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Researchers at Rice University have developed a process that can recover fluorine from PFAS waste and convert it into silver fluoride, a valuable reagent used in chemical manufacturing.
The approach targets fluorinated waste streams such as aqueous film-forming firefighting foam, offering a potential route to recover useful materials rather than simply neutralising contaminated waste.
The method was developed by a team led by James Tour, the T.T. and W.F. Chao Professor of Chemistry at Rice and reported in Nature Chemical Engineering.
It builds on earlier work in which the researchers used activated carbon to remove PFAS from contaminated water and transformed the carbon into graphene while capturing the fluorine as calcium fluoride.
Testing showed that the new process removed more than 99.9% of the available fluoride from PFAS, with around 90% recovered as silver fluoride.
The resulting material was comparable to commercially available silver fluoride, while the silver used in the process could also be recovered and reused.
Turning PFAS waste into a resource
PFAS, or per- and polyfluoroalkyl substances, are a large group of highly persistent fluorinated chemicals that have been widely used in products and industrial applications.
Their resistance to degradation makes them particularly challenging to remove and treat once they enter the environment.
The Rice team had previously demonstrated that PFAS could be captured from water using activated carbon. During subsequent treatment, the fluorine could be converted into calcium fluoride, a stable and non-toxic mineral.
However, this left the fluorine effectively locked away as another waste product. The latest research addresses that limitation by recovering the element in a form that can be fed back into chemical production.
Fluorine is an important component of numerous pharmaceuticals, agrochemicals, and advanced materials, creating an opportunity to connect PFAS remediation with resource recovery.
Rapid heating unlocks fluorine recovery
The new technique, known as flash encapsulated fluorination, uses activated carbon loaded with PFAS alongside silver nitrate. Short electrical pulses rapidly heat the material to several hundred degrees Celsius.
At these temperatures, fluorine is released from the PFAS molecules. Nearby silver captures the released fluorine, producing silver fluoride, which can subsequently be used to introduce fluorine into organic compounds.
The researchers faced a technical challenge during development. The heated carbon creates a reducing environment that can cause newly formed silver fluoride to revert to metallic silver, undermining recovery.
To overcome this, the team separated the carbon and silver using a porous quartz-fibre barrier. Fluorine-containing gases can cross the barrier, while the solid carbon and silver remain physically separated.
Supporting a circular approach to PFAS treatment
The laboratory results suggest the process could shift the focus of PFAS waste treatment from destruction alone towards recovering valuable chemical resources.
Silver fluoride produced through the process performed comparably to commercial material used in chemical synthesis. Importantly, after transferring its fluorine to an organic compound, the silver can be recovered and returned to the treatment cycle.
The researchers say the combination of PFAS removal, fluoride recovery and silver reuse could provide a more circular approach to managing fluorinated waste.
Further development will be needed to determine how effectively the process can be scaled beyond laboratory conditions and applied to complex real-world waste streams.
