A blue pigment favored by artists could suck precious metals out of your discarded cell phone

The Great Wave off Kanagawa, Hokusai (1831). Credit: Wikimedia Commons.

Computer chips can be found in just about anything these days. They’re in the device you’re currently using to read this article, and dozens more can be found in your vehicle, helping regulate engine temperature and stabilize suspension systems. You’ll find chips in Wi-Fi routers, refrigerators, and even toasters. Just about anything you plug into an outlet now has a tiny computer inside.

The fact is that the modern world runs on computer chips, but they can also consume many rare minerals and especially precious metals like gold and platinum – and recycling them is no easy task. Seeking to address this challenge, researchers from Nagoya University, in collaboration with the Tokyo Institute of Technology, have discovered an unlikely solution in the form of Prussian blue, the world’s first synthetic pigment that changed forever the art of painting.

If you piled up the contents of a ton of cell phones, you would find up to 400 grams of gold inside. That might not seem like a lot, but it’s still up to 80 times more than what you’d find in a ton of natural ore. With the right technology to extract all those tiny amounts of metal from each device, it could be much more cost effective to recycle gold and platinum from e-waste than to extract it. Gold mining is also one of the most destructive industries in the world, which can contaminate drinking water and soil, and destroy pristine environments due to mercury and cyanide pollution, endangering the health of people and ecosystems.

From Picasso to the dump

Credit: Reiko Matsushita, Shinta Watanabe.

Before Prussian blue was invented by accident by the German painter Johann Jacob Diesbach at the turn of the 18th century, painters had to use only natural pigments, such as indigo dye or the very expensive ultramarine made from lapis- lazuli to create deep blue hues. Armed with a new chemical recipe, Diesbach was now able to produce virtually unlimited quantities of Prussian blue. Other chemists then began to produce other synthetic pigments, making them much more affordable and transforming the art.

You can find Prussian blue in many masterpieces, like that of Vincent van Gogh The starry Night or that of Hokusai The Great Wave off Kanagawa. During his famous blue period, Picasso used Prussian blue in virtually every one of his acclaimed works.

Today, the pigment has fallen out of favor among modern painters, who have better options available to them. However, Prussian blue is still used for two very different purposes. Prussian blue pills are often used in emergency medical situations to treat heavy metal poisoning. The pigment forms a jungle-like network with nano-sized spaces, ideal for trapping individual metal ions, including toxic metals like radioactive thallium or cesium.

Prussian blue was also widely used in the aftermath of the 2011 tsunami that caused the nuclear accident at the Fukushima power plant, sucking up radioactive cesium from the ground near the disaster site. This is how Japanese researchers came up with the idea of ​​studying the pigment’s ability to recover metals from electronic waste.

Previously, the team led by Jun Onoe, an engineering professor at Nagoya University, showed that Prussian blue pigments could trap rare metals like molybdenum, as well as ruthenium, rhodium and palladium, between other platinum group metals on the periodic table.

In their new study, Onoe and his colleagues used X-rays and ultraviolet spectroscopy to learn more about how the pigment accomplishes these feats.

“I was surprised to find that Prussian blue absorbs platinum-group precious metals by substitution with iron ions in the frame while retaining the jungle-gym structure,” Professor Onoe explained, adding that this mechanism allows the pigment to absorb more gold and platinum. metals than any other biobased absorbent.

In addition to helping solve our growing e-waste problem, Prussian blue could also be a solution for nuclear waste, the disposal of which is incredibly complex and risk-prone. Spent nuclear fuel rods are usually reprocessed and turned into a glass-like state for long-term storage in geologically isolated facilities, sometimes underground “nuclear tombs” miles deep. During this process, platinum group metals can deposit on the side wall of the melter used in the nuclear waste reprocessing plant, which must be flushed to preserve the stability of vitrified objects. Prussian blue could be an easy and cheap solution in this case.

“Our results demonstrate that Prussian blue or its analogues are candidates for enhancing the recycling of precious metals from nuclear and electronic waste,” says Professor Onoe. “Especially compared to conventionally used bio-based adsorbents/activated carbons.”

From a painter’s palette to cleaning up electronic and nuclear waste, Prussian blue has been quite the trick so far.

The results are published in the journal Scientific reports.