Additive-Free Ball Milling in Stainless Steel Mills Enables Destruction of PFAS on Granular Activated Carbon

Granular activated carbon (GAC) is widely employed for the removal of per- and polyfluoroalkyl substances (PFAS) from aqueous systems. However, the safe management of spent, PFAS-laden GAC remains a pressing environmental challenge. Mechanochemical ball milling has recently emerged as a novel treatment paradigm for PFAS destruction under ambient conditions, typically requiring co-milling reagents such as SiO₂, KOH, or boron nitride. In this study, we report an unprecedented finding that PFAS adsorbed on GAC can be degraded by milling with stainless steel (SS) balls in SS jars, without the need for additional reagents. In this process, the SS balls and jars not only provide mechanical energy but also act as electron donors, transferring electrons to the carbon substrate that subsequently mediates PFAS defluorination. This approach achieved degradation of PFOS spiked on Calgon Carbon Filtrasorb 400, accompanied by quantitative fluorine recovery (∼100% defluorination efficiency). Beyond laboratory-prepared samples, the strategy demonstrated universal applicability in degrading diverse PFAS species on field-collected GAC, achieving PFAS degradation regardless of chain length or headgroup. Furthermore, leaching tests confirmed that no residual PFAS was released from the milled GAC, supporting the feasibility of its safe landfill disposal.