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{{Use dmy dates|date=February 2021}}
{{Infobox palladium}}
'''Palladium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Pd''' and [[atomic number]] 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist [[William Hyde Wollaston]]. He named it after the [[2 Pallas|asteroid Pallas]] (formally 2 Pallas), which was itself named after the [[epithet]] of the Greek goddess [[Athena]], acquired by her when she slew [[Pallas (daughter of Triton)|Pallas]]. Palladium, [[platinum]], [[rhodium]], [[ruthenium]], [[iridium]] and [[osmium]] form a group of elements referred to as the [[platinum group]] metals (PGMs). They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.
More than half the supply of palladium and its [[Congener (chemistry)|congener]] platinum is used in [[catalytic converter]]s, which convert as much as 90% of the harmful gases in automobile exhaust ([[hydrocarbon]]s, [[carbon monoxide]], and [[nitrogen dioxide]]) into nontoxic substances ([[nitrogen]], [[carbon dioxide]] and [[water vapor]]). Palladium is also used in electronics, [[dentistry]], [[medicine]], [[hydrogen purification]], chemical applications, [[Groundwater remediation|groundwater treatment]], and jewelry. Palladium is a key component of [[fuel cell]]s, in which hydrogen and oxygen react to produce electricity, heat, and water.
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Palladium can be found as a free metal alloyed with gold and other [[Platinum group|platinum-group]] metals in [[placer mining|placer]] deposits of the [[Ural Mountains]], [[Australia]], [[Ethiopia]], [[North America|North]] and [[South America]]. For the production of palladium, these deposits play only a minor role. The most important commercial sources are [[nickel]]-[[copper]] deposits found in the [[Sudbury Basin]], [[Ontario]], and the [[Norilsk|Norilsk–Talnakh]] deposits in [[Siberia]]. The other large deposit is the [[Merensky Reef]] platinum group metals deposit within the [[Bushveld Igneous Complex]] [[South Africa]]. The [[Stillwater igneous complex]] of [[Montana]] and the Roby zone ore body of the [[Lac des Îles igneous complex]] of Ontario are the two other sources of palladium in Canada and the United States.<ref name="USGS07CS" /><ref name="USGS07YB">{{cite web|url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2007-plati.pdf|title=Platinum-Group Metals|date=January 2007|work=Mineral Yearbook 2007|publisher=[[United States Geological Survey]]}}</ref> Palladium is found in the rare minerals [[cooperite (mineral)|cooperite]]<ref>{{cite journal|journal=Mineralogical Magazine|date=1994|volume=58|issue= 2|pages=223–234|title=Compositional variation of cooperite, braggite, and vysotskite from the Bushveld Complex|first1=Sabine M. C.| last1 =Verryn|first2=Roland K. W.|last2=Merkle|doi=10.1180/minmag.1994.058.391.05|bibcode=1994MinM...58..223V|citeseerx=10.1.1.610.640|s2cid=53128786 }}</ref> and [[polarite]].<ref>{{cite journal|last1 = Genkin|first1 = A. D.|last2 = Evstigneeva|first2 = T. L.|date = 1986|title = Associations of platinum- group minerals of the Norilsk copper-nickel sulfide ores|journal = Economic Geology|volume = 81|pages = 1203–1212|doi = 10.2113/gsecongeo.81.5.1203|issue = 5| bibcode=1986EcGeo..81.1203G }}</ref> Many more Pd minerals are known, but all of them are very rare.<ref>{{Cite web|url=https://www.mindat.org/|title=Mindat.org - Mines, Minerals and More|website=www.mindat.org}}</ref>
Palladium is also produced in [[nuclear fission]] reactors and can be extracted from [[spent nuclear fuel]] (see [[synthesis of precious metals]]), though this source for palladium is not used. None of the existing [[nuclear reprocessing]] facilities are equipped to extract palladium from the [[high-level radioactive waste]].<ref>{{cite journal|title = Recovery of Value Fission Platinoids from Spent Nuclear Fuel. Part I PART I: General Considerations and Basic Chemistry|url =http://www.platinummetalsreview.com/pdf/pmr-v47-i2-074-087.pdf| first1 =Zdenek|last1 =Kolarik|first2 =Edouard V.|last2 =Renard| journal = Platinum Metals Review|volume = 47|issue = 2|date = 2003|pages = 74–87|doi =10.1595/003214003X4727487}}</ref> A complication for the recovery of palladium in spent fuel is the presence of {{chem|107|Pd}}, a slightly radioactive [[long-lived fission product]]. Depending on end use, the radioactivity contributed by the {{chem|107|Pd}} might make the recovered palladium unusable without a costly step of [[isotope separation]].
==Applications==
[[File:Aufgeschnittener Metall Katalysator für ein Auto.jpg|thumb|Cross section of a [[Catalytic converter|metal-core catalytic converter]]]]
[[File:25 rubles palladium 1989 Ivan III.jpg|thumb|The Soviet 25-rouble commemorative [[palladium coin]] is a rare example of the monetary usage of palladium.]]
