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'''Strontium''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Sr''' and [[atomic number]] 38. An [[alkaline earth metal]], it is a soft silver-white yellowish [[metal]]lic element that is highly [[Reactivity (chemistry)|chemically reactive]]. The metal forms a dark oxide layer when it is exposed to air. Strontium has physical and chemical properties similar to those of its two vertical neighbors in the periodic table, [[calcium]] and [[barium]]. It occurs naturally mainly in the [[minerals]] [[Celestine (mineral)|celestine]] and [[strontianite]], and is mostly mined from these.

Both strontium and strontianite are named after [[Strontian]], a village in Scotland near which the mineral was discovered in 1790 by [[Adair Crawford]] and [[William Cruickshank (chemist)|William Cruickshank]]; it was identified as a new element the next year from its crimson-red [[flame test]] color. Strontium was first isolated as a metal in 1808 by [[Humphry Davy]] using the then newly discovered process of [[electrolysis]]. During the 19th century, strontium was mostly used in the production of sugar from [[sugar beet]]s (see [[strontian process]]). At the peak of production of television [[cathode-ray tube]]s, as much as 75% of strontium consumption in the United States was used for the faceplate glass.<ref name="USGS">{{cite web |url=https://www.earthmagazine.org/article/mineral-resource-month-strontium|title=Mineral Resource of the Month: Strontium|publisher=U.S. Geological Survey|access-date=16 August 2015|date=8 December 2014}}</ref> With the replacement of cathode-ray tubes with other display methods, consumption of strontium has dramatically declined.<ref name="USGS" />

While natural strontium (which is mostly the [[isotope]] strontium-88) is stable, the synthetic [[strontium-90]] is radioactive and is one of the most dangerous components of [[nuclear fallout]], as strontium is absorbed by the body in a similar manner to calcium. Natural stable strontium, on the other hand, is not hazardous to health.

==Characteristics==
[[File:Strontium 1.jpg|thumb|left|upright|Oxidized [[Dendrite (crystal)|dendritic]] strontium]]

Strontium is a [[divalent]] silvery metal with a pale yellow tint whose properties are mostly intermediate between and similar to those of its group neighbors [[calcium]] and [[barium]].<ref name="Greenwood112">Greenwood and Earnshaw, pp. 112–13</ref> It is softer than calcium and harder than barium. Its melting (777&nbsp;°C) and boiling (1377&nbsp;°C) points are lower than those of calcium (842&nbsp;°C and 1484&nbsp;°C respectively); barium continues this downward trend in the melting point (727&nbsp;°C), but not in the boiling point (1900&nbsp;°C). The density of strontium (2.64&nbsp;g/cm<sup>3</sup>) is similarly intermediate between those of calcium (1.54&nbsp;g/cm<sup>3</sup>) and barium (3.594&nbsp;g/cm<sup>3</sup>).<ref name="CRC">C. R. Hammond ''The elements'' (pp. 4–35) in {{RubberBible86th}}</ref> Three [[Allotropy|allotropes]] of metallic strontium exist, with [[transition point]]s at 235 and 540&nbsp;°C.{{cn|date=September 2023}}

The [[standard electrode potential]] for the Sr<sup>2+</sup>/Sr couple is −2.89&nbsp;V, approximately midway between those of the Ca<sup>2+</sup>/Ca (−2.84&nbsp;V) and Ba<sup>2+</sup>/Ba (−2.92&nbsp;V) couples, and close to those of the neighboring [[alkali metal]]s.<ref name="Greenwood111" /> Strontium is intermediate between calcium and barium in its reactivity toward water, with which it reacts on contact to produce [[strontium hydroxide]] and [[hydrogen]] gas. Strontium metal burns in air to produce both [[strontium oxide]] and [[strontium nitride]], but since it does not react with [[nitrogen]] below 380&nbsp;°C, at room temperature it forms only the oxide spontaneously.<ref name="CRC" /> Besides the simple oxide SrO, the [[peroxide]] {{chem2|SrO2}} can be made by direct oxidation of strontium metal under a high pressure of oxygen, and there is some evidence for a yellow [[superoxide]] {{chem2|Sr(O2)2}}.<ref>Greenwood and Earnshaw, p. 119</ref> [[Strontium hydroxide]], {{chem2|Sr(OH)2}}, is a strong base, though it is not as strong as the hydroxides of barium or the alkali metals.<ref>Greenwood and Earnshaw, p. 121</ref> All four dihalides of strontium are known.<ref>Greenwood and Earnshaw, p. 117</ref>

Due to the large size of the heavy [[s-block]] elements, including strontium, a vast range of [[coordination number]]s is known, from 2, 3, or 4 all the way to 22 or 24 in {{chem2|SrCd11}} and {{chem2|SrZn13}}. The Sr<sup>2+</sup> ion is quite large, so that high coordination numbers are the rule.<ref>Greenwood and Earnshaw, p. 115</ref> The large size of strontium and barium plays a significant part in stabilising strontium complexes with [[denticity|polydentate]] [[macrocycle|macrocyclic]] ligands such as [[crown ether]]s: for example, while [[18-crown-6]] forms relatively weak complexes with calcium and the alkali metals, its strontium and barium complexes are much stronger.<ref>Greenwood and Earnshaw, p. 124</ref>

Organostrontium compounds contain one or more strontium–carbon bonds. They have been reported as intermediates in [[Barbier reaction|Barbier-type]] reactions.<ref>{{Cite journal| doi = 10.1246/bcsj.77.341| title = The Barbier-Type Alkylation of Aldehydes with Alkyl Halides in the Presence of Metallic Strontium| year = 2004| last1 = Miyoshi | first1 = N.| last2 = Kamiura | first2 = K.| last3 = Oka | first3 = H.| last4 = Kita | first4 = A.| last5 = Kuwata | first5 = R.| last6 = Ikehara | first6 = D.| last7 = Wada | first7 = M.| journal = Bulletin of the Chemical Society of Japan| volume = 77| issue = 2| page = 341 }}</ref><ref>{{Cite journal| doi = 10.1246/cl.2005.760| title = The Chemistry of Alkylstrontium Halide Analogues: Barbier-type Alkylation of Imines with Alkyl Halides| year = 2005| last1 = Miyoshi | first1 = N.| last2 = Ikehara | first2 = D.| last3 = Kohno | first3 = T.| last4 = Matsui | first4 = A.| last5 = Wada | first5 = M.| journal = Chemistry Letters| volume = 34| issue = 6| page = 760 }}</ref><ref>{{Cite journal| doi = 10.1002/ejoc.200500484| title = The Chemistry of Alkylstrontium Halide Analogues, Part 2: Barbier-Type Dialkylation of Esters with Alkyl Halides| year = 2005| last1 = Miyoshi | first1 = N.| last2 = Matsuo | first2 = T.| last3 = Wada | first3 = M.| journal = European Journal of Organic Chemistry| volume = 2005| issue = 20| page = 4253 }}</ref> Although strontium is in the same group as magnesium, and [[organomagnesium compound]]s are very commonly used throughout chemistry, organostrontium compounds are not similarly widespread because they are more difficult to make and more reactive. Organostrontium compounds tend to be more similar to organo[[europium]] or organo[[samarium]] compounds due to the similar [[ionic radius|ionic radii]] of these elements (Sr<sup>2+</sup> 118&nbsp;pm; Eu<sup>2+</sup> 117&nbsp;pm; Sm<sup>2+</sup> 122&nbsp;pm). Most of these compounds can only be prepared at low temperatures; bulky ligands tend to favor stability. For example, strontium di[[cyclopentadienyl]], {{chem2|Sr(C5H5)2}}, must be made by directly reacting strontium metal with [[mercurocene]] or [[cyclopentadiene]] itself; replacing the {{chem2|C5H5}} ligand with the bulkier {{chem2|C5(CH3)5}} ligand on the other hand increases the compound's solubility, volatility, and kinetic stability.<ref>Greenwood and Earnshaw, pp. 136–37</ref>

