Willner, et al., reported in 2018 that the demand for indium is increasing every year. This metal is mainly used as indium tin oxide (ITO) in the production of transparent conductive coatings for liquid crystal displays (LCD). This paper focuses on biohydrometallurgical methods used for the recovery of indium and tin from LCD sourced from spent mobile phones. Bioleaching experiments were carried out in two different leaching media: 9K medium and H2SO4 solution, using mixed, adapted bacteria Acidothiobacillus ferrooxidans and Acidothiobacillus thiooxidans.
The main aim of this study was to evaluate the potential and efficiency of indium and tin extraction in the presence of acidophilic microorganisms. Within 35 days, using 9K medium, 55.6% of indium was bioleached, whereas the chemical leaching resulted in a value of 3.4%. Leaching efficiency of tin was 90.2% on the 14th day of the experiment for the biological system (9K) and 93.4% on 21st day of control leaching.
The authors concluded that based on the results of bioleaching studies of used LCD panels by an adapted culture of bacteria, it was found that the extraction of these metals is different in the applied leaching solutions. The highest leaching rate of indium (55.6%) was obtained using a 9K medium inoculated with microorganisms. It suggests that bacteria play a key role, intensifying the dissolution of indium oxide present in ITO. Tin leaching proceeded with efficiency of > 90% both in biological and control systems with 9K medium. It seems that presence of ferrous/ferric ions plays the important role in tin extraction from LCD. The increase in indium recovery rate in the solution is accompanied by a simultaneous decrease in the content of tin. The observed relationship may be useful to separate indium from tin, however, it certainly should be investigated further.
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