# A Review on the Recovery and Separation of Gallium and Indium from Waste
## 1 Introduction
The provisions of the RoHS directive (Restriction of Hazardous Substances) specify the permissible content of harmful substances (lead, mercury, cadmium, hexavalent chromium, and polybrominated compounds) used by manufacturers in electrical and electronic equipment (EEE). Gallium and indium are not on this list, so their compounds may become  
Figure 1: Global e-waste generated per year (Mt/y) and per capita (kg/c); the data for 2023–2030 are estimated. substitutes for harmful substances currently used in EEE. Substitution of hazardous substances in EEE should be a priority and carried out in such a way as to be compatible with the health and safety of users of EEE [13]. Due to the increasing demand for gallium and indium caused by the development of the electrical and electronic equipment industry, production needs are growing. As can be seen in Figure 2a, approximately 210 tons of high-purity gallium were produced in 2019. The largest manufacturers were China, Slovakia, Japan, and the United States. The so-called primary gallium, characterized by its lower quality, was produced in the amount of 324 tons, and its main suppliers were the United States, China, Japan, Russia, Ukraine, and Korea. In 2022, the production of refined gallium amounted to 290 tons, which was a 16% increase compared to 250 tons in 2021. This had and still has an impact on the prices: in 2019, a customer had to pay about USD 573 per kilogram of refined gallium and USD 153 for low-purity primary gallium, while in 2022 the gallium price was, respectively, USD 640 and USD 420 per kilogram of high-purity refined gallium and low-purity primary gallium (Figure 2b). As can be seen, the prices across the years for both types of gallium increased, and Canada joined the group of significant producers. In the case of indium, only the data about the production of refined metal are available; in 2019, it amounted to 760 tons, while in 2018 it was 741 tons. In 2021 and 2022, indium production increased to 932 and 900 tons, respectively--see Figure 2c. The main manufacturers of indium are China, Peru, Korea, Canada, and Japan. Figure 2d shows that prices of indium have not changed significantly over the previous years. In 2018, a customer had to pay USD 310 per kilogram of indium, in 2019--USD 390, and in 2020--USD 395. This is presumably related to the existing effective substitutes for ITO in the strategic application fields of indium [7; 14; 15; 16]. Gallium comes primarily from the processing of bauxite and zinc ores, while the main primary source of indium is actually ores containing zinc sulfides. Production of gallium and indium from ores is only a side process and benefit, and the amount obtained depends largely on the demand for the main products (e.g., zinc) [16]. Some amounts of these metals come from the recycling of used equipment, which is carried out mainly in Canada, the United States, Korea, and Japan [14]. In the case of gallium, substantial quantities of new scrap, generated during the manufacture of GaAs-based devices, are reprocessed to recover high-purity gallium at only one facility in  
Figure 2: World production of high-purity and low-purity refined gallium (**a**), estimated average free market prices of high-purity and low-purity refined gallium (**b**), world refinery production of indium without U.S. Data (**c**), and estimated average free market and free-on-board U.S. warehouse prices of indium (**d**). New York [16]. Most of the indium is recovered from ITO scrap in Japan and Korea [7]. However, this amount is certainly not sufficient and is related to the fact that only about 20% of all discarded electronics are properly recycled through organized and regulated channels. Even in the EU, which is a global leader in e-waste recycling, only 35 percent of e-waste is reported as properly managed and recycled. It is not entirely clear what happens to the remaining 80% of indium--its fate depends primarily on the country in which it found itself.