View source for Cerium

{{Distinguish|text=[[caesium]] (also spelled "cesium") or [[curium]]}}
{{Use American English|date=December 2020}}
{{Infobox cerium}}
'''Cerium''' is a [[chemical element]]; it has [[Chemical symbol|symbol]] '''Ce''' and [[atomic number]] 58. It is a [[hardness|soft]], [[ductile]], and silvery-white [[metal]] that tarnishes when exposed to air. Cerium is the second element in the [[lanthanide]] series, and while it often shows the [[oxidation state]] of +3 characteristic of the series, it also has a stable +4 state that does not oxidize water. It is considered one of the [[rare-earth element]]s. Cerium has no known biological role in humans but is not particularly toxic, except with intense or continued exposure.

Despite always occurring in combination with the other rare-earth elements in minerals such as those of the [[monazite]] and [[bastnäsite]] groups, cerium is easy to extract from its ores, as it can be distinguished among the lanthanides by its unique ability to be oxidized to the +4 state in aqueous solution. It is the most common of the lanthanides, followed by [[neodymium]], [[lanthanum]], and [[praseodymium]]. Its estimated [[abundance of elements in Earth's crust|abundance in the Earth's crust]] is 68&nbsp;[[parts per million|ppm]].

Cerium was the first of the lanthanides to be discovered, in [[Bastnäs]], Sweden. It was discovered by [[Jöns Jakob Berzelius]] and [[Wilhelm Hisinger]] in 1803, and independently by [[Martin Heinrich Klaproth]] in Germany in the same year. In 1839 [[Carl Gustaf Mosander]] separated cerium(III) oxide from other rare earths, and in 1875 [[William Francis Hillebrand]] became the first to isolate the metal. Today, cerium and its compounds have a variety of uses: for example, [[cerium(IV) oxide]] is used to polish glass and is an important part of [[catalytic converter]]s. Cerium metal is used in [[ferrocerium]] lighters for its [[pyrophoric]] properties. Cerium-doped [[Yttrium aluminium garnet|YAG]] phosphor is used in conjunction with blue [[light-emitting diode]]s to produce white light in most commercial white LED light sources.

== Characteristics ==

=== Physical ===
Cerium is the second element of the [[lanthanide]] series. In the periodic table, it appears between the lanthanides [[lanthanum]] to its left and [[praseodymium]] to its right, and above the [[actinide]] [[thorium]]. It is a [[ductile]] metal with a hardness similar to that of [[silver]].<ref name="CRC">{{RubberBible86th}}</ref> Its 58 electrons are arranged in the [[electron configuration|configuration]] [Xe]4f{{sup|1}}5d{{sup|1}}6s{{sup|2}}, of which the four outer electrons are [[valence electron]]s.{{sfn|Greenwood|Earnshaw|1997|pages=1232–5}} The 4f, 5d, and 6s energy levels are very close to each other, and the transfer of one electron to the 5d shell is due to strong interelectronic repulsion in the compact 4f shell. This effect is overwhelmed when the atom is positively ionised; thus Ce{{sup|2+}} on its own has instead the regular configuration [Xe]4f{{sup|2}}, although in some solid solutions it may be [Xe]4f{{sup|1}}5d{{sup|1}}.<ref>{{cite journal |last1=Jørgensen |first1=Christian |date=1973 |title=The Loose Connection between Electron Configuration and the Chemical Behavior of the Heavy Elements (Transuranics) |journal=Angewandte Chemie International Edition |volume=12 |issue=1 |pages=12–19 |doi=10.1002/anie.197300121}}</ref> Most lanthanides can use only three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium is an exception because of the stability of the empty f-shell in Ce{{sup|4+}} and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until [[neodymium]] to allow the removal of the fourth valence electron by chemical means.<ref name="Holleman">{{Holleman&Wiberg|pages=1703–5}}</ref>

Cerium has a variable [[electronic structure]]. The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalized in the metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valence states. For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. In its high pressure phase (α-Cerium), the 4f electrons are also delocalized and itinerate, as opposed to localized 4f electrons in low pressure phase (γ-Cerium).<ref>{{Cite journal |last1=Wills |first1=J. M. |last2=Eriksson |first2=Olle |last3=Boring |first3=A. M. |date=1991-10-14 |title=Theoretical studies of the high pressure phases in cerium |url=https://link.aps.org/doi/10.1103/PhysRevLett.67.2215 |journal=Physical Review Letters |language=en |volume=67 |issue=16 |pages=2215–2218 |doi=10.1103/PhysRevLett.67.2215 |pmid=10044368 |bibcode=1991PhRvL..67.2215W |issn=0031-9007|url-access=subscription }}</ref> It appears that the valence changes from about 3 to 4 when it is cooled or compressed.<ref>{{cite journal|last1=Johansson|first1=Börje|last2=Luo|first2=Wei|last3=Li|first3=Sa|last4=Ahuja|first4=Rajeev|date=17 September 2014|title=Cerium; Crystal Structure and Position in The Periodic Table|journal=Scientific Reports|volume=4|pages=6398|bibcode=2014NatSR...4.6398J|doi=10.1038/srep06398|pmc=4165975|pmid=25227991}}</ref>

===Chemical properties of the element===
Like the other lanthanides, cerium metal is a good [[reducing agent]], having [[Reduction potential#Standard reduction potential|standard reduction potential]] of ''E''{{sup|⦵}}&nbsp;=&nbsp;−2.34&nbsp;V for the Ce{{sup|3+}}/Ce couple.{{sfn|Greenwood|Earnshaw|1997|pages=1244-8}} It tarnishes in air, forming a [[Passivation (chemistry)|passivating]] oxide layer like [[iron]] rust. A centimeter-sized sample of cerium metal corrodes completely in about a year. More dramatically, metallic cerium can be highly [[pyrophoric]]:<ref name="The Elements">{{cite book |last=Gray |first=Theodore |title=The Elements |date=2010 |isbn=978-1-57912-895-1 |publisher=Black Dog & Leventhal Pub}}</ref> 
:{{chem2|Ce + O2 → CeO2}}
Being highly [[Electronegativity|electropositive]], cerium reacts with water. The reaction is slow with cold water but speeds up with increasing temperature, producing cerium(III) hydroxide and hydrogen gas:<ref name="webelements">{{cite web| url =https://www.webelements.com/cerium/chemistry.html| title =Chemical reactions of Cerium| publisher=Webelements| access-date=9 July 2016}}</ref>
:{{chem2|2 Ce + 6 H2O → 2 Ce(OH)3 + 3 H2}}

=== Allotropes ===
[[File:Cerium phase diagram.jpg|Phase diagram of cerium|upright=1.35|center|thumb|alt=Cerium phase diagram]]

