Electronic waste turns into gold
A team of researchers at ETH Zurich is extracting the precious metal gold from electronic waste. The new method is considered particularly sustainable: it is based on a protein fibre sponge that the scientists produce from whey, a by-product of the food industry. The researchers were able to extract a 22-carat gold nugget weighing 450 milligrammes from 20 old computer circuit boards. As the method utilises various waste and industrial by-products, it is not only sustainable but also cost-effective.
Turning base metals into gold was one of the unachieved goals of the alchemists in the Middle Ages and early modern period. However, what Raffaele Mezzenga, a professor in the Department of Health Sciences and Technology at ETH Zurich, has now achieved also falls under the same motto. Of course, he has not transformed another chemical element into gold, as the alchemists attempted to do. But he has succeeded in extracting gold from electronic waste using a by-product of cheese production.
Electronic waste contains various valuable metals, including copper, cobalt and also significant quantities of gold. Recovering these from end-of-life smartphones and computers is of great interest due to the rising demand for the precious metal. However, existing recovery processes are energy-intensive and often require highly toxic chemicals. ETH Professor Mezzenga’s group has now presented a highly efficient, cost-effective and, above all, much more sustainable method: using a sponge made from a protein network, they have succeeded in extracting gold from electronic waste.
Selective gold absorption
To produce the sponge, Mohammad Peydayesh, a senior research assistant in Mezzenga’s group, and his colleagues used whey proteins. They denatured these using high heat and acid, causing them to aggregate into protein nanofibres within a gel. The scientists dried this gel, creating a sponge made of these protein fibres. To recover gold in a laboratory experiment, the researchers took the circuit boards from 20 old computers and removed the metal parts. They dissolved these in an acid bath, so that the metals were present as ions.
When the researchers placed the protein-fibre sponge into the metal-ion solution, the gold ions deposited onto the protein fibres. Other metal ions can also attach themselves to the fibres, but gold ions attach much more efficiently than these. In the next step, the researchers heated the sponge. This caused the gold ions to crystallise into flakes, which the scientists were eventually able to melt down into a gold nugget. In this way, they obtained a nugget weighing around 450 milligrammes from the 20 computer circuit boards, with gold accounting for 91 per cent of the total mass (the rest being copper), which corresponds to just under 22 carats.
Economically viable
The new technology is economically viable, as Mezzenga calculates: the combined cost of sourcing the raw materials and the energy required for the entire process is 50 times lower than the value of the gold that can be recovered.
Next, the researchers aim to develop the technology to market readiness. Although electronic waste is the most promising source material from which they wish to extract gold, there are other potential sources. These include, for example, industrial waste from microchip manufacturing or gold plating. The scientists also intend to investigate whether they can produce the protein fibre sponges from other protein-containing by-products or waste materials from the food industry.
“What I like best is that we’re using a by-product of the food industry to extract gold from electronic waste,” says Mezzenga. One could therefore rightly say that the method transforms two waste materials into gold. “It doesn’t get much more sustainable than that.”
Source: ETH Zurich