US researchers have demonstrated a technology that converts waste PFAS captured by granular activated carbon into a resource for lithium recovery, offering potential environmental and efficiency benefits.
Scientists have developed a new approach to lithium extraction that recycles problematic chemical contaminants known as PFAS to recover lithium from highly saline brine.
The technology, reported in the journal Nature Water, could provide an alternative route to producing lithium used in batteries, while also addressing persistent waste problems.
The study was conducted by a team at Rice University led by postdoctoral researcher Yi Chen, under the direction of James Tour.
Rather than focusing solely on removing PFAS (short for per- and polyfluoroalkyl substances) from the environment, scientists investigated whether these fluorine-rich compounds could be used productively in industrial processes.
Their findings suggest that PFAS recovered during environmental cleanup have the potential to facilitate lithium recovery from saline water resources and reduce both waste and environmental footprint associated with the lithium supply chain.
Challenges of recovering lithium from salt water
With the expansion of electric vehicles and energy storage technology, demand for lithium is rapidly increasing.
Although lithium can be mined from hard rock deposits, many producers rely on saline resources, or groundwater with high salt concentrations that contain dissolved lithium and other salts.
Compared to conventional mining, brine-based lithium extraction is considered less destructive to the surface. However, technical hurdles still exist in this process.
Selectively extracting lithium from mixtures containing many dissolved minerals can be difficult, and current approaches often require the use of large amounts of water, long processing times, and large energy inputs.
Researchers have sought ways to improve the efficiency and sustainability of lithium recovery from these brine waters.
Uses PFAS collected with granular activated carbon
Rice Team’s method starts with PFAS, which has already been removed from contaminants such as firefighting foam. These compounds are often captured using granular activated carbon, a filtration material that absorbs and traps PFAS molecules.
Granular activated carbon is effective at removing PFAS from water and other samples, but the material itself becomes contaminated. Once PFAS is saturated, it is typically treated as hazardous waste.
In the new study, researchers viewed this spent carbon as a potential chemical resource rather than a disposal problem.
PFAS molecules contain strong carbon-fluorine bonds. Fluorine, an anion, can form stable salts with certain positively charged metal ions.
Scientists hypothesized that fluorine released from PFAS could combine with lithium ions present in salt water to form lithium fluoride, a compound useful in battery technology.
Electric heating accelerates chemical reactions
To test this idea, the researchers mixed PFAS-loaded granular activated carbon with salt water containing lithium and other dissolved metals such as magnesium and calcium.
They then applied electrothermal heating, a technique that uses electrical current to rapidly increase temperature. The mixture was briefly heated above 1,000 °C and then rapidly cooled.
These extreme but short-term conditions free the fluorine atoms within the PFAS molecules from their original bonds. When fluorine is released, it reacts with metal ions in the brine to form fluoride salts.
The resulting mixture contained lithium fluoride along with magnesium fluoride and calcium fluoride. The heating process also turned the carbon material into a non-toxic residue after the fluorine was removed.
Selective recovery of lithium is possible by distillation
Additional steps were required to separate lithium fluoride from other fluoride salts. The researchers relied on differences in boiling points between the compounds.
Lithium fluoride evaporates at approximately 1,676°C, which is significantly lower than the boiling points of magnesium and calcium fluoride.
By reheating the mixture under carefully controlled electrical heating conditions, the scientists vaporized the lithium fluoride while leaving the other salts behind.
The vapor was then condensed and collected, yielding lithium fluoride with approximately 99% purity. According to the study, this process recovered approximately 82% of the lithium fluoride present in the brine.
Testing battery applications
To assess whether the recovered material could be used in energy storage technology, the research team incorporated purified lithium fluoride into the electrolyte of a lithium-ion battery.
Laboratory tests showed that the electrolyte containing the recovered compounds remained stable and supported battery performance.
These results suggest that lithium obtained by this method has the potential to meet quality requirements for battery-related applications.
Consideration for the environment and efficiency
The researchers also compared their process to established brine-based lithium extraction techniques. Their analysis showed that PFAS-based methods may require less water and energy than common commercial approaches.
Electrothermal processes operate quickly, so the reaction and separation steps are completed within minutes rather than hours or days.
The study also estimated a smaller contribution to greenhouse gas emissions compared to traditional brine extraction methods.
Additionally, this approach also addresses the growing waste problem associated with PFAS-contaminated filter media.
Linking waste management and critical mineral supplies
PFAS contamination is a global environmental problem, and these persistent chemicals have been detected in water, soil, and industrial waste streams.
Finding productive uses for captured PFAS could help offset the costs and challenges associated with cleanup.
Researchers are proposing a process that combines two environmental challenges: managing harmful pollutants and providing critical minerals for batteries by converting PFAS trapped in granular activated carbon into a fluorine source for lithium recovery.
Although further work is needed before large-scale implementation, this study reveals how waste can be integrated into resource recovery technologies and has the potential to reshape how industry approaches both environmental remediation and lithium production.
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