Lutetium is a chemical element with 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 among
the rare earths.
Lutetium is sometimes considered the first
element of the 6th-period transition metals,
although lanthanum is more often considered
as such.
Lutetium was independently discovered in 1907
by French scientist Georges Urbain, Austrian
mineralogist Baron Carl Auer von Welsbach,
and American chemist Charles James.
All of these researchers found lutetium as
an impurity in the mineral ytterbia, which
was previously thought to consist entirely
of ytterbium.
The dispute on the priority of the discovery
occurred shortly after, with Urbain and Welsbach
accusing each other of publishing results
influenced by the published research of the
other; the naming honor went to Urbain, as
he had published his results earlier.
He chose the name lutecium for the new element,
but in 1949 the spelling of element 71 was
changed to lutetium.
In 1909, the priority was finally granted
to Urbain and his names were adopted as official
ones; however, the name cassiopeium (or later
cassiopium) for element 71 proposed by Welsbach
was used by many German scientists until the
1950s.
Lutetium is not a particularly abundant element,
although it is significantly more common than
silver in the earth's crust.
It has few specific uses.
Lutetium-176 is a relatively abundant (2.5%)
radioactive isotope with a half-life of about
38 billion years, used to determine the age
of minerals and meteorites.
Lutetium usually occurs in association with
the element yttrium and is sometimes used
in metal alloys and as a catalyst in various
chemical reactions.
177Lu-DOTA-TATE is used for radionuclide therapy
(see Nuclear medicine) on neuroendocrine tumours.
Lutetium has the highest Brinell hardness
of any lanthanide, at 890–1300 MPa.
== Characteristics ==
=== 
Physical properties ===
A lutetium atom has 71 electrons, arranged
in the configuration [Xe] 4f145d16s2.
When entering a chemical reaction, the atom
loses its two outermost electrons and the
single 5d-electron.
The lutetium atom is the smallest among the
lanthanide atoms, due to the lanthanide contraction,
and as a result lutetium has the highest density,
melting point, and hardness of the lanthanides.
=== Chemical properties and compounds ===
Lutetium's compounds always contain the element
in the oxidation state +3.
Aqueous solutions of most lutetium salts are
colorless and form white crystalline solids
upon drying, with the common exception of
the iodide.
The soluble salts, such as nitrate, sulfate
and acetate form hydrates upon crystallization.
The oxide, hydroxide, fluoride, carbonate,
phosphate and oxalate are insoluble in water.Lutetium
metal is slightly unstable in air at standard
conditions, but it burns readily at 150 °C
to form lutetium oxide.
The resulting compound is known to absorb
water and carbon dioxide, and may be used
to remove vapors of these compounds from closed
atmospheres.
Similar observations are made during reaction
between lutetium and water (slow when cold
and fast when hot); lutetium hydroxide is
formed in the reaction.
Lutetium metal is known to react with the
four lightest halogens to form trihalides;
all of them (except the fluoride) are soluble
in water.
Lutetium dissolves readily in weak acids and
dilute sulfuric acid to form solutions containing
the colorless lutetium ions, which are coordinated
by between seven and nine water molecules,
the average being [Lu(H2O)8.2]3+.
2 Lu + 3 H2SO4 → 2 Lu3+ + 3 SO2–4 + 3
H2↑
=== Isotopes ===
Lutetium occurs on the Earth in form of two
isotopes: lutetium-175 and lutetium-176.
Out of these two, only the former is stable,
making the element monoisotopic.
The latter one, lutetium-176, decays via beta
decay with a half-life of 3.78×1010 years;
it makes up about 2.5% of natural lutetium.
To date, 32 synthetic radioisotopes of the
element have been characterized, ranging in
mass from 149.973 (lutetium-150) to 183.961
(lutetium-184); the most stable such isotopes
are lutetium-174 with a half-life of 3.31
years, and lutetium-173 with a half-life of
1.37 years.
All of the remaining radioactive isotopes
have half-lives that are less than 9 days,
and the majority of these have half-lives
that are less than half an hour.
Isotopes lighter than the stable lutetium-175
decay via electron capture (to produce isotopes
of ytterbium), with some alpha and positron
emission; the heavier isotopes decay primarily
via beta decay, producing hafnium isotopes.The
element also has 42 nuclear isomers, with
masses of 150, 151, 153–162, 166–180 (not
every mass number corresponds to only one
isomer).
The most stable of them are lutetium-177m,
with half-life of 160.4 days and lutetium-174m,
with half-life of 142 days; this is longer
than half-lives of the ground states of all
radioactive lutetium isotopes, except only
for lutetium-173, 174, and 176.
== History ==
Lutetium, derived from the Latin Lutetia (Paris),
was independently discovered in 1907 by French
scientist Georges Urbain, Austrian mineralogist
Baron Carl Auer von Welsbach, and American
chemist Charles James.
They found it as an impurity in ytterbia,
which was thought by Swiss chemist Jean Charles
Galissard de Marignac to consist entirely
of ytterbium.
The scientists proposed different names for
the elements: Urbain chose neoytterbium and
lutecium, whereas Welsbach chose aldebaranium
and cassiopeium (after Aldebaran and Cassiopeia).
Both of these articles accused the other man
of publishing results based on those of the
author.
