Lithium is a critical raw material for developing current lithium-ion batteries and prospective next-generation batteries. Its reserves are concentrated in a handful of countries. It is primarily extracted from continental brines, wherein Li⁺ is relatively concentrated (0.3 –1.5 wt%) in a complex mixture of many more components with relatively large water solubilities.

Current practices to extract lithium from continental brines involve evaporation, i.e., >90% of water. Eventually, the concentration of Li⁺ intensifies up to 6–7%, in a brine which follows numerous chemical processing steps, to ultimately produce battery-grade lithium chemicals. Despite being the easiest and currently most cost-effective practices, these are inefficient and unsustainable (chemical-intensive, requires extensive land use and time, and delivers large volumes of waste), especially in the context of the sharp increase in the demand for lithium that is already happening and is expected to endure in the coming decades.

To sustainably meet the future demand for lithium, it is imperative to develop more efficient extraction methods, which are faster, less climate/weather reliant, minimize waste production, and especially deal with water differently than current industrial processing (i.e., circumventing evaporation). Besides being applicable to concentrated lithium brines, characteristic of primary extraction, these methods should especially be applicable to dilute brines (i.e., geothermal, oilfield, seawater, wastewater,—which contain 0.01–0.3 mg of Li⁺ per L of brine), as these have more recently prospected for Li recovery. Together with lithium recycling from spent batteries, these hold the promise of delocalizing raw lithium sourcing.

New extraction technologies have emerged within the past decade, including adsorption and the use of membranes. In addition to being insufficient for an effective recovery, some alternatives seem to imply a harsher environmental impact than current practices, whereas others would be disadvantageous to treat the large volumes of fluid associated with lithium extraction. Especially, electrochemical methods for Li⁺ recovery are (re)surging.^[1] The use of Li⁺ insertion electrodes coupled to membranes and membrane electrolysis are notoriously thriving.^[1,2] However, the first approach bears the limitation of requiring extremely thin and large area electrodes to process large brine volumes, and the second one suffers from being energy-intensive, plus current investigations show the constant addition of chemicals for pH adjustment, and produce chloride- and hypochlorite-anions rich solutions which are neither economic nor sustainable.^[2] Furthermore, in membrane electrolysis swelling of the ion exchange membrane could be an issue^[3] that has not been addressed in Li⁺ recovery studies; if excessive, this could lead to membrane deformations and ultimately to the blockage of the flow channels within the reactor. Despite the aforementioned limitations, electrochemical methods are a more sustainable and versatile option, with latent competitiveness vs. current industrial practices. Thus, ideal solutions should have the added value of circumventing the limitations of the state-of-the-art electrochemical approaches mentioned above. This aim was pursued in the present work.

Gas diffusion electrodes (GDEs) are broadly used in electrochemical energy-conversion devices, such as fuel cells and metal-air batteries, as well as in electrolyzers aiming at chemical synthesis, like in the chlor-alkali industry, hydrogen peroxide production, CO₂ conversions to fuels and fine chemicals, or N₂ reduction to ammonia. Recently, the use of GDEs was pioneered for metal recovery in a process named gas-diffusion electrocrystallization (GDEx).^[4–7] This talk will explain the underlying principles of GDEx and its successful application in the recovery of highly dilute lithium (<300 mg L^-1) in synthetic brines containing up to 150 mg L^-1 NaCl, as well as in real geothermal brines with Li+ concentrations below 50 mg L^-1. Up to 50% of direct lithium extraction from the brine can be achieved, selectively, forming solid materials with lithium concentrations >0.5%, which are promising as a starting material for the direct conversion into battery-grade lithium hydroxide or carbonate.

References:

[1] Battistel A., et al. (2020) Adv Mater 32, 1905440.

[2] Torres W.R., et al. (2020) J Membrane Sci, 615, 118416.

[3] Paidar, M., Faleev V., Bouzek K. (2016) Electrochim Acta, 209, 737.

[4] Prato et al. (2019) Sci Rep https://doi.org/10.1038/s41598-019-51185-x

[5] Prato et al. (2020) J Mat Chem A https://doi.org/ 10.1039/D0TA00633E

[6] Pozo et al. (2020) Nanoscale https://doi.org/10.1039/C9NR09884D

[7] Eggermont et al. (2021) React Chem Eng https://doi.org/10.1039/D0RE00463D

Acknowledgements:

This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654100 (CHPM2030 project). Support from the Flemish SIM MaRes programme, under grant agreement No 150626 (Get-A-Met project) is also acknowledged. The author thanks Elisabet Andres Garcia, Luis Fernando Leon Fernandez and Erwin Maes for their valuable contributions to this work.