Efficient Phosphate Adsorption by Ball-Milled Fe 3 O 4 –Modified Biochar Derived from Agricultural Waste

High Resolution Image Download MS PowerPoint Slide Phosphorus is a critical factor contributing to eutrophication in aquatic environments, with agricultural nonpoint source pollution identified as its primary source. The development of efficient, eco-friendly, and renewable adsorbents is of significant importance for controlling phosphorus pollution in rural aquatic bodies. Biochar, a porous carbonaceous material, has demonstrated considerable adsorption potential; yet it exhibits limited affinity for phosphate, necessitating performance enhancements through modification. In this study, biochar was prepared from pig manure and wheat husk via high-temperature pyrolysis, and modified by loading nano-Fe 3 O 4 using a ball milling process, which offers a greener alternative to chemical treatments. The material’s structure was characterized using Brunauer–Emmett–Teller analysis and scanning electron microscopy. Adsorption experiments, including kinetic modeling, isotherm fitting, pH variation, ion interference, and regeneration assessments, were conducted to investigate phosphate removal performance. The wheat husk-derived biochar modified with iron oxide at 800 °C exhibited a specific surface area of 181.71 m 2 ·g –1, approximately 420 times greater than that of its unmodified counterpart. It followed a pseudo-second-order kinetic model and Langmuir isotherm, with a maximum phosphate adsorption capacity of 125.38 mg·g –1 under an initial concentration of (50 mg·L –1, pH 7.0, and 8 h equilibrium time), indicating that chemisorption may play a role in the adsorption process. The material demonstrated optimal performance at neutral pH, with calcium ions showing the greatest inhibitory effect on adsorption. After five adsorption–desorption cycles, the removal efficiency remained above 89%, confirming the material’s robust regeneration capacity. Overall, the ball-milled iron oxide modification provides a sustainable and effective means to enhance biochar functionality. The resulting magnetic biochar exhibits high adsorption efficiency, rapid kinetics, pH sensitivity, and excellent reusability, making it a promising candidate for addressing nonpoint source phosphorus pollution in aquatic systems.