| Summary: | 碩士 === 國立臺灣大學 === 環境工程學研究所 === 105 === Indium is a kind of rare metal because of its scarcity in the earth’s crust and difficulty in refining. The major application of indium is indium tin oxide (ITO), a transparent current-conductive material playing a critical role in the liquid crystal display (LCD) function. With the mass production of LCD screens, indium resource was estimated to be exhausted by 2025. Therefore, the recovery of indium from waste LCD is important and urgent.
The indium recovery process in this study incorporates the microwave-induced pyrolysis in the hydrometallurgy to enhance the recovery efficiency of indium from waste LCD and get high purity and concentration of indium aqueous solution. The process include four steps: microwave-induced pyrolysis, leaching, extraction, and stripping.
First, the microwave-induced pyrolysis process can remove the organics and make the separation between the layers of LCD panel to enhance the leaching rate in the following process. According to the thermal gravimetric analysis (TGA) results, the maximum decay rate of waste LCD occurred at 361.2 °C. Consequently, The microwave-induced pyrolysis process was carried out at the microwave power of 150 W for the processing time of 50 min.
Secondly, in the leaching process, indium can be dissolved in the acid solution. 98.27 wt.% of the indium was leached out in 0.5M sulfuric acid with 1:10 solid/liquid ratio, 2 hr, 90 ℃ and stirring at 360 rpm. The purity and concentration of indium are 40.07 % and 25.97 ppm.
Thirdly, di(2-ethylhexly)phosphoric acid (D2EHPA) can extract indium from the sulfuric acid solution to separate indium from the other metals and enrich the indium concentration. In the extraction process, the best condition for indium was 20 % (v/v) D2EHPA dissolved in the kerosene at organic-to-aqueous phase ratio (O/A) of 1:10. The purity, concentration and recovery rate of indium are 86.17 %, 228.23 ppm and 81.7 wt.%.
Finally, indium in the loaded organic phase can be stripped by hydrochloric acid to separate and enrich indium again. In the stripping process, 68.99 wt.% of the indium was recovered in 6 M hydrochloric acid at O/A of 10:1. The purity and concentration of indium in the final production are 99.98 % and 1892.38 ppm.
In this study, the final product (hydrochloric acid solution) containing high purity and high concentration of indium is beneficial to electrolytic refining or replacement to get indium metal. The result indicates that the recovery process of indium from waste LCD by microwave-induced pyrolysis is a promising technique.
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