# A Review on the Recovery and Separation of Gallium and Indium from Waste
## 4 Summary  
Gallium and indium are metals of great importance for many different areas of life, from medicine and telecommunications to the entertainment industry. They are used in the form of pure metals, alloys, admixtures, oxides, compounds with other elements, such as nitrogen or arsenic, and organometallic compounds. This article addressed the issue of recovery of these metals from waste, which is an extremely important issue for several reasons. The first is the large dispersion of gallium and indium in nature, as well as the rarity of natural minerals, which is related to the great difficulties in their isolation and separation from primary sources. Gallium and indium are obtained as the byproducts during the processing of other metal ores. In the case of gallium, the most important sources are bauxite and zinc sulfides, while for indium, zinc sulfides and (to a much lesser extent) sulfides of copper, iron, tin, and lead are the most important sources. The second reason for the importance of this topic is the fact that gallium and indium are already on the European Union's list of critical and strategic raw materials. This is caused by the global problem of depletion of natural resources and the threat that in several dozen years many of them will run out, including gallium and indium. It is also connected to the growing demand for these metals, mainly for the production of semiconductors and LCD panels. The third important aspect is the problem of increasing pollution of the Earth, which is caused by toxic e-waste, the consumption of which has increased significantly in recent years. Therefore, developing and implementing methods that enable the recovery of valuable elements from waste, while limiting emissions of harmful substances into the environment, should be a priority. This will both reduce the negative impact of human activity on the environment and will bring profits because electrical and electronic waste contains many valuable elements. In addition to gallium and indium, in e-waste there are also, for example, gold, copper, and silver. This literature review showed that it is impossible to propose a universal method of dealing with all electronic waste due to their different specificities. It can be noted, however, that the waste disposal methods described in this work are mostly hydrometallurgical processing methods and focus on the recovery of gallium and indium in relatively mild conditions. It is possible to combine different methods to recover gallium and indium from electronic waste of a given type to achieve high efficiency and repeatability of the process. GaAs and GaN wastes are the main sources of gallium recycling, while the proportion of gallium recycling of IGZO (GZO) display and CIGS scrap is relatively low. Recovery of gallium from GaN waste is usually done through fire or wet methods, whereas the wet method is used for GaAs waste. The gallium and indium obtained from IGZO (GZO) display are mostly through acid leaching. According to the sources, indium is not being recovered from WEEE in the European Union (EU), even though this type of waste is generally well-collected and has high concentrations of indium. To recover indium from discarded LCDs, the process could generally involve (1) collecting LCDs, (2) dismantling them either manually or mechanically, (3) treating the displays with methods such as crushing or pyrolysis, and (4) properly recovering the indium. There are several techniques for separating and purifying indium, including solvent extraction, ion exchange resins, biological metallurgy, cross-current leaching with zinc cementation, vacuum chlorinated separation, and vacuum carbon reduction. Combining these techniques could potentially increase process yields and reduce operating costs. Despite the promise of many of these processes, a complete recycling system for end-of-life (EoL) indium has not yet been established in the EU. The suggestions for research mentioned earlier can help make the recovery of gallium and indium a profitable and common technology.