Recycling of metals (Ga, In, As and Ag) from waste light-emitting diodes in sub/supercritical ethanol

In this study, waste light-emitting diodes (LEDs) containing gallium (Ga), indium (In), arsenic (As) and silver (Ag) were used as the research objects. The theoretical and experimental research were done on the recycling of Ga, In, As and Ag in LEDs. Firstly, anhydrous ethanol as solvent is beneficial for the separation of the surface mounted LED support and the colorless transparent encapsulation material containing LED chip and silver line. The optimum experimental conditions are as follows, 250 degrees C heating temperature, 200 ml anhydrous ethanol (7.5 MPa autogenous pressure) and 90 min heat preservation time. The separation efficiency is the highest in the experimental range, about 82.32%. The subcritical water-ethanol mixture is beneficial to the degradation of colorless transparent packaging resin at the preferential conditions of 300 degrees C heating temperature, 60% water in the water-ethanol mixture and 240 min heat preservation time, the recovery of Ga, In, As and Ag can reach 93.10%, 85.72%, 93.79% and 99.99%, respectively. This study can provide a high efficiency and environmentally friendly method to recycle the metals from waste LEDs.