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= Antimony =
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Introduction
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Antimony is a chemical element; it has symbol Sb () and atomic number
51. A lustrous grey metal or metalloid, it is found in nature mainly
as the sulfide mineral stibnite (). Antimony compounds have been known
since ancient times and were powdered for use as medicine and
cosmetics, often known by the Arabic name kohl. The earliest known
description of this metalloid in the West was written in 1540 by
Vannoccio Biringuccio.
China is the largest producer of antimony and its compounds, with most
production coming from the Xikuangshan Mine in Hunan. The industrial
methods for refining antimony from stibnite are roasting followed by
reduction with carbon, or direct reduction of stibnite with iron.
The most common applications for metallic antimony are in alloys with
lead and tin, which have improved properties for solders, bullets, and
plain bearings. It improves the rigidity of lead-alloy plates in
lead-acid batteries. Antimony trioxide is a prominent additive for
halogen-containing flame retardants. Antimony is used as a dopant in
semiconductor devices.
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, if heated, it
reacts with oxygen to produce antimony trioxide,.
Antimony is a silvery, lustrous gray metalloid with a Mohs scale
hardness of 3, which is too soft to mark hard objects. Coins of
antimony were issued in China's Guizhou in 1931; durability was poor,
and minting was soon discontinued because of its softness and
toxicity. Antimony is resistant to attack by acids.
The only stable allotrope of antimony under standard conditions is
metallic, brittle, silver-white, and shiny. It crystallises in a
trigonal cell, isomorphic with bismuth and the gray allotrope of
arsenic, and is formed when molten antimony is cooled slowly.
Amorphous black antimony is formed upon rapid cooling of antimony
vapor, and is only stable as a thin film (thickness in nanometres);
thicker samples spontaneously transform into the metallic form. It
oxidizes in air and may ignite spontaneously. At 100 °C, it gradually
transforms into the stable form. The supposed yellow allotrope of
antimony, generated only by oxidation of stibine () at −90 °C, is also
impure and not a true allotrope; above this temperature and in ambient
light, it transforms into the more stable black allotrope. A rare
explosive form of antimony can be formed from the electrolysis of
antimony trichloride, but it always contains appreciable chlorine and
is not really an antimony allotrope. 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.
Elemental antimony adopts a layered structure (space group Rm No. 166)
whose 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: {{chem2|^{121}Sb}} with a natural
abundance of 57.36% and {{chem2|^{123}Sb}} with a natural abundance of
42.64%. It also has 35 radioisotopes, of which the longest-lived is
{{chem2|^{125}Sb}} with a half-life of 2.75 years. In addition, 29
metastable states have been characterized. The most stable of these is
{{chem2|^{120m1}Sb}} with a half-life of 5.76 days. Isotopes that are
lighter than the stable {{chem2|^{123}Sb}} tend to decay by β+ decay,
and those that are heavier tend to decay by β− decay, with some
exceptions. Antimony is the lightest element to have an isotope with
an alpha decay branch, excluding {{chem2|^{8}Be|link=Beryllium-8}} and
other light nuclides with beta-delayed alpha emission.
Occurrence
============
The abundance of antimony in the Earth's crust is estimated at 0.2
parts per million, comparable to thallium at 0.5 ppm and silver at
0.07 ppm. It is the 63rd most abundant element in the crust. 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 () which is the predominant ore mineral.
Compounds
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Antimony compounds are often classified according to their oxidation
state: Sb(III) and Sb(V). The +5 oxidation state is more common.
Oxides and hydroxides
=======================
Antimony trioxide is formed when antimony is burnt in air. In the gas
phase, the molecule of the compound is , but it polymerizes upon
condensing. Antimony pentoxide () can be formed only by oxidation with
concentrated nitric acid. Antimony also forms a mixed-valence oxide,
antimony tetroxide (), 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 is unknown, but the conjugate base sodium antimonite
() forms upon fusing sodium oxide and . Transition metal antimonites
are also known. Antimonic acid exists only as the hydrate , forming
salts as the antimonate anion . When a solution containing this anion
is dehydrated, the precipitate contains mixed oxides.
The most important antimony ore is stibnite (). Other sulfide minerals
include pyrargyrite (), zinkenite, jamesonite, and boulangerite.
Antimony pentasulfide is non-stoichiometric, which features antimony
in the +3 oxidation state and S-S bonds. Several thioantimonides are
known, such as and .
