Chelator-induced recovery of rare earths from end-of-life fluorescent lamps with the aid of mechano-chemical energy

Rare-earths (REs) are key components for the transition to a greener energy profile and low carbon society. The elements turn out to be of limited availability in the market, due to the supply-demand issues, exponential price rises, or geopolitics, which has led to a focus on the exploration of secondary sources for RE reclamation. End-of-life (EoL) nickel-metal hydride batteries, permanent magnets, and fluorescent lamps (FL) have been the primary sources for recyclable REs, while the recovery of REs in EoL FL (Ce, Eu, La, Tb, or Y) includes comparatively fewer processing steps than the other potential sources. In the current work, we proposed a simple, energy-efficient protocol for EoL FL processing, using chelators in combination with ball milling. The parameters for optimum chelator-assisted recovery (chelator concentration, solid-to-liquid ratio, solution pH), and milling variables (ball size, ball weight, milling speed, milling duration), were evaluated at room temperature (RT, 25 ± 2 °C). The dissolution of REs with ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid, methylglycinediacetic Acid, or 3-hydroxy-2,2′-iminodisuccinic acid, was compared at RT, while EDTA was used as the reference chelator throughout. Increasing the system temperature from 25 to 135 °C achieved at least double Eu and Y recovery, relative to that at RT, whereas the recovery rate improvement for Ce, La or Tb was insignificant. Mechano-chemical treatment at RT, via wet milling of EoL FL, with chelators, yielded a five order of magnitude increase in Ce, La and Tb recovery, however, plus a two-order increase for Eu or Y, compared with non-abetted operating conditions. It was also found that higher impact energy achieved improved recovery over a reduced milling duration with this technique having the added advantage of minimal acid consumption and reduced effluent production.