Because of its extreme reactivity with [[oxygen]] and water, strontium occurs naturally only in compounds with other elements, such as in the minerals [[strontianite]] and [[celestine (mineral)|celestine]]. It is kept under a liquid [[hydrocarbon]] such as [[mineral oil]] or [[kerosene]] to prevent [[oxidation]]; freshly exposed strontium metal rapidly turns a yellowish color with the formation of the oxide. Finely powdered strontium metal is [[pyrophoric]], meaning that it will ignite spontaneously in air at room temperature. Volatile strontium salts impart a bright red color to flames, and these salts are used in [[pyrotechnic]]s and in the production of [[Flare (pyrotechnic)|flares]].<ref name="CRC" /> Like calcium and barium, as well as the alkali metals and the divalent [[lanthanide]]s [[europium]] and [[ytterbium]], strontium metal dissolves directly in liquid [[ammonia]] to give a dark blue solution of solvated electrons.<ref name="Greenwood112" />

===Isotopes===
{{main|Isotopes of strontium}}

Natural strontium is a mixture of four stable [[isotope]]s: <sup>84</sup>Sr, <sup>86</sup>Sr, <sup>87</sup>Sr, and <sup>88</sup>Sr.<ref name="NB2020">{{NUBASE2020}}</ref> Of these isotopes, <sup>88</sup>Sr is the most abundant, making up about 82.6% of all natural strontium, though the abundance varies somewhat due to the production of [[radiogenic]] <sup>87</sup>Sr as the daughter of long-lived [[beta-decay]]ing <sup>87</sup>[[Isotopes of rubidium|Rb]].<ref>Greenwood and Earnshaw, p. 19</ref> This is the basis of [[rubidium–strontium dating]].

Of the unstable isotopes, the primary decay mode of the isotopes lighter than <sup>86</sup>Sr is [[electron capture]] or [[positron emission]] to isotopes of rubidium, and that of the isotopes heavier than <sup>88</sup>Sr is [[electron emission]] to isotopes of [[yttrium]].<ref name="NB2020"/> Of special note are [[strontium-89|<sup>89</sup>Sr]] and [[strontium-90|<sup>90</sup>Sr]]. The former has a [[half-life]] of 50.56&nbsp;days and is used to treat [[bone cancer]] due to strontium's chemical similarity and hence ability to replace calcium.<ref name="HalperinPerez2008">{{cite book|last1=Halperin|first1=Edward C.|last2=Perez|first2=Carlos A.|last3=Brady|first3=Luther W.|title=Perez and Brady's principles and practice of radiation oncology|url=https://books.google.com/books?id=NyeE6-aKnSYC&pg=PA1997|access-date=19 July 2011|year=2008|publisher=Lippincott Williams & Wilkins|isbn=978-0-7817-6369-1|pages=1997–}}</ref><ref name="BaumanCharette2005">{{cite journal|last1=Bauman|first1=Glenn|last2=Charette|first2=Manya|last3=Reid|first3=Robert|last4=Sathya|first4=Jinka|title=Radiopharmaceuticals for the palliation of painful bone metastases – a systematic review|journal=Radiotherapy and Oncology|volume=75|issue=3|year=2005|pages=258.E1–258.E13|doi=10.1016/j.radonc.2005.03.003|pmid=16299924}}</ref> While <sup>90</sup>Sr (half-life 28.91&nbsp;years) has been used similarly, it is more an isotope of concern in [[nuclear fallout|fallout]] from [[nuclear weapons]] and [[nuclear accidents]] due to its longer life (both are produced as [[fission product]]s). Its presence in bones, where all strontium accumulates, can cause bone cancer, cancer of nearby tissues, and [[leukemia]].<ref name="EPA">{{cite web |url=http://www.epa.gov/rpdweb00/radionuclides/strontium.html#environment |archive-url=https://web.archive.org/web/20080407221917/http://www.epa.gov/rpdweb00/radionuclides/strontium.html#environment |url-status=dead |archive-date=7 April 2008 |title=Strontium {{pipe}} Radiation Protection {{pipe}} US EPA |publisher=[[United States Environmental Protection Agency|EPA]] |date=24 April 2012 |access-date=18 June 2012}}</ref> The [[Chernobyl accident|1986 Chernobyl nuclear accident]] contaminated about 30,000&nbsp;km<sup>2</sup> with greater than 10&nbsp;kBq/m<sup>2</sup> of <sup>90</sup>Sr, or an estimated 5% of the reactor's total content of <sup>90</sup>Sr.<ref name="OECD02-Ch1">{{cite web| url=https://www.oecd-nea.org/rp/reports/2003/nea3508-chernobyl.pdf |title=Chernobyl: Assessment of Radiological and Health Impact, 2002 update; Chapter I – The site and accident sequence |publisher=OECD-NEA | year=2002 |access-date=3 June 2015}}</ref>

==History==
[[Image:FlammenfärbungSr.png|thumb|left|upright=0.6|[[Flame test]] for strontium]]

Strontium is named after the Scottish village of [[Strontian]] ({{Langx|gd|Sròn an t-Sìthein}}), where it was discovered in the ores of the lead mines.<ref>{{cite book|author=Murray, W. H.|date=1977|title=The Companion Guide to the West Highlands of Scotland|location=London|publisher=Collins|isbn=978-0-00-211135-5|url-access=registration|url=https://archive.org/details/companionguideto00murr}}</ref>

