A team of researchers at ETH Zurich is retrieving gold from electronic scrap metals. This new method is seen as especially sustainable: For example, it is based on a protein-fibre sponge which scientists produce from whey, a byproduct of the food industry. From 20 old computer main boards, the researchers retrieved 450-milligram, 22-carat gold nugget. As the method uses different waste and industrial byproducts, it is not only sustainable but also low-cost.
Turning base materials into gold was one of the never-achieved goals of alchemists in the medieval and early modern period. But the same motto applies to the achievements of Raffaele Mezzenga, professor at the department of Health Sciences and Technology at ETH Zurich. Of course he didn’t turn another chemical element into gold, as the alchemists tried to do. But he succeeded in retrieving gold from electronic scrap with the help of a byproduct from cheese production.
Electronic scrap contains different precious metals, among them copper, cobalt and relevant amounts of gold. Extracting these from retired smartphones and computers is of great interest due to the increased demand for the noble metal. Hitherto, procedures for retrieval have however been energy intensive and often required highly toxic chemicals. The team around ETH professor Mezzenga now presents a very efficient, low-cost and above all much more sustainable method: Using a sponge consisting of a protein mesh, they managed to fish gold out of electronic scrap.
Selective gold uptake
To produce the sponge, Mohammed Peydayesh, the head assistant in Mezzenga’s team, and his colleagues used whey proteins. Denaturation at great heat and with the help of acid resulted in coagulation into a gel of protein nanofibres. The researchers dried this gel, which resulted in a sponge made of these protein fibres. In order to retrieve gold in laboratory tests, the scientists took electronic main boards from 20 old computers and removed the metal parts. They then dissolved these parts in an acid bath, so that the metals were then present as ions.
When the scientists placed the sponge into the solution containing metal ions, the gold ions attached to the protein fibres. Other metal ions also are able to attach to fibres, but gold is much more efficient at doing so. In a next step, the scientists heated the sponge up. This caused the gold ions to crystallise into flakes which the researchers could melt down into a nugget. This way, from 20 computer main boards, they manages to retrieve an approximately 450-milligram nugget with a gold content of 91 percent total mass (the rest is copper), which corresponds to just about 22 carat.
A profitable business
The new technology can turn a profit, as Mezzenga demonstrates by calculation: the cost for acquiring the raw materials and the energy costs of the entire process together are 50 times less then the worth of the gold which is retrieved.
Next, the researchers want to develop the technology further and bring it to market. Even if electronic scrap is the most promising raw material for extracting gold, there are other possible sources. Among these are, for example, industrial waste from microchip production or from gilding. The scientists also want to research whether the protein-fibre sponges can also be obtained from other byproducts or waste material from the food industry which also contain protein.
“What I like best is that we are using a byproduct from the food industry to retrieve gold from electronic junk”, says Mezzenga. Therefore it is said one can rightfully suggest this method turns two waste products to gold. “It doesn’t get more sustainable.”
Source: ETH Zürich