Lanthanum is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol La 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 every ...
57. It is a
soft,
ductile
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
, silvery-white
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
that tarnishes slowly when exposed to air. It is the eponym of the
lanthanide series, a group of 15 similar elements between lanthanum and
lutetium
Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted am ...
in the
periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the
rare earth elements. Like most other rare earth elements, the usual
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
is +3. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.
Lanthanum usually occurs together with
cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
and the other rare earth elements. Lanthanum was first found by the Swedish chemist
Carl Gustaf Mosander
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium.
Early life and education
Born in Kalmar, Mosander attended school there until he moved ...
in 1839 as an impurity in
cerium nitrate
Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state. Often these compounds contain water, hydroxide, or hydronium ions in addition to cerium and nitrate. Double nitrates of cerium also exist.
Cerium(III) nitrat ...
– hence the name ''lanthanum'', from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
(), meaning 'to lie hidden'. Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
. In minerals such as
monazite
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
and
bastnäsite
The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-( Ce) with a formula of (Ce, La)CO3F, bastnäsite-( La) with a formula of (La, Ce)CO3F, and bastnäsite-( Y) with a formul ...
, lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.
Lanthanum compounds have numerous applications as
catalysts
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in
lighter
A lighter is a portable device which creates a flame, and can be used to ignite a variety of items, such as cigarettes, gas lighter, fireworks, candles or campfires. It consists of a metal or plastic container filled with a flammable liquid or ...
s and torches,
electron cathodes,
scintillators,
gas tungsten arc welding
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atm ...
electrodes, and other things.
Lanthanum carbonate
Lanthanum carbonate, La( C O3)3, is the salt formed by lanthanum(III) cations and carbonate anions. It is an ore of lanthanum metal (bastnäsite), along with monazite.
Chemistry
Lanthanum carbonate is used as a starting material in lanthanum c ...
is used as a
phosphate binder Phosphate binders are medications used to reduce the absorption of dietary phosphate; they are taken along with meals and snacks. They are frequently used in people with chronic kidney failure (CKF), who are less able to excrete phosphate, resulting ...
in cases of
high levels of phosphate in the blood seen with
kidney failure
Kidney failure, also known as end-stage kidney disease, is a medical condition in which the kidneys can no longer adequately filter waste products from the blood, functioning at less than 15% of normal levels. Kidney failure is classified as eit ...
.
Characteristics
Physical
Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the
alkaline earth metal
The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).. The elements have very similar properties: they are all ...
barium and to the left of the lanthanide cerium. Its placement has been disputed, but most who study the matter along with a 2021 IUPAC provisional report consider lanthanum to be best placed as the first of the f-block elements.
[
] The 57 electrons of a lanthanum atom are arranged in the
configuration ed
16s
2, with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s
subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas
xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
.
[Greenwood and Earnshaw, p. 1106] Some lanthanum(II) compounds are also known, but they are much less stable.
Among the lanthanides, lanthanum is exceptional as it has no 4f electrons as a single gas-phase atom. Thus it is only very weakly
paramagnetic
Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, ...
, unlike the strongly paramagnetic later lanthanides (with the exceptions of the last two,
ytterbium
Ytterbium is a chemical element with the symbol Yb and atomic number 70. It is a metal, the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. However, like the othe ...
and
lutetium
Lutetium is a chemical element with the symbol Lu and atomic number 71. It is a silvery white metal, which resists corrosion in dry air, but not in moist air. Lutetium is the last element in the lanthanide series, and it is traditionally counted am ...
, where the 4f shell is completely full). However, the 4f shell of lanthanum can become partially occupied in chemical environments and participate in chemical bonding.
For example, the melting points of the trivalent lanthanides (all but
europium and ytterbium) are related to the extent of hybridisation of the 6s, 5d, and 4f electrons (lowering with increasing 4f involvement), and lanthanum has the second-lowest melting point among them: 920 °C. (Europium and ytterbium have lower melting points because they delocalise about two electrons per atom rather than three.) This chemical availability of f orbitals justifies lanthanum's placement in the f-block despite its anomalous ground-state configuration
(which is merely the result of strong interelectronic repulsion making it less profitable to occupy the 4f shell, as it is small and close to the core electrons).
