Editing Tantalum

{{Short description|Chemical element with atomic number 73}}
{{Good article}}
{{infobox tantalum}}

'''Tantalum''' is a [[chemical element]]; it has [[Symbol (chemistry)|symbol]] '''Ta''' and [[atomic number]] 73. It is named after [[Tantalus]], a figure in Greek mythology.<ref>[[Euripides]], ''[[Orestes (play)|Orestes]]''</ref> Tantalum is a very hard, [[ductility|ductile]], [[lustre (mineralogy)|lustrous]], blue-gray [[transition metal]] that is highly corrosion-resistant. It is part of the [[refractory metals]] group, which are widely used as components of strong [[superalloy|high-melting-point alloy]]s. It is a [[group 5 element]], along with [[vanadium]] and [[niobium]], and it always occurs in geologic sources together with the chemically similar niobium, mainly in the [[mineral]] groups [[tantalite]], [[columbite]], and [[coltan]]. 

The chemical inertness and very high melting point of tantalum make it valuable for laboratory and industrial equipment such as [[Chemical reactor|reaction vessels]] and [[vacuum furnace]]s. It is used in [[tantalum capacitor]]s for electronic equipment such as computers. It is being investigated for use as a material for high-quality superconducting resonators in [[quantum processor]]s.

==History==
Tantalum was discovered in Sweden in 1802 by [[Anders Ekeberg]], in two mineral samples – one from Sweden and the other from Finland.<ref>{{cite journal | journal = Journal of Natural Philosophy, Chemistry, and the Arts | pages = 251–255 | volume = 3 | year = 1802| first = Anders | last = Ekeberg | title = Of the Properties of the Earth Yttria, compared with those of Glucine; of Fossils, in which the first of these Earths in contained; and of the Discovery of a metallic Nature (Tantalium) | url = https://www.biodiversitylibrary.org/item/15589#page/265/mode/1up}}</ref><ref>{{cite journal | journal = Kungliga Svenska Vetenskapsakademiens Handlingar |year = 1802 | pages = [https://archive.org/details/kungligasvenskav2231kung/page/68 68]–83 | volume = 23| first = Anders | last = Ekeberg | title = Uplysning om Ytterjorden egenskaper, i synnerhet i aemforelse med Berylljorden:om de Fossilier, havari förstnemnde jord innehales, samt om en ny uptäckt kropp af metallik natur | url = https://archive.org/details/kungligasvenskav2231kung}}</ref> One year earlier, [[Charles Hatchett]] had discovered [[columbium]] (now niobium).<ref>{{cite journal|title = Charles Hatchett FRS (1765–1847), Chemist and Discoverer of Niobium|first = William P.|last = Griffith|author2=Morris, Peter J. T. |journal = Notes and Records of the Royal Society of London|volume = 57|issue = 3|pages = 299–316|date = 2003|jstor = 3557720|doi = 10.1098/rsnr.2003.0216|s2cid = 144857368}}</ref> In 1809, the English chemist [[William Hyde Wollaston]] compared the oxides of columbium and tantalum, [[columbite]] and [[tantalite]]. Although the two oxides had different measured densities of 5.918&nbsp;g/cm<sup>3</sup> and 7.935&nbsp;g/cm<sup>3</sup>, he concluded that they were identical and kept the name tantalum.<ref name="Wolla">{{cite journal|title = On the Identity of Columbium and Tantalum|pages = 246–252|journal = Philosophical Transactions of the Royal Society of London|first = William Hyde|last = Wollaston|author-link = William Hyde Wollaston|doi = 10.1098/rstl.1809.0017| jstor = 107264|volume = 99|date = 1809|s2cid = 110567235}}</ref> After [[Friedrich Wöhler]] confirmed these results, it was thought that columbium and tantalum were the same element. This conclusion was disputed in 1846 by the German chemist [[Heinrich Rose]], who argued that there were two additional elements in the tantalite sample, and he named them after the children of [[Tantalus]]: niobium (from [[Niobe]]), and pelopium (from [[Pelops]]).<ref name="Pelop">{{cite journal|title = Ueber die Zusammensetzung der Tantalite und ein im Tantalite von Baiern enthaltenes neues Metall|pages = 317–341|journal = Annalen der Physik|author-link = Heinrich Rose|language=de|first = Heinrich|last = Rose|doi = 10.1002/andp.18441391006|url = http://gallica.bnf.fr/ark:/12148/bpt6k15148n/f327.table|volume = 139|issue = 10|date = 1844|bibcode = 1844AnP...139..317R }}</ref><ref>{{cite journal|title = Ueber die Säure im Columbit von Nordamérika|language=de|pages = 572–577|first = Heinrich|last = Rose|journal = Annalen der Physik|doi = 10.1002/andp.18471460410|url = http://gallica.bnf.fr/ark:/12148/bpt6k15155x/f586.table |date=1847| volume = 146|issue = 4|author-link = Heinrich Rose|bibcode = 1847AnP...146..572R }}</ref> The supposed element "pelopium" was later identified as a mixture of tantalum and niobium, and it was found that the niobium was identical to the columbium already discovered in 1801 by Hatchett.{{Cn|date=October 2024}}

The differences between tantalum and niobium were demonstrated unequivocally in 1864 by [[Christian Wilhelm Blomstrand]],<ref name="Ilmen" /> and [[Henri Etienne Sainte-Claire Deville]], as well as by [[Louis J. Troost]], who determined the empirical formulas of some of their compounds in 1865.<ref name="Ilmen">{{cite journal|title = Tantalsäure, Niobsäure, (Ilmensäure) und Titansäure|journal = Fresenius' Journal of Analytical Chemistry|volume = 5|issue = 1|date = 1866|doi = 10.1007/BF01302537|pages = 384–389|author= Marignac, Blomstrand|author2= H. Deville|author3= L. Troost|author4= R. Hermann|s2cid = 97246260|name-list-style= amp}}</ref><ref name="Gupta" /> Further confirmation came from the Swiss chemist [[Jean Charles Galissard de Marignac]],<ref>{{cite journal|journal = Annales de Chimie et de Physique|title = Recherches sur les combinaisons du niobium|pages = 7–75|author-link = Jean Charles Galissard de Marignac|language=fr| first = M. C.|last= Marignac|url = http://gallica.bnf.fr/ark:/12148/bpt6k34818t/f4.table|date= 1866|volume = 4|issue = 8}}</ref> in 1866, who proved that there were only two elements. These discoveries did not stop scientists from publishing articles about the so-called ''[[ilmenium]]'' until 1871.<ref>{{cite journal|title = Fortgesetzte Untersuchungen über die Verbindungen von Ilmenium und Niobium, sowie über die Zusammensetzung der Niobmineralien (Further research about the compounds of ilmenium and niobium, as well as the composition of niobium minerals)|first = R.|last = Hermann|journal = Journal für Praktische Chemie|language=de|volume = 3|issue = 1|pages =373–427|doi = 10.1002/prac.18710030137|date = 1871|url = https://zenodo.org/record/1427850}}</ref> De Marignac was the first to produce the metallic form of tantalum in 1864, when he [[redox|reduced]] tantalum chloride by heating it in an atmosphere of [[hydrogen]].{{Citation needed|date=February 2025}} Early investigators had only been able to produce impure tantalum, and the first relatively pure ductile metal was produced by [[Werner von Bolton]] in [[Charlottenburg]] in 1903. Wires made with metallic tantalum were used for [[light bulb]] filaments until [[tungsten]] replaced it in widespread use.<ref>{{cite journal|title = Scanning Our Past from London The Filament Lamp and New Materials|journal = Proceedings of the IEEE|volume = 89|issue = 3|date = 2001|doi = 10.1109/5.915382|author = Bowers, B.|page = 413|s2cid = 28155048}}</ref>