In 1790, [[Adair Crawford]], a physician engaged in the preparation of barium, and his colleague [[William Cruickshank (chemist)|William Cruickshank]], recognised that the Strontian ores exhibited properties that differed from those in other "heavy spars" sources.<ref>{{cite journal | first = Adair | last = Crawford | date= 1790 | title = On the medicinal properties of the muriated barytes | journal = Medical Communications| volume = 2 | pages = 301–59 | url = https://books.google.com/books?id=bHI_AAAAcAAJ&pg=P301}}</ref> This allowed Crawford to conclude on page 355 "...&nbsp;it is probable indeed, that the scotch mineral is a new species of earth which has not hitherto been sufficiently examined." The physician and mineral collector [[Friedrich Gabriel Sulzer]] analysed together with [[Johann Friedrich Blumenbach]] the mineral from Strontian and named it strontianite. He also came to the conclusion that it was distinct from the [[witherite]] and contained a new earth (neue Grunderde).<ref>{{cite journal | url =https://books.google.com/books?id=gCY7AAAAcAAJ&pg=PA433 | journal =Bergmännisches Journal | title = Über den Strontianit, ein Schottisches Foßil, das ebenfalls eine neue Grunderde zu enthalten scheint| last1 =Sulzer| first1 =Friedrich Gabriel | first2 = Johann Friedrich | last2 = Blumenbach| date =1791 | pages = 433–36}}</ref> In 1793 [[Thomas Charles Hope]], a professor of chemistry at the University of Glasgow studied the mineral<ref>{{cite web|url=http://www.chem.ed.ac.uk/about-us/history/professors/thomas-charles-hope|title=Thomas Charles Hope, MD, FRSE, FRS (1766-1844) - School of Chemistry|website=www.chem.ed.ac.uk|date=16 February 2024 }}</ref><ref>{{cite web| url = http://www.chem.ed.ac.uk/about/professors/hope.html| author = Doyle, W.P.| title = Thomas Charles Hope, MD, FRSE, FRS (1766–1844)| publisher = The University of Edinburgh| url-status = dead| archive-url = https://web.archive.org/web/20130602122314/http://www.chem.ed.ac.uk/about/professors/hope.html| archive-date = 2 June 2013| df = dmy-all}}</ref> and proposed the name ''strontites''.<ref>Although Thomas C. Hope had investigated strontium ores since 1791, his research was published in: {{cite journal | first =Thomas Charles | last =Hope | date = 1798 | title = Account of a mineral from Strontian and of a particular species of earth which it contains | journal = Transactions of the Royal Society of Edinburgh| volume = 4 | issue = 2 | pages =3–39| url = https://books.google.com/books?id=5TEeAQAAMAAJ&pg=RA1-PA3 | doi =10.1017/S0080456800030726| s2cid =251579302 | url-access = subscription }}</ref><ref>{{cite journal |author=Murray, T. |date=1993| title= Elementary Scots: The Discovery of Strontium |journal = Scottish Medical Journal| volume = 38 |pages = 188–89 |pmid=8146640 |issue=6 |doi=10.1177/003693309303800611|s2cid=20396691}}</ref><ref>{{cite journal | first =Thomas Charles | last =Hope | date = 1794 | title = Account of a mineral from Strontian and of a particular species of earth which it contains | journal = Transactions of the Royal Society of Edinburgh| volume = 3 | issue = 2 | pages =141–49| url =https://books.google.com/books?id=7StFAAAAcAAJ&pg=PA143 | doi =10.1017/S0080456800020275| s2cid =251579281 | url-access =subscription }}</ref><!--https://books.google.com/books?id=3GQ7AQAAIAAJ&pg=PA134--> He confirmed the earlier work of Crawford and recounted: "...&nbsp;Considering it a peculiar earth I thought it necessary to give it an name. I have called it Strontites, from the place it was found; a mode of derivation in my opinion, fully as proper as any quality it may possess, which is the present fashion." The element was eventually isolated by Sir [[Humphry Davy]] in 1808 by the [[electrolysis]] of a mixture containing [[strontium chloride]] and [[mercuric oxide]], and announced by him in a lecture to the Royal Society on 30 June 1808.<ref>{{cite journal | last1 = Davy | first1 = H. | date = 1808 | title = Electro-chemical researches on the decomposition of the earths; with observations on the metals obtained from the alkaline earths, and on the amalgam procured from ammonia | url = https://books.google.com/books?id=gpwEAAAAYAAJ&pg=102 | journal = Philosophical Transactions of the Royal Society of London | volume = 98 | pages = 333–70 | doi=10.1098/rstl.1808.0023| doi-access =  | bibcode = 1808RSPT...98..333D | s2cid = 96364168 | url-access = subscription }}</ref> In keeping with the naming of the other alkaline earths, he changed the name to ''strontium''.<ref>{{cite web|url=http://www.lochaber-news.co.uk/news/fullstory.php/aid/2644/Strontian_gets_set_for_anniversary.html|author=Taylor, Stuart|title=Strontian gets set for anniversary|publisher=Lochaber News|date=19 June 2008|url-status=bot: unknown|archive-url=https://web.archive.org/web/20090113005443/http://www.lochaber-news.co.uk/news/fullstory.php/aid/2644/Strontian_gets_set_for_anniversary.html|archive-date=13 January 2009|df=dmy-all}}</ref><ref>{{cite journal |author = Weeks, Mary Elvira |author-link=Mary Elvira Weeks|title = The discovery of the elements: X. The alkaline earth metals and magnesium and cadmium |journal = Journal of Chemical Education |date = 1932 |volume = 9 |pages = 1046–57 |doi = 10.1021/ed009p1046 |issue = 6 |bibcode = 1932JChEd...9.1046W }}</ref><ref>{{cite journal |doi = 10.1080/00033794200201411 |title = The early history of strontium |date = 1942 |last1 = Partington |first1 = J. R. |journal = Annals of Science |volume = 5 |page = 157 |issue = 2}}</ref><ref>{{cite journal | doi = 10.1080/00033795100202211 | title = The early history of strontium. Part II | date = 1951 | last1 = Partington | first1 = J. R. | journal = Annals of Science | volume = 7 | page = 95}}</ref><!-- The google book https://books.google.com/books?id=LagWAAAAYAAJ&pg=PA139 could help with original literature--><ref>Many other early investigators examined strontium ore, among them: '''(1)''' Martin Heinrich Klaproth, "Chemische Versuche über die Strontianerde" (Chemical experiments on strontian ore), ''Crell's Annalen'' (September 1793) no. ii, pp. 189–202 ; and "Nachtrag zu den Versuchen über die Strontianerde" (Addition to the Experiments on Strontian Ore), ''Crell's Annalen'' (February 1794) no. i, p. 99 ; also '''(2)''' {{cite journal | last1 = Kirwan | first1 = Richard | date = 1794 | title = Experiments on a new earth found near Stronthian in Scotland | journal = The Transactions of the Royal Irish Academy | volume = 5 | pages = 243–56 }}</ref>

The first large-scale application of strontium was in the production of sugar from [[sugar beet]]. Although a crystallisation process using strontium hydroxide was patented by [[Augustin-Pierre Dubrunfaut]] in 1849<ref name="Metalle in der Elektrochemie">{{cite book | url = https://books.google.com/books?id=xDkoAQAAIAAJ&q=dubrunfaut+strontium| title =Metalle in der Elektrochemie | pages = 158–62 | author1 = Fachgruppe Geschichte Der Chemie, Gesellschaft Deutscher Chemiker | date = 2005}}</ref> the large scale introduction came with the improvement of the process in the early 1870s. The German [[sugar industry]] used the process well into the 20th century. Before [[World War I]] the beet sugar industry used 100,000 to 150,000 tons of strontium hydroxide for this [[Strontian process|process]] per year.<ref name="books.google.de">{{cite book | chapter = strontium saccharate process | chapter-url = https://books.google.com/books?id=-vd_cn4K8NUC&pg=PA341 | isbn = 978-1-4437-2504-0 | title = Manufacture of Sugar from the Cane and Beet | author1 = Heriot, T. H. P | date = 2008| publisher=Read Books }}</ref> The strontium hydroxide was recycled in the process, but the demand to substitute losses during production was high enough to create a significant demand initiating mining of strontianite in the [[Münsterland]]. The mining of strontianite in Germany ended when mining of the [[celestine (mineral)|celestine]] deposits in [[Gloucestershire]] started.<ref>{{cite web | url = http://www.lwl.org/LWL/Kultur/Westfalen_Regional/Wirtschaft/Bergbau/Strontianitbergbau/ | title = Der Strontianitbergbau im Münsterland | first = Martin | last = Börnchen | access-date = 9 November 2010 | url-status = dead | archive-url = https://web.archive.org/web/20141211085517/http://www.lwl.org/LWL/Kultur/Westfalen_Regional/Wirtschaft/Bergbau/Strontianitbergbau/ | archive-date = 11 December 2014 | df = dmy-all }}</ref> These mines supplied most of the world strontium supply from 1884 to 1941. Although the celestine deposits in the [[Granada basin]] were known for some time the large scale mining did not start before the 1950s.<ref>{{cite journal | doi = 10.1016/0037-0738(84)90055-1 | title = Genesis and evolution of strontium deposits of the granada basin (Southeastern Spain): Evidence of diagenetic replacement of a stromatolite belt | date = 1984 | last1 = Martin | first1 = Josèm | last2 = Ortega-Huertas | first2 = Miguel | last3 = Torres-Ruiz | first3 = Jose | journal = Sedimentary Geology | volume = 39 | issue = 3–4 | page = 281|bibcode = 1984SedG...39..281M }}</ref>

During atmospheric [[nuclear weapons testing]], it was observed that strontium-90 is one of the [[nuclear fission product]]s with a relatively high yield. The similarity to calcium and the chance that the strontium-90 might become enriched in bones made research on the metabolism of strontium an important topic.<ref>{{cite web | url = http://www-nds.iaea.org/sgnucdat/c1.htm | publisher = iaea.org| title = Chain Fission Yields }}</ref><ref>{{cite journal | pmc = 1985251 | date = 1968 | last1 = Nordin | first1 = B. E. | title = Strontium Comes of Age | volume = 1 | issue = 5591 | page = 566 | journal = British Medical Journal | doi = 10.1136/bmj.1.5591.566}}</ref>

==Occurrence==
{{Category see also|Strontium minerals}}
[[Image:Celestine Poland.jpg|thumb|left|The mineral celestine ({{chem2|SrSO4}})]]

