Adsorption Removal of Organophosphates from Water by Steel Slag: Modification, Performance, and Energy Site Analysis

Organophosphates are a type of emerging environmental contaminant, which can be removed effectively by adsorption. Here, modified steel slag was examined for its adsorptive performance in the removal of hydroxyethylidene diphosphonic acid (HEDP) from water. Compared to acid (55.3%, maximum removal rate) and base (85.5%) modification, high-temperature modification (90.6%) significantly enhanced steel slag’s adsorption capacity for HEDP, surpassing that of unmodified slag (71.2%). Kinetic analyses elucidated a two-phase adsorption process—initial rapid adsorption followed by a slower equilibrium phase. The results of adsorption energy analysis showed that modified steel slag preferentially occupied the sites with higher energy, which promoted the adsorption. After five regeneration cycles, the adsorption properties of the material were not significantly reduced, which indicates that the material has good application potential. Microscopic and spectroscopic techniques, including SEM-EDS, FTIR, and XPS, were employed to uncover the surface chemistry and structural changes responsible for the enhanced adsorption efficiency. The adsorption mechanism of HEDP on steel slag is a complete process guided by hydrogen bonding interactions, strengthened surface complexation, and optimized ligand exchange. This study advances the sustainable utilization of industrial waste materials and contributes significantly to the development of innovative water treatment technologies.