The International Commission on Atomic Weights,
which was then responsible for the attribution
of new element names, settled the dispute
in 1909 by granting priority to Urbain and
adopting his names as official ones, based
on the fact that the separation of lutetium
from Marignac's ytterbium was first described
by Urbain; after Urbain's names were recognized,
neoytterbium was reverted to ytterbium.
Until the 1950s, some German-speaking chemists
called lutetium by Welsbach's name, cassiopeium;
in 1949, the spelling of element 71 was changed
to lutetium.
The reason for this was that Welsbach's 1907
samples of lutetium had been pure, while Urbain's
1907 samples only contained traces of lutetium.
This later misled Urbain into thinking that
he had discovered element 72, which he named
celtium, which was actually very pure lutetium.
The later discrediting of Urbain's work on
element 72 led to a reappraisal of Welsbach's
work on element 71, so that the element was
renamed to cassiopeium in German-speaking
countries for some time.
Charles James, who stayed out of the priority
argument, worked on a much larger scale and
possessed the largest supply of lutetium at
the time.
Pure lutetium metal was first produced in
1953.
== Occurrence and production ==
Found with almost all other rare-earth metals
but never by itself, lutetium is very difficult
to separate from other elements.
Its principal commercial source is as a by-product
from the processing of the rare earth phosphate
mineral monazite (Ce,La,...)PO4, which has
concentrations of only 0.0001% of the element,
not much higher than the abundance of lutetium
in the Earth crust of about 0.5 mg/kg.
No lutetium-dominant minerals are currently
known.
The main mining areas are China, United States,
Brazil, India, Sri Lanka and Australia.
The world production of lutetium (in the form
of oxide) is about 10 tonnes per year.
Pure lutetium metal is very difficult to prepare.
It is one of the rarest and most expensive
of the rare earth metals with the price about
US$10,000 per kilogram, or about one-fourth
that of gold.Crushed minerals are treated
with hot concentrated sulfuric acid to produce
water-soluble sulfates of rare earths.
Thorium precipitates out of solution as hydroxide
and is removed.
After that the solution is treated with ammonium
oxalate to convert rare earths into their
insoluble oxalates.
The oxalates are converted to oxides by annealing.
The oxides are dissolved in nitric acid that
excludes one of the main components, cerium,
whose oxide is insoluble in HNO3.
Several rare earth metals, including lutetium,
are separated as a double salt with ammonium
nitrate by crystallization.
Lutetium is separated by ion exchange.
In this process, rare-earth ions are sorbed
onto suitable ion-exchange resin by exchange
with hydrogen, ammonium or cupric ions present
in the resin.
Lutetium salts are then selectively washed
out by suitable complexing agent.
Lutetium metal is then obtained by reduction
of anhydrous LuCl3 or LuF3 by either an alkali
metal or alkaline earth metal.
2 LuCl3 + 3 Ca → 2 Lu + 3 CaCl2
== Applications ==
Because of production difficulty and high
price, lutetium has very few commercial uses,
especially since it is rarer than most of
the other lanthanides but is chemically not
very different.
However, stable lutetium can be used as catalysts
in petroleum cracking in refineries and can
also be used in alkylation, hydrogenation,
and polymerization applications.Lutetium aluminium
garnet (Al5Lu3O12) has been proposed for use
as a lens material in high refractive index
immersion lithography.
Additionally, a tiny amount of lutetium is
added as a dopant to gadolinium gallium garnet
(GGG), which is used in magnetic bubble memory
devices.
Cerium-doped lutetium oxyorthosilicate (LSO)
is currently the preferred compound for detectors
in positron emission tomography (PET).
Lutetium aluminium garnet (LuAG) is used as
a phosphor in LED light bulbs.Aside from stable
lutetium, its radioactive isotopes have several
specific uses.
The suitable half-life and decay mode made
lutetium-176 used as a pure beta emitter,
using lutetium which has been exposed to neutron
activation, and in lutetium–hafnium dating
to date meteorites.
The synthetic isotope lutetium-177 bound to
octreotate (a somatostatin analogue), is used
experimentally in targeted radionuclide therapy
for neuroendocrine tumors.
Indeed, lutetium-177 is seeing increasing
use as a radionuclide, in neuroendrocine tumor
therapy and bone pain palliation.
Research indicates that lutetium-ion atomic
clocks could provide greater accuracy than
any existing atomic clock.Lutetium tantalate
(LuTaO4) is the densest known stable white
material (density 9.81 g/cm3) and therefore
is an ideal host for X-ray phosphors.
The only denser white material is thorium
dioxide, with density of 10 g/cm3, but the
thorium it contains is radioactive.
== Precautions ==
Like other rare-earth metals, lutetium is
regarded as having a low degree of toxicity,
but its compounds should be handled with care
nonetheless: for example, lutetium fluoride
inhalation is dangerous and the compound irritates
skin.
Lutetium nitrate may be dangerous as it may
explode and burn once heated.
Lutetium oxide powder is toxic as well if
inhaled or ingested.Similarly to the other
rare-earth metals, lutetium has no known biological
role, but it is found even in humans, concentrating
in bones, and to a lesser extent in the liver
and kidneys.
Lutetium salts are known to occur together
with other lanthanide salts in nature; the
element is the least abundant in the human
body of all lanthanides.
Human diets have not been monitored for lutetium
content, so it is not known how much the average
human takes in, but estimations show the amount
is only about several micrograms per year,
all coming from tiny amounts taken by plants.
Soluble lutetium salts are mildly toxic, but
insoluble ones are not.
== See also