The name tantalum was derived from the name of the mythological Tantalus, the father of Niobe in [[Greek mythology]]. In the story, he had been punished after death by being condemned to stand knee-deep in water with perfect fruit growing above his head, both of which eternally ''tantalized'' him. (If he bent to drink the water, it drained below the level he could reach, and if he reached for the fruit, the branches moved out of his grasp.)<ref>{{cite book |last1=Lempriere |first1=John |title=Lempriere's Classical Dictionary |date=1887 |page=[https://archive.org/details/lemprieresclassi00lemp_0/page/659 659] |url=https://archive.org/details/lemprieresclassi00lemp_0}}</ref> Anders Ekeberg wrote "This metal I call ''tantalum'' ... partly in allusion to its incapacity, when immersed in acid, to absorb any and be saturated."<ref>{{Greenwood&Earnshaw|page=1138}}</ref>

For decades, the commercial technology for separating tantalum from niobium involved the [[fractional crystallization (chemistry)|fractional crystallization]] of [[potassium heptafluorotantalate]] away from potassium oxypentafluoroniobate monohydrate, a process that was discovered by [[Jean Charles Galissard de Marignac]] in 1866. This method has been supplanted by [[solvent extraction]] from fluoride-containing solutions of tantalum.<ref name="Gupta">{{cite book|title = Extractive Metallurgy of Niobium|first = C. K.|last = Gupta|author2=Suri, A. K. |publisher = CRC Press|date = 1994|isbn = 978-0-8493-6071-8}}</ref>

==Characteristics==

===Physical properties===
Tantalum is dark (blue-gray),<ref>{{cite book | chapter = Tantalum | chapter-url = https://books.google.com/books?id=5o3Lr2Swz8sC&pg=PA204 | isbn = 978-0-86516-573-1 | title = Classical Mythology & More: A Reader Workbook | author1 = Colakis, Marianthe | author2 = Masello, Mary Joan | date = 2007-06-30| publisher=Bolchazy-Carducci Publishers }}</ref> dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is highly resistant to [[corrosion]] by [[acid]]s: at temperatures below 150&nbsp;°[[Celsius|C]] tantalum is almost completely immune to attack by the normally aggressive [[aqua regia]]. It can be dissolved with [[hydrofluoric acid]] or acidic solutions containing the [[fluoride]] ion and [[sulfur trioxide]], as well as with molten [[potassium hydroxide]]. Tantalum's high melting point of 3017&nbsp;°C (boiling point 5458&nbsp;°C) is exceeded among the elements only by [[tungsten]], [[rhenium]], and [[osmium]] for metals, and [[carbon]].

Tantalum exists in two crystalline phases, alpha and beta. The alpha phase is stable at all temperatures up to the melting point and has [[body-centered cubic]] structure with lattice constant ''a'' = 0.33029&nbsp;nm at 20&nbsp;°C.<ref name="Arblaster 2018" /> It is relatively [[Ductility|ductile]], has [[Knoop hardness test|Knoop hardness]] 200–400 HN and electrical resistivity 15–60 μΩ⋅cm. The beta phase is hard and brittle; its crystal symmetry is [[tetragonal]] (space group ''P42/mnm'', ''a'' = 1.0194&nbsp;nm, ''c'' = 0.5313&nbsp;nm), Knoop hardness is 1000–1300 HN and electrical resistivity is relatively high at 170–210 μΩ⋅cm. The beta phase is metastable and converts to the alpha phase upon heating to 750–775&nbsp;°C. Bulk tantalum is almost entirely alpha phase, and the beta phase usually exists as thin films<ref>{{cite journal|title=Electronic structure of β-Ta films from X-ray photoelectron spectroscopy and first-principles calculations|date=2019|last1=Magnuson|first1=M.|journal=Applied Surface Science|volume=470|pages=607–612|last2=Greczynski|first2=G.|last3=Eriksson|first3=F.|last4=Hultman|first4=L.|last5=Hogberg|first5=H.|doi=10.1016/j.apsusc.2018.11.096|url=http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-152876|bibcode=2019ApSS..470..607M|s2cid=54079998}}</ref> obtained by magnetron
[[sputtering]], [[chemical vapor deposition]] or [[Electrochemistry|electrochemical deposition]] from a [[Eutectic system|eutectic]] molten salt solution.<ref>{{cite journal|doi=10.1016/j.surfcoat.2003.06.008|title=Texture, structure and phase transformation in sputter beta tantalum coating|date=2004|last1=Lee|first1=S.|journal=Surface and Coatings Technology|volume=177–178|page=44|last2=Doxbeck|first2=M.|last3=Mueller|first3=J.|last4=Cipollo|first4=M.|last5=Cote|first5=P.|url=https://zenodo.org/record/1259369}}</ref>

===Isotopes===
{{Main|Isotopes of tantalum}}

Natural tantalum consists of two stable [[isotope]]s: <sup>180m</sup>Ta (0.012%) and <sup>181</sup>Ta (99.988%). <sup>180m</sup>Ta (''m'' denotes a metastable state) is predicted to decay in three ways: [[isomeric transition]] to the [[ground state]] of <sup>180</sup>Ta, [[beta decay]] to <sup>180</sup>[[Tungsten|W]], or electron capture to <sup>180</sup>[[Hafnium|Hf]]. However, radioactivity of this [[nuclear isomer]] has never been observed, and only a lower limit on its [[half-life]] of 2.9{{e|17}}&nbsp;years has been set.<ref>{{cite journal | author= Majorana Collaboration | title=Constraints on the Decay of <sup>180m</sup>Ta | journal=Physical Review Letters | volume=131 | issue=15 | date=2023-10-11 | page=152501 | issn=0031-9007 | doi=10.1103/PhysRevLett.131.152501| pmid=37897780 | arxiv=2306.01965 }}</ref> The ground state of <sup>180</sup>Ta has a half-life of only 8 hours. <sup>180m</sup>Ta is the only naturally occurring [[nuclear isomer]] (excluding [[radiogenic]] and [[cosmogenic]] short-lived nuclides). It is also the rarest primordial isotope in the Universe, taking into account the elemental abundance of tantalum and isotopic abundance of <sup>180m</sup>Ta in the natural mixture of isotopes (and again excluding radiogenic and cosmogenic short-lived nuclides).<ref name="NUBASE">{{NUBASE 2003}}</ref>

