<p>Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have garnered significant attention due to their high efficiency in removing refractory organic pollutants (ROPs) from wastewater. The development of highly active, cost-effective, and environmentally friendly catalysts is crucial. In this study, a novel Fe-containing biochar (RMBC) obtained by one-step co-pyrolysis of red mud (mining waste) and shaddock peel (fruit waste) was synthesized, and its potential for PMS activation was evaluated by degrading an azo dye, acid orange 7 (AO7), in water. Remarkably, the RMBC/PMS catalytic system nearly completely degraded AO7 at an initial concentration of 50&#xa0;mg/L in less than 20&#xa0;min with catalyst dose of 0.5&#xa0;g/L and PMS concentration of 8 mM. RMBC also showed a stable catalytic efficiency in 5 successive reuse cycles. The reactive oxygen species (SO₄⁻·, ·OH, ·O₂⁻) were responsible for the radicial pathway of degrading AO7, while the electrons from Fe⁰ on RMBC and ¹O₂ generated in RMBC/PMS system were responsible for the nonradical pathways of AO7 breakdown. In addition, the graphitic carbon structure of RMBC composite facilitated AO7 removal by providing the electron transfer pathway. This study offers valuable insights into how Fe-containing biochar activates peroxymonosulfate (PMS) for the treatment of dye-contaminated wastewaters, elucidating the mechanisms of the process and main variables involved.</p> Graphical Abstract <p></p>