Environmentally friendly electrochemical recycling of indium from scrap ITO glass and PET

Indium, the key raw material used in liquid crystal displays (LCDs), light-emitting diodes (LEDs), and solar cells, is a rare metal. The demand for devices that use touch panels has grown enormously, and Indium has become a vital and indispensible material. However, the worldwide depletion of indium resources has made it necessary to recycle as much indium as possible. This is done not only for commercial purposes but also to protect the environment. Although direct electrochemical methods can be used to remove the indium-tin oxide (ITO) layer from intact discarded or defective thin-film transistor (TFT)-LCDs or from flexible polyethylene terephthalate (PET) touch panels, it is not possible to do this with broken or cracked panels, large numbers of glass fragments, or deformed PET material because the necessary electrical connections cannot be made. Therefore, in this study, an indirect electric discharge process was used. Tests were made using DC straight polarity and DC reverse polarity, and a multicylinder electrode was used to conduct carrying out of positive (or negative) electrical discharge in the electrode assembly without the need for electrical connection to the workpiece. An electric field is created by electrical discharge between the cathode and anode through the electrolyte to create an electrical field between the electrode and the ITO surfaces. There is no likelihood of the electrodes making direct contact with the ITO glass fragments, and so, the danger of short circuits is avoided. This method facilitates the smooth and highly efficient recycling of indium avoiding methods that use strong acids and other chemicals that are harmful to the environment. The higher the current used, the faster the feed rate of the workpiece can be, and removal will also be more efficient. A small gap between the electrodes (1 mm) will also speed up the removal rate. Pulsed DC current is conducive to the rapid removal of deposits of electrochemical by-product and also allows a higher feed rate. However, this raises the total electrical power input. The use of ultrasonics speeds up ITO removal as does an increase in electrolyte temperature. A small-diameter anode and a small gap between the electrodes also speed up the removal rate.