Iron-modified coal gangue/rice husk biochar composites for enhanced removal of aqueous As(V)

Addressing the severe arsenic pollution issue in coal mining areas is crucial for environmental protection and human health. Adhering to the principles of a circular economy, we have innovatively employed ball milling technology to successfully develop a pioneering composite material of iron-modified coal gangue (CG-Fe) and rice husk (RH) biochar, which holds significant importance in the conservation of the environment and the preservation of human health. Using aqueous batch experiments, As(V) adsorption by the pristine biochar and iron-modified coal gangue was compared to that of composites made with varying biochar and coal gangue ratios under varying conditions. The composite containing 40% biochar by weight (40%-RH/CG-Fe) exhibited the highest adsorption of As(V). It had a high pore volume (0.087 cm3 g- 1) and specific surface area (24.5 m2/g), which were larger than those of the balled milled Fe-treated coal gangue. Adsorption isotherm and kinetics experiments demonstrated that 40%-RH/CG-Fe had a maximum As(V) adsorption capacity of 76.3 mg/g, reached equilibrium after approximately 48 h, and took place in a two-step process. The adsorption of As(V) by 40%-RH/ CG-Fe remained effective even in the presence of humic acid, heavy metal cations, and most anions. Other analyses, including XRD, FTIR, XPS, and zeta potential, suggested that the removal of As(V) by the composite was predominantly due to electrostatic attraction on surface sites, but might also involve redox reactions with Fe and complexation with functional groups. Five consecutive adsorption regeneration cycles demonstrated that 40%RH/CG-Fe can be reused in the As(V) treatment. Iron-modified coal gangue/rice husk biochar composites demonstrate great potential as an efficient and cost-effective green sorbent for mitigating arsenic contamination in soils and waters of coal mine regions.