Cheesemaking Byproduct Holds Key to Salvaging Gold From Electronic Waste

When the arachnophobic "Little Miss Muffet" sat on her tuffet in the 1805 nursery rhyme, young readers at the time could have hardly envisioned a future world in which her curds-and-whey snack would provide one of the ingredients for an eco-friendly way of salvaging gold from electronic waste.

Researchers at ETH Zurich reported that they have successfully recovered gold from old computer motherboards utilizing sponges derived from whey, the liquid that is leftover after curds are drained during the cheesemaking process.

Because the method utilizes various waste and industry byproducts, it is not only sustainable, but cost effective.

“The fact I love the most is that we’re using a food industry byproduct to obtain gold from electronic waste,” noted professor Raffaele Mezzenga from the Department of Health Sciences and Technology at ETH Zurich.

In a very real sense, he observed, the method transforms two waste products into gold.

“You can’t get much more sustainable than that!” he said.

Researchers explained that electronic waste contains a variety of valuable metals, including copper, cobalt and even significant amounts of gold. The downside of recycling is that the current methods use a lot of energy and employ highly toxic chemicals.

The far more sustainable method described in the journal Advanced Materials simply requires a sponge made from a protein matrix.

ETH Zurich senior scientist Mohammad Peydayesh and his colleagues denatured whey proteins under acidic conditions and high temperatures, forming a gel. Then they dried the gel, which transformed it into a sponge of protein fibrils.

In their experiment, they extracted the metal parts from 20 motherboards and dissolved them in an acid bath to ionize the metals.

When the sponge was placed in the ionized metal solution, the gold ions adhered to the protein fibers. While other metals also adhered the the fibers, gold ions did so more efficiently, the researchers reported. From 20 motherboards, they were able to extract 450 milligrams of gold at a purity level of about 91%, or 22 karats.

The business case for moving forward with this method of recycling is simple. According to the researchers, the cost of materials and energy for the entire process is 50 times lower than the value of the gold that can be recovered.

Credits: Motherboards image by Crista Castellanos, CC BY-SA 4.0, via Wikimedia Commons. Arthur Rackham illustration via William Fayal Clarke, Public domain, via Wikimedia Commons.