Recovery of gallium from waste light emitting diodes by oxalic acidic leaching

Abstract

Recovery of gallium from light emitting diodes (LEDs) is receiving great attention due to both high content of gallium and potential risk of environmental pollution. In this study, a novel environment-friendly route was proposed for efficient recovery of gallium from surface mounted device (SMD) of LEDs by using organic acid. Reduction of non-metallic components, selection of lixiviants, optimization of leaching parameters, and possible mechanism of gallium were investigated. Results showed that pyrolysis could reduce non-metallic components effectively, and 22% weight loss was achieved at 733 K. Selection of lixiviant experiments indicated that 83.42% gallium could be extracted from SMD LEDs by oxalic acid, which was much higher than that of 79.89% by hydrochloric acid, 70.62% by citric acid, and 71.69% by DL-malic acid. Further investigation revealed that 90 °C of leaching temperature, 10 g L−1 of pulp density, 0.7 M of oxalic acid and 48–75 μm of particle size were the optimum conditions for effective gallium leaching by oxalic acid. After optimization, the gallium recovery efficiency reached as high as 90.36% in 60 min. Such efficient gallium leaching came from the higher dissociation constant of oxalic acid and the formation of ferrous oxalate which would promote the generation and maintenance of H+. Hence, oxalic acid could be a promising lixiviant for efficient recovery of gallium from SMD LEDs.