Palladium is a silvery-white metal, element 46, symbol Pd, atomic mass 106.42, specific gravity 12.02, melting point 1550ºC. There are six stable isotopes, like platinum. It has the lowest melting point and lowest density of the six PGE, and is the least refractory and most geochemically reactive metal of the group. It is very malleable and ductile. The mean abundance of Pd in upper continental crust is estimated at just 0.52 ppb, similar to platinum, and rarer than gold (1.5 ppb) and silver (53 ppb).
English scientist William Hyde Wollaston, who discovered how to render platinum malleable, isolated palladium from crude (native) platinum in 1803. He named it for Pallas, the second asteroid to be observed, which was recognized the previous year by Olbers and named by him for the Greek goddess Pallas Athena.
Palladium is recovered as a byproduct of magmatic copper-nickel sulphide ores, and in certain mafic-ultramafic intrusions, both in sulphide-poor layers (“reefs”) and in disseminated semi-massive to massive sulphide ores, most famously in the Noril’sk-Talnakh “ore junction” associated with the Siberian flood basalts, of Permian age. Other notably Pd-enriched ores are recovered from the only two currently (2011) operating primary-PGE mines in North America, in the J-M Reef of the Stillwater complex in southern Montana, U.S.A., and the texturally-complex ores of the Lac des Iles mine in northwest Ontario (both of late Archean age).
Palladium is an essential constituent of far more discrete minerals than any other PGE, in much the same way that there are far more minerals of silver than of gold. The most common Pd minerals include compounds of Pd with one or more of tellurium, bismuth, antimony and sulphur. Palladium-rich minerals first described in Canada include sudburyite, froodite and michenerite. It may also be concentrated to relatively high levels in solid solution in some more-common ore minerals, such as the iron-nickel sulphide pentlandite.
The chief producing country for palladium has long been Russia, due largely to the mines of the Noril’sk-Talnakh area of the Siberian shield. In 2009, the supply was dominated by Russia (51%), followed by South Africa (33%) and North America (11%). The latter has long seen byproduct production of PGE from the Sudbury nickel mines, supplemented in the past two decades by two mines worked principally for palladium, at Lac des Iles in northwest Ontario and the Stillwater complex of Montana, U.S.A.
The largest uses are currently autocatalysts, electronics, jewellery and a legion of roles in the industrial sector (including dental applications). It can absorb large volumes of some gases, particularly hydrogen, and when finely divided is a fine catalyst. It is excellent for the production of noise-free, tarnish-proof electrical contacts. It is used in high-temperature solders. Palladium-silver alloys can be used to braze stainless steel. It is employed in computers, mobile phones, fuel cells and other products. Alloyed with ruthenium, another of the PGE, palladium makes a white metal thought good for the settings of diamond jewellery. Palladium figures, second to platinum, as an investment in exchange-traded funds which have sought PGE since the price run-up which has dominated the metal markets since the start of 2009.
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