The lanthanides become harder as the series is traversed: as expected, lanthanum is a soft metal. Lanthanum has a relatively high
resistivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
of 615 nΩm at room temperature; in comparison, the value for the good conductor aluminium is only 26.50 nΩm.
[Greenwood and Earnshaw, p. 1429] Lanthanum is the least volatile of the lanthanides.
Like most of the lanthanides, lanthanum has a
hexagonal crystal structure at room temperature. At 310 °C, lanthanum changes to a
face-centered cubic
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of ...
structure, and at 865 °C, it changes to a
body-centered cubic
In crystallography, the cubic (or isometric) crystal system is a crystal system where the unit cell is in the shape of a cube. This is one of the most common and simplest shapes found in crystals and minerals.
There are three main varieties of ...
structure.
Chemical
As expected from
periodic trends, lanthanum has the largest
atomic radius
The atomic radius of a chemical element is a measure of the size of its atom, usually the mean or typical distance from the center of the nucleus to the outermost isolated electron. Since the boundary is not a well-defined physical entity, there ...
of the lanthanides. Hence, it is the most reactive among them, tarnishing quite rapidly in air, turning completely dark after several hours and can readily burn to form
lanthanum(III) oxide
Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedsto ...
, La
2O
3, which is almost as
basic as
calcium oxide
Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ...
.
[Greenwood and Earnshaw, p. 1105–7] A centimeter-sized sample of lanthanum will corrode completely in a year as its oxide
spalls off like iron
rust
Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and iron(III) oxide-hydroxide (FeO( ...
, instead of forming a protective oxide coating like
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. I ...
, scandium, yttrium, and lutetium. Lanthanum reacts with the
halogens at room temperature to form the trihalides, and upon warming will form
binary compound
In materials chemistry, a binary phase or binary compound is a chemical compound containing two different elements. Some binary phase compounds are molecular, e.g. carbon tetrachloride (CCl4). More typically binary phase refers to extended soli ...
s with the nonmetals nitrogen, carbon, sulfur, phosphorus, boron, selenium, silicon and arsenic.
Lanthanum reacts slowly with water to form
lanthanum(III) hydroxide, La(OH)
3.
In dilute
sulfuric acid, lanthanum readily forms the aquated tripositive ion : this is colorless in aqueous solution since La
3+ has no d or f electrons.
Lanthanum is the strongest and
hardest base among the
rare earth elements, which is again expected from its being the largest of them.
[Greenwood and Earnshaw, p. 1434]
Some lanthanum(II) compounds are also known, but they are much less stable.
Therefore, in officially naming compounds of lanthanum its oxidation number always is to be mentioned.
Isotopes
Naturally occurring lanthanum is made up of two isotopes, the stable
139La and the
primordial long-lived radioisotope 138La.
139La is by far the most abundant, making up 99.910% of natural lanthanum: it is produced in the
s-process (slow
neutron
The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
capture, which occurs in low- to medium-mass stars) and the
r-process (rapid neutron capture, which occurs in core-collapse
supernovae). It is the only stable isotope of lanthanum.
The very rare isotope
138La is one of the few primordial
odd–odd nuclei
In nuclear physics, properties of a nucleus depend on evenness or oddness of its atomic number (proton number) ''Z'', neutron number ''N'' and, consequently, of their sum, the mass number ''A''. Most importantly, oddness of both ''Z'' and ''N'' ...
, with a long half-life of 1.05×10
11 years. It is one of the proton-rich
p-nuclei
p-nuclei (''p'' stands for proton-rich) are certain proton-rich, naturally occurring isotopes of some elements between selenium and mercury inclusive which cannot be produced in either the s- or the r-process.
Definition
The classical, gro ...
which cannot be produced in the
s- or
r-processes.
138La, along with the even rarer
180mTa, is produced in the ν-process, where
neutrino
A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
s interact with stable nuclei.
All other lanthanum isotopes are
synthetic: with the exception of
137La with a half-life of about 60,000 years, all of them have half-lives less than a day, and most have half-lives less than a minute. The isotopes
139La and
140La occur as
fission products of uranium.
