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Palladium, 46Pd
Palladium
Pronunciation/pəˈleɪdiəm/ ⓘ ​(pə-LAY-dee-əm)
Appearancesilvery white
Standard atomic weight Ar°(Pd)
Palladium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ni
↑
Pd
↓
Pt
rhodium ← palladium → silver
Atomic number (Z)46
Groupgroup 10
Periodperiod 5
Block  d-block
Electron configuration[Kr] 4d10
Electrons per shell2, 8, 18, 18
Physical properties
Phase at STPsolid
Melting point1828.05 K ​(1554.9 °C, ​2830.82 °F)
Boiling point3236 K ​(2963 °C, ​5365 °F)
Density (at 20° C)12.007 g/cm3[3]
when liquid (at m.p.)10.38 g/cm3
Heat of fusion16.74 kJ/mol
Heat of vaporization358 kJ/mol
Molar heat capacity25.98 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1721 1897 2117 2395 2753 3234
Atomic properties
Oxidation statescommon: 0, +2, +4
+1,[4] +3,[5] +5[6]
ElectronegativityPauling scale: 2.20
Ionization energies
  • 1st: 804.4 kJ/mol
  • 2nd: 1870 kJ/mol
  • 3rd: 3177 kJ/mol
Atomic radiusempirical: 137 pm
Covalent radius139±6 pm
Van der Waals radius163 pm
Color lines in a spectral range
Spectral lines of palladium
Other properties
Natural occurrenceprimordial
Crystal structure ​face-centered cubic (fcc) (cF4)
Lattice constant
Face-centered cubic crystal structure for palladium
a = 389.02 pm (at 20 °C)[3]
Thermal expansion11.77×10−6/K (at 20 °C)[3]
Thermal conductivity71.8 W/(m⋅K)
Electrical resistivity105.4 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[7]
Molar magnetic susceptibility+567.4×10−6 cm3/mol (288 K)[8]
Young's modulus121 GPa
Shear modulus44 GPa
Bulk modulus180 GPa
Speed of sound thin rod3070 m/s (at 20 °C)
Poisson ratio0.39
Mohs hardness4.75
Vickers hardness400–600 MPa
Brinell hardness320–610 MPa
CAS Number7440-05-3
History
Namingafter asteroid Pallas, itself named after Pallas Athena
Discovery and first isolationWilliam Hyde Wollaston (1802)
Isotopes of palladium
Main isotopes[9] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
100Pd synth 3.63 d ε 100Rh
102Pd 1.02% stable
103Pd synth 16.99 d ε 103Rh
104Pd 11.1% stable
105Pd 22.3% stable
106Pd 27.3% stable
107Pd trace 6.5×106 y β− 107Ag
108Pd 26.5% stable
110Pd 11.7% stable
 Category: Palladium
| references

Palladium is a chemical element; it has 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 asteroid Pallas (formally 2 Pallas), which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form together a group of elements referred to as the platinum group metals. 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 platinum is used in catalytic converters, which convert as much as 90% of the harmful gases in automobile exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide[10]) into nontoxic substances (nitrogen, carbon dioxide and water vapor). Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications,[11][12] electrochemical sensors,[13] electrosynthesis,[14][15] groundwater treatment, and jewellery. Palladium is a key component of fuel cells, in which hydrogen and oxygen react to produce electricity, heat, and water.

Ore deposits of palladium and other platinum group metals are rare. The most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex covering the Transvaal Basin in South Africa; the Stillwater Complex in Montana, United States; the Sudbury Basin and Thunder Bay District of Ontario, Canada; and the Norilsk Complex in Russia. Recycling is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable investment interest.

Characteristics

[edit]

Palladium belongs to group 10 in the periodic table, but the configuration in the outermost electrons is in accordance with Hund's rule. Electrons that by the Madelung rule would be expected to occupy the 5s instead fill the 4d orbitals, as it is more energetically favorable to have a completely filled 4d10 shell instead of the 5s2 4d8 configuration.[clarification needed]

Z Element No. of electrons/shell
28 nickel 2, 8, 16, 2 (or 2, 8, 17, 1)
46 palladium 2, 8, 18, 18, 0
78 platinum 2, 8, 18, 32, 17, 1
110 darmstadtium 2, 8, 18, 32, 32, 16, 2 (predicted)[16]

This 5s0 configuration, unique in period 5, makes palladium the heaviest element having only one incomplete electron shell, with all shells above it empty.

Palladium has the appearance of a soft silver-white metal that resembles platinum. It is the least dense and has the lowest melting point of the platinum group metals. It is soft and ductile when annealed and is greatly increased in strength and hardness when cold-worked. Palladium dissolves slowly in concentrated nitric acid, in hot, concentrated sulfuric acid, and when finely ground, in hydrochloric acid.[17] It dissolves readily at room temperature in aqua regia.

Palladium does not react with oxygen at standard temperature (and thus does not tarnish in air). Palladium heated to 800 °C will produce a layer of palladium(II) oxide (PdO). It may slowly develop a slight brownish coloration over time, likely due to the formation of a surface layer of its monoxide.

Palladium films with defects produced by alpha particle bombardment at low temperature exhibit superconductivity having Tc = 3.2 K.[18]

Isotopes

[edit]
Main article: Isotopes of palladium

Naturally occurring palladium is composed of six stable isotopes. The most stable radioisotopes are 107Pd with a half-life of 6.5 million years (traces found in nature), 103Pd with a half-life of 16.99 days, and 100Pd with a half-life of 3.63 days. There are 25 other radioisotopes characterized ranging from 91Pd to 129Pd. These have half-lives of less than thirty minutes, except 101Pd (8.47 hours), 109Pd (13.6 hours), and 112Pd (21.0 hours).[19]

For isotopes with atomic masses less than that of the most abundant stable isotope, 106Pd, the primary decay mode is electron capture with the primary decay product being rhodium. The primary mode of decay for those isotopes of Pd with atomic mass greater than 106 is beta decay with the primary product of this decay being silver.[19]

Radiogenic 107Ag is a decay product of 107Pd and was first discovered in 1978[20] in the Santa Clara[21] meteorite of 1976. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. 107Pd versus Ag correlations observed in Solar System bodies must reflect the presence of short-lived nuclides in the early Solar System.[22]

107
Pd is also produced as a fission product in spontaneous or induced fission of 235
U. As it is not very mobile in the environment and has a relatively low decay energy, 107
Pd is usually considered to be among the more benign of the long-lived fission products.

Compounds

[edit]
Main article: Palladium compounds

Palladium compounds exist primarily in the 0 and +2 oxidation state. Other less common states are also recognized. Generally the compounds of palladium are more similar to those of platinum than those of any other element.

  • Structure of α-PdCl2
    Structure of α-PdCl2
  • Structure of β-PdCl2
    Structure of β-PdCl2

Palladium(II)

[edit]

Palladium(II) chloride is the principal starting material for other palladium compounds. It arises by the reaction of palladium with chlorine. It is used to prepare heterogeneous palladium catalysts such as palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon.[23] Solutions of PdCl2 in nitric acid react with acetic acid to give palladium(II) acetate, also a versatile reagent. PdCl2 reacts with ligands (L) to give square planar complexes of the type PdCl2L2. One example of such complexes is the benzonitrile derivative PdCl2(PhCN)2.[24][25]

PdCl2 + 2 L → PdCl2L2 (L = PhCN, PPh3, NH3, etc.)

