# A Review on the Recovery and Separation of Gallium and Indium from Waste
## 1 Introduction  
Over the past decades, there has been a rapid development of the electronics industry, which continues to this day. Devices such as diodes, integrated circuits, or transmitters have started to accompany us in everyday life in increasing numbers. They provide us with the latest news and entertainment and enable remote work and quick contact with loved ones. We can find them both in the hospital and in our living rooms--or even closer, on the wrist or in the pocket. Unfortunately, the life of many devices containing electronic circuits is short. This is due not only to the failure rate and difficulty of repair, but also to the very pace at which new models are created. Many people willingly follow the trends and want to be up to date with the latest technologies, which is why they change their devices to newer ones more often than just when the old ones stop fulfilling their functions [1]. The competition between electronics companies has been going on for many years, recently focusing on GPU graphics systems (graphics cards for cryptocurrency mining). The near future is the production of new processors designed specifically to support AI algorithms. We are currently observing a technological trend that allows for the introduction of artificial intelligence everywhere, from consumer processors, through server systems, to dedicated computing systems. Although miniaturized, new processors designed to support AI algorithms contain hundreds, millions, or even billions of electronic components, which are made of semiconductor materials. It can therefore be predicted that soon the earth willbe covered with miniaturized e-waste, which will require specialized disposal due to the presence of valuable semiconductor materials such as GaAs or GaN. In Europe alone, around 10 million tons of WEEE (Waste of Electrical and Electronic Equipment) are produced annually; this accounts for approximately 13% of all municipal waste registered on this continent. It is estimated that the amount of produced WEEE will gradually increase by 3-5% per year in the upcoming years [2]. Data characterizing global WEEE production show similar trends; for example, in 2019 around 53.6 megatons of electronic and electrical waste were produced, and in 2014 around 44.4 megatons. Based on these data, it can be calculated that this amount may increase to 74.7 megatons in 2030 (Figure 1) [3]. Gallium and indium are considered rare metals from a technological point of view. The raising interest in these elements began over a hundred years ago (1920, USSR) when it was announced that, together with germanium, selenium, and tellurium, Ga and In joined a group of rare elements and a dispersed subgroup [2]. Over the past decades, they have gained more and more applications and are now almost an inseparable component of many electrical and electronic devices [4; 5; 6]. Gallium is crucial to the modern electronic industry, where it is used mainly to manufacture semiconductor materials [7]. The use of pure In has also greatly increased with the use of indium-tin-oxide (ITO) electrode material for liquid crystal display (LCD) panels. A dynamically developing field--just like LED technology--is the production of modern CIGS solar cells (copper indium gallium (di)selenide) [4; 5]. Gallium is currently classified as a critical raw material (CRM) and associated with high supply risk. Both gallium and indium are among the 30 critical raw materials (CRMs) on the 2020 EU list; however, indium has been removed from the EU CRM list which was published in 2023. This is because both the supply risk and the economic importance of indium used in flat-panel displays (FPD) dropped below the thresholds and the EU indium production is higher than the EU consumption [8]. On the other hand, new applications of indium are becoming increasingly important. Indium-added pure tin solders may replace lead--tin eutectic solders soon. As is widely known, Pb-Sn alloys pose significant hazards to both the environment and human health due to the toxicity of lead [9; 10; 11; 12].