Cheese-making waste used to extract gold from e-waste

Researchers at ETH Zurich developed a porous aerogel from whey protein and used it to recover gold from acid-dissolved electronic waste. The work, led by Professor Raffaele Mezzenga and published in Advanced Materials in 2024, demonstrated selective gold recovery in laboratory experiments.

The team converted whey protein, a byproduct of cheese production, into protein nanofibrils by applying acid and heat, then dried the material into an amyloid aerogel. Metal components removed from circuit boards were dissolved in an acid bath to form a mixed-metal solution. Exposing that solution to the aerogel caused gold ions to bind to the protein structure, separating them from other metals.

In tests the aerogel showed a gold adsorption capacity of about 166.7 milligrams per gram and captured roughly 93% of gold from solution in reported trials. The loaded aerogel reached about 20% of its own weight in gold during those experiments. To demonstrate the method, the researchers dissolved metal parts from 20 discarded computer motherboards and recovered a 450-milligram piece of 22-carat gold.

Mezzenga wrote, “Our approach uses food by-products, so the starting raw materials are extremely inexpensive and sustainable.” The research team estimated procurement and energy costs could be reduced by up to 50 times compared with conventional inputs. The process does not use cyanide or mercury.

Global electronic waste was estimated at 61.3 million metric tons in 2023. Electronic devices concentrate precious metals; industry figures indicate e-waste can contain up to 100 times more gold per ton than typical mined ore.

The experiments were carried out at laboratory scale. The authors note further work is required to scale the process, integrate it into existing recycling streams and test its performance on larger and more varied batches of e-waste before commercial use.