Chemists in the Belgian university KU Leuven have developed an innovative process based on ionic liquid technology to recycle the metal “europium” (an extremely scarce solid metal in nature) and “yttrium” (a rare earth although very abundant) used in fluorescent and low consumption lamps. These metals can be reused in new lamps.
Natural resources are scarce, and in some cases even more. The Catholic University of Leuven KU in Belgium has presented a study explaining how to recover the elements known as “rare earth”. Compared with traditional solvents, the ionic liquid has a multitude of advantages, including its selection ability for metal dissolution and its reuse.
Scarce elements in nature
Many electronic applications and renewable technologies face the challenge of finding raw materials that are very scarce in nature but crucial for creating such high-tech products. Therefore, it becomes imperative to recover them.
They are known as “rare earth” elements, which are not rare per se but because they are difficult to obtain and subsequently to purify. Moreover, because most operating mines are located in China, the offer is subject to geopolitical tensions. Worldwide there is an increased interest to recycle these “rare earth” from waste streams to mitigate the supply risk.
The televisions tube
The two “rare earth” under investigation, europium and yttrium, are used for the phosphors of the red lamps, ie, they are substances that convert ultraviolet light into red light, but this phosphor has also been used for over 40 years in color TV screens and fluorescent tubes.
“Because it is very difficult to replace the red phosphor with a mixture free of rare earths, the focus is on the recyclability of red phosphor fraction of fluorescent lamps. Although it is now mandatory to collect fluorescent and low consumption lamps at the end of their life, and the recycling process focuses heavily on the safe disposal of mercury waste, it allows us to investigate further. Because of the technical complexity to recover europium and yttrium using traditional solvents, the powder containing these two critical metals is usually not reused, “explains Professor Koen Binnemans.
Ionic liquid to recycle
To address this problem, the Belgian university KU Leuven has developed an alternative method. “Instead of using an acid as a solvent, an ionic liquid is used: it is an organic solvent agent consisting entirely of ions or electrically charged particles. It does not evaporate, it is flammable and works very selectively: we can design in such a way that only the phosphor of the red lamp dissolves. The recycled europium and yttrium can be reused directly. Furthermore, the ionic liquid is also reusable for a next cycle, “says David Dupont.
With this new method, recycling requires less chemicals and energy, adds Koen Binnemans, “from both a technical and environmental perspective, this approach is an interesting alternative to traditional solvents.”