Antimony is a chemical element with symbol
Sb (from Latin: stibium) and atomic number
51.
A lustrous gray metalloid, it is found in
nature mainly as the sulfide mineral stibnite
(Sb2S3).
Antimony compounds have been known since ancient
times and were powdered for use as medicine
and cosmetics, often known by the Arabic name,
kohl.
Metallic antimony was also known, but it was
erroneously identified as lead upon its discovery.
The earliest known description of the metal
in the West was written in 1540 by Vannoccio
Biringuccio.
For some time, China has been the largest
producer of antimony and its compounds, with
most production coming from the Xikuangshan
Mine in Hunan.
The industrial methods for refining antimony
are roasting and reduction with carbon or
direct reduction of stibnite with iron.
The largest applications for metallic antimony
is an alloy with lead and tin and the lead
antimony plates in lead–acid batteries.
Alloys of lead and tin with antimony have
improved properties for solders, bullets,
and plain bearings.
Antimony compounds are prominent additives
for chlorine and bromine-containing fire retardants
found in many commercial and domestic products.
An emerging application is the use of antimony
in microelectronics.
== Characteristics ==
=== 
Properties ===
Antimony is a member of group 15 of the periodic
table, one of the elements called pnictogens,
and has an electronegativity of 2.05.
In accordance with periodic trends, it is
more electronegative than tin or bismuth,
and less electronegative than tellurium or
arsenic.
Antimony is stable in air at room temperature,
but reacts with oxygen if heated to produce
antimony trioxide, Sb2O3.Antimony is a silvery,
lustrous gray metalloid with a Mohs scale
hardness of 3, which is too soft to make hard
objects; coins of antimony were issued in
China's Guizhou province in 1931 but the durability
was poor and the minting was soon discontinued.
Antimony is resistant to attack by acids.
Four allotropes of antimony are known: a stable
metallic form and three metastable forms (explosive,
black and yellow).
Elemental antimony is a brittle, silver-white
shiny metalloid.
When slowly cooled, molten antimony crystallizes
in a trigonal cell, isomorphic with the gray
allotrope of arsenic.
A rare explosive form of antimony can be formed
from the electrolysis of antimony trichloride.
When scratched with a sharp implement, an
exothermic reaction occurs and white fumes
are given off as metallic antimony forms;
when rubbed with a pestle in a mortar, a strong
detonation occurs.
Black antimony is formed upon rapid cooling
of antimony vapor.
It has the same crystal structure as red phosphorus
and black arsenic, it oxidizes in air and
may ignite spontaneously.
At 100 °C, it gradually transforms into the
stable form.
The yellow allotrope of antimony is the most
unstable.
It has only been generated by oxidation of
stibine (SbH3) at −90 °C. Above this temperature
and in ambient light, this metastable allotrope
transforms into the more stable black allotrope.Elemental
antimony adopts a layered structure (space
group R3m No. 166) in which layers consist
of fused, ruffled, six-membered rings.
The nearest and next-nearest neighbors form
an irregular octahedral complex, with the
three atoms in each double layer slightly
closer than the three atoms in the next.
This relatively close packing leads to a high
density of 6.697 g/cm3, but the weak bonding
between the layers leads to the low hardness
and brittleness of antimony.
=== Isotopes ===
Antimony has two stable isotopes: 121Sb with
a natural abundance of 57.36% and 123Sb with
a natural abundance of 42.64%.
It also has 35 radioisotopes, of which the
longest-lived is 125Sb with a half-life of
2.75 years.
In addition, 29 metastable states have been
characterized.
The most stable of these is 120m1Sb with a
half-life of 5.76 days.
Isotopes that are lighter than the stable
123Sb tend to decay by β+ decay, and those
that are heavier tend to decay by β− decay,
with some exceptions.
=== Occurrence ===
The abundance of antimony in the Earth's crust
is estimated to be 0.2 to 0.5 parts per million,
comparable to thallium at 0.5 parts per million
and silver at 0.07 ppm.
Even though this element is not abundant,
it is found in more than 100 mineral species.
Antimony is sometimes found natively (e.g.
on Antimony Peak), but more frequently it
is found in the sulfide stibnite (Sb2S3) which
is the predominant ore mineral.
