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

This study aimed to carry out the adapted pre-treatment and subsequent characterization of spent surface mounted device (SMD) light emitting diodes (LEDs) as well as strong acids leaching and selective leaching of gallium (Ga) and indium (In) using desferrioxamine E (DFOE). The results show that the pre-treated spent SMD LED powder fraction (< 500 μm) contained the highest concentration of Ga and In, 290.4 ± 21.2 mg/kg and 64.9 ± 20.2 mg/kg, respectively. The use of strong acid 3 M HCl and 30% H2O2 was found to the highly effective in achieving a high leaching yield for Ga and In, 97 ± 6 % and 98 ± 4 %, respectively. However, the associated leaching of highly concentrated non-targeted elements (i.e. Cu, Pb, Al, and Fe) was found to be significantly higher than the targeted metals (Ga and In). Therefore, selective leaching could offer a promising approach to recover targeted metals from waste streams. It is the first attempt to test DFOE for the selective leaching of Ga and In from spent LEDs by adjusting the pH, solid/liquid (S/L) ratio, molar concentration ratio of DFOE and Ga (n = n(DFOE)/n(Ga)), and temperature 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, the competing elements (Al and Fe), can have a significant effect on the efficiency of the Ga leaching process. Concerning In recovery, selective leaching could achieve maximum In recovery yield (24%) within 24 hours at pH 7.3. This study provides deep knowledge to better understand the development of sustainable processes for the selective recovery of critical metals from spent SMD LEDs by DFOE.