Sampling of granite rocks in the core shelter. © ES-Géothermie (ESG)
Author: ÉS-GÉOTHERMIE [ÉS-G]
Among European geothermal sites, the Upper Rhine Graben (URG) has a great potential for a lithium (Li) production from geothermal brines due to its high concentration and the significant water flows exploited by the geothermal power plants in this area.
Despite its great potential, certain gaps in the basic knowledge of the geochemistry of the URG rocks are persisting, as there is scarce conclusive investigation carried out in the past to estimate the Li content as well as the mechanisms of Li recharge in brine. Identifying Li-rich geological units are essential to target areas with higher Li concentrations for exploration and to ensure the sustainability of this resource.
In geothermal systems, hydrothermal fluids circulate through the fractured and porous rock formations, undergoing complex interactions with the surrounding lithology. Various processes, such as leaching, dissolution, and precipitation, can occur and they can significantly influence the concentration of Li in the circulating fluids. Knowing the chemistry of the reservoir rocks could help us understand chemical reactions occurring between the hydrothermal fluids and the rocks and therefore how Li is mobilised and transported into the geothermal brine.
In the LiCORNE project, ESG is conducting detailed geochemical analysis of several core drills including granite, sandstone, and limestone from geothermal wells drilled in Northern Alsace. Researchers finalised the rock sampling task at the beginning of 2024, while the chemical measurements are expected at the end of June, current year.
Sampling of granite rocks in the core shelter. © ES-Géothermie (ESG)
In total, 57 samples were collected and closely studied, which facilitates understanding of the chemical elements behaviour in the rock before and after the hydrothermal circulation/alteration. Comparing the results of this on-going investigation with the few data available in literature and referring to the Li concentration in URG rocks could reveal an unexpected behaviour of Li in the geothermal reservoir rocks.
After careful analysis of the chemical composition, isotopic analysis of the same rock will follow which will show more accurately potential sources of Li in the geothermal brine.
A. Fresh monzogranite sampled at 1774.5 m depth); B. Hydrothermally altered granite showing argillic alteration sampled at 2159.30 m depth. © ES-Géothermie (ESG)
The most recent political events and regulatory context have highlighted on several occasions a growing demand for lithium (Li), primarily fuelled by the increasing use of lithium-ion batteries (LIBs). The concentration of the largest mining sites for Li outside of Europe leads to a strong dependence on third countries, which can pose economic and strategic challenges for the EU. To mitigate the resources scarcity, the EU has implemented regulations promoting sustainable battery practices, and is actively exploring diversified domestic resources of Li, such as the geothermal brines located in the Rhine Graben region.
Researchers at Fraunhofer ICT recently attended the German Geothermal Conference in Essen (Germany), where they submitted a scientific poster that portrays the characteristics of the Li resources identified in the geothermal brines in the Rhine Graben region and the challenges raised by the Li extraction. Due to the high concentration of salt load, the selective separation of Li and sodium (Na) remains the primary challenge to solve. Within the LiCORNE project, researchers are testing a manganese-based (Mn-based) adsorption setup to provide Li enriched solutions from geothermal brines. Despite recent developments, impurities persist, and additional separation steps are required.
During the German Geothermal Conference, the research team at Fraunhofer ICT presented the free-flow electrophoresis (FFE) used for the selective separation of Li and Na ions. This separation relies on the ions’ migration velocity in an electrified field, being significantly influenced by their charge, size and hydrate shell.
The main advantage of the FFE lies in its capacity to prevent mixing of individual streams with the background eluent, allowing separate collection of the individual streams at the end of the chamber. Additional benefits of the FFE:
Testing the method with different parameters, various concentrations of the sample solution and altering the eluent solution, researchers reported a complete separation of Li and Na ions by FFE, with over 80% separation efficiency. Future efforts will focus on testing the actual desorption solutions, optimizing throughput, scaling up, and reducing costs.
Download the original poster, available in German, here