents for the removal of Pb(II).