The complex bis(triphenylphosphine)palladium(II) dichloride is a useful catalyst.[26]

Palladium(II) acetate
Platinum-palladium ore from the Stillwater mine in the Beartooth Mountains, Montana, US
Sulfidic serpentintite (platinum-palladium ore) from the Stillwater mine in Montana

Palladium(0)

[edit]

Palladium forms a range of zerovalent complexes with the formula PdL4, PdL3 and PdL2. For example, reduction of a mixture of PdCl2(PPh3)2 and PPh3 gives tetrakis(triphenylphosphine)palladium(0):[27]

2 PdCl2(PPh3)2 + 4 PPh3 + 5 N2H4 → 2 Pd(PPh3)4 + N2 + 4 N2H+5Cl−

Another major palladium(0) complex, tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3), is prepared by reducing sodium tetrachloropalladate in the presence of dibenzylideneacetone.[28]

Palladium(0), as well as palladium(II), are catalysts in coupling reactions, as has been recognized by the 2010 Nobel Prize in Chemistry to Richard F. Heck, Ei-ichi Negishi, and Akira Suzuki. Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include the Heck, Suzuki, Sonogashira coupling, Stille reactions, and the Kumada coupling. Palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0) (Pd(PPh3)4), and tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) serve either as catalysts or precatalysts.[29]

Other oxidation states

[edit]

Although Pd(IV) compounds are comparatively rare, one example is sodium hexachloropalladate(IV), Na2[PdCl6]. Pd(II) and Pd(IV) can transform into each other under certain electrochemical conditions.[30][31] A few compounds of palladium(III) are also known.[32] Palladium(VI) was claimed to have been synthesized in 2002,[33][34] but subsequently disproven.[35][36]

Mixed valence palladium complexes exist, e.g. Pd4(CO)4(OAc)4Pd(acac)2 forms an infinite Pd chain structure, with alternatively interconnected Pd4(CO)4(OAc)4 and Pd(acac)2 units.[37]

When alloyed with a more electropositive element, palladium can acquire a negative charge. Such compounds are known as palladides, such as gallium palladide.[38] Palladides with the stoichiometry RPd3 exist where R is scandium, yttrium, or any of the lanthanides.[39]

Occurrence

[edit]
Palladium output in 2005

As overall mine production of palladium reached 210,000 kilograms in 2022, Russia was the top producer with 88,000 kilograms, followed by South Africa, Canada, the U.S., and Zimbabwe.[40] Russia's company Norilsk Nickel ranks first among the largest palladium producers globally, accounting for 39% of the world's production.[41]

Palladium can be found as a free metal alloyed with gold and other platinum-group metals in placer deposits of the Ural Mountains, Australia, Ethiopia, 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–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.[42][43] Palladium is found in the rare minerals cooperite[44] and polarite.[45] Many more Pd minerals are known, but all of them are very rare.[46]

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.[47] A complication for the recovery of palladium in spent fuel is the presence of 107
Pd, a slightly radioactive long-lived fission product. Depending on end use, the radioactivity contributed by the 107
Pd might make the recovered palladium unusable without a costly step of isotope separation.

Applications

[edit]
Cross-section of a metal-core catalytic converter
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.[48] Palladium is also used in jewellery, dentistry,[48][49] watch making, blood sugar test strips, aircraft spark plugs, surgical instruments, and electrical contacts.[50] Palladium is also used to make some professional transverse (concert or classical) flutes.[51] As a commodity, palladium bullion has ISO currency codes of XPD and 964. Palladium is one of only four metals to have such codes, the others being gold, silver and platinum.[52] Because it adsorbs hydrogen, palladium was a key component of the controversial cold fusion experiments of the late 1980s.[53]

Catalysis

[edit]
See also: Palladium-catalyzed coupling reactions

When it is finely divided, as with palladium on carbon, palladium forms a versatile catalyst; it speeds heterogeneous catalytic processes like hydrogenation, dehydrogenation, and petroleum cracking. Palladium is also essential to the Lindlar catalyst, also called Lindlar's Palladium.[54] A large number of carbon–carbon bonding reactions in organic chemistry are facilitated by palladium compound catalysts. For example:

When dispersed on conductive materials, palladium is an excellent electrocatalyst for oxidation of primary alcohols in alkaline media.[55] Palladium is also a versatile metal for homogeneous catalysis, used in combination with a broad variety of ligands for highly selective chemical transformations.

In 2010 the Nobel Prize in Chemistry was awarded "for palladium-catalyzed cross couplings in organic synthesis" to Richard F. Heck, Ei-ichi Negishi and Akira Suzuki. A 2008 study showed that palladium is an effective catalyst for carbon–fluorine bonds.[56]

Catalytic cycle for Kumada cross coupling reaction, which is widely used in the synthesis of fine chemicals

Palladium catalysis is primarily employed in organic chemistry and industrial applications, although its use is growing as a tool for synthetic biology; in 2017, effective in vivo catalytic activity of palladium nanoparticles was demonstrated in mammals to treat disease.[57]

Palladium is also used as a catalyst in the production of biofuels.[58]

Electronics

[edit]

The primary application of palladium in electronics is in multi-layer ceramic capacitors[59] in which palladium (and palladium-silver alloy) is used for electrodes.[48] Palladium (sometimes alloyed with nickel) is or can be used for component and connector plating in consumer electronics[60][61] and in soldering materials. The electronic sector consumed 33 tonnes (1.07 million troy ounces) of palladium in 2006, according to a Johnson Matthey report.[62] Palladium is used in the production of printed circuit boards.[63]

Technology

[edit]

Hydrogen easily diffuses through heated palladium,[17] and membrane reactors with Pd membranes are used in the production of high purity hydrogen.[64] Palladium is used in palladium-hydrogen electrodes in electrochemical studies. Palladium(II) chloride readily catalyzes carbon monoxide gas to carbon dioxide and is useful in carbon monoxide detectors.[65]

Palladium has been used to produce metallic glass by fast cooling alloys, avoiding their crystallisation, thus reducing brittleness and leading to stronger materials.[66]

Hydrogen storage

[edit]
Main article: Palladium hydride

Palladium readily adsorbs hydrogen at room temperatures, forming palladium hydride PdHx with x less than 1.[67] While this property is common to many transition metals, palladium has a uniquely high absorption capacity and does not lose its ductility until x approaches 1.[68] This property has been investigated in designing an efficient and safe hydrogen fuel storage medium, though palladium itself is currently prohibitively expensive for this purpose.[69] The content of hydrogen in palladium can be linked to magnetic susceptibility, which decreases with the increase of hydrogen and becomes zero for PdH0.62. At any higher ratio, the solid solution becomes diamagnetic.[70]

Palladium is used for purification of hydrogen on a laboratory[71] but not industrial scale.[72]

Medicine

[edit]

Palladium is used in small amounts (about 0.5%) in some alloys of dental amalgam to decrease corrosion and increase the metallic lustre of the final restoration.[73][74] Palladium is also used in the production of pacemakers.[75]

