Abstract
Per- and polyfluoroalkyl substances (PFAS) are recalcitrant and bioaccumulative environmental pollutants. Whereas substantial efforts have been made to degrade PFAS, the potential for effectively using these fluoride resources has been overlooked. Here we develop an electrothermal fluorination method to selectively fluorinate brine salts using granular activated carbon (GAC)-sorbed aqueous film-forming foam (AFFF) as a fluorination agent. During this process, GAC and PFAS in AFFF are converted to graphene, whereas fluorine atoms are effectively mineralized into metal fluorides. Followed by washing and flash distillation, lithium can be recovered from other alkali and alkaline-earth metal cations in brine (Na+, Mg2+, K+, Ca2+) in the form of lithium fluoride, with an ~99% lithium purity and ~82% yield. The recovered lithium fluoride is demonstrated as an additive to stabilize electrolytes and improve the performance of lithium-ion batteries. Life-cycle assessment and techno-economic analysis indicate that this process greatly reduces greenhouse gas emissions and costs compared to the industrial lithium extraction method. This highlights the potential of the process to manage pollutants while providing a sustainable lithium supply, and this fluorination strategy shows promise to be extended to other metal extraction processes.
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All data needed to support the conclusions in the paper are present in the paper and/or Supplementary Information. Additional data related to this paper are available upon reasonable request from the corresponding authors.
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Acknowledgements
We thank W. Guo for the assistance of cryo-TEM characterizations, B. Chen for helpful discussion on XPS results, T. Terlier for developing ICP methods and X. Wang for the NMR test. The funding of the research is provided by the Air Force Office of Scientific Research (FA9550-22-1-0526, J.M.T.), the US Army Corps of Engineers, ERDC grant (W912HZ-21-2-0050, and W912HZ-24-2-0027, J.M.T.), Rice Academy Fellowship (Y. Cheng), the Strategic Environmental Research and Development Program (SERDP) award (ER22-3258, M.S.W.), and Rice WaTER Institute and Sustainability Institute Postdoctoral Fellowship (Y. Chung). The characterization equipment used in this project is partly from the Shared Equipment Authority (SEA) at Rice University.
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Y. Cheng and J.M.T. conceived the idea and designed the experiments. Y. Cheng conducted the thermodynamic analyses. Y. Cheng conducted the Li recovery experiments and most of the characterizations with the help of Q.L., P.S., T.X, J.S. and S.C. Y. Cheng and C.K. built the flash distillation system. C.G. provided the AFFF samples. L.E. built and maintained the electrical system. K.J.S. helped with the GC-MS detection. P.S., B.L. and T.S. helped with the NMR test. Y. Cheng conducted the electrochemical tests of the LIBs with the help of J.C. and O.E.O. Y. Chung and M.S.W. conducted the liquid characterizations. Y. Cheng and R.A.N. conducted the scale-up experiments with the help of H.Y. A.E.L. conducted the techno-economic analysis and life-cycle assessment and analysed the results with Y. Cheng. Y. Cheng and J.M.T. wrote and edited the paper. All aspects of the research were overseen by J.M.T. All authors have discussed the results and given approval to the final version of the paper.
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Rice University owns intellectual property on the electrothermal fluorination strategy for lithium recovery from brine salt. A provisional patent was filed by Rice University, where Y. Cheng and J.M.T. are listed as the inventors, which has not yet been licensed. The other authors declare no competing interests.
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Extended data
Extended Data Fig. 1 Physical properties of different chlorides components in brine salts.
a, Vapor pressure-temperature relationship. The horizontal dash line denotes atmospheric pressure of ~105 Pa. b, Water solubility at 25 °C.
Extended Data Fig. 2 Characterizations of field-collected AFFF before and after GAC adsorption.
a, Pictures of field-collected AFFF solution before (left) and after GAC adsorption (right). b, pH values of field-collected AFFF before and after GAC adsorption. c, Total dissolved organic carbon analysis of field-collected AFFF before and after GAC adsorption.
Extended Data Fig. 3 DSC results for AFFF decomposition.
a, AFFF/GAC. b, LiCl. c, AFFF/GAC mixed with LiCl with the F/Li ratio of 1.
Extended Data Fig. 4 XRD patterns of fluorination products from the reaction between AFFF/GAC with different metal chlorides at an input voltage of 100 V.
a, AFFF/GAC before ETF. b–f, Reaction products of AFFF/GAC with LiCl (b), NaCl (c), KCl (d), MgCl2 (e), and CaCl2 (f) after ETF.
Extended Data Fig. 5 GC-MS results of the fluorination evolved gas during the ETF process.
a, GC-MS chromatogram of the gases for the AFFF/GAC. b, Mass spectrum corresponds to the main peak with a retention time of 1.55 min in a. c, GC-MS chromatogram of the gases for the mixture of brine salt and AFFF/GAC (10% mole excessive of F). d, Mass spectrum corresponds to the main peak with a retention time of 1.55 min in c.
Extended Data Fig. 6 Scaling up sample mass to 60 g per batch.
a, Picture of the experiment setup for brine salt fluorinations. b, Picture of the sample during scale-up ETF. c, Real-time temperature curve recorded by an infrared thermometer with a detecting range of 1000–3000 °C. d, XRD patterns of fluorinated products. e, Purity and yield of the recovered Li after following washing and distillation processes.
Extended Data Fig. 7 31P NMR spectra of different electrolytes after storage for 1 month.
a, 31P NMR spectra. b, Zoom-in 31P NMR spectra. The peaks in the range from −15 to −25 ppm are ascribed to F2PO2−, degraded from LiPF6 in the electrolytes.
Extended Data Fig. 8 Morphology of the surface of Li chip in Li | |Li symmetric cells after cycling for 100 cycles.
a, Using the electrolyte without LiF. b, Using the electrolyte with LiF. The red circles labeled the formed lithium dendrites after cycling.
Extended Data Fig. 9 Material flow of different scenarios for lithium extraction from brine.
a, ETF process using AFFF/GAC as the fluorination agent. Gr denotes graphene. GAC and PFAS were converted to flash graphene during the process. b, Material flow of the industrial sorption process for lithium recovery from brine. c, Material flow of the industrial evaporation-precipitation process for lithium recovery from brine. C-brine-X means the concentrated brine, where X indicates different steps, and the chemicals in the brackets after are the components in the C-brine.
Extended Data Fig. 10 LCA and TEA results.
a, Average CED of four scenarios. b, Average GWP in CO2 equivalent of four scenarios. c, Average WRD of four scenarios. d, Average operating cost of four scenarios. e, Average revenue of four scenarios. f, Average profit of four scenarios.
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Cheng, Y., Lathem, A.E., Scotland, P. et al. Waste per- and polyfluoroalkyl substance-assisted flash fluorination for lithium recovery from brine. Nat Water 4, 369–380 (2026). https://doi.org/10.1038/s44221-026-00593-1
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DOI: https://doi.org/10.1038/s44221-026-00593-1
