Recovery of indium from liquid crystal displays

• Zinc cementation was applied to recover indium from end-of-life LCDs.
• A 10-min cementation determined >95% recovery of indium.
• High recovery efficiencies were found at pH 3 with Zn in the range 5–100 mg/L.
• Similar results were observed at pH 2 only with 100 mg/L Zn.
• The recovery process of indium determined relevant benefits to the environment.

Indium is a critical raw material with economic importance and high supply risk. In the present study, we recovered indium by means of cementation from a leaching solution of waste liquid crystal display panels. Cementation with zinc powder was optimized through the investigation of the effects of different variables (zinc concentration, pH, cementation time) on cementation efficiency and purity of the solid product. Almost all the indium present in the leaching solution passed to the solid phase when cementation was performed with a low (2–5 g/L), a medium (15–20 g/L) and a high (100 g/L) concentration of zinc, at pH 3. At pH 2, a complete cementation was obtained only with the highest concentration of zinc. Moreover, the highest purity of the indium product (62% indium percentage in the solid product, calculated in the 4-metal system indium-aluminum-calcium-iron) was achieved after a cementation of 10 min, whereas the presence of impurities increased with time. An empirical model successfully fitted the experimental data and suggested that the highest purity of the cemented product was expected at pH 2. A quantification of the environmental impact of the process for indium recovery from end-of-life liquid crystal display panels was also carried out through a life cycle analysis approach, and it outlined that relevant benefits to the environment were obtained thanks to the recovery of indium from waste electric and electronic equipment. The results obtained in the present study are promising since this is the first time that cementation was applied to a leaching solution of waste liquid crystal display panels. In this paper we found that indium cementation took place also with low concentrations of zinc at pH 3, allowing important reagent saving. Investigations in progress are aimed at increasing the purity of indium and at improving the environmental sustainability of the process. The approach presented here is considered extremely useful in the frame of urban mining strategies. It can help ensure progress towards sustainable societies, encourage industrial innovation of the recycling companies and the implementation of cleaner processes.