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.
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