The largest use of palladium today is in catalytic converters.<ref name="unctad" /> Palladium is also used in jewelry, [[dentistry]],<ref name="unctad" /><ref>{{cite journal|journal = Platinum Metals Review|title = Palladium in Restorative Dentistry: Superior Physical Properties make Palladium an Ideal Dental Metal|first = Roy|last = Rushforth|volume = 48|issue = 1|date = 2004|
===Catalysis===
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===Precautions===
Like other [[platinum-group metal]]s, bulk Pd is quite inert. Although [[contact dermatitis]] has been reported, data on the effects are limited. It has been shown that people with an allergic reaction to palladium also react to nickel, making it advisable to avoid the use of dental alloys containing palladium on those so allergic.<ref name="Kiel">{{cite journal|last1 = Kielhorn|first1 = Janet|last2 = Melber|first2 = Christine|last3 = Keller|first3 = Detlef|last4 = Mangelsdorf|first4 = Inge|title = Palladium – A review of exposure and effects to human health|journal = International Journal of Hygiene and Environmental Health|volume = 205|issue = 6|pages = 417–32|date = 2002|pmid = 12455264|doi = 10.1078/1438-4639-00180| bibcode=2002IJHEH.205..417K }}</ref><ref>{{cite book|pages = 549–563|chapter = Health Risk Potential of Palladium|chapter-url = https://books.google.com/books?id=OnNZqylS_Z8C&pg=PA549|title = Palladium emissions in the environment: analytical methods, environmental assessment and health effects|first1 = Fathi|last1 =Zereini|first2 = Friedrich|last2 = Alt|publisher = Springer Science & Business|date = 2006|isbn = 978-3-540-29219-7}}</ref><ref>{{cite journal|last1 = Wataha|first1 = J. C.|last2 = Hanks|first2 = C. T.|title = Biological effects of palladium and risk of using palladium in dental casting alloys|journal = Journal of Oral Rehabilitation|volume = 23|issue = 5|pages = 309–20|date = 1996|pmid = 8736443|doi = 10.1111/j.1365-2842.1996.tb00858.x}}</ref><ref>{{cite journal|last1 = Aberer|first1 = Werner|last2 = Holub|first2 = Henriette|last3 = Strohal|first3 = Robert|last4 = Slavicek|first4 = Rudolf|title = Palladium in dental alloys – the dermatologists' responsibility to warn?|journal = Contact Dermatitis|volume = 28|issue = 3|pages = 163–5|date = 1993|pmid = 8462294|doi = 10.1111/j.1600-0536.1993.tb03379.x|s2cid = 43020912}}</ref><ref>{{cite journal|last1 = Wataha|first1 = John C.|last2 = Shor|first2 = Kavita|title = Palladium alloys for biomedical devices|journal = Expert Review of Medical Devices|volume = 7|issue = 4|pages = 489–501|date = 2010|pmid = 20583886|doi = 10.1586/erd.10.25|s2cid = 41325428}}</ref>
Some palladium is emitted with the exhaust gases of cars with [[catalytic converter]]s. Between 4 and 108 ng/km of palladium particulate is released by such cars, while the total uptake from food is estimated to be less than 2 μg per person a day. The second possible source of palladium is dental restoration, from which the uptake of palladium is estimated to be less than 15 μg per person per day. People working with palladium or its compounds might have a considerably greater uptake. For soluble compounds such as [[palladium chloride]], 99% is eliminated from the body within three days.<ref name="Kiel" />
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==History==
[[File:Wollaston William Hyde Jackson color.jpg|thumb|upright|left|[[William Hyde Wollaston]]]]
[[File:Potw1749a Pallas crop.png|thumb|192x192px|[[Very Large Telescope]] image of [[2 Pallas]], the asteroid after which Palladium was named.]]