Tantalum has been examined theoretically as a "[[Salted bomb|salting]]" material for [[nuclear weapon]]s ([[cobalt]] is the better-known hypothetical salting material). An external shell of <sup>181</sup>Ta would be irradiated by the intensive high-energy neutron flux from a hypothetical exploding nuclear weapon. This would transmute the tantalum into the radioactive isotope <sup>182</sup>Ta, which has a [[half-life]] of 114.4 days and produces [[gamma ray]]s with approximately 1.12 million electron-volts (MeV) of energy apiece, which would significantly increase the radioactivity of the [[nuclear fallout]] from the explosion for several months. Such "salted" weapons have never been built or tested, as far as is publicly known, and certainly never used as weapons.<ref>{{cite journal|last1=Win|first1=David Tin|last2=Al Masum|first2=Mohammed|title=Weapons of Mass Destruction|date=2003|journal=Assumption University Journal of Technology|volume=6|issue=4|pages=199–219|url=http://www.journal.au.edu/au_techno/2003/apr2003/aujt6-4_article07.pdf}}</ref>

Tantalum can be used as a target material for accelerated proton beams for the production of various short-lived isotopes including <sup>8</sup>Li, <sup>80</sup>Rb, and <sup>160</sup>Yb.<ref>{{cite web |title=Tantalum Target Yields – ISAC Yield Database – TRIUMF: Canada's National Laboratory for Particle and Nuclear Physics |url=https://mis.triumf.ca/science/planning/yield/target/Ta |website=mis.triumf.ca}}</ref>

==Chemical compounds==
Tantalum forms compounds in oxidation states −3 to +5. Most commonly encountered are oxides of Ta(V), which includes all minerals. The chemical properties of Ta and Nb are very similar. In aqueous media, Ta only exhibits the +5 oxidation state. Like niobium, tantalum is barely soluble in dilute solutions of [[Hydrochloric acid|hydrochloric]], [[Sulfuric acid|sulfuric]], [[Nitric acid|nitric]] and [[phosphoric acid]]s due to the precipitation of hydrous Ta(V) oxide.<ref name="Aguly" /> In basic media, Ta can be solubilized due to the formation of polyoxotantalate species.<ref>{{Cite journal|last1=Deblonde|first1=Gauthier J. -P.|last2=Chagnes|first2=Alexandre|last3=Bélair|first3=Sarah|last4=Cote|first4=Gérard|date=2015-07-01|title=Solubility of niobium(V) and tantalum(V) under mild alkaline conditions|journal=Hydrometallurgy|volume=156|pages=99–106|doi=10.1016/j.hydromet.2015.05.015|bibcode=2015HydMe.156...99D |issn=0304-386X}}</ref>

===Oxides, nitrides, carbides, sulfides===
[[Tantalum pentoxide]] (Ta<sub>2</sub>O<sub>5</sub>) is the most important compound from the perspective of applications. Oxides of tantalum in lower oxidation states are numerous, including many [[defect structure]]s, and are lightly studied or poorly characterized.<ref>{{Greenwood&Earnshaw2nd}}</ref>

Tantalates, compounds containing [TaO<sub>4</sub>]<sup>3−</sup> or [TaO<sub>3</sub>]<sup>−</sup> are numerous. [[Lithium tantalate]] (LiTaO<sub>3</sub>) adopts a perovskite structure. [[Lanthanum]] tantalate (LaTaO<sub>4</sub>) contains isolated {{chem|TaO|4|3−}} tetrahedra.<ref name="HollemanAF">{{cite book|title=Lehrbuch der Anorganischen Chemie|date=2007|publisher=de Gruyter|isbn=978-3-11-017770-1|edition=102nd|language=de|author=Holleman, A. F.|author2=Wiberg, E.|author3=Wiberg, N.}}</ref>

As in the cases of other [[refractory metal]]s, the hardest known compounds of tantalum are nitrides and carbides. [[Tantalum carbide]], TaC, like the more commonly used [[tungsten carbide]], is a hard [[ceramic]] that is used in cutting tools. Tantalum(III) nitride is used as a thin film insulator in some microelectronic fabrication processes.<ref>{{cite journal|title=Microstructure of amorphous tantalum nitride thin films|first=S.|last=Tsukimoto| author2= Moriyama, M.| author3= Murakami, Masanori| journal=Thin Solid Films|date=1961|volume= 460|issue=1–2|pages=222–226|doi=10.1016/j.tsf.2004.01.073|bibcode = 2004TSF...460..222T }}</ref>

The best studied chalcogenide is [[Tantalum(IV) sulfide|Tantalum sulfide]] (TaS<sub>2</sub>), a layered [[semiconductor]], as seen for other [[transition metal dichalcogenide]]s. A tantalum-tellurium alloy forms [[quasicrystal]]s.<ref name="HollemanAF" />

===Halides===
Tantalum halides span the oxidation states of +5, +4, and +3. [[Tantalum pentafluoride]] (TaF<sub>5</sub>) is a white solid with a melting point of 97.0&nbsp;°C. The anion [TaF<sub>7</sub>]<sup>2-</sup> is used for its separation from niobium.<ref name="ICE">{{cite journal|title=Staff-Industry Collaborative Report: Tantalum and Niobium|first=Donald J.|last=Soisson|author2=McLafferty, J. J. |author3=Pierret, James A. | journal=Ind. Eng. Chem.|date=1961|volume= 53|issue=11|pages=861–868|doi=10.1021/ie50623a016}}</ref> The chloride [[tantalum(V) chloride|{{chem|TaCl|5}}]], which exists as a dimer, is the main reagent in synthesis of new Ta compounds. It hydrolyzes readily to an [[oxychloride]]. The lower halides {{chem|TaX|4}} and {{chem|TaX|3}}, feature Ta-Ta bonds.<ref name="HollemanAF" /><ref name="Aguly">{{cite book|first=Anatoly|last=Agulyansky|title=The Chemistry of Tantalum and Niobium Fluoride Compounds|publisher=Elsevier|date=2004| isbn=978-0-444-51604-6| url=https://books.google.com/books?id=Z-4QXNB5Hp8C|access-date=2008-09-02}}</ref>

===Organotantalum compounds===
[[Organotantalum chemistry|Organotantalum compound]]s include [[pentamethyltantalum]], mixed alkyltantalum chlorides, alkyltantalum hydrides, alkylidene complexes, as well as cyclopentadienyl derivatives of the same.<ref name="Schrock">{{Cite journal|last=Schrock|first=Richard R.|date=1979-03-01|title=Alkylidene complexes of niobium and tantalum|journal=Accounts of Chemical Research|volume=12|issue=3|pages=98–104|doi=10.1021/ar50135a004|issn=0001-4842}}</ref><ref>{{cite journal|doi=10.1021/om701189e|title=Ethylene Complexes of the Early Transition Metals: Crystal Structures of {{chem|[HfEt|4|(C|2|H|4|)|2-|]}} and the Negative-Oxidation-State Species {{chem|[TaHEt(C|2|H|4|)|3|3-|]}} and {{chem|[WH(C|2|H|4|)|4|3-|]}}|author=Morse, P. M.|journal=Organometallics|date=2008|volume=27|issue=5|page=984|display-authors=1|author2=Shelby, Q. D. |author3=Kim, D. Y. |author4=Girolami, G. S. |name-list-style=amp}}</ref> Diverse salts and substituted derivatives are known for the hexacarbonyl [Ta(CO)<sub>6</sub>]<sup>−</sup> and related [[isocyanide]]s.
[[File:DOSBIWoneRotamer.png|144px|thumb|Ta(CH<sub>3</sub>)<sub>5</sub>.]]

