F. Bu, Lei Han, Hongxia Guo, Yu Liang, Haihong Yan
Phosphorus (P) scarcity and pollution demand sustainable recovery strategies. This study engineered a functional straw biochar (F-SBC) from corn straw through synergistic KOH activation and MgCl2 modification for efficient P recovery and slow release. Characterization revealed that KOH pretreatment expanded pore size and enhanced MgO loading. Batch adsorption experiments demonstrated F-SBC achieved a remarkable P adsorption capacity of 24.70 ± 0.57 mg·g−1, and exhibited > 95% removal efficiency across pH 5~9. Adsorption kinetics followed the pseudo-second-order model, and isotherms fitted the Langmuir model, indicating chemisorption-dominated monolayer adsorption. Mechanistic studies identified synergistic contributions from chemical precipitation, inner-sphere complexation, bi-metallic electrostatic attraction, and physical confinement. F-SBC exhibited slow-release properties, alongside sustained adsorption capacity. Competitive anions (HCO3−/CO32−) significantly promoted desorption, while Cl− showed minimal impact. This KOH/MgCl2 co-modification strategy creates a cost-effective, regenerable biochar with superior P recovery and controlled-release potential, advancing sustainable P management from agricultural waste towards a circular bioeconomy.