Four [[allotropy|allotropic]] forms of cerium are known to exist at standard pressure and are given the common labels of α to δ:<ref name="KGP">{{Cite journal | doi = 10.1016/0022-0248(74)90098-0| title = Preparation of single phase β and α cerium samples for low temperature measurements| journal = Journal of Crystal Growth| volume = 22| issue = 3| pages = 225–229| year = 1974| last1 = Koskimaki | first1 = D. C. | last2 = Gschneidner | first2 = K. A. | last3 = Panousis | first3 = N. T. |bibcode = 1974JCrGr..22..225K }}</ref>
* The high-temperature form, δ-cerium, has a bcc ([[body-centered cubic]]) crystal structure and exists above 726&nbsp;°C.
* The stable form below 726&nbsp;°C to approximately room temperature is γ-cerium, with an fcc ([[face-centered cubic]]) crystal structure.
* The DHCP (double [[Hexagonal lattice system|hexagonal close-packed]]) form β-cerium is the equilibrium structure approximately from room temperature to −150&nbsp;°C.
* The fcc form α-cerium is stable below about −150&nbsp;°C; it has a density of 8.16&nbsp;g/cm{{sup|3}}.
* Other solid phases occurring only at high pressures are shown on the phase diagram.
* Both γ and β forms are quite stable at room temperature, although the equilibrium transformation temperature is estimated at 75&nbsp;°C.<ref name="KGP" />

At lower temperatures the behavior of cerium is complicated by the slow rates of transformation. Transformation temperatures are subject to substantial hysteresis and values quoted here are approximate. Upon cooling below −15&nbsp;°C, γ-cerium starts to change to β-cerium, but the transformation involves a volume increase and, as more β forms, the internal stresses build up and suppress further transformation.<ref name="KGP" /> Cooling below approximately −160&nbsp;°C will start formation of α-cerium but this is only from remaining γ-cerium. β-cerium does not significantly transform to α-cerium except in the presence of stress or deformation.<ref name="KGP" /> At atmospheric pressure, liquid cerium is more dense than its solid form at the melting
point.<ref name="CRC" /><ref>{{cite journal|doi=10.1103/PhysRevB.19.5746|title=Lattice and spin dynamics of γ-Ce|date=1979|author=Stassis, C.|journal=Physical Review B|volume=19|issue=11|pages=5746–5753|last2=Gould|first2=T.|last3=McMasters|first3=O.|last4=Gschneidner|first4=K.|last5=Nicklow|first5=R.|bibcode = 1979PhRvB..19.5746S }}</ref><ref name="patnaik">{{cite book | last =Patnaik | first =Pradyot | date = 2003 | title =Handbook of Inorganic Chemical Compounds | publisher = McGraw-Hill | pages = 199–200| isbn =978-0-07-049439-8 | url= https://books.google.com/books?id=Xqj-TTzkvTEC&pg=PA200}}</ref>

=== Isotopes ===
{{Main|Isotopes of cerium}}
Naturally occurring cerium is made up of four isotopes: {{sup|136}}Ce (0.19%), {{sup|138}}Ce (0.25%), {{sup|140}}Ce (88.4%), and {{sup|142}}Ce (11.1%). All four are [[observationally stable]], though the light isotopes {{sup|136}}Ce and {{sup|138}}Ce are theoretically expected to undergo [[double electron capture]] to isotopes of [[barium]], and the heaviest isotope <sup>142</sup>Ce is expected to undergo double beta decay to <sup>142</sup>Nd or alpha decay to <sup>138</sup>Ba. Thus, <sup>140</sup>Ce is the only theoretically [[stable isotope]]. None of these decay modes have yet been observed, though the double beta decay of <sup>136</sup>Ce, <sup>138</sup>Ce, and <sup>142</sup>Ce have been experimentally searched for. The current experimental limits for their half-lives are:{{NUBASE2016|ref}}
:<sup>136</sup>Ce: &gt;3.8×10<sup>16</sup> y
:<sup>138</sup>Ce: &gt;5.7×10<sup>16</sup> y
:<sup>142</sup>Ce: &gt;5.0×10<sup>16</sup> y

All other cerium isotopes are [[synthetic radioisotope|synthetic]] and [[radioactivity|radioactive]]. The most stable of them are <sup>144</sup>Ce with a half-life of 284.9&nbsp;days, <sup>139</sup>Ce with a half-life of 137.6&nbsp;days, and <sup>141</sup>Ce with a half-life of 32.5&nbsp;days. All other radioactive cerium isotopes have half-lives under four days, and most of them have half-lives under ten minutes.{{NUBASE2016|ref}} The isotopes between <sup>140</sup>Ce and <sup>144</sup>Ce inclusive occur as [[fission product]]s of [[uranium]].{{NUBASE2016|ref}} The primary decay mode of the isotopes lighter than <sup>140</sup>Ce is [[beta plus decay|inverse beta decay]] or [[electron capture]] to [[isotopes of lanthanum]], while that of the heavier isotopes is [[beta decay]] to [[isotopes of praseodymium]].{{NUBASE2016|ref}} Some [[isotopes of neodymium]] can [[alpha decay]] or are predicted to decay to isotopes of cerium.<ref name="rare_decays">{{cite journal |last1=Belli |first1=P. |last2=Bernabei |first2=R. |last3=Danevich |first3=F. A. |last4=Incicchitti |first4=A. |last5=Tretyak |first5=V. I. |title=Experimental searches for rare alpha and beta decays |date=2019 |journal=[[European Physical Journal A]] |volume=55 |number=140 |pages=4–6 <!--data table--> |doi=10.1140/epja/i2019-12823-2|arxiv=1908.11458 |bibcode=2019EPJA...55..140B |s2cid=201664098 }}</ref>

The rarity of the proton-rich <sup>136</sup>Ce and <sup>138</sup>Ce is explained by the fact that they cannot be made in the most common processes of [[stellar nucleosynthesis]] for elements beyond iron, the [[s-process]] (slow [[neutron capture]]) and the [[r-process]] (rapid neutron capture). This is so because they are bypassed by the reaction flow of the s-process, and the r-process nuclides are blocked from decaying to them by more neutron-rich stable nuclides. Such nuclei are called [[p-nuclei]], and their origin is not yet well understood: some speculated mechanisms for their formation include [[proton capture]] as well as [[photodisintegration]].<ref name="Cameron">{{cite journal | last1 = Cameron |first1 = A. G. W. | year = 1973 | title = Abundance of the Elements in the Solar System | url = https://pubs.giss.nasa.gov/docs/1973/1973_Cameron_ca06310p.pdf | journal = Space Science Reviews | volume = 15 |issue = 1 | pages = 121–146 | doi = 10.1007/BF00172440 | bibcode = 1973SSRv...15..121C |s2cid = 120201972 }}</ref> <sup>140</sup>Ce is the most common isotope of cerium, as it can be produced in both the s- and r-processes, while <sup>142</sup>Ce can only be produced in the r-process. Another reason for the abundance of <sup>140</sup>Ce is that it is a [[magic nucleus]], having a closed neutron shell (it has 82 neutrons), and hence it has a very low [[cross section (physics)|cross section]] towards further neutron capture. Although its proton number of 58 is not magic, it is granted additional stability, as its eight additional protons past the magic number 50 enter and complete the 1g{{sub|7/2}} proton orbital.<ref name="Cameron" /> The abundances of the cerium isotopes may differ very slightly in natural sources, because {{sup|138}}Ce and {{sup|140}}Ce are the daughters of the long-lived [[primordial radionuclide]]s {{sup|138}}La and {{sup|144}}Nd, respectively.{{NUBASE2016|ref}}

