Rare earth recycling from waste lamps

KU Leuven Chemists have developed a new 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 re-usable in new lamps. Compared to traditional solvents, the ionic liquid has a multitude of advantages, including its selectivity for metal dissolution and its re-usability.

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 in recycling 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 to 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 re-used,” explained 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 re-used. Furthermore, the ionic liquid is also re-usable for a next cycle.” With this new method the recycling requires fewer chemicals and energy, added Binnemans. “Both from a technical and environmental perspective, this approach is a very interesting alternative for traditional solvents.”