Using Gypsum-modified Biochar to Adsorb Phosphate from Water: Adsorption Performance and Mechanism

This study explored the use of gypsum-modified biochar (GBC) for phosphate adsorption from water. GBC, composed of an equal weight mixture of gypsum (CaSO4·2H2O) and straw biochar subjected to pyrolysis, demonstrated strong resistance to interfering anions (NO ₃ ⁻ , Cl ⁻ , and HCO ₃ ⁻ ) and high adsorption efficiency across a wide pH range (7–11). The adsorption behavior was well described by the Pseudo-Second-Order kinetic and Langmuir models, with a maximum capacity of 247 mg∙g ⁻¹ at 303 K. The adsorption mechanisms involved ligand exchange, electrostatic attraction, and micro-precipitation. These findings highlight GBC as a simple and effective adsorbent for phosphate removal.