Indium is a very soft, ductile and malleable metal and its earth crust occurrence can be compared to the one of silver or mercury. It got its name from its indigo blue spectral line. Nowadays its main uses can be found as indium-tin oxide in flat panel devices. Other applications include alloys and solders, thin film solar panels, thermal interface materials, light emitting diodes (LEDs) and laser diodes. In transparent conducting oxides (TCOs) used in flat panels displays and in amorphous silicon and CdTe PV cells, indium can be replaced by other TCOs. There is no commercially available substitute for indium in semiconductors used in thin-film solar cells.
Indium rarely forms its own minerals or occurs in its elemental form. Instead, it is mainly found in host metals such as zinc, lead, tin and copper. Approximately 95% of the refined indium produced globally comes from the processing of zinc ores.
Indium is produced exclusively as a by-product during the processing of other ore minerals. It is most commonly recovered from the zinc-sulfide ore mineral sphalerite. More than half of the global production of refined indium comes from China, followed by France, South Korea, Japan, Canada and South America.
Besides is primary production, indium is also produced from secondary production. World secondary refined indium production resulted almost exclusively from the recycling of manufacturing waste rather than recovery from end-of-life (EOL). Only around 1 % of indium is recycled from these products because of indium is usual used only in minor concentrations. Overall, the secondary supply has been a significant contributor to the total supply.
Indium can be considered a critical material for display technology because there are few substitutes. Because indium is recovered as a byproduct of zinc production, the supply of primary indium is determined by the supply of zinc, regardless of the market demand for indium. Additionally, a large portion of the indium contained in zinc ores and concentrates is not recovered—most zinc smelters are not equipped to extract indium. At the few smelters that do include indium- processing circuits, the average indium recovery rate is only about 50 percent (ranging from 30 to 80 percent). Increased consumption of indium is expected to be satisfied by increased recycling and additional primary supply through improved recovery rates, the construction of new plants, and expansions at existing recovery circuits.
Study on the EU’s list of Critical Raw Materials (2020)
USGS Open-File Report, Mineral Commodity Profiles: Indium
USGS Mineral Commodity Summaries, Indium
USGS Critical Mineral Resources of the United States—Economic and Environmental Geology and Prospects for Future Supply
CRM Alliance, Indium