New way to recycle metals from electronics discovered

By James Gamble via SWNS

A new way of recycling metals from old electronic devices using the main ingredient in Marmite has been developed.

A study found the economically important metals zinc, aluminum, copper and nickel could be separated and recovered using brewer's yeast, also used in the spread.

The common byproduct of beer brewing is both cheap and widely available and was found to recover as much as 90 percent of some metals.

Researchers now hope to conduct further tests on the potential applications of these reclaimed metals.

When we recycle electronic devices we can no longer use, we expect and aim to make the most out of the precious natural resources that go into building them.

However, electronic waste is notoriously difficult to recycle due to difficulties in separating the different metals from one another.

Researchers in Austria now believe they may have found a way to selectively capture metals from a waste stream using spent brewer's yeast - a byproduct of beer brewing that is the main ingredient in Marmite.

The scientists behind the study, published in the journal Frontiers in Bioengineering and Biotechnology, also hailed the fact that the yeast can be reused, making the process even more eco-friendly.

Dr. Klemens Kremser, a lead author of the study from the University of Natural Resources and Life Sciences in the Austrian capital of Vienna, explained: "Electronic waste is difficult to recycle because it is very heterogeneous.

"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."

Existing options for separating different component metals of electronic waste include other 'biosorbents': biological materials that can be used to soak up pollution.

But these all tend to have significant downsides.

Chemical precipitation, for example, produces contaminated 'slag', whilst biochar - a biosorbent similar to charcoal - is difficult to separate from the wastewater.

The researchers therefore turned their attention to brewer’s yeast, which, being a common byproduct of beer brewing, is both cheap and widely available.

The research team acquired 20 liters of spent brewer’s yeast, separated the biomass from leftover brewing residues and dried it out.

Electrostatic interactions on the surface of the yeast then allow metal ions to stick to that surface in a process called adsorption.

Changing the pH level of this solution alters the interactions, which can allow the yeast to adsorb more or different metal ions depending on the contents of the solution and the specific pH.

In their study, the scientists chose to test the yeast biomass against zinc, aluminum, copper, and nickel - all economically important metals.

The scientists tested each metal solution at a range of different pHs and temperatures, to assess whether it was possible to increase the strength of the interactions and recover more metal.

They also tested the yeast against a real polymetallic waste stream.

Although similar methods are already in use, Anna Sieber, a Ph.D. fellow of the Austrian metallurgical research center K1-MET and first author of the article, said the team's experiments proved how using brewer's yeast was a more economical approach to metal recovery.

“Using waste biomass for metal recovery is not a completely new process, but the selectivity of biosorption processes is a key factor for efficient metal recovery from polymetallic waste streams,” she said.

“We demonstrated high metal recovery rates from a complex metal solution using an environmentally friendly and cheap biomass.

"Yeast biomass is considered a safe organism, and the demonstrated reusability of the biomass makes it an economically feasible approach.”

The researchers found they were able to recover more than 50 percent of aluminum, over 40 percent of copper and more than 70 percent of zinc from the test metal solutions.

More than half of copper and over 90 percent of zinc were retrieved from the polymetallic waste stream they tested the yeast on.

Changing the temperature was found to have relatively little impact on efficiency except for zinc, where it raised the recovery rate by 7.6 percent.

Similarly, adjusting pH levels had a limited effect on most of the metal solutions except for aluminum, where it improved the efficiency of recovery by 16 percent.

“The metals can be removed from the yeast surface by acid treatment and thus could be recycled,” Sieber said.

“It would be interesting to investigate potential applications for these reclaimed metals.”

The researchers added that the brewer's yeast itself could also be recycled without heavily impacting its ability to recover metal; using their batch five times to recover different metals.

However, they cautioned that the metal recovery process needs testing with far larger studies in real-life conditions before it can be implemented on an industrial scale.

“The metal removal process in this study was optimized for the four metals in question,” Dr. Kremser said.

“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.”