The element is a semi-conductor and was used to develop the first transistor because it is able to transport electrical charges extremely quickly. Nowadays, silicon-germanium alloy is indispensable to modern life, crucial in making computers, smartphones and fiber-optic cables.
Transparent in infra-red light, germanium is also used in intelligent steering systems and parking sensors for vehicles.
Yet although germanium is present in soil all over the world, it is difficult to extract, and most supplies currently come from China. Now scientists at Freiburg University of Mining and Technology think they have found a revolutionary way to obtain it from their own soil – with a little help from the natural world.
Biology professor Hermann Heilmeier is one of the scientists using common plants for this uncommon process.
“What is being cultivated in this field are various energy crops — for example sunflowers, corn, reed canary grass – but instead of using them for energy purposes we want to use them for phytomining. In German we call it ‘mining with plants’. We want to bring elements that are present in the soil into the roots and shoots of the plants, harvest them and then extract these elements from the plants after they have been used for energy, that is to say fermented,” he said, showing off his field of crops as he measured the moisture levels of the soil.
The process is still in its early stages, but Heilmeier says they have now identified the plants that could allow them to scale the attempt up. The next stage of the process takes place in a laboratory at the university in Freiburg, where head of industrial chemistry Professor Martin Bertau has been overseeing the project. He said the region is very well-suited to the extraction of germanium due to the composition of the soil.
“There is zinc ore present here, the ground is very rich in zinc. We have the remains of waste rock piles from mining, which germanium-rich water can drain better through. And when you cultivate plants here and give them that water, they can build up germanium reserves through normal physiological processes. We unlock these reserves through fermentation with the help of bacteria and thus we are able to mobilize the germanium,” Bertau explained.
Economically, the process is efficient, because the extraction of germanium can happen after plants are processed for use as biogas. Thus many of the costs are already covered in existing biogas plants.
“We use the normal biogas process, collect the products of fermentation and all there is left to do then is extract the germanium from them. The processing costs of this downstream step are manageable, so even with these low amounts it is still economically viable,” Bertau said.
The potential for industry could be enormous, but there is still work to do before the benefits can be reaped. At the moment germanium can only be harvested in extremely small quantities, just a few milligrams per liter. Scientists need to achieve at least one gram per liter, which at the moment is only possible through a process of concentrating the extract.
“It is as it so often is: industry is still waiting because they want to see a facility where everything is already working. Then they say: ‘we’ll have it’. But of course we have to complete the step in between first. Thanks to the support of the BMBF (German ministry for education and research), we have now actually found a solution to an intractable problem and have got to the point where we can upscale the process. So we will be able to work with bigger amounts, with apparatus with a capacity of 1,000 liters or 10 cubic meters instead of 20 liters,” Bertau said.