Antimony

• 1. Introduction

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  Antimony, element number 51 with the chemical symbol Sb, has been rubbed around human eyes for thousands of years. The powder came from crushed antimony sulfide, known as kohl. People applied it with a metal rod moistened with spittle, and the ancients thought it helped cure eye infections. The habit is still seen in Yemen and other Muslim countries. Yet the same element is toxic, and most of the world's supply of it comes from a handful of places. This documentary asks why a brittle grey metalloid turns up in so many unexpected products. It asks where the strange name came from, and who first isolated the metal. It also asks why governments in Europe and the United States now worry about where their antimony will come from.

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• 2. A Brittle Silver Metal

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  On the Mohs scale, antimony rates only 3. It is a silvery, lustrous grey solid that stays stable in air at room temperature. Heat it, and it reacts with oxygen to form antimony trioxide. Oxidizing acids attack it.

  Inside the solid, atoms form layers of fused, ruffled six-membered rings. Close packing within the layers gives antimony a high density of 6.697 grams per cubic centimetre. Weak bonding between the layers explains why the metal is soft and brittle.

  Antimony belongs to group 15 of the periodic table, among the elements called pnictogens. Its electronegativity is 2.05. That makes it more electronegative than tin or bismuth, and less so than tellurium or arsenic.

  Nature supplies antimony as two stable isotopes, with abundances of 57.21 percent and 42.79 percent. Researchers have also recorded 37 artificial radioactive isotopes, with mass numbers from 104 to 142. The longest-lived is a fission product with a half-life of 2.758 years. Among the numerous meta states, the most stable lasts 5.76 days.

  A yellow form of antimony appears when stibine is oxidized with air or oxygen at minus 90 degrees Celsius. At ambient temperatures and in ambient light, it turns into the more stable black form. A rarer explosive form comes from the electrolysis of antimony trichloride. It always contains appreciable chlorine, so it is not truly a form of the pure element. Scratch it with a sharp implement and an exothermic reaction gives off white fumes as metallic antimony forms. Rub it with a pestle in a mortar and the result is a strong detonation.

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• 3. Scarce but Everywhere

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  Estimates put antimony at 0.2 parts per million of the Earth's crust, which makes it the 63rd most abundant element. Thallium is estimated at 0.5 parts per million and silver at 0.07. Even so, antimony appears in more than 100 mineral species.

  Native metal is sometimes found, for instance on Antimony Peak. Far more often the element sits in stibnite, a sulfide and the predominant ore mineral. Other sulfide minerals include pyrargyrite, zinkenite, jamesonite and boulangerite.

  Chemists sort antimony compounds by two oxidation states, written Sb(III) and Sb(V). The +5 state is the more common. Burning antimony in air forms the trioxide. The pentoxide can be made only by oxidation with concentrated nitric acid. Unlike the oxides of phosphorus and arsenic, these oxides do not form well-defined oxoacids.

  Dissolving stibnite in hydrochloric acid yields antimony trichloride. Arsenic sulfides are not readily attacked by hydrochloric acid, so this route gives antimony free of arsenic. Antimony pentafluoride is a powerful Lewis acid, and it is used to make the superacid fluoroantimonic acid.

  Treating antimonides with acid produces stibine, a highly unstable gas that decomposes spontaneously at room temperature. Because its heat of formation is positive, antimony does not react with hydrogen directly. Chemists also prepare organoantimony compounds such as triphenylstibine and pentaphenylantimony from antimony halides and Grignard reagents.

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• 4. Tracing the Name

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  Attic tragic poets of the 5th century BC used the Greek word stimmi for the substance. It may be a loan word from Arabic or from the Egyptian stm. The Egyptians called antimony mśdmt or stm. The Arabic word for the substance, as opposed to the cosmetic, appears in forms such as ithmid, athmoud, othmod and uthmod. The ancient words mostly mean kohl, the sulfide of antimony.

  The modern name descends from medieval Latin antimonium, which also gave late Byzantine Greek its word. Its earliest uses appear in the translations that Constantine the African made of Arabic medical treatises between 1050 and 1100. Its true origin is uncertain, and every suggestion has some difficulty of form or interpretation.

  One popular theory points to the Greek anti-monachos or the French antimoine, meaning monk-killer. The story goes that many early alchemists were monks, and some antimony compounds were poisonous. Another theory proposes a hypothetical Greek word antimonos, meaning against aloneness, since the element is not found as a metal on its own. Critics note that ancient Greek would more naturally express a pure negative with the prefix a-.

  Edmund Oscar von Lippmann conjectured a hypothetical Greek word anthemonion, meaning floret. Several authorities instead think antimonium is a scribal corruption of an Arabic form. Meyerhof derives it from ithmid, and other possibilities include athimar and a hypothetical as-stimmi.

  The two-letter symbol is easier to explain. Jöns Jakob Berzelius is credited with deriving Sb from the Latin stibium.

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• 5. A Disputed Discovery

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  Around 3100 BC, in predynastic Egypt, antimony sulfide was already in use as the eye cosmetic kohl. That date coincides with the invention of the cosmetic palette.