Strontium commonly occurs in nature, being the 15th most [[Abundance of the chemical elements|abundant element]] on Earth (its heavier congener barium being the 14th), estimated to average approximately 360&nbsp;[[parts per million]] in the [[Abundance of elements in Earth's crust|Earth's crust]]<ref>{{cite journal|last1=Turekian|first1=K. K.|last2=Wedepohl|first2=K. H.|title=Distribution of the elements in some major units of the Earth's crust|journal=Geological Society of America Bulletin|volume=72|issue=2|pages=175–92|doi=10.1130/0016-7606(1961)72[175:DOTEIS]2.0.CO;2|bibcode = 1961GSAB...72..175T |year=1961|doi-access=free}}</ref> and is found chiefly as the [[sulfate]] [[mineral]] [[Celestine (mineral)|celestine]] ({{chem2|SrSO4}}) and the [[carbonate]] [[strontianite]] ({{chem2|SrCO3}}). Of the two, celestine occurs much more frequently in deposits of sufficient size for mining. Because strontium is used most often in the carbonate form, strontianite would be the more useful of the two common minerals, but few deposits have been discovered that are suitable for development.<ref name="usgs10">{{cite web |publisher = United States Geological Survey |access-date = 14 May 2010 |title = Mineral Commodity Summaries 2010: Strontium |first = Joyce A. |last = Ober |url = https://minerals.usgs.gov/minerals/pubs/commodity/strontium/mcs-2010-stron.pdf |archive-date = 16 July 2010 |archive-url = https://web.archive.org/web/20100716142558/http://minerals.usgs.gov/minerals/pubs/commodity/strontium/mcs-2010-stron.pdf |url-status = dead }}</ref> Because of the way it reacts with air and water, strontium only exists in nature when combined to form minerals. Naturally occurring strontium is stable, but its synthetic isotope Sr-90 is only produced by nuclear fallout.

In groundwater strontium behaves chemically much like calcium. At intermediate to acidic [[pH]] Sr<sup>2+</sup> is the dominant strontium species. In the presence of calcium ions, strontium commonly forms [[Coprecipitation|coprecipitates]] with calcium minerals such as [[calcite]] and anhydrite at an increased pH. At intermediate to acidic pH, dissolved strontium is bound to soil particles by [[Cation-exchange capacity|cation exchange]].<ref name="Heuel-Fabianek">{{cite journal |journal=Berichte des Forschungszentrums Jülich |volume=4375 |date=2014 |author=Heuel-Fabianek, B. |title= Partition Coefficients (Kd) for the Modelling of Transport Processes of Radionuclides in Groundwater | url = http://juser.fz-juelich.de/record/154001/files/FZJ-2014-03430.pdf | issn=0944-2952 }}</ref>

The mean strontium content of ocean water is 8&nbsp;mg/L.<ref>{{cite book|chapter=Strontium|title=Artesian water in Tertiary limestone in the southeastern States |chapter-url = https://books.google.com/books?id=8eQqAQAAIAAJ&pg=PA138| pages =138–39 |series = Geological Survey Professional Paper|publisher=United States Government Printing Office|author=Stringfield, V. T. |date = 1966}}</ref><ref>{{cite journal | doi = 10.1016/0009-2541(66)90013-1 | title = Observed variations in the strontium concentration of sea water | date = 1966 | last1 = Angino | first1 = Ernest E. | last2 = Billings | first2 = Gale K. | last3 = Andersen | first3 = Neil | journal = Chemical Geology | volume = 1 | page = 145| bibcode = 1966ChGeo...1..145A }}</ref> At a concentration between 82 and 90 μmol/L of strontium, the concentration is considerably lower than the calcium concentration, which is normally between 9.6 and 11.6&nbsp;mmol/L.<ref>{{cite journal | doi = 10.1007/s00338-004-0467-x | title = Influence of seawater Sr content on coral Sr/Ca and Sr thermometry | date = 2005 | last1 = Sun | first1 = Y. | last2 = Sun | first2 = M. | last3 = Lee | first3 = T. | last4 = Nie | first4 = B. | journal = Coral Reefs | volume = 24 | page = 23| s2cid = 31543482 }}</ref><ref>{{cite book |url = https://books.google.com/books?id=zNicdkuulE4C&pg=PA928 |title = Industrial Minerals & Rocks: Commodities, Markets, and Uses |isbn = 978-0-87335-233-8 |last1 = Kogel |first1 = Jessica Elzea |last2 = Trivedi |first2 = Nikhil C. |last3 = Barker |first3 = James M. |date = 5 March 2006}}</ref> It is nevertheless much higher than that of barium, 13&nbsp;μg/L.<ref name="CRC" />

==Production==
The major producers of strontium as celestine as of January 2024 are Spain (200,000&nbsp;[[metric ton|t]]), Iran (200,000&nbsp;t), China (80,000&nbsp;t), Mexico (35,000&nbsp;t); and Argentina (700&nbsp;t).<ref name="USGSMinRep24">{{Cite report |url=https://pubs.usgs.gov/publication/mcs2024 |title=Mineral commodity summaries 2024 |series=Mineral Commodity Summaries |date=January 2024 |doi=10.3133/mcs2024 |isbn=978-1-4113-4544-7 |publisher=U.S. Geological Survey |location=Reston, VA |language=en}}</ref> Although strontium deposits occur widely in the United States, they have not been mined since 1959.<ref name="USGSMinRep24" />

A large proportion of mined celestine is converted to the carbonate by two processes. Either the celestine is directly leached with sodium carbonate solution or the celestine is roasted with coal to form the sulfide. The second stage produces a dark-coloured material containing mostly [[strontium sulfide]]. This so-called "black ash" is dissolved in water and filtered. Strontium carbonate is precipitated from the strontium sulfide solution by introduction of [[carbon dioxide]].<ref>{{cite book | url = https://books.google.com/books?id=5smDPzkw0wEC&pg=PA401 | title = Production of SrCO<sub>3</sub> by black ash process: Determination of reductive roasting parameters| page = 401 | isbn = 978-90-5410-829-0 | last1 = Kemal | first1 = Mevlüt | last2 = Arslan | first2 = V. | last3 = Akar | first3 = A. | last4 = Canbazoglu | first4 = M. | date = 1996| publisher = CRC Press}}</ref> The sulfate is [[Redox|reduced]] to the [[sulfide]] by the [[carbothermic reduction]]:
:{{chem2|SrSO4 + 2 C -> SrS + 2 CO2}}

About 300,000 tons are processed in this way annually.<ref name="Ullmann" />

The metal is produced commercially by reducing strontium [[oxide]] with [[aluminium]]. The strontium is [[distillation|distilled]] from the mixture.<ref name="Ullmann" /> Strontium metal can also be prepared on a small scale by [[electrolysis]] of a solution of [[strontium chloride]] in molten [[potassium chloride]]:<ref name="Greenwood111" />
:{{chem2|Sr+ + 2 e- -> Sr}}
:{{chem2|2 Cl− -> Cl2 + 2 e-}}

==Applications==
[[File:Monitor.arp.jpg|thumb|Most of the world's production of strontium used to be consumed in the production of cathode-ray tube (CRT) displays. The glass contained strontium and barium oxide to block X-rays.]]

Consuming 75% of production, the primary use for strontium was in glass for colour television [[cathode-ray tube]]s,<ref name="Ullmann" /> where it prevented [[X-ray]] emission.<ref>{{cite web |title = Cathode Ray Tube Glass-To-Glass Recycling |publisher = ICF Incorporated, USEP Agency |url = http://yosemite.epa.gov/ee/epa/riafile.nsf/419e576a3df1421685256470007e3141/5a52093c460136ac85256cf6008062d0/$FILE/S99-23.pdf |archive-url = https://web.archive.org/web/20081219162330/http://yosemite.epa.gov/ee/epa/riafile.nsf/419e576a3df1421685256470007e3141/5a52093c460136ac85256cf6008062d0/$FILE/S99-23.pdf |archive-date = 19 December 2008 | access-date = 7 January 2012}}</ref><ref>{{cite web |publisher = United States Geological Survey |access-date = 14 October 2008 |title = Mineral Yearbook 2007: Strontium |first = Joyce A. |last = Ober |author2 = Polyak, Désirée E. |url = https://minerals.usgs.gov/minerals/pubs/commodity/strontium/myb1-2007-stron.pdf |archive-date = 20 September 2008 |archive-url = https://web.archive.org/web/20080920070543/http://minerals.usgs.gov/minerals/pubs/commodity/strontium/myb1-2007-stron.pdf |url-status = dead }}</ref> This application for strontium has been declining because CRTs are being replaced by other display methods. This decline has a significant influence on the mining and refining of strontium.<ref name="usgs10" /> All parts of the CRT must absorb X-rays. In the neck and the funnel of the tube, lead glass is used for this purpose, but this type of glass shows a browning effect due to the interaction of the X-rays with the glass. Therefore, the front panel is made from a different glass mixture with strontium and barium to absorb the X-rays. The average values for the glass mixture determined for a recycling study in 2005 is 8.5% [[strontium oxide]] and 10% [[barium oxide]].<ref>{{cite journal |doi = 10.1016/j.wasman.2005.11.017 |pmid = 16427267 |date = 2006 |last1 = Méar |first1 = F. |last2 = Yot |first2 = P. |last3 = Cambon |first3 = M. |last4 = Ribes |first4 = M. |title = The characterization of waste cathode-ray tube glass |volume = 26 |issue = 12 |pages = 1468–76 |journal = Waste Management |bibcode = 2006WaMan..26.1468M }}</ref>