== Compounds ==
Antimony compounds are often classified according
to their oxidation state: Sb(III) and Sb(V).
The +5 oxidation state is more stable.
=== Oxides and hydroxides ===
Antimony trioxide is formed when antimony
is burnt in air.
In the gas phase, the molecule of the compound
is Sb4O6, but it polymerizes upon condensing.
Antimony pentoxide (Sb4O5) can be formed only
by oxidation with concentrated nitric acid.
Antimony also forms a mixed-valence oxide,
antimony tetroxide (Sb2O4), which features
both Sb(III) and Sb(V).
Unlike oxides of phosphorus and arsenic, these
oxides are amphoteric, do not form well-defined
oxoacids, and react with acids to form antimony
salts.
Antimonous acid Sb(OH)3 is unknown, but the
conjugate base sodium antimonite ([Na3SbO3]4)
forms upon fusing sodium oxide and Sb4O6.
Transition metal antimonites are also known.
Antimonic acid exists only as the hydrate
HSb(OH)6, forming salts as the antimonate
anion Sb(OH)−6.
When a solution containing this anion is dehydrated,
the precipitate contains mixed oxides.Many
antimony ores are sulfides, including stibnite
(Sb2S3), pyrargyrite (Ag3SbS3), zinkenite,
jamesonite, and boulangerite.
Antimony pentasulfide is non-stoichiometric
and features antimony in the +3 oxidation
state and S-S bonds.
Several thioantimonides are known, such as
[Sb6S10]2− and [Sb8S13]2−.
=== Halides ===
Antimony forms two series of halides: SbX3
and SbX5.
The trihalides SbF3, SbCl3, SbBr3, and SbI3
are all molecular compounds having trigonal
pyramidal molecular geometry.
The trifluoride SbF3 is prepared by the reaction
of Sb2O3 with HF:
Sb2O3 + 6 HF → 2 SbF3 + 3 H2OIt is Lewis
acidic and readily accepts fluoride ions to
form the complex anions SbF−4 and SbF2−5.
Molten SbF3 is a weak electrical conductor.
The trichloride SbCl3 is prepared by dissolving
Sb2S3 in hydrochloric acid:
Sb2S3 + 6 HCl → 2 SbCl3 + 3 H2S
The pentahalides SbF5 and SbCl5 have trigonal
bipyramidal molecular geometry in the gas
phase, but in the liquid phase, SbF5 is polymeric,
whereas SbCl5 is monomeric.
SbF5 is a powerful Lewis acid used to make
the superacid fluoroantimonic acid ("H2SbF7").
Oxyhalides are more common for antimony than
for arsenic and phosphorus.
Antimony trioxide dissolves in concentrated
acid to form oxoantimonyl compounds such as
SbOCl and (SbO)2SO4.
=== Antimonides, hydrides, and organoantimony
compounds ===
Compounds in this class generally are described
as derivatives of Sb3−.
Antimony forms antimonides with metals, such
as indium antimonide (InSb) and silver antimonide
(Ag3Sb).
The alkali metal and zinc antimonides, such
as Na3Sb and Zn3Sb2, are more reactive.
Treating these antimonides with acid produces
the highly unstable gas stibine, SbH3:
Sb3− + 3 H+ → SbH3Stibine can also be
produced by treating Sb3+ salts with hydride
reagents such as sodium borohydride.
Stibine decomposes spontaneously at room temperature.
Because stibine has a positive heat of formation,
it is thermodynamically unstable and thus
antimony does not react with hydrogen directly.Organoantimony
compounds are typically prepared by alkylation
of antimony halides with Grignard reagents.
A large variety of compounds are known with
both Sb(III) and Sb(V) centers, including
mixed chloro-organic derivatives, anions,
and cations.
Examples include Sb(C6H5)3 (triphenylstibine),
Sb2(C6H5)4 (with an Sb-Sb bond), and cyclic
[Sb(C6H5)]n.
Pentacoordinated organoantimony compounds
are common, examples being Sb(C6H5)5 and several
related halides.
