Rice's electrical pulses recover nine tenths of PFAS fluorine as silver fluoride

The two reported percentages multiply out to about 90 percent: 0.999 times 0.90 is 0.899, so roughly nine parts in ten of the fluorine in the treated waste comes off as a usable reagent ^[8]. About one part in ten of what is removed goes somewhere other than the product ^[20].

The pulsed step starts with activated carbon that has already taken up the PFAS, mixed with silver nitrate ^[4]. In the group's earlier work that carbon came from adsorbing PFAS out of water, and flashing it made graphene while the fluoride ended up as calcium fluoride, the nontoxic mineral form, which nobody could then use ^[11]. Getting PFAS out of dilute water happens before any of this. A site still has to push the same volume through carbon.

The design problem was the heat source itself. "The biggest challenge was that the hot carbon needed to release fluorine also creates a reducing environment that can convert newly formed silver fluoride back to metallic silver," said Bowen Li, a co-first author and former Tour lab postdoctoral fellow, now a professor at Soochow University ^[5][14]. "We solved this by physically separating the carbon and silver with a porous quartz-fiber barrier. Fluorine-containing gaseous species can pass through the barrier, while the solid carbon and silver remain separated," Li said ^[6].

A bigger reactor has to reproduce that arrangement: hot solids held apart, fluorine crossing between them as a gas.

The silver is the part an operator has to buy. Rice reports that once the silver fluoride has handed its fluoride to an organic substrate, the silver can be collected and run through the process again ^[10]. Rice does not report cost, energy use, throughput, or where the uncollected fluoride ends up ^[17]. How many cycles the silver survives would decide whether the inventory is a one-time capital charge or a recurring loss. A pilot would have to measure that.

So the claim the evidence supports is a chemical one, made on lab-scale material ^[19]. "We saw this as an opportunity to turn this from a waste-destruction problem into a resource-utilization problem," said Yi Chen, a former Rice Academy Fellow and co-first author who is now an assistant professor at Fudan University ^[12]. Tour, the corresponding author, described the output in similar terms: "This takes PFAS waste treatment from a process focused on neutralizing and removing waste into circular materials chemistry" ^[13][16].