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| View of the laboratory: An adsorbent based on a lithium-manganese oxide with a special crystal structure serves as a lithium-ion sieve. Photo Credit: Dr. Monika Bäuerle, IAM-ESS / KIT |
Researchers at KIT and EnBW show lithium-ion sieve for geothermal soles - lithium extraction can complement electricity generation and heat supply
Geothermal energy not only enables a sustainable supply of electricity and heat, but also a regional lithium extraction. Researchers at 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. The use of domestic lithium sources can help to meet the increasing demand for light metal, which is indispensable as energy storage material. The researchers reported in the journal Energy Advances, who now recognizes the work as one of the "Outstanding Paper 2022".
A sustainable energy supply requires efficient energy storage. Lithium is indispensable - the light metal is in the batteries of many technical devices and vehicles, from smartphones to notebooks to electric cars. Demand has risen sharply worldwide in recent years. Europe is still dependent on imports. However, there are also European lithium deposits, namely thermal waters a few kilometers deep. They contain high concentrations of lithium ions. In this way, geothermal plants that extract hot water from the depths can not only be used for sustainable electricity and heat supply, but also for environmentally friendly regional lithium production.
High lithium concentrations in the North German Basin and in the Upper Rhine Trench
"Depending on geological origin, geothermal soles 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) of the KIT. Lithium concentrations of up to 240 milligrams per liter were measured in the North German Basin, in the Upper Rhine Trench up to 200 milligrams per liter. "However, obtaining lithium from geothermal soles is a major challenge because the lithium ions compete with many other ions," explains Ehrenberg.
A promising way to extract lithium from hot deep water is adsorption, i.e. the attachment of lithium ions to the surface of porous solids. This requires suitable adsorbents that are not only lithium-selective, but can also be manufactured, used and disposed of in an environmentally friendly manner, as well as suitable desorption solutions to remove the lithium ions from the adsorbent. Researchers from the IAM-ESS of KIT, together with the Research & Development department of EnBW Energie Baden-Württemberg AG, as well as scientists from the Fraunhofer Institute for Chemical Technology ICT and Hydrosion GmbH, produced a lithium-ion sieve and tested it in the laboratory.
Lithium-ion sieve with a special crystal structure
The lithium-ion sieve presented is based on a lithium-manganese oxide with a special crystal structure called spinel. The researchers produced it via hydrothermal synthesis, in which substances from aqueous solutions crystallize 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 the EnBW, which is located between Karlsruhe and Heidelberg in the Upper Rhine Graben. There, the Research & Development department of EnBW examines lithium production from thermal water in various projects.
For the work published in Energy Advances, the researchers then tested various desorption solutions for the adsorption of lithium, with acetic acid producing the best results in terms of lithium extraction and adsorbent conservation. However, with all tested desorption solutions, especially 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 reduce the adsorption capacity for lithium.
Further research is now faced with 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 impaired in the process, as well as scaling the process from the laboratory to the pilot scale. Then the lithium extraction from geothermal brines can support the establishment of a European lithium supply in the future.
Published in journal: Energy Advances
Source/Credit: Karlsruhe Institute of Technology
Reference Number: tn041923_01
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