A geothermal energy plant requires deep boreholes, and these may yield raw materials as well as geothermal energy. VITO is researching the combined approach at the Balmatt energy plant in Mol.

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The European CHPM2030 project intends to use sites with deep geothermal drilling (at least 4,000 metres) to also extract valuable metals from the earth. That combination may make geothermal energy more profitable, while at the same time making Europe less dependent on the import of critical metals. A good location is crucial in making this successful.

Two stages

The extraction of metals from geothermal fluid takes place in two stages. The first is an electrolytic extraction process, in which metals are removed by electrodes. This technology is used by companies such as Umicore to extract copper and zinc, for example. The second stage is a new process that has been developed by VITO, in which a gas infusion is used to cause metals to precipitate on electrodes. The resulting metal oxides are highly valuable, and are used in the glass, medical and semiconductor industries, among others.

Good location

Metal extraction is, of course, dependent on the presence of metals in the earth. What is more, those metals need to be partially dissolved in the ground water. If the substratum only contains metals in solid form, leaching may offer a solution. Joost Helsen from VITO explains: “In the case of geothermal energy, we not only pump up ground water, we also return the cooled water to the earth. We need to do that in order to maintain the stability of the substratum. When we inject water in this way, we have the ideal time opportunity to add leaching agents in order to extract the metals by leaching. This creates an Enhanced Geothermal System (EGS) with a high concentration of metals in the geothermal fluid.”

Additional energy source

There is a third way of utilising ground water in addition to geothermal energy and metal extraction. The salt concentration in the geothermal brine is used as an energy source. Reverse electrodialysis brings the salt water into contact with a liquid of lower salinity, creating a difference in electric potential, which generates electricity. “Both metal extraction and electrodialysis are still in the conceptual stage. We are using tests in a lab plant to attempt to demonstrate the technical feasibility and economic potential,” states Joost. “We would like to build a pilot plant on the Balmatt site in Mol by 2030. An operational, cost-effective site may not be possible before 2050.”