Because strontium is so similar to calcium, it is incorporated in the bone. All four stable isotopes are incorporated, in roughly the same proportions they are found in nature. However, the actual distribution of the isotopes tends to vary greatly from one geographical location to another. Thus, analyzing the bone of an individual can help determine the region it came from.<ref name="PriceSchoeninger1985">{{cite journal|last1=Price|first1=T. Douglas|last2=Schoeninger|first2=Margaret J.|author2-link=Margaret Schoeninger|last3=Armelagos|first3=George J.|title=Bone chemistry and past behavior: an overview|journal=Journal of Human Evolution|volume=14|issue=5|year=1985|pages=419–47|doi=10.1016/S0047-2484(85)80022-1|bibcode=1985JHumE..14..419P }}</ref><ref name="SteadmanBrudevold1958">{{cite journal|last1=Steadman|first1=Luville T.|last2=Brudevold|first2=Finn|last3=Smith|first3=Frank A.|title=Distribution of strontium in teeth from different geographic areas|journal=The Journal of the American Dental Association|volume=57|issue=3|year=1958|pages=340–44|doi=10.14219/jada.archive.1958.0161|pmid=13575071}}</ref> This approach helps to identify the ancient migration patterns and the origin of commingled human remains in battlefield burial sites.<ref name="SchweissingGrupe2003">{{cite journal|last1=Schweissing|first1=Matthew Mike|last2=Grupe|first2=Gisela|title=Stable strontium isotopes in human teeth and bone: a key to migration events of the late Roman period in Bavaria|journal=Journal of Archaeological Science|volume=30|issue=11|year=2003|pages=1373–83|doi=10.1016/S0305-4403(03)00025-6|bibcode=2003JArSc..30.1373S }}</ref>

<sup>87</sup>Sr/<sup>86</sup>Sr ratios are commonly used to determine the likely provenance areas of sediment in natural systems, especially in [[Marine environments|marine]] and [[River|fluvial]] environments. Dasch (1969) showed that surface sediments of Atlantic displayed <sup>87</sup>Sr/<sup>86</sup>Sr ratios that could be regarded as bulk averages of the <sup>87</sup>Sr/<sup>86</sup>Sr ratios of geological terrains from adjacent landmasses.<ref name="Dasch">{{cite journal |journal=Geochimica et Cosmochimica Acta |volume=33 |issue=12 |pages=1521–52 |date=1969 |last=Dasch |first = J.| title=Strontium isotopes in weathering profiles, deep-sea sediments, and sedimentary rocks| doi = 10.1016/0016-7037(69)90153-7 |bibcode = 1969GeCoA..33.1521D }}</ref> A good example of a fluvial-marine system to which Sr isotope provenance studies have been successfully employed is the River Nile-Mediterranean system.<ref name="Krom1999">{{cite journal |journal=Marine Geology |volume=155 |issue=3–4 |pages=319–30 |date=1999 |last1= Krom |first1 = M. D. |last2= Cliff |first2 =R.| last3=Eijsink |first3 = L. M. |last4= Herut |first4 =B. |title=The characterisation of Saharan dusts and Nile particulate matter in surface sediments from the Levantine basin using Sr isotopes |doi = 10.1016/S0025-3227(98)00130-3 |last5=Chester |first5=R. |bibcode=1999MGeol.155..319K }}</ref><!--.<ref name=Krom2002>{{cite journal |journal=Geology |volume=30 |issue=1 |pages=71–74 |date=2002 |first1 = Michael D. |last1=Krom |first2 = J. Daniel |last2=Stanley |first3 = Robert A. |last3=Cliff |first4 = Jamie C. |last4= Woodward |title=Nile River sediment fluctuations over the past 7000 yr and their key role in sapropel development |doi = 10.1130/0091-7613(2002)030<0071:NRSFOT>2.0.CO;2 |year=2002 |bibcode = 2002Geo....30...71K }}</ref><ref name=Talbot>{{cite journal |journal=Geology |volume=28 |issue=4 |pages=343–46| date=2000 |author=Talbot, M. R. et al.| title=Strontium isotope evidence for late Pleistocene reestablishment of an integrated Nile drainage network |doi = 10.1130/0091-7613(2000)28<343:SIEFLP>2.0.CO;2 |year=2000 |bibcode = 2000Geo....28..343T }}</ref>--> Due to the differing ages of the rocks that constitute the majority of the [[Blue Nile|Blue]] and [[White Nile]], [[catchment area]]s of the changing provenance of sediment reaching the [[River Nile Delta]] and East Mediterranean Sea can be discerned through strontium isotopic studies. Such changes are climatically controlled in the [[Late Quaternary]].<ref name="Krom1999" />

More recently, <sup>87</sup>Sr/<sup>86</sup>Sr ratios have also been used to determine the source of ancient archaeological materials such as timbers and corn in [[Chaca Canyon, New Mexico|Chaco Canyon, New Mexico]].<ref name="Benson">{{cite journal |journal=Proceedings of the National Academy of Sciences |volume=100 |issue=22 |pages=13111–15 |date=2003 |author=Benson, L. |author2=Cordell, L. |author3=Vincent, K. |author4=Taylor, H. |author5=Stein, J. |author6=Farmer, G. |author7=Kiyoto, F. |name-list-style=amp |pmid=14563925 |title= Ancient maize from Chacoan great houses: where was it grown?|pmc=240753 |doi = 10.1073/pnas.2135068100 |bibcode = 2003PNAS..10013111B |doi-access=free }}</ref><ref name="English">{{cite journal |journal=Proc Natl Acad Sci USA |volume=98 |issue=21 |pages=11891–96 |date=October 2001 |author=English NB |author2=Betancourt JL |author3=Dean JS |author4=Quade J. |title=Strontium isotopes reveal distant sources of architectural timber in Chaco Canyon, New Mexico|pmid=11572943 |doi = 10.1073/pnas.211305498 |pmc=59738 |bibcode = 2001PNAS...9811891E |doi-access=free }}</ref> <sup>87</sup>Sr/<sup>86</sup>Sr ratios in teeth may also be used to [[Animal migration tracking|track animal migrations]].<ref name="Barnett-Johnson">{{cite journal |journal=Canadian Journal of Fisheries and Aquatic Sciences |volume=64 |issue=12 |pages=1683–92 |date=2007 |author=Barnett-Johnson, Rachel |title=Identifying the contribution of wild and hatchery Chinook salmon (Oncorhynchus tshawytscha) to the ocean fishery using otolith microstructure as natural tags |doi = 10.1139/F07-129 |last2=Grimes |first2=Churchill B. |last3=Royer |first3=Chantell F. |last4=Donohoe |first4=Christopher J. |bibcode=2007CJFAS..64.1683B |s2cid=54885632 |url=https://zenodo.org/record/1235897 }}</ref><ref name="Porder">{{cite journal |journal=Paleobiology |volume=29 |issue=2 |pages=197–204 |author=Porder, S. |author2=Paytan, A. |author3=E.A. Hadly |name-list-style=amp |title=Mapping the origin of faunal assemblages using strontium isotopes |doi = 10.1666/0094-8373(2003)029<0197:MTOOFA>2.0.CO;2 |year=2003 |s2cid=44206756 }}</ref>

[[Strontium aluminate]] is frequently used in [[Phosphorescence|glow in the dark]] toys, as it is chemically and biologically inert.<ref>{{cite journal |last1=Van der Heggen |first1=David |title=Persistent Luminescence in Strontium Aluminate: A Roadmap to a Brighter Future |journal=Advanced Functional Materials |date=October 2022 |volume=32 |issue=52 |article-number=2208809 |doi=10.1002/adfm.202208809 |bibcode=2022AdvFM..3208809V |url=https://onlinelibrary.wiley.com/doi/10.1002/adfm.202208809 |access-date=21 April 2023|hdl=1854/LU-01GJ1338HX6QQBT438E4QW442N |s2cid=253347258 |hdl-access=free }}</ref>

[[File:Ignis Brunensis 2010-05-22 (5).jpg|alt=red fireworks|thumb|upright|Strontium salts are added to fireworks in order to create red colors.]]

