# A Review on the Recovery and Separation of Gallium and Indium from Waste
## 3 Methods of Recovering Gallium and Indium from Secondary Sources
### Waste Pretreatment
#### 3.1.1 Disassembly and Sorting  
This stage allows for the separation of elements containing hazardous substances and other compounds, which are included in Annex VII of Directive 2012/19/EU. Batteries, external electrical wiring, bromine-containing plastics, mercury-containing backlights, printed circuit boards, and liquid crystal displays are listed there [22].  
However, dismantling is not only conducted to meet the EU requirements. It is usually focused on extracting the most valuable materials from the waste, such as processors or RAM. The separation of elements containing valuable metals from plastic and ceramics and their segregation significantly improves the efficiency of the recycling process and makes it more economical [21].  
Disassembly is carried out manually or with a special machine, with the first method being better in terms of efficiency, price, and the initial condition of the item. Despite this, some companies have already opted for automated systems, now using circular saws, lasers, or even water-jet cutting. Research is also underway to improve their operations [22].  
Sorting usually consists of dividing elements into groups with similar physical properties, such as density, mass, shape, and magnetic and electrical properties [21].  
After dismantling and assigning the elements to appropriate groups, the composition of the mixture they form is usually further simplified. This is accomplished both with further mechanical disassembly of the elements and by subjecting them to various types of physical and chemical separation techniques [23].  
For example, in the case of LCD panels, the polarizing film and liquid crystal are removed, leaving only the ITO coating. This is achieved in various ways. The material can be pyrolyzed in a nitrogen atmosphere or vacuum, which will lead to the incineration of the organic components of the panels and allow for the obtainment of purified ITO glass. A physicochemical method is also used, which is more ecological and easier to use than pyrolysis. The panels are heated to about 230-240 \({}^{\circ}\)C which causes most of the foil to peel off, and the residues are easy to remove with a brush. The glass is then crushed and subjected to washing with acetone while treating it with ultrasound to remove the liquid crystal. On the other hand, the process of so-called electrical disintegration uses high current. It is the most environmentally friendly of the mentioned methods; moreover, it allows for the obtainment of glass from the ITO without the need to crush it, thus avoiding the accompanying losses [23].  
Another example of research aimed at increasing the recycling efficiency is a system to sort electronic components from printed circuit boards (PCBs) via elemental composition. Current methods of treating waste PCBs (WPCBs), which consist first of crushing and then of grinding, produce a powder with a highly complex and heterogeneous chemical composition. The new method should allow for sorting wastes according to their chemical composition, leading to an enrichment of many targeted elements. It combines a convolutional-neural-network-based optical recognition with multienergy X-ray transmission spectroscopy, demonstrating up to 96.9% accuracy in controlled conditions. Hence, with the elemental enrichments of up to 10,000 for targeted elements, this method renders economically viable recovery of previously unrecycled critical metals by enriching sorting groups in many important metals [24].