What Are Platinum Group Metals or PGMs?

The platinum group metals or PGMs are a cluster of six transition metals on the periodic table. They are noble and precious metals with chemical and physical properties similar to that of platinum and occurring in the same ore deposits. The platinum group metals are rare, durable, useful, and highly valuable.

Here is a list of platinum group metals, a look at their common properties, their uses, and their sources.

List of the Platinum Group Metals

The six platinum group metals are:

• Ruthenium (Ru)
• Rhodium (Rh)
• Palladium (Pd)
• Osmium (Os)
• Iridium (Ir)
• Platinum (Pt)

Properties of Platinum Group Metals

The PGMs share several common properties:

• All of the platinum group metals are d-block transition metal elements.
• They are all silver-colored metals.
• The metals are extremely dense. The elements with highest density (osmium and iridium) are PGMs. The densest platinum group metals are around 11% more dense than gold. The lightest PGMs (palladium, rhodium, and ruthenium) have density values comparable to that of silver.
• They resist corrosion, tarnish, and chemical attack.
• They are highly resistant to wear.
• The platinum group metals display excellent catalytic properties.
• The metals are stable at high temperatures.
• The PGMs have stable electrical properties.
• Ruthenium and osmium crystallize in the hexagonal close-packed system. This gives these two elements greater hardness than the other platinum group metals, which crystallize in the face-centered cubic system. The crystal structure also makes ruthenium and osmium hard and brittle.
• Compared to the other PGMs, platinum and palladium are soft and ductile.

Platinum Group Metal Uses

The platinum group metals have many uses.

• Platinum, rhodium, and iridium find use in jewelry. Sometimes they are coatings over softer metals, such as silver.
• PGMs are important catalysts,. They are used in the petroleum industry. Platinum, palladium, and rhodium find use in the automotive industry in catalytic converters. The metals catalysts in organic chemical reactions. Platinum or platinum-rhodium alloys catalyze the partial oxidation of ammonia into nitric acid, which serves as a raw material in chemical production.
• Iridium and platinum are part of pacemakers and other medical implants.
• Due to their desirable electrical properties, PGM alloys act as electrical contacts, circuits, electrodes, and thermocouples.
• Platinum group metals act as alloying additives to improve the properties of other metals.
• PGMs make excellent crucibles for growing single crystals of oxides.

Sources of Platinum Group Metals

The word “platinum” comes from the Spanish word platina, meaning “little silver.” The name reflects the source of the platinum group metals because the Spaniards considered platinum to be an undesirable impurity in Columbian silver mines. The platinum group metals occur together in ores. Ultramafic and mafic igneous rocks are rich in PGMs, while granites are low in the metals.

Rich platinum group metal deposits include mafic layered intrusions, such the Bushveld complex. Platinum metals occur in North and South America and the Ural mountains, among other places.

Nickel mines are another source of platinum group metals, where PGMs are a by-product of nickel mining and processing. The light platinum group metals (ruthenium, rhodium, palladium) form as nuclear reactor fission products.

Extraction

The platinum group metals are not easily separated from one another. The first step involves dissolving ore in acid. Usually, the acid is aqua regia, because the metals resist many common strong acids. The result is a solution containing multiple metal complexes. Isolating the different elements relies on their differing reactivities and solubility values in different solvents. The details of the extraction process are trade secrets.

It’s also possible to get platinum group metals from spent reactor fuel. At one time, the recovery process was too expensive. But, the demand for the metals makes extraction from nuclear fuel a viable option today.

History

Platinum and its alloys occur in native form, so the metals found use by ancient people, including pre-Columbian Americans. However, platinum isn’t mentioned in literature until the 16th century. In 1557, Julius Caesar Scalinger wrote about a strange metal used in Central America that was unknown to European metallurgists.

References

• Kolarik, Zdenek; Renard, Edouard V. (2005). “Potential Applications of Fission Platinoids in Industry.” Platinum Metals Review. 49 (2): 79. doi:10.1595/147106705X35263
• Renner, H.; Schlamp, G.; Kleinwächter, I.; Drost, E.; Lüschow, H. M.; Tews, P.; Panster, P.; Diehl, M.; et al. (2002). “Platinum group metals and compounds”. Ullmann’s Encyclopedia of Industrial Chemistry. Wiley. doi:10.1002/14356007.a21_075
• Weeks, M. E. (1968). Discovery of the Elements (7th ed.). Journal of Chemical Education. 385–407. ISBN 0-8486-8579-2.
• Woods, Ian (2004). The Elements: Platinum. Benchmark Books. ISBN 978-0-7614-1550-3.
• Xiao, Z.; Laplante, A. R. (2004). “Characterizing and recovering the platinum group minerals—a review.” Minerals Engineering. 17 (9–10): 961–979. doi:10.1016/j.mineng.2004.04.001