In the quest to improve precious metals recovery, Austrian scientists have turned to the key component of a favourite Australian breakfast spread.
Vegemite – often dubbed a ‘concentrated yeast extract’ – is made by taking spent yeast used in the beer-making process. That same waste product may show promise for metal recovery.
Electronic waste often consists of several different materials, making the process of reclaiming them a challenge for recyclers.
Bacteria, algae, clay and charcoal-like biochar have been trialled as potential options to achieve metal absorption, but often against singular targets.
Brewer’s yeast might offer an opportunity though, with results published by a group from the University of Natural Resources and Life Sciences in Vienna and K1-MET GmbH, a metallurgical competence centre, showing the addition of dried yeast waste recovered more than half of aluminium, 40% of copper and 70% of zinc from test solutions.
When added to wastewater, around 90% of suspended zinc and 50% of copper were retrieved.
Tweaking pH and temperature improves metal recovery
Brewer’s yeast retrieves metal from water through a process called adsorption, where electrical interactions on the yeast surface attract metallic ions, which attach to its solid surface.
But yeast needs to be ‘configured’ to attract and recover specific metals. This was done by altering the pH and temperature of the solution, effectively acting like a switch to enable specific metals to bind with the yeast.
While the effect was limited, pH alterations improved aluminium recovery by 16%. Temperature improved zinc recovery by 7.6%
The yeast was itself recyclable – able to be used five times without loss of potency. That’s an added appeal for using this cheap and widely available material, at least while humans keep drinking beer.
“Electronic waste is difficult to recycle because it is very heterogeneous,” said Dr Klemens Kremser of the University of Natural Resources and Life Sciences.
“Getting the metals in solution is a first step, but the selective recovery of the metals remains a challenge.
“Compared to processes such as chemical precipitation, biosorption using spent brewer’s yeast presents a cheap and environmentally friendly approach.”
Kremser warns, though, that this is a very early breakthrough. Lab-based testing isn’t the same as operating a metal recovery program at a large scale, particularly where wastewater for treatment will likely have highly variable compositions of metals.
“The metal removal process in this study was optimized for the four metals in question,” said Kremser. “The concentration of potentially interfering metal ions was very low in our starting solutions, but this would be important to consider when applying this approach to different mixed metal solutions.”
