Tantalum is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
with the
symbol Ta and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of ever ...
73. Previously known as ''tantalium'', it is named after
Tantalus, a villain in Greek mythology. Tantalum is a very hard,
ductile,
lustrous, blue-gray
transition metal
In chemistry, a transition metal (or transition element) is a chemical element in the d-block of the periodic table (groups 3 to 12), though the elements of group 12 (and less often group 3) are sometimes excluded. They are the elements that can ...
that is highly corrosion-resistant. It is part of the
refractory metals
Refractory metals are a class of metals that are extraordinarily resistant to heat and wear. The expression is mostly used in the context of materials science, metallurgy and engineering. The definition of which elements belong to this group d ...
group, which are widely used as components of strong
high-melting-point alloys. 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
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
groups
tantalite
The mineral group tantalite Fe,_manganese.html"_;"title="iron.html"_;"title="iron">Fe,_manganese">Mn)Tantalum">Ta2oxygen.html" ;"title="manganese">Mn)Tantalum.html" ;"title="iron">Fe,_manganese.html" ;"title="iron.html" ;"title="iron">Fe, mang ...
,
columbite
Columbite, also called niobite, niobite-tantalite and columbate [], is a black mineral group that is an ore of niobium. It has a submetallic Lustre (mineralogy), luster and a high density and is a niobate of iron and manganese. This mineral group w ...
and
coltan
Coltan (short for columbite–tantalites and known industrially as tantalite) is a dull black metallic ore from which the elements niobium and tantalum are extracted. The niobium-dominant mineral in coltan is columbite (after niobium's original ...
.
The chemical inertness and very high melting point of tantalum make it valuable for laboratory and industrial equipment such as
reaction vessels and
vacuum furnaces. It is used in
tantalum capacitor
A tantalum electrolytic capacitor is an electrolytic capacitor, a passive component of electronic circuits. It consists of a pellet of porous tantalum metal as an anode, covered by an insulating oxide layer that forms the dielectric, surrounde ...
s for
electronic equipment such as
computer
A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations ( computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...
s. Tantalum is considered a
technology-critical element by the European Commission.
History
Tantalum was discovered in Sweden in 1802 by
Anders Ekeberg
Anders Gustaf Ekeberg ( Stockholm, Sweden, 16 January 1767 – Uppsala, Sweden, 11 February 1813) was a Swedish analytical chemist who discovered tantalum in 1802. - subscription required
He was notably deaf.
Education
Anders Gustav Ekebe ...
, in two mineral samples – one from Sweden and the other from Finland. One year earlier,
Charles Hatchett
Charles Hatchett FRS FRSE (2 January 1765 – 10 March 1847) was an English mineralogist and analytical chemist who discovered the element niobium, for which he proposed the name "columbium".
Hatchett was elected a Fellow of the Linnaean Soci ...
had discovered
columbium (now niobium), and in 1809 the English chemist
William Hyde Wollaston
William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable ingot ...
compared its oxide,
columbite
Columbite, also called niobite, niobite-tantalite and columbate [], is a black mineral group that is an ore of niobium. It has a submetallic Lustre (mineralogy), luster and a high density and is a niobate of iron and manganese. This mineral group w ...
with a density of 5.918 g/cm
3, to that of tantalum,
tantalite
The mineral group tantalite Fe,_manganese.html"_;"title="iron.html"_;"title="iron">Fe,_manganese">Mn)Tantalum">Ta2oxygen.html" ;"title="manganese">Mn)Tantalum.html" ;"title="iron">Fe,_manganese.html" ;"title="iron.html" ;"title="iron">Fe, mang ...
with a density of 7.935 g/cm
3. He concluded that the two oxides, despite their difference in measured density, were identical and kept the name tantalum.
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
Heinrich Rose (6 August 1795 – 27 January 1864) was a German mineralogist and analytical chemist. He was the brother of the mineralogist Gustav Rose and a son of Valentin Rose.
Rose's early works on phosphorescence were noted in the Quarte ...
, who argued that there were two additional elements in the tantalite sample, and he named them after the children of
Tantalus: niobium (from
Niobe
In Greek mythology, Niobe (; grc-gre, Νιόβη ) was a daughter of Tantalus and of either Dione (mythology), Dione, the most frequently cited, or of Eurythemista or Euryanassa, the wife of Amphion and the sister of Pelops and Broteas.