==Occurrence==
[[File:Tantalite.jpg|thumb|left|Tantalite, [[Pilbara|Pilbara district]], Australia]]

Tantalum is estimated to make up about 1&nbsp;[[Parts per million|ppm]]<ref name="Emsley">{{cite book |last=Emsley |first=John |title=Nature's Building Blocks: An A–Z Guide to the Elements |date=2001 |publisher=Oxford University Press |isbn=978-0-19-850340-8 |location=Oxford, England, UK |page=[https://archive.org/details/naturesbuildingb0000emsl/page/420 420] |chapter=Tantalum |chapter-url=https://archive.org/details/naturesbuildingb0000emsl/page/420}}</ref> or 2&nbsp;[[Parts per million|ppm]]<ref name="Aguly" /> of the [[Abundance of elements in Earth's crust|Earth's crust by weight]]. There are many species of tantalum minerals, only some of which are so far being used by industry as raw materials: [[tantalite]] (a series consisting of tantalite-(Fe), tantalite-(Mn), and tantalite-(Mg)), [[microlite]] (now a group name), [[wodginite]], [[euxenite]] (actually euxenite-(Y)), and [[polycrase]] (actually polycrase-(Y)).<ref name="mindat.org">{{cite web |url=http://www.mindat.org |title= Mines, Minerals and More |publisher=Mindat.org}}</ref> Tantalite ([[iron|Fe]], [[manganese|Mn]])Ta<sub>2</sub>[[oxygen|O]]<sub>6</sub> is the most important mineral for tantalum extraction. Tantalite has the same mineral structure as [[columbite]] ([[iron|Fe]], [[manganese|Mn]]) (Ta, [[niobium|Nb]])<sub>2</sub>[[oxygen|O]]<sub>6</sub>; when there is more tantalum than niobium it is called tantalite and when there is more niobium than tantalum is it called columbite (or [[niobite]]). The high density of tantalite and other tantalum containing minerals makes the use of [[Gravity separation|gravitational separation]] the best method. Other minerals include [[samarskite]] and [[fergusonite]].

[[File:World Tantalum Production 2015.svg|upright=1.4|thumb|Tantalum producers in 2015 with Rwanda being the main producer|alt=Grey and white world map with China, Australia, Brazil and Kongo colored blue representing less than 10% of the tantalum world production each and Rwanda colored in green representing 60% of tantalum world production]]

[[Australia]] was the main producer of tantalum prior to the 2010s, with [[Global Advanced Metals]] (formerly known as [[Talison Minerals]]) being the largest tantalum mining company in that country. They operate two mines in Western Australia, [[Greenbushes, Western Australia|Greenbushes]] in the southwest and [[Wodgina mine|Wodgina]] in the [[Pilbara]] region. The Wodgina mine was reopened in January 2011 after mining at the site was suspended in late 2008 due to the [[2008 financial crisis]].<ref>{{cite news| url = https://af.reuters.com/article/drcNews/idAFLDE6530TW20100609 | archive-url = https://web.archive.org/web/20110119030657/http://af.reuters.com/article/drcNews/idAFLDE6530TW20100609 | url-status = dead | archive-date = 2011-01-19 | work = Reuters |title = Talison Tantalum eyes mid-2011 Wodgina restart 2010-06-09 | access-date = 2010-08-27 | date=2010-06-09}}</ref> Less than a year after it reopened, Global Advanced Metals announced that due to again "... softening tantalum demand ...", and other factors, tantalum mining operations were to cease at the end of February 2012.<ref name="Wodgina-tant-closed">{{cite news| url=http://au.news.yahoo.com/thewest/business/a/-/business/12702333/gam-closes-wodgina-tantalum-mine/| title=GAM closes Wodgina tantalum mine| last=Emery| first=Kate| date=24 Jan 2012| work=[[The West Australian]]| access-date=20 March 2012| quote=Worldwide softening tantalum demand and delays in receiving Governmental approval for installation of necessary crushing equipment are among contributing factors in this decision| url-status=dead| archive-url=https://web.archive.org/web/20121204055041/http://au.news.yahoo.com/thewest/business/a/-/business/12702333/gam-closes-wodgina-tantalum-mine/| archive-date=4 December 2012}}
</ref> Wodgina produces a primary tantalum concentrate which is further upgraded at the Greenbushes operation before being sold to customers.<ref name="Talison">{{cite web|publisher = Global Advanced Metals|date = 2008|url = http://globaladvancedmetals.com/our-operations/gam-resources/wodgina-australia.aspx|title = Wodgina Operations|access-date = 2011-03-28|archive-date = 2016-10-06|archive-url = https://web.archive.org/web/20161006170703/http://www.globaladvancedmetals.com/our-operations/gam-resources/wodgina-australia.aspx|url-status = dead}}</ref> Whereas the large-scale producers of niobium are in [[Brazil]] and [[Canada]], the ore there also yields a small percentage of tantalum. Some other countries such as [[China]], [[Ethiopia]], and [[Mozambique]] mine ores with a higher percentage of tantalum, and they produce a significant percentage of the world's output of it. Tantalum is also produced in [[Thailand]] and [[Malaysia]] as a by-product of the [[tin]] mining there. During gravitational separation of the ores from placer deposits, not only is [[cassiterite]] (SnO<sub>2</sub>) found, but a small percentage of tantalite also included. The slag from the tin smelters then contains economically useful amounts of tantalum, which is leached from the slag.<ref name="Gupta" /><ref name="USGS2006">{{cite web|publisher = US Geological Survey|last = Papp|first = John F.|title = 2006 Minerals Yearbook Nb & Ta|date = 2006|url = http://minerals.usgs.gov/minerals/pubs/commodity/niobium/#pubs|access-date = 2008-06-03}}</ref>

[[File:World Tantalum Production 2006.svg|upright=1.4|thumb|Tantalum producers in 2006 with Australia being the main producer|alt=Grey and white world map with Canada, Brazil and Mozambique colored blue representing less than 20% of the tantalum world production each and Australia colored in green representing 60% of tantalum world production]]

World tantalum mine production has undergone an important geographic shift since the start of the 21st century when production was predominantly from Australia and Brazil. Beginning in 2007 and through 2014, the major sources of tantalum production from mines dramatically shifted to the [[Democratic Republic of the Congo]], [[Rwanda]], and some other African countries.<ref>{{cite web| url = http://pubs.usgs.gov/fs/2015/3079/fs20153079.pdf | title = Shift in Global Tantalum Mine Production, 2000–2014 | last1 = Bleiwas | first1 = Donald I. | last2 =Papp| first2 = John F.| last3 =Yager | first3 = Thomas R. | publisher = U.S. Geological Survey | year = 2015}}</ref> Future sources of supply of tantalum, in order of estimated size, are being explored in [[Saudi Arabia]], [[Egypt]], [[Greenland]], China, Mozambique, Canada, Australia, the [[United States]], [[Finland]], and Brazil.<ref name="Mining Journal">{{cite journal|journal = Mining Journal|author = M. J.|title = Tantalum supplement|date = November 2007|url = http://www.noventa.net/pdf/presentations/tanatalumSCR_presentation.pdf|access-date = 2008-06-03|archive-date = 2008-09-10|archive-url = https://web.archive.org/web/20080910143749/http://www.noventa.net/pdf/presentations/tanatalumSCR_presentation.pdf|url-status = dead}}</ref><ref>{{cite journal |title=International tantalum resources – exploration and mining |url=http://www.doir.wa.gov.au/documents/gswa/gsdMRB_22_chap10.pdf |journal=GSWA Mineral Resources Bulletin |volume=22 |issue=10 |archive-url=https://web.archive.org/web/20070926195547/http://www.doir.wa.gov.au/documents/gswa/gsdMRB_22_chap10.pdf |archive-date=2007-09-26}}</ref>