Compounds
Lanthanum oxide
Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock ...
is a white solid that can be prepared by direct reaction of its constituent elements. Due to the large size of the La
3+ ion, La
2O
3 adopts a hexagonal 7-coordinate structure that changes to the 6-coordinate structure of
scandium oxide
Scandium(III) oxide or scandia is a inorganic compound with formula Sc2 O3. It is one of several oxides of rare earth elements with a high melting point. It is used in the preparation of other scandium compounds as well as in high-temperature sys ...
(Sc
2O
3) and
yttrium oxide Yttrium oxide may refer to:
* Yttrium(II) oxide, YO, a dark brown solid
* Yttrium(III) oxide
Yttrium oxide, also known as yttria, is Y2 O3. It is an air-stable, white solid substance.
The thermal conductivity of yttrium oxide is 27 W/(m·K).
...
(Y
2O
3) at high temperature. When it reacts with water,
lanthanum hydroxide is formed:
a lot of heat is evolved in the reaction and a hissing sound is heard. Lanthanum hydroxide will react with atmospheric
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
to form the basic carbonate.
[Greenwood and Earnshaw, p. 1107–8]
Lanthanum fluoride is insoluble in water and can be used as a
qualitative test for the presence of La
3+. The heavier halides are all very soluble
deliquescent
Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance' ...
compounds. The anhydrous halides are produced by direct reaction of their elements, as heating the hydrates causes hydrolysis: for example, heating hydrated LaCl
3 produces LaOCl.
Lanthanum reacts exothermically with hydrogen to produce the dihydride LaH
2, a black,
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolit ...
, brittle, conducting compound with the
calcium fluoride
Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.
...
structure.
This is a non-stoichiometric compound, and further absorption of hydrogen is possible, with a concomitant loss of electrical conductivity, until the more salt-like LaH
3 is reached.
Like LaI
2 and LaI, LaH
2 is probably an
electride compound.
Due to the large ionic radius and great electropositivity of La
3+, there is not much covalent contribution to its bonding and hence it has a limited
coordination chemistry, like yttrium and the other lanthanides.
[Greenwood and Earnshaw, pp. 1108–9] Lanthanum oxalate does not dissolve very much in alkali-metal oxalate solutions, and
3(H2O)2">a(acac)3(H2O)2decomposes around 500 °C. Oxygen is the most common
donor atom in lanthanum complexes, which are mostly ionic and often have high coordination numbers over 6: 8 is the most characteristic, forming
square antiprism
In geometry, the square antiprism is the second in an infinite family of antiprisms formed by an even-numbered sequence of triangle sides closed by two polygon caps. It is also known as an ''anticube''.
If all its faces are regular, it is a sem ...
atic and
dodecadeltahedral structures. These high-coordinate species, reaching up to coordination number 12 with the use of
chelating ligands such as in La
2(SO
4)
3·9H
2O, often have a low degree of symmetry because of stereo-chemical factors.
Lanthanum chemistry tends not to involve π bonding due to the electron configuration of the element: thus its organometallic chemistry is quite limited. The best characterized organolanthanum compounds are the
cyclopentadienyl complex La(C
5H
5)
3, which is produced by reacting anhydrous LaCl
3 with NaC
5H
5 in
tetrahydrofuran
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
, and its methyl-substituted derivatives.
[Greenwood and Earnshaw, p. 1110]
History
In 1751, the Swedish mineralogist
Axel Fredrik Cronstedt
Baron Axel Fredrik Cronstedt (''/kroonstet/'' 23 December 1722 – 19 August 1765) was a Swedish mineralogist and chemist who discovered the element nickel in 1751 as a mining expert with the Bureau of Mines.
Cronstedt is considered a founder ...
discovered a heavy mineral from the mine at
Bastnäs, later named
cerite. Thirty years later, the fifteen-year-old
Wilhelm Hisinger
Wilhelm Hisinger (23 December 1766 – 28 June 1852) was a Swedish physicist and chemist who in 1807, working in coordination with Jöns Jakob Berzelius, noted that in electrolysis any given substance always went to the same pole, and that substan ...
