Optimization and kinetic study of leaching process in recycling of Ga from waste LED

In this research, the recovery of the gallium from a waste light-emitting diode (LED) was carried out by a hydrometallurgical method. This process involves the chip separation from the LED, oxidation of the chips and gallium leaching in hydrochloric acid medium. Since gallium is present in an insoluble nitride phase in the LED chip, the chip must be separated from the LED, and then an oxidation step is needed to convert the nitride phase to oxide. After these steps, the oxidized chips were subjected to the leaching process. Various variables such as leaching temperature, leaching time and hydrochloric acid concentration have been investigated in the leaching experiments and optimal conditions have been determined. The design of experiment was done through the surface response method. The optimum conditions after performing the experiments and analyzing the final solutions were determined. At optimum leaching conditions of 4 M hydrochloric acid, 93 ºC and 120 minutes, the gallium leaching recovery was 91.4%. It can be found that the leaching temperature is the most effective parameter in this process. Further experiments were performed to determine the mechanism and kinetic analysis of the process. These studies showed that at 50 °C, the chemical reaction controls the rate of the leaching process. However, the reaction mechanism was changed to diffusion-controlled as the temperature increases to 65 and 80 °C.