Recovery of phosphate from aqueous solution by modified biochar with concentrated seawater and its potential application as fertilizer

Concentrated seawater as a byproduct of seawater desalination, its resource utilization potential has attracted widespread attention because of its rich inorganic salt resources. Concentrated seawater-modified biochar for phosphate recovery is undoubtedly a promising and sustainable option for resource utilization and eutrophication control. In this study, peanut shells as a carbon source, and modified biochar composites were successfully synthesized by co-precipitation with concentrated seawater for phosphate removal from aqueous solution. Meanwhile, the potential of phosphorus-enriched modified biochar as a soil slow-release fertilizer was evaluated. A series of characterization results showed that magnesium/calcium in the form of Mg(OH)2 and CaCO3 were successfully loaded onto the modified biochar composites. Furthermore, the pseudo-second-order kinetic model and Langmuir model can describe the adsorption process more accurately. According to the Langmuir model calculations, the maximum adsorption of phosphate by modified biochar composite was 173.09 mg/g, which can be compared with those of many Ca/Mg biochar composites. The primary sorption mechanism is electrostatic adsorption, ligand exchange and chemical precipitation interactions between phosphate and modified biochar composites. In addition, it was shown that the phosphorus-rich modified biochar embodied significant effects in improving the germination rate as well as the growth of plants, and had great potential as a slow-release fertilizer for agricultural soils.