Why An 18th Century Paint Pigment May One Day Help Recycle Your Cell Phone:

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The pigment Prussian Blue has been used by artists since the 18th century to create affordable blue paints. These days, the pigment’s main purpose is to treat heavy metal poisoning and radioactive waste cleanup, but recently researchers from Japan suggested that it could perhaps also be used to recycle old electronic waste.

If you’ve seen large swathes of bright blue in artworks from the 18th or 19th century, you’ve probably laid your eyes on Prussian Blue. Van Gogh used this pigment to paint Starry Night (1889) and it featured prominently in Hokusai’s print The Great Wave off Kanagawa (painted between 1830–1833).

Before Prussian Blue, artists only used naturally occurring pigments in their work. Prussian Blue was the first paint pigment that was created in a chemistry lab – but it was not entirely intentional! In 1704, Johann Jacob Diesbach tried to create a red pigment, but to his surprise found that he had created a blue dye instead. After figuring out that it was caused by a contaminated batch of potash, he found himself with a recipe for a new blue pigment.

Even though it was not entirely designed on purpose, this new blue pigment was a hit. As early as 1710 it was being sold to artists in Berlin and by 1724 it was being distributed across Europe. Prussian Blue was so popular because it made blue paint a lot more affordable. Until it became available, painters had to rely on a pigment derived from lapis lazuli, which was much too expensive for most artists.

Since the 20th century, Prussian Blue has mostly been replaced by other blue pigments on artists’ palettes, but it remains popular in two very different settings: emergency medicine and nuclear waste cleanup.

Thanks to its ability to capture metals from its environment, Prussian blue pills are often used to treat heavy metal poisoning. The pigment forms a network structure that can trap individual metal ions, such as those from thallium or radioactive cesium, and prevent them from being taken up by the body.

That same ability to trap heavy metals also makes Prussian Blue a useful tool for environmental cleanup. After the 2011 tsunami caused a nuclear accident at the Fukushima power plant, Prussian Blue was one of the tools used to clean up radioactive cesium from the soil in the surrounding area.

That got researchers thinking: what else can Prussian Blue do? Earlier this year, scientists from Japan shared how they used the pigment to trap rare metals like molybdenum and metals from the platinum group in the periodic table (which includes ruthenium, rhodium and palladium, among others). Jun Onoe, Professor of Engineering at Nagoya University, led the research study and told his university that he was surprised that Prussian Blue kept its “jungle gym” lattice structure when trapping these metals.

Learning how Prussian Blue traps different types of metal ions means that the pigment could potentially be used in more situations than previously thought, including trapping metals that are currently quite difficult to remove from certain waste products. “Our findings demonstrate that Prussian blue or its analogues are a candidate for improving the recycling of precious metals from nuclear and electronic wastes,” Onoe told Nagoya University, “especially when compared to conventionally used bio-based adsorbents / activated carbons.”

This could potentially make recycling electronic waste products such as cell phones more efficient and environmentally friendly, because it would make it easier to remove and reuse rare and valuable metals from the phone parts.

Prussian Blue has already had an exciting journey in the past three centuries.

From painters’ palettes to medical emergency kits and nuclear clean-up operations, and perhaps a next stop at recycling centers. Not bad for a pigment that was only created by accident!

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