Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are potentially harmful substances known as “forever chemicals” because they are so difficult to destroy. An emerging technique for degrading PFASs is to forcefully crush them with metal balls in a moving container, but this technique may require corrosive additives. Now, ACS’ researchers Environmental Science and Technology Letters report on a new type of “ball mill” additive that completely decomposes PFAS at room temperature and pressure.
Solid PFAS contamination is an ongoing problem for soil near waste sites, manufacturing sites, and facilities that frequently use fire fighting foam. The US Environmental Protection Agency currently recommends incineration to destroy these substances, but concerns remain about whether this energy-intensive method can effectively prevent environmental contamination.
Another option is ball milling, a process that mixes PFAS and additives with metal balls at high speeds. The collisions between the balls and the additives create solid-state reactions that break the carbon-fluorine bonds in PFASs and convert them into less harmful products. A common additive for this process is potassium hydroxide (KOH), but it forms troublesome clumps and is corrosive. To overcome these limitations, Yang Yang and his colleagues turned to boron nitride, a piezoelectric material that generates partial electrical charges and can accept electrons when deformed by mechanical forces. They now report a ball milling process that uses boron nitride as a non-corrosive additive to react with and destroy PFAS.
As a proof of concept for the new additive, the team ball ground two legacy PFAS compounds with boron nitride and analyzed the products. By optimizing the ratio of boron nitride to PFAS, the team almost completely removed the fluorine atoms from the PFAS within four hours at room temperature and pressure, effectively destroying it. The method also decomposed 80% of PFASs known from fire-fighting foam-contaminated soils after six hours. In both experiments, boron nitride degraded PFAS more efficiently than when KOH was used. Further analysis suggests that boron nitride accepts electrons and fluorine atoms from the PFAS, which then breaks down into fluoroalkyl radical species that react with oxygen or other radicals to ultimately produce harmless minerals. This new method could open the door to future mechanical force-based PFAS remediation strategies, the researchers say.