Metal Recycling Using a Beer Byproduct

🌱 Can e-waste be recycled using yeast?

Scientists at the University of Natural Resources and Life Sciences in Vienna, Austria recently developed a new method of recycling metals from e-waste that uses spent brewer’s yeast. The yeast is a byproduct of the brewing industry, and it is sometimes used to produce Marmite. Using the new method, it is possible to “selectively remov[e] metals such as zinc, aluminum, copper and nickel from complex waste solutions”.

🌱 How does the process work?

At the start of the process, biomass is separated from other residue from the brewing process. This biomass is dried and then used in a separation process. The cell walls of yeast “contain compounds such as chitin and glucan, which have a high binding capacity for heavy metals”. The yeast therefore behaves like a sponge. It absorbs metal ions through biosorption. In this process, “electrostatic interactions on the surface of the yeast make metal ions stick to the surface”. Notably, “[y]east cells are covered with surface active groups which can change their nature by [the] changing of the pH”. Changing the solution’s pH therefore “allows the yeast to attract more metal ions or different metal ions”.

🌱 Is the process efficient?

E-waste typically contains various metals that are not easy to separate for proper recycling. Many conventional methods therefore result in contaminated byproducts. The new method using brewer's yeast, however, offers “promising recovery rates” and results. From a mock metal waste solution, scientists managed to retrieve “more than 50% of aluminum, more than 40% of copper, and more than 70% of zinc”, by altering the temperature and pH of the solution. They also managed to retrieve “over 50% of copper and over 90% of zinc” from a real polymetallic waste stream. The process uses an acid treatment to remove the metals from the yeast’s surface and the brewer's yeast can be reused five (or more) times. Overall, the new method “is less energy-intensive, does not require the use of harsh chemicals, and can be carried out at room temperature”.

🌱 What potential is there?

For their initial experiments, the scientists used 20 liters of spent brewer’s yeast, which they got from a local brewing company. As brewer's yeast is typically considered a waste product, it is a cost-effective source. As it is readily available and a renewable resource, brewer's yeast could play a role in a more circular and sustainable management of e-waste. How the technique will fare in real world conditions, and whether it can be used on an industrial scale for mixed metal solutions, still needs to be researched. The researchers, however, hope the “technique could be used to reclaim metals lost in the electrical recycling process, and prevent heavy metal pollution”.