== Compounds ==
Cerium exists in two main oxidation states, Ce(III) and Ce(IV).  This pair of adjacent oxidation states dominates several aspects of the chemistry of this element. Cerium(IV) aqueous solutions may be prepared by reacting cerium(III) solutions with the strong oxidizing agents [[peroxodisulfate]] or [[bismuthate]]. The value of ''E''{{sup|⦵}}(Ce{{sup|4+}}/Ce{{sup|3+}}) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72&nbsp;V is representative. Cerium is the only lanthanide which has important aqueous and coordination chemistry in the +4 oxidation state.{{sfn|Greenwood|Earnshaw|1997|pages=1244-8}}

===Halides===
Cerium forms all four trihalides CeX{{sub|3}} (X = F, Cl, Br, I) usually by reaction of the oxides with the hydrogen halides. The anhydrous halides are pale-colored, paramagnetic, hygroscopic solids.  Upon hydration, the trihalides convert to complexes containing aquo complexes [Ce(H{{sub|2}}O){{sub|8-9}}]{{sup|3+}}. Unlike most lanthanides, Ce forms a tetrafluoride, a white solid.  It also forms a bronze-colored diiodide, which has metallic properties.{{sfn|Greenwood|Earnshaw|1997|pages=1240-2}} Aside from the binary halide phases, a number of anionic halide complexes are known. The fluoride gives the Ce(IV) derivatives {{chem2|CeF8(4-)}} and {{chem2|CeF6(2-)}}.  The chloride gives the orange {{chem2|CeCl6(2-)}}.{{sfn|Greenwood|Earnshaw|1997|pages=1244-8}}

===Oxides and chalcogenides===
[[Cerium(IV) oxide]] ("ceria") has the [[fluorite]] structure, similarly to the dioxides of praseodymium and [[terbium]].  Ceria is a [[nonstoichiometric compound]], meaning that the real formula is CeO{{sub|2−x}}, where x is about 0.2.  Thus, the material is not perfectly described as Ce(IV).  Ceria reduces to [[cerium(III) oxide]] with hydrogen gas.{{sfn|Greenwood|Earnshaw|1997|pages=1238-9}} Many [[nonstoichiometric]] [[chalcogen]]ides are also known, along with the trivalent Ce{{sub|2}}Z{{sub|3}} (Z = [[sulfur|S]], [[selenium|Se]], [[tellurium|Te]]). The monochalcogenides CeZ conduct electricity and would better be formulated as Ce{{sup|3+}}Z{{sup|2−}}e{{sup|−}}. While CeZ{{sub|2}} are known, they are polychalcogenides with cerium(III): cerium(IV) derivatives of S, Se, and Te are unknown.{{sfn|Greenwood|Earnshaw|1997|pages=1238-9}}

===Cerium(IV) complexes===
[[File:Ceric ammonium nitrate.jpg|thumb|right|Ceric ammonium nitrate|alt=Ceric ammonium nitrate]]

The compound [[ceric ammonium nitrate]] (CAN) {{chem2|(NH{{sub|4}}){{sub|2}}[Ce(NO3)6]}} is the most common cerium compound encountered in the laboratory.  The six nitrate ligands bind as [[bidentate ligand]]s. The complex {{chem2|[Ce(NO3)6](2-)}} is 12-coordinate, a high coordination number which emphasizes the large size of the Ce<sup>4+</sup> ion. CAN is a popular oxidant in [[organic synthesis]], both as a stoichiometric reagent<ref>{{cite journal |doi=10.1021/cr068408n|title=Cerium(IV) Ammonium Nitrate: A Versatile Single-Electron Oxidant |year=2007 |last1=Nair |first1=Vijay |last2=Deepthi |first2=Ani |journal=Chemical Reviews |volume=107 |issue=5 |pages=1862–1891 |pmid=17432919 }}</ref> and as a catalyst.<ref name="Sridharan">{{cite journal |doi=10.1021/cr100004p|title=Cerium(IV) Ammonium Nitrate as a Catalyst in Organic Synthesis |year=2010 |last1=Sridharan |first1=Vellaisamy |last2=Menéndez |first2=J. Carlos |journal=Chemical Reviews |volume=110 |issue=6 |pages=3805–3849 |pmid=20359233 }}</ref> It is inexpensive, stable in air, easily handled, and of low toxicity.<ref name="Sridharan" /> It operates by one-electron redox. Cerium nitrates also form 4:3 and 1:1 complexes with [[18-crown-6]] (the ratio referring to that between the nitrate and the [[crown ether]]). Classically, CAN is a primary standard for quantitative analysis.<ref name="CRC" /><ref name="appl">{{cite book| page = 30| url = https://books.google.com/books?id=F0Bte_XhzoAC&pg=PA30| title = Extractive metallurgy of rare earths| author = Gupta, C. K.| author2 = Krishnamurthy, Nagaiyar| name-list-style = amp | publisher =CRC Press| date = 2004| isbn =978-0-415-33340-5}}</ref>  Cerium(IV) salts, especially [[cerium(IV) sulfate]], are often used as standard reagents for [[volumetric analysis]] in [[cerimetry|cerimetric titrations]].<ref>{{cite book|title=Handbook on the Physics and Chemistry of Rare Earths, Volume 36|year=2006|publisher=Elsevier|location=The Netherlands|isbn=978-0-444-52142-2|pages=286–288|editor=Gschneidner K.A.|chapter-url=https://books.google.com/books?id=_Ro3Fqtz4xgC&q=cerimetry&pg=PA286|chapter=Chapter 229: Applications of tetravalent cerium compounds}}</ref>

[[File:5 mm Tinted White LED (on).jpg|right|thumb|A white LED in operation: the diode produces monochromatic blue light but the Ce:YAG phosphor converts some of it into yellow light; the combination is perceived as white by the human eye.|alt=A white LED in operation]]
<!--
Cerium(III) and terbium(III) have [[ultraviolet]] absorption bands of relatively high intensity compared with the other lanthanides, as their configurations (one electron more than an empty or half-filled f-subshell respectively) make it easier for the extra f electron to undergo f→d transitions instead of the forbidden f→f transitions of the other lanthanides.{{sfn|Greenwood|Earnshaw|1997|pages=1242-4}} [[Cerium(III) sulfate]] is one of the few salts whose [[solubility]] in water decreases with rising temperature.<ref name="RegerGoode2009">{{cite book|author1=Daniel L. Reger|author2=Scott R. Goode|author3=David Warren Ball|title=Chemistry: Principles and Practice|url=https://books.google.com/books?id=OUIaM1V3ThsC&pg=PA482|access-date=23 March 2013|date=2 January 2009|publisher=Cengage Learning|isbn=978-0-534-42012-3|page=482}}</ref>
-->

