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Μέθοδοι επεξεργασίας για την ανάκτηση ινδίου σε οθόνες υγρών κρυστάλλων από απόβλητα ηλεκτρονικού εξοπλισμού

Karagianni Aikaterini

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Summary

In recent years, CRTs (cathode Ray Tube) have been replaced by LCDs (liquid crystal displays). The increasing production of LCDs causes a major concern regarding their management after the end of their lifespan. Recently, the interest of the scientific community is focused on critical metals contained in waste LCDs aiming at secondary production through recovery activities. As critical metals are defined the elements that present economic and strategic importance to the global economy and have a high risk associated with their supply. Also, their extraction constitutes an economically and environmentally costly process. Indium is a critical metal, which is widely used in LCDs. The aim of this study is focused on development and comparison of different pre-treatment methods in waste LCD monitors towards indium recovery. In the first step, manual dismantling, shredding and removal of liquid crystals using solvents were carried out. Then, the following pre-treatment methods were performed: mechanical crushing, sieving, gravimetric separation, pyrolysis, thermal shock, and combinations of them. The efficiency of these methods was evaluated based on indium pre-concentration. The pre-concentration yield was determined taking into account the concentration of indium (mg/kg) in pre-treated fraction, as well as the mass of the pre-treated fraction to the initial indium concentration and the initial mass of LCD used (%). Thus, the fate of indium and its losses during the pre-treatment of LCD screens were thoroughly investigated. The results obtained showed that mechanical pre-treatment followed by sieving leads to fractions enriched in indium. However, during mechanical crushing, there are high indium losses (dust, etc.). The gravimetric method was not effective as agglomeration between particles was observed. Therefore, the most effective method was the thermal shock at a temperature of 200 oC with a pre-concentration yield of 60,5%, followed by pyrolysis which resulted in 53,9% pre-concentration yield.

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