Electronic waste, full of valuable metals such as copper, cobalt and considerable amounts of gold, represents an attractive source of resources. However, conventional recovery methods consume considerable energy and often rely on highly toxic chemicals. However, a group of scientists from the Department of Health Sciences and Technology at ETH Zurich has developed an efficient, economical and, above all, sustainable method: a sponge made from a protein matrix, capable of extracting gold from electronic waste.
To make the sponge, scientists denatured whey proteins under acidic conditions and high temperatures, forming protein nanofibrils in a gel. They then dried the gel, resulting in a sponge made up of these protein fibrils.
In the laboratory experiment, the team salvaged electronic motherboards from 20 old computers and extracted metal parts to recover gold. These pieces were dissolved in an acid bath to ionize the metals.
By introducing the protein fiber sponge into the metal ion solution, the gold ions efficiently adhered to the protein fibers. Although other metal ions could also adhere, the effectiveness of gold ions was notably superior, as demonstrated in the article published in Advanced Materials.
In the next step, the researchers heated the sponge, reducing the gold ions to flakes, which were later melted to form a gold nugget. The end result was a nugget of approximately 450 milligrams from the 20 motherboards, with a purity of 91%, equivalent to 22 carats.
The new technology has proven to be commercially viable. According to scientists, the costs of raw materials plus the energy costs of the process are 50 times lower than the value of the gold recovered.
The researchers now plan to improve the technology to prepare it for the market. While e-waste is the most promising initial source for gold extraction, other possible sources include industrial waste from microchip manufacturing or gold plating processes. Additionally, scientists are exploring the possibility of making protein fibril sponges from other protein-rich byproducts or waste from the food industry.
Source: Advanced Materials
