Sustainable lithium from geothermal power plants

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lithium
Spreading of lithium-depleted thermal water around the injection borehole along the fault zone after 30 years. Image: Valentin Goldberg and Fabian Nitschke

On the road to climate neutrality, Europe will need large amounts of lithium for battery storage systems. So far, however, its share in the worldwide lithium extraction volume is 1%. Because of this, researchers at the Karlsruhe Institute of Technology (KIT) have looked at ways to extract lithium from geothermal sources.

“In theory, geothermal power plants in the Upper Rhine Valley and Northern German Basin might cover between 2 and 12% of Germany’s annual lithium demand,” said Valentin Goldberg from KIT’s Institute of Applied Geosciences (AGW). With his team, he calculated this potential based on an extensive data analysis. However, it has not been clear for how long extraction will be possible. Another study of the researchers now offers an optimistic perspective.

“According to our findings, lithium extraction will be possible for many years at low environmental cost,” Goldberg said.

“The model developed for our study describes lithium extraction in the Upper Rhine Valley. But parameters are chosen such that they can also be transferred to other joint systems.“

Modelling geothermal lithium production

Extraction of lithium from thermal waters is not conventional mining, which is why no conventional methods could be applied for analysis.

“The lithium dissolved in water exists in a widely branched network of joints and cavities in the rock. However, it can only be accessed at certain points via individual wells,” said Fabian Nitschke, AGW, who was also involved in this study.

“The reservoir dimension, hence, depends on the amount of water that can be accessed hydraulically via wells.”

To calculate the lithium production potential, researchers had to consider the potential water extraction volume, its lithium concentration, and lithium extraction per unit time.

“We use a dynamic transport model adapted to underground conditions in the Upper Rhine Valley. It couples thermal, hydraulic, and chemical processes. Similar models are known from petroleum and gas industry, but have not yet been applied to lithium,” Nitschke added.

When using geothermal energy, the extracted water is pumped back into the ground via a second borehole. Researchers wanted to find out whether lithium concentration of the deep water decreases with time. The results show that lithium concentration in the extraction borehole decreases by 30 to 50% in the first third of the investigation period of 30 years, as the deep water is diluted by the returned water. Then, lithium concentration remains constant.

“This can be attributed to the open joint system that continuously supplies fresh deep water from other directions,” Nitschke said.

Modeling suggests that continuous lithium extraction will be possible for decades.

“Actually, extraction of this unconventional resource shows the classical cyclic behaviour. Yields of hydrocarbon extraction or ore mining are also highest in the beginning and then start to decrease gradually.”

Thomas Kohl from AGW, who directs the corresponding research activities as professor for geothermal energy and reservoir technology, said the research results are another argument for the wide use of geothermal energy.

“We already knew that geothermal sources can supply baseload-capable, renewable energy for decades. Our study now reveals that a single power plant in the Upper Rhine Valley could additionally cover up to 3% of the annual German lithium consumption.”

Kohl’s group is now working on solutions for practical implementation. Recently, it published a study in Desalination on the preliminary treatment of thermal water for resource extraction.

“The next step now is to transfer this technology to the industrial scale,” Kohl said.

Publications

Goldberg, V.; Dashti, A.; Egert, R.; Benny, B.; Kohl, T.; Nitschke, F.: Challenges and Opportunities for Lithium Extraction from Geothermal Systems in Germany – Part 3: The Return of the Extraction Brine. Energies, 2023. DOI: 10.3390/en16165899

Goldberg, V.; Winter, D.; Nitschke, F.; Held, S.; Groß, F.; Pfeiffle, D.; Uhde, J.; Morata, D.; Koschikowski, J.; Kohl, T.: Development of a continuous silica treatment strategy for metal extraction processes in operating geothermal plants. Desalination, 2023. DOI: 10.1016/j.desal.2023.116775

Jim Cornall is editor of Deeptech Digest and publisher at Ayr Coastal Media. He is an award-winning writer, editor, photographer, broadcaster, designer and author. Contact Jim here.