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German scientists devise ‘phytomining’ technique to extract rare metals from plants

Humans have been extracting useful materials from plants for millennia, but in the past few years, we’ve gotten particularly good at it. Case in point? German scientists from Freiburg University of Mining and Technology have discovered a way to mine plants for chemicals that can be used for manufacturing and industrial purposes. Biology professor Hermann Heilmeier and industrial chemistry Professor Martin Bertau are spearheading this technique they call “phytomining.” Working together at Freiburg U, the pair have developed a method to harvest germanium, an important metalloid component used in computers, smartphones and fiber-optic cables.

Germanium is found in soils worldwide, but it is hard to mine since it must be extracted from zinc, silver, lead or copper ore. More than 100 tons of germanium are produced annually with China producing the bulk of the global supply. Approximately 35 percent of worldwide germanium comes from recycling efforts that recoup the metal from existing sources. Heilmeier has found a way to circumvent these time-consuming extraction and recycling procedures using nature’s own concentrator, the plant.

Heilmeier grows his plants in a germanium-rich water that is available in waste rock piles at mines. The plants uptake this germanium-laden water and create a natural reserve of the element using the plant’s normal physiological processes. The plants are then harvested and the germanium recovered from the biomass using bacterial fermentation.

To make the process even more economical, the researchers are piggybacking on top of existing biogas plants that grow plants for energy. By growing these energy plants in germanium-rich water, the team creates an affordable source of germanium that can be mined easily after the plants have been used for energy generation. The bulk of the cost of growing and harvesting the plants is covered by the biogas plants, which already are growing the plants for fuel.  The final step of germanium recovery  is relatively cheap, making germanium phytomining a cost-effective technique.

As it is with most new procedures, there are many hurdles to overcome. For the germanium researchers, they must overcome low yield. Right now, germanium is harvested in minuscule quantities, just a few milligrams of germanium per liter.  The team hopes to upscale this process to an industry level where they are working with apparatus capable of handling a 1,000 liters of plant material at a time and producing yields of at least one gram of germanium per liter.