PGEs

Platinum group elements (PGEs) are six metallic elements: ruthenium, rhodium, palladium, osmium, iridium, and platinum. They share properties such as high melting points, corrosion resistance, and exceptional catalytic activity. They are rare in the Earth's crust and occur together in mineral deposits, often alongside nickel and copper ores.

Occurrence and geochemistry: In nature they occur in ultramafic rocks and in sulfide ore deposits; extraction often requires complex refining after mining. They are typically dispersed as tiny grains and are difficult to separate; refining uses smelting and chemical processes such as aqua regia dissolution and solvent extraction or chloride refining.

Applications: The largest application is catalytic converters in automobiles, where Pt, Pd, and Rh accelerate oxidation and reduction reactions to reduce emissions. Other uses include petroleum refining catalysts, chemical production catalysts, electrical contacts and thick-film resistors, jewelry (Pt and Pd), and laboratory equipment. Iridium is used in high-temperature alloys and crucibles, while ruthenium and osmium find specialized uses in coatings and alloying.

Economy and supply: Major producers include South Africa, Russia, Canada, the United States and Zimbabwe; about two-thirds of world PGE production comes from South Africa's Bushveld Complex and Russian mines. Prices are volatile and sensitive to automotive demand and mining politics. Recycling from used catalytic converters and industrial scrubbers provides an important secondary source.

Environmental and safety: Mining and refining pose environmental challenges due to energy use and waste streams. Some osmium compounds, such as osmium tetroxide, are highly toxic, requiring careful handling and regulatory controls in processing and application.