Jewellery

[edit]

Palladium has been used as a precious metal in jewellery since 1939 as an alternative to platinum in the alloys called "white gold", where the naturally white color of palladium does not require rhodium plating. Palladium, being much less dense than platinum, is similar to gold in that it can be beaten into leaf as thin as 100 nm (1⁄250,000 in).[17] Unlike platinum, palladium may discolor at temperatures above 400 °C (752 °F)[76] due to oxidation, making it more brittle and thus less suitable for use in jewellery; to prevent this, palladium intended for jewellery is heated under controlled conditions.[77]

Prior to 2004, the principal use of palladium in jewellery was the manufacture of white gold. Palladium is one of the three most popular alloying metals in white gold (nickel and silver can also be used).[48] Palladium-gold is more expensive than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur).[78]

When platinum became a strategic resource during World War II, many jewellery bands were made out of palladium. Palladium was little used in jewellery because of the technical difficulty of casting. With the casting problem resolved[79] the use of palladium in jewellery increased, originally because platinum increased in price whilst the price of palladium decreased.[80] In early 2004, when gold and platinum prices rose steeply, China began fabricating volumes of palladium jewellery, consuming 37 tonnes in 2005. Subsequent changes in the relative price of platinum lowered demand for palladium to 17.4 tonnes in 2009.[81][82] Demand for palladium as a catalyst has increased the price of palladium to about 50% higher than that of platinum in January 2019.[83]

In January 2010, hallmarks for palladium were introduced by assay offices in the United Kingdom, and hallmarking became mandatory for all jewellery advertising pure or alloyed palladium. Articles can be marked as 500, 950, or 999 parts of palladium per thousand of the alloy.

Photography

[edit]

In the platinotype printing process, photographers make fine-art black-and-white prints using platinum or palladium salts. Often used with platinum, palladium provides an alternative to silver.[84] But palladium is more inert than the silver used in silver bromide prints, so such photographs are better archived than conventional prints and convey details more clearly.[85][86]

Effects on health

[edit]

Toxicity

[edit]
Palladium
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H317
P261, P273, P280, P302+P352, P321, P333+P313, P363, P501[87]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
0
0

Palladium is a metal with low toxicity as conventionally measured (e.g. LD50). Recent research on the mechanism of palladium toxicity suggests high toxicity if measured on a longer timeframe and at the cellular level in the liver and kidney.[88] Mitochondria appear to have a key role in palladium toxicity via mitochondrial membrane potential collapse and depletion of the cellular glutathione (GSH) level. Until that recent work, it had been thought that palladium was poorly absorbed by the human body when ingested. Plants such as the water hyacinth are killed by low levels of palladium salts, but most other plants tolerate it, although tests show that, at levels above 0.0003%, growth is affected. High doses of palladium could be poisonous; tests on rodents suggest it may be carcinogenic, though until the recent research cited above, no clear evidence indicated that the element harms humans.[89]

Precautions

[edit]

Like other platinum-group metals, 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.[90][91][92][93][94]

Some palladium is emitted with the exhaust gases of cars with catalytic converters. 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.[90]

The median lethal dose (LD50) of soluble palladium compounds in mice is 200 mg/kg for oral and 5 mg/kg for intravenous administration.[90]

History

[edit]
William Hyde Wollaston
Very Large Telescope image of 2 Pallas, the asteroid after which Palladium was named.

William Hyde Wollaston noted the 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 previously considered a planet).[17] 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, 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.[95] 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.[96][97] He disclosed that he was the discoverer of palladium in a publication in 1805.[95][98]

Wollaston found palladium in crude platinum ore from South America by dissolving the ore in aqua regia, neutralizing the solution with sodium hydroxide, and precipitating platinum as ammonium chloroplatinate with ammonium chloride. He added mercuric cyanide to form the compound palladium(II) cyanide, which was heated to extract palladium metal.[96]

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 side-effects, and was later replaced by more effective drugs.[99]

Most palladium is used for catalytic converters in the automobile industry.[90] 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.[100] The ensuing market panic drove the price to an all-time high of $1,340 per troy ounce ($43/g) in January 2001.[101] 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 US$1 billion.[102]

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 tonnes in 2006 according to the United States Geological Survey.[42] Many were concerned about a steady supply of palladium in the wake of Russia's 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.[103] Those concerns pushed palladium prices to their highest level since 2001.[104] 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.[105] In January 2019 palladium futures climbed past $1,344 per ounce for the first time on record, mainly due to the strong demand from the automotive industry.[106] Palladium reached $2,024.64 per troy ounce ($65.094/g) on 6 January 2020, passing $2,000 per troy ounce the first time.[107] The price rose above $3,000 per troy ounce in May 2021 and March 2022.[108]

Palladium as investment

[edit]
Palladium prices – US dollars per troy ounce

Global palladium sales were 8.84 million troy ounces (275 t) in 2017,[109] of which 86% was used in the manufacturing of automotive catalytic converters, followed by industrial, jewellery, and investment usages.[110] More than 75% of global platinum and 40% of palladium are mined in South Africa. Russia's mining company, Norilsk Nickel, produces another 44% of palladium, with US and Canada-based mines producing most of the rest.

The price for palladium reached an all-time high of $2,981.40 per troy ounce on May 3, 2021,[111][112] driven mainly on speculation of the catalytic converter demand from the automobile industry. Over the following few years the price fell by over two-thirds. Palladium is traded in the spot market with the code "XPD". When settled in USD, the code is "XPDUSD". A later surplus of the metal was caused by the Russian government selling stockpiles from the Soviet era, at a rate of about 1.6 to 2 million troy ounces (50 to 62 t) a year. The amount and status of this stockpile are a state secret.

Palladium producers

[edit]

Exchange-traded products

[edit]

WisdomTree Physical Palladium (LSE: PHPD) is backed by allocated palladium bullion and was the world's first palladium ETF. It is listed on the London Stock Exchange as PHPD,[113] Xetra Trading System, Euronext and Milan. ETFS Physical Palladium Shares (NYSE: PALL) is an ETF traded on the New York Stock Exchange.

Bullion coins and bars

[edit]
See also: Palladium coin

A traditional way of investing in palladium is buying bullion coins and bars made of palladium. Available palladium coins include the Canadian Palladium Maple Leaf, the Chinese Panda, and the American Palladium Eagle. The liquidity of direct palladium bullion investment is poorer than that of gold, platinum, and silver because there is a lower circulation of palladium coins than the big three precious metals.[114]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Palladium

View on Grokipedia
from Grokipedia

Palladium is a with the symbol Pd and 46. It is a dense, silvery-white in group 10 of the periodic table, classified among the six platinum-group metals (PGMs).
Discovered in 1803 by English chemist , who isolated it from crude ore and named it after the asteroid Pallas, palladium exhibits notable properties including high malleability, , and exceptional capacity to absorb —up to 900 times its volume at .
The element's primary industrial applications leverage its catalytic efficacy, particularly in automotive catalytic converters for reducing vehicle emissions, which account for 80-85% of global demand; it is also used in jewelry alloys, electronic components, dental materials, and hydrogen purification membranes.
As one of the rarer PGMs, palladium occurs in low concentrations in and is chiefly produced as a byproduct of and , with major output from and , rendering global supply susceptible to geopolitical disruptions and contributing to historical price volatility.

