Delithiation and lithiation of LiFePO4: Implications for direct Li extraction from synthetic solutions and geothermal brines
Rebekka Reich, Elisabeth Eiche, Jochen Kolb
Abstract
The demand for Li is and will be increasing in the future, and the development of a direct Li extraction (DLE) technology from unconventional resources, like geothermal brines, may contribute to a resilient supply in the future. This study investigates the deintercalation from and intercalation of Li in LiFePO4 (LFP) at 25–80 °C, near neutral to acidic pH and the effect of high salinity on the Li extraction performance. The (de-)lithiation is a fully reversible redox process between triphylite and heterosite. Lithium is delithiated from LFP using 0.1 M Na2S2O8 at 42–43 mg/g. The lithiation kinetics increase with temperature, but show a complex relationship to reducing agent (Na2S2O3) concentration. The maximum re-intercalation is achieved in synthetic LiCl + 0.5 M Na2S2O3 solution at 39 mg/g, 25 °C and 7 days, whereas 27 mg/g and 1.3 mg/g Li are intercalated to LFP within 3–4 h in experiments with Bruchsal and synthetic Neustadt-Glewe geothermal brines at 60 °C, respectively. At optimal parameters, >99 % Li are recovered from both geothermal brines in laboratory experiments. This shows that LFP can be used for DLE from geothermal brines under specific conditions in a purely chemical process.