Her ...
, the goddess of tears), and pelopium (from
Pelops).
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.
The differences between tantalum and niobium were demonstrated unequivocally in 1864 by
Christian Wilhelm Blomstrand,
and
Henri Etienne Sainte-Claire Deville
Henri is an Estonian, Finnish, French, German and Luxembourgish form of the masculine given name Henry.
People with this given name
; French noblemen
:'' See the ' List of rulers named Henry' for Kings of France named Henri.''
* Henri I de Mon ...
, as well as by
Louis J. Troost, who determined the empirical formulas of some of their compounds in 1865.
Further confirmation came from the Swiss chemist
Jean Charles Galissard de Marignac, 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. De Marignac was the first to produce the metallic form of tantalum in 1864, when he
reduced tantalum chloride by heating it in an atmosphere of
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
.
Early investigators had only been able to produce impure tantalum, and the first relatively pure ductile metal was produced by
Werner von Bolton
Werner von Bolton (8 April 1868 – 28 October 1912) was a German chemist and materials scientist. He devised a technique for producing filaments for incandescent light bulb made out of tantalum in 1902.
Life
Werner von Bolton was born in Tiflis ...
in
Charlottenburg in 1903. Wires made with metallic tantalum were used for
light bulb filaments until
tungsten replaced it in widespread use.
The name tantalum was derived from the name of the mythological Tantalus, the father of Niobe in
Greek mythology
A major branch of classical mythology, Greek mythology is the body of myths originally told by the ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the origin and nature of the world, the lives and activities o ...
. 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.) Anders Ekeberg wrote "This metal I call ''tantalum'' ... partly in allusion to its incapacity, when immersed in acid, to absorb any and be saturated."
For decades, the commercial technology for separating tantalum from niobium involved the
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.
Characteristics
Physical properties
Tantalum is dark (blue-gray), dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
by
acids; in fact, at temperatures below 150 °
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 a solution of
potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
. Tantalum's high melting point of 3017 °C (boiling point 5458 °C) is exceeded among the elements only by
tungsten,
rhenium and
osmium for metals, and
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
.
Tantalum exists in two crystalline phases, alpha and beta. The alpha phase is relatively
ductile and soft; it has
body-centered cubic structure (
space group ''Im3m'', lattice constant ''a'' = 0.33058 nm),
Knoop hardness
The Knoop hardness test is a microhardness test – a test for mechanical hardness used particularly for very brittle materials or thin sheets, where only a small indentation may be made for testing purposes. A pyramidal diamond point is pressed ...
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 nm, ''c'' = 0.5313 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 °C. Bulk tantalum is almost entirely alpha phase, and the beta phase usually exists as thin films obtained by magnetron
sputtering,
chemical vapor deposition or
electrochemical deposition from a
eutectic molten salt solution.
Isotopes
Natural tantalum consists of two
isotope
Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...
s:
180mTa (0.012%) and
181Ta (99.988%).
181Ta is a
stable isotope.
180mTa (''m'' denotes a metastable state) is predicted to decay in three ways:
isomeric transition to the
ground state of
180Ta,
beta decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
to
180 W, or electron capture to
180 Hf. However, radioactivity of this
nuclear isomer has never been observed, and only a lower limit on its
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
of 2.0 × 10
16 years has been set. The ground state of
180Ta has a half-life of only 8 hours.
180mTa 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
180mTa in the natural mixture of isotopes (and again excluding radiogenic and cosmogenic short-lived nuclides).
Tantalum has been examined theoretically as a "
salting" material for
nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions ( thermonuclear bomb), producing a nuclear explosion. Both bomb ...
s (
cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
is the better-known hypothetical salting material). An external shell of
181Ta 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
182Ta, which has a
half-life
Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ...
of 114.4 days and produces
gamma ray
A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
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.
Tantalum can be used as a target material for accelerated proton beams for the production of various short-lived isotopes including
8Li,
80Rb, and
160Yb.
Chemical compounds
Tantalum forms compounds in oxidation states −III to +V. 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 exhibit the +V oxidation state. Like niobium, tantalum is barely soluble in dilute solutions of
hydrochloric,
sulfuric
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
,
nitric and
phosphoric acids due to the precipitation of hydrous Ta(V) oxide.
