Copper Smelting Slag-Derived Fe₃O₄@Mesoporous Silica for Peroxymonosulfate Activation and Tetracycline Degradation:...

Tetracycline (TC) is a widely used antibiotic that is frequently detected in rivers, lakes and wastewater. Because TC is poorly removed by conventional biological treatment, its residues can harm aquatic organisms and promote the spread of antibiotic resistance; efficient and low-cost technologies for removing TC from water are therefore needed. In this study, copper smelting slag (CSS), an abundant industrial solid waste, was converted into a catalyst composed of Fe₃O₄ particles loaded on mesoporous silica (denoted Fe₃O₄@MS) via an alkali fusion-hydrothermal method. The catalyst was used to activate peroxymonosulfate (PMS), forming the Fe₃O₄@MS/PMS treatment system for the degradation of TC in aqueous solution. The effects of the main operating parameters (catalyst dosage, PMS concentration, initial pH and reaction temperature) on TC degradation were systematically evaluated. Under the optimized conditions (catalyst 0.5 g/L, PMS 1.0 mmol/L, initial pH 6.5, 25 °C), the Fe₃O₄@MS/PMS system removed 98.70% of 50 mg/L TC within 60 min. Radical quenching experiments and electron paramagnetic resonance (EPR) analysis revealed that TC was degraded through both radical pathways (hydroxyl •OH, sulfate SO₄^•- and superoxide O₂^•- radicals) and a non-radical pathway involving singlet oxygen (¹O₂), with •OH being the dominant reactive species. Nine degradation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS), based on which three degradation pathways were proposed. Toxicity estimation indicated that ring-opening and deamination reactions are the key steps for detoxification. In addition, a life cycle assessment (LCA) across five selected impact categories identified the main environmental burdens associated with catalyst production. Overall, this work demonstrates that CSS-derived Fe₃O₄@MS is an efficient, low-cost and sustainable catalyst for PMS-based antibiotic removal from water, offering a circular-economy approach that couples solid-waste valorization with clean water production.