Enhanced removal of roxarsone and inorganic arsenic using ball-milled heating pad waste to activate peroxymonosulfate: Critical role of non-radical pathways

The simultaneous removal of roxarsone (ROX) and inorganic arsenic was achieved by designing a heterogeneous catalytic system. In this study, iron-rich heating pad waste (HPW) was modified by ball milling (BM), and a BM-HPW activated peroxymonosulfate (PMS) system was constructed to control ROX pollution. Results show that during the ball milling process, Fe0 and Fe3O4 crystalline phases were formed, and the surface area of the material got improved. BM-HPW/PMS system performed effectively in ROX degradation and inorganic arsenic adsorption. Sulfate radical (SO4−), surface-bound species, singlet oxygen (1O2) and Fe(IV) were generated in the BM-HPW/PMS system, and the surface-bound species played a dominant role in ROX degradation. In addition, the possible degradation pathways of ROX were proposed according to the detected intermediates. This study adopted a green and environmentally-friendly mechanochemical method to achieve the recycle application of waste iron resources, which provides a new insight for PMS activation in water treatment.