Recovery of gallium from waste LEDs by oxidation and subsequent leaching

In this paper, gallium recycling from waste light emitting diode (LED) by oxidation and subsequent leaching was studied. Gallium is present in the LED chip as gallium nitride. Disassembling and crushing of the LEDs were carried out after burning the polymeric parts, and then the chip is separated from the LED. Leaching of the gallium from the chips was performed after oxidation step at optimum temperature of 1100 degrees C. The oxidation heat treatment was carried out at 1000, 1100 and 1200 degrees C and the oxidation mechanism was studied in detail. Oxidation causes depletion of nitrogen gas and absorption of oxygen atoms by the gallium nitride structure, which results in the formation of a porous oxide structure. The minimum transformation temperature of gallium nitride to gallium oxide, was 1100 degrees C. In the final oxide phase, comparison of the structure and morphology of the chip surface after oxidation at 1200 degrees C and 1100 degrees C shows that at higher oxidation temperature the surface area decreases and the grain size increases. Changing the solubility of the phase containing the gallium by oxidation at different temperatures considering has been investigated. Leaching experiments were designed using design of experiment (DOE) method. At optimum leaching conditions of 4 M hydrochloric acid, 93 degrees C and 120 min, the gallium leaching recovery was 91.4%. Based on the results, leaching temperature is the most effective parameter in this process.