A comprehensive aqueous processing of waste LED light bulbs to recover valuable metals and compounds

Abstract

White LED bulbs contain significant quantities of Cu, Sn, Pb, Al and appreciable amounts of Ga and traces of In. A feasible recovery of the valuable components – either in metallic or compound forms - has been devised and examined. Leaching the assemblies with 4 M HNO3 at 80 °C could leach Cu, Fe, Pb and Ag, while Al is passivated and Sn precipitates. In this step, the LED beads are detached from the aluminium base plates. The solid residue comprises of practically pure Al plates and Sn(OH)4. Pure Cu hydroxide was recovered by precipitation. The physically liberated solid bodies of the detached LED beads were roasted to convert Ga and In into soluble compounds. While a simple oxidative roasting could assure ∼80% recovery, alkaline fusion with NaOH or roasting with Na2CO3 yielded >90% recoveries. Leaching the roasted material with 1–6 M NaOH could efficiently dissolve Ga, while In was only slightly attacked. However, the major portion of In could be leached by applying as high as 10–11 M NaOH with similar efficiencies. Finally, the extractions of Ga and In were studied by electrowinning from the alkaline solutions yielding 99.99% pure Ga and 99.9% pure In deposits, respectively.