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The Audi Environmental Foundation, a subsidiary of AUDI AG founded in 2009, has joined forces with the Freiberg University of Mining and Technology to research new ways of mining high-tech elements. As depletable resources, metallic raw materials are needed for many future technologies, including electromobility; indium and germanium, cobalt, lithium, and rare earths are on the 2020 list of critical raw materials for the EU. This list of economically critical raw materials with a high supply risk is intended to help in the negotiation of trade agreements as well as drive research, innovation, and sustainable procurement.
Many primary raw materials are found in only a few countries worldwide. Their geographic distribution is uneven, and they are difficult to access. In some cases, they occur in such small quantities that extraction is unprofitable. Moreover, mining activities have a drastic impact on the environment.
The Audi Environmental Foundation supported a two-year research project using a newly developed membrane mining system developed at the Institute of Thermal, Environmental and Resources’ Process Engineering at the Freiberg University of Mining and Technology. The researchers put theory into practice both in the laboratory and underground in real operating environments in a research mine.
The aim is to extract high-tech elements from ores without destroying the natural environment through large-scale drilling and blasting. In contrast to conventional ore mining, microinvasive methods similar to modern surgical practices are used here.
This has several advantages: No heavy machinery, much less energy, and fewer chemicals are used, and there is also no damage to the landscape.
The process is environmentally friendly and innovative, as major mining activities are largely avoided and even small quantities of ore can be extracted.
—Rüdiger Recknagel, Director of the Audi Environmental Foundation
According to Recknagel, this strengthens import independence, thus increasing supply security.
The process, known as in-situ bioleaching, was developed and optimized in the laboratory before finally being tested under real conditions in the research mine. Researchers first drill small holes in the ore vein underground. Through leaching, metal ions are dissolved from the ore with the help of the microorganisms naturally occurring in the mine and fed to a new membrane plant as a metal-rich solution.
The bacteria are little miners that help transfer the metal ions to a solution.
—Roland Haseneder of the Institute of Institute of Thermal, Environmental and Resources’ Process Engineering
The two-stage membrane treatment separates the microorganisms and returns them to the leaching process and also selects and concentrates the desired ions.
From this multicomponent mixture, the Freiberg scientists then enriched indium and germanium.
The experts wanted to find out how the system would perform at a depth of 147 meters under conditions with more than 90% humidity and dripping acidic water at 10 degrees Celsius (50 ˚F). Important parameters included the composition of the bacterial solution, enrichment with target elements, the process parameters used, and the yield of target elements. The tests proved the efficiency of the system.
The team adjusted the pressure, flow rate, and purification processes to significantly improve separation, said Haseneder. The separation efficiency for germanium was increased by 20% compared to the laboratory experiments.
In the future, this sustainable extraction process will also be used for other elements such as cobalt in other deposits. The process is especially suitable for the extraction of valuable elements both from low-grade ores with a low concentration of valuable materials and from secondary raw materials well as for use at existing mining sites using the infrastructure that is already in place.
Haseneder also suggests the process could find application in other fields such as urban mining. At the Freiberg University of Mining and Technology, the search for suitable partners for application at other sites is in full swing. The ultimate vision is to implement microinvasive mining globally.
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