Due to [[charge-transfer complex|ligand-to-metal charge transfer]], aqueous cerium(IV) ions are orange-yellow.<ref name="SroorEdelmann2012">{{cite book|last1=Sroor|first1=Farid M.A.|title=Encyclopedia of Inorganic and Bioinorganic Chemistry|last2=Edelmann|first2=Frank T.|year=2012|doi=10.1002/9781119951438.eibc2033|chapter=Lanthanides: Tetravalent Inorganic|isbn=978-1-119-95143-8}}</ref> Aqueous cerium(IV) is metastable in water<ref>{{Ullmann|volume=31|page=190|last1=McGill|first1=Ian|contribution=Rare Earth Elements|doi=10.1002/14356007.a22_607}}</ref> and is a strong oxidizing agent that oxidizes [[hydrochloric acid]] to give [[chlorine]] gas.{{sfn|Greenwood|Earnshaw|1997|pages=1244-8}} In the [[Belousov–Zhabotinsky reaction]], cerium oscillates between the +4 and +3 oxidation states to catalyze the reaction.<ref>{{ cite journal | author = B. P. Belousov | title = Периодически действующая реакция и ее механизм |trans-title=Periodically acting reaction and its mechanism | journal = Сборник рефератов по радиационной медицине | year = 1959 | volume = 147 | page = 145 |language=ru}}</ref>

===Organocerium compounds===
[[Organocerium chemistry]] is similar to that of the other [[organolanthanide chemistry|lanthanides]], often involving complexes of [[cyclopentadienyl]] and [[Cyclooctatetraenide anion|cyclooctatetraenyl]] ligands. [[Cerocene]] {{chem2|(Ce(C8H8)2)}} adopts the [[uranocene]] molecular structure.{{sfn|Greenwood|Earnshaw|1997|pages=1248-9}} The 4f electron in cerocene is poised ambiguously between being localized and delocalized and this compound is considered intermediate-valent.<ref name="nature">{{cite journal |last=Schelter |first=Eric J. |date=20 March 2013 |title=Cerium under the lens |journal=Nature Chemistry |volume=5 |issue=4 |pages=348 |doi=10.1038/nchem.1602 |pmid=23511425 |bibcode=2013NatCh...5..348S|doi-access=free }}</ref> 
[[Alkyl]], [[alkynyl]], and [[alkenyl]] organocerium derivatives are prepared from the [[transmetallation]] of the respective [[organolithium]] or [[Grignard reagent|Grignard]] reagents, and are more [[Nucleophile|nucleophilic]] but less basic than their precursors.<ref>{{cite journal|title=Molecular compounds of "new" divalent lanthanides|author=Mikhail N. Bochkarev|journal=Coordination Chemistry Reviews|volume=248|issue=9–10|date=2004|pages=835–851|doi=10.1016/j.ccr.2004.04.004}}</ref><ref>{{cite journal|title=Aspects of non-classical organolanthanide chemistry|author=M. Cristina Cassani|author2=Yurii K. Gun'ko|author3=Peter B. Hitchcock|author4=Alexander G. Hulkes|author5= Alexei V. Khvostov|author6=Michael F. Lappert|author7=Andrey V. Protchenko|journal=Journal of Organometallic Chemistry|volume=647|issue=1–2|date=2002|pages=71–83|doi=10.1016/s0022-328x(01)01484-x}}</ref>

== History ==
[[File:Ceres - RC3 - Haulani Crater (22381131691).jpg|thumb|right|The [[dwarf planet]] and [[asteroid]] [[Ceres (dwarf planet)|Ceres]], after which cerium is named|alt=The dwarf planet Ceres.]]
[[File:Jöns Jacob Berzelius x Johan Way.jpg|thumb|left|Jöns Jakob Berzelius, one of the discoverers of cerium|alt=Jöns Jakob Berzelius]]
Cerium was discovered in [[Bastnäs]] in Sweden by [[Jöns Jakob Berzelius]] and [[Wilhelm Hisinger]], and independently in Germany by [[Martin Heinrich Klaproth]], both in 1803.<ref name="rsc">{{cite web |url= http://www.rsc.org/periodic-table/element/58/cerium |title= Visual Elements: Cerium |date= 1999–2012 |publisher= Royal Society of Chemistry |location= London |access-date= December 31, 2009}}</ref> Cerium was [[Ceres (dwarf planet)#Name and symbol|named]] by Berzelius after the asteroid [[Ceres (dwarf planet)|Ceres]], formally 1 Ceres, discovered two years earlier.<ref name="rsc" /><ref name="Emsley">{{cite book|author=Emsley, John |title=Nature's Building Blocks: An A-Z Guide to the Elements|url=https://books.google.com/books?id=4BAg769RfKoC&pg=PA123|date=2011|publisher=Oxford University Press|isbn=978-0-19-960563-7|pages=120–125}}</ref> Ceres was [[List of former planets|initially considered to be a planet]] at the time. The asteroid is itself named after the Roman goddess [[Ceres (mythology)|Ceres]], goddess of agriculture, grain crops, fertility and motherly relationships.<ref name="rsc" />

Cerium was originally isolated in the form of its oxide, which was named ''ceria'', a term that is still used. The metal itself was too electropositive to be isolated by then-current smelting technology, a characteristic of rare-earth metals in general. After the development of [[electrochemistry]] by [[Humphry Davy]] five years later, the earths soon yielded the metals they contained. Ceria, as isolated in 1803, contained all of the lanthanides present in the cerite ore from Bastnäs, Sweden, and thus only contained about 45% of what is now known to be pure ceria. It was not until [[Carl Gustaf Mosander]] succeeded in removing lanthana and [[Didymium|"didymia"]] in the late 1830s that ceria was obtained pure. Wilhelm Hisinger was a wealthy mine-owner and amateur scientist, and sponsor of Berzelius. He owned and controlled the mine at Bastnäs, and had been trying for years to find out the composition of the abundant heavy gangue rock (the "Tungsten of Bastnäs", which despite its name contained no [[tungsten]]), now known as cerite, that he had in his mine.<ref name="Emsley" /> Mosander and his family lived for many years in the same house as Berzelius, and Mosander was undoubtedly persuaded by Berzelius to investigate ceria further.<ref name="Weeks">{{cite book |last1=Weeks |first1=Mary Elvira |title=The discovery of the elements |date=1956 |publisher=Journal of Chemical Education |location=Easton, PA |url=https://archive.org/details/discoveryoftheel002045mbp |edition=6th}}</ref><ref name="XI">{{cite journal |doi=10.1021/ed009p1231 |last=Weeks |first=Mary Elvira |author-link=Mary Elvira Weeks |title=The Discovery of the Elements: XI. Some Elements Isolated with the Aid of Potassium and Sodium: Zirconium, Titanium, Cerium and Thorium |journal=The Journal of Chemical Education |date=1932 |volume=9 |issue=7 |pages=1231–1243 |bibcode=1932JChEd...9.1231W}}</ref><ref name="Beginnings">{{cite journal |last1=Marshall |first1=James L. Marshall |last2=Marshall |first2=Virginia R. Marshall |title=Rediscovery of the elements: The Rare Earths–The Beginnings |journal=The Hexagon |date=2015 |pages=41–45 |url=http://www.chem.unt.edu/~jimm/REDISCOVERY%207-09-2018/Hexagon%20Articles/rare%20earths%20I.pdf |access-date=30 December 2019}}</ref><ref name="Virginia">{{cite journal |last1=Marshall |first1=James L. Marshall |last2=Marshall |first2=Virginia R. Marshall |title=Rediscovery of the elements: The Rare Earths–The Confusing Years |journal=The Hexagon |date=2015 |pages=72–77 |url=http://www.chem.unt.edu/~jimm/REDISCOVERY%207-09-2018/Hexagon%20Articles/rare%20earths%20II.pdf |access-date=30 December 2019}}</ref>

