Researchers from the KU Leuven department of chemical engineering have discovered a method to separate two rare earth elements – europium and yttrium – with UV light instead of with traditional solvents.

As Europium and yttrium are difficult to mine there is a great interest in recycling them, and they can be recovered from red lamp phosphor, a powder that is used in fluorescent lamps such as neon tubes.

According to Professor Tom Van Gerven from the Leuven department, 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.

However, this process leaves much to be desired in terms of efficiency and purity: it needs to be repeated dozens of times to recover a high percentage of a particular rare earth metal, and there will still be traces of yttrium in the europium-containing liquid and vice versa.

Separating rare earth elements with UV light. Photo courtesy KU Leuven – CIT.
Separating rare earth elements with UV light. Photo courtesy KU Leuven – CIT.

Cleaner process

In collaboration with KU Leuven chemists the researchers 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,’ said Bart Van den Bogaert, who is preparing a PhD on the subject. ‘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.’ UV light does not leave behind any harmful chemicals in the liquid, he added.

Using this method, more than 95% of the europium is recovered from the solution while the precipitate itself is 98.5% pure, so it contains hardly any traces of yttrium. A similar purity was obtained with industrial mixtures, but the efficiency of the separation still needs to be improved, which will be one of the next projects tackled by the KU Leuven researchers.

The findings were published in Green Chemistry.

This story is reprinted from material from UV Leuven, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier.