Eggshell based biochar for highly efficient adsorption and recovery of phosphorus from aqueous solution: Kinetics, mechanism and potential as phosphorus fertilizer

Development of an efficient and green adsorbent is of great significance for phosphorus removal and recovery from eutrophic water. This work prepared an eggshell modified biochar (ESBC) by co-pyrolysis of eggshells and corn stalk. ESBC exhibited an excellent performance for phosphorus adsorption over a wide pH range (5-13), and achieved a maximum adsorption of 557.0 mg P/g. The adsorption process was well fitted by pseudo-second-order model (R² > 0.962) and Sips model (R² > 0.965), and it was endothermic (ΔH⁰ > 0) and spontaneous (ΔG⁰ < 0) according to thermodynamic analysis. The column experiment confirmed the feasibility of ESBC as a filter media for phosphorus removal in flow condition, and obtained a P removal of 460.0 mg/g. Soil burial tests indicated P-laden ESBC has a good P slow-release performance (maintained for up to 25 days). Overall, ESBC has a promising application potential as an efficient adsorbent for phosphorus recovery and subsequently as a slow-release fertilizer.