The element played a role in the [[Manhattan Project]], where cerium compounds were investigated in the [[Calutron|Berkeley]] site as materials for [[crucible]]s for [[uranium]] and [[plutonium]] casting.<ref name=":0">{{Cite journal|last1=Hirai|first1=Shinji|last2=Shimakage|first2=Kazuyoshi|last3=Saitou|first3=Yasushi|last4=Nishimura|first4=Toshiyuki|last5=Uemura|first5=Yoichiro|last6=Mitomo|first6=Mamoru|last7=Brewer|first7=Leo|date=2005-01-21|title=Synthesis and Sintering of Cerium(III) Sulfide Powders|url=http://doi.wiley.com/10.1111/j.1151-2916.1998.tb02306.x|journal=Journal of the American Ceramic Society|language=en|volume=81|issue=1|pages=145–151|doi=10.1111/j.1151-2916.1998.tb02306.x|url-access=subscription}}</ref> For this reason, [[Ames Project#Cerium|new methods]] for the preparation and casting of cerium were developed within the scope of the [[Ames Project|Ames]] daughter project (now the [[Ames Laboratory]]).<ref name=":1">{{Cite book|url=https://www.osti.gov/opennet/manhattan_district|title=Manhattan District History|publisher=United States Army Corps of Engineers|year=1946|editor-last=Hadden|editor-first=Gavin|volume=4|location=Washington, D.C.|chapter=Chapter 11 - Ames Project}}</ref> Production of extremely pure cerium in Ames commenced in mid-1944 and continued until August 1945.<ref name=":1" />

== Occurrence and production ==
Cerium is the most abundant of all the lanthanides and the 25th most abundant element, making up 68&nbsp;[[parts per million|ppm]] of the Earth's crust.<ref>{{Cite book |last=Emsley |first=John |url=https://books.google.com/books?id=j-Xu07p3cKwC&dq=%2225th+most+abundant+element%22&pg=PA103 |title=Nature's Building Blocks: An A-Z Guide to the Elements |date=2003 |publisher=Oxford University Press |isbn=978-0-19-850340-8 |language=en}}</ref> This value is the same of [[copper]], and cerium is even more abundant than common metals such as [[lead]] (13&nbsp;ppm) and [[tin]] (2.1&nbsp;ppm). Thus, despite its position as one of the so-called [[rare-earth metal]]s, cerium is actually not rare at all.{{sfn|Greenwood|Earnshaw|1997|pages=1294}} Cerium content in the soil varies between 2 and 150&nbsp;ppm, with an average of 50&nbsp;ppm; seawater contains 1.5 parts per trillion of cerium.<ref name="Emsley" /> Cerium occurs in various minerals, but the most important commercial sources are the minerals of the [[monazite]] and [[bastnäsite]] groups, where it makes up about half of the lanthanide content. Monazite-(Ce) is the most common representative of the monazites, with "-Ce" being the Levinson suffix informing on the dominance of the particular REE element representative.<ref name="Burke">{{cite journal |journal=Elements |last1=Burke |first1=Ernst A.J. |title=The use of suffixes in mineral names |url=http://elementsmagazine.org/archives/e4_2/e4_2_dep_mineralmatters.pdf |date=2008 |volume=4 |issue=2 |page=96 |access-date=7 December 2019 |archive-date=19 December 2019 |archive-url=https://web.archive.org/web/20191219014458/http://elementsmagazine.org/archives/e4_2/e4_2_dep_mineralmatters.pdf |url-status=dead }}</ref><ref>{{Cite web|url=https://www.mindat.org/min-2751.html|title=Monazite-(Ce): Mineral information, data and localities.|website=www.mindat.org}}</ref><ref name="auto">{{Cite web|url=http://nrmima.nrm.se/|title=CNMNC|website=nrmima.nrm.se|access-date=2018-10-06|archive-url=https://web.archive.org/web/20190810195707/http://nrmima.nrm.se//|archive-date=2019-08-10|url-status=dead}}</ref> Also the cerium-dominant bastnäsite-(Ce) is the most important of the bastnäsites.<ref>{{Cite web|url=https://www.mindat.org/min-560.html|title=Bastnäsite-(Ce): Mineral information, data and localities.|website=www.mindat.org}}</ref><ref name="Burke" /> Cerium is the easiest lanthanide to extract from its minerals because it is the only one that can reach a stable +4 oxidation state in aqueous solution.{{sfn|Greenwood|Earnshaw|1997|pages=1229–1232}} Because of the decreased solubility of cerium in the +4 oxidation state, cerium is sometimes depleted from rocks relative to the other rare-earth elements and is incorporated into [[zircon]], since Ce<sup>4+</sup> and [[zirconium|Zr]]<sup>4+</sup> have the same charge and similar ionic radii.<ref>{{cite journal | last1 = Thomas | first1 = J. B. | last2 = Bodnar | first2 = R. J. | last3 = Shimizu | first3 = N. | last4 = Chesner | first4 = C. A. | year = 2003 | title = Melt inclusions in zircon | journal = Reviews in Mineralogy and Geochemistry | volume = 53 | issue = 1| pages = 63–87 | doi=10.2113/0530063| bibcode = 2003RvMG...53...63T }}</ref> In extreme cases, cerium(IV) can form its own minerals separated from the other rare-earth elements, such as [[cerianite]]-(Ce)<ref>{{Cite web | url=https://www.mindat.org/min-929.html | title=Cerianite-(Ce): Mineral information, data and localities |website=www.mindat.org}}</ref><ref name="auto" /><ref name="Burke" /> and {{chem2|(Ce,Th)O2}}.<ref>{{cite journal | last1 = Graham | first1 = A. R. | year = 1955 | title = Cerianite CeO<sub>2</sub>: a new rare-earth oxide mineral | journal = American Mineralogist | volume = 40 | pages = 560–564 }}</ref>

[[File:Bastnaesite crystal structure.png|thumb|upright=1.6|Crystal structure of bastnäsite-(Ce). Color code: carbon, C, blue-gray; fluorine, F, green; cerium, Ce, white; oxygen, O, red.|left|alt=Crystal structure of basntäsite-(Ce).]]
Bastnäsite, Ln{{sup|III}}CO{{sub|3}}F, is usually lacking in [[thorium]] and the heavy lanthanides beyond [[samarium]] and [[europium]], and hence the extraction of cerium from it is quite direct. First, the bastnäsite is purified, using dilute [[hydrochloric acid]] to remove [[calcium carbonate]] impurities. The ore is then roasted in the air to oxidize it to the lanthanide oxides: while most of the lanthanides will be oxidized to the sesquioxides {{chem2|Ln2O3}}, cerium will be oxidized to the dioxide CeO{{sub|2}}. This is insoluble in water and can be leached out with 0.5&nbsp;M hydrochloric acid, leaving the other lanthanides behind.{{sfn|Greenwood|Earnshaw|1997|pages=1229–1232}}

