Preparation of Ca/Mg-based mineral-modified biochar materials and their phosphorus adsorption performance

To address eutrophication from excessive phosphorus, this study developed a strategy using pomelo peel as the biomass feedstock and phosphoric acid tailings as a calcium/magnesium-rich modifier for biochar. Meanwhile, calcium- and magnesium-modified biochar materials were prepared using chemical reagents (CaO, MgO) for performance comparison. Characterization results indicated that the physical and chemical properties of the modified materials had changed significantly, making them suitable for phosphate adsorption. By investigating the phosphate adsorption performance of the materials under different influencing factors, it was found that the phosphoric acid tailings-modified biochar exhibited excellent phosphate adsorption performance at a pyrolysis temperature of 800 °C, a dosage of 0.5 g, and a pH of 8, with a maximum adsorption capacity of 242.94 mg/g. Adsorption kinetic experiments verified that the adsorption process followed the pseudo-second-order kinetic model, indicating that chemical adsorption was the dominant mechanism. Adsorption isotherm experiments demonstrated that the Langmuir model provided a better fit than the Freundlich model, suggesting that monolayer adsorption was predominant. Combined with various characterization methods, the adsorption mechanism was found to be chemical precipitation and ligand exchange. This study provides a new approach for addressing water eutrophication.