==Status as a conflict resource==
{{See also|Coltan mining and ethics|Coltan#Ethics of mining in the Democratic Republic of Congo}}
Tantalum is considered a [[conflict resource]]. [[Coltan]], the industrial name for a [[columbite]]–[[tantalite]] mineral from which niobium and tantalum are extracted,<ref>[http://www.tanb.org/coltan Tantalum-Niobium International Study Center: Coltan] {{Webarchive|url=https://web.archive.org/web/20160114090751/http://www.tanb.org/coltan |date=2016-01-14 }} Retrieved 2008-01-27</ref> can also be found in [[Central Africa]], which is why tantalum is being linked to [[Second Congo War|warfare in the Democratic Republic of the Congo]] (formerly [[Zaire]]). According to an October 23, 2003 [[United Nations]] report,<ref>{{cite web|title = S/2003/1027|date = 2003-10-26|url = https://documents.un.org/doc/undoc/gen/n03/567/36/pdf/n0356736.pdf|access-date =2008-04-19}}</ref> the smuggling and exportation of coltan has helped fuel the war in the Congo, a crisis that has resulted in approximately 5.4 million deaths since 1998<ref>{{cite web|publisher = International Rescue Committee|title = Special Report: Congo|url = http://www.rescue.org/special-reports/special-report-congo-y|access-date = 2008-04-19|archive-date = 2012-03-05|archive-url = https://web.archive.org/web/20120305202726/http://www.rescue.org/special-reports/special-report-congo-y|url-status = dead}}</ref> – making it the world's deadliest documented conflict since [[World War II]]. Ethical questions have been raised about responsible corporate behavior, human rights, and endangering wildlife, due to the exploitation of resources such as coltan in the armed conflict regions of the [[Congo Basin]].<ref>{{cite journal|title = Coltan Mining in the Democratic Republic of Congo: How tantalum-using industries can commit to the reconstruction of the DRC|first = Karen|last = Hayes|author2=Burge, Richard |journal = Fauna & Flora|isbn = 978-1-903703-10-6|pages = 1–64|year = 2003}}</ref><ref>{{cite web|url = http://pulitzercenter.org/video/congos-bloody-coltan|date=January 6, 2011|work=Pulitzer Center on Crisis Reporting|author=Dizolele, Mvemba Phezo|title=Congo's Bloody Coltan|access-date=2009-08-08}}</ref><ref>{{cite web|url=http://www1.american.edu/ted/ice/congo-coltan.htm|title=Congo War and the Role of Coltan|access-date=2009-08-08|url-status=dead|archive-url=https://web.archive.org/web/20090713173610/http://www1.american.edu/TED/ice/congo-coltan.htm|archive-date=2009-07-13}}</ref><ref>{{cite web|url = http://www.panda.org/what_we_do/where_we_work/congo_basin_forests/problems/mining/coltan_mining/ |archive-url = https://web.archive.org/web/20090330005811/http://www.panda.org/what_we_do/where_we_work/congo_basin_forests/problems/mining/coltan_mining/ |archive-date = 2009-03-30 |title=Coltan mining in the Congo River Basin|access-date =2009-08-08}}</ref> The [[United States Geological Survey]] reports in its yearbook that this region produced a little less than 1% of the world's tantalum output in 2002–2006, peaking at 10% in 2000 and 2008.<ref name="USGS2006" /> USGS data published in January 2021 indicated that close to 40% of the world's tantalum mine production came from the Democratic Republic of the Congo, with another 18% coming from neighboring [[Rwanda]] and [[Burundi]].<ref>{{cite web|title = USGS Mineral Commodities Summary: Tantalum|date = January 2021|url = https://pubs.usgs.gov/periodicals/mcs2021/mcs2021-tantalum.pdf|access-date = 2021-04-22|author = United States Geological Survey}}</ref>

== Production and fabrication ==
[[File:Tantalum world production.svg|thumb|upright=1|Time trend of tantalum production until 2012<ref>{{Cite web|url=http://minerals.usgs.gov/ds/2005/140|archive-url=https://web.archive.org/web/20130604121254/http://minerals.usgs.gov/ds/2005/140/|url-status=dead|title=Mineral Resources Program|archive-date=June 4, 2013|website=minerals.usgs.gov}}</ref>]]
Several steps are involved in the extraction of tantalum from tantalite. First, the mineral is [[crusher|crushed]] and concentrated by [[gravity separation]]. This is generally carried out near the [[mining|mine]] site.

=== Refining ===
The refining of tantalum from its ores is one of the more demanding separation processes in industrial metallurgy. The chief problem is that tantalum ores contain significant amounts of [[niobium]], which has chemical properties almost identical to those of Ta. A large number of procedures have been developed to address this challenge.

In modern times, the separation is achieved by [[hydrometallurgy]].<ref name="Chang">{{cite journal |last1=Zhu |first1=Zhaowu |last2=Cheng |first2=Chu Yong |year=2011 |title=Solvent extraction technology for the separation and purification of niobium and tantalum: A review |journal=Hydrometallurgy |volume=107 |issue=1–2 |pages=1–12 |doi=10.1016/j.hydromet.2010.12.015|bibcode=2011HydMe.107....1Z }}</ref> Extraction begins with [[Leaching (metallurgy)|leaching]] the ore with [[hydrofluoric acid]] together with [[sulfuric acid]] or [[hydrochloric acid]]. This step allows the tantalum and niobium to be separated from the various non-metallic impurities in the rock. Although Ta occurs as various minerals, it is conveniently represented as the pentoxide, since most oxides of tantalum(V) behave similarly under these conditions. A simplified equation for its extraction is thus:

: Ta<sub>2</sub>O<sub>5</sub> + 14 HF → 2 H<sub>2</sub>[TaF<sub>7</sub>] + 5 H<sub>2</sub>O

Completely analogous reactions occur for the niobium component, but the hexafluoride is typically predominant under the conditions of the extraction.
: Nb<sub>2</sub>O<sub>5</sub> + 12 HF → 2 H[NbF<sub>6</sub>] + 5 H<sub>2</sub>O
These equations are simplified: it is suspected that bisulfate (HSO<sub>4</sub><sup>−</sup>) and chloride compete as ligands for the Nb(V) and Ta(V) ions, when sulfuric and hydrochloric acids are used, respectively.<ref name="Chang" /> The tantalum and niobium fluoride complexes are then removed from the [[aqueous]] solution by [[Liquid–liquid extraction|liquid-liquid extraction]] into [[organic solvents]], such as [[cyclohexanone]], [[octanol]], and [[methyl isobutyl ketone]]. This simple procedure allows the removal of most metal-containing impurities (e.g. iron, manganese, titanium, zirconium), which remain in the aqueous phase in the form of their [[fluoride]]s and other complexes.