The procedure for [[monazite]], {{chem2|(Ln,Th)PO4}}, which usually contains all the rare earths, as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with [[sodium hydroxide]] to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with [[ammonium oxalate]] to convert rare earths to their insoluble [[oxalate]]s. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid, but cerium oxide is insoluble in HNO<sub>3</sub> and hence precipitates out.<ref name="patnaik" /> Care must be taken when handling some of the residues as they contain [[radium-228|<sup>228</sup>Ra]], the daughter of <sup>232</sup>Th, which is a strong gamma emitter.{{sfn|Greenwood|Earnshaw|1997|pages=1229–1232}}

== Applications ==
[[File:Auer von Welsbach.jpg|thumb|right|upright|Carl Auer von Welsbach, who discovered many applications of cerium|alt=Carl Auer von Welsbach]]

Cerium has two main applications, both of which use CeO<sub>2</sub>. The industrial application of ceria is for polishing, especially [[Chemical-mechanical polishing|chemical-mechanical planarization]] (CMP). In its other main application, CeO<sub>2</sub> is used to decolorize glass. It functions by converting green-tinted ferrous impurities to nearly colorless ferric oxides.<ref>{{Ullmann|author1=Klaus Reinhardt |author2=Herwig Winkler |title=Cerium Mischmetal, Cerium Alloys, and Cerium Compounds|year=2000|doi=10.1002/14356007.a06_139}}.</ref> Ceria has also been used as a substitute for its radioactive congener [[thorium dioxide|thoria]], for example in the manufacture of electrodes used in [[gas tungsten arc welding]], where cerium as an alloying element improves arc stability and ease of starting while decreasing burn-off.<ref>{{cite book|title=AWS D10.11M/D10.11 - An American National Standard - Guide for Root Pass Welding of Pipe Without Backing|date=2007|publisher=American Welding Society}}</ref>

=== Gas mantles and pyrophoric alloys ===
The first use of cerium was in [[gas mantle]]s, invented by Austrian chemist [[Carl Auer von Welsbach]]. In 1885, he had previously experimented with mixtures of [[magnesium]], lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful.<ref>{{cite EB1911 |wstitle=Lighting |volume=16 |page=656 |first=Vivian Byam |last=Lewes}}</ref> Six years later, he discovered that pure [[thorium oxide]] produced a much better, though blue, light, and that mixing it with cerium dioxide resulted in a bright white light.<ref>{{cite book |last1=Wickleder |first1=Mathias S. |first2=Blandine |last2=Fourest |first3=Peter K. |last3=Dorhout |contribution=Thorium |title=The Chemistry of the Actinide and Transactinide Elements |editor1-first=Lester R. |editor1-last=Morss |editor2-first=Norman M. |editor2-last=Edelstein |editor3-first=Jean |editor3-last=Fuger |edition=3rd |date=2006 |volume=3 |publisher=Springer |location=Dordrecht, the Netherlands |pages=52–160|doi=10.1007/1-4020-3598-5_3|url= http://radchem.nevada.edu/classes/rdch710/files/thorium.pdf |url-status=dead |archive-date=2016-03-07 |archive-url=https://web.archive.org/web/20160307160941/http://radchem.nevada.edu/classes/rdch710/files/Thorium.pdf|isbn=978-1-4020-3555-5}}</ref> Cerium dioxide also acts as a catalyst for the combustion of thorium oxide.{{cn|date=August 2023}}

This resulted in commercial success for von Welsbach and his invention, and created great demand for thorium. Its production resulted in a large amount of lanthanides being simultaneously extracted as by-products.{{sfn|Greenwood|Earnshaw|1997|pages=1228}} Applications were soon found for them, especially in the pyrophoric alloy known as "[[mischmetal]]" composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints.{{sfn|Greenwood|Earnshaw|1997|pages=1228}} Usually iron is added to form the alloy [[ferrocerium]], also invented by von Welsbach.<ref>Klaus Reinhardt and Herwig Winkler in "Cerium Mischmetal, Cerium Alloys, and Cerium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry 2000, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a06_139}}</ref> Due to the chemical similarities of the lanthanides, chemical separation is not usually required for their applications, such as the addition of mischmetal to steel as an inclusion modifier to improve mechanical properties, or as catalysts for the cracking of petroleum.{{sfn|Greenwood|Earnshaw|1997|pages=1229–1232}} This property of cerium saved the life of writer [[Primo Levi]] at the [[Auschwitz concentration camp]], when he found a supply of ferrocerium alloy and bartered it for food.<ref>{{cite news |last=Wilkinson |first=Tom |date=6 November 2009 |title=Book Of A Lifetime: The Periodic Table, By Primo Levi |url=https://www.independent.co.uk/arts-entertainment/books/reviews/book-of-a-lifetime-the-periodic-table-by-primo-levi-1815315.html |newspaper=The Independent |access-date=25 October 2016}}</ref>
=== Pigments and phosphors ===
The photostability of [[pigment]]s can be enhanced by the addition of cerium, as it provides pigments with [[lightfastness]] and prevents clear polymers from darkening in sunlight.<ref>{{Cite journal |last1=Gleń |first1=Marta |last2=Grzmil |first2=Barbara |last3=Sreńscek-Nazzal |first3=Joanna |last4=Kic |first4=Bogumił |date=2011-04-01 |title=Effect of CeO2 and Sb2O3 on the phase transformation and optical properties of photostable titanium dioxide |journal=Chemical Papers |language=en |volume=65 |issue=2 |pages=203–212 |doi=10.2478/s11696-010-0103-x |s2cid=94458692 |issn=1336-9075}}</ref> An example of a cerium compound used on its own as an [[List of inorganic pigments|inorganic pigment]] is the vivid red [[cerium(III) sulfide]] (cerium sulfide red), which stays chemically inert up to very high temperatures. The pigment is a safer alternative to lightfast but toxic [[Cadmium pigments|cadmium selenide-based pigments]].<ref name="Emsley"/> The addition of cerium oxide to older [[cathode-ray tube]] television glass plates was beneficial, as it suppresses the darkening effect from the creation of [[F-center]] defects due to the continuous electron bombardment during operation. Cerium is also an essential component as a [[dopant]] for [[phosphor]]s used in CRT TV screens, fluorescent lamps, and later [[Light-emitting diode#White LEDs and the illumination breakthrough|white light-emitting diodes]].<ref name="r1">[http://www.nanopartikel.info/cms/lang/en/Wissensbasis/Cerdioxid Cerium dioxide] {{webarchive|url=https://web.archive.org/web/20130302081012/http://www.nanopartikel.info/cms/lang/en/Wissensbasis/Cerdioxid |date=2013-03-02}}. nanopartikel.info (2011-02-02)</ref><ref name="cerium">{{cite book| url=https://books.google.com/books?id=X2z9WdN3-WgC| title=Catalysis by ceria and related materials| author=Trovarelli, Alessandro| publisher=Imperial College Press| date=2002| isbn=978-1-86094-299-0| pages=6–11}}</ref><!--{{cite journal |doi=10.1080/10643389.2014.900240 |volume=45 |title=Rare Earth Elements Recovery from Waste Fluorescent Lamps: A Review |year=2014 |journal=Critical Reviews in Environmental Science and Technology |pages=749–776 |last1=Tan |first1=Quanyin |last2=Li |first2=Jinhui |last3=Zeng |first3=Xianlai}}--> The most commonly used example is [[Yttrium aluminium garnet#Ce:YAG|cerium(III)-doped yttrium aluminium garnet]] (Ce:YAG) which emits green to yellow-green light (550–530&nbsp;nm) and also behaves as a [[scintillator]].<ref>{{Cite journal |last1=Lu |first1=Chung-Hsin |last2=Hong |first2=Hsin-Cheng |last3=Jagannathan |first3=R. |date=2002-01-01 |title=Sol–gel synthesis and photoluminescent properties of cerium-ion doped yttrium aluminium garnet powders |url=https://pubs.rsc.org/en/content/articlelanding/2002/jm/b200776m |journal=Journal of Materials Chemistry |language=en |volume=12 |issue=8 |pages=2525–2530 |doi=10.1039/B200776M |issn=1364-5501|url-access=subscription }}</ref>

