When you get rid of an old phone or tablet, you're likely to remove your valuable information from it, but what about the valuable materials – like gold – that it contains?
Naturally, such substances are too hard for consumers to retrieve, which might be why, according to the University of Edinburgh (UE), about seven percent of the world's gold supply is currently locked inside of electronics. While removing that gold has heretofore been a highly toxic and inefficient proposition, researchers now think that a new process will make prospecting for gold in electronics heaps more achievable than ever.
Gold is often found on printed circuit boards, particularly under keyboards where its durability is an advantage. According to the UE researchers, about 300 tonnes of the metal are used in electronics each year.
The new process to remove it uses a mild acid as opposed to harsher chemicals such as cyanide or mercury that are currently used to extract gold.
First, printed circuit boards are dissolved in the acid which turns all of the metal in the board to liquid. Then, an oily solvent made from toluene is added, kicking off a process known as solvent extraction. Toluene is an aromatic hydrocarbon commonly found in paint thinners. The toluene solvent pulls the gold free from the other materials in the acid wash where the metal can be recovered and used again. Likewise, the solvent and acid can be reused, cutting down on waste.
"The solvent extraction technique is great in that the recycling of reagents and acid are integral to the process," lead researcher Jason Love of UE's School of Chemistry told New Atlas.
Love also says that it might be possible to extract other metals using the process.
"Once you have dissolved metals in acid, you can use solvent extraction to separate all of them," he said. "So, in principle, we could devise a process that would be able to separate all of the metals in electronic waste, which of course would have environmental and potentially economic benefits, but this would depend on the prices of metals and the cost of the process."
The work Love and his team carried out is part of a student- and staff-led initiative at UE to promote the circular economy, which focuses on the efficient use of materials and their reuse as well.

Along with its use in jewellery, gold also has numerous applications in fields such as electronics and scientific research. It's a handy material, but – of course – it's also expensive. That's why researchers at ETH Zurich have developed a new way of making a small amount of gold go a long way. They've created a gold foam that looks much like solid gold, but is actually 98 parts air to two parts solid material. As an added bonus, the aerogel-type foam can also be made in non-gold colors such as dark red.
According to lead scientist Prof. Raffaele Mezzenga, the foam is one one-thousandths the weight of a same-sized piece of a conventional gold alloy. This makes it lighter than water, and almost as light as air. It still looks shiny and metallic, but unlike solid gold, it's malleable enough that it can be shaped by hand.
The solid material within the foam consists of approximately four-fifths actual gold, and about one-fifth milk proteins. Purity-wise, the foam comes out at around 20 carats.
Mezzenga and his team made the foam by first heating the proteins to convert them into tiny fibers, known as amyloid fibrils. When these fibrils were added to a solution of gold salt, they responded by interlacing themselves into a three-dimensional lattice-like structure. As they were in the process of doing so, the gold crystallized into tiny microparticles that became embedded in the fibrils.
The resulting gel-like structure was then dried to create the finished foam, using a labor-intensive process that involved exposing it to carbon dioxide. Air-drying would have been much easier, but could also have damaged the material before it dried.
Additionally, by changing the reaction conditions in the "gold salt" step of the process, the researchers were able to make the gold crystallize into even smaller nanoparticles. Because these had different optical qualities than the larger particles, the completed gold foam took on a dark red color.
Not only could the foam be used in many of the same applications as regular, more costly gold, but it might also be utilized in highly-sensitive pressure sensors. "At normal atmospheric pressure the individual gold particles in the material do not touch, and the gold aerogel does not conduct electricity," says Mezzenga. "But when the pressure is increased, the material gets compressed and the particles begin to touch, making the material conductive."