Preparation of biochar/iron mineral composites and their adsorption of methyl orange

Biochar-supported iron-containing minerals have received much attention due to their synergistic mechanism of decontamination in environmental pollution remediation. In this work, two types of iron/biochar were prepared from different biomasses using ferric chloride as the Fe source and rice husks and peanut shell as biomasses. The formation of fayalite (Fe₂SiO₄) and magnetite (Fe₃O₄) in rice husk and peanut shell derived biochar was proved by X-ray diffraction. These minerals not only optimized the physicochemical properties of the biochar but also enhanced its capacity to adsorb methyl orange (MO). Peanut shell-based biochar (PBC) and rice husk-based biochar (RBC) sequestered 3.9 mg g^-1 and 4.5 mg g^-1 of MO, respectively. In contrast, iron peanut shell-based biochar (Fe-PBC) and iron rice husk-based biochar (Fe-RBC) adsorbed 6.0 mg g^-1 and 17.2 mg g^-1, outperforming their pristine biochar. The removal of MO showed a synergistic effect due to the loading of iron-bearing minerals. The mechanisms of MO immobilization by biochar samples were explored by experimental and characterization methods. It was found that the mechanisms responsible for MO immobilization on composites were conducted by electrostatic attraction, complexation with oxygen-containing functional groups, π-π interaction and hydrogen bond formation. This finding clarified the relationship among biomass composition, iron mineral evolution, and the adsorption capacity of iron-modified biochar, which is essential for the development of a cost-effective adsorbent.