In basic media, Ta can be solubilized due to the formation of polyoxotantalate species.
Oxides, nitrides, carbides, sulfides
Tantalum pentoxide (Ta
2O
5) is the most important compound from the perspective of applications. Oxides of tantalum in lower oxidation states are numerous, including many
defect structure
A crystallographic defect is an interruption of the regular patterns of arrangement of atoms or molecules in crystalline solids. The positions and orientations of particles, which are repeating at fixed distances determined by the unit cell para ...
s, and are lightly studied or poorly characterized.
Tantalates, compounds containing
4">aO4sup>3− or
3">aO3sup>− are numerous.
Lithium tantalate (LiTaO
3) adopts a perovskite structure.
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between l ...
tantalate (LaTaO
4) contains isolated tetrahedra.
As in the cases of other
refractory metals, the hardest known compounds of tantalum are nitrides and carbides.
Tantalum carbide
Tantalum carbides (TaC) form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaC''x'', where ''x'' usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metal ...
, TaC, like the more commonly used
tungsten carbide, is a hard
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...
that is used in cutting tools. Tantalum(III) nitride is used as a thin film insulator in some microelectronic fabrication processes.
The best studied chalcogenide is TaS
2, a layered
semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way ...
, as seen for other
transition metal dichalcogenide : 220px, Cadmium sulfide, a prototypical metal chalcogenide, is used as a yellow pigment.
A chalcogenide is a chemical compound consisting of at least one chalcogen anion and at least one more electropositive element. Although all group 16 elements ...
s. A tantalum-tellurium alloy forms
quasicrystals.
Halides
Tantalum halides span the oxidation states of +5, +4, and +3.
Tantalum pentafluoride (TaF
5) is a white solid with a melting point of 97.0 °C. The anion
7">aF7sup>2- is used for its separation from niobium.
The chloride
, which exists as a dimer, is the main reagent in synthesis of new Ta compounds. It hydrolyzes readily to an
oxychloride
In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula , where X = fluorine (F), chlor ...
. The lower halides and , feature Ta-Ta bonds.
Organotantalum compounds
Organotantalum compounds include
pentamethyltantalum
Pentamethyltantalum is a homoleptic organotantalum compound.
It has a propensity to explode when it is melted. Its discovery was part of a sequence that lead to Richard R. Schrock's Nobel Prize discovery in olefin metathesis.
Production
Pentame ...
, mixed alkyltantalum chlorides, alkyltantalum hydrides, alkylidene complexes as well as cyclopentadienyl derivatives of the same.
Diverse salts and substituted derivatives are known for the hexacarbonyl
6">a(CO)6sup>− and related
isocyanides.
Occurrence
Tantalum is estimated to make up about 1
ppm or 2
ppm of the
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
The mineral group tantalite Fe,_manganese.html"_;"title="iron.html"_;"title="iron">Fe,_manganese">Mn)Tantalum">Ta2oxygen.html" ;"title="manganese">Mn)Tantalum.html" ;"title="iron">Fe,_manganese.html" ;"title="iron.html" ;"title="iron">Fe, mang ...
(a series consisting of tantalite-(Fe), tantalite-(Mn) and tantalite-(Mg))
microlite
Microlite was once known as a pale-yellow, reddish-brown, or black isometric mineral composed of sodium calcium tantalum oxide with a small amount of fluorine. Its chemical formula is. Today it is a name of a group of oxide minerals of a similar ...
(now a group name),
wodginite,
euxenite (actually euxenite-(Y)), and
polycrase
Polycrase or polycrase-(Y) is a black or brown metallic complex uranium yttrium oxide mineral with the chemical formula . It is amorphous. It has a Mohs hardness of 5 to 6 and a specific gravity of 5. It is radioactive due to its uranium content (a ...
(actually polycrase-(Y)).
Tantalite (
Fe,
Mn)Ta
2 O6 is the most important mineral for tantalum extraction. Tantalite has the same mineral structure as
columbite
Columbite, also called niobite, niobite-tantalite and columbate [], is a black mineral group that is an ore of niobium. It has a submetallic Lustre (mineralogy), luster and a high density and is a niobate of iron and manganese. This mineral group w ...
