Highly Efficient Recovery of Phosphate from Water Using Cerium Carbonate Hydroxide-Decorated Magnetic Biochar: A Slow-Release Phosphate Fertilizer for Agricultural Reuse

Phosphate removal plays a pivotal role in alleviating eutrophication and maintaining water quality. Cerium (Ce) demonstrates considerable promise in phosphate removal, attributed to its strong affinity for phosphate ions. This study provides a dual utilization strategy for synthesizing Fe₂O₃- and CeCO₃OH-decorated hydrophilic porous biochar (Fe/Ce@HPBC), designed for phosphate recovery from eutrophic waters and followed by its application as a slow-release phosphate fertilizer. Fe/Ce@HPBC possessed excellent phosphate adsorption quantity, achieving a maximum uptake of 203.88 mg/g in accordance with the Sips model. Furthermore, the slow-release experiment demonstrated that Fe/Ce@HPBC used as a fertilizer after phosphate recovery could sustainably release 39.8% of its phosphate content within 28 days. Fe/Ce@HPBC-P could also significantly increase the effective phosphorus content of soil by 65.51% and promote the phosphorus uptake of maize seedlings by 70.36%. Mechanistic investigation revealed that the outstanding phosphate adsorption by Fe/Ce@HPBC was attributed to the formation of inner-sphere complexation through ligand exchange between phosphate and Ce(HCO₃)²⁺/Ce–OH, in addition to electrostatic attraction caused by enhanced surface protonation. Overall, this study contributes to the advancement of phosphate recovery techniques and promotes the development of sustainable agriculture by presenting an effective strategy for mitigating eutrophication.