Lithium metal is among the most critical substances in the energy transition. It’s lightweight, has a high electrochemical potential and high energy density with efficient ion transport, characteristics that make it a primary ingredient in modern batteries, which are experiencing a surge in demand due to growth in the electric vehicle market and increased electrification worldwide.
How Lithium Is Extracted From the Environment
Lithium is extracted primarily from underground brine pools and to a slightly lesser degree, hard rock mining. In its natural form, lithium is found in compounds with other elements and minerals. To make it usable for batteries, lithium must be separated from these substances and purified.
Lithium extraction from brine pools starts with pumping lithium-rich brine from underground sources to the surface, where it sits in ponds for months or years as the water evaporates and leaves behind lithium carbonate and other salts. In general, extraction from brine pools is relatively inexpensive but uses considerable time and requires large amounts of land for the evaporation ponds. Depending on the local geology, the significant, permanent removal of underground water from the brine pools can have an adverse impact on the aquifer and water table.
Hard rock mining involves ore extraction of spodumene, petalite, lepidolite and other minerals from open pit or underground mines. This method takes much less time but is considerably more expensive and has a more destructive impact on surface land than evaporation ponds.
In small – but growing – amounts, lithium is being recycled from used batteries.
To meet the surging global demand for lithium, the lithium extraction industry is developing better ways to harvest lithium. One of these methods is direct lithium extraction (DLE), which taps underground brine pools but cuts the time of extraction from years to hours with a far smaller impact on land and water resources.
Reverse osmosis removes water from the brine, further concentrating the lithium ions. This technology may also be used to separate certain dissolved salts and minerals from lithium.
How DLE Isolates Lithium From Brine
In direct lithium extraction, lithium-bearing brine is pumped up from underground pools and subjected to a series of technologies to separate lithium from the brine, after which the water is returned underground.
The process typically starts with specialty sorbents designed to have high affinity for lithium. When the brine is passed over the sorbent material, lithium ions are adsorbed onto the surface of the sorbent, isolating them from the other ions. The lithium is then harvested from the sorbent using a recovery solution and collected for further purification or processing.
The sorbent stage often leaves behind a significant amount of lithium in the brine, so the brine will continue treatment with subsequent technologies that harvest more lithium by separating it from all other impurities. These technologies may include nanofiltration, reverse osmosis and polishing resin, the precise order of these being determined by the specific brine composition and chemistry.
Nanofiltration is a selective filtration technique based on ion size. With pore sizes in the 1 to 10 nanometer range, nanofiltration membranes can selectively filter out calcium, magnesium and other large ions while allowing smaller ions like lithium through. As impurities are removed from the brine, the concentration of lithium in the brine increases.
Reverse osmosis removes water from the brine, further concentrating the lithium ions. This technology may also be used to separate certain dissolved salts and minerals from lithium.
Polishing with IX Resin to Achieve Maximum Quality
To produce the highest purity lithium solution, ion exchange (IX) resins come into play in the polishing stage to remove trace amounts of calcium, magnesium, potassium, iron and other multivalent ions.
IX resins remove trace impurities by exchanging the unwanted ions in the solution with ions that are bound to the resin. IX resins are highly selective and therefore can remove specific ions while leaving lithium in the concentrate. When the lithium-rich solution is passed through the resin, the unwanted ions are trapped in the resin, while the lithium ions are not. This selectivity ensures that only non-lithium ions are removed from the solution, leading to a purer final lithium concentrate. Cation exchange resins are often used in lithium extraction, given the common need to remove positively charged metal contaminants.
Once the resin is saturated with impurities, it can be regenerated quickly and easily. This reusability delivers benefits in the form of lower disposal and media change-out costs and reduced waste.
DLE Using Ion Exchange Is Faster, Unlocks Untapped Lithium Sources and Has Environmental Benefits
The major advantage of DLE is that it reduces extraction time from as slowly as years to as quickly as hours. This increase in speed will help the lithium extraction industry scale up faster to meet the surge in global demand for purified lithium.
Another key advantage is that through a combination of technologies that include an IX resin polishing stage, DLE can achieve higher recovery rates and access to untapped reserves. DLE with ion exchange can extract lithium from lower-grade brines, geothermal waters and other sources that are uneconomical to process with evaporation ponds.
From an environmental standpoint, DLE has much less impact on land than either evaporation ponds or hard rock mining, reducing land cost and creating far less disruption and impact on the landscape surface. It also can reduce effects on the local aquifer. After removing lithium from the brine, most DLE systems can reinject that water back into the geothermal well or brine pool it came from, minimizing potential adverse environmental impact on the local aquifer and water table. And because this brine is reinjected back underground, there is no saline waste to contain and manage as there is with evaporation ponds, reducing the risk of salt contamination in the local ecosystem.
Another perceived challenge is that because brine sources have unique chemistries, DLE will need to be customized for each location.
The Downsides of DLE and How Those are Mitigated
Commercial development of DLE is still considered an emerging technology that hasn’t stood the test of time. However, early adopters are experiencing consistent success, and many companies are actively conducting pilot-scale and full-scale projects. This offers an opportunity for lithium extraction companies to make significant competitive leaps.
Another perceived challenge is that because brine sources have unique chemistries, DLE will need to be customized for each location. But the technologies involved – ion exchange, nanofiltration and reverse osmosis – are well suited for tailored solutions, so this will not be hard for commercial providers to overcome.
DLE requires more energy and upfront costs than evaporation ponds, but the tradeoff with gains in speed of production will more than make up for these costs. Operation costs can be controlled due to the reusability and long life of the IX resins, which can be regenerated again and again.
DLE: The Next Evolution in Lithium Processing
Direct Lithium Extraction using ion exchange is an important new technology in lithium extraction that offers a faster, more productive and environmentally responsible alternative to evaporation ponds. By selectively isolating lithium ions in diverse brine mixtures, DLE can recover high-purity lithium with reduced impact on water and land resources. DLE with ion exchange is poised to help companies meet the surging demand for lithium in the transition to battery-powered energy.
