Generally speaking, data is considered to be the oil of 16. Century. But one raw material would also be entitled to this title: lithium. It is an elementary component of lithium-ion batteries and is what makes smartphones, laptops and electric vehicles mobile in the first place. In addition, there are non-rechargeable lithium batteries, which have prevailed especially in small electronics. Lithium technology is light, compact and offers excellent energy and power density. Serious alternatives such as sodium ion accumulators and magnesium-sulfur batteries are currently still in the laboratory stage.

A group of scientists at the Karlsruhe Institute of Technology (KIT) has now worked out a process in which lithium is a quasi Waste produced in the generation of energy in geothermal plants. A pilot plant is supposed to produce lithium from Germany until the end of the year.

Today the extraction of lithium is problematic. It is currently mined mainly from salt lakes in the South American triangle of Chile, Argentina and Bolivia and from solid rock – mainly in Australia.

Salt deserts are created In South America, the raw material is obtained by evaporating lithium-containing water in large salt lakes. The process can take over a year. The primary problem: You need a lot of water to get lithium in the concentration that is necessary for battery cell production. In the affected areas, however, water is at least as valuable a raw material as the lithium salt to be extracted for industry. “Since the mining areas in the Atacama Desert, for example, are very dry, the effects on hydrology can be severe,” according to a study by the Freiburg Eco-Institute. The water reserves at the Salar de Atacama in Chile are between 2002 and 2017 at a rate of 1, 16 millimeters per year decreased, which also causes the last river courses and meadows to dry up.

Extraction from solid rock in Australia, on the other hand, requires a lot of energy and generates a large amount of overburden. Long transport routes to production sites for battery technology in Europe are another ecological and economic problem.

But the transport routes could be shortened in the future. Jens Grimmer, geologist at KIT, and his colleague Florence Saravia have developed a comparatively simple process to mine lithium in the Upper Rhine Graben. There are geothermal systems that transport hot water up from the deep underground to produce electricity. The underground thermal water reservoirs not only supply energy, lithium is also dissolved in them – and in considerable quantities. Grimmer assumes 200 milligrams per liter. The total potential in the Upper Rhine Graben amounts to several thousand tons of recoverable lithium per year.

800 tons of lithium in Bruchsal The KIT scientists already want Use existing geothermal systems, of which there are currently five on the German and French sides, namely at the Bruchsal, Landau, Insheim, Soultz-sous-Forêts and Rittershoffen locations. Alone through the Bruchsal geothermal plant flow every second since 2010 liters of thermal water. This means that roughly 200 tons of lithium chloride are extracted per year of operation and reinjected unused, As the system operator EnBW reports.

Each of these systems basically has two water pipes down into the depths. The thermal water flows through one of them into a heat exchanger, where it releases part of its energy. It then flows back into the deep underground through the so-called intake pipe. This is exactly where the scientists want to start and filter out lithium ions with a system upgrade.

Only through the pipes of the geothermal system Bruchsal has about in the year .

(Image: Amadeus Bramsiepe / KIT)

For this part of the procedure, the KIT experts use a semi-permeable membrane through which they press the water at high pressure. In this way, they overcome the osmotic pressure that counteracts the concentration of dissolved ions. The method can be compared in a simplified way with that of seawater desalination plants. As a result, the KIT membrane separates water with dissolved lithium ions from the rest of the thermal water.

Overall, this process step requires a very considerable membrane area, in a complete system probably several hundred square kilometers. However, this membrane can be rolled up to save space and packaged in several modules. “That is the reason why we probably don’t need a lot of space,” says Grimmer.

Two procedural steps are necessary The lithium concentration achieved in the first step is not yet sufficient to chemically precipitate the lithium. In order to concentrate on 2020 to 6000 To increase milligrams per liter, the researchers heat the water in a second process step. The additional amounts of energy required for this are manageable, as even the temperature of the cooled thermal water before re-injection into the depths of the rock layers 60 to 70 degrees Celsius.

The result of these two process steps is lithium carbonate – an intermediate product that can be processed by industry. Grimmer expects that this end product will have to be purified in a further process step. But the question of the water required for this should not be as sensitive in this country as in the salt deserts of South America. In the future, a central system for the entire Upper Rhine Graben could bring together and purify the lithium carbonate extracted.