Separation of the tantalum ''from'' niobium is then achieved by lowering the [[ionic strength]] of the acid mixture, which causes the niobium to dissolve in the aqueous phase. It is proposed that [[oxyfluoride]] H<sub>2</sub>[NbOF<sub>5</sub>] is formed under these conditions. Subsequent to removal of the niobium, the solution of purified H<sub>2</sub>[TaF<sub>7</sub>] is neutralised with aqueous [[ammonia]] to precipitate hydrated tantalum oxide as a solid, which can be [[calcination|calcined]] to [[tantalum pentoxide]] (Ta<sub>2</sub>O<sub>5</sub>).<ref>{{cite book|last=Agulyanski|first=Anatoly|title=Chemistry of Tantalum and Niobium Fluoride Compounds|date=2004|publisher=Elsevier|location=Burlington|isbn=9780080529028|edition=1st}}</ref>

Instead of hydrolysis, the H<sub>2</sub>[TaF<sub>7</sub>] can be treated with [[potassium fluoride]] to produce [[potassium heptafluorotantalate]]:
: H<sub>2</sub>[TaF<sub>7</sub>] + 2 KF → K<sub>2</sub>[TaF<sub>7</sub>] + 2 HF
Unlike H<sub>2</sub>[TaF<sub>7</sub>], the potassium salt is readily crystallized and handled as a solid.

K<sub>2</sub>[TaF<sub>7</sub>] can be converted to metallic tantalum by [[reduction-oxidation|reduction]] with [[sodium]], at approximately 800&nbsp;°C in [[molten salt]].<ref>{{cite journal|last=Okabe|first=Toru H.|author2=Sadoway, Donald R. |title=Metallothermic reduction as an electronically mediated reaction|journal=Journal of Materials Research|date=1998|volume=13|issue=12|pages=3372–3377|doi=10.1557/JMR.1998.0459|bibcode = 1998JMatR..13.3372O |s2cid=98753880}}</ref>

: K<sub>2</sub>[TaF<sub>7</sub>] + 5 Na → Ta + 5 NaF + 2 KF

In an older method, called the [[Jean Charles Galissard de Marignac|Marignac]] process, the mixture of H<sub>2</sub>[TaF<sub>7</sub>] and H<sub>2</sub>[NbOF<sub>5</sub>] was converted to a ''mixture'' of K<sub>2</sub>[TaF<sub>7</sub>] and K<sub>2</sub>[NbOF<sub>5</sub>], which was then separated by [[Fractional crystallization (chemistry)|fractional crystallization]], exploiting their different water solubilities.

=== Electrolysis ===

{{See also|FFC Cambridge process}}

Tantalum can also be refined by electrolysis, using a modified version of the [[Hall–Héroult process]]. Instead of requiring the input oxide and output metal to be in liquid form, tantalum electrolysis operates on non-liquid powdered oxides. The initial discovery came in 1997 when Cambridge University researchers immersed small samples of certain oxides in baths of molten salt and reduced the oxide with electric current. The cathode uses powdered metal oxide. The anode is made of carbon. The molten salt at {{convert|1000|C|F}} is the electrolyte. The first refinery has enough capacity to supply 3–4% of annual global demand.<ref>{{cite news|url=https://www.economist.com/news/science-and-technology/21571847-exotic-useful-metals-such-tantalum-and-titanium-are-about-become-cheap |title=Manufacturing metals: A tantalising prospect |newspaper=The Economist |date=2013-02-16 |access-date=2013-04-17}}</ref>

=== Fabrication and metalworking ===

All [[welding]] of tantalum must be done in an inert atmosphere of [[argon]] or [[helium]] in order to shield it from contamination with atmospheric gases. Tantalum is not [[solderable]]. Grinding tantalum is difficult, especially so for [[Annealing (metallurgy)|annealed]] tantalum. In the annealed condition, tantalum is extremely [[ductile]] and can be readily formed as metal sheets.<ref>{{Cite web|url = http://www.nfpa.org/assets/files/aboutthecodes/484/nfpa484-2002.pdf|title = NFPA 484 – Standard for Combustible Metals, Metal Powders, and Metal Dusts – 2002 Edition|date = 2002-08-13|access-date = 2016-02-12|website = National Fire Protection Association|publisher = NFPA|archive-date = 2023-08-12|archive-url = https://web.archive.org/web/20230812215322/https://www.nfpa.org/assets/files/aboutthecodes/484/nfpa484-2002.pdf|url-status = dead}}</ref>

==Applications==

===Electronics===
[[File:Tantal-Perle-Wiki-07-02-25-P1040364b.jpg|thumb|upright|Tantalum electrolytic capacitor]]
The major use for tantalum, as the metal powder, is in the production of electronic components, mainly [[capacitor]]s and some high-power [[resistor]]s. [[tantalum capacitor|Tantalum electrolytic capacitors]] exploit the tendency of tantalum to form a protective [[oxide]] surface layer, using tantalum powder, pressed into a pellet shape, as one "plate" of the capacitor, the oxide as the [[dielectric]], and an electrolytic solution or conductive solid as the other "plate". Because the [[Relative static permittivity|dielectric layer]] can be very thin (thinner than the similar layer in, for instance, an aluminium electrolytic capacitor), a high [[capacitance]] can be achieved in a small volume. Because of the size and weight advantages, tantalum capacitors are attractive for [[portable telephone]]s, [[personal computer]]s, [[automotive electronics]] and [[cameras]].<ref name="USGSCR08">{{cite web|url = http://minerals.usgs.gov/minerals/pubs/commodity/niobium/mcs-2008-tanta.pdf|title = Commodity Report 2008: Tantalum|publisher = United States Geological Survey|access-date = 2008-10-24}}</ref>

===Alloys===
Tantalum is also used to produce a variety of [[alloy]]s that have high melting points, strength, and ductility. Alloyed with other metals, it is also used in making carbide tools for metalworking equipment and in the production of [[superalloy]]s for jet engine components, chemical process equipment, [[nuclear reactor]]s, missile parts, heat exchangers, tanks, and vessels.<ref>{{Cite news|url=https://www.admatinc.com/tantalum/sheetplate/|title=Tantalum Products: Tantalum Sheet & Plate {{!}} Admat Inc|work=Admat Inc.|access-date=2018-08-28|language=en-US|archive-date=2018-08-29|archive-url=https://web.archive.org/web/20180829000208/https://www.admatinc.com/tantalum/sheetplate/|url-status=dead}}</ref><ref name="USGSCR08" /><ref>{{cite journal|title = New applications for tantalum and tantalum alloys|journal = JOM: Journal of the Minerals, Metals and Materials Society|volume = 52|issue = 3|date = 2000|doi = 10.1007/s11837-000-0100-6|page=40|first = R. W. Jr.|last = Buckman|bibcode = 2000JOM....52c..40B |s2cid = 136550744}}</ref> Because of its ductility, tantalum can be drawn into fine wires or filaments, which are used for evaporating metals such as [[aluminium]]. 

