Red mud modified biochar for peracetic acid activation to degrade sulfamethazine: A non-radical-dominated mechanism

The ecological risks posed by over 3.5 billion tons of accumulated red mud, together with antibiotic contamination in aquatic environments, present pressing environmental challenges. In this study, an iron-based biochar (RMgt800) was synthesized via co-pyrolysis of red mud and tea residue, following a "waste control by waste" strategy, and was applied for the first time to activate peracetic acid (PAA) for the efficient degradation of sulfamethazine (SMZ). RMgt800 exhibited enhanced PAA activation performance, achieving 96.99 % SMZ removal (k_obs = 0.0697 min^-1) within 60 minutes-12.7 times higher than that of biochar or red mud alone. Electron paramagnetic resonance (EPR) analysis revealed that non-radical oxidation, primarily mediated by singlet oxygen (¹O₂), dominated the degradation pathway. The formation of ¹O₂ was attributed to O-O bond cleavage in PAA, facilitated by Fe species and surface -OH functional groups. At the same time, although the degradation efficiency was moderately inhibited in the presence of high concentrations of HCO₃^- and humic acid (HA), the system maintained over 90 % removal efficiency in the presence of Cl^- and SO₄^2-, demonstrating good applicability across various real water matrices. This work developed a green catalyst for PAA activation and provided a feasible approach for red mud valorization and aquatic antibiotic contamination control.