Fast extraction The KIT process is very fast compared to other forms of mining: While extraction from salt lakes takes months, the KIT scientists assume that the lithium is in the thermal water cycle of the geothermal system can be extracted continuously within hours. Europe would have to import smaller quantities of lithium, which reduces the risk of supply chain failure.

(Image: EnBW)

Another advantage of the new process is the targeted filtering of lithium ions. All other ingredients flow back into the depths with the thermal water used. This means that they do not cause any problems in the system – for example, by clogging pipes in the form of precipitates and causing maintenance work. The principle of the process by Grimmer and Saravia is: Only the lithium ions are removed from the water.

Requirements for the pilot plant At the same time, this is an important condition that the procedure must meet. “The water that is used for geothermal energy also contains substances that you do not want on the surface,” explains Grimmer. These include heavy metals, for example. “We know that there will be no problems if we send the water back down as it is. We don’t know what reactions we would cause in the reservoir if we were to change it significantly.” Implementing this technically is one of the requirements for the future pilot plant.

Another is to cope with the high flow rates of the thermal water. These are the prerequisites for operating geothermal energy economically. Lithium concentration and flow rate are the decisive factors, because the product of both results in the potential that the participating partners can leverage. Ultimately, the decision was made in favor of membrane technology because of the high flow rates.

However, there are challenges not only in terms of technology. “As soon as you intervene in the thermal water cycle, it always requires approval from the mining authorities,” says Grimmer. So there are also administrative hurdles to overcome.

Increasing demand expected Martin Wedig knows that such approval procedures can drag on. He is the managing director of the Vereinigung Rohstoffe und Bergbau, a trade association for the German raw material industry. And in his opinion, the regulatory hurdles are one of the reasons why such projects in this country have a hard time finding investors. But basically he sees the activities of the KIT scientists as positive. “Every project to set up your own lithium production in Germany or Europe is worth supporting,” says Wedig. He advocates anything that leads to being less dependent on foreign supplies. The corona crisis showed how quickly supply chains can break.

The KIT researchers assume that lithium production with their process will be cheaper than extraction from solid rock or with salt lakes – if the process works can be coupled to existing geothermal power plants.

The world market price for lithium carbonate has been subject to large fluctuations for several years and is currently around 7, 25 US dollars on the London Metal Exchange are relatively low – partly because the expansion of electric mobility is not progressing as quickly as expected . But the German raw materials agency expects a significant increase in demand in the coming years.

Further projects The possibility of obtaining lithium from thermal water has therefore found other interested parties. For example, Pfalzwerke geofuture, a subsidiary of the Pfalzwerke energy provider from Ludwigshafen, has signed a letter of intent with the Australian company Vulcan to extract lithium. The two partners want to use the Insheim geothermal power plant for this. Here flow in the second 50 to 70 liters of hot water from the depths, with up to 200 Milligrams of lithium salts per liter.

Other interested parties in lithium production in Oberrheingraben have already applied for mining rights, including Deutsche Erdwärme from Karlsruhe and, on the French side, the Fonroche company.

This Pfalzwerke project is still at a very early stage; laboratory tests are just starting. Jörg Uhde, Managing Director of Pfalzwerke geofuture, assumes that the prerequisites for the first pilot tests in the geothermal power plant will be in place in about two years. The partners expect about 70 tons of lithium annually at the Insheim location alone to be able to promote. With new wells in the Ortenau on the right Upper Rhine, the company can produce ten times as much lithium, Vulcan expects.

Trial of the procedure within two years In two years, the procedure of the KIT should be tried and tested long ago. The scientists from Karlsruhe want their pilot plant to be integrated into the thermal water cycle in one of the existing geothermal power plants in the Install Oberrheingraben. In doing so, they not only want to prove the feasibility, but also determine the cost at which lithium production is possible. “This prototype is relatively small and In principle, it could be placed on a desk, “explains Grimmer.” We will initially only work with low flow rates of ten liters per minute. ”

Various experiments will then be carried out with the pilot system. Among other things, the scientists want to test different pressure strengths and membrane types. The data from the prototype should also show whether the process can be economical. The pilot phase will take about half a year.

If operation in the prototype Scale works, one can plan and build a large-scale system. The process is designed so that it can also be accommodated on the same site as the existing geothermal power plants. Grimmer estimates that the large-scale system will take a year to build. If everything goes well, they could Project partners will deliver significant amounts of lithium carbonate in two years.

This article comes from c ‘ t 22 / 2020 .

(agr)