Membrane mining

Essential in the manufacture of modern technologies such as fibre optics, photovoltaics, and semiconductors, rare earth metals are required in increasing volumes for the future. But extracting these elements from the earth in an environmentally friendly and sustainable manner presents a challenge to mining that the Audi Environmental Foundation is exploring along with the Freiberg University of Mining and Technology.

Many of the high-tech metals like indium and germanium, cobalt, lithium and rare earths are found in only a few countries worldwide and their geographic distribution is uneven. In addition to that, they are difficult to access and in some cases, they occur in such small quantities that extraction is unprofitable. 

Then of course there is the fact that mining activities have a drastic impact on the environment which prompted the Audi Environmental Foundation, together with the Institute of Thermal, Environmental and Resources’ Process Engineering at the Freiberg University of Mining and Technology, to establish alternative extraction methods for securing raw materials. The two-year research project addressed the question of how to make mining more sustainable. To this end, 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,” says 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 optimised in the laboratory before being tested under real conditions in the research mine at the Freiberg University of Mining and Technology. It works by having researchers drill small holes in the ore vein underground and then through leaching, the valuable elements are dissolved from the ore with the help of micro-organisms that are already present in the mine. 

“The bacteria are little miners that help transfer the metal ions to a solution,” explains Roland Haseneder of the Institute of Institute of Thermal, Environmental and Resources’ Process Engineering. 

“Working on site means there are no transport costs or logistics efforts,” says Haseneder. Additionally, the plant separates the micro-organisms and returns them to the leaching process – similar to the way a circular economy operates.

The aim of this process is to separate and enrich indium and germanium from a multicomponent mixture – these two strategic metals alone used for an array of high-tech products such as flat screens, touch screens, navigation systems, fibre optic technology, computer chips, photovoltaic systems, and automotive bearings.

The process works in real terms and even under particularly difficult conditions as demonstrated in the testing – at a depth of 147 metres under conditions with over 90 percent humidity and dripping acidic water at 10 degrees Celsius – where is performed faultlessly.

In the future, this sustainable extraction process will also be used for other elements such as cobalt in other deposits. It 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 says 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 with the ultimate vision to implement microinvasive mining globally.

Click here to see how the  the membrane mining system actually works.