== History ==
Antimony(III) sulfide, Sb2S3, was recognized
in predynastic Egypt as an eye cosmetic (kohl)
as early as about 3100 BC, when the cosmetic
palette was invented.An artifact, said to
be part of a vase, made of antimony dating
to about 3000 BC was found at Telloh, Chaldea
(part of present-day Iraq), and a copper object
plated with antimony dating between 2500 BC
and 2200 BC has been found in Egypt.
Austen, at a lecture by Herbert Gladstone
in 1892 commented that "we only know of antimony
at the present day as a highly brittle and
crystalline metal, which could hardly be fashioned
into a useful vase, and therefore this remarkable
'find' (artifact mentioned above) must represent
the lost art of rendering antimony malleable."Moorey
was unconvinced the artifact was indeed a
vase, mentioning that Selimkhanov, after his
analysis of the Tello object (published in
1975), "attempted to relate the metal to Transcaucasian
natural antimony" (i.e. native metal) and
that "the antimony objects from Transcaucasia
are all small personal ornaments."
This weakens the evidence for a lost art "of
rendering antimony malleable."The Roman scholar
Pliny the Elder described several ways of
preparing antimony sulfide for medical purposes
in his treatise Natural History.
Pliny the Elder also made a distinction between
"male" and "female" forms of antimony; the
male form is probably the sulfide, while the
female form, which is superior, heavier, and
less friable, has been suspected to be native
metallic antimony.The Roman naturalist Pedanius
Dioscorides mentioned that antimony sulfide
could be roasted by heating by a current of
air.
It is thought that this produced metallic
antimony.
The first description of a procedure for isolating
antimony is in the 1540 book De la pirotechnia
by Vannoccio Biringuccio, predating the more
famous 1556 book by Agricola, De re metallica.
In this context Agricola has been often incorrectly
credited with the discovery of metallic antimony.
The book Currus Triumphalis Antimonii (The
Triumphal Chariot of Antimony), describing
the preparation of metallic antimony, was
published in Germany in 1604.
It was purported to be written by a Benedictine
monk, writing under the name Basilius Valentinus
in the 15th century; if it were authentic,
which it is not, it would predate Biringuccio.The
metal antimony was known to German chemist
Andreas Libavius in 1615 who obtained it by
adding iron to a molten mixture of antimony
sulfide, salt and potassium tartrate.
This procedure produced antimony with a crystalline
or starred surface.With the advent of challenges
to phlogiston theory, it was recognized that
antimony is an element forming sulfides, oxides,
and other compounds, as do other metals.The
first natural occurrence of pure antimony
in the Earth's crust was described by the
Swedish scientist and local mine district
engineer Anton von Swab in 1783; the type-sample
was collected from the Sala Silver Mine in
the Bergslagen mining district of Sala, Västmanland,
Sweden.
=== Etymology ===
The medieval Latin form, from which the modern
languages and late Byzantine Greek take their
names for antimony, is antimonium.
The origin of this is uncertain; all suggestions
have some difficulty either of form or interpretation.
The popular etymology, from ἀντίμοναχός
anti-monachos or French antimoine, still has
adherents; this would mean "monk-killer",
and is explained by many early alchemists
being monks, and antimony being poisonous.Another
popular etymology is the hypothetical Greek
word ἀντίμόνος antimonos, "against
aloneness", explained as "not found as metal",
or "not found unalloyed".
Lippmann conjectured a hypothetical Greek
word ανθήμόνιον anthemonion, which
would mean "floret", and cites several examples
of related Greek words (but not that one)
which describe chemical or biological efflorescence.The
early uses of antimonium include the translations,
in 1050–1100, by Constantine the African
of Arabic medical treatises.
Several authorities believe antimonium is
a scribal corruption of some Arabic form;
Meyerhof derives it from ithmid; other possibilities
include athimar, the Arabic name of the metalloid,
and a hypothetical as-stimmi, derived from
or parallel to the Greek.The standard chemical
symbol for antimony (Sb) is credited to Jöns
Jakob Berzelius, who derived the abbreviation
from stibium.The ancient words for antimony
mostly have, as their chief meaning, kohl,
the sulfide of antimony.
The Egyptians called antimony mśdmt; in hieroglyphs,
the vowels are uncertain, but the Coptic form
of the word is ⲥⲧⲏⲙ (stēm).