[[William Hyde Wollaston]] noted the [[discovery of the chemical elements|discovery]] of a new noble metal in July 1802 in his lab book and named it palladium in August of the same year. He named the element after the asteroid [[2 Pallas]], which had been discovered two months earlier (and which was [[List of former planets|previously considered a planet]]).<ref name="CRC" /> Wollaston purified a quantity of the material and offered it, without naming the discoverer, in a small shop in [[Soho]] in April 1803. After harsh criticism from [[Richard Chenevix (chemist)|Richard Chenevix]], who claimed that palladium was an alloy of platinum and mercury, Wollaston anonymously offered a reward of £20 for 20 grains of synthetic palladium ''alloy''.<ref name="contr">{{cite journal|doi = 10.1080/00033797800200431|title = The Wollaston/Chenevix controversy over the elemental nature of palladium: A curious episode in the history of chemistry|date = 1978|last1 = Usselman|first1 = Melvyn|journal = Annals of Science|volume = 35|issue = 6|pages = 551–579}}</ref> Chenevix received the [[Copley Medal]] in 1803 after he published his experiments on palladium. Wollaston published the discovery of [[rhodium]] in 1804 and mentions some of his work on palladium.<ref name="Disco">{{cite journal|journal=Platinum Metals Review
[[Palladium chloride]] was at one time prescribed as a [[tuberculosis]] treatment at the rate of 0.065 g per day (approximately one milligram per kilogram of body weight). This treatment had many negative [[Adverse effect (medicine)|side-effects]], and was later replaced by more effective drugs.<ref>{{cite journal|title=The Art of Meeting Palladium Specifications in Active Pharmaceutical Ingredients Produced by Pd-Catalyzed Reactions|first=Christine E. |last=Garrett|author2=Prasad, Kapa|journal= Advanced Synthesis & Catalysis|volume=346 |issue=8 |date=2004 |pages=889–900 |doi=10.1002/adsc.200404071|s2cid=94929244 }}</ref>
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Most palladium is used for [[catalytic converter]]s in the automobile industry.<ref name="Kiel" /> Catalytic converters are targets for thieves because they contain palladium and other rare metals. In the run up to year 2000, the Russian supply of palladium to the global market was repeatedly delayed and disrupted; for political reasons, the export quota was not granted on time.<ref>{{cite web|url=http://www.lbma.org.uk/assets/5d_Williamson_lbmaconf2003.pdf|title=Russian PGM Stocks|last=Williamson|first=Alan|work=The LBMA Precious Metals Conference 2003|publisher=The London Bullion Market Association|access-date=2 October 2010|archive-date=21 October 2013|archive-url=https://web.archive.org/web/20131021171646/http://www.lbma.org.uk/assets/5d_Williamson_lbmaconf2003.pdf|url-status=dead}}</ref> The ensuing market panic drove the price to an all-time high of {{convert|1340|$/ozt|$/g|lk=on}} in January 2001.<ref name="chart-all">{{cite web |url=http://www.infomine.com/investment/metal-prices/palladium/all/ |title=Historical Palladium Prices and Price Chart |access-date=2015-01-27 |publisher=InvestmentMine}}</ref> Around that time, the [[Ford Motor Company]], fearing that automobile production would be disrupted by a palladium shortage, stockpiled the metal. When prices fell in early 2001, Ford lost nearly [[United States dollar|US$]]1 billion.<ref>{{cite news|date=16 January 2002|title=Ford fears first loss in a decade|work=BBC News|url=http://news.bbc.co.uk/1/hi/business/1763406.stm|access-date=19 September 2008}}</ref>
World demand for palladium increased from 100 tons in 1990 to nearly 300 tons in 2000. The global production of palladium from mines was 222 [[tonne]]s in 2006 according to the [[United States Geological Survey]].<ref name="USGS07CS">{{cite web|url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/platimcs07.pdf|title=Platinum-Group Metals|date=January 2007|work=Mineral Commodity Summaries|publisher=[[United States Geological Survey]]}}</ref> Many were concerned about a steady supply of palladium in the wake of Russia's [[Annexation of Crimea by the Russian Federation|annexation of Crimea]], partly as sanctions could hamper Russian palladium exports; any restrictions on Russian palladium exports could have exacerbated what was already expected to be a large palladium deficit in 2014.<ref>{{cite web |author=Nat Rudarakanchana |date=2014-03-27 |title=Palladium Fund Launches in South Africa, As Russian Supply Fears Warm Prices |url=http://www.ibtimes.com/palladium-fund-launches-south-africa-russian-supply-fears-warm-prices-1563708|website=International Business Times}}</ref> Those concerns pushed palladium prices to their highest level since 2001.<ref>{{Cite news|url=https://www.cnbc.com/2014/08/20/palladium-prices-russia-conflict-pushes-price-for-commodity-higher.html|title=The other commodity that's leaping on Ukraine war|last=Rosenfeld|first=Everett|date=2014-08-20|work=CNBC|access-date=2018-01-29}}</ref> In September 2014 they soared above the $900 per ounce mark. In 2016 however palladium cost around $614 per ounce as Russia managed to maintain stable supplies.<ref>{{Cite news|url=https://www.bloomberg.com/view/articles/2017-08-30/palladium-rally-is-about-more-than-just-autos|title=Palladium Rally Is About More Than Just Autos|date=2017-08-30|work=Bloomberg.com|access-date=2018-01-29|language=en}}</ref> In January 2019 palladium [[Futures contract|futures]] climbed past $1,344 per ounce for the first time on record, mainly due to the strong demand from the automotive industry.<ref>{{Cite web|url=https://oilprice.com/Metals/Commodities/Dont-Expect-Palladium-Prices-to-Plunge.html|title=Don't Expect Palladium Prices To Plunge {{!}} OilPrice.com|website=OilPrice.com|language=en|access-date=2018-01-29}}</ref> Palladium reached {{convert|2024.64|$/ozt|$/g}} on 6 January 2020, passing $2,000 per troy ounce the first time.<ref>{{Cite news|url=https://www.reuters.com/article/us-global-precious/gold-soars-as-middle-east-tensions-brew-perfect-storm-idUSKBN1Z50D9|title=Gold soars as Middle East tensions brew perfect storm
==Palladium as investment==
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