Photochemical recycling of europium from Eu/Y mixtures in red lamp phosphor waste streams

Abstract

Europium is one of the most critical rare-earth elements due to the combination of a high demand for the production of red lamp phosphors and the limited supply of this element. Hence, the recycling of europium from end-of-life lamp phosphors has gained a lot of interest. Separation of europium from rare-earth mixtures can be done very efficiently by selective reduction of Eu(III) to Eu(II) and subsequent removal of Eu(II) by EuSO₄ precipitation. The present study shows that full separation of europium from non-equimolar binary europium/yttrium mixtures, which reflect the rare earth composition of red lamp phosphors, can be achieved by photochemical reduction of Eu(III). Eu/Y molar ratios up to 1/20 were tested in the presence of an isopropanol radical scavenger, a less harmful and toxic compound than the commonly used formic acid scavenger. Moreover, in contrast to using the very acidic formic acid, higher pH values could be reached with isopropanol, which is advantageous for the formation and the stability of the reduced Eu(II) species. Faster europium removal was obtained at higher pH values up to pH 4, halving the illumination time to reach 88% of europium recovery. Efficiencies of over 95% were reached, with purities of 98.5% of the EuSO₄ precipitate. Europium recovery of industrial YOX powder was also achieved from a Eu/Y 1/30 ratio, with 50% yield of EuSO₄ and a purity of 96%.