Leuven, Belgium — Chemists at Katholieke Universiteit Leuven have developed an innovative process, based on ionic liquid technology, for the recycling of the metals europium and yttrium from collected fluorescent and energy saving lamps. The metals are directly reusable in new lamps. Compared to traditional solvents, the ionic liquid has a multitude of advantages, including its selectivity for metal dissolution and its reusability.
For many modern electronic and cleantech applications rare-earth elements are indispensable. Although rare earths are not per se „rare“, they are difficult to mine and to purify. Furthermore, because the majority of the operational mines are located in China, the supply is subject to geopolitical tensions. Worldwide there is an increased interest to recycle rare earths from waste streams to mitigate the supply risk.
Two critical rare earths, europium and yttrium, are used in red lamp phosphor, a substance which transforms ultraviolet light into red light. This phosphor has been used for more than 40 years in the colour screens of televisions and in the tubes of fluorescent lamps. „Because it is very difficult to replace the red phosphor with a rare-earth free mixture, attention goes out the recyclability of the red phosphor fraction from fluorescent lamps. Although it is already obligatory to collect end-of-life fluorescent and energy saving lamps, the involved recycling is strongly focused on the safe removal of mercury from the waste. Because of the technical complexity to recuperate europium and yttrium using traditional solvents, the powder containing these two critical metals is typically not reused“, explains Professor Koen Binnemans.
To tackle this problem, KU Leuven chemists developed an alternative method. David Dupont: „Instead of employing an acid as the solvent, we use an ionic liquid: This is an organic dissolving agent that consists entirely of ions or electrically loaded particles. It does not evaporate, it is inflammable and it works very selectively: We can design it in such a way that it only dissolves the red lamp phosphor. The recycled europium and yttrium can be directly reused. Furthermore, the ionic liquid is also reusable for a next cycle.“ With this new method the recycling requires less chemicals and energy, adds Koen Binnemans: „Both from a technical and environmental perspective, this approach is a very interesting alternative for traditional solvents.“
The full text of the study „Rare-earth recycling using a functionalized ionic liquid for the selective dissolution and revalorization of Y2O3:Eu3+ from lamp phosphor waste“ by David Dupont and Koen Binnemans is available from the website of the journal Green Chemistry. This research is performed in the doctoral research work of David Dupont, which is financed by the FWO. It is part of the research activities of the KU Leuven Knowledge Platform RARE³, which investigates the recycling of rare earths and other critical metals.
Source: Katholieke Universiteit Leuven