Highly Efficient\nRecovery of Phosphate from Water\nUsing Cerium Carbonate Hydroxide-Decorated Magnetic Biochar: A Slow-Release\nPhosphate Fertilizer for Agricultural Reuse

Phosphate removal plays a pivotal role in alleviating\neutrophication\nand maintaining water quality. Cerium (Ce) demonstrates considerable\npromise in phosphate removal, attributed to its strong affinity for\nphosphate ions. This study provides a dual utilization strategy for\nsynthesizing Fe<sub>2</sub>O<sub>3</sub>- and CeCO<sub>3</sub>OH-decorated\nhydrophilic porous biochar (Fe/Ce@HPBC), designed for phosphate recovery\nfrom eutrophic waters and followed by its application as a slow-release\nphosphate fertilizer. Fe/Ce@HPBC possessed excellent phosphate adsorption\nquantity, achieving a maximum uptake of 203.88 mg/g in accordance\nwith the Sips model. Furthermore, the slow-release experiment demonstrated\nthat Fe/Ce@HPBC used as a fertilizer after phosphate recovery could\nsustainably release 39.8% of its phosphate content within 28 days.\nFe/Ce@HPBC-P could also significantly increase the effective phosphorus\ncontent of soil by 65.51% and promote the phosphorus uptake of maize\nseedlings by 70.36%. Mechanistic investigation revealed that the outstanding\nphosphate adsorption by Fe/Ce@HPBC was attributed to the formation\nof inner-sphere complexation through ligand exchange between phosphate\nand Ce(HCO<sub>3</sub>)<sup>2+</sup>/Ce–OH, in addition to\nelectrostatic attraction caused by enhanced surface protonation. Overall,\nthis study contributes to the advancement of phosphate recovery techniques\nand promotes the development of sustainable agriculture by presenting\nan effective strategy for mitigating eutrophication.