Lithium provides powers to almost all the electronic equipment that use batteries. In the current world, there are two approaches to acquiring lithium resources, either by mining spodumene, or by extracting from brine, which both impose negative impacts on environment. Fortunately, a replaceable, more environment-friendly lithium extraction process was developed, and is optimizing all around the word.
This cutting-edge process called Direct Lithium Extraction(DLE). Essentially, this process directly extract lithium ions while leaving other unnecessary ions behind in the subsurface reservoir. Due to different features of every layers of subsurface reservoir, detailed DLE solution must be customized according to specific geological conditions.
Generally speaking, there are four major paths to achieve extraction goals. The first is extraction, whose theory is using an insoluble aluminium-base material as absorbent. When contacting with aluminum,lithium ions will embed or insert into the surface or atomic shell of lithium particles. Once absorbent is in full saturation, the warm diluted lithium chloride solution will be adopted to remove lithium ions.
Similar effect can be achieved through ion exchange, which normally use magnesium-base or titanium-base absorbent. As a sieve, these absorbent will block bigger ion-alike materials, and only allow lithium ion and hydrogen ion to pass. Instead of embedding in particle structures of these absorbent, lithium ion will exchange with hydrogen ion or proton, and then be eluted by solution of lower pH value.
Those two methods averagely cost one to six hours to complete. Additionally, unlike evaporation pond, water used for these two methods can be reused within a closed system.
Another method is solution extraction, which uses different solubilities of various compounds. In essence, a selective organic solution will choose to combine with lithium of solution to generate a new compound, and then strip lithium through the second procedure. In general, kerosene, benzene, chloroform, cyclohexane and other petrochemical derivatives are used as organic solutions; and hydrochloric acid or sulfuric acid are used in the second procedure, which will inevitably cause pollution. Additionally, the operating cost of solution extraction is rather high. However, compared to absorption process, solution extraction is quicker. It takes about only four hours to release lithium, with an extraction efficiency of more than 90%. In industrial practices, this method is usually used as a follow-up procedure to purify final products so that they can reach battery-grade.
The forth method conducts the least environmental impact. It uses membrane to filtrate lithium from brines in physical means. Pressure-assisted membrane is employed to separate multivalence(e.g. magnesium and calcium) from monovalence(e.g. lithium, sodium and potassium).
In 2024, International Lithium Association conducted detailed analyses on every DLE method, compared differences of CO2 emissions, water consumptions, and land utilizations among DLE, solar evaporation, and hard-rock mining.
It is estimated that DLE uses far less than 100m3 water to produce one tonne of lithium carbonate. For DLE facilities that use closed water system (for example, the ion exchange project in Kachi, Argentina), water consumption can even be 11m3. While, water consumption of evaporation ponds is totally depend on measuring objects. Normally, it takes 30m3 of water to produce one tonne of lithium carbonate through an evaporation pond; but if evaporated water caused by direct sunlight in 18 months were calculated, the average water consumption for producing one tonne of lithium carbonate will be 450m3.
When measuring land utilizations, contractions will be quite shocking. DLE facilities only occupy a rather small area, usually 16m2 for producing one tonne of lithium carbonate. While for a typical hard-rock factory, like those in west Australia, to produce one tonne of lithium carbonate, about 335m2 will be occupied. And for those large evaporation ponds in Acatama, Chile, every tonne of lithium carbonate will cost 3656m2 of land.
And carbon footprint of each method varies per parameters as well as the way of acquiring energies. For example, research on the early brine lithium extraction project in Clayton Valley Nevada founds that carbon dioxide emission of producing one tonne of lithium carbonate powered by diesel motor is 22 tonnes, while that of being powered by electricity is slightly higher than 17 tonnes. And if the power comes from photovoltaic panels, the carbon dioxide emission can reduced to only 7.6 tonnes. According to an essay published by the International Lithium Association, globally, for hard-rock mining, it averagely emit 20 tonnes of carbon dioxide to produce one tonne of lithium carbonate; and carbon dioxide emissions for evaporation ponds and DLE are 3 tonnes and 3-7 tonnes respectively. Yet, compared to evaporation ponds, DLE has modular advantages, which enables it to be seamlessly integrated with renewable energies to comprehensively offset carbon dioxide emission. If a DLE system is designed to utilize geothermal brines that including necessary thermal energy, then its carbon footprint will infinitely approach to zero.
Of course, DLE is not perfect; there will be following challenges for DLE operators. The first one is about finance. Not only DLE costs more than traditional lithium extraction techniques, the turbulent and uncertain international lithium market also makes major investors flinch. The second challenge caused by salt lake itself. Since every salt lake has its unique composition, there is no “one for all ” solution. Every new DLE facilities must be designed in accordance with actual situations and specific operational concerns. Last but not lease, like all other new energy project, DLE operators must do every possible thing to accommodate all regulations to get relevant permits from governments.
However, from the technical perspective, DLE is a quickly-developing and promising technology. New progresses are made everyday in this field to improve lithium yield and optimise extraction efficiency, and minimize mining activities’ impact on local water resources and ecological system, as well as reducing greenhouse gases emission to the utmost extent.