Abstract

This study used red mud (RM), steel slag (SS), and desulfurization slag (DS) as raw materials to construct three catalytic oxidation systems, namely RM-DCDA/H2O2, SS-DS/H2O2, and SS-DS/peroxymonosulfate (PMS), to promote the utilization of industrial solid waste and enhance the treatment of recalcitrant antibiotic wastewater. The ciprofloxacin (CIP) degradation performances, influencing factors, and preliminary reaction mechanisms of these systems were investigated. RM formed an Fe3N/C composite structure after acidification and dicyandiamide-assisted calcination. The Fe3N active phase, coexistence of Fe2+/Fe3+, and N-doped C structure facilitated H2O2 activation and electron transfer. The SS-DS catalyst exhibited a rough and porous structure and contained Fe, Ca, and S species, which could provide reactive sites for H2O2 and PMS activation, following acid modification and urea-assisted calcination. Under the necessary reaction conditions, the CIP degradation efficiencies of the RM-DCDA/H2O2, SS-DS/H2O2, and SS-DS/PMS systems reached 94.60%, 92.58%, and 95.17%, respectively. These results indicate that RM- and SS-derived materials can be used for CIP oxidative degradation; however, the values should not be interpreted as a strict comparison of the intrinsic catalytic activity because the operating conditions differed among the systems. Parametric experiments showed that the catalyst dosage, oxidant concentration, and initial pH influenced the degradation efficiency. The H2O2-based systems were more suitable under acidic conditions, whereas the SS-DS/PMS system showed wider pH adaptability. Coexisting anion and humic acid experiments indicated that the systems were tolerant to natural organic matter, whereas HCO3− and HPO42− inhibited degradation. CIP was further oxidized in total organic C and recycling experiments; however, it was difficult to completely mineralize it within a short reaction time, and the catalyst retained relatively high activity after repeated use. Radical quenching experiments suggested that ·OH and ·O2− participated in the degradation reactions in the RM-DCDA/H2O2 and SS-DS/H2O2 systems. In the SS-DS/PMS system, comparative quenching experiments revealed that non-radical singlet oxygen (1O2) was the dominant reactive species, while SO4−· and ·OH contributed only marginally. In conclusion, RM and SS-DS can be used as low-cost raw materials to prepare industrial solid-waste-derived catalysts for the oxidative degradation of CIP, thereby providing a reference for industrial solid waste valorization and antibiotic wastewater treatment.

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