, from the family owning the mine, sent a sample of it to
Carl Scheele
Carl Wilhelm Scheele (, ; 9 December 1742 – 21 May 1786) was a Swedish German pharmaceutical chemist.
Scheele discovered oxygen (although Joseph Priestley published his findings first), and identified molybdenum, tungsten, barium, hydro ...
, who did not find any new elements within. In 1803, after Hisinger had become an ironmaster, he returned to the mineral with
Jöns Jacob Berzelius and isolated a new oxide which they named ''ceria'' after the
dwarf planet
A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun, smaller than any of the eight classical planets but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of dwarf planets to ...
Ceres, which had been discovered two years earlier. Ceria was simultaneously independently isolated in Germany by
Martin Heinrich Klaproth
Martin Heinrich Klaproth (1 December 1743 – 1 January 1817) was a German chemist. He trained and worked for much of his life as an apothecary, moving in later life to the university. His shop became the second-largest apothecary in Berlin, and ...
.
[Greenwood and Earnshaw, p. 1424] Between 1839 and 1843, ceria was shown to be a mixture of oxides by the Swedish surgeon and chemist
Carl Gustaf Mosander
Carl Gustaf Mosander (10 September 1797 – 15 October 1858) was a Swedish chemist. He discovered the rare earth elements lanthanum, erbium and terbium.
Early life and education
Born in Kalmar, Mosander attended school there until he moved ...
, who lived in the same house as Berzelius and studied under him: he separated out two other oxides which he named ''lanthana'' and ''
didymia''.
He partially decomposed a sample of
cerium nitrate
Cerium nitrate refers to a family of nitrates of cerium in the +3 or +4 oxidation state. Often these compounds contain water, hydroxide, or hydronium ions in addition to cerium and nitrate. Double nitrates of cerium also exist.
Cerium(III) nitrat ...
by roasting it in air and then treating the resulting oxide with dilute
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
. That same year,
Axel Erdmann, a student also at the Karolinska Institute, discovered lanthanum in a new mineral from Låven island located in a Norwegian fjord.
Finally, Mosander explained his delay, saying that he had extracted a second element from cerium, and this he called didymium. Although he didn't realise it, didymium too was a mixture, and in 1885 it was separated into praseodymium and neodymium.
Since lanthanum's properties differed only slightly from those of cerium, and occurred along with it in its salts, he named it from the
Ancient Greek
Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...
''λανθάνειν''
anthanein(lit. ''to lie hidden'').
Relatively pure lanthanum metal was first isolated in 1923.
Occurrence and production
Lanthanum is the third-most abundant of all the lanthanides, making up 39 mg/kg of the Earth's crust, behind
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishe ...
at 41.5 mg/kg and cerium at 66.5 mg/kg. It is almost three times as abundant as
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
in the Earth's crust. Despite being among the so-called "rare earth metals", lanthanum is thus not rare at all, but it is historically so named because it is rarer than "common earths" such as lime and magnesia, and historically only a few deposits were known. Lanthanum is considered a rare earth metal because the process to mine it is difficult, time-consuming, and expensive.
Lanthanum is rarely the dominant lanthanide found in the rare earth minerals, and in their chemical formulae it is usually preceded by cerium. Rare examples of La-dominant minerals are monazite-(La) and lanthanite-(La).
The La
3+ ion is similarly sized to the early lanthanides of the cerium group (those up to
samarium
Samarium is a chemical element with symbol Sm and atomic number 62. It is a moderately hard silvery metal that slowly oxidizes in air. Being a typical member of the lanthanide series, samarium usually has the oxidation state +3. Compounds of samar ...
and
europium) that immediately follow in the periodic table, and hence it tends to occur along with them in
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
,
silicate and
carbonate
A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word ''carbonate'' may also refer to a carbonate ester, an organic compound containing the carbonate ...
minerals, such as
monazite
Monazite is a primarily reddish-brown phosphate mineral that contains rare-earth elements. Due to variability in composition, monazite is considered a group of minerals. The most common species of the group is monazite-(Ce), that is, the ceriu ...
