A look into the laboratory: An adsorbent based on a lithium-manganese oxide with a special crystal structure serves as a lithium-ion sieve. (Photo: Dr. Monika Bäuerle, IAM-ESS/KIT)
Geothermal energy not only enables a sustainable supply of electricity and heat, but also regional lithium production. Researchers from the Karlsruhe Institute of Technology (KIT) and EnBW have produced a lithium-ion sieve from a lithium-manganese oxide and used it to adsorb lithium from geothermal brines. In the future, the use of domestic lithium sources can help to meet the increasing demand for the light metal, which is indispensable as an energy storage material. The researchers reported in the journal Energy Advances , which now recognizes the work as one of the "Outstanding Papers 2022". (DOI: 10.1039/d2ya00099g )
A sustainable energy supply requires efficient energy storage. Lithium has become indispensable - the light metal is in the batteries of many technical devices and vehicles, from smartphones and notebooks to electric cars. In recent years, demand has risen sharply worldwide. Up until now, Europe has been dependent on imports. However, there are also European deposits for lithium, namely thermal waters at a depth of a few kilometers. They contain high concentrations of lithium ions. In this way, geothermal systems, which pump hot water from the depths, can not only be used for the sustainable supply of electricity and heat, but also for environmentally friendly regional lithium production.
"Depending on the geological origin, geothermal brines contain between 0.1 and 500 milligrams of lithium per liter," explains Professor Helmut Ehrenberg, head of the Institute for Applied Materials - Energy Storage Systems (IAM-ESS) at KIT. Lithium concentrations of up to 240 milligrams per liter were measured in the North German Basin, and up to 200 milligrams per liter in the Upper Rhine Graben. "However, the extraction of lithium from geothermal brines represents a major challenge because the lithium ions compete with many other ions," explains Ehrenberg.
A promising way of extracting lithium from hot deep water is adsorption, i.e. the accumulation of lithium ions on the surface of porous solids. This requires suitable adsorbents that are not only lithium-selective but can also be produced, used and disposed of in an environmentally friendly manner, as well as suitable desorption solutions to release the lithium ions from the adsorbent again. Researchers from the IAM-ESS of the KIT, together with the Research & Development department of EnBW Energie Baden-Württemberg AG and scientists from the Fraunhofer Institute for Chemical Technology ICT and Hydrosion GmbH, have produced a lithium-ion sieve and tested it in the laboratory. They report on this in the journal Energy Advances.
The lithium-ion sieve presented is based on a lithium-manganese oxide with a special crystal structure known as spinel. The researchers produced it using hydrothermal synthesis, in which substances crystallize from aqueous solutions at high temperatures and pressures. In laboratory tests, the research team used this substance to adsorb lithium ions from geothermal brine. The brine comes from the Bruchsal geothermal plant operated by EnBW, which is located between Karlsruhe and Heidelberg in the Upper Rhine Graben. There, the Research & Development department of EnBW is investigating lithium production from thermal water in various projects.
For the work published in Energy Advances, the researchers tested various desorption solutions after the adsorption of lithium, with acetic acid giving the best results in terms of lithium recovery and adsorbent preservation. However, with all tested desorption solutions, especially with acetic acid, the lithium-ion sieve was enriched with competing ions. This is due to the high mineral content of the brine in Bruchsal. Enrichment with competing ions can decrease the lithium adsorption capacity.
Further research now faces the challenges of further developing the lithium-ion sieve in such a way that it is easier to handle and its adsorption capacity is only slightly affected in the process, as well as scaling up the process from laboratory to pilot scale. Then lithium extraction from geothermal brines can support the development of a European lithium supply in the future.
Original publication (Open Access)
Laura Herrmann, Helmut Ehrenberg, Magdalena Graczyk-Zajac, Elif Kaymakci, Thomas Kölbel, Lena Kölbel and Jens Tübke: Lithium recovery from geothermal brine – an investigation into the desorption of lithium ions using manganese oxide adsorbents. Energy Advances, 2022. DOI: 10.1039/d2ya00099g