Tantalum is inert against most acids except [[hydrofluoric acid]] and hot [[sulfuric acid]], and hot [[alkaline]] solutions also cause tantalum to corrode. This property makes it a useful metal for chemical reaction vessels and pipes for corrosive liquids. Heat exchanging coils for the steam heating of hydrochloric acid are made from tantalum.<ref name="Balke">{{cite journal|page= 1166|journal = Industrial and Engineering Chemistry|volume = 20|issue = 10|title = Columbium and Tantalum|first = Clarence W.|last = Balke|doi=10.1021/ie50310a022|date= 1935}}</ref> Tantalum was extensively used in the production of [[ultra high frequency]] [[Vacuum tube|electron tubes]] for radio transmitters. Tantalum is capable of capturing oxygen and nitrogen by forming nitrides and oxides and therefore helped to sustain the high vacuum needed for the tubes when used for internal parts such as grids and plates.<ref name="ICE" /><ref name="Balke" />

===Surgical uses===
Tantalum is widely used in surgery because of two unique characteristics of tantalum.  Tantalum's hardness and ductility is useful in making sharp, durable surgical instruments and also for monofilament sutures. However, a completely unrelated use for tantalum in surgery arises from its unique ability to form a lasting and durable structural bond with human hard tissue, making it uniquely useful for bone and dental implants.<ref name="Gerald L. Burke 1940">{{cite journal|last=Burke|first=Gerald L. |title =The Corrosion of Metals in Tissues; and An Introduction to Tantalum |pages=125–128|date=August 1940|journal=Canadian Medical Association Journal|volume=43|issue=2|pmid=20321780 |pmc=538079 }}</ref>  Tantalum coatings are increasingly used in the construction of complex tantalum-coated titanium surgical implants due to the tantalum plating's ability to form a strong and biologically stable bond to hard tissue.<ref>{{cite journal|first1 = R.|last1 = Cohen|date = 2006|title = Applications of porous tantalum in total hip arthroplasty|journal = Journal of the American Academy of Orthopaedic Surgeons|volume = 14|pmid=17077337|last2 = Della Valle|first2 = C. J.|last3 = Jacobs|first3 = J. J.|issue = 12|pages = 646–55|doi = 10.5435/00124635-200611000-00008}}</ref> An incidental consequence of its use for durable surgical implants is that tantalum implants are considered to be acceptable for patients undergoing MRI procedures because tantalum is a non-ferrous, non-magnetic metal.<ref name="PaganiasTsakotos2012">{{cite journal|last1=Paganias|first1=Christos G.|last2=Tsakotos|first2=George A.|last3=Koutsostathis|first3=Stephanos D.|last4=Macheras|first4=George A.|title=Osseous integration in porous tantalum implants|journal=Indian Journal of Orthopaedics|volume=46|issue=5|year=2012|pages=505–13|issn=0019-5413|doi=10.4103/0019-5413.101032|pmid=23162141|pmc=3491782 |doi-access=free }}</ref><!--10.1016/j.actbio.2010.01.046 -->

===Other uses===
[[File:Tantalio.png|thumb|320x320px|[[Bi-metallic coin|Bimetallic]] coins minted by the Bank of [[Kazakhstan]] with silver ring and tantalum center. These two feature the [[Apollo–Soyuz]] and the [[International Space Station]]]]

Tantalum was used by [[NASA]] to shield components of spacecraft, such as ''[[Voyager 1]]'' and ''[[Voyager 2]]'', from radiation.<ref>{{Cite book|last=Bell|first=Jim|title=The Interstellar Age: the story of the NASA men and women who flew the forty-year Voyager mission|publisher=Dutton|year=2015|isbn=978-0-525-95432-3|location=New York|pages=110}}</ref> The high melting point and oxidation resistance led to the use of the metal in the production of [[vacuum furnace]] parts. Tantalum is extremely inert and is therefore formed into a variety of corrosion resistant parts, such as [[thermowell]]s, valve bodies, and tantalum fasteners. Due to its high density, [[shaped charge]] and [[explosively formed penetrator]] liners have been constructed from tantalum.<ref>{{cite journal|title = Microstructure of high-strain, high-strain-rate deformed tantalum|first = Sia|last = Nemat-Nasser|author2 = Isaacs, Jon B.|author3 = Liu, Mingqi|journal = Acta Materialia|volume = 46|page= 1307|date = 1998|doi = 10.1016/S1359-6454(97)00746-5|issue = 4|bibcode = 1998AcMat..46.1307N}}</ref> Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point.<ref>{{cite journal|doi = 10.1016/S0734-743X(01)00135-X|title = The penetration resistance of a titanium alloy against jets from tantalum shaped charge liners|date = 2001|last1 = Walters|first1 = William|author2 = Cooch, William|author3 = Burkins, Matthew|journal = International Journal of Impact Engineering|volume = 26|issue = 1–10|page= 823|last4 = Burkins|first4 = Matthew| bibcode=2001IJIE...26..823W | s2cid=92307431 |url = https://zenodo.org/record/1260077}}</ref><ref>{{cite book |author=Russell |first1=Alan M. |url=https://books.google.com/books?id=fIu58uZTE-gC&pg=PA129 |title=Structure-property relations in nonferrous metals |last2=Lee |first2=Kok Loong |date=2005 |publisher=Wiley-Interscience |isbn=978-0-471-64952-6 |location=Hoboken, New Jersey |page=218 |language=en-us}}</ref> <!--http://www.meyersgroup.ucsd.edu/papers/journals/Meyers 176.pdf LE Murr, S Pappu, C Kennedy, CS Niou, M Meyers – Tantalum, 1996 http://www.osti.gov/bridge/servlets/purl/274177-TGUy10/webviewable/274177.pdf--> It is also occasionally used in precious [[watch]]es e.g. from [[Audemars Piguet]], [[F. P. Journe]], [[Hublot]], [[Montblanc (pens)|Montblanc]], [[Omega SA|Omega]], and [[Panerai]]. Tantalum oxide is used to make special high [[refractive index]] [[glass]] for [[camera]] lenses.<ref>{{cite book|title = Optical Materials: An Introduction to Selection and Application|chapter = Optical Glass Composition|first = Solomon|last = Musikant|publisher = CRC Press|date = 1985|page = 28|isbn = 978-0-8247-7309-0|chapter-url = https://books.google.com/books?id=iJEXMF3JBtQC&pg=PA28}}</ref> Spherical tantalum powder, produced by atomizing molten tantalum using gas or liquid, is commonly used in [[additive manufacturing]] due to its uniform shape, excellent [[flowability]], and high melting point.<ref>{{cite web |url=https://www.refractorymetal.org/spherical-tantalum-powder-for-3d-printing/ |title=Spherical Tantalum Powder for 3D Printing |website=Advanced Refractory Metals |date=30 May 2023 |access-date=Sep 22, 2024}}</ref><ref>{{cite journal |last1=Li |first1=Qiqi |last2=Zhang |first2=Baicheng |last3=Wen |first3=Yaojie |year=2022 |title=A comprehensive study of tantalum powder preparation for additive manufacturing |journal=Spplied Surface Science |volume=593 |page=153357 |doi=10.1016/j.apsusc.2022.153357|bibcode=2022ApSS..59353357L }}</ref>