Properties

Physical and atomic properties

Palladium is a with the symbol Pd and 46. Its is 106.42(1). The ground-state of neutral palladium atoms is [Kr] 4d¹⁰, with term symbol ¹S₀. Palladium is a ductile, malleable solid metal at , exhibiting a silvery-white appearance. It possesses a face-centered cubic . The density of palladium is 12.02 g/cm³ at 20 °C. Its is 1554.9 °C, and the is 2963 °C. Palladium demonstrates high thermal and electrical conductivity, with values of approximately 71.8 W/(m·K) and 9.5 × 10⁶ S/m at , respectively. It is paramagnetic and has a Mohs hardness of 4.75. The element readily absorbs gas, forming a that can contain up to 900 times its own volume of at and .

Isotopes

Palladium (^{46}Pd) occurs naturally as a of six isotopes: ^{102}Pd, ^{104}Pd, ^{105}Pd, ^{106}Pd, ^{108}Pd, and ^{110}Pd. These isotopes constitute the entirety of primordial palladium, with no significant contribution from decay products of heavier elements. The natural isotopic abundances, as determined by , are as follows:
IsotopeMass numberNatural abundance (atom %)
^{102}Pd1021.02
^{104}Pd10411.14
^{105}Pd10522.33
^{106}Pd10627.33
^{108}Pd10826.46
^{110}Pd11011.72
Thirty-three radioactive isotopes of palladium have been synthesized and characterized, spanning mass numbers from 94 to 128, though the range of observed nuclides is typically 96 to 119 for those with measurable half-lives. The longest-lived radioisotope is ^{107}Pd, with a half-life of approximately 6.5 \times 10^6 years, present in natural palladium at trace levels (around 1.25 \times 10^{-5} % abundance) as a primordial remnant from nucleosynthesis. Shorter-lived isotopes decay primarily via beta emission or electron capture, with half-lives ranging from microseconds to days. Notable among the radioactive isotopes is ^{103}Pd, which has a of 16.99 days and emits low-energy X-rays suitable for medical applications; it is produced via of ^{102}Pd or ^{104}Pd and used in sealed radioactive seeds for treatment of and ocular tumors. Another isotope, ^{103m}Pd (metastable), has a of about 17 days but is less commonly referenced in natural contexts due to its artificial production. Isotopic enrichment techniques, such as those using salts or metal powders, enable separation for and , with commercial availability for stable isotopes like ^{102}Pd at enrichments up to 78%.

Occurrence and Production

Natural occurrence


Palladium occurs in the at an average concentration of 0.015 parts per million by weight, making it one of the rarer elements among the platinum-group metals (PGMs). This scarcity reflects its siderophile nature, with much of the planetary inventory concentrated in during Earth's differentiation, leaving only trace amounts in the crust. It is seldom found in native form but has been identified as uncombined nuggets or grains, typically alloyed with , , or , in placer deposits such as those in and the Ural Mountains of . Most palladium, however, resides in primary magmatic deposits within minerals, including braggite ((Pd,Pt,Fe,Ni)S) and cooperite (PtS, with palladium substitution), often disseminated in or as microscopic inclusions in base-metal sulfides like and . These occurrences are linked to large-scale mafic-ultramafic intrusions where incompatible PGMs concentrate via immiscible sulfide liquid segregation during . Economic concentrations are rare, with palladium deposits approximately 73 times less abundant than deposits globally, primarily hosted in layered intrusions such as South Africa's Bushveld Complex and Russia's Norilsk region, as well as ophiolite-related chromitites and nickel-copper systems. In these settings, palladium enrichment correlates with high-grade platinum-group element anomalies, often exceeding 1 gram per in -rich zones.

Extraction and refining processes

Palladium is extracted primarily from ores rich in metals (PGMs), typically as a during and operations. The initial employs open-pit techniques for shallower deposits, as in Russian operations, or underground methods for deeper seams, such as those in . Extracted ore undergoes crushing and milling to produce fine powder, liberating palladium-bearing minerals for subsequent processing. Beneficiation relies on , incorporating sulfhydryl-based collectors, alcohol frothers, and polymer depressants to achieve over 80% PGM recovery into a concentrated fraction. This concentrate is then smelted at high temperatures with silica flux under low oxygen (10⁻¹⁰ to 10⁻⁷ ), directing palladium preferentially into the molten matte with distribution coefficients exceeding 10³. Matte conversion via air-blown processes in reactors removes iron and impurities, yielding blister metals or upgraded matte while minimizing PGM losses. refining follows: is electrorefined in electrolyte, capturing PGMs in anode slime; undergoes leaching, isolating PGMs in solid residue. PGM-rich materials are leached with acids, such as sulfuric-nitric mixtures or , to solubilize palladium and associated metals. Leach solutions undergo impurity removal, followed by selective palladium as diammine dichloropalladium(II) yellow salt or via extraction with organosulfide agents to separate it from other PGMs. The precipitated palladium salt is reduced chemically to metallic sponge, often using reducing agents, and subsequently smelted to yield purified palladium metal exceeding 99.9% purity. This final step transforms the into ingots or other forms suitable for industrial applications.

Major producers and supply dynamics

Russia remains the world's leading palladium producer, with mine output reaching 87 metric tons in 2023 before declining to an estimated 75 metric tons in 2024, attributable to , reduced ore grades, ongoing effects from the Russia-Ukraine conflict, and processing plant outages. The primary mining operations are concentrated in , dominated by PJSC MMC , which accounts for the bulk of Russian output and a significant share of global supply. South Africa ranks second, producing 74.9 metric tons in 2023 and an estimated 72 metric tons in 2024, constrained by falling metal prices, elevated operational costs, labor unrest, and persistent electricity supply interruptions from state utility . Key producers include Anglo American Platinum, Impala Platinum Holdings, and , operating primarily in the Bushveld Complex. Smaller contributors include (15.9 metric tons in 2023; 15 metric tons estimated for 2024), (16.1 metric tons in 2023; 15 metric tons estimated for 2024), and the (10.3 metric tons in 2023 from the Stillwater Complex in ; 8 metric tons estimated for 2024). Global mine production totaled 208 metric tons in 2023, falling to an estimated 190 metric tons in 2024 amid these disruptions.
Country2023 Production (metric tons)2024 Estimated Production (metric tons)
8775
74.972
15.915
16.115
10.38
Other4.24.2
World Total208190
Supply dynamics are characterized by high geographic concentration, with and supplying over 75% of mined palladium, exposing the market to geopolitical risks, sanctions, and infrastructure vulnerabilities. The USGS Mineral Commodity Summaries 2025 does not provide a specific numerical value for global palladium reserves, stating that quantitative information on palladium reserves is not available, but reserves are large and associated with platinum-group metals reserves primarily in South Africa and Russia. Secondary supply from , particularly spent automotive catalytic converters, supplements primary output, with global recovery of palladium and platinum combined estimated at 120 metric tons in 2024. This stream mitigates some supply tightness but remains dependent on end-user availability and economic incentives tied to prices.