(M
IIIPO
4) and
bastnäsite
The mineral bastnäsite (or bastnaesite) is one of a family of three carbonate-fluoride minerals, which includes bastnäsite-( Ce) with a formula of (Ce, La)CO3F, bastnäsite-( La) with a formula of (La, Ce)CO3F, and bastnäsite-( Y) with a formul ...
(M
IIICO
3F), where M refers to all the rare earth metals except scandium and the radioactive
promethium (mostly Ce, La, and Y).
[Greenwood and Earnshaw, p. 1103] Bastnäsite is usually lacking in
thorium
Thorium is a weakly radioactive metallic chemical element with the symbol Th and atomic number 90. Thorium is silvery and tarnishes black when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high ...
and the heavy lanthanides, and the purification of the light lanthanides from it is less involved. The ore, after being crushed and ground, is first treated with hot concentrated sulfuric acid, evolving carbon dioxide,
hydrogen fluoride, and
silicon tetrafluoride
Silicon tetrafluoride or tetrafluorosilane is a chemical compound with the formula Si F4. This colorless gas is notable for having a narrow liquid range: its boiling point is only 4 °C above its melting point. It was first prepared in 1771 ...
: the product is then dried and leached with water, leaving the early lanthanide ions, including lanthanum, in solution.
[Greenwood and Earnshaw, p. 1426–9]
The procedure for monazite, which usually contains all the rare earths as well as thorium, is more involved. Monazite, because of its magnetic properties, can be separated by repeated electromagnetic separation. After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths. The acidic filtrates are partially neutralized with
sodium hydroxide to pH 3–4. Thorium precipitates out of solution as hydroxide and is removed. After that, the solution is treated with
ammonium oxalate to convert rare earths to their insoluble
oxalate
Oxalate (IUPAC: ethanedioate) is an anion with the formula C2O42−. This dianion is colorless. It occurs naturally, including in some foods. It forms a variety of salts, for example sodium oxalate (Na2C2O4), and several esters such as dimethyl ...
s. The oxalates are converted to oxides by annealing. The oxides are dissolved in nitric acid that excludes one of the main components,
cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. Cerium is a soft, ductile, and silvery-white metal that tarnishes when exposed to air. Cerium is the second element in the lanthanide series, and while it often shows the +3 ...
, whose oxide is insoluble in HNO
3. Lanthanum is separated as a double salt with ammonium nitrate by crystallization. This salt is relatively less soluble than other rare earth double salts and therefore stays in the residue.
Care must be taken when handling some of the residues as they contain
228Ra, the daughter of
232Th, which is a strong gamma emitter.
Lanthanum is relatively easy to extract as it has only one neighbouring lanthanide, cerium, which can be removed by making use of its ability to be oxidised to the +4 state; thereafter, lanthanum may be separated out by the historical method of
fractional crystallization of La(NO
3)
3·2NH
4NO
3·4H
2O, or by
ion-exchange techniques when higher purity is desired.
Lanthanum metal is obtained from its oxide by heating it with
ammonium chloride or fluoride and hydrofluoric acid at 300-400 °C to produce the chloride or fluoride:
:La
2O
3 + 6 NH
4Cl → 2 LaCl
3 + 6 NH
3 + 3 H
2O
This is followed by reduction with alkali or alkaline earth metals in vacuum or argon atmosphere:
:LaCl
3 + 3 Li → La + 3 LiCl
Also, pure lanthanum can be produced by electrolysis of molten mixture of anhydrous LaCl
3 and NaCl or KCl at elevated temperatures.
Applications
The first historical application of lanthanum was in gas lantern
mantles.
Carl Auer von Welsbach
Carl Auer von Welsbach (1 September 1858 – 4 August 1929), who received the Austrian noble title of Freiherr Auer von Welsbach in 1901, was an Austrian scientist and inventor, who separated didymium into the elements neodymium and praseo ...
used a mixture of
lanthanum oxide
Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock ...
and
zirconium oxide
Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant stabi ...
, which he called ''Actinophor'' and patented in 1886. The original mantles gave a green-tinted light and were not very successful, and his first company, which established a factory in
Atzgersdorf
Atzgersdorf (; Central Bavarian: ''Atzgasduaf'') is a former municipality in Lower Austria that is now a part of the 23rd Viennese district Liesing. A small part of the former municipality today is part of the 12th Viennese district Meidling.
