Advanced magnetic adsorbents for enhanced phosphorus and fluoride removal from wastewater: Mechanistic insights and applications

A novel mesoporous magnetic nanoparticle adsorbent, Fe3O4@CSH-AAO, was synthesized using the atomization-precipitation method, effectively removing phosphorus (P) and fluoride (F) from wastewater, particularly from the recirculating water of wet-process phosphoric acid. The adsorbent achieved removal efficiencies of 99.6 % for P and 73.5 % for F under conditions of 20 g/L adsorbent dosage, pH ≈ 4, with initial P and F concentrations at 115 mg/L and 38 mg/L, respectively. Equilibrium adsorption data indicated that the adsorption kinetics followed the pseudo-second-order model for F and the pseudo-first-order model for P. The adsorption isotherms fitted the Langmuir model for P and the Freundlich model for F, with maximum adsorption capacities of 37.86 mg P/g and 6.764 mg F/g at pH 4 and 298 K. The surface properties, functionality, and crystallinity were analyzed using BET, SEM, TEM, XRD, and XRF. Furthermore, XPS analyses and molecular dynamics (MD) simulations elucidated that surface Ca in CSH and the exposed Al atoms on the γ-Al2O3 (1 1 0) surface serve as optimal adsorption sites for P and F. The steric hindrance imposed by phosphorus contributes to its preferentially higher adsorption capacity over fluoride. This study not only presents an effective method for the removal of phosphorus and fluoride suitable for practical applications but also provides deep insights into the adsorption mechanism, highlighting the pivotal role of steric hindrance in facilitating ion adsorption.