Lithium, this silvery-white metal, has become the lifeblood of the modern world, powering everything from smartphones to electric cars. But as demand for lithium soars, the race to secure it has grown increasingly fraught.
The precious lithium is extracted through mining from rock ores, which is costly, slow, and environmentally damaging. But, perhaps surprisingly, most lithium extraction relies on evaporating brine in huge ponds under the sun for a year or more. The process leaves behind a lithium-rich solution. But heavy use of potentially toxic chemicals is required to finish the job.
Now, researchers at Imperial College London have unveiled a new technology that could be a game changer in how we harvest lithium from the salty waters of lakes and geothermal springs.
The researchers have devised a polymer membrane with tiny, precisely engineered hourglass-shaped pores that can selectively filter lithium ions from complex brine solutions. These salty solutions are rich in lithium but also contain other ions like sodium, potassium, and magnesium. Traditional methods of lithium extraction struggled to separate these ions efficiently.
A Faster, Cleaner Way to Extract Lithium
Traditional lithium extraction from brine is a slow and resource-intensive process. It involves pumping brine into massive evaporation ponds, where it can take months — or even years — for the water to evaporate and the lithium to concentrate. The process consumes vast amounts of water and chemicals, and it generates greenhouse gas emissions.
The new membrane technology promises cheaper operation and less contamination. Made from a class of materials known as polymers of intrinsic microporosity (PIMs), the membrane contains subnanometer-sized pores that act like molecular sieves. These pores are lined with hydrophilic, or water-attracting, functional groups that help guide lithium ions through the membrane while blocking larger ions.
In experiments, the membrane let through 200 lithium ions for every magnesium ion. This performance surpasses most existing membrane materials, which often struggle to achieve even a 10-to-1 selectivity ratio.
When integrated into an electrodialysis device, the membrane uses an electric current to pull lithium ions through its pores, leaving behind magnesium and other impurities. In tests using simulated salt-lake brines, the system produced high-purity, battery-grade lithium carbonate.
The polymers used to create the membranes are soluble in common solvents and can be manufactured using existing industrial techniques. This makes the technology scalable, so it can quickly be adapted for large-scale use.
“We are in the process of establishing a climate tech company and are keen to build partnerships with companies to extract lithium at a large scale using real brine solutions,” said lead author Dr. Qilei Song.
A Sustainable Solution for a Growing Demand
The need for sustainable lithium extraction is urgent. Global demand for lithium is skyrocketing as the world transitions to electric vehicles and renewable energy storage. Extracting lithium from brine using membranes could offer a more sustainable and cost-effective alternative to traditional methods, especially if the process is powered by renewable energy.
The team has already scaled up their membranes and tested them in larger electrodialysis stacks, a first step toward industrial application. In one experiment, they were able to concentrate lithium from a mixed brine solution to over 3 moles per liter, a level suitable for producing high-purity lithium carbonate, the key ingredient in batteries.
The same technology could also be used to purify water, recover valuable metals from mining wastewater, or even extract copper and other critical materials.
“This technology has tremendous potential in a variety of commercially important areas, from energy storage to water purification to recovery of critical materials in a circular economy,” said Professor Sandro Macchietto, Director of Enterprise in the Department of Chemical Engineering at Imperial.
The findings appeared in the journal Nature Water.
