Ionizing Radiation Sustains Fenton Oxidation through Radiolytic Fe Redox Cycling for Deep Mineralization of Refractory Pollutants

Abstract The limited regeneration of Fe(II) from Fe(III) constrains sustained oxidation and mineralization in conventional Fenton processes. Here, we investigate an ionizing radiation-assisted Fenton process (IRFP) in which radiolytic Fe redox cycling sustains Fe-mediated oxidation. Using sulfasalazine as a model pollutant, we demonstrate that radiolytically generated hydrated electrons support two coupled pathways: rapid H2O2 activation and the conversion of Fe(III) to Fe(II). The resulting Fe redox cycling dynamically replenishes the Fe(II) pool alongside radiolytic H2O2 activation, thereby sustaining oxidative transformation beyond the initial degradation stage. Compared with irradiation and conventional Fenton treatment, IRFP promoted deeper fragmentation of azo, sulfonamide, and aromatic structures, resulting in enhanced mineralization. Transformation-product analysis further showed that continued transformation in IRFP reduced the persistence of complex intermediates with elevated predicted toxicity. In real pharmaceutical and coking wastewaters, IRFP achieved effective treatment under near-neutral conditions with substantially lower H2O2 and Fe(II) requirements than Fenton treatment and lower absorbed doses than irradiation alone. Although its electricity demand remained higher than short-time Fenton treatment, the markedly lower dosage of chemicals reduced the potential iron sludge burden and resulted in lower estimated COD-normalized treatment costs under the investigated conditions. These findings establish radiolytic Fe redox cycling as a strategy for sustaining Fe-mediated oxidation and promoting deeper transformation and mineralization of refractory pollutants.