[[Strontium carbonate]] and other strontium [[Salt (chemistry)|salts]] are added to fireworks to give a deep red colour.<ref>{{cite web |url=http://chemistry.about.com/od/fireworkspyrotechnics/a/fireworkcolors.htm |title=Chemistry of Firework Colors – How Fireworks Are Colored |publisher=Chemistry.about.com |date=10 April 2012 |access-date=14 April 2012 |archive-date=13 May 2008 |archive-url=https://web.archive.org/web/20080513202402/http://chemistry.about.com/od/fireworkspyrotechnics/a/fireworkcolors.htm |url-status=dead }}</ref> This same effect identifies strontium [[cations]] in the [[flame test]]. Fireworks consume about 5% of the world's production.<ref name="Ullmann">MacMillan, J. Paul; Park, Jai Won; Gerstenberg, Rolf; Wagner, Heinz; Köhler, Karl and Wallbrecht, Peter (2002) "Strontium and Strontium Compounds" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a25_321}}.</ref> Strontium carbonate is used in the manufacturing of hard [[ferrite (magnet)|ferrite]] magnets.<ref>{{cite web |url=http://www.arnoldmagnetics.com/Ferrite.aspx |title=Ferrite Permanent Magnets |author=<!--Staff writer(s); no by-line.--> |publisher=Arnold Magnetic Technologies |access-date=18 January 2014 |url-status=dead |archive-url=https://web.archive.org/web/20120514152507/http://www.arnoldmagnetics.com/Ferrite.aspx |archive-date=14 May 2012 |df=dmy-all }}</ref><ref>{{cite web |url=http://www.cpc-us.com/products/barium-carbonate.html |title=Barium Carbonate |author=<!--Staff writer(s); no by-line.--> |publisher=Chemical Products Corporation |access-date=18 January 2014 |url-status=dead |archive-url=https://web.archive.org/web/20141006124351/http://www.cpc-us.com/products/barium-carbonate.html |archive-date=6 October 2014 |df=dmy-all }}</ref>

[[Strontium chloride]] is sometimes used in toothpastes for sensitive teeth. One popular brand includes 10% total strontium chloride hexahydrate by weight.<ref>{{cite book | url = https://books.google.com/books?id=cwom9OTMmGYC&pg=PA885 | page = 885 | title = Textbook of Oral Medicine | isbn = 978-81-8061-431-6 | author1 = Ghom | date = 1 December 2005 | publisher = Jaypee Brothers, Medical Publishers }}{{Dead link|date=August 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Small amounts are used in the refining of zinc to remove small amounts of lead impurities.<ref name="CRC" /> The metal itself has a limited use as a [[getter]], to remove unwanted gases in vacuums by reacting with them, although barium may also be used for this purpose.<ref name="Greenwood111">Greenwood and Earnshaw, p. 111</ref>

The ultra-narrow optical transition between the [Kr]5s<sub>2</sub> <sup>1</sup>S<sub>0</sub> electronic [[ground state]] and the [[Metastability|metastable]] [Kr]5s5p <sup>3</sup>P<sub>0</sub> excited state of <sup>87</sup>Sr is one of the leading candidates for the future re-definition of the [[second]] in terms of an optical transition as opposed to the current definition derived from a microwave transition between different [[Hyperfine structure|hyperfine]] ground states of [[Caesium|<sup>133</sup>Cs.]]<ref>{{Cite web|url=https://www.science.org/content/article/better-atomic-clocks-scientists-prepare-redefine-second|title=With better atomic clocks, scientists prepare to redefine the second|last1=Cartlidge|first1=Edwin|date=2018-02-28|website=Science {{!}} AAAS|language=en|access-date=2019-02-10}}</ref> Current optical [[atomic clock]]s operating on this transition already surpass the precision and accuracy of the current definition of the second.<ref>{{Cite web |title=Recommended values of standard frequencies - BIPM |url=https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies?version=1.4&t=1637238077933&download=true |access-date=2023-05-21 |website=www.bipm.org}}</ref>

===Radioactive strontium===
[[File:Soviet RTG.jpg|thumb|RTGs from Soviet-era lighthouses]]

[[strontium-89|<sup>89</sup>Sr]] is the active ingredient in [[Metastron]],<ref>{{cite web |title=FDA ANDA Generic Drug Approvals |url=https://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/DrugandBiologicApprovalReports/ANDAGenericDrugApprovals/UCM064272 |archive-url=https://web.archive.org/web/20100310215720/http://www.fda.gov/Drugs/DevelopmentApprovalProcess/HowDrugsareDevelopedandApproved/DrugandBiologicApprovalReports/ANDAGenericDrugApprovals/UCM064272 |url-status=dead |archive-date=10 March 2010 |publisher=[[Food and Drug Administration]]}}</ref> a [[radiopharmaceutical]] used for bone pain secondary to [[metastatic]] [[bone cancer]]. The strontium is processed like calcium by the body, preferentially incorporating it into bone at sites of increased [[osteogenesis]]. This localization focuses the radiation exposure on the cancerous lesion.<ref name="BaumanCharette2005" />

[[strontium-90|<sup>90</sup>Sr]] has been used as a power source for [[radioisotope thermoelectric generator]]s (RTGs). <sup>90</sup>Sr produces approximately 0.93 watts of heat per gram (it is lower for the form of <sup>90</sup>Sr used in RTGs, which is [[strontium fluoride]]).<ref>{{cite web |url=http://www.qrg.northwestern.edu/projects/vss/docs/Power/3-what-are-the-fuels-for-rtgs.html |title=What are the fuels for radioisotope thermoelectric generators?|work=qrg.northwestern.edu}}</ref><!--Search for a better source--> However, <sup>90</sup>Sr has one third the lifetime and a lower density than [[plutonium-238|<sup>238</sup>Pu]], another RTG fuel. The main advantage of <sup>90</sup>Sr is that it is significantly cheaper than <sup>238</sup>Pu and is found in [[nuclear waste]]. The latter must be prepared by irradiating <sup>237</sup>Np with neutrons then separating the modest amounts of  <sup>238</sup>Pu. The principal disadvantage of <sup>90</sup>Sr is the high energy beta particles produce [[Bremsstrahlung]] as they encounter nuclei of other nearby heavy atoms such as adjacent strontium. This is mostly in the range of X-rays. Thus strong beta emitters also emit significant secondary X-rays in most cases. This requires significant shielding measures which complicates the design of RTGs using <sup>90</sup>Sr. The [[Soviet Union]] deployed nearly 1000 of these RTGs on its northern coast as a power source for lighthouses and meteorology stations.<ref>{{cite book |page = 459 |url = https://books.google.com/books?id=8WOza_y3IkQC&pg=PA459 |title = Nuclear safeguards, security and nonproliferation: achieving security with technology and policy |isbn = 978-0-7506-8673-0 |author1 = Doyle, James |date = 30 June 2008| publisher=Elsevier }}</ref><ref name="O'BrienAmbrosi2008">{{cite journal|last1=O'Brien|first1=R. C.|last2=Ambrosi|first2=R. M.|last3=Bannister|first3=N. P.|last4=Howe|first4=S. D.|last5=Atkinson|first5=H. V.|title=Safe radioisotope thermoelectric generators and heat sources for space applications|journal=Journal of Nuclear Materials|volume=377|issue=3|year=2008|pages=506–21|doi=10.1016/j.jnucmat.2008.04.009|bibcode=2008JNuM..377..506O}}</ref>

