The transformation of basic materials into gold was one of the elusive goals of the alchemists of the past. Now Professor Raffaele Mezzenga from the Department of Health Sciences and Technology at ETH Zurich has undertaken a modern parallel of this quest. While it didn’t turn any chemical elements into gold as the alchemists imagined, it did manage to successfully extract gold from e-waste using a byproduct of the cheese-making process.

E-waste contains a variety of precious metals, including copper, cobalt, and even significant amounts of gold. Recovering this gold from end-of-life smartphones and computers is an attractive proposition given the growing demand for the precious metal. However, recovery methods developed today are energy intensive and often require the use of highly toxic chemicals. Now a group led by ETH Professor Mezzenga has invented a very efficient, cost-effective and, above all, much more sustainable method: Researchers have managed to successfully extract gold from e-waste with the help of a sponge made of protein matrix.

Selective adsorption of gold

To make the sponge, Mohammad Peydayesh, a senior scientist in Mezzenga’s group, and colleagues denatured whey proteins under acidic conditions and high temperatures, allowing them to assemble into protein nanofibrils in the gel. The scientists then dried the gel and created a sponge from these protein fibrils.

To recover the gold in the laboratory experiment, the team salvaged electronic motherboards and removed metal parts from 20 old computer motherboards. They dissolved these pieces in an acid bath to ionize the metals.

When they placed a sponge with protein fibers in a solution of metal ions, the gold ions stuck to the protein fibers. Other metal ions can also adhere to fibers, but gold ions do so much more effectively. The researchers showed this in their article published in the journal. Advanced Materials.

The next step was to heat the sponge. This turned the gold ions into flakes, which scientists then melted into a gold nugget. In this way, they obtained approximately 450 milligrams of grain from 20 computer motherboards. The nugget consisted of 91% gold (the rest was copper), corresponding to 22 carats.

Economically beneficial

As Mezzenga’s calculations show, the new technology is commercially viable: The cost of purchasing raw materials, added to the energy costs of the entire process, is 50 times lower than the cost of gold that can be mined.

Next, researchers want to improve the technology to make it market-ready. Although the most promising raw material from which they want to extract gold is e-waste, there are other possible sources. These include industrial waste from microchip production or gold plating processes. In addition, the scientists plan to investigate whether they can make protein fibril sponges from other protein-rich byproducts or food industry waste.

“What I like most is that we are using a byproduct of the food industry to extract gold from e-waste,” says Mezzenga. He states that the method literally turns two wastes into gold. “There is nothing more sustainable than this!”