Most research on “forever chemicals” focuses on how best to remove them from the environment. But solutions to tricky problems often emerge from the most unexpected of places—as demonstrated by a new study that instead redirects the pollutants into becoming tools for extracting precious lithium.
In a recent Nature Water study, a team led by Rice University researchers describes a novel way to use spent perfluoroalkyl and polyfluoroalkyl substances, or PFAS, to recover lithium from high-salinity brine pools. The team tapped into the fluorine content inside PFAS leftovers, using it to attract lithium from briny water. Remarkably, the team was able to collect lithium fluoride at 99% purity and confirmed that the sample was pure enough to boost the stability and performance of lithium-ion batteries.
“By thinking about waste as a potentially useful compound, we were able to convert the problematic GAC-sorbed [activated carbon from spent PFAS] PFAS into a valuable metal that can be used in batteries, for example,” said Yi Chang, the study’s lead author and a postdoctoral associate at Rice University, in a statement.
Two problems in one
PFAS is everywhere. According to the U.S. Environmental Protection Agency (EPA), thousands of different PFAS have been used in all sorts of consumer products since the 1940s. These manufactured chemicals take a long time to break down, and researchers have detected PFAS in natural sources like soil, wind, and clouds, but also in most human organs and foodstuffs, like beer, sugar, or apples.
Surveys conducted by the Centers for Disease Control and Prevention (CDC) say most people in the U.S. have been exposed to PFAS, according to the EPA. However, research is still ongoing regarding the extent to which this exposure could lead to adverse health effects, such as increased cancer risk or decreased fertility.
On the other hand, lithium is a much-valued resource for a variety of industries, most famously for its use in batteries for mobile phones, laptops, and electric vehicles, according to the Royal Society of Chemistry. Although the element itself isn’t extremely rare, high and increasing demand for the metal has some experts projecting a serious worldwide shortage by the end of 2030.
Breathing new life into PFAS?
The new method essentially tacks on additional steps to the end of the PFAS life cycle—that is, when the chemical truly becomes an environmental liability. Specifically, the team gathered PFAS-saturated granular activated carbon, or a filtering material that removes harmful chemicals from firefighting foam.
“Rather than treating this spent material as an endpoint, the [team] used it as an input,” the researchers said in the statement. Fascinatingly, the team created a system akin to an electrode using the PFAS-soaked carbon scrap and very salty brine containing different elements.
When the mixture was rapidly heated up to 1,832 degrees Fahrenheit (1,000 degrees Celsius) and then rapidly cooled down again, the fluoride in the PFAS broke apart and bonded with positive ions in the brine, creating new compounds including lithium fluoride. What’s more, this treatment turned the PFAS-laden carbon into “nontoxic waste,” the researchers said.
The researchers then reheated the system to lithium fluoride’s boiling point, 3,049 degrees F (1,676 degrees C), to separate the lithium from the amalgam. Doing so enabled the team to recover 82% of the available lithium fluoride at 99% purity, according to the paper.
Great science from uncanny ideas
Most importantly, the team incorporated the recovered lithium fluoride into lithium-ion battery electrolytes, monitoring how the addition affected battery performance compared to blank cells without the treatment. A month later, the team identified clear signs that the batteries with the extracted lithium displayed higher, more consistent capacity.
Next, the team compared their method to existing lithium extraction techniques to see whether their discovery, although exciting, could also be practically superior. In the paper, the team argues that the method indeed has a lower environmental impact and could generate five times more profit than other processes.
That’s arguably an ambitious claim to make, and we’ll need to give independent experts some time to pick apart the analysis. Still, the findings showcase how the slightest perspective shift can give rise to fascinating results. And if the team delivers on their promises, we’ll really be killing two birds with one stone for some of the trickiest challenges we face.
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