== Environmental issues ==
Tantalum receives far less attention in the environmental field than it does in other geosciences. Upper Crust Concentration (UCC) and the Nb/Ta ratio in the upper crust and in minerals are available because these measurements are useful as a geochemical tool.<ref>{{Cite journal|last=Green|first=TH.|date=1995|title=Significance of Nb/Ta as an indicator of geochemical processes in the crust-mantle system|journal=Chemical Geology|volume=120|issue=3–4|pages=347–359|bibcode=1995ChGeo.120..347G|doi=10.1016/0009-2541(94)00145-X}}</ref> The latest value for upper crust concentration is 0.92 ppm, and the Nb/Ta(w/w) ratio stands at 12.7.<ref>{{Cite journal|last1=Hu|first1=Z.|last2=Gao|first2=S.|date=2008|title=Upper crustal abundances of trace elements: a revision and update|journal=Chemical Geology|volume=253|issue=3–4|pages=205|bibcode=2008ChGeo.253..205H|doi=10.1016/j.chemgeo.2008.05.010}}</ref>

Little data is available on tantalum concentrations in the different environmental compartments, especially in natural waters where reliable estimates of ‘dissolved’ tantalum concentrations in seawater and freshwaters have not even been produced.<ref name=":0">{{Cite journal|last=Filella|first=M.|date=2017|title=Tantalum in the environment|journal=Earth-Science Reviews|volume=173|pages=122–140|doi=10.1016/j.earscirev.2017.07.002|bibcode=2017ESRv..173..122F}}</ref> Some values on dissolved concentrations in oceans have been published, but they are contradictory. Values in freshwaters fare little better, but, in all cases, they are probably below 1&nbsp;ng L<sup>−1</sup>, since ‘dissolved’ concentrations in natural waters are well below most current analytical capabilities.<ref>{{Cite journal|last1=Filella|first1=M.|last2=Rodushkin|first2=I.|date=2018|title=A concise guide for the determination of less-studied technology-critical elements (Nb, Ta, Ga, In, Ge, Te) by inductively coupled plasma mass spectrometry in environmental samples|journal=Spectrochimica Acta Part B|volume=141|pages=80–84|doi=10.1016/j.sab.2018.01.004|bibcode=2018AcSpB.141...80F}}</ref> Analysis requires pre-concentration procedures that, for the moment, do not give consistent results. And in any case, tantalum appears to be present in natural waters mostly as particulate matter rather than dissolved.<ref name=":0" />

Values for concentrations in soils, bed sediments and atmospheric aerosols are easier to come by.<ref name=":0" /> Values in soils are close to 1 ppm and thus to UCC values. This indicates detrital origin. For atmospheric aerosols the values available are scattered and limited. When tantalum enrichment is observed, it is probably due to loss of more water-soluble elements in aerosols in the clouds.<ref>{{Cite journal|last1=Vlastelic|first1=I.|last2=Suchorski|first2=K.|last3=Sellegri|first3=K.|last4=Colomb|first4=A.|last5=Nauret|first5=F.|last6=Bouvier|first6=L.|last7=Piro|first7=J-L.|date=2015|title=The high field strength element budget of atmospheric aerosols (puy de Dôme, France)|journal=Geochimica et Cosmochimica Acta|volume=167|pages=253–268|bibcode=2015GeCoA.167..253V|doi=10.1016/j.gca.2015.07.006}}</ref>

Pollution linked to human use of the element has not been detected.<ref>{{Cite journal|last1=Filella|first1=M.|last2=Rodríguez-Murillo|first2=JC.|date=2017|title=Less-studied TCE: are their environmental concentrations increasing due to their use in new technologies?|journal=Chemosphere|volume=182|pages=605–616|doi=10.1016/j.chemosphere.2017.05.024|pmid=28525874|bibcode=2017Chmsp.182..605F}}</ref> Tantalum appears to be a very conservative element in biogeochemical terms, but its cycling and reactivity are still not fully understood.

==Precautions==
Compounds containing tantalum are rarely encountered in the laboratory. The metal is highly [[biocompatible]]<ref name="Gerald L. Burke 1940">{{cite journal|last=Burke|first=Gerald L. |title =The Corrosion of Metals in Tissues; and An Introduction to Tantalum |pages=125–128|date=August 1940|journal=Canadian Medical Association Journal|volume=43|issue=2|pmid=20321780 |pmc=538079 }}</ref> and is used for body [[implant (medicine)|implants]] and [[coating]]s, therefore attention may be focused on other elements or the physical nature of the [[chemical compound]].<ref>{{cite journal |author=Matsuno |first1=H. |last2=Yokoyama |first2=A. |last3=Watari |first3=F. |last4=Uo |first4=M. |last5=Kawasaki |first5=T. |date=2001 |title=Biocompatibility and osteogenesis of refractory metal implants, titanium, hafnium, niobium, tantalum and rhenium. Biocompatibility of tantalum. |journal=Biomaterials |volume=22 |issue=11 |pages=1253–1262 |doi=10.1016/S0142-9612(00)00275-1 |pmid=11336297}}</ref>

People can be exposed to tantalum in the workplace by breathing it in, skin contact, or eye contact. The [[Occupational Safety and Health Administration]] (OSHA) has set the legal limit ([[permissible exposure limit]]) for tantalum exposure in the workplace as 5&nbsp;mg/m<sup>3</sup> over an 8-hour workday. The [[National Institute for Occupational Safety and Health]] (NIOSH) has set a [[recommended exposure limit]] (REL) of 5&nbsp;mg/m<sup>3</sup> over an 8-hour workday and a short-term limit of 10&nbsp;mg/m<sup>3</sup>. There is a paradox arising because of Tantalum's ability to form a strong and permanent bond with bone tissue: at levels of 2500&nbsp;mg/m<sup>3</sup>, tantalum '''dust''' becomes [[IDLH|immediately dangerous to life and health]] if Tantalum dust accidentally bonds with the wrong tissue.<ref>{{Cite web|title = CDC – NIOSH Pocket Guide to Chemical Hazards – Tantalum (metal and oxide dust, as Ta)|url = https://www.cdc.gov/niosh/npg/npgd0585.html|website = www.cdc.gov|access-date = 2015-11-24}}</ref>

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

==External links==
{{Wiktionary|tantalum}}
{{Commons|Tantalum}}
* [http://tanb.org/ Tantalum-Niobium International Study Center]
* [https://www.cdc.gov/niosh/npg/npgd0585.html CDC – NIOSH Pocket Guide to Chemical Hazards]

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{{Tantalum compounds}}
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[[Category:Tantalum| ]]
[[Category:Biomaterials]]
[[Category:Chemical elements with body-centered cubic structure]]
[[Category:Chemical elements]]
[[Category:Native element minerals]]
[[Category:Noble metals]]
[[Category:Refractory metals]]
[[Category:Transition metals]]