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.
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