Chemical Compounds

Palladium(II) compounds

Palladium(II) compounds contain palladium in the +2 , the most stable and prevalent for the element, arising from its d⁸ electronic configuration that promotes square planar coordination and low-spin complexes. These frequently adopt oligomeric structures, such as dimers or chains, via bridging ligands like or carboxylates, which influences their solubility and reactivity. Pd(II) compounds are sparingly soluble in but often dissolve in donor solvents or acids, forming anionic complexes like [PdX₄]²⁻ (X = ). They serve as versatile precursors in inorganic synthesis and , particularly for carbon-carbon bond formations, due to facile and pathways. Palladium(II) chloride (PdCl₂), with molecular formula Cl₂Pd and molar mass 177.33 g/mol, manifests as a rust-colored or dark brown hygroscopic powder. It exhibits low solubility in water (approximately 0.006 g/100 mL at 20°C) but forms soluble chloro complexes in aqueous HCl, such as [PdCl₄]²⁻. The solid state features polymeric chains in the α-form (layered structure) and discrete clusters in the β-polymorph, both decomposing above 500°C without melting. PdCl₂ acts as a mild oxidizing agent and precursor for other Pd(II) species, including through ligand exchange reactions. Palladium(II) acetate (Pd(OAc)₂, where OAc = CH₃COO⁻) appears as a red-brown crystalline trimer in the solid state, with the formula [Pd₃(OAc)₆] adopting a trinuclear core bridged by ligands. Synthesized via reaction of PdCl₂ with in acetic acid, it yields a product with 224.51 g/mol (monomer basis) and solubility in polar organic solvents like acetone or . This compound is a staple in , facilitating oxidative additions in reactions such as the Heck arylation or as a source for Pd(0) species . Other notable Pd(II) halides include palladium(II) (PdBr₂) and (PdI₂), both dark powders analogous to PdCl₂ in forming bridged polymers and serving catalytic roles, though less soluble and more prone to reduction. Palladium(II) oxide (PdO) exists as a black, amorphous or tetragonal powder, prepared by of Pd(NO₃)₂ at 800°C, and decomposes to elemental Pd above 800°C; it functions in dehydrogenation and CO oxidation processes. Sulfides like PdS occur naturally or synthetically as semiconductors, while and β-diketonate complexes, such as Pd(acac)₂ (acac = acetylacetonate), provide volatile precursors for .

Palladium(0) and other low oxidation states

Palladium(0) denotes compounds in which the palladium atom exhibits a zero formal , typically as square-planar or tetrahedral coordination complexes stabilized by π-acceptor ligands such as tertiary phosphines, olefins, or to achieve 14- or 18-electron configurations. These species are inherently electron-rich and prone to with electrophiles like alkyl or aryl halides, a fundamental step in palladium-catalyzed cross-coupling reactions such as the Heck, , and Negishi processes. Pd(0) complexes are generally air-sensitive and thermally labile without stabilizing ligands, reflecting the metal's preference for d10 in low oxidation states. Prominent examples include tetrakis(triphenylphosphine)palladium(0), Pd(PPh3)4, a coordinatively saturated, 18-electron complex synthesized by reducing palladium(II) chloride with hydrazine in the presence of excess triphenylphosphine, yielding a yellow, crystalline solid that decomposes in air. Another is tris(dibenzylideneacetone)dipalladium(0), [Pd2(dba)3], a dimeric olefin complex prepared via reduction of palladium(II) acetate with dibenzylideneacetone, valued for its solubility and use as a precatalyst often activated by monodentate phosphines. Mononuclear carbonyl complexes like Pd(CO)(PPh3)3 are accessed by treating Pd(PPh3)4 with carbon monoxide under mild conditions, exhibiting stability attributable to the strong π-backbonding from Pd(0) to CO. More specialized Pd(0) species, such as Pd(COD)(DQ) (COD = 1,5-cyclooctadiene; DQ = duroquinone), demonstrate enhanced air stability due to the bidentate olefin and quinone ligands, synthesized by displacing labile ligands from Pd2(dba)3. Palladium(I), an uncommon +1 , manifests primarily in transient intermediates or stabilized dimers rather than mononuclear forms, owing to the odd-electron d9 configuration's tendency toward to Pd(0) and Pd(II). Isolated mononuclear Pd(I) compounds, such as those supported by bulky ligands, have been characterized via , revealing reactivity toward further reduction or oxidation in catalytic cycles. For instance, reduction of Pd(II) precursors with PtBu3 ligands can yield Pd(I) species instead of direct Pd(0), highlighting ligand-dependent pathways in precatalyst activation. These low-valent states underscore palladium's versatility in two-electron processes, with Pd(0) dominating synthetic applications due to its accessibility and reactivity.

Higher oxidation states and organopalladium chemistry

Palladium(IV) fluoride (PdF4) is a stable representative of the +4 , featuring a layered with square-planar PdF4 units linked by fluoride bridges. hexachloropalladate(IV) (K2PdCl6) adopts an octahedral around Pd(IV) and appears as red-brown crystals, synthesized by chlorination of Pd(II) precursors under oxidizing conditions. These Pd(IV) species are more reactive than lower valent analogs, often undergoing facile reduction, as evidenced by calculations showing Pd(IV) centers prone to ligand dissociation and . Palladium(III) remains elusive in mononuclear form without specialized stabilization, with most characterized examples being dinuclear Pd2(III,III) complexes featuring Pd-Pd bonds, such as those supported by or ligands, or rare mononuclear variants using tridentate chelates like tacn (1,4,7-trimethyl-1,4,7-triazacyclononane). Fluoride systems like NaPdF4 provide early evidence of Pd(III) stabilization, though structural confirmation relies on spectroscopic and computational methods due to instability. Organopalladium chemistry centers on Pd-C σ-bonds, enabling key transformations in synthesis via , , and steps. These intermediates drive cross-coupling reactions, such as the Suzuki-Miyaura coupling of arylboronic acids with halides (developed in 1979, yielding biaryls under mild conditions with Pd(PPh3)4 ), the (1983, coupling aryl halides with alkenes to form stilbenes), and (1977, organometallics with halides for stereospecific C-C formation). While classical cycles operate between Pd(0) and Pd(II), higher-valent pathways involving Pd(III) or Pd(IV) organometallics—often generated by two-electron oxidation—facilitate C-H activation and ligand-directed functionalizations, as in directed ortho-metalation or CH activation with hypervalent iodine oxidants. Such Pd(IV) alkyl or aryl complexes, like [Pd(IV)(Me)3(tacn)]+, demonstrate homolysis or direct functionalization, expanding reactivity beyond traditional two-state mechanisms.

