Double use: Geothermal sources as raw material and drinking water supplier

The numerous salt lakes of the Chilean Atacama Desert contain large lithium deposits. At the same time, due to its geology and geographical location on the western slope of the Andes, the country has one of the most extensive geothermal resources in the world, with well over 200 different volcanic systems. This results in a high potential for the use of geothermal reservoirs for power generation or heat utilization. However, Chile's geographic location also means that the north and especially the Atacama Desert are among the driest regions in the world. Natural freshwater resources are often scarce in these regions and can lead to water use conflicts between mining companies and small villages and indigenous peoples.

A research team led by Prof. Dr. Thomas Kohl, professor of geothermal energy at KIT's Institute of Applied Geosciences (AGW), is investigating geothermal brines in Chile in the BrineMine project together with German and Chilean partners. The aim is to use these brines by means of innovative technologies both as a source of energy and for fresh water production, thereby reducing the potential for conflict. "On the one hand, we are geochemically investigating the hydrothermal springs in northern Chile and the volcanic environment in the south of the country. The geothermal brines in these areas very often contain recoverable valuable materials such as lithium or magnesium. The goal is to develop a multi-stage process that can concentrate the brines to such an extent that minerals can be selectively separated and fresh water can be obtained," says Valentin Goldberg, a research associate in the team, describing the project. Geochemical as well as geophysical investigations have already been partially carried out. "Based on the findings of our investigations so far, we have developed a prototype that has been tested in Germany. In the next step, the plant is to be transported to Chile and put into operation there," says Prof. Kohl about the current status. On the one hand, the team wants to test the technical feasibility of the newly developed process, and on the other hand, it hopes to benefit international knowledge building by investigating the technical and economic conditions for using geothermal sources as a mineral supplier, thus demonstrating their potential as a complementary technology to conventional mining.

Think Global - Act Local

While BrineMine deals with the topics of raw material potential and processability of geothermal waters on an international level, technologies are being developed at KIT in another project in order to be able to exploit the domestic lithium resource in the future and thus become more independent from the global raw material market. "Taking into account the planned expansion of battery cell production in Germany, lithium extraction in domestic regions seems to make sense," explains Prof. Dr. Jochen Kolb, Professor of Geochemistry & Deposit Science at the KIT Institute of Applied Geosciences. In the UnLimited project, his team and partners are developing technologies for lithium extraction from hot deep waters in Germany.

The joint project, led by the energy company EnBW, specializes in the development and testing of a process that will enable lithium extraction in geothermal power plants from the produced deep waters in the Upper Rhine Graben and the North German Basin concomitant with their geothermal use. The focus of KIT's investigations is the selection of particularly qualified, lithium-selective adsorbents. "Besides lithium, geothermal waters contain many other chemical elements. It is important in the selection of the adsorbent that it is highly selective and separates only the lithium. After a number of tests, manganese oxide proved to be particularly suitable, as it only sorbs other substances to an extremely small extent," explains Prof. Kolb. The team has already been able to conduct the first targeted experiments on geothermal waters with manganese oxide. "We have extracted lithium carbonate from geothermal water in the laboratory. Now it's a matter of transferring these experiments into practice," says Prof. Kolb. The researchers are currently in the process of setting up a pilot plant at EnBW's geothermal power plant in Bruchsal. A bypass has already been constructed in the geothermal plant for this purpose. "With the help of this bypass, we can branch off geothermal water to enrich it with the manganese oxide. When the lithium is adsorbed to the manganese oxide, we separate the solid from the geothermal water by filtering. Using a weak hydrochloric acid, the lithium is again separated (desorbed) from the manganese oxide. The resulting lithium chloride solution can be further treated to obtain battery-grade lithium carbonate or lithium hydroxide," Prof. Kolb explains the procedure. The aim of these preliminary investigations is to set up a comprehensive pilot plant in the next few years in order to prepare for the step into widespread practice. "The amount of lithium that has so far been extracted unused annually at the geothermal plant in Bruchsal during 8,000 operating hours is sufficient to produce about 20,000 car batteries. Thus, we cannot cover the long-term demand for domestic battery production, but we can at least contribute a significant share," Prof. Kolb describes the potential. The holistic research at KIT not only has the economic advantage of diversifying the supply chains, but also contributes ecologically to a more sustainable extraction of the overseas resources on which Germany will depend in the future. In short, less dependence on global commodity markets and price fluctuations as well as simplified supply chains and reduced, more sustainable transport routes from overseas.