Recovering gold from electronic waste using whey? A reality

Garbage worth gold. Literally. The electronics industry struggles to recycle devices that have become useless and to isolate metals from them, particularly those that are expensive, such as gold. But four researchers from ETH Zurich (Swiss Federal Institute of Technology) have made a discovery that could change everything. In a study published in the journal Advanced Materials in January 2024, they detail their method… surprising to say the least, for extracting gold from common electronic waste in a sustainable manner.

“Current gold recovery methods are resource-intensive, requiring the development of more efficient extraction solutions,” point out the researchers. They therefore explored a new avenue, that of the amyloid substance (an aggregate of proteins) derived from whey – nicknamed “whey” – to develop a method that was as effective as it was ecological. Dairy waste to recycle gold, “we can’t get more sustainable than that!” »enthuses Raffaele Mezzenga, co-author of the study, in a press release.

Also read: Do you know Daisy, the Apple robot that recycles iPhones?

Whey to get gold nuggets

The solution most often used to recover gold is recycling with activated carbon. This process releases 116 g of CO2 per gram of gold extracted from WEEE (waste electrical and electronic equipment). With the whey technique from ETH Zurich, the method produces “only” 87 g per 1 gram of gold. This consists of transforming this whey into amyloid fibrils. These are protein aggregates composed of nanofibers. Dried, they become like sponges and appear like an aerogel (very porous solid).

It is then sufficient to immerse this airgel in the bath in which the metallic components of electronic waste are immersed to be dissolved. In this “aqua regia”, a mixture of hydrochloric acid and nitric acid, these nanofibers then have the particularity of only absorbing gold ions. All that remains is to heat these amyloid fibrils to obtain gold nuggets.

Improving the recycling of WEEE, a necessity

According to the United Nations, no less than 62 million tonnes of WEEE were generated in 2022. And their volume is growing five times faster than the proportion recycled even though we would have every interest in recovering the materials they contain for reuse in the production of new devices to reduce mining and its heavy environmental impact.

With this method developed from milk by-products and fifty times cheaper than the price of gold, there is hope. In a test of this new process, the four scientists immersed twenty used computer motherboards in the dissolution bath and then used their amyloid airgel. Result ? No less than 450 milligrams of gold (21 to 22 carats) recovered during this operation. This is 93.3% of the precious metal present in the solution. Finally, regarding purity, only 9% iron was absorbed by the airgel. The nuggets obtained have a purity of 90.8%.

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