Developing an Eco-Friendly Method to Extract Europium from Waste

Researchers at ETH are developing a nature-inspired technique for effectively recovering europium from outdated fluorescent lights. The strategy might result in rare earth metal recycling, which has been long overdue. The study was published in the journal Nature Communication.

The name “rare earth metals” does not accurately describe their rarity. They are necessary for the modern economy. After all, these 17 metals are essential building blocks for the energy shift and digitalization. They are present in computers, smartphones, screens, and batteries; without them, no wind turbine or electric motor could function. Since Europe is almost entirely dependent on imports from China, these raw materials are critical.

However, the extraction of rare earth metals makes them equally important. Natural ores always contain them in complex form, but it can be challenging to separate them because of their close chemical resemblance.

As a result, traditional separation techniques need many extraction steps and are very chemically and energy-intensive. This makes obtaining and purifying these metals costly, time- and resource-consuming, and incredibly damaging to the environment.

“Rare earth metals are hardly ever recycled in Europe,” said Victor Mougel, Professor at the Laboratory of Inorganic Chemistry at ETH Zurich.

Mougel is leading a group of researchers who aim to alter this. “There is an urgent need for sustainable and uncomplicated methods for separating and recovering these strategic raw materials from various sources,” said the chemist.

The researchers have shown a remarkably straightforward technique for effectively isolating and retrieving the rare earth metal europium from intricate combinations containing other rare earth metals.

Inspired by Nature

Existing separation methods are based on hundreds of liquid-liquid extraction steps and are inefficient–the recycling of europium has so far been impractical. In their study, they show how a simple inorganic reagent can significantly improve separation. This allows us to obtain europium in a few simple steps–and in quantities that are at least 50 times higher than with previous separation methods.

Marie Perrin, Study First Author and Doctoral Student, ETH Zurich

Tetrathiometallates, tiny inorganic compounds with four sulfur atoms around tungsten or molybdenum, hold the secret to this method. The researchers were inspired by the world of proteins.

Tetrathiometallates are employed as active agents against cancer and illnesses related to copper metabolism. They are found in natural enzymes as a binding site for metals.

Tetrathiometallates are being employed as ligands for the extraction of rare earth metals for the first time. By converting europium to its uncommon divalent state, which simplifies separation from the other trivalent rare earth elements, its special redox characteristics come into play here.

The principle is so efficient and robust that we can apply it directly to used fluorescent lamps without the usual pre-treatment steps.

Victor Mougel, Professor, Laboratory of Inorganic Chemistry, ETH Zurich

Keeping Europium in Circulation

One significant but underutilized source of rare earth metals is electronic waste.

If this source were tapped into, the lamp waste that Switzerland currently sends abroad to be disposed of in a landfill could be recycled here in Switzerland instead. Lamp waste could reduce Switzerland's reliance on imports by acting as an urban europium mine.

Victor Mougel, Professor, Laboratory of Inorganic Chemistry, ETH Zurich

Europium was once primarily used as a phosphor in flat displays and fluorescent lights, which drove up market prices. The demand has decreased due to the steady phase-out of fluorescent lamps, making the earlier techniques of recycling europium no longer financially feasible.

Nonetheless, more effective separation techniques are preferred and may facilitate the utilization of the enormous amounts of low-cost fluorescent light waste, which has a rare earth metal composition approximately 17 times greater than that of natural ores.

Reduce Demand

Due to this, it is even more critical to recover rare metals at the end of a product's life and maintain their availability; yet, the EU's recovery rate for rare earth elements is still less than 1%.

In theory, rare earth metals can be recovered from trash and extracted from ore using any method of separation. However, the researchers are purposefully emphasizing raw material recycling in their approach since it is both more environmentally and financially sound.

Mougel said, “Our recycling approach is significantly more environmentally friendly than all conventional methods for extracting rare earth metals from mineral ores.”

The researchers are establishing a start-up company named REEcover to commercialize their patented technology in the future. They are also modifying the separation procedure for other rare earth metals present in magnets, such as dysprosium and neodymium. If all goes well, Marie Perrin hopes to finish her degree, expand the startup, and put rare earth metal recycling into action.

Rapid recycling of europium from fluorescent lamps. Video Credit: Marie Perrin/ETH Zurich

Journal Reference:

Perrin, M. A., et al. (2024) Recovery of europium from E-waste using redox active tetrathiotungstate ligands. Nature Communications. doi.org/10.1038/s41467-024-48733-z.