Lithium has become one of the most sought-after commodities globally. Its unique properties make it the key ingredient in rechargeable lithium-ion batteries powering electric vehicles (EVs) and large-scale energy storage systems. The metal’s ability to store significant energy has positioned it at the forefront of the worldwide transition toward sustainable energy. Extracting lithium is complex, as it is not found in its pure state but locked within subsurface brines or hard rock minerals. Current industry practice relies on two distinct methods: one leveraging natural evaporation and the other involving intensive mining and thermal processing.
Extraction from Subsurface Brine Deposits
Extracting lithium from subsurface brine is predominantly used in the high-altitude salt flats, or salars, of the “Lithium Triangle” (Chile, Argentina, and Bolivia). This method begins by drilling wells and pumping the highly saline, lithium-rich liquid from underground reservoirs to the surface. The brine typically contains lithium chloride alongside other dissolved salts, such as potassium and magnesium chlorides.
Once on the surface, the brine is piped into massive, shallow solar evaporation ponds. The arid climate and high solar radiation naturally drive the concentration process. Over a period that often lasts 12 to 18 months, the water evaporates, causing less-soluble salts to precipitate out.
Chemical agents, such as hydrated lime, are periodically added to selectively remove impurities like magnesium. As the brine reaches a high concentration of lithium chloride, it is transferred to a recovery facility. Chemical treatment with sodium carbonate is then used to induce a precipitation reaction, separating the lithium from the liquid to yield a solid, crude lithium carbonate concentrate.
Mining and Processing of Hard Rock Ore
The second major pathway for obtaining lithium involves traditional hard rock mining, primarily targeting the mineral spodumene (LiAlSi₂O₆). This method is common in places like Australia and North America, where lithium is locked within pegmatite deposits. Extraction begins with conventional open-pit mining, requiring blasting and excavating large quantities of ore.
The raw ore, which typically contains a low concentration of lithium oxide (Li₂O) between 1% and 2%, is then subjected to beneficiation. This physical process involves crushing the ore and grinding it into a fine powder. The spodumene mineral is separated from the waste rock using techniques like gravity separation and froth flotation, which uses chemical reagents to make the lithium-bearing particles hydrophobic.
This mechanical separation yields a spodumene concentrate with a much higher lithium content, typically around 6% Li₂O. To chemically unlock the lithium, the concentrate undergoes a high-temperature thermal treatment known as roasting or calcination. The concentrate is heated in a kiln to approximately 1,100°C to transform stable alpha-spodumene into the more reactive beta-spodumene. This phase change is necessary because the alpha form is resistant to chemical attack.
The beta-spodumene is then treated with sulfuric acid (H₂SO₄) at high temperatures, a process called acid leaching, to dissolve the lithium and form a lithium sulfate solution.
Refining the Lithium Product
Regardless of the source, the resulting crude concentrate requires further purification to meet the stringent standards for battery manufacturing. The initial products, such as lithium carbonate or crude lithium sulfate solution, are not pure enough for use in high-performance batteries. This downstream step focuses on achieving battery-grade purity by removing trace contaminants like iron, calcium, and magnesium.
The refining process involves a multi-step chemical purification sequence, including precipitation, filtration, and crystallization. Many battery manufacturers require high-purity lithium hydroxide (LiOH) instead of lithium carbonate, especially for cathodes with high-nickel chemistries that offer greater energy density. Converting lithium carbonate to lithium hydroxide is achieved by reacting it with hydrated lime, followed by further purification steps like ion exchange and a second crystallization stage.
Environmental Context of Lithium Extraction
The two primary methods of lithium extraction have distinct environmental trade-offs, relevant given the rapid growth of the EV market. Brine extraction is generally less carbon-intensive than hard rock mining, but it faces significant challenges related to water consumption and land use. The process relies on the evaporation of massive amounts of water in arid regions, which can lead to the depletion of local aquifers and increased water stress.
The solar evaporation ponds also require a vast land footprint. Conversely, hard rock mining is notably more energy-intensive, primarily due to the high-temperature roasting step. This thermal processing contributes to a significantly higher carbon footprint, with hard rock sources sometimes being three to five times more carbon-intensive than brine operations.
Hard rock mining also involves the physical disturbance of the landscape through open-pit operations and the generation of substantial volumes of solid waste and tailings. While hard rock processing requires more water for chemical and thermal reactions, the overall water consumption impact is often localized compared to the broad regional water table effects seen in brine evaporation.