Resource recycling of gallium arsenide scrap using leaching-selective precipitation

The use of light-emitting diodes (LED) has increased rapidly in Taiwan, because their energy losses are lower than traditional illuminants. Scrap is produced in the manufacturing process for LEDs, which contains valuable metals (i.e., Ga) and harmful component (i.e., As). For sustainable environmental reasons, this study develops a recycling technique for GaAs scrap. The GaAs scrap was firstly ground and sieved to pass 100 mesh sieve. The powder sample was leached, using 1.5 N nitric acid at 40°C for 1.5 h, and the dissolution of Ga and As was close to 100%. Sodium sulfide solution was added into the leachate as a precipitating agent and As was selectively precipitated from the solution. In the optimal conditions, using a 0.1 M of sodium sulfide and a flow rate of 5 mL/min, the precipitation percentages of As and Ga were 98.5 and 1.5%, respectively. The purified Ga solution was recovered, and the As was concentrated in the sediment. The precipitate was examined using X-ray diffraction and the major phase was identified as As2O3 which can be stabilized using the ferrite process or used as a raw material in a related industry. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 471–475, 2015