Lithium refining is the complex series of physical and chemical processes required to convert raw, lithium-bearing materials into highly pure chemical compounds suitable for industrial use. This transformation is necessary because lithium is not found in nature in a pure, elemental state. The primary goal of refining is to remove all contaminants to meet the stringent purity specifications demanded by the technology sector, often for the production of lithium-ion batteries.
Sources of Raw Lithium
The refining process begins with the raw source material, which determines the initial chemical pathway chosen. Lithium is primarily sourced from two distinct geological formations: hard rock mineral deposits and subterranean brine solutions. Hard rock deposits, most commonly the mineral spodumene, are typically mined using conventional techniques and contain lithium chemically bound within a crystalline structure, requiring intense mechanical and thermal processing to liberate the lithium.
Subterranean brine deposits, found in salt flats or salars, contain lithium salts dissolved in a liquid solution, often alongside high concentrations of other salts like magnesium, potassium, and calcium. The presence of these impurities means that the refining approach for brine is fundamentally different from that used for hard rock. The choice of source material dictates the entire subsequent refining sequence, energy requirements, and production timeline.
Refining Processes for Hard Rock Ore
Refining lithium from hard rock, such as spodumene, is a mechanically and chemically intensive process that begins with pyrometallurgy. The initial step is calcination, where the concentrated spodumene ore is roasted at extremely high temperatures (1,000°C to 1,100°C). This heating changes the crystal structure of the mineral, converting the unreactive alpha-spodumene into beta-spodumene.
Once the crystal structure is altered, the material undergoes hydrometallurgy known as acid leaching. The roasted ore is cooled and mixed with a concentrated chemical, typically sulfuric acid (\(\text{H}_2\text{SO}_4\)), sometimes followed by a second, lower-temperature roast around 200°C. This acid treatment dissolves the lithium, extracting it from the rock matrix and forming water-soluble lithium sulfate (\(\text{Li}_2\text{SO}_4\)).
The resulting lithium sulfate solution is subjected to several stages of purification to remove residual impurities like iron and aluminum, often through precipitation and filtration. Finally, the purified solution is treated with sodium carbonate (\(\text{Na}_2\text{CO}_3\)) or other reagents to precipitate the final, marketable lithium compound. This sequence, involving high-temperature roasting followed by wet chemistry, is an energy-intensive pathway.
Refining Processes for Brine
Refining lithium from subterranean brine solutions relies heavily on natural energy sources and chemical precipitation. The process begins by pumping the lithium-rich brine to the surface and channeling it into vast, shallow evaporation ponds. Over a period of several months to a few years, solar energy and wind naturally evaporate the water, progressively concentrating the lithium salts.
As the water evaporates, less soluble salts precipitate out, naturally reducing the concentration of some contaminants. Chemical reagents, such as hydrated lime (\(\text{Ca}(\text{OH})_2\)), are added during this concentration phase to selectively remove persistent unwanted salts, particularly magnesium compounds. Magnesium is a common impurity that must be substantially reduced before the final conversion step because it is difficult to separate from lithium.
The highly concentrated lithium solution, now a lithium chloride intermediate, is ready for the final chemical conversion. By introducing soda ash, or sodium carbonate (\(\text{Na}_2\text{CO}_3\)), the lithium is selectively precipitated as solid lithium carbonate (\(\text{Li}_2\text{CO}_3\)). This solid is washed, dried, and packaged, or further processed into lithium hydroxide.
The Output: Lithium Compounds and Purity Standards
The refining process culminates in the production of two primary marketable compounds: lithium carbonate (\(\text{Li}_2\text{CO}_3\)) and lithium hydroxide (\(\text{LiOH}\)). These compounds are the raw materials for manufacturing the cathode components of lithium-ion batteries. Lithium carbonate is often used in batteries with lower-energy-density cathode chemistries, such as lithium iron phosphate (LFP).
Lithium hydroxide has gained importance because it is preferred for the synthesis of high-nickel cathode materials, such as those used in nickel-manganese-cobalt (NMC) batteries, which deliver the higher energy density required for long-range electric vehicles. The refining process must achieve extremely high purity standards to ensure battery performance and safety. Battery-grade lithium carbonate typically requires a minimum purity of 99.5%, and lithium hydroxide monohydrate requires a minimum of 56.5% LiOH content. The sequence is controlled to eliminate trace contaminants like iron, sodium, calcium, and heavy metals, which can otherwise compromise battery cycle life and performance.