The Greek word, στίμμι stimmi, is probably
a loan word from Arabic or from Egyptian stm
and is used by Attic tragic poets of the 5th
century BC.
Later Greeks also used στἰβι stibi,
as did Celsus and Pliny, writing in Latin,
in the first century AD.
Pliny also gives the names stimi [sic], larbaris,
alabaster, and the "very common" platyophthalmos,
"wide-eye" (from the effect of the cosmetic).
Later Latin authors adapted the word to Latin
as stibium.
The Arabic word for the substance, as opposed
to the cosmetic, can appear as إثمد ithmid,
athmoud, othmod, or uthmod.
Littré suggests the first form, which is
the earliest, derives from stimmida, an accusative
for stimmi.
== Production ==
=== 
Top producers and production volumes ===
The British Geological Survey (BGS) reported
that in 2005 China was the top producer of
antimony with approximately 84% of the world
share, followed at a distance by South Africa,
Bolivia and Tajikistan.
Xikuangshan Mine in Hunan province has the
largest deposits in China with an estimated
deposit of 2.1 million metric tons.In 2016,
according to the US Geological Survey, China
accounted for 76.9% of total antimony production,
followed in second place by Russia with 6.9%
and Tajikistan with 6.2%.
Chinese production of antimony is expected
to decline in the future as mines and smelters
are closed down by the government as part
of pollution control.
Especially due to a new environmental protection
law having gone into effect on January 2015
and revised “Emission Standards of Pollutants
for Stanum, Antimony, and Mercury” having
gone into effect, hurdles for economic production
are higher.
According to the National Bureau of Statistics
in China, by September 2015 50% of antimony
production capacity in the Hunan province
(the province with biggest antimony reserves
in China) had not been used.Reported production
of antimony in China has fallen and is unlikely
to increase in the coming years, according
to the Roskill report.
No significant antimony deposits in China
have been developed for about ten years, and
the remaining economic reserves are being
rapidly depleted.The world's largest antimony
producers, according to Roskill, are listed
below:
=== Reserves ===
According to statistics from the USGS, current
global reserves of antimony will be depleted
in 13 years.
However, the USGS expects more resources will
be found.
=== Production process ===
The extraction of antimony from ores depends
on the quality and composition of the ore.
Most antimony is mined as the sulfide; lower-grade
ores are concentrated by froth flotation,
while higher-grade ores are heated to 500–600
°C, the temperature at which stibnite melts
and separates from the gangue minerals.
Antimony can be isolated from the crude antimony
sulfide by reduction with scrap iron:
Sb2S3 + 3 Fe → 2 Sb + 3 FeSThe sulfide is
converted to an oxide; the product is then
roasted, sometimes for the purpose of vaporizing
the volatile antimony(III) oxide, which is
recovered.
This material is often used directly for the
main applications, impurities being arsenic
and sulfide.
Antimony is isolated from the oxide by a carbothermal
reduction:
2 Sb2O3 + 3 C → 4 Sb + 3 CO2The lower-grade
ores are reduced in blast furnaces while the
higher-grade ores are reduced in reverberatory
furnaces.
=== Supply risk and critical mineral rankings
===
Antimony has consistently been ranked high
in European and US risk lists concerning criticality
of the element indicating the relative risk
to the supply of chemical elements or element
groups required to maintain the current economy
and lifestyle.
With most of the antimony imported into Europe
and the US coming from China, Chinese production
is critical to supply.
As China is revising and increasing environmental
control standards, antimony production is
becoming increasingly restricted.
Additionally Chinese export quotas for antimony
have been decreasing in the past years.
These two factors increase supply risk for
both Europe and US.
==== Europe ====
According to the BGS Risk List 2015, antimony
is ranked second highest (after rare earth
elements) on the relative supply risk index.
This indicates that it has currently the second
highest supply risk for chemical elements
or element groups which are of economic value
to the British economy and lifestyle.
Furthermore, antimony was identified as one
of 20 critical raw materials for the EU in
a report published in 2014 (which revised
the initial report published in 2011).
As seen in Figure xxx antimony maintains high
supply risk relative to its economic importance.
92% of the antimony is imported from China,
which is a significantly high concentration
of production.
