Mineral‐Soybean Dregs Biochar Composites: Phosphate Adsorption From Water and Reuse as Slow‐Release Fertilizer

ABSTRACT Phosphorus (P) recovery from aquatic environments is increasingly critical for alleviating eutrophication and mitigating the looming crisis of phosphate resource depletion. In this study, a dolomite‐soybean dregs biochar composite (9ODBC‐900) was successfully synthesized and achieved efficient phosphate adsorption from water and subsequently used as a slow‐release fertilizer. The experimental results showed that the biochar composite could efficiently adsorb phosphorus in water, with a high adsorption capacity of 192.02 mg/g. The primary mechanism of adsorption was attributed to the precipitation of Ca 2+ /Mg 2+ ions, with additional contributions from surface complexation and electrostatic interactions. Additionally, the phosphorus‐enriched biochar composite demonstrated considerable promise as a slow‐release fertilizer, releasing 6.2 mg/g of phosphorus over a standard 14‐day dissolution period. In trials involving hydroponic wheat cultivation, compared with the control group, the application of phosphorus‐containing biochar composite material in the experimental group was beneficial to the accumulation of aboveground biomass of wheat, which confirmed its potential as a fertilizer. Consequently, this biochar composite offers a cost‐efficient approach to phosphorus recycling, providing a sustainable method for resource recovery and reuse.