Mechanochemical remediation of perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) amended sand and aqueous film-forming foam (AFFF) impacted soil by planetary ball milling

Highlights: • First demonstration of PFAS destruction in porous media by planetary ball milling • PFOS and PFOA concentrations in sand can be reduced up to 99%. • PFAS concentrations in AFFF impacted soils can be reduced by co-milling with KOH. Per- and polyfluoroalkyl substances (PFAS) are manmade, fluorinated organic chemicals which have been identified as persistent organic pollutants. PFAS have surface active properties that have made them suitable for applications in oil- and water-resistant products, as well as many firefighting foams. No on-site remediation strategies exist to treat PFAS impacted soils. Mechanochemical remediation of PFOS- and PFOA-amended sand via a planetary ball mill was studied. The effect of sand mass, KOH as a co-milling reagent, and water saturation on the degradation of PFOA and PFOS was evaluated. By 4 h of milling concentrations were reduced by up to 98% for PFOS-amended dry sand and 99% for PFOA-amended dry sand without the addition of a co-milling reagent. Water saturation was determined to be a significant hindrance on the mechanochemical destruction of PFOS and PFOA. A maximum of 89% of fluoride was recovered from PFOS-amended sand when KOH was used as a co-milling reagent. It is hypothesized that reactive particles generated from the fracture of sand grains react with PFAS molecules to initiate destruction, which can result in full defluorination. Milling experiments were also conducted on soils from a Canadian firefighting training area (FFTA), demonstrating that PFOS concentrations can be reduced by up to 96% in site soils. For the first time, ball milling for the remediation of PFAS in environmental media has been demonstrated using amended sand and legacy soils from a FFTA.