Recovering 99.9% pure lithium from salt pools

RESEARCHERS have devised a method for recovering 99.9% pure lithium solution from natural brine salt pools, saving on the need for resource-intensive purification to manufacture lithium-ion batteries.

Traditional methods of recovery and purification of lithium and lithium carbonate from salt lake deposits involve pumping up the brine and concentrating it by evaporation in large pools under the sun. At this stage the lithium solution is typically 95% pure.

The impure lithium is then purified by melting the solid in an inert atmosphere, and maintained at temperatures up to 700°C and pressures of less than 10 Pa. The impurities are vapourised and are then condensed at a temperature of less than 100°C. The purified lithium is recovered in molten form; however, 10% or more lithium is typically lost during purification.

The team from Lappeenranta University of Technology (LUT), Finland has used solvent extraction for purifying the solution. In this process, the separation occurs between two insoluble liquid phases. In this case, impurities, calcium and magnesium were separated from the concentrated lithium salt solution into an organic solution consisting primarily of kerosene.

Using the solvent extraction method, lithium loss is reduced to around 3–5%. The team is also able to recover other useful metals from the solution with 99–100% purity of calcium and also over 90% of magnesium.

Sami Virolainen, a post-doctoral researcher at LUT, said: “In traditional methods, the purification outcome is either weaker, the lithium loss is more substantial, or both.”

Virolainen also said the solvent extraction process is a more profitable alternative to traditional extraction when the product is required to have the purity of 99.9% and a high recovery of the target metal is demanded.

“The extraction process we use is more expensive than regular precipitation but, as the study indicates, separation is more efficient and easier. This simplifies the overall process, which also makes it an economically sensible alternative,” said Virolainen.

The team has demonstrated the solvent method at a pilot scale, achieving flow rate of 1–5 l/h. The team is now looking to scale the process to industrial levels. They also believe the method would be suitable to recover lithium from electronic waste, as currently 3% of lithium is recycled in the EU.

“The need for lithium might increase by up to four times by 2025. As the demand grows, recycling of products containing lithium and the use of new alternative sources for raw material must be increased,” added Virolainen.

The lithium carbonate recovered in both methods is of 99.0–99.5% pure, suitable for some other uses, but for battery use 99.9% purity is needed.