Materials

Pulling gold out of e-waste suddenly becomes super-profitable

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Using a food industry byproduct, researchers have extracted 22-karat gold from old motherboards
Using a food industry byproduct, researchers have extracted 22-karat gold from old motherboards
Schematic of the process of recovering gold from electronic waste using a food industry byproduct
Peydayesh et al.

A new method for recovering high-purity gold from discarded electronics is paying back US$50 for every dollar spent, according to researchers – who found the key gold-filtering substance in cheesemaking, of all places.

Society has held gold in high esteem for millennia. More recently, for its technical applications across electronics and microelectronics, aerospace, medicine, biotechnology, and nanotechnology. However, like any metal, gold is a non-renewable resource. And increasingly valuable.

In a new study, researchers from ETH Zurich, Switzerland, have detailed a sustainable, cost-effective method of selectively extracting gold from electronic waste or e-waste.

“The fact I love the most is that we’re using a food industry byproduct to obtain gold from electronic waste,” said Raffaele Mezzenga, the study’s corresponding author. “You can’t get more sustainable than that!”

The food industry byproduct Mezzanga is referring to is whey, the watery portion of milk that separates from the curds when making cheese. Here, the researchers turned this dairy waste into a matrix of protein amyloid fibrils they used as an adsorbent to selectively remove gold from e-waste.

Under acidic conditions and high temperatures, the whey proteins were denatured – the destruction of the protein’s structure into a looser, more random one – causing them to aggregate into nanofibrils in a gel. The gel was dried and formed into a sponge.

Schematic of the process of recovering gold from electronic waste using a food industry byproduct
Peydayesh et al.

The researchers extracted the metal parts from 20 old computer motherboards and dissolved them in an acid bath to ionize the metals or separate them into positive and negative ions. When the protein fibril sponge was placed in the metal ion solution, the gold ions stuck to it. While other metals – copper and iron, for example – were also absorbed by the sponge, gold was absorbed far more efficiently.

After absorbing the gold ions, the protein fibril sponge was subjected to heat, reducing the ions to flakes which eventually melted down into a gold nugget with a mass of around 500 mg. Analysis revealed that the nugget was made predominantly of gold (90.8 wt%), with copper and nickel contributing 10.9 wt% and 0.018 wt%, respectively. The findings demonstrate the high purity of the nugget, corresponding to 21 or 22 karats.

In their paper, the researchers demonstrated their method’s commercial viability. Including both source material procurement costs and the energy costs for the entire process, the total cost of recovering 1 g of gold from e-waste was 50 times lower than the value of the gold recovered.

And the method is better from an environmental standpoint. Using conventional activated carbon to recover 1 g of gold from e-waste would produce around 116 g of carbon dioxide, whereas the protein fibril sponge’s carbon footprint is lower, resulting in approximately 87 g of the greenhouse gas. The main reason for the higher environmental impact of using activated carbon is its higher energy consumption during production, predominantly due to non-renewable fuel sources, coupled with a lower adsorption capacity than the sponge.

Previous attempts to extract gold have all had their drawbacks, such as scalability.

Because whey is an animal-based protein, the protein fibril sponge will likely cause more ecosystem damage than activated carbon. As such, the researchers will explore whether plant-based proteins, such as those derived from peas and potatoes, can be used instead of whey.

The researchers plan to ready the technology for the market. While e-waste is a promising starting source to extract gold, they are eyeing others, including industrial waste from microchip manufacturing or gold-plating processes.

The study was published in the journal Advanced Materials.

Source: ETH Zurich

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7 comments
Rustgecko
If it’s only half true they’ll have a queue of potential investors.
reader
Plant-based protein from peas and potatoe monocultures are not less damaging to ecosystems. They use pesticides and chemical fertilizers and are basically devoid of life. Rotationally grazed pastures are full of life and actually build soil organic matter (ie regenerative) instead of just mining it for cash crops. And the carbon/methane cycle of dairy cows is a closed loop. Whey protein is a waste product from cheese production. Think pizzas, not peas.

As Robert Murray-Smith pointed out in his video about this a few weeks ago, perhaps the most important application of these protein sponges will be removing heavy metals from industrial waste water.
TechGazer
Will all new processes have a blurb about how they reduce greenhouse gas, even if it's insignificant compared to the main sources?
zort
I wonder how it will work to extract gold from its various natural ores?
Hopefully it will help reduce the amount of toxic wastes produced by the current methods of extraction.
Daishi
Tons of e-waste has been dumped in poor countries. Hopefully they have an opportunity to capitalize on this. Maybe with some financial inventive the process of throwing away e-waste will improve too.
johanschaller
Gold extracted using a whey-based sponge? More holes in that than a piece of Swiss cheese!
jerryd
They do it better with vinegar and many other ways online, flakes the gold off and purified melting to make a gold bar seems cheaper.