=== Other uses ===
Cerium salts, such as the sulfides [[Cerium(III) sulfide|Ce<sub>2</sub>S<sub>3</sub>]] and Ce<sub>3</sub>S<sub>4</sub>, were considered during the [[Manhattan Project]] as advanced [[Refractory|refractory materials]] for the construction of crucibles which could withstand the high temperatures and strongly [[Redox|reducing]] conditions when casting plutonium metal.<ref name=":0" /><ref name=":1" /> Despite desirable properties, these sulfides were never widely adopted due to practical issues with their synthesis.<ref name=":0" /> Cerium is used as alloying element in aluminium to create castable eutectic [[aluminium alloys]] with 6–16 wt.% Ce, to which other elements such as Mg, Ni, Fe and Mn can be added. These Al-Ce alloys have excellent high temperature strength and are suitable for automotive applications (e.g. in [[cylinder head]]s).<ref>{{Cite journal|last=Sims|first=Zachary |date=2016|title=Cerium-Based, Intermetallic-Strengthened Aluminum Casting Alloy: High-Volume Co-product Development |journal=JOM|volume=68|issue=7|pages=1940–1947 |bibcode=2016JOM....68g1940S|doi=10.1007/s11837-016-1943-9 |osti=1346625|s2cid=138835874}}</ref> Other alloys of cerium include Pu-Ce and Pu-Ce-Co [[Plutonium#Alloys|plutonium alloys]], which have been used as [[nuclear fuel]].<ref>{{Cite report |url=https://www.osti.gov/biblio/4650650 |title=PREPARATION OF TERNARY PLUTONIUM ALLOYS FOR CORE TEST FACILITY PROGRAM |last1=Leary |first1=J. A. |last2=Mullins |first2=L. J. |date=1964-11-01 |publisher=Los Alamos National Lab. (LANL), Los Alamos, NM (United States) |issue=LA-3209 |osti=4650650 |language=English}}</ref>

Other [[automotive]] applications for the lower sesquioxide are as a [[catalytic converter]] for the oxidation of CO and [[NOx|NO{{sub|''x''}}]] emissions in the exhaust gases from motor vehicles.<ref>Bleiwas, D.I. (2013). [https://purl.fdlp.gov/GPO/gpo36871 Potential for Recovery of Cerium Contained in Automotive Catalytic Converters.] Reston, Va.: [[United States Department of the Interior|U.S. Department of the Interior]], [[United States Geological Survey|U.S. Geological Survey]].</ref><ref>{{cite web|title=Argonne's deNOx Catalyst Begins Extensive Diesel Engine Exhaust Testing|publisher=Argonne National Laboratory |url=http://www.transportation.anl.gov/engines/cerium-oxide_catalyst.html|access-date=2014-06-02|archive-url=https://web.archive.org/web/20150907191148/http://www.transportation.anl.gov/engines/cerium-oxide_catalyst.html |archive-date=2015-09-07|url-status=dead}}</ref>

== Biological role and precautions ==
{{Chembox
|container_only = yes
| Section7 = {{Chembox Hazards
| ExternalSDS =
| GHSPictograms = {{GHS02}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|H228}}
| PPhrases = {{P-phrases|P210}}

| GHS_ref  = <ref>{{cite web |url=https://www.sigmaaldrich.com/catalog/product/aldrich/gf39030353?lang=en&region=US |title=Cerium GF39030353 |date=2021-09-22 |accessdate=2021-12-22}}</ref>

| NFPA-H = 2
| NFPA-F = 0
| NFPA-R = 0
| NFPA-S = 
| NFPA_ref = 
 }}
}}
The early lanthanides have been found to be essential to some [[methanotrophic]] bacteria living in [[Mudpot|volcanic mudpots]], such as ''[[Methylacidiphilum fumariolicum]]'': [[lanthanum]], [[cerium]], [[praseodymium]], and [[neodymium]] are about equally effective.<ref>{{cite journal |doi=10.1111/1462-2920.12249 |pmid=24034209 |title=Rare earth metals are essential for methanotrophic life in volcanic mudpots |date=2013 |last1=Pol |first1=Arjan |last2=Barends |first2=Thomas R. M. |last3=Dietl |first3=Andreas |last4=Khadem |first4=Ahmad F. |last5=Eygensteyn |first5=Jelle |last6=Jetten |first6=Mike S. M. |last7=Op Den Camp |first7=Huub J. M. |journal=Environmental Microbiology |volume=16 |issue=1 |pages=255–64|url=https://repository.ubn.ru.nl//bitstream/handle/2066/128108/128108.pdf }}</ref><ref>{{Cite journal|last1=Kang |first1=L. |last2=Shen |first2=Z. |last3=Jin |first3=C. |title=Neodymium cations Nd<sup>3+</sup> were transported to the interior of ''Euglena gracilis'' 277 |journal=Chin. Sci. Bull. |volume=45 |pages=585–592 |date=April 2000 |issue=7 |doi=10.1007/BF02886032|bibcode=2000ChSBu..45..585K }}</ref> Cerium is otherwise not known to have biological role in any other organisms, but is not very toxic either; it does not accumulate in the food chain to any appreciable extent.<ref>{{Cite journal |last1=Hawthorne |first1=Joseph |last2=De la Torre Roche |first2=Roberto |last3=Xing |first3=Baoshan |last4=Newman |first4=Lee A. |last5=Ma |first5=Xingmao |last6=Majumdar |first6=Sanghamitra |last7=Gardea-Torresdey |first7=Jorge |last8=White |first8=Jason C. |date=2014-11-18 |title=Particle-Size Dependent Accumulation and Trophic Transfer of Cerium Oxide through a Terrestrial Food Chain |url=https://pubs.acs.org/doi/10.1021/es503792f |journal=Environmental Science & Technology |language=en |volume=48 |issue=22 |pages=13102–13109 |doi=10.1021/es503792f |pmid=25340623 |bibcode=2014EnST...4813102H |issn=0013-936X|url-access=subscription }}</ref><ref>{{Cite journal |last1=Majumdar |first1=Sanghamitra |last2=Trujillo-Reyes |first2=Jesica |last3=Hernandez-Viezcas |first3=Jose A. |last4=White |first4=Jason C. |last5=Peralta-Videa |first5=Jose R. |last6=Gardea-Torresdey |first6=Jorge L. |date=2016-07-05 |title=Cerium Biomagnification in a Terrestrial Food Chain: Influence of Particle Size and Growth Stage |url=https://pubs.acs.org/doi/10.1021/acs.est.5b04784 |journal=Environmental Science & Technology |language=en |volume=50 |issue=13 |pages=6782–6792 |doi=10.1021/acs.est.5b04784 |pmid=26690677 |bibcode=2016EnST...50.6782M |issn=0013-936X|url-access=subscription }}</ref><ref>{{Citation |last1=Gupta |first1=Govind Sharan |title=Impact of Nanomaterials on the Aquatic Food Chain |date=2017 |url=https://doi.org/10.1007/978-3-319-58496-6_11 |work=Nanoscience in Food and Agriculture 5 |pages=309–333 |editor-last=Ranjan |editor-first=Shivendu |access-date=2023-08-12 |series=Sustainable Agriculture Reviews |place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-319-58496-6_11 |isbn=978-3-319-58496-6 |last2=Shanker |first2=Rishi |last3=Dhawan |first3=Alok |last4=Kumar |first4=Ashutosh |volume=26 |editor2-last=Dasgupta |editor2-first=Nandita |editor3-last=Lichtfouse |editor3-first=Eric|url-access=subscription }}</ref> Because it often occurs together with calcium in [[phosphate mineral]]s, and bones are primarily [[calcium phosphate]], cerium can accumulate in bones in small amounts that are not considered dangerous.<ref>{{Cite journal|last1=Jakupec |first1=M. A. |title=Pharmacological properties of cerium compunds |date=2005 |url=http://link.springer.com/10.1007/s10254-004-0024-6 |journal=Reviews of Physiology, Biochemistry and Pharmacology |volume=153 |pages=101–111 |access-date=2023-08-05 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/s10254-004-0024-6 |isbn=978-3-540-24012-9 |last2=Unfried |first2=P. |last3=Keppler |first3=B. K.|pmid=15674649 |url-access=subscription }}</ref>