==== U.S.
====
Much analysis has been conducted in the U.S.
toward defining which metals should be called
strategic or critical to the nation's security.
Exact definitions do not exist, and views
as to what constitutes a strategic or critical
mineral to U.S. security diverge.In 2015,
no antimony was mined in the U.S.
The metal is imported from foreign countries.
From 2011-2014 68% of America's antimony came
from China, 14% from India, 4% from Mexico,
and 14% from other sources.
There are no government stockpiles in place
currently.
The U.S. “Subcommittee on Critical and Strategic
Mineral Supply Chains” has screened 78 mineral
resources from 1996-2008.
It found that a small subset of minerals including
antimony has fallen into the category of potentially
critical minerals consistently.
In the future, a second assessment will be
made of the found subset of minerals to identify
which should be defined of significant risk
and critical to U.S. interests.
== Applications ==
About 60% of antimony is consumed in flame
retardants, and 20% is used in alloys for
batteries, plain bearings, and solders.
=== Flame retardants ===
Antimony is mainly used in the trioxide for
flame-proofing compounds, always in combination
with halogenated flame retardants except in
halogen-containing polymers.
The flame retarding effect of antimony trioxide
is produced by the formation of halogenated
antimony compounds, which react with hydrogen
atoms, and probably also with oxygen atoms
and OH radicals, thus inhibiting fire.
Markets for these flame-retardants include
children's clothing, toys, aircraft, and automobile
seat covers.
They are also added to polyester resins in
fiberglass composites for such items as light
aircraft engine covers.
The resin will burn in the presence of an
externally generated flame, but will extinguish
when the external flame is removed.
=== Alloys ===
Antimony forms a highly useful alloy with
lead, increasing its hardness and mechanical
strength.
For most applications involving lead, varying
amounts of antimony are used as alloying metal.
In lead–acid batteries, this addition improves
plate strength and charging characteristics.
It is used in antifriction alloys (such as
Babbitt metal), in bullets and lead shot,
electrical cable sheathing, type metal (for
example, for linotype printing machines),
solder (some "lead-free" solders contain 5%
Sb), in pewter, and in hardening alloys with
low tin content in the manufacturing of organ
pipes.
=== Other applications ===
Three other applications consume nearly all
the rest of the world's supply.
One application is a stabilizer and a catalyst
for the production of polyethyleneterephthalate.
Another is a fining agent to remove microscopic
bubbles in glass, mostly for TV screens; antimony
ions interact with oxygen, suppressing the
tendency of the latter to form bubbles.
The third application is pigments.Antimony
is increasingly being used in semiconductors
as a dopant in n-type silicon wafers for diodes,
infrared detectors, and Hall-effect devices.
In the 1950s, the emitters and collectors
of n-p-n alloy junction transistors were doped
with tiny beads of a lead-antimony alloy.
Indium antimonide is used as a material for
mid-infrared detectors.Biology and medicine
have few uses for antimony.
Treatments containing antimony, known as antimonials,
are used as emetics.
Antimony compounds are used as antiprotozoan
drugs.
Potassium antimonyl tartrate, or tartar emetic,
was once used as an anti-schistosomal drug
from 1919 on.
It was subsequently replaced by praziquantel.
Antimony and its compounds are used in several
veterinary preparations, such as anthiomaline
and lithium antimony thiomalate, as a skin
conditioner in ruminants.
Antimony has a nourishing or conditioning
effect on keratinized tissues in animals.
Antimony-based drugs, such as meglumine antimoniate,
are also considered the drugs of choice for
treatment of leishmaniasis in domestic animals.
Unfortunately, besides having low therapeutic
indices, the drugs have minimal penetration
of the bone marrow, where some of the Leishmania
amastigotes reside, and curing the disease
– especially the visceral form – is very
difficult.
Elemental antimony as an antimony pill was
once used as a medicine.
It could be reused by others after ingestion
and elimination.Antimony(III) sulfide is used
in the heads of some safety matches.Antimony
sulfides help to stabilize the friction coefficient
in automotive brake pad materials.Antimony
is used in bullets, bullet tracers, paint,
glass art, and as an opacifier in enamel.
