Recovery of gallium (and indium) from spent LEDs: Strong acids leaching versus selective leaching by siderophore desferrioxamine E

Abstract

This study carried out the adapted pre-treatment and characterization of spent surface mounted device (SMD) light emitting diodes (LEDs) followed by the recovery of gallium (Ga) and indium (In) by strong acids leaching and selective leaching with desferrioxamine E (DFOE). The pre-treated spent SMD LED powder fraction (<500 μm) contained the highest concentrations of Ga and In, 290.4 ± 21.2 mg/kg and 64.9 ± 20.2 mg/kg, respectively. Strong acid leaching with 3 M HCl and 30% H2O2 was shown to be highly effective in reaching substantial leaching yields (Ga and In reaching 97 ± 6% and 98 ± 4%, respectively). However, this approach resulted in a considerably higher amount of non-targeted elements such as Cu, Pb, Al, and Fe compared to the targeted metals (Ga and In). Therefore, selective leaching emerges as a promising approach to recover targeted metals from waste streams. This study represents the first attempt to test DFOE for selective leaching of Ga and In from spent SMD LEDs. Various parameters, including pH, solid-to-liquid (S/L) ratio, molar mass ratio (n) of DFOE and Ga, and temperature, were adjusted to investigate the behavior of metal-DFOE complexation. The highest Ga leaching efficiency (12%) was found to be at pH 4, with a S/L ratio of 5 g/L and n = 20 at 40 °C. However, competing elements (i.e. Al and Fe), can significantly impact the efficiency of the Ga leaching process. Concerning In recovery, selective leaching demonstrated its ability to achieve maximum In recovery yield (24%) within 24 h at pH 7.3. This study elucidates the mechanism of metal-DFOE complexation and highlights the potential of DFOE-assisted leaching for selectively recovering critical metals from waste streams and recycling used DFOE.