Energy efficient light bulbs are often criticized for their reliance on rare earth metals that are difficult and very polluting to mine as well as being costly to recycle. But researchers from the KU Leuven Department of Chemical Engineering have discovered a new process that will increase the opportunities for the recycling of fluorescent lamps and energy efficient light bulbs. They have developed a method to separate two rare earth elements – europium and yttrium – with UV light instead of with traditional solvents.
Separating the two rare earth elements is a complicated process. Professor Tom Van Gerven from the Department of Chemical Engineering explains: “The traditional method dissolves europium and yttrium in aqueous acid. An extractant and a solvent are then added to the aqueous liquid, leading to two separate layers known as ‘phases’: an aqueous layer containing the rare earth metals and a solvent layer with the extractant. When the two layers come into contact, one of the two rare earth metals is extracted to the solvent, while the other rare earth metal remains in the aqueous layer.”
The use of solvent to separate the rare earth elements is very inefficient as it need to be repeated dozens of times to recover a high percentage, the resulting yttrium and europium lack purity and don’t forget the need for the harmful solvent chemical.a
The researchers, in collaboraqtion with KU Leuven chemists, have now managed to recover europium from the liquid mixture with UV light instead of a solvent.
“The UV light influences the electrically charged particles known as ions. Both europium and yttrium have three positive charges per ion. When we shine UV light upon the solution of europium and yttrium, we add energy to the system. As a result, one positive charge per europium ion is neutralised. When we add sulphate, only the europium reacts with it. The result is a precipitate that can easily be filtered, while the yttrium remains in the solution,” says Bart Van den Bogaert, who is preparing a PhD on the subject.
Their process does not leave behind any harmful chemicals in the liquid and the efficiency and purity of is very high: more than 95% of the europium is recovered from the solution. The precipitate itself is 98,5% pure, so it contains hardly any traces of yttrium.
One of the next projects the authors of the study will tackle next is improving the purity of the process when used with industrial mixtures.
The full text of the study “Photochemical recycling of europium from Eu/Y mixtures in red lamp phosphor waste streams” by Bart Van den Bogaert, Daphné Havaux, Koen Binnemans and Tom Van Gerven was published in the journal Green Chemistry (DOI: 10.1039/C4GC02140A). Copies can also be obtained from the authors.
This research is part of Bart Van den Bogaert’s doctoral research, which is funded by IWT (the government agency for Innovation by Science and Technology) and by KU Leuven Internal Funds (BOF and IOF). It is part of the research activities of the KU Leuven knowledge platform RARE3, a collaboration with chemists, chemical technologists and material engineers, among others, to investigate the recycling of rare earth and other critical metals. For more information, see http://www.
Tracey is an accountant and entrepreneur with a passion for nature. This passion is what spurred her interest in renewable energy, and the rest is history as they say. Tracey is a principal in Energy Think Group, the publisher of Solar Thermal Magazine and Tek-Think. She is also the principal at Women's Financial Help Desk. She spends her free time in the outdoors with her horses and dogs. She loves to travel.