Fascination Technology How whey extracts gold from electronic waste

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In our "Fascination Technology" section, we present impressive projects from research and development to engineers every week. Today: how researchers extract gold from electronic waste using a sustainable method.

Electronic waste contains various valuable metals, including copper, cobalt, and also significant amounts of gold. Recycling this from discarded smartphones and computers is of great interest due to the increasing demand for the precious metal. However, current recovery methods are energy-intensive and often require highly toxic chemicals. The group led by ETH Professor Mezzenga now presents a very efficient, cost-effective and above all much more sustainable method: Using a sponge made of a protein mesh, they have succeeded in fishing out gold from electronic waste.

What I like best is that we use a by-product of the food industry to extract gold from electronic waste. So, one could say that the method turns two wastes into gold. It doesn't get much more sustainable than that.

ETH-Professor Mezzenga

Selective gold uptake from old computers.

• For the manufacture of the sponge, Mohammad Peydayesh, senior associate in Mezzenga's group, and his colleagues used whey proteins. They denatured them at high heat and with acid, causing them to aggregate into a gel of protein nanofibers. The scientists then dried this gel, resulting in a sponge made of these protein fibers.

• In order to recover gold in a laboratory trial, the researchers took the electronic circuit boards from 20 old computers and removed the metal parts. They dissolved these in an acid bath, so that the metals were present in it as ions.

• When the researchers placed the protein fiber sponge in the metal ion solution, the gold ions attached themselves to the protein fibers. Other metal ions can also attach themselves to the fibers, but gold ions attach themselves much more efficiently.

• In the next step, the researchers heated the sponge. This caused the gold ions to crystallize into flakes, which the scientists could then melt into a gold nugget. Thus, they obtained a nugget weighing around 450 milligrams with a 91 percent gold content (the rest is copper), which is equivalent to just under 22 carats, from the 20 computer circuit boards.

Economically viable process

The new technology is economical, as Mezzenga calculates: The costs for the procurement of the starting materials and the energy costs of the whole process are together 50 times lower than the value of the gold that can be recovered.

Next, the researchers want to develop the technology to market maturity. Even though electronic waste is the most promising starting product from which they want to mine gold, there are still other possible sources. These include industrial waste from microchip manufacturing or from gold plating, for example. In addition, the scientists want to investigate whether they can also produce the protein fiber sponges from other protein-containing by-products or waste products of the food industry.

Reference

Peydayesh M, Boschi E, Donat F, Mezzenga R: Gold Recovery from E-​Waste by Food-​Waste Amyloid Aerogels. Advanced Materials 2024, 2310642, doi: 10.1002/adma.202310642