Lithium, a soft, silvery-white metal, is central to the clean energy transition. The vast majority of rechargeable batteries, powering everything from mobile phones to electric vehicles, rely on lithium-ion technology. Because lithium does not exist in a pure elemental state in nature, it must be chemically separated and purified from its host material. This complex process uses different technologies depending on the source, primarily underground saltwater reservoirs or hard rock minerals.
Extracting Lithium from Brine Sources
Extraction from brine, which is saltwater rich in dissolved lithium salts, represents a significant portion of global lithium production. This method is common in the “Lithium Triangle” of South America, where arid conditions and high solar radiation favor the process. The initial step involves pumping the lithium-rich brine, typically containing lithium chloride (LiCl), from subterranean reservoirs to the surface.
The pumped brine is channeled into a vast network of shallow evaporation ponds. Over a period of nine months to two years, solar energy and wind cause the water to evaporate, progressively concentrating the lithium and other dissolved salts.
As the brine concentrates, unwanted salts such as sodium chloride, potassium chloride, and magnesium salts precipitate out. Hydrated lime (calcium hydroxide) is often added to help remove impurities, especially magnesium. The final concentrated brine, enriched with lithium chloride, is then transported to a chemical plant for further purification and conversion.
Extracting Lithium from Hard Rock Sources
The alternative primary method involves mining hard rock deposits, with the mineral spodumene (LiAlSi₂O₆) being the most common source. This process is distinct from brine extraction as it involves traditional mining techniques like drilling and blasting, followed by mechanical and thermal processing.
Once the ore is mined, it undergoes crushing and grinding to reduce it to a fine powder. This is followed by a beneficiation process, such as froth flotation, to create a spodumene concentrate containing 5% to 7% lithium oxide (Li₂O). The chemical stability of the raw mineral requires a high-energy treatment to unlock the lithium.
This thermal step, known as calcination, involves heating the concentrate to high temperatures, often around 1,100°C, in a rotary kiln. The heat changes the crystal structure, converting the stable alpha-spodumene into the more reactive beta-spodumene. The beta-spodumene is then mixed with sulfuric acid and roasted again at approximately 250°C, allowing the lithium to dissolve and form water-soluble lithium sulfate (Li₂SO₄) through leaching.
Emerging and Advanced Extraction Technologies
Newer technologies are being developed to address the slow pace and environmental footprint of conventional extraction methods. Direct Lithium Extraction (DLE) is a collection of technologies designed to selectively extract lithium ions from brine more quickly. DLE processes significantly reduce the use of land and water compared to solar evaporation ponds, cutting extraction time from many months to a matter of hours or days.
DLE methods typically involve advanced separation techniques. Adsorption-based DLE uses specialized sorbent materials to selectively capture lithium ions from the pre-treated brine. Ion exchange involves swapping lithium ions with other ions on a solid resin material, while solvent extraction transfers lithium ions into an organic liquid phase.
Once captured, the lithium is stripped from the sorbent or solvent using a mild chemical solution, yielding a concentrated lithium chloride solution. The spent brine, with most dissolved salts intact, can then be reinjected into the underground reservoir, minimizing water loss and environmental impact. DLE is also being explored for non-traditional sources, including geothermal brines and oilfield wastewater, where lithium is recovered as a byproduct.
Converting Raw Lithium into Battery Materials
The compounds yielded from the initial extraction—primarily lithium chloride (LiCl) or lithium sulfate (Li₂SO₄)—are only intermediate products. These crude materials must undergo further chemical processing to become high-purity, battery-grade compounds suitable for cathode manufacturing. The two primary final products are lithium carbonate (Li₂CO₃) and lithium hydroxide (LiOH).
Lithium carbonate is often produced by treating the lithium solution with sodium carbonate (soda ash), causing the lithium carbonate to precipitate out. While historically the standard battery material, lithium hydroxide is increasingly preferred for high-energy density batteries, particularly those with high-nickel cathode chemistries. This preference is because lithium hydroxide facilitates a more efficient manufacturing process for the cathode material.
Producing lithium hydroxide traditionally involves an additional causticization step, where lithium carbonate is reacted with calcium hydroxide. Newer conversion methods are being developed to produce lithium hydroxide directly from the lithium chloride or sulfate solutions, bypassing the intermediate lithium carbonate step. This direct conversion aims to simplify the refining process, reduce chemical usage, and lower energy consumption.