...
in 1887, failed in 1889.
Modern uses of lanthanum include:
* One material used for anodic material of
nickel-metal hydride batteries is . Due to high cost to extract the other lanthanides, a
mischmetal
Mischmetal (from german: Mischmetall – "mixed metal") is an alloy of rare-earth elements. It is also called cerium mischmetal, or rare-earth mischmetal. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15 ...
with more than 50% of lanthanum is used instead of pure lanthanum. The compound is an
intermetallic
An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic eleme ...
component of the type.
NiMH NIMH may refer to:
*Nickel–metal hydride battery (NiMH), a type of electrical battery
*National Institute of Mental Health, an agency of the United States government
*National Institute of Medical Herbalists, a professional organisation in the Un ...
batteries can be found in many models of the
Toyota Prius
The is a car built by Toyota which has a hybrid drivetrain, combining an internal combustion engine with an electric motor. Initially offered as a four-door sedan, it has been produced only as a five-door liftback since 2003.
In 2007, ...
sold in the US. These larger nickel-metal hydride batteries require massive quantities of lanthanum for the production. The 2008
Toyota Prius
The is a car built by Toyota which has a hybrid drivetrain, combining an internal combustion engine with an electric motor. Initially offered as a four-door sedan, it has been produced only as a five-door liftback since 2003.
In 2007, ...
NiMH NIMH may refer to:
*Nickel–metal hydride battery (NiMH), a type of electrical battery
*National Institute of Mental Health, an agency of the United States government
*National Institute of Medical Herbalists, a professional organisation in the Un ...
battery requires of lanthanum. As engineers push the technology to increase fuel efficiency, twice that amount of lanthanum could be required per vehicle.
* Hydrogen sponge alloys can contain lanthanum. These alloys are capable of storing up to 400 times their own volume of hydrogen gas in a reversible adsorption process. Heat energy is released every time they do so; therefore these alloys have possibilities in energy conservation systems.
*
Mischmetal
Mischmetal (from german: Mischmetall – "mixed metal") is an alloy of rare-earth elements. It is also called cerium mischmetal, or rare-earth mischmetal. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15 ...
, a
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolit ...
alloy used in lighter flints, contains 25% to 45% lanthanum.
*
Lanthanum oxide
Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedstock ...
and the
boride A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some bo ...
are used in electronic
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
The type known as ...
s as
hot cathode
In vacuum tubes and gas-filled tubes, a hot cathode or thermionic cathode is a cathode electrode which is heated to make it emit electrons due to thermionic emission. This is in contrast to a cold cathode, which does not have a heating elemen ...
materials with strong emissivity of
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no ...
s. Crystals of are used in high-brightness, extended-life, thermionic electron emission sources for
electron microscope
An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
s and
Hall-effect thruster
In spacecraft propulsion, a Hall-effect thruster (HET) is a type of ion thruster in which the propellant is accelerated by an electric field. Hall-effect thrusters (based on the discovery by Edwin Hall) are sometimes referred to as Hall thruste ...
s.
*
Lanthanum trifluoride
Lanthanum trifluoride is a refractory ionic compound of lanthanum and fluorine.
The LaF3 structure
Bonding is ionic with lanthanum highly coordinated. The cation sits at the center of a trigonal prism. Nine fluorine atoms are close: three a ...
() is an essential component of a heavy fluoride glass named
ZBLAN
ZBLAN is the most stable, and consequently the most used, fluoride glass, a subcategory of the heavy metal fluoride glass (HMFG) group. Typically its composition is 53% ZrF4, 20% BaF2, 4% LaF3, 3% AlF3 and 20% NaF. ZBLAN is not a single mat ...
. This glass has superior transmittance in the infrared range and is therefore used for fiber-optical communication systems.
