Gold and some other precious metals are key ingredients in computer chips, including those used in consumer electronics like smart phones. But it can be difficult to recover and recycle these metals from e-waste. Japanese researchers have found that a pigment widely used by artists called Prussian blue can extract gold and platinum group metals from electronic waste much more efficiently than conventional bio-based absorbents, according to a recent paper published in the journal Scientific Reports.
“The amount of gold contained in a ton of mobile phones is 300 to 400 grams, which is much higher by 10 to 80 times than that contained in a ton of natural ore,” the authors wrote. “Other elements have a similar situation. Therefore, recovering these valuable elements from e-waste is much more efficient and effective compared to collecting them from natural ore.”
Prussian blue is the first modern synthetic pigment. Certainly, there was once a pigment known as Egyptian blue that was used in ancient Egypt for millennia; the Romans called it caeruleum. But after the collapse of the Roman Empire, the pigment was not widely used, and the secret of its manufacture was eventually lost. (Scientists have since figured out how to recreate the process.) So before the discovery of Prussian blue, painters had to use indigo dye, smalt, or expensive ultramarine made from lapis lazuli for dark blue hues.
It is believed that Prussian blue was first synthesized by accident by a Berlin painter named Johann Jacob Diesbach around 1706. Diesbach was trying to make a red pigment, which involved mixing potash, ferric sulfate and cochineal dried. But the potash he used was apparently stained with blood – it is believed to have been a cut finger or similar minor injury. The ensuing reaction created a distinctive blue iron ferrocyanide, and was eventually called Prussian blue (or Berlin blue).
The first known painting to use Prussian blue is currently that of Pieter van den Werff Entombment of Christ (1709), but the recipe was published in 1734, and Prussian blue soon spread among artists. Hokusai’s famous works of art, The Great Wave off Kanagawais one of the most famous works using the pigment, with that of Vincent van Gogh The starry Night and numerous paintings from Pablo Picasso’s “blue period”.
The pigment has other uses. It is often used to treat heavy metal poisoning from radioactive thallium or cesium because its lattice-like lattice structure, similar to a jungle gymnasium, can trap the metal ions of these metals and prevent them from dying. be absorbed by the body. Prussian blue helped remove cesium from the ground around the Fukushima power plant after the 2011 tsunami. Prussian blue nanoparticles are used in some cosmetic products and are used by pathologists as a dye to detect iron in , for example, bone marrow biopsy specimens.
It is therefore a very useful substance, which is why the Japanese authors of this latest article decided to explore other potential practical applications. They analyzed how Prussian blue absorbs multivalent metals – such as platinum, ruthenium, rhodium, molybdenum, osmium and palladium, among others – using X-ray and ultraviolet spectroscopy. They were surprised at how well the pigment retained its jungle-gym structure while replacing iron ions in the frame – the secret to its impressive absorption efficiency compared to bio-based absorbents. This is great news for e-waste recycling.
Prussian blue could also solve one of the challenges of disposing of nuclear waste, according to the authors. Current practice is to convert liquid radioactive waste to a glass-like state in a reprocessing plant, prior to disposal. But platinum group metals can build up on the walls of melters, eventually causing uneven heat distribution. The melters must therefore be rinsed after each use, which increases costs. Prussian blue could remove these deposits without the need to rinse the melters after each use.
DOI: Scientific Reports, 2022. 10.1038/s41598-022-08838-1 (About DOIs).
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