High adsorption capacity of Mg-Al-modified biochar for phosphate and its potential for phosphate interception in soil

In this study, Mg and/or Al modified biochars (MABC¹, MBC², ABC³) prepared by co-precipitation were to explore their phosphate adsorption capacity from aqueous solution and the potential for soil phosphate interception. The results revealed that MABC composites contained more functional groups than MBC and showed a higher surface area than ABC. The surface of MABC contained dispersed MgAl₂O₄, Mg(OH)₂, AlOOH and Al₂O₃ crystals that were associated with its enhanced maximum phosphate adsorption capacity (153.40 mg g^-1). According to Langmuir model, the maximum adsorption capacity of MABC was 15.91, 1.85, and 93.54 times the capacity of MBC, ABC, and raw biochar (BC⁴), respectively. The addition of MABC in red soil could significantly slow down the release of soil phosphorus, and MABC also had a stronger phosphate interception capacity (59.89%) than other BCs. In summary, MABC exhibits superior phosphate adsorption and interception capacity, making it ideal for treatment and prevention of phosphorus-polluted water.