[[Cerium nitrate]] is an effective topical antimicrobial treatment for [[third-degree burn]]s,<ref name="Emsley" /><ref>{{cite journal |last1=Dai |first1=Tianhong |last2=Huang |first2=Ying-Ying |last3=Sharma |first3=Sulbha K. |last4=Hashmi |first4=Javad T. |last5=Kurup |first5=Divya B. |last6=Hamblin |first6=Michael R. |date=2010 |title=Topical antimicrobials for burn wound infections |journal=Recent Pat Anti-Infect Drug Discov |volume=5 |issue=2 |pages=124–151 |pmid=20429870 |pmc=2935806 |doi=10.2174/157489110791233522}}</ref> although large doses can lead to cerium poisoning and [[methemoglobinemia]].<ref>{{cite journal |last1=Attof |first1=Rachid |last2=Magnin |first2=Christophe |last3=Bertin-Maghit |first3=Marc |last4=Olivier |first4=Laure |last5=Tissot |first5=Sylvie |last6=Petit |first6=Paul |date=2007 |title=Methemoglobinemia by cerium nitrate poisoning |journal=Burns |volume=32 |issue=8 |pages=1060–1061 |doi=10.1016/j.burns.2006.04.005 |pmid=17027160}}</ref> 
Like all rare-earth metals, cerium is of low to moderate toxicity.<ref name=":2">{{Cite journal |last1=Rim |first1=Kyung Taek |last2=Koo |first2=Kwon Ho |last3=Park |first3=Jung Sun |date=March 2013 |title=Toxicological Evaluations of Rare Earths and Their Health Impacts to Workers: A Literature Review |journal=Safety and Health at Work |language=en |volume=4 |issue=1 |pages=12–26 |doi=10.5491/SHAW.2013.4.1.12 |pmc=3601293 |pmid=23516020}}</ref> A strong reducing agent, it ignites spontaneously in air at 65 to 80&nbsp;°C. Fumes from cerium fires are toxic.<ref name="Emsley" /> Cerium reacts with water to produce hydrogen gas, and thus cerium fires can only be effectively extinguished using [[Fire extinguisher#Dry powder and metal fire extinguishers|class D dry powder]] extinguishing media.<ref>{{Cite book |last=Spellman |first=Frank R. |url=https://books.google.com/books?id=a2ObEAAAQBAJ |title=The Science of Rare Earth Elements: Concepts and Applications |date=2022-12-30 |publisher=CRC Press |isbn=978-1-000-82129-1 |pages=104–105 |language=en}}</ref> Workers exposed to cerium have experienced itching, sensitivity to heat, and skin lesions. Cerium is not toxic when eaten, but animals injected with large doses of cerium have died due to cardiovascular collapse. Cerium is more dangerous to aquatic organisms because it damages cell membranes; it is not very soluble in water and can cause environmental contamination.<ref name="Emsley" />

Cerium oxide, the most prevalent cerium compound in industrial applications, is not regulated in the United States by the [[Occupational Safety and Health Administration]] (OSHA) as a hazardous substance.<ref>{{Cite web |date=March 27, 2024 |title=Cerium(IV) oxide, REacton Safety Data Sheet |url=https://www.fishersci.com/store/msds?partNumber=AA4466236&productDescription=CERIUM+IV+OXIDE+500G&vendorId=VN00024248&countryCode=US&language=en |access-date=August 27, 2024 |website=[[Fisher Scientific]]}}</ref> In Russia, its [[occupational exposure limit]] is 5&nbsp;mg/m{{sup|3}}.<ref name=":2" /> Elemental cerium has no established occupational or permissible exposure limits by the OSHA or [[American Conference of Governmental Industrial Hygienists]], though it is classified as a flammable solid and regulated as such under the [[Globally Harmonized System of Classification and Labelling of Chemicals]].<ref>{{Cite web |date=January 26, 2016 |title=Cerium Safety Data Sheet |url=https://www.ameslab.gov/sites/default/files/inline-files/58_Cerium_SDS.pdf |access-date=August 27, 2024 |website=Ames Laboratory, [[U. S. Department of Energy]]}}</ref> Toxicological reports on cerium compounds have noted their [[cytotoxicity]]<ref name=":2" /> and contributions to [[Interstitial lung disease|pulmonary interstitial fibrosis]] in workers.<ref>{{Cite report |url=https://iris.epa.gov/static/pdfs/1018tr.pdf |title=Toxicological Review of Cerium Oxide and Cerium Compounds |last=Environmental Protection Agency |date=September 2009 |location=Washington, D.C.}}</ref>
{{clear}}

== References ==
{{reflist|30em}}

== Bibliography ==
*{{Greenwood&Earnshaw2nd}}

{{Clear}}
{{Periodic table (navbox)}}
{{Cerium compounds}}

{{Authority control}}

[[Category:Cerium| ]]
[[Category:Chemical elements]]
[[Category:Chemical elements with double hexagonal close-packed structure]]
[[Category:Lanthanides]]
[[Category:Reducing agents]]
[[Category:Pyrophoric materials]]
[[Category:Materials that expand upon freezing]]