Recovery of indium from LCD screens of discarded cell phones

摘要

Advances in technological development have resulted in high consumption of electrical and electronic equipment (EEE), amongst which are cell phones, which have LCD (liquid crystal display) screens as one of their main components. These multilayer screens are composed of different materials, some with high added value, as in the case of the indium present in the form of indium tin oxide (ITO, or tin-doped indium oxide). Indium is a precious metal with relatively limited natural reserves (Dodbida et al., 2012), so it can be profitable to recover it from discarded LCD screens. The objective of this study was to develop a complete process for recovering indium from LCD screens. Firstly, the screens were manually removed from cell phones. In the next step, a pretreatment was developed for removal of the polarizing film from the glass of the LCD panels, because the adherence of this film to the glass complicated the comminution process. The choice of mill was based on tests using different equipment (knife mill, hammer mill, and ball mill) to disintegrate the LCD screens, either before or after removal of the polarizing film. In the leaching process, it was possible to extract 96.4 wt.% of the indium under the following conditions: 1.0 M H_2SO_4, 1:50 solid/liquid ratio, 90 ℃, 1 h, and stirring at 500 rpm. The results showed that the best experimental conditions enabled extraction of 613 mg of indium/kg of LCD powder. Finally, precipitation of the indium with NH_4OH was tested at different pH values, and 99.8 wt.% precipitation was achieved at pH 7.4.