Tailoring Hydrophobicity and Selectivity in Organo-Modified Steel Slag Adsorbents for Aromatic Hydrocarbon Remediation from Petroleum Wastewater

The reutilization of industrial steel slag (SS) as an adsorbent for petroleum wastewater treatment was achieved through acid activation and subsequent surface modification with quaternary ammonium surfactants to yield organo-functionalized silica-rich materials (organo-SRSs). Acid activation exposed a highly hydroxylated SiO₂ matrix, enabling effective organic grafting and imparting enhanced hydrophobicity. Among the prepared materials, benzalkonium chloride functionalized silica-rich material (BC-SRS) exhibited superior performance, achieving a maximum naphthalene (NA) adsorption capacity of 462.9   mg/g due to synergistic π–π stacking, hydrophobic interactions, and weak electrostatic forces. Adsorption followed pseudo-second-order kinetics and Freundlich isotherms, with thermodynamic analysis indicating spontaneous and endothermic behavior for BC-SRS. The material demonstrated excellent reusability and selectivity under complex water chemistries. This work presents a sustainable strategy for converting industrial waste into high-efficiency adsorbents, advancing green remediation and circular resource utilization.