Applications

Catalytic uses

Palladium serves as a key component in automotive , where it catalyzes the conversion of toxic exhaust gases from internal engines into less harmful substances. In three-way , palladium oxidizes to and hydrocarbons to and , while also aiding in the reduction of nitrogen oxides to and oxygen. This application accounted for approximately 82% of global palladium consumption in 2023, reflecting its dominance in emissions control systems. Palladium's effectiveness stems from its high catalytic activity at elevated temperatures, often used in combination with and , though formulations with palladium alone have been developed for cost efficiency. Beyond automotive uses, palladium catalyzes industrial oxidation processes, notably the Wacker process, which converts ethylene to acetaldehyde using palladium(II) chloride and copper(II) chloride in aqueous solution under oxygen. Commercialized in 1959 by Wacker Chemie, this process historically produced millions of tons of acetaldehyde annually for acetic acid and other derivatives, though its scale has diminished due to competing technologies like direct ethylene oxidation. The reaction involves electrophilic addition of palladium to the alkene, followed by nucleophilic attack and reductive elimination, with copper regenerating the palladium catalyst. In , palladium enables cross-coupling reactions essential for pharmaceutical and production, forming carbon-carbon and carbon-nitrogen bonds with high selectivity. Reactions such as -Miyaura, Heck-Mizoroki, and Buchwald-Hartwig aminations rely on palladium complexes to couple aryl or vinyl halides with organoboranes, alkenes, or amines, respectively, under mild conditions. These transformations, recognized by the 2010 for variants developed by , Heck, and Negishi, facilitate the synthesis of complex molecules in industry, with palladium loadings typically in the parts-per-million range for efficiency. Palladium also supports reactions, often as (Pd/C), for reducing alkenes, alkynes, and nitro groups in fine chemicals manufacturing. Overall, catalytic applications drive the majority of palladium demand, with automotive uses comprising the bulk, supplemented by chemical processes that leverage palladium's ability to facilitate and reactions at low loadings due to its favorable electronic properties and tunability. Global palladium demand for remained stable in at around 9.33 million ounces, underscoring its irreplaceable role despite substitution efforts in response to supply constraints.

Electronics and technology

Palladium's high electrical conductivity, resistance, and stability make it valuable in electronic components, where it serves as a material for connectors and circuit elements to ensure reliable performance under varying conditions. In such as smartphones and computers, palladium alloys facilitate energy storage and conduction in multilayer ceramic capacitors (MLCCs) and other devices, contributing to compact, high-performance designs. A primary application is in MLCCs, where palladium forms part of the internal electrodes, particularly in high-reliability variants used in and equipment. These capacitors leverage palladium's ability to withstand oxidation and maintain in demanding environments, though newer formulations have shifted toward electrodes to reduce costs since the commercialization milestone. Waste MLCCs can yield significant palladium quantities, with recovery processes extracting up to 50 grams per in high-content scrap, underscoring its embedded prevalence in obsolete electronics. Palladium is also electroplated onto electrical contacts and connectors for its low , fretting wear resistance, and , often as a substitute in printed circuit boards (PCBs) and lead frames. Palladium-nickel alloys, for instance, endure high mating cycles and harsh conditions without tarnishing, as seen in applications requiring thousands of insertions, such as hardware. This usage extends to coating electrodes in broader electronic products, enhancing durability against environmental stressors like humidity and temperature fluctuations.

Hydrogen storage and energy applications

Palladium exhibits exceptional absorption properties, capable of occluding up to approximately 900 volumes of gas per volume of metal at , forming interstitial (PdH_x) where x typically reaches 0.6–0.7 in the β-phase. This reversible process occurs at ambient conditions without requiring elevated pressures or cryogenic temperatures, driven by dissociation on the palladium surface followed by atomic into the face-centered cubic lattice. The from α (low H content) to β (high H content) enables high volumetric storage density, around 150–200 kg H₂/m³, though gravimetric capacity remains limited at about 0.6 wt% for pure palladium due to the metal's . In applications, palladium's capacity supports niche uses such as portable power sources and electrochemical cells, where nanoparticles or alloys enhance performance; for instance, Pd-Pt solid solutions with 8–21 at% Pt achieve higher storage than pure Pd by stabilizing the hydride phase and reducing hysteresis. However, practical limitations including hydrogen-induced embrittlement from lattice expansion (up to 10% volume increase in β-phase) and high material costs restrict scalability for large-scale vehicular storage, prompting research into thin films, scaffolds, or composites like Pd-decorated oxide, which have demonstrated up to 6.62 wt% uptake under near-ambient conditions. Electrochemical charging in Pd-based electrodes has yielded capacities approaching 1750 mAh/g, equivalent to substantial equivalents for battery-like . Beyond storage, palladium enables energy applications through selective hydrogen permeation membranes, often alloyed with silver (e.g., Pd-23% Ag) to improve durability and flux rates exceeding 0.5 mol /·s at –°C, purifying streams for feeds by exploiting atomic differences across the metal foil. In proton exchange membrane s (PEMFCs), palladium serves as an alternative cathode catalyst to , with Pd nanoparticles offering comparable oxygen reduction activity while tolerating impurities like CO; studies show Pd-Co alloys maintaining performance over 1000 hours under operational loads. Additionally, palladium's sensitivity to supports systems, including sensors detecting leaks via resistance changes in Pd thin films, critical for handling compressed H₂ at pressures up to 700 bar. Despite these roles, palladium's scarcity and price volatility—peaking above $3000/oz in —pose challenges to widespread adoption in a .

Medical and pharmaceutical uses

Palladium alloys are extensively employed in for crowns, bridges, and other prosthetic restorations due to their durability, corrosion resistance, and cost-effectiveness as alternatives to gold-based materials. These alloys, often combining palladium with silver or other metals, exhibit high strength and hardness, enabling their use in high-stress oral environments, with palladium content typically ranging from minor additives to major constituents exceeding 50% in Pd-based formulations. While generally biocompatible, palladium in dental alloys has raised concerns regarding potential allergic reactions, though clinical rates remain low compared to other metals like . In , palladium-103 (¹⁰³Pd) isotopes serve as radioactive seeds for , particularly in treating early-stage by delivering localized low-energy gamma radiation directly to tumor tissue. These seeds, implanted via minimally invasive procedures, provide precise with a of approximately 17 days, minimizing exposure to surrounding healthy tissues and achieving high local control rates in low-risk cases. Palladium-103 has also been explored for applications, though remains the primary indication. Palladium compounds contribute to pharmaceutical manufacturing through catalysis in cross-coupling reactions, such as Suzuki-Miyaura couplings, which facilitate the synthesis of complex molecules, though residual palladium levels in final products are rigorously controlled to below 10 ppm to avoid toxicity risks. Emerging research investigates palladium(II) complexes and nanoparticles for direct therapeutic roles, including antitumor agents with profiles akin to but less toxic than drugs, and as carriers for or photothermal ablation in cancer models. These applications, however, remain preclinical, with palladium nanostructures showing promise in and activation but lacking widespread clinical validation.