Halides
=========
Antimony forms two series of halides: and . The trihalides , , , and
are all molecular compounds having trigonal pyramidal molecular
geometry. The trifluoride is prepared by the reaction of antimony
trioxide with hydrofluoric acid:
:
It is Lewis acidic and readily accepts fluoride ions to form the
complex anions and . Molten antimony trifluoride is a weak electrical
conductor. The trichloride is prepared by dissolving stibnite in
hydrochloric acid:
:
Arsenic sulfides are not readily attacked by the hydrochloric acid, so
this method offers a route to As-free Sb.
The pentahalides and have trigonal bipyramidal molecular geometry in
the gas phase, but in the liquid phase, is polymeric, whereas is
monomeric. Antimony pentafluoride is a powerful Lewis acid used to
make the superacid fluoroantimonic acid ().
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 .
Antimonides, hydrides, and organoantimony compounds
=====================================================
Compounds in this class generally are described as derivatives of .
Antimony forms antimonides with metals, such as indium antimonide
(InSb) and silver antimonide (). The alkali metal and zinc
antimonides, such as and , are more reactive. Treating these
antimonides with acid produces the highly unstable gas stibine, :
:
Stibine can also be produced by treating 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
triphenylstibine () and pentaphenylantimony ().
History
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Antimony(III) sulfide, , 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."
The British archaeologist Roger 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', around 77 AD. 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 Greek 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.
Antimony was frequently described in alchemical manuscripts, including
the 'Summa Perfectionis' of Pseudo-Geber, written around the 14th
century. A description of a procedure for isolating antimony is later
given 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 discovery of naturally occurring 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 '. The origin of
that is uncertain, and all suggestions have some difficulty either of
form or interpretation. The popular etymology, from ἀντίμοναχός
'anti-monachos' or French , would mean "monk-killer", which is
explained by the fact that many early alchemists were monks, and some
antimony compounds were poisonous.
Another popular etymology is the hypothetical Greek word ἀντίμόνος
'antimonos', "against aloneness", explained as "not found as metal",
or "not found unalloyed". However, ancient Greek would more naturally
express the pure negative as 'α-' ("not"). Edmund Oscar von 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' or 'stm'.
The Arabic word for the substance, as opposed to the cosmetic, can
appear as 'ithmid, athmoud, othmod', or 'uthmod'. Littré suggests the
first form, which is the earliest, derives from 'stimmida', an
accusative for 'stimmi'. The Greek word στίμμι (stimmi) is used by
Attic tragic poets of the 5th century BC, and is possibly a loan word
from Arabic or from Egyptian 'stm'.
Process
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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:
:
The sulfide is converted to an oxide by roasting. The product is
further purified by vaporizing the volatile antimony(III) oxide, which
is recovered. This sublimate is often used directly for the main
applications, impurities being arsenic and sulfide. Antimony is
isolated from the oxide by a carbothermal reduction:
:
The lower-grade ores are reduced in blast furnaces while the
higher-grade ores are reduced in reverberatory furnaces.
Top producers and production volumes
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In 2022, according to the US Geological Survey, China accounted for
54.5% of total antimony production, followed in second place by Russia
with 18.2% and Tajikistan with 15.5%.
Antimony mining in 2022
Country !! Tonnes !! % of total
| |60,000 |54.5
| |20,000 |18.2
| |17,000 |15.5
| |4,000 |3.6
| |4,000 |3.6
|'Top 5' |105,000 |95.5
!Total world !110,000 !100.0
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 an environmental protection law
having gone into effect in January 2015 and revised "Emission
Standards of Pollutants for Stanum, Antimony, and Mercury" having gone
into effect, hurdles for economic production are higher.
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.
Reserves
==========
World antimony reserves in 2022
Country !! Reserves (tonnes)
| |350,000
| |350,000
| |310,000
| |260,000
| |140,000
| |120,000
| |100,000
| |78,000
| |60,000
| |60,000
| |50,000
!Total world !>1,800,000
Supply risk
=============
For antimony-importing regions, such as Europe and the U.S., antimony
is considered to be a critical mineral for industrial manufacturing
that is at risk of supply chain disruption. With global production
coming mainly from China (74%), Tajikistan (8%), and Russia (4%),
these sources are critical to supply.
*European Union: Antimony is considered a critical raw material for
defense, automotive, construction and textiles. The E.U. sources are
100% imported, coming mainly from Turkey (62%), Bolivia (20%) and
Guatemala (7%).
*United Kingdom: The British Geological Survey's 2015 risk list ranks
antimony second highest (after rare earth elements) on the relative
supply risk index.