* Cerium-doped
lanthanum bromide
Lanthanum(III) bromide (LaBr3) is an inorganic halide salt of lanthanum. When pure, it is a colorless white powder. The single crystals of LaBr3 are hexagonal crystals with melting point of 783 °C. It is highly hygroscopic and water-soluble. ...
and
lanthanum chloride are the recent inorganic
scintillators, which have a combination of high light yield, best energy resolution, and fast response. Their high yield converts into superior energy resolution; moreover, the light output is very stable and quite high over a very wide range of temperatures, making it particularly attractive for high-temperature applications. These scintillators are already widely used commercially in detectors of
neutrons or
gamma rays
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 ...
.
*
Carbon arc lamps use a mixture of rare earth elements to improve the light quality. This application, especially by the
motion picture industry for studio lighting and projection, consumed about 25% of the rare-earth compounds produced until the phase out of carbon arc lamps.
*
Lanthanum(III) oxide
Lanthanum(III) oxide, also known as lanthana, chemical formula , is an inorganic compound containing the rare earth element lanthanum and oxygen. It is used in some ferroelectric materials, as a component of optical materials, and is a feedsto ...
() improves the alkali resistance of
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 ( quenching ...
and is used in making special optical glasses, such as infrared-absorbing glass, as well as
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 a ...
and
telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observ ...
lenses, because of the 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, or ...
and low dispersion of rare-earth glasses.
Lanthanum oxide is also used as a grain-growth additive during the liquid-phase
sintering
Clinker nodules produced by sintering
Sintering or frittage is the process of compacting and forming a solid mass of material by pressure or heat without melting it to the point of liquefaction.
Sintering happens as part of a manufacturing ...
of
silicon nitride
Silicon nitride is a chemical compound of the elements silicon and nitrogen. is the most thermodynamically stable and commercially important of the silicon nitrides, and the term "silicon nitride" commonly refers to this specific composition. It ...
and
zirconium diboride
Zirconium diboride (ZrB2) is a highly covalent refractory ceramic material with a hexagonal crystal structure. ZrB2 is an ultra high temperature ceramic (UHTC) with a melting point of 3246 °C. This along with its relatively low density of ...
.
* Small amounts of lanthanum added to
steel improves its
malleability, resistance to impact, and
ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile str ...
, whereas addition of lanthanum to
molybdenum decreases its hardness and sensitivity to temperature variations.
* Small amounts of lanthanum are present in many pool products to remove the phosphates that feed algae.
* Lanthanum oxide additive to tungsten is used in
gas tungsten arc welding
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is an arc welding process that uses a non-consumable tungsten electrode to produce the weld. The weld area and electrode are protected from oxidation or other atm ...
electrodes, as a substitute for
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
thorium.
* Various compounds of lanthanum and other rare-earth elements (oxides, chlorides, etc.) are components of various catalysis, such as
petroleum cracking
In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic compound, organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, b ...
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
s.
* Lanthanum-barium
radiometric dating
Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...
is used to estimate age of rocks and ores, though the technique has limited popularity.
*
Lanthanum carbonate
Lanthanum carbonate, La( C O3)3, is the salt formed by lanthanum(III) cations and carbonate anions. It is an ore of lanthanum metal (bastnäsite), along with monazite.
Chemistry
Lanthanum carbonate is used as a starting material in lanthanum c ...
was approved as a medication (Fosrenol,
Shire Pharmaceuticals) to absorb excess
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
in cases of
hyperphosphatemia
Hyperphosphatemia is an electrolyte disorder in which there is an elevated level of phosphate in the blood. Most people have no symptoms while others develop calcium deposits in the soft tissue. Often there is also low calcium levels which can ...
seen in
end-stage kidney disease
Chronic kidney disease (CKD) is a type of kidney disease in which a gradual loss of kidney function occurs over a period of months to years. Initially generally no symptoms are seen, but later symptoms may include leg swelling, feeling tired, vo ...
.
* Lanthanum fluoride is used in phosphor lamp coatings. Mixed with europium fluoride, it is also applied in the crystal membrane of
fluoride ion-selective electrodes.
* Like
horseradish peroxidase, lanthanum is used as an electron-dense tracer in
molecular biology
Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and physi ...
.
* Lanthanum-modified bentonite (or
phoslock) is used to remove phosphates from water in lake treatments.
