Enhanced Sorption of Cadmium by using Biochar Nanoparticles from Ball Milling in a Sandy Soil

Two sizes of particles have been employed from wood-derived biochar which produced by slow pyrolysis at 650°C under Ar gas flow to investigate size and dosage effects of biochar at cadmium (Cd) sorption via batch experiment in a sandy soil. The macro (MBC) (0.5–1 mm) and nano size (NBC) of biochar divided by sieving and milling by planetary ball mill processes from pristine biochar, respectively. X-ray diffraction analysis of NBC indicated the presence of magnesian-calcite mineral with turbostratic crystallites. Also, NBC differs from MBC by a higher intensity and different types of surface functional groups such as hydroxyl and carboxyl, and by more polarity, aromaticity and less C–C bands based on FTIR analysis. The zeta potential of NBC ranged from +16.2 to –71.8 mV which can be an effective factor in the agglomeration of particles. NBC particles have a higher specific surface area (approximately 210%) and total pore volume and external surface area, and greater mean pore diameter than MBC. Isotherm equations, namely, Freundlich, Langmuir, Temkin, and Dubinin–Radushkevich were applied to evaluate which model provides the best fit predicted data with experimental results. The Langmuir isotherm provided the best fit according to adjusted R2 and reduced chi-square parameters. By adding 2% (w/w) of MBC and NBC to sandy soil samples, maximum sorption of cadmium reached 328.9 and 1062.4 mg kg–1 which were 58.6% and 412.2% more than control soil. The findings of the study confirmed that ball milling proposes nanobiochar which is more effective at cadmium sorption from contaminated solutions.