*United States: Antimony is a mineral commodity considered critical to
the economic and national security. In 2022, no antimony was mined in
the U.S.
Applications
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Approximately 48% of antimony is consumed in flame retardants, 33% in
lead-acid batteries, and 8% in plastics.
Flame retardants
==================
Antimony is mainly used as 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. When casting it increases fluidity
of the melt and reduces shrinkage during cooling. 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. For sailboats, lead keels are
used to provide righting moment, ranging from 600 lbs to over 200 tons
for the largest sailing superyachts; to improve hardness and tensile
strength of the lead keel, antimony is mixed with lead between 2% and
5% by volume. Antimony 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 as a stabilizer and catalyst for the
production of polyethylene terephthalate. Another is as 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.
In the 1990s antimony was 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 (InSb) is used as a material
for mid-infrared detectors.
The material is used as for phase-change memory, a type of computer
memory.
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. Early
treatments used antimony(III) species (trivalent antimonials), but in
1922 Upendranath Brahmachari invented a much safer antimony(V) drug,
and since then so-called pentavalent antimonials have been the
standard first-line treatment. However, 'Leishmania' strains in Bihar
and neighboring regions have developed resistance to antimony.
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.
The powder derived from crushed antimony sulfide ('kohl') has been
used for millennia as an eye cosmetic. Historically it was applied to
the eyes with a metal rod and with one's spittle, and was thought by
the ancients to aid in curing eye infections. The practice is still
seen in Yemen and in other Muslim countries.
Precautions
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Antimony and many of its compounds are toxic, and the effects of
antimony poisoning are similar to arsenic poisoning. The toxicity of
antimony is far lower than that of arsenic; this might be caused by
the significant differences of uptake, metabolism and excretion
between arsenic and antimony. The uptake of antimony(III) or
antimony(V) in the gastrointestinal tract is at most 20%. Antimony(V)
is not quantitatively reduced to antimony(III) in the cell (in fact
antimony(III) is oxidised to antimony(V) instead).
Since methylation of antimony does not occur, the excretion of
antimony(V) in urine is the main way of elimination. Like arsenic, the
most serious effect of acute antimony poisoning is cardiotoxicity and
the resulting myocarditis; however, it can also manifest as
Adams-Stokes syndrome, which arsenic does not. Reported cases of
intoxication by antimony equivalent to 90 mg antimony potassium
tartrate dissolved from enamel has been reported to show only short
term effects. An intoxication with 6 g of antimony potassium tartrate
was reported to result in death after three days.
Inhalation of antimony dust is harmful and in certain cases may be
fatal; in small doses, antimony causes headaches, dizziness, and
depression. Larger doses such as prolonged skin contact may cause
dermatitis, or damage the kidneys and the liver, causing violent and
frequent vomiting, leading to death in a few days.
Antimony is incompatible with strong oxidizing agents, strong acids,
halogen acids, chlorine, or fluorine. It should be kept away from
heat.
Antimony leaches from polyethylene terephthalate (PET) bottles into
liquids. While levels observed for bottled water are below drinking
water guidelines, fruit juice concentrates (for which no guidelines
are established) produced in the UK were found to contain up to 44.7
μg/L of antimony, well above the EU limits for tap water of 5 μg/L.
The 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/L
The tolerable daily intake (TDI) proposed by WHO is 6 μg antimony per
kilogram of body weight. The immediately dangerous to life or health
(IDLH) 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. The
presence of low levels of antimony in saliva may also be associated
with dental decay.
External links
======================================================================
*
[
https://web.archive.org/web/20090115095847/http://www.atsdr.cdc.gov/toxprofiles/phs23.html
Public Health Statement for Antimony]
* [
http://www.antimony.com/ International Antimony Association vzw
(i2a])
* [
http://www.rsc.org/chemistryworld/podcast/element.asp Chemistry in
its element podcast] (MP3) from the Royal Society of Chemistry's
Chemistry World:
[
http://www.rsc.org/images/CIIE_antimony_48kbps_tcm18-128033.mp3
Antimony]
* [
http://www.periodicvideos.com/videos/051.htm Antimony] at 'The
Periodic Table of Videos' (University of Nottingham)
* [
https://www.cdc.gov/niosh/npg/npgd0036.html CDC - NIOSH Pocket
Guide to Chemical Hazards - Antimony]
* [
http://webmineral.com/data/Antimony.shtml Antimony Mineral data and
specimen images]
License
=========
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Original Article:
http://en.wikipedia.org/wiki/Antimony
