Ethyl Cellulose Co-Encapsulation of Steel Slag–Persulfate Long-Term Petroleum Hydrocarbon Remediation

Petroleum hydrocarbon (PH) contamination in groundwater necessitates sustainable remediation solutions. This study develops a novel co-encapsulated composite by embedding steel slag (SS) and sodium persulfate (SPS) within an ethyl cellulose (EC) matrix ((SS + SPS)/EC) for permeable reactive barrier applications. The EC matrix enables controlled release of SPS oxidant and gradual leaching of alkaline components (Ca2+/OH−) and Fe2+/Fe3+ activators from SS, synergistically sustaining radical generation while buffering pH extremes. Optimized at a 10:7 SS:SPS mass ratio, the composite achieves 66.3% PH removal via dual pathways: (1) sulfate radical (SO4−•) oxidation from Fe2+-activated persulfate (S2O82− + Fe2+→SO4−• + SO42− + Fe3+), and (2) direct electron transfer by surface-bound Fe3+. In situ material evolution enhances functionality—nitrogen physisorption reveals a 156% increase in surface area and 476% pore volume expansion, facilitating contaminant transport while precipitating stable sulfate minerals (Na2SO4, Na3Fe(SO4)3) within pores. Crucially, the composite maintains robust performance under groundwater-relevant conditions: 54% removal at 15 °C (attributed to pH-buffered activation) and >55% efficiency with common interfering anions (Cl−, HCO3−, 50 mg·L−1). This waste-derived design demonstrates a self-regulating system that concurrently addresses oxidant longevity (≥70 h), geochemical stability (pH 8.5→10.4), and low-temperature activity, establishing a promising strategy for sustainable groundwater remediation. Continuous-flow column validation (60 d, 5 mg·L−1 gasoline) demonstrates sustained >80% removal efficiency and systematically stable effluent pH (9.8–10.2) via alkaline leaching.