(
Fe,
Mn) (Ta,
Nb)
2 O6; 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
Columbite, also called niobite, niobite-tantalite and columbate [], is a black mineral group that is an ore of niobium. It has a submetallic Lustre (mineralogy), luster and a high density and is a niobate of iron and manganese. This mineral group w ...
). The high density of tantalite and other tantalum containing minerals makes the use of
gravitational separation the best method. Other minerals include
samarskite and
fergusonite.
Australia
Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
was the main producer of tantalum prior to the 2010s, with
Global Advanced Metals Talison Minerals Pty Ltd was a mining company based in Australia. It was split into Talison Lithium (as of 2020 a 51:49 jv between Tianqi Lithium and Albemarle Corporation) and Talison Tantalum, now known as Global Advanced Metals, in 2009. The t ...
(formerly known as
Talison Minerals) being the largest tantalum mining company in that country. They operate two mines in Western Australia,
Greenbushes in the southwest and
Wodgina
The Wodgina mine is an exhausted iron ore mine located in the Pilbara region of Western Australia, 90 kilometres south of Port Hedland.
The mine was operated by Atlas Iron Limited. The facilities and tenements are shared, by contract, with Glo ...
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
global financial crisis. 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.
[
] Wodgina produces a primary tantalum concentrate which is further upgraded at the Greenbushes operation before being sold to customers.
Whereas the large-scale producers of niobium are in
Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
and
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...
, the ore there also yields a small percentage of tantalum. Some other countries such as
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
,
Ethiopia
Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...
, 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
Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
and
Malaysia
Malaysia ( ; ) is a country in Southeast Asia. The federal constitutional monarchy consists of thirteen states and three federal territories, separated by the South China Sea into two regions: Peninsular Malaysia and Borneo's East Mal ...
as a by-product of the
tin mining there. During gravitational separation of the ores from placer deposits, not only is
cassiterite (SnO
2) 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.
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
The Democratic Republic of the Congo (french: République démocratique du Congo (RDC), colloquially "La RDC" ), informally Congo-Kinshasa, DR Congo, the DRC, the DROC, or the Congo, and formerly and also colloquially Zaire, is a country in ...
,
Rwanda, and some other African countries. Future sources of supply of tantalum, in order of estimated size, are being explored in
Saudi Arabia
Saudi Arabia, officially the Kingdom of Saudi Arabia (KSA), is a country in Western Asia. It covers the bulk of the Arabian Peninsula, and has a land area of about , making it the fifth-largest country in Asia, the second-largest in the Ara ...
,
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a List of transcontinental countries, transcontinental country spanning the North Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via a land bridg ...
,
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland ...
, China, Mozambique, Canada, Australia, the
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
,
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bot ...
, and Brazil.
It is estimated that tantalum resources will run out around 2060, based on extraction at current rates, demonstrating the need for increased
recycling
Recycling is the process of converting waste materials into new materials and objects. The Energy recycling, recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability t ...
.
Status as a conflict resource
Tantalum is considered a
conflict resource.
Coltan
Coltan (short for columbite–tantalites and known industrially as tantalite) is a dull black metallic ore from which the elements niobium and tantalum are extracted. The niobium-dominant mineral in coltan is columbite (after niobium's original ...
, the industrial name for a
columbite
Columbite, also called niobite, niobite-tantalite and columbate [], is a black mineral group that is an ore of niobium. It has a submetallic Lustre (mineralogy), luster and a high density and is a niobate of iron and manganese. This mineral group w ...
–
tantalite
The mineral group tantalite Fe,_manganese.html"_;"title="iron.html"_;"title="iron">Fe,_manganese">Mn)Tantalum">Ta2oxygen.html" ;"title="manganese">Mn)Tantalum.html" ;"title="iron">Fe,_manganese.html" ;"title="iron.html" ;"title="iron">Fe, mang ...
mineral from which niobium and tantalum are extracted, can also be found in
Central Africa
Central Africa is a subregion of the African continent comprising various countries according to different definitions. Angola, Burundi, the Central African Republic, Chad, the Democratic Republic of the Congo, the Republic of the Co ...
