Enhancing the Efficacy of Mechanochemical Dehalogenation for Perfluorooctanoic Acid (PFOA) and Perfluorooctane Sulfonate (PFOS) In Contaminated Soils Using Ball Milling: Unveiling Rapid and Sustainable PFAS Remediation Pathways

Per- and polyfluoroalkyl substances (PFAS) contamination poses significant environmental and health risks due to their persistence and adverse effects. This study examines the efficacy of a special method, that is, dehalogenation by mechanochemical reaction (DMCR), comprising the application of a base metal in combination with a slightly acidic hydrogen source to dehalogenate per and/or polyhalogenated pollutants in different matrices in a ball mill, as a potential approach for remediating PFAS-contaminated soil. Laboratory-scale experiments were conducted using a planetary ball mill under controlled conditions to investigate the degradation of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) in sand serving as a contaminated model soil. The experiments were carried out in two stages: initially, with sand alone, and subsequently, with the addition of milling agents. Sodium (Na) metal, Na with butylamine (BA), Na with ethylenediamine (EDA), and Na with bis(3‑aminopropyl)amine (APA) were employed as the co-milling agents in specific ratios. The results demonstrated remarkably high degradation efficacy of PFOA and PFOS (approximately 100%) following ultra-high-performance liquid chromatography (UHPLC) coupled with a high-resolution mass spectrometer (LC-MS Orbitrap), as well as fluoride recovery employing a fluoride sensitive electrode (around 100%, within the experimental error), achieved within a strikingly short reaction time of just 5 min using Na in combination with EDA. Regarding Na with BA and APA, complete PFOA and PFOS removal was achieved after 10 min of milling, while complete fluoride recovery was achieved after 30 min. Na acted as a strong reductively defluorinating agent, enhancing the degradation process by facilitating the formation of reactive intermediates and promoting the breakdown of PFAS molecules. The amines, EDA, BA, and APA, simultaneously acted possibly as hydrogen sources as well as catalysts that could be providing solvated electrons, thus significantly enhancing the reactivity of the system under DMCR conditions, promoting PFOA and PFOS degradation, and facilitating complete fluoride recovery. Further experiments with sodium hydride (NaH), boron nitride (BN), and potassium hydroxide (KOH) were also performed for comparative analysis, following the same experimental conditions. In contrast, NaH, KOH, and BN systems showed comparatively lower fluoride mineralization despite moderate PFAS degradation, indicating kinetic limitations and incomplete defluorination under short milling durations. The enhanced degradation performance observed in Na–amine systems is attributed to synergistic mechanochemical interactions involving reactive intermediate formation, improved energy transfer, sustained thermal activity, and possible solvated electron generation that collectively accelerate PFAS defluorination. Overall, the findings of this study highlight the promising potential of DMCR or specially designed mechanochemical dehalogenation (MCD) for efficient and rapid remediation of PFAS-contaminated soil and open up new pathways for rapid and sustainable tackling of PFAS-contaminated soils and other toxic and hazardous contaminated matter, thus providing opportunities for more sustainable and expedient remediation strategies.