==Biological role==
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[[Acantharea]], a relatively large group of marine [[radiolaria]]n [[protozoa]], produce intricate mineral [[skeleton]]s composed of [[strontium sulfate]].<ref>{{cite journal | doi = 10.1023/B:HYDR.0000027333.02017.50 | title = On the celestite-secreting Acantharia and their effect on seawater strontium to calcium ratios | date = 2004 | last1 = De Deckker | first1 = Patrick | journal = Hydrobiologia | volume = 517 | issue = 1–3 | page = 1| bibcode = 2004HyBio.517....1D | s2cid = 42526332 }}</ref> In biological systems, calcium is substituted to a small extent by strontium.<ref>{{cite journal | doi = 10.1016/j.bone.2004.04.026 | title = The biological role of strontium | date = 2004 | last1 = Pors Nielsen | first1 = S. | journal = Bone | volume = 35 | issue = 3 | pages = 583–88 | pmid = 15336592}}</ref> In the human body, most of the absorbed strontium is deposited in the bones. The ratio of strontium to calcium in human bones is between 1:1000 and 1:2000, roughly in the same range as in the blood serum.<ref>{{cite journal | doi =10.1359/jbmr.1999.14.5.661 | title =Strontium and Bone | date =1999 | last1 =Cabrera | first1 =Walter E. | last2 =Schrooten | first2 =Iris | last3 =De Broe | first3 =Marc E. | last4 =d'Haese | first4 =Patrick C. | journal =Journal of Bone and Mineral Research | volume =14 | issue =5 | pages =661–68 | pmid =10320513| s2cid =32627349 | doi-access =free }}</ref>

=== Effect on the human body ===
The human body absorbs strontium as if it were its lighter congener calcium. Because the elements are chemically very similar, stable strontium isotopes do not pose a significant health threat. The average human has an intake of about two milligrams of strontium a day.<ref name="nbb">{{cite book |page=507 |title=Nature's building blocks: an A–Z guide to the elements |first=John|last=Emsley |publisher=Oxford University Press |isbn=978-0-19-960563-7 |date=2011}}</ref> In adults, strontium consumed tends to attach only to the surface of bones, but in children, strontium can replace calcium in the mineral of the growing bones and thus lead to bone growth problems.<ref>{{cite web |url=https://wwwn.cdc.gov/TSP/PHS/PHS.aspx?phsid=654&toxid=120 |title=Strontium {{!}} Public Health Statement {{!}} ATSDR|author=Agency for Toxic Substances and Disease Registry |date=26 March 2014 |website=cdc.gov |publisher=Agency for Toxic Substances and Disease Registry |access-date=12 January 2024}}</ref>

The [[biological half-life]] of strontium in humans has variously been reported as from 14 to 600 days,<ref>{{citation |chapter-url=http://hanford-site.pnnl.gov/envreport/2001/env01_45.pdf |title=Hanford Site 2001 Environmental Report |chapter=4.5 Fish and Wildlife Surveillance |last1=Tiller |first1=B. L. |publisher=DOE |year=2001 |access-date=14 January 2014 |archive-date=11 May 2013 |archive-url=https://web.archive.org/web/20130511040509/http://hanford-site.pnnl.gov/envreport/2001/env01_45.pdf |url-status=dead }}</ref><ref>{{citation |url=http://www.osti.gov/bridge/servlets/purl/10136486-6sLptZ/native/10136486.pdf |title=Ecotoxicity Literature Review of Selected Hanford Site Contaminants |doi=10.2172/10136486 |publisher=DOE |last1=Driver |first1=C. J. |year=1994 |osti=10136486 |access-date=14 January 2014}}</ref> 1,000 days,<ref>{{cite web |url=http://www.areaivenvirothon.org/freshwaterecology.htm |title=Freshwater Ecology and Human Influence |publisher=Area IV Envirothon |access-date=14 January 2014 |archive-url=https://web.archive.org/web/20140101063834/http://www.areaivenvirothon.org/freshwaterecology.htm |archive-date=1 January 2014 |url-status=dead |df=dmy-all}}</ref> 18 years,<ref>{{cite web |url=https://epi.alaska.gov/eh/radiation/RadioisotopesInFood.pdf |title=Radioisotopes That May Impact Food Resources |access-date=14 January 2014 |publisher=Epidemiology, Health and Social Services, State of Alaska |url-status=bot: unknown |archive-url=https://web.archive.org/web/20140821162026/http://epi.alaska.gov/eh/radiation/RadioisotopesInFood.pdf |archive-date=21 August 2014 |df=dmy-all}}</ref> 30 years<ref>{{cite web |url=http://www.gsseser.com/FactSheet/Strontium.pdf |title=Human Health Fact Sheet: Strontium |publisher=Argonne National Laboratory |date=October 2001 |access-date=14 January 2014 |archive-url=https://web.archive.org/web/20140124000858/http://www.gsseser.com/FactSheet/Strontium.pdf |archive-date=24 January 2014 |url-status=dead |df=dmy-all}}</ref> and, at an upper limit, 49 years.<ref>{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/biohalf.html |title=Biological Half-life |publisher=HyperPhysics |access-date=14 January 2014}}</ref> The wide-ranging published biological half-life figures are explained by strontium's complex metabolism within the body. However, by averaging all excretion paths, the overall biological half-life is estimated to be about 18 years.<ref>{{cite book |chapter-url=http://www.fourmilab.ch/etexts/www/effects/eonw_12.pdf |title=The effects of Nuclear Weapons |last1=Glasstone |first1=Samuel |last2=Dolan |first2=Philip J. |year=1977 |access-date=14 January 2014 |chapter=XII: Biological Effects |page=605}}</ref> The elimination rate of strontium is strongly affected by age and sex, due to differences in [[bone metabolism]].<ref name="ShaginaBougrov2006">{{cite journal |last1=Shagina |first1=N. B. |last2=Bougrov |first2=N. G. |last3=Degteva |first3=M. O. |last4=Kozheurov |first4=V. P. |last5=Tolstykh |first5=E. I. |title=An application of in vivo whole body counting technique for studying strontium metabolism and internal dose reconstruction for the Techa River population |journal=Journal of Physics: Conference Series |volume=41 |issue=1 |year=2006 |pages=433–40 |doi=10.1088/1742-6596/41/1/048|bibcode=2006JPhCS..41..433S |s2cid=32732782 |doi-access=free}}</ref>