, which is why tantalum is being linked to
warfare in the Democratic Republic of the Congo (formerly
Zaire). According to an October 23, 2003
United Nations
The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmoni ...
report, 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 – making it the world's deadliest documented conflict since
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. 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. The
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
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.
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.
The stated aim of the ''Solutions for Hope Tantalum Project'' is to "source conflict-free tantalum from the Democratic Republic of Congo"
Production and fabrication
Several steps are involved in the extraction of tantalum from tantalite. First, the mineral is
crushed
Crushed may refer to:
* "Crushed" (''Ms. Marvel''), a 2022 episode of the American television series ''Ms. Marvel''
* "Crushed" (Roland Lee Gift song) a 2009 single by Roland Lee Gift
* "Crushed" (''The Suite Life of Zack & Cody'' episode), an ...
and concentrated by
gravity separation. This is generally carried out near the
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.
Extraction begins with
leaching the ore with
hydrofluoric acid together with
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
or
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
. 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
2O
5 + 14 HF → 2 H
2 7">aF7+ 5 H
2O
Completely analogous reactions occur for the niobium component, but the hexafluoride is typically predominant under the conditions of the extraction.
: Nb
2O
5 + 12 HF → 2 H
6">bF6+ 5 H
2O
These equations are simplified: it is suspected that bisulfate (HSO
4−) and chloride compete as ligands for the Nb(V) and Ta(V) ions, when sulfuric and hydrochloric acids are used, respectively.
The tantalum and niobium fluoride complexes are then removed from the
aqueous solution by
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
fluorides 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
In chemistry, molecular oxohalides (oxyhalides) are a group of chemical compounds in which both oxygen and halogen atoms are attached to another chemical element A in a single molecule. They have the general formula , where X = fluorine (F), chlor ...
H
2 5">bOF5is formed under these conditions. Subsequent to removal of the niobium, the solution of purified H
2 7">aF7is neutralised with aqueous
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
to precipitate hydrated tantalum oxide as a solid, which can be
calcined to
tantalum pentoxide (Ta
2O
5).
Instead of hydrolysis, the H
2 7">aF7can be treated with
potassium fluoride to produce
potassium heptafluorotantalate:
: H
2 7">aF7+ 2 KF → K
2 7">aF7+ 2 HF
Unlike H
2 7">aF7 the potassium salt is readily crystallized and handled as a solid.
K
2 7">aF7can be converted to metallic tantalum by
reduction with
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
, at approximately 800 °C in
molten salt.
: K
2 7">aF7+ 5 Na → Ta + 5 NaF + 2 KF
In an older method, called the
Marignac process, the mixture of H
2 7">aF7and H
2 5">bOF5was converted to a ''mixture'' of K
2 7">aF7and K
2 5">bOF5 which was then be separated by
fractional crystallization, exploiting their different water solubilities.
Electrolysis
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 is the electrolyte. The first refinery has enough capacity to supply 3–4% of annual global demand.
Fabrication and metalworking
All
welding of tantalum must be done in an inert atmosphere of
argon
Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
or
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic ta ...
in order to shield it from contamination with atmospheric gases. Tantalum is not
solderable. Grinding tantalum is difficult, especially so for
annealed tantalum. In the annealed condition, tantalum is extremely
ductile and can be readily formed as metal sheets.
Applications
Electronics
The major use for tantalum, as the metal powder, is in the production of electronic components, mainly
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s and some high-power
resistors.
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
In electromagnetism, a dielectric (or dielectric medium) is an electrical insulator that can be polarised by an applied electric field. When a dielectric material is placed in an electric field, electric charges do not flow through the ma ...
, and an electrolytic solution or conductive solid as the other "plate". Because the
dielectric layer can be very thin (thinner than the similar layer in, for instance, an aluminium electrolytic capacitor), a high
capacitance
Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
can be achieved in a small volume. Because of the size and weight advantages, tantalum capacitors are attractive for
portable telephones,
personal computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or te ...
s,
automotive electronics and
cameras
A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with a ...
.
Alloys
Tantalum is also used to produce a variety of
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductili ...
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
A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, ...
s for jet engine components, chemical process equipment,
nuclear reactor
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat fr ...
s, missile parts, heat exchangers, tanks, and vessels.
