Gold and some other precious metals are key ingredients in computer chips, including those used in consumer electronics such as smartphones. But recovering and recycling these metals from e-waste can be difficult. Japanese researchers have found that a pigment that is widely used by artists is called Prussian bluecan extract gold and platinum group metals from e-waste much more efficiently than conventional bio-based absorbents. recent paper published in the journal Scientific Reports.
“The amount of gold in one ton of mobile phones is 300-400 grams, which is 10-80 times more than in one ton of natural ore,” the authors write. “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. Of course, there was once a pigment known as Egyptian blue used in Ancient Egypt for millennia; the Romans called it caeruleum. But after the Roman Empire disintegrated, the pigment was used little, and in the end the secret of how it was made was lost. (Since then, scientists have figured out how to recreate this process.) Before Prussian blue was discovered, artists had to use indigo dye, smalt, or expensive ultramarine made from lazurite for deep blue shades.
It is believed that Prussian blue was first synthesized by chance by a Berlin paint maker named Johann Jacob Disbach around 1706. Disbach tried to make a red pigment that included a mixture of potash, ferrous sulfate and dried cochineal. But the potassium he used was apparently stained with blood – presumably from a cut on his finger or a similar minor injury. The next reaction created the characteristic iron ferrocyanide of a blue hue, which was eventually named Prussian Blue (or Berlin Blue).
The earliest known painting using Prussian blue today is Peter van der Werff The burial of Christ (1709), but the recipe was published in 1734, and soon the Prussian blue became widespread among artists. the famous work of Hakusai, Big wave near Kanagawais one of the most famous works in which pigment is used, along with Vincent van Gogh Starry night and many paintings by Pablo Picasso »Blue period».
The pigment has other uses. It is often used to treat heavy metal poisoning from thallium or radioactive cesium because its network structure, similar to a gym in the jungle, can trap metal ions from these metals and prevent them from being absorbed by the body. The Prussian blue helped remove cesium from the soil around the Fukushima power plant after the 2011 tsunami. Prussian blue nanoparticles are used in some cosmetics and are used by pathologists as a spot to detect iron in, for example, bone marrow biopsy specimens.
Therefore, it is a very useful substance, so the Japanese authors of this latest work decided to explore other potential practical applications. They analyzed how Prussian blue absorbs polyvalent metals such as platinum, ruthenium, rhodium, molybdenum, osmium and palladium and others using X-ray and ultraviolet spectroscopy. They were amazed at how well the pigment retained its structure in the jungle, replacing iron ions in the carcass – the secret of its impressive absorption efficiency over bio-based absorbents. This is great news for e-waste recycling.
The Prussian blue may also solve one of the problems of nuclear waste disposal, the authors believe. Current practice involves the conversion of radioactive liquid waste into a glassy state at a recycling plant before disposal. But platinum group metals can accumulate on the walls of the melters, which eventually causes uneven heat distribution. Therefore, the melters need to be flushed after each use, which in turn increases costs. Prussian blue can remove these deposits without having to flush the melters after each use.
DOI: Scientific Reports, 2022. 10.1038 / s41598-022-08838-1 (About DOI).