Study On Recovery Of Rare Metal Gallium From Waste Light Emitting Diodes

With the increasing scale of the semiconductor market,the number of discarded semiconductor materials such as light emitting diodes?LEDs?which are rich in a variety of rare and valuable metals including gallium,copper and gold are increasing.At present,China's gallium recovery capacity is weak and gallium has been listed as strategic resource by EU,Japan,USA and China.Therefore,aiming at the harmfulness of waste light emitting diodes to the environment and the recyclable resource,recycling of metal resources from LEDs becomes an effective way to reduce the threat of the environment and also provides a new idea for solving the resource crisis.This study put forward a new idea of gallium leaching by organic oxalic acid leaching.Pyrolysis-ball milling-acid leaching process was established.We studied metal leaching efficiency by varieties of acids in waste LEDs and analyzed the effect of different conditions on the gallium leaching efficiency.We also discussed the efficient selective leaching mechanism of gallium by oxalic acid and conducted orthogonal experiment to test the parameter optimization.Besides,we could increase the effect through enhancing leaching method and used precipitation method to recycle products.Finally,we discussed the possibility of the formation of gallium oxide hydroxide by direct aging precipitation method.The main results are as follows:?1?In order to recover gallium from waste LEDs,gallium was leaching through pyrolysis-ball-milling and acid-leaching process.Single-factor experiment was conducted to explore the effects of temperature,particle size,pulp density and acid concentration in the leaching reaction.Also,the possible gallium leaching mechanism from waste LEDs by oxalic acid was discussed.The results showed that 20%reduction rate was obtained by pyrolysis-ball-milling process and gallium concentration enrichment was nearly 5 times.The optimal parameters for leaching reaction are temperature of 90°C,particle size of 48-75?m,pulp density of 10 g/L,the acid concentration of 0.7 mol/L.86.36%gallium leaching efficiency was obtained in single-factor experiment.The efficient leaching mechanism of oxalic acid on gallium was due to the strong reduction of oxalic acid on iron?III?.The formation of ferrous oxalate precipitate during leaching promoted the ionization of oxalic acid and the chelation of oxalic acid on gallium increased gallium leaching efficiency.?2?In order to improve the leaching efficiency of gallium,orthogonal optimization test,ball-milling activation test and selective leaching test were carried out respectively.Results showed that under temperature of 90°C,particle size of 48-75?m,pulp density of 10 g/L,acid concentration of 0.7 mol/L,gallium leaching efficiency was up to 90.36%,iron and copper leaching efficiency were 6.56%and 1.2%,respectively.Leaching reaction was controlled by inner-diffusion process,the apparent activation energy was 13.59 kJ/mol.Optimal particle size of 48-150?m was obtained under the activation condition of rotation speed at 300 rpm for 15min.The addition of ascorbic acid had a significant effect on the removal of[Fe?C₂O₄?₃³]^-in the solution.?3?In order to obtain gallium recovery products from gallium-rich leaching solution,we used stepwise precipitation method and gallium oxide hydroxide materials were prepared from simulated gallium leaching solution.The results showed that the recovery rate and grade of the product could be improved by adjusting the pH value of the solution to weak acidity?pH=5.5?first and adjust to alkalinity?pH>10?second.When pH=5.5,gallium recovery rate was 92.88%and its grade was 99.58wt.%.Gallium oxide hydroxide was successfully prepared by ammonia aging precipitation method.The preparation method was green and simple which provided a new idea for the recovery and reutilization of rare metal gallium from Waste Electrical and Electronic Equipment.