Resources Conservation and Recycling

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.

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