Magnetic catalysts (MCs) derived from iron-rich drinking water treatment residuals (WTRs) were prepared through pyrolysis treatment and introduced as activators of peroxymonosulfate (PMS) for refractory atrazine (ATZ) degradation. Comprehensive characterization analysis indicated that pyrolytic temperature could manipulate the crystalline structure evolution of the MCs and influence their physicochemical and catalytic properties. The catalytic performances of the as-prepared samples pyrolyzed at 600 degrees C (MC-600) and 1000 degrees C (MC-1000) were evaluated, and MC-1000 exhibited far more excellent catalytic reactivity than MC-600 in PMS oxidation system. Such difference was mainly attributed to that Fe3O4 and Fe are the dominant active ingredients of MC-600 and MC-1000, respectively. The electron spin resonance (ESR) tests and radical quenching experiments revealed that hydroxyl radical ((OH)-O-center dot) and sulfate radical (SO4 center dot-) predominated in the MC-600/PMS and MC-1000/PMS systems, respectively. The mechanisms of the MCs-mediated PMS activation process were elucidated, among which the role of iron mineral phase was emphatically explored. Furtherly, possible degradation by-products were identified by LC-MS, and potential degradation pathways were proposed. Ultimately, the effects of pivotal parameters (i.e. MC-1000 dosage, PMS concentration, initial pH, and water matrix species) on ATZ degradation were investigated to assess the applicability of the MC-1000/PMS system.