Other industrial applications

Palladium alloys are widely employed in for fabricating crowns, bridges, inlays, and restorations owing to the metal's high , resistance, and mechanical strength. These alloys typically incorporate palladium with silver, , , or to tailor properties for specific applications, such as long-span bridges or veneering. Since the late 1970s, palladium has served as a core component in global crown and bridge alloys, often comprising a substantial portion alongside silver to reduce costs while maintaining performance. In dental amalgams, trace amounts of palladium—around 0.5%—enhance durability, reduce , and improve luster. In jewelry manufacturing, palladium features in alloys for rings, necklaces, and other items, valued for its lustrous white appearance, properties, and resistance to tarnishing. Palladium-silver alloys constitute a significant share of fine jewelry production, offering an alternative to with similar aesthetics at lower density. It is also alloyed with gold to produce 18-karat white gold, replacing to avoid skin sensitization while preserving hardness and color stability. Palladium's role extends to minting investment products, including coins and bars, where its purity and malleability facilitate precise stamping and anti-counterfeiting features. Examples include commemorative coins like Russia's 25-ruble palladium pieces issued in , leveraging the metal's intrinsic value and workability.[float-right]

Health and Environmental Impacts

Toxicity and biological effects

Palladium metal demonstrates relatively low , with values exceeding standard measurement thresholds in conventional assays. However, palladium compounds, particularly salts, exhibit irritant properties, causing and eye upon contact. The primary health risk stems from its potent sensitizing capacity, where minute exposures—often below 1 μg/cm²—trigger reactions in predisposed individuals, frequently those already sensitized to . Allergic contact dermatitis represents the most documented biological effect, manifesting as eczematous rashes at sites of exposure such as earlobes from palladium-alloyed jewelry or from dental prostheses. Clinical patch testing in cohorts reveals palladium sensitivity rates of 3-10%, with higher concordance in nickel-allergic patients due to or co-exposure in alloys. Systemic dissemination of the can provoke generalized or exacerbate respiratory symptoms in severe cases, though such outcomes remain rare outside occupational contexts. Inhalation of palladium dust or fumes, relevant to refining and catalytic manufacturing, induces irritation and potential pneumoconiosis-like in chronic animal models, with palladium accumulating preferentially in tissue. Nanoparticulate forms, emerging in advanced applications, penetrate alveolar barriers more readily, eliciting , mitochondrial dysfunction, and inflammatory cytokine release in cell lines, potentially arresting cell cycles and promoting . inhalation studies confirm deposition without overt carcinogenicity, but highlight altered toxicological profiles when co-exposed with environmental pollutants like cigarette smoke. Biological uptake of palladium across species underscores its high among platinum-group metals, facilitating tissue accumulation via chloride complex formation in physiological fluids, which may impair renal or cardiac function at elevated systemic levels. Experimental administrations reveal ancillary effects including , fever, and localized , though human data on or parenteral routes derive mainly from therapeutic trials with limited sample sizes. No conclusive evidence links palladium to or oncogenesis , despite indications of DNA interaction under reductive conditions.

Occupational and environmental precautions

Occupational handling of palladium requires protective measures to mitigate risks from dust, fumes, or contact with powders and compounds, which can cause skin and eye irritation or respiratory issues. Workers should wear protective gloves, clothing, eye protection, and face shields when dealing with palladium powders or during processes generating dust or aerosols. Adequate ventilation, including local exhaust systems, is essential to maintain exposures below applicable limits and prevent inhalation. No specific permissible exposure limit (PEL) has been established by OSHA for palladium metal, but general industrial hygiene practices recommend monitoring airborne concentrations, particularly for soluble palladium salts that may pose higher toxicity risks. High-risk occupations include , dental technician work, and , where exposure to palladium dust or vapors may lead to reactions, such as or urticaria, especially among individuals with allergies. Contaminated work clothing should not be taken home and must be laundered separately to avoid secondary exposure. After handling, thorough washing of exposed skin is advised to prevent irritation. For environmental precautions, spills of palladium-containing materials should be contained using absorbent materials, and contaminated areas flushed with only after collection to avoid runoff into waterways. Releases into drains, , or must be prevented, as palladium can persist in the environment and potentially bioaccumulate in aquatic organisms, though on long-term ecological impacts remain limited. Waste disposal should follow local regulations, with palladium residues treated as hazardous to minimize environmental release, often through or specialized .

Mining and production environmental concerns

Palladium mining, predominantly conducted in and which together supply approximately 80% of global output, generates substantial environmental pressures due to the ore's low concentrations requiring extensive extraction and processing. These activities involve deep underground operations in South Africa's and both underground and open-pit methods in Russia's region, leading to and soil disturbance across thousands of hectares. In , platinum group metal (PGM) mining, including palladium, is highly water-intensive, with operations consuming millions of cubic meters annually amid regional scarcity exacerbated by droughts and competing agricultural demands. Tailings from beneficiation and processes often contain such as , , and platinum group elements, which can leach into and rivers, contributing to risks that lower levels and mobilize toxins harmful to aquatic ecosystems. Energy demands for milling, , and account for a notable share of national usage, translating to elevated from coal-dependent power grids, with PGM production emitting up to several tons of CO2 equivalent per kilogram of metal recovered. Russia's Norilsk operations, dominated by Nornickel, have historically released around 1.9 million metric tons of annually from ores rich in , , and , fostering that damages vegetation and contaminates soils with like and lead over vast areas. These emissions, combined with particulate matter, have rendered one of the world's most polluted sites, correlating with elevated respiratory diseases among local populations and in sensitive ecosystems. Weaker enforcement of environmental standards in relative to enables lower production costs but perpetuates higher pollution intensities, though Nornickel has invested over $4 billion since 2019 to capture , achieving a 24% emissions reduction by 2024. Overall, the low yield of palladium—often 2-6 grams per ton of ore—amplifies and waste generation, with volumes posing long-term stability risks from dam failures, as seen in broader contexts. Recycling from autocatalysts offers a partial by reducing primary needs, but current rates remain below 30% globally, underscoring the persistence of these upstream impacts.

Historical Development

Discovery and early characterization

Palladium was discovered by English chemist in 1803 during his efforts to refine crude platinum ore sourced from . Wollaston isolated the element from the aqua regia-soluble residues of the ore, which contained impurities not precipitating with . He processed these residues to obtain a rose-colored solution, from which palladium was precipitated as a metallic powder and subsequently fused into ingots. In February 1803, Wollaston anonymously advertised samples of the new metal, dubbing it "new silver," for sale to researchers, marking its initial public introduction. The entire stock was purchased by Irish chemist Richard Chenevix, who analyzed it and contended that palladium was not a new element but a compound , possibly involving mercury, , and . This sparked a scientific controversy, with Chenevix publishing his findings in the Royal Society's Philosophical Transactions, challenging its elemental status. Wollaston withheld his identity during the dispute but revealed himself in 1805, publishing a detailed account in Philosophical Transactions that included reproducible isolation methods and evidence of its indivisibility, affirming palladium's status as a distinct element. He named the element palladium in reference to the asteroid Pallas, discovered in 1802 and named after the Greek goddess of wisdom, reflecting the contemporaneous astronomical event. Early characterizations by Wollaston described palladium as a lustrous, silvery-white metal with properties intermediate between platinum and mercury, including high malleability, , and a specific of approximately 11.8 to 12. It fused at a , formed alloys with other metals, and resisted many acids, though soluble in and under certain conditions. These observations, supported by analytical experiments demonstrating consistent composition across samples, established its fundamental metallic nature distinct from known elements.