Antimony-124 is used together with beryllium
in neutron sources; the gamma rays emitted
by antimony-124 initiate the photodisintegration
of beryllium.
The emitted neutrons have an average energy
of 24 keV.
Natural antimony is used in startup neutron
sources.
== Precautions ==
The effects of antimony and its compounds
on human and environmental health differ widely.
The elemental antimony metal does not affect
human and environmental health.
Inhalation of antimony trioxide (and similar
poorly soluble Sb(III) dust particles such
as antimony dust) is considered harmful and
suspected of causing cancer.
However, these effects are only observed with
female rats and after long-term exposure to
high dust concentrations.
The effects are hypothesized to be attributed
to inhalation of poorly soluble Sb particles
leading to impaired lung clearance, lung overload,
inflammation and ultimately tumour formation,
not to exposure to antimony ions (OECD, 2008).
Antimony chlorides are corrosive to skin.
The effects of antimony are not comparable
to arsenic; this might be caused by the significant
differences of uptake, metabolism and excretion
between arsenic and antimony.
For oral absorption, ICRP (1994) recommended
values of 10% for tartar emetic and 1% for
all other antimony compounds.
Dermal absorption for metals is estimated
at most 1% (HERAG, 2007).
Inhalation absorption of antimony trioxide
and other poorly soluble Sb(III) substances
(such as antimony dust) is estimated at 6.8%
(OECD, 2008), whereas a value <1% is derived
for Sb(V) substances.
Antimony(V) is not quantitatively reduced
to antimony(III) in the cell, and both species
exist simultaneously.
Antimony is mainly excreted from the human
body via urine.
Antimony and its compounds do not cause acute
human health effects, with the exception of
antimony potassium tartrate ("tartar emetic"),
a prodrug that is intentionally used to treat
leishmaniasis patients.
Prolonged skin contact with antimony dust
may cause dermatitis.
However, it was agreed at the European Union
level that the skin rashes observed are not
substance-specific, but most probably due
to a physical blocking of sweat ducts (ECHA/PR/09/09,
Helsinki, 6 July 2009).
Antimony dust may also be explosive when dispersed
in the air; when in a bulk solid it is not
combustible.Antimony is incompatible with
strong acids, halogenated acids, and oxidizers;
when exposed to newly formed hydrogen it may
form stibine (SbH3).The 8-hour time-weighted
average (TWA) is set at 0.5 mg/m3 by the American
Conference of Governmental Industrial Hygienists
and by the Occupational Safety and Health
Administration (OSHA) as a legal permissible
exposure limit (PEL) in the workplace.
The National Institute for Occupational Safety
and Health (NIOSH) has set a recommended exposure
limit (REL) of 0.5 mg/m3 as an 8 hour TWA.
Antimony compounds are used as catalysts for
polyethylene terephthalate (PET) production.
Some studies report minor antimony leaching
from PET bottles into liquids, but levels
are below drinking water guidelines.
Antimony concentrations in fruit juice concentrates
were somewhat higher (up to 44.7 µg/L of
antimony), but juices do not fall under the
drinking water regulations.
The drinking water guidelines are:
World Health Organization: 20 µg/L
Japan: 15 µg/L
United States Environmental Protection Agency,
Health Canada and the Ontario Ministry of
Environment: 6 µg/L
EU and German Federal Ministry of Environment:
5 µg/LThe TDI proposed by WHO is 6 µg antimony
per kilogram of body weight.
The IDLH (immediately dangerous to life and
health) value for antimony is 50 mg/m3.
=== Toxicity ===
Certain compounds of antimony appear to be
toxic, particularly antimony trioxide and
antimony potassium tartrate.
Effects may be similar to arsenic poisoning.
Occupational exposure may cause respiratory
irritation, pneumoconiosis, antimony spots
on the skin, gastrointestinal symptoms and
cardiac arrhythmias.
In addition antimony trioxide is potentially
carcinogenic to humans.Adverse health effects
have been observed in humans and animals following
inhalation, oral, or dermal exposure to antimony
and antimony compounds.
Antimony toxicity typically occurs either
due to occupational exposure, during therapy
or from accidental ingestion.
It is unclear if antimony can enter the body
through the skin.
== See also ==
Phase change memory
== Notes