* Lanthanum telluride (La
3Te
4) is considered to be applied in the field of radioisotope power system (nuclear power plant) due to its significant conversion capabilities. The transmuted elements and isotopes in the segment will not react with the material itself, thus presenting no harm to the safety of the power plant. Though iodine, which can be generated during transmutation, is suspected to react with La
3Te
4 segment, the quantity of iodine is small enough to possess threat to the power system.
Biological role
Lanthanum has no known biological role in humans. The element is very poorly absorbed after oral administration and when injected its elimination is very slow.
Lanthanum carbonate
Lanthanum carbonate, La( C O3)3, is the salt formed by lanthanum(III) cations and carbonate anions. It is an ore of lanthanum metal (bastnäsite), along with monazite.
Chemistry
Lanthanum carbonate is used as a starting material in lanthanum c ...
(Fosrenol) was approved as a
phosphate binder Phosphate binders are medications used to reduce the absorption of dietary phosphate; they are taken along with meals and snacks. They are frequently used in people with chronic kidney failure (CKF), who are less able to excrete phosphate, resulting ...
to absorb excess phosphate in cases of
end stage renal disease.
While lanthanum has pharmacological effects on several receptors and ion channels, its specificity for the
GABA receptor is unique among trivalent cations. Lanthanum acts at the same modulatory site on the
GABA receptor as
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, a known negative
allosteric modulator. The lanthanum cation La
3+ is a positive allosteric modulator at native and recombinant GABA receptors, increasing open channel time and decreasing desensitization in a subunit configuration dependent manner.
Lanthanum is an essential cofactor for the methanol dehydrogenase of the
methanotrophic bacterium ''
Methylacidiphilum fumariolicum'' SolV, although the great chemical similarity of the lanthanides means that it may be substituted with cerium, praseodymium, or neodymium without ill effects, and with the smaller samarium, europium, or gadolinium giving no side effects other than slower growth.
Precautions
Lanthanum has a low to moderate level of toxicity and should be handled with care. The injection of lanthanum solutions produces
hyperglycemia, low blood pressure, degeneration of the
spleen
The spleen is an organ found in almost all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes . and
hepatic alterations. The application in carbon arc light led to the exposure of people to rare earth element oxides and fluorides, which sometimes led to
pneumoconiosis. As the La
3+ ion is similar in size to the Ca
2+ ion, it is sometimes used as an easily traced substitute for the latter in medical studies.
Lanthanum, like the other lanthanides, is known to affect human metabolism, lowering cholesterol levels, blood pressure, appetite, and risk of blood coagulation. When injected into the brain, it acts as a painkiller, similarly to
morphine
Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
and other opiates, though the mechanism behind this is still unknown.
Prices
The price for a (metric) ton
000 kgof ''Lanthanum oxide 99% (FOB China in USD/Mt)'' is given by the Institute of Rare Earths Elements and Strategic Metals as below $2,000 for most of the period from early 2001 to September 2010 (at $10,000 in the short term in 2008); it rose steeply to $140,000 in mid-2011 and fell back just as rapidly to $38,000 by early 2012. The average price for the last six months (April to September 2022) is given by the Institute as follows: ''Lanthanum Oxide - 99.9%min FOB China - 1308 EUR/mt'' and for ''Lanthanum Metal - 99%min FOB China - 3706 EUR/mt''.
[Information and notation: .access-date=27 October 2022.]
See also
, CASNo_Ref =
, CASNo = 7439-91-0
, UNII_Ref =
, UNII = 6I3K30563S
References
Bibliography
*
Further reading
* ''The Industrial Chemistry of the Lanthanons, Yttrium, Thorium and Uranium'', by R. J. Callow, Pergamon Press, 1967
* ''Extractive Metallurgy of Rare Earths'', by C. K. Gupta and N. Krishnamurthy, CRC Press, 2005
* ''Nouveau Traite de Chimie Minerale, Vol. VII. Scandium, Yttrium, Elements des Terres Rares, Actinium'', P. Pascal, Editor, Masson & Cie, 1959
* ''Chemistry of the Lanthanons'', by R. C. Vickery, Butterworths 1953
{{Good article
Chemical elements
Chemical elements with double hexagonal close-packed structure
Lanthanides
Reducing agents
GABAA receptor positive allosteric modulators