Phosphate adsorption performance and mechanisms by nanoporous biochar-iron oxides from aqueous solutions

To evaluate the adsorption mechanism and performance of phosphate onto the composite of low-cost biochar and iron oxide, four biochar-iron oxides, namely biochar-magnetite (BC-M), biochar-ferrihydrite (BC-F), biochar-goethite (BC-G), and biochar-hematite (BC-H), were prepared by fabricating iron oxide to porous biochar. The biochar-iron oxides had huge surface areas of 691-864 m²/g and average pore diameters of 3.4-4.0 nm. Based on the characterization analysis of FTIR, XRD, XPS, and zeta potential, the interactions of electrostatic attraction, ligand exchange, and deposition dominated the phosphate adsorption onto biochar-iron oxides. The maximum adsorption capacity of phosphate followed the order of BC-G > BC-F > BC-H > BC-M. The isotherm data of BC-M and BC-H were well fitted by the Langmuir and Freundlich models, while those of BC-G and BC-F followed the Langmuir model. In addition, BC-M, BC-F, BC-G, and BC-H owned excellent regeneration ability and adsorption performance in practical (simulated) wastewater environment. Then the biochar-iron oxides exerted extensive and satisfactory prospect in wastewater remediation and recycling application in soil.