The drug [[strontium ranelate]] aids [[bone]] growth, increases bone density, and lessens the incidence of vertebral, peripheral, and hip [[Bone fracture|fractures]].<ref>{{cite journal |author=Meunier P. J. |author2=Roux C. |author3=Seeman E. |title=The effects of strontium ranelate on the risk of vertebral fracture in women with postmenopausal osteoporosis |journal=New England Journal of Medicine |volume=350 |date=January 2004 |pages=459–68 |pmid=14749454 |doi=10.1056/NEJMoa022436|last4=Ortolani |first4=S.|last5=Badurski |first5=J. E. |last6=Spector |first6=T. D.|last7=Cannata |first7=J.|last8=Balogh |first8=A.|last9=Lemmel |first9=E. M.|last10=Pors-Nielsen |first10=S.|last11=Rizzoli |first11=R. |last12=Genant |first12=H. K.|last13=Reginster |first13=J. Y.|issue=5 |hdl=2268/7937 |url=http://espace.library.uq.edu.au/view/UQ:315180/UQ315180_OA.pdf}}</ref><ref>{{cite journal |author=Reginster JY |author2=Seeman E |author3=De Vernejoul MC |title=Strontium ranelate reduces the risk of nonvertebral fractures in postmenopausal women with osteoporosis: treatment of peripheral osteoporosis (TROPOS) study |journal=The Journal of Clinical Endocrinology & Metabolism|volume=90 |date=May 2005 |pages=2816–22 |pmid=15728210 |doi=10.1210/jc.2004-1774 |first4=S. |last4=Adami|first5=J. |last5=Compston|first6=C. |last6=Phenekos|first7=J. P. |last7=Devogelaer|first8=M. |last8=Diaz Curiel|first9=A. |last9=Sawicki|first10=S. |last10=Goemaere|first11=O. H. |last11=Sorensen|last12=Felsenberg |first12=D.|last13=Meunier |first13=P. J. |issue=5 |url=http://orbi.ulg.ac.be/bitstream/2268/20123/1/Strontium%20ranelate%20reduces%20the%20risk%20of%20nonvertebral%20fractures%20in%20postmenopausal%20women%20with%20osteoporosis%20Treatment%20of%20Peripheral%20Osteoporosis%20%28TROPOS%29%20study.pdf |doi-access=free }}</ref> However, strontium ranelate also increases the risk of venous thromboembolism, pulmonary embolism, and serious cardiovascular disorders, including myocardial infarction. Its use is therefore now restricted.<ref>{{cite web|title=Strontium ranelate: cardiovascular risk – restricted indication and new monitoring requirements |date= March 2014|url=http://www.mhra.gov.uk/Safetyinformation/DrugSafetyUpdate/CON392870|publisher=Medicines and Healthcare products Regulatory Agency, UK}}</ref> Its beneficial effects are also questionable, since the increased bone density is partially caused by the increased density of strontium over the calcium which it replaces. Strontium also [[bioaccumulation|bioaccumulates]] in the body.<ref>{{cite journal |last1=Price |first1=Charles T. |last2=Langford |first2=Joshua R. |last3=Liporace |first3=Frank A. |date=5 April 2012 |title=Essential Nutrients for Bone Health and a Review of their Availability in the Average North American Diet |pmc=3330619 |journal=Open Orthop. J. |volume=6 |pages=143–49 |doi=10.2174/1874325001206010143|pmid=22523525}}</ref> Despite restrictions on [[strontium ranelate]], strontium is still contained in some supplements.<ref name="WebMD-Strontium">{{cite web |url=https://www.webmd.com/vitamins-supplements/ingredientmono-1077-strontium.aspx?activeingredientid=1077& |title=Strontium |website=[[WebMD]] |access-date=20 November 2017}}</ref><ref name="WebMD-StrontiumOsteoporosis">{{cite web |url=https://www.webmd.com/osteoporosis/guide/strontium-treatment-osteoporosis |title=Strontium for Osteoporosis |publisher=[[WebMD]] |access-date=20 November 2017}}</ref> There is not much scientific evidence on risks of strontium chloride when taken by mouth. Those with a personal or family history of blood clotting disorders are advised to avoid strontium.<ref name="WebMD-Strontium" /><ref name="WebMD-StrontiumOsteoporosis" />

Strontium has been shown to inhibit sensory irritation when applied topically to the skin.<ref>{{cite journal |journal=Dermatologic Surgery |volume=25 |issue=9 |pages=689–94|author=Hahn, G.S.|date=1999 |title=Strontium Is a Potent and Selective Inhibitor of Sensory Irritation |pmid=10491058|doi=10.1046/j.1524-4725.1999.99099.x |url=http://refinityskinscience.com/wp-content/themes/refinity/pdf/1_strontium_is_a_potent_selective_inhibitor.pdf|url-status=dead|archive-url=https://web.archive.org/web/20160531110553/http://refinityskinscience.com/wp-content/themes/refinity/pdf/1_strontium_is_a_potent_selective_inhibitor.pdf|archive-date=31 May 2016|df=dmy-all}}</ref><ref>{{cite book |author1=Hahn, G.S. |date=2001 |chapter=Anti-irritants for Sensory Irritation |page=285 |title=Handbook of Cosmetic Science and Technology |publisher=CRC Press |url=https://books.google.com/books?id=3dzCrVrGuigC |isbn=978-0-8247-0292-2}}</ref> Topically applied, strontium has been shown to accelerate the recovery rate of the epidermal permeability barrier (skin barrier).<ref>{{cite journal |url=http://210.101.116.107/kda/english/view.asp?year=2006&page=1309&vol=44&iss=11 |page=1309 |author1=Kim, Hyun Jeong |author2=Kim, Min Jung |author3=Jeong, Se Kyoo |title=The Effects of Strontium Ions on Epidermal Permeability Barrier |journal=The Korean Dermatological Association, Korean Journal of Dermatology |number=11 |volume=44 |date=2006 |access-date=31 March 2014 |archive-date=4 June 2021 |archive-url=https://web.archive.org/web/20210604054749/http://210.101.116.107/kda/english/view.asp?year=2006&page=1309&vol=44&iss=11 |url-status=dead }}</ref>

== Nuclear waste ==
{{Main|Strontium-90}}

Strontium-90 is a [[radioactive]] fission product produced by [[nuclear reactors]] used in [[nuclear power]]. It is a major component of high-level radioactivity of [[nuclear waste]] and [[spent nuclear fuel]]. Its 29-year half-life is short enough that its [[radioisotope thermoelectric generator|decay heat has been used to power]] arctic lighthouses, but long enough that it can take hundreds of years to decay to safe levels. Exposure from contaminated water and food may increase the risk of [[leukemia]], [[bone cancer]]<ref name="Potera">{{cite journal |last=Potera |first=Carol |title=HAZARDOUS WASTE: Pond Algae Sequester Strontium-90 |journal=Environ Health Perspect |date=2011 |volume=119 |issue=6 |pages=A244 |pmid=21628117 |doi=10.1289/ehp.119-a244|pmc=3114833 |doi-access=free }}</ref> and [[primary hyperparathyroidism]].<ref>{{cite journal |last1=Boehm |first1=BO |last2=Rosinger |first2=S |last3=Belyi |first3=D |last4=Dietrich |first4=JW |title=The parathyroid as a target for radiation damage. |journal=The New England Journal of Medicine |date=18 August 2011 |volume=365 |issue=7 |pages=676–8 |doi=10.1056/NEJMc1104982 |pmid=21848480|doi-access=free }}</ref>

=== Remediation ===
Algae has shown selectivity for strontium in studies, where most plants used in [[bioremediation]] have not shown selectivity between calcium and strontium, often becoming saturated with calcium, which is greater in quantity and also present in nuclear waste.<ref name="Potera" />

Researchers have looked at the bioaccumulation of strontium by ''[[Scenedesmus|Scenedesmus spinosus]]'' ([[algae]]) in simulated wastewater. The study claims a highly selective [[biosorption]] capacity for strontium of ''S.&nbsp;spinosus'', suggesting that it may be appropriate for use in treating nuclear wastewater.<ref>{{cite journal |title=Biosorption of Strontium from Simulated Nuclear Wastewater by Scenedesmus spinosus under Culture Conditions: Adsorption and Bioaccumulation Processes and Models |journal=Int J Environ Res Public Health |date=2014 |doi=10.3390/ijerph110606099|doi-access=free |last1=Liu |first1=Mingxue |last2=Dong |first2=Faqin |last3=Kang |first3=Wu |last4=Sun |first4=Shiyong |last5=Wei |first5=Hongfu |last6=Zhang |first6=Wei |last7=Nie |first7=Xiaoqin |last8=Guo |first8=Yuting |last9=Huang |first9=Ting |last10=Liu |first10=Yuanyuan |volume=11 |issue=6 |pages=6099–6118 |pmid=24919131 |pmc=4078568 }}</ref>

A study of the pond alga ''[[Closterium|Closterium moniliferum]]'' using non-radioactive strontium found that varying the ratio of [[barium]] to strontium in water improved strontium selectivity.<ref name="Potera" />

==See also==
{{Portal bar|Chemistry}}

==References==
{{Reflist}}

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

==External links==
{{Sister project links |wikt=strontium |commons=y |n= |q= |s= |b= |v=Strontium atom}} 
* [http://www.webelements.com/strontium/ WebElements.com – Strontium]
* [http://www.periodicvideos.com/videos/038.htm Strontium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)

{{Periodic table (navbox)}}
{{Strontium compounds}}
{{alkaline earth metals}}
{{Authority control}}

[[Category:Strontium| ]]
[[Category:Chemical elements]]
[[Category:Alkaline earth metals]]
[[Category:Reducing agents]]
[[Category:Lochaber]]
[[Category:Chemical elements with face-centered cubic structure]]