For decades, commercial lithium production relied upon mineral ore sources such as spodumene, petalite and lepidolite. Extracting lithium from such sources, however, is significantly more costly than extracting the metal from lithium-containing brines. In fact, it is estimated that the cost of extracting lithium from hard rock is double that of producing from brines, explaining why most such sources have been priced out of the market over the past 20 years.
Salar brines can be described as underground reservoirs that contain high concentrations of dissolved salts, such as lithium, potassium and sodium. These are generally found below the surface of dried lakebeds, known as salars.
In order to extract lithium from brines, the salt-rich waters must first be pumped to the surface into a series of evaporation ponds where solar evaporation occurs over a number of months. Because salar brines naturally occur at high altitudes and in areas of low rainfall, solar evaporation is an ideal and cost-effective method for precipitating salts.
Potassium is often first harvested from early ponds, while later ponds have increasingly high concentrations of lithium. Economical lithium-source brines normally contain anywhere from a few hundred parts per million of lithium to upwards of 7000ppm.
When the lithium chloride in the evaporation ponds reaches an optimum concentration, the solution is pumped to a recovery plant where extraction and filtering removes any unwanted boron or magnesium. It is then treated with sodium carbonate (soda ash), thereby precipitating lithium carbonate. The lithium carbonate is filtered, dried and ready for delivery. Excess residual brines are pumped back into the salar.
Lithium carbonate is a stable white powder, which is a key intermediary in the lithium market because it can be converted into specific industrial salts and chemicals, or processed into lithium metal.
Extraction of lithium from spodumene and other minerals, in contrast with salar brine sources, requires a wide range of hydrometallurgical processes.
Galaxy Resources, which mines spodumene mined in Australia, for example, first crushes and heats the ore in a rotary calcining kiln in order to convert the lithium crystal phase from alpha to beta (a process referred to as decrepitation). This allows the lithium present in the ore to be displaced by sodium.
The resulting spodumene concentrate is cooled and milled into a fine powder before being mixed with sulpheric acid and roasted again.
A thickener-filter system then separates waste from the concentrated liquor, while precipitation removes magnesium and calcium from this solution.
Finally, soda ash is added and lithium carbonate is crystallized, heated, filtered and dried as 99 percent pure lithium carbonate.
Converting lithium into metal form is done in an electrolytic cell using lithium chloride.
The chloride is mixed with potassium chloride in a ratio of 55 percent lithium chloride to 45 percent potassium chloride in order to produce a molten eutectic electrolyte. Potassium chloride is added to increase the conductivity of the lithium while lowering the fusion temperature.
When fused and electrolyzed at about 450°C chlorine gas is liberated while molten lithium rises to the surface of the electrolyte, collecting in cast iron enclosures. The pure lithium produced is wrapped in paraffin wax to prevent oxidization. The conversion ratio of lithium carbonate to lithium metal is about 5.3 to 1.
Although Chile and Australia are the world's largest lithium sources, the US, Argentina and China are also major producers. The market for lithium is heavily dominated by four companies: Sociedad Química y Minera de Chile (Chile), Chemetall (Germany), FMC (USA) and Talison (Australia). Lithium carbonate is generally sold on three to five year contracts from miners to refiners, including those listed above, who produce and market downstream chemicals and lithium metal.
In 2012, the US Geological Survey (USGS) estimated global production of lithium to be over 37,000 metric tonnes. While most of this is used as salts and chemicals, only a small fraction - likely, less than 10 percent - is ultimately electrolyzed and used as a metal.
Recycling of lithium has also grown notably since Japan opened the first lithium-ion battery recycling plant in 1992. Facilities in Belgium, Germany, Japan, the US and Canada can now all process batteries for their lithium and other components.
Kunasz, Ihor. "Lithium Resources". Industrial Minerals and Rocks: Commodities, Markets, and Users. Ed. Jessica Elzea Kogel, Nikhil C. Trivedi, James M. Barker.
Barrett, Wayne T. and Bernard J. O'Neill Jr. "Recovery of Lithium From Saline Brines Using Solar Evaporation". Foote Mineral Company. Source: Saltinstitute.org