Lithium and Rubidium in the Upper Rhine Graben: Sustainable Geothermal Lithium Extraction in Europe’s Rhine Valley
Lithium and Rubidium in the Rhine Valley: Europe’s Hidden Treasure Beneath Our Feet
Electric vehicles, renewable power, data centers and advanced electronics all depend on a handful of “critical metals” , and two of the most important, lithium and rubidium, may be flowing right under Europe’s feet in the Upper Rhine Graben between France and Germany.
Instead of digging new open‑pit mines, scientists are now looking at deep geothermal waters as a low‑carbon, local source of these strategic metals.
In the Upper Rhine Valley (also called the Fossé rhénan), hot, very salty brines more than 2.5 kilometers below the surface are already used for geothermal power and heat. A new wave of research shows that these brines contain some of the highest lithium and rubidium concentrations in the world, creating a tantalizing opportunity: produce clean energy and extract critical metals at the same time.
Why Lithium and Rubidium Matter for Europe’s Future
Lithium has become synonymous with the clean‑energy transition. It is a core ingredient in lithium‑ion batteries that power electric cars, stationary storage systems and countless portable electronics. Demand is rising steeply as governments push to decarbonize transport and electricity, and analysts expect global lithium production to keep growing toward the 2030s.
Rubidium is less well known outside specialist circles, but it plays an important role in high‑value niche markets. It is used in advanced optics, specialized photovoltaic technologies, electronics and atomic clocks, where even tiny quantities can be crucial.Global production today is extremely small—on the order of a few tonnes per year—so a single large resource can significantly reshape the market. Not long ago Hydrogen was shunned but today it's also being tapped alongside geothermal.
For Europe, both metals have a strategic dimension. The continent currently depends heavily on imports, particularly from China and a handful of other producer countries. Finding robust, local, lower‑impact sources is a major policy priority to secure supply chains, support domestic industry and reduce geopolitical risk.
The Upper Rhine Graben: A Natural Geothermal Laboratory
The Upper Rhine Graben stretches between Basel and Frankfurt, forming a long geological depression filled with sedimentary rocks and underlain by granites. Over millions of years, ancient seawater and rainwater infiltrated this structure and became trapped as highly saline brines. These fluids now circulate through deep sandstone and granite reservoirs at temperatures that often exceed 200 °C at depths of 4–5 kilometers.
Geothermal plants in Alsace and across the border in Germany already tap into this heat. They pump the hot brine to the surface, use it to produce electricity and heat, and then reinject the cooled fluid back into the subsurface in a closed loop. This existing infrastructure is what makes the Rhine Valley such an attractive test bed: the wells, pipes and pumps are already there, and the brine is continuously being brought to the surface.
The brines themselves are unusual. On average, they contain around 174 milligrams of lithium per liter and about 25 milligrams of rubidium per liter. These levels put the Upper Rhine Graben among the richest known geothermal brine systems for these metals worldwide, making it a prime candidate for integrated energy and metals production.
How Geothermal Brines Become Rich in Lithium and Rubidium
The key to this resource lies in the interaction between hot water and rock. As geothermal brines circulate through the deep reservoirs, they slowly alter minerals such as micas, which are common in granitic rocks. Over time, these micas transform into illite, a clay mineral typical of hydrothermal alteration processes.
This transformation is not just a mineralogical curiosity. When micas break down and illite forms, lithium and rubidium that were locked inside the crystal structure are released into the surrounding fluid. Chemical and isotopic analyses of both rocks and brines suggest that this alteration mechanism is likely the main process controlling lithium and rubidium concentrations in the geothermal waters.
The temperature and circulation pattern also matter. Most brines appear to have reached chemical equilibrium at around 225 °C (plus or minus 25 °C), which is consistent with origins in the central part of the Upper Rhine Graben, where reservoirs are deepest and hottest.From there, the fluids migrate along complex networks of faults and fractures toward the eastern and western margins, feeding the geothermal systems exploited today.
From Old Estimates to New Potential: Millions of Tonnes of Lithium
Back in 1991, the French geological survey (BRGM) attempted a first estimate of the lithium resources in the Upper Rhine Valley brines.Using simplified assumptions and limited data, they arrived at a range of 0.3 to 2.2 million tonnes of lithium, with a central estimate of roughly one million tonnes.
Recent work revisits those numbers with much richer datasets. By incorporating new measurements, improved understanding of the subsurface geology and an explicit contribution from granite‑hosted brines, scientists have significantly revised the estimates. The updated range now stretches from about 1 million to 16 million tonnes of lithium, with an average around 6.2 million tonnes.
