The platinum-group elements (PGE) include platinum, palladium, rhodium, ruthenium, iridium, and osmium. These metals have similar physical and chemical properties and occur together in nature. The properties of PGE, such as high melting points, corrosion resistance, and catalytic qualities, make them indispensable to many industrial applications.
Pre-Columbian peoples found naturally occurring platinum and platinum-rich alloys in stream deposits in Colombia and Ecuador and used them to make jewelry. In the 1500s, Europeans described platinum from the New World as “a substance which it has not hitherto been possible to melt by fire or by any of the Spanish arts.” The Spaniards found platinum grains intermingled with gold nuggets they recovered from stream deposits and called the metal “platina.” The metal had no known use and was considered worthless. Small samples of platinum-enriched nuggets from South America reached Europe during the 1740s. Platinum was described as a new metal in 1750, followed by iridium and osmium in 1803, palladium and rhodium in 1804, and ruthenium in 1807.
How Do We Use PGE
Although platinum is well known for its use as jewelry and as an investment commodity, the major applications of PGE are industrial. Their leading use is in catalytic converters, which decrease hydrocarbon, carbon monoxide, and nitrous oxide emissions in automobile exhaust. The chemical industry uses platinum or platinum-rhodium alloys to manufacture specialty silicones and to make nitric oxide, the raw material for fertilizers, explosives, and nitric acid. In the petrochemical industry, platinum-supported catalysts are needed to refine crude oil and to produce high-octane gasoline. In the electronics industry, PGE components increase storage capacities in computer hard disk drives and are ubiquitous in electronic devices, multilayer ceramic capacitors, and hybridized integrated circuits. The glass manufacturing industry uses PGE to produce fiberglass and liquid-crystal and flat-panel displays. PGE alloys are exceptionally hard and durable, making them the best coating for the industrial crucibles used to manufacture chemicals and synthetic materials, including the high-purity sapphire crystals used to make light-emitting diodes. Because platinum does not corrode inside the human body and allergic reactions to platinum are rare, it is used in medical implants such as pacemakers. PGE are also used in cancer-fighting drugs.
Their white coloration, strength, and tarnish resistance make platinum alloys an ideal choice for jewelry. Platinum, palladium, and rhodium are used for investment in the form of coins and bars, and as stocks, mutual funds, or exchange-traded funds.
Where Do PGE Come From?
PGE are among the rarest metals on earth; the upper crust of the Earth contains about 0.0005 parts per million (ppm) platinum. Today, the average grade of PGE in ores mined primarily for their PGE concen-trations range from 5 to 15 ppm. Over 100 minerals contain PGE as an essential component. In most rocks, platinum-group minerals are very small, ranging in size from less than a micron to a few hundred microns in diameter. Geologists can spend a lifetime working on rocks enriched in PGE and never see a platinum-group mineral in a hand specimen, so the presence of PGE must be confirmed by laboratory analysis. Most of the world’s PGE are concentrated in magmatic ore deposits, which form during the cooling and crystallization of magma. If mafic to ultramafic magmas become saturated in sulfur, an immiscible sulfide liquid will separate from the silicate magma and form globules that naturally concentrate metals like copper, nickel, and PGE. As the magma cools, the PGE-enriched sulfide globules accumulate and crystallize to form PGE mineral deposits. Most magmatic copper-nickel-PGE deposits are found with volcanic and plutonic rocks that form where large volumes of mafic magma move from the Earth’s mantle into the crust. Erosion of PGE-enriched rocks and physical concentrations of heavy mineral particles, by the action of moving water, can produce PGE-enriched placer deposits.