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

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.