Researchers in Finland are developing new methods for lithium recovery from natural brine with increasingly effective recovery of lithium and purity of the lithium solution increasing from 95% to 99.9%—difficult and resource-intensive to accomplish using traditional methods. A paper on their studies is published in the journal Hydrometallurgy.
Lithium and lithium carbonate used in batteries are primarily produced from salt lake deposits. Prior to the actual separation process, the brine is pumped up and concentrated by evaporation of water which usually takes place in large pools under the sun. Finally, the concentrated solution is led into a process in which the solution is purified of impurities and the lithium is separated.
Researchers at Lappeenranta University of Technology (LUT) have been using solvent extraction for purifying the solution. In this process, the separation occurs between two insoluble liquid phases. The impurities—calcium and magnesium—were separated from the concentrated lithium salt solution into an organic solution consisting primarily of kerosene.
We were typically able to purify 99–100% of calcium and also over 90% of magnesium. Lithium loss only amounted to 3–5%. In traditional methods, the purification outcome is either weaker, the lithium loss is more substantial, or both.—Sami Virolainen, a post-doc at LUT
The researchers demonstrated the new separation process on a pilot scale. Flow rates in the extraction varied from one liter to five liters per hour.
According to Virolainen, solvent extraction is a profitable alternative to an extraction process when the product is required to have the purity of nearly 100% 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.—Sami Virolainen
Sami Virolainen, Mojtaba Fallah Fini, Ville Miettinen, Antero Laitinen, Mika Haapalainen, Tuomo Sainio (2016) “Removal of calcium and magnesium from lithium brine concentrate via continuous counter-current solvent extraction,” Hydrometallurgy, Volume 162, Pages 9-15, doi: 10.1016/j.hydromet.2016.02.010