The world’s demand for lithium extraction is growing every day and is especially driven by increased lithium use in new consumer electronic battery technologies and electric cars. While you’ve likely heard of lithium batteries, you might still want to know where all that lithium comes from and how it’s produced. If so, you may be asking “what is lithium extraction and how does it work?”
Lithium extraction and processing can depend heavily upon the source of the metal, so in this article, we’ll take a look at some of the more typical lithium production strategies and how they compare.
What is lithium extraction?
Lithium is a highly reactive alkali metal that offers excellent heat and electrical conductivity. These properties make it particularly useful for the manufacture of glass, high-temperature lubricants, chemicals, pharmaceuticals, and lithium-ion batteries for electric cars and consumer electronics. However, because of its high reactivity, pure elemental lithium is not found in nature but is instead present as a constituent of salts or other compounds. Similarly, most commercial lithium is available in the form of lithium carbonate, which is a comparatively stable compound that can be easily converted to other salts or chemicals.
Lithium salts are found in underground deposits of brine, mineral ore, and clay, as well as in seawater and geothermal well brines/water. By definition, lithium extraction is a set of chemical processes where lithium is isolated from a sample and converted to a saleable form of lithium, generally a stable yet readily convertible compound such as lithium carbonate. Most lithium extraction processes entail some form of mining to reach underground deposits of lithium-rich minerals or brines.
While lithium is fairly abundant in both land and sea, only a few sources are considered economically viable. This is expected to change in the coming years as new technologies make extraction from alternative lithium sources more cost-competitive.
How does lithium extraction work?
Commercial lithium arises from two major sources: underground brine deposits and mineral ore deposits. The methods of lithium extraction and processing vary depending upon the source material, and include the following:
Conventional lithium brine extraction
An overwhelming quantity of today’s lithium is extracted from liquid brine reservoirs that are located beneath salt flats, known as salars, most of which are located in southwestern South America and China. Other lithium-rich brine resources include geothermal and oil field brines, which are addressed below.
Lithium brine recovery is typically a straightforward but lengthy process that can take anywhere from several months to a few years to complete. Drilling is required to access the underground salar brine deposits, and the brine is then pumped to the surface and distributed to evaporation ponds. The brine remains in the evaporation pond for a period of months or years until most of the liquid water content has been removed through solar evaporation. Salar brines are very concentrated and, in addition to lithium, typically contain potassium and sodium as well. Facilities usually operate several large evaporation ponds of various ages and may extract other metals (e.g. potassium) from younger ponds while waiting for the lithium content to reach a concentration optimal for further processing. In some cases, reverse osmosis (RO) is used to concentrate the lithium brine to speed up the evaporation process.
Once the brine in an evaporation pond has reached an ideal lithium concentration, the brine is pumped to a lithium recovery facility for extraction. This process varies depending upon the brine field composition, but usually entails the following steps:
Pretreatment. This step usually employs filtration and/or ion exchange (IX) purification to remove any contaminants or unwanted constituents from the brine.
Chemical treatment. Next, a series of chemical solvents and reagents may be applied to isolate desirable products and byproducts through precipitation.
Filtration. The brine is then filtered to separate out precipitated solids.
Saleable lithium production. The brine is finally treated with a reagent, such as sodium carbonate to form lithium carbonate, and the product is then filtered and dried for sale. Depending upon the desired product, different reagents may be applied to produce other commonly sold forms of lithium, such as lithium hydroxide, lithium chloride, lithium bromide, and butyl lithium.
Once the lithium extraction process is complete, the remaining brine solution is returned to the underground reservoir.
Hard rock / spodumene lithium extraction
While accounting for a relatively small share of the world’s lithium production, mineral ore deposits yield nearly 20 tons of lithium annually. Well over 100 different minerals contain some amount of lithium, however, only five are actively mined for lithium production. These include spodumene, which is the most common by far, as well as lepidolite, petalite, amblygonite, and eucryptite.
Mineral ore deposits are often richer in lithium content than are salar brines, however, they are costly to access since they must be mined from hard rock formations. Due to the added energy consumption, chemicals, and materials involved in extracting lithium from mineral ore, the process can run twice the cost of brine recovery, a factor that has contributed to its smaller market share.
The process for recovering lithium from ore can vary based on the specific mineral deposit in question. In general, the process entails removing the mineral material from the earth then heating and pulverizing it. The crushed mineral powder is combined with chemical reactants, such as sulfuric acid, then the slurry is heated, filtered, and concentrated through an evaporation process to form saleable lithium carbonate, while the resulting wastewater is treated for reuse or disposal.
Other lithium extraction processes
Beyond salar brine and mineral ore, lithium can be produced from a few other sources, though such production is not widespread at this time. These other lithium sources include:
Hectorite clay. Extensive research and development have been invested in developing effective clay processing techniques, including acid, alkaline, chloride, and sulfate leaching, as well as water disaggregation and hydrothermal treatment. To date, none of these technologies has proven economically viable for extracting lithium from clay.
Seawater. Hundreds of billions of tons of lithium are estimated to exist in our oceans, making them an attractive source for meeting future lithium demand. While existing processes—including a co-precipitation extraction process and a hybrid IX-sorption process—have succeeded in extracting lithium from seawater, newer membrane technologies are showing greater promise for bringing the costs of seawater extraction down.
Recycled brines from energy plants. Efforts to retrieve lithium from geothermal brines are gaining popularity as worldwide demand for lithium increases and as new technologies emerge. The processes used follow conventional brine extraction, though they might be adapted based on the content of the brine stream.
Recovered oil field brine. Retrieval of lithium from oil field brines is technically just another form of conventional brine extraction, with the difference being the source of the brine.
Recycled electronics. Lithium battery recycling doesn’t truly meet the definition of extraction, however, as demand grows, lithium-ion battery recycling will become an increasingly valuable source of the metal.
While each of these poses a potentially valuable source of lithium, the technologies to extract brine from them are not yet developed enough to make them cost-effective or viable alternatives to salar brine mining or mineral ore mining.
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