Boelens, P. / Lei, Z. / Drobot, B. / Rudolph, M. / Li, Z. / Franzreb, M. / Eckert, K. / Lederer, F. (2021)

Minerals 2021, 11, 1116, doi.org/10.3390/min11101116

Abstract:

In an ongoing effort towards a more sustainable rare-earth element market, there is a high
potential for an efficient recycling of rare-earth elements from end-of-life compact fluorescent lamps
by physical separation of the individual phosphors. In this study, we investigate the separation of
five fluorescent lamp particles by high-gradient magnetic separation in a rotary permanent magnet
separator. We thoroughly characterize the phosphors by ICP-MS, laser diffraction analysis, gas
displacement pycnometry, surface area analysis, SQUID-VSM, and Time-Resolved Laser-Induced
Fluorescence Spectroscopy. We present a fast and reliable quantification method for mixtures of
the investigated phosphors, based on a combination of Time-Resolved Laser-Induced Fluorescence
Spectroscopy and parallel factor analysis. With this method, we were able to monitor each phosphors’
removal dynamics in the high-gradient magnetic separator and we estimate that the particles’ removal
efficiencies are proportional to (d2 ·χ)1/3. Finally, we have found that the removed phosphors can
readily be recovered easily from the separation cell by backwashing with an intermittent air–water
flow. This work should contribute to a better understanding of the phosphors’ separability by high-
gradient magnetic separation and can simultaneously be considered to be an important preparation
for an upscalable separation process with (bio)functionalized superparamagnetic carriers.

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