To put that in perspective, global lithium production in 2023 was roughly 230 000 tonnes, and projections suggest it might reach around 800 000 tonnes per year by 2031. In other words, the Upper Rhine Graben alone could, depending on the final recoverable fraction, represent a major long‑term resource for Europe’s battery and clean‑energy industries.
Rubidium: A Small Market with a Big Upside
The story for rubidium is similar, but the scale of its current market makes the Rhine Valley even more significant. Updated evaluations suggest that the geothermal brines in this region may hold between 150 000 and 2.3 million tonnes of rubidium, with an average estimate of about 900 000 tonnes. That is huge when set against a global production that is currently estimated at slightly under eight tonnes per year.
Because rubidium is used mostly in specialist, high‑value applications, even a moderate industrial project could transform supply dynamics. It could provide a stable, long‑term source for European high‑tech manufacturers, from optics and electronics to precision timing systems.
A New Kind of Mining: Direct Lithium Extraction from Geothermal Brine
What makes this vision particularly attractive is the possibility of coupling geothermal power with “direct lithium extraction” (DLE) technologies.Instead of building evaporation ponds or digging open‑pit mines, operators add a processing stage to the existing geothermal loop.
In a typical setup, hot brine is pumped from deep underground and passes through a heat exchanger to produce electricity.
Before the cooled brine is reinjected, it flows through a DLE unit where lithium is selectively captured using sorbents, membranes or ion‑exchange materials.[5] The lithium is then stripped from the material and processed into lithium carbonate or other battery‑grade chemicals.
Pilot projects in California and elsewhere show that DLE can extract lithium with high recovery rates in a matter of hours, rather than the months required for traditional evaporation ponds. The process can be competitive with hard‑rock mining in terms of cost, while generating less surface disturbance and avoiding massive evaporation ponds.
Alsace as a European Hub for Low‑Carbon Lithium
Alsace is already emerging as a European pioneer in geothermal lithium. At the Rittershoffen geothermal plant, a pilot project led by the French mining group Eramet and Électricité de Strasbourg has successfully produced the first kilograms of lithium carbonate from geothermal brine.[9] The technology uses a solid “sponge” material that selectively absorbs lithium from the brine before it is reinjected.
The partners have been testing this process since 2020 at two geothermal sites, Rittershoffen and Soultz‑sous‑Forêts, and early results are considered promising.[9] If the technology proves robust under local conditions—where the brine is still hot and under pressure when it reaches the surface—it could pave the way for industrial‑scale production.
Plans under discussion include producing at least 10 000 tonnes of lithium carbonate per year in Alsace by 2030, enough to equip roughly 250 000 electric vehicle batteries annually. For France and the wider European Union, such projects support the ambition of building a domestic, low‑carbon battery value chain from raw materials to finished cells.
How Much Lithium Could Geothermal Wells Deliver?
The potential output from a single geothermal well can be surprisingly high. Technical studies suggest that at a brine production rate of 50 liters per second and a lithium recovery efficiency of about 90%, a plant could produce roughly 1 300 tonnes of lithium carbonate per year.Multiplying this by a network of wells and plants paints a picture of significant, scalable production over time.
In the Upper Rhine Graben, researchers estimate that with around twenty geothermal wells in operation, annual lithium production could reach between 3 000 and 9 000 tonnes. That would cover roughly 25–50% of France’s projected lithium needs for 2035, which are estimated at up to 19 000 tonnes per year.Because the resource base is large and the brine circulation is naturally replenished, simulations indicate that production could remain relatively stable over several decades.
Even more striking, long‑term modeling suggests that these geothermal lithium resources would not be quickly depleted. Depending on extraction rates and reservoir behavior, exploitation could potentially last hundreds or even thousands of years.For policymakers and investors, that kind of resilience is particularly attractive.
Environmental and Social Challenges: Seismicity, Trust and Technology
Despite its promise, geothermal lithium development faces several challenges that go beyond the chemistry of brines. One of the most sensitive issues is induced seismicity—the small earthquakes that can sometimes accompany deep geothermal operations.Communities near past projects have raised concerns, and any new activity must demonstrate that risks are understood and controlled.
There are also technical questions about how to optimize well locations and designs to target the most productive zones in a complex subsurface. Understanding the precise paths of fluid circulation through sandstone and granite reservoirs, and the role of faults and fractures, remains an active area of research.Getting this wrong could lead to costly industrial setbacks.
On the technology side, direct lithium extraction is still maturing. Many DLE processes are at the pilot or demonstration stage, and scaling them up to full industrial plants will require further engineering and investment. Operators must prove not only high recovery rates and product quality, but also long‑term durability of sorbents and minimal environmental footprint.Without public trust and clear evidence of safety, projects risk delays or opposition.
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Source The Conversation Econ, BRGM
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