Because of its ductility, tantalum can be drawn into fine wires or filaments, which are used for evaporating metals such as
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
. Since it resists attack by body fluids and is nonirritating, tantalum is widely used in making surgical instruments and implants. For example, porous tantalum coatings are used in the construction of orthopedic implants due to tantalum's ability to form a direct bond to hard tissue.
Tantalum is inert against most acids except
hydrofluoric acid and hot
sulfuric acid
Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular fo ...
, 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.
Tantalum was extensively used in the production of
ultra high frequency
Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...
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.
Other uses
Tantalum was used by NASA to shield components of spacecraft, such as ''
Voyager 1
''Voyager 1'' is a space probe launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System and interstellar space beyond the Sun's heliosphere. Launched 16 days after its twin '' Voyager 2'', ''V ...
'' and ''
Voyager 2
''Voyager 2'' is a space probe launched by NASA on August 20, 1977, to study the outer planets and interstellar space beyond the Sun's heliosphere. As a part of the Voyager program, it was launched 16 days before its twin, '' Voyager 1'', ...
'', from radiation. 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
thermowells, valve bodies, and tantalum fasteners. Due to its high density,
shaped charge
A shaped charge is an explosive charge shaped to form an explosively formed penetrator (EFP) to focus the effect of the explosive's energy. Different types of shaped charges are used for various purposes such as cutting and forming metal, ini ...
and
explosively formed penetrator liners have been constructed from tantalum. Tantalum greatly increases the armor penetration capabilities of a shaped charge due to its high density and high melting point.
It is also occasionally used in precious
watch
A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached ...
es e.g. from
Audemars Piguet,
F.P. Journe,
Hublot,
Montblanc,
Omega, and
Panerai
Officine Panerai (also known simply as Panerai) is an Italian luxury watch manufacturer, and a wholly owned subsidiary of Compagnie Financière Richemont S.A.
Officine Panerai designs, manufactures and markets watches through authorized dealer ...
. Tantalum is also highly bioinert and is used as an orthopedic implant material.
The high stiffness of tantalum makes it necessary to use it as highly porous foam or scaffold with lower stiffness for hip replacement implants to avoid
stress shielding
Stress shielding is the reduction in bone density (osteopenia) as a result of removal of typical stress from the bone by an implant (for instance, the femoral component of a hip prosthesis). This is because by Wolff's law
Wolff's law, developed ...
. Because tantalum is a non-ferrous, non-magnetic metal, these implants are considered to be acceptable for patients undergoing MRI procedures.
The oxide is used to make special high
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, ...
glass
Glass is a non- crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling (quenchin ...
for
camera
A camera is an optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), with ...
lenses.
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. The latest value for upper crust concentration is 0.92 ppm, and the Nb/Ta(w/w) ratio stands at 12.7.
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.
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 ng L
−1, since ‘dissolved’ concentrations in natural waters are well below most current analytical capabilities. 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.
Values for concentrations in soils, bed sediments and atmospheric aerosols are easier to come by.
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.
Pollution linked to human use of the element has not been detected. 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 and is used for body
implants and
coating
A coating is a covering that is applied to the surface of an object, usually referred to as the substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. Pow ...
s, therefore attention may be focused on other elements or the physical nature of the
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
.
People can be exposed to tantalum in the workplace by breathing it in, skin contact, or eye contact. The
Occupational Safety and Health Administration
The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agen ...
(OSHA) has set the legal limit (
permissible exposure limit
The permissible exposure limit (PEL or OSHA PEL) is a legal limit in the United States for exposure of an employee to a chemical substance or physical agent such as high level noise. Permissible exposure limits are established by the Occupationa ...
) for tantalum exposure in the workplace as 5 mg/m
3 over an 8-hour workday. The
National Institute for Occupational Safety and Health (NIOSH) has set a
recommended exposure limit (REL) of 5 mg/m
3 over an 8-hour workday and a short-term limit of 10 mg/m
3. At levels of 2500 mg/m
3, tantalum is
immediately dangerous to life and health.
References
External links
Tantalum-Niobium International Study Center
{{Authority control
Biomaterials
Chemical elements with body-centered cubic structure
Chemical elements
Native element minerals
Noble metals
Refractory metals
Transition metals