Commercial exploitation and key milestones

![Platinum-palladium ore from Stillwater mine][float-right] Commercial exploitation of palladium began shortly after its discovery, with selling small quantities to jewelers as a substitute in the early 1800s, though supply constraints limited its viability. Early industrial applications emerged in the and , including dental alloys for corrosion resistance and electrical contacts for their conductivity and durability. Deposits in South Africa's Bushveld Complex and facilitated initial scaling of production during this period, primarily as a byproduct of and . The pivotal milestone in palladium's commercial history occurred in the 1970s, when stringent automobile emission regulations, such as the U.S. Clean Air Act amendments of 1970, mandated catalytic converters, where palladium's catalytic properties proved essential for oxidizing hydrocarbons and in gasoline engines. Initially sharing roles with and , palladium's use expanded in the mid-1990s due to its effectiveness in higher-temperature environments and cost advantages, driving demand growth as global standards tightened. By 1989, automotive catalysts had become the dominant application, accounting for over 80% of consumption by the 2010s. Key production developments include the establishment of large-scale mining in Russia's region and South Africa's belt, with global output reaching approximately 210,000 kilograms annually by 2022, led by (88,000 kg) and (around 80,000 kg). Recycling from spent catalysts emerged as a significant , contributing about 25-30% of supply in recent decades, underscoring the metal's entrenched industrial role. These milestones transformed palladium from a niche to a critical , with automotive demand propelling market value despite geopolitical supply risks.

Economic and Geopolitical Dimensions

Palladium prices have exhibited significant volatility over the past decade, peaking above $3,000 per troy in early 2020 before declining to around $1,220 per troy in mid-2024, driven by reduced automotive demand amid the shift to electric vehicles and substitution with in catalytic converters. As of February 15, 2026, the spot price stood at $1,678.00 USD per troy ounce (bid) with an ask price of $1,718.00 USD per troy ounce, showing a +$78.00 (+4.88%) change; other sources reported similar values around $1,700–$1,722 USD per ounce, including $1,717.91 from JM Bullion and $1,722.00 for March 2026 futures on CME, reflecting recent gains amid geopolitical tensions and supply constraints from major producers like . Year-to-date through October 2025, prices have risen approximately 19%, influenced by persistent deficits estimated at 3% of demand, or 300,000 , due to mine supply contractions and steady industrial usage. Demand for palladium remains dominated by the automotive sector, accounting for over 80% of global consumption primarily in gasoline-engine catalytic converters, though this is eroding with adoption and regulatory pushes for lower emissions standards. Emerging applications in purification and provide offsets, but forecasts indicate a potential market surplus of 897,000 ounces by late 2025 if substitution accelerates, contrasting with earlier deficit projections from analysts like . Supply is concentrated, with contributing about 40% of mined output, exposing the market to sanctions and export restrictions that have tightened availability since 2022. Investors consider palladium for portfolio diversification due to its industrial utility and low with equities, accessible via physical bars—though retail availability of products such as 1 oz bars and coins remains limited at many dealers compared to gold or silver, contributing to tighter supply for individual investors seeking physical holdings—exchange-traded funds like the Aberdeen Standard Physical Palladium ETF, or futures contracts on exchanges such as the NYMEX. However, high volatility—evident in 2020-2025 swings exceeding 50% annually—poses risks, amplified by automotive demand uncertainty and geopolitical supply disruptions. Physical holdings require secure storage and , adding costs, while ETFs face tracking errors and regulatory changes; analysts recommend limiting exposure to 5-10% of a precious metals allocation given palladium's narrower demand profile compared to or . Long-term forecasts vary, with some predicting stabilization around $1,400-1,700 per ounce through 2026 if deficits persist, though proliferation could pressure prices downward absent new growth.

Supply chain vulnerabilities and geopolitical influences

The global palladium supply chain is characterized by extreme geographic concentration, with and together accounting for approximately 75-80% of annual mine production. In 2023, produced 81 metric tons, primarily from PJSC MMC Norilsk Nickel's operations in , while yielded 78 metric tons, mainly as a byproduct of platinum mining in the Bushveld Complex. and each contributed around 15-19 metric tons, underscoring the dominance of the top two producers and exposing downstream industries—such as automotive manufacturing—to disruptions from localized events like strikes, power failures, or export restrictions. This reliance amplifies vulnerabilities, as alternative sources lack the scale to rapidly offset shortfalls, with global output hovering around 200-210 metric tons annually.
CountryProduction (metric tons, 2023)Approximate Global Share (%)
8140
7838
199
157
Others~106
Russia's pivotal role introduces acute geopolitical risks, exacerbated by the 2022 invasion of and ensuing Western sanctions. Although palladium exports faced fewer direct curbs than commodities like or aluminum, U.S. imports from surged 34% from 2021 to 2024, comprising 40% of total U.S. palladium inflows despite diversification mandates. In October 2024, prospective U.S. trade actions targeting Russian palladium—aimed at bolstering domestic producers like those in —sparked market fears of tightened supply, driving prices above $1,150 per ounce amid potential export bans or tariffs. The partially mitigated risks by redirecting imports to , , and post-invasion, reducing Russian unwrought palladium inflows, yet Nickel's state-influenced operations retain leverage over global pricing and availability. Analysts note that full sanctions could eliminate 40% of supply overnight, cascading into automotive sector shortages given palladium's irreplaceable role in gasoline-engine emissions control. South Africa's contributions, while substantial, are hampered by chronic infrastructure and socioeconomic vulnerabilities that compound supply instability. Persistent electricity shortages from state utility have repeatedly curtailed mining output, with blackouts in 2023-2024 forcing intermittent shutdowns at key palladium-bearing platinum mines. Labor unrest, including wildcat strikes in the platinum group metals sector, further erodes reliability, as seen in production dips during wage disputes. Weaker governance and stringent environmental regulations—enforced amid and tailings management challenges—elevate operational costs and delay expansions, positioning South Africa as a secondary vector despite lower geopolitical tensions than . These factors have strained global palladium flows, prompting automakers and refiners to explore and substitution, though primary remains indispensable for meeting demand projected at 250-300 metric tons annually by 2030.

Price volatility drivers and forecasts

Palladium prices experience significant volatility due to supply concentration in and , which account for over 80% of global mine production, exposing the market to regional disruptions such as labor strikes, power shortages, and export restrictions. , producing approximately 40% of the world's palladium, faces ongoing Western sanctions related to the invasion of , leading to supply shocks that have driven recent price surges, including a 26% rise in October 2025 to around $1,500 per ounce. Demand volatility stems largely from the automotive sector, which consumes about 80% of palladium in catalytic converters to meet emission standards, linking prices to global vehicle sales, diesel-to-gasoline engine shifts, and the gradual adoption of electric vehicles that bypass catalytic needs. Additional factors include speculative investment flows, potential U.S. tariffs on Russian imports, and substitution with cheaper in autocatalysts, which can rapidly alter market balances. As of February 15, 2026, spot prices stood at $1,678.00 USD per troy ounce (bid) with an ask of $1,718.00, showing a +4.88% change, with corroborating values around $1,700–$1,722 USD per ounce amid these pressures. Market forecasts for 2025 diverge, with projecting an average of $1,100 per ounce based on expected supply recovery and softening automotive demand, while CoinPriceForecast anticipates $1,700 by year-end due to persistent deficits. The LBMA analyst survey highlights downside risks from potential oversupply and weak industrial uptake, forecasting subdued prices overall. Extending to , projections range from $1,135 per ounce () to $2,000 (CoinPriceForecast), contingent on geopolitical stabilization, total supply dipping to 9.3 million ounces in 2025 before rebounding, and demand declining to 9.42 million ounces.

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