  An artifact from Telloh in Chaldea, in present-day Iraq, is dated to about 3000 BC and said to be part of a vase made of antimony. A copper object plated with antimony, from between 2500 BC and 2200 BC, has been found in Egypt. At a lecture by Herbert Gladstone in 1892, Austen argued that antimony is too brittle to shape into a vase. He suggested the find represented a lost art of rendering antimony malleable.

  The British archaeologist Roger Moorey was unconvinced that the object was a vase. Selimkhanov analysed it and published in 1975, relating the metal to natural antimony from Transcaucasia. Moorey added that the antimony objects from Transcaucasia are all small personal ornaments, which weakens the lost-art idea.

  Around 77 AD, the Roman scholar Pliny the Elder described several ways of preparing antimony sulfide for medicine in his Natural History. He distinguished a male and a female form. The male is probably the sulfide. The female, which he considered superior, heavier and less friable, has been suspected to be native metallic antimony. The Greek naturalist Pedanius Dioscorides noted that the sulfide could be roasted in a current of air, which is thought to have produced the metal.

  Alchemical manuscripts described antimony often, including the Summa Perfectionis of Pseudo-Geber, written around the 14th century. A procedure for isolating it appeared in the 1540 book De la pirotechnia by Vannoccio Biringuccio. That predates the more famous 1556 De re metallica by Agricola, who has often been wrongly credited with discovering the metal.

  The 1604 German book Currus Triumphalis Antimonii, meaning The Triumphal Chariot of Antimony, described making the metal. It claimed to come from a Benedictine monk writing as Basilius Valentinus in the 15th century. It is not authentic.

  Andreas Libavius, a German chemist, knew the metal by 1615. He obtained it by adding iron to a molten mixture of antimony sulfide, salt and potassium tartrate, which gave a crystalline or starred surface. Once phlogiston theory faced challenges, antimony was recognized as an element forming sulfides and oxides like other metals.

  Naturally occurring pure antimony was first described in 1783 by a Swedish scientist who served as a local mine district engineer. The type sample came from the Sala Silver Mine in the Bergslagen mining district of Sala, Västmanland, Sweden.

  In 1931, China's Guizhou issued coins of antimony. Their durability was poor, and minting soon stopped because of the metal's softness and toxicity.

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• 6. Mines and Supply Risk

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  In 2022, China produced 54.5 percent of the world's antimony, according to the US Geological Survey. Russia followed with 18.2 percent and Tajikistan with 15.5 percent. The top five countries together made 95.5 percent of a world total of 110,000 tonnes. Most Chinese output comes from the Xikuangshan Mine in Hunan.

  How antimony is extracted depends on the quality of the ore. Lower-grade ores are concentrated by froth flotation. Higher-grade ores are heated to between 500 and 600 degrees Celsius, where stibnite melts and separates from the waste rock. The crude sulfide can then be reduced with scrap iron. Alternatively, it is roasted to an oxide and reduced with carbon. Lower-grade ores go to blast furnaces, and higher-grade ores to reverberatory furnaces.

  A report from Roskill concluded that Chinese output has fallen and is unlikely to rise. No significant Chinese deposit has been developed for about ten years, and the remaining economic reserves are being rapidly depleted. An environmental protection law took effect in January 2015, alongside revised emission standards for tin, antimony and mercury. Government closures of mines and smelters are expected to continue. Myanmar faces supply disruptions because of political unrest.

  In 2019, China supplied 74 percent of global production, Tajikistan 8 percent and Russia 4 percent. The European Union treats antimony as a critical raw material for defense, automotive, construction and textiles. That year it imported all of its supply, mainly from Turkey at 62 percent, Bolivia at 20 percent and Guatemala at 7 percent.

  The British Geological Survey's 2015 risk list ranked antimony second highest for supply risk, behind only rare-earth elements. In 2021, the United States mined no antimony at all. Then, in December 2024, China banned the export of critical minerals.

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• 7. Fire, Lead, and Glass

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  In 2017, about 48 percent of antimony went into flame retardants, 33 percent into lead-acid batteries and 8 percent into plastics.

  Flame retardants use antimony trioxide, almost always alongside halogenated compounds. The two form halogenated antimony compounds that react with hydrogen atoms, and probably with oxygen atoms and hydroxyl radicals, which inhibits fire. Markets include children's clothing, toys, aircraft and automobile seat covers. Fiberglass engine covers for light aircraft use polyester resin treated this way. The resin burns in an external flame but goes out when that flame is removed. In electronics, the trioxide works with brominated retardants in housings to meet flammability standards such as UL 94.

  Alloying antimony with lead increases hardness and strength. In casting, it makes the molten metal flow better and reduces shrinkage as it cools. In batteries, it improves plate strength and charging behavior. Sailboat keels rely on lead to provide righting moment, from 600 pounds to over 200 tons on the largest superyachts. Between 2 and 5 percent antimony by volume is mixed in to harden them.

  The list of alloy uses is long. It includes Babbitt metal for reducing friction, bullets, lead shot, cable sheathing, and type metal for Linotype machines. Some lead-free solders contain 5 percent antimony. It also appears in pewter and in hardening alloys for organ pipes.

  Three further uses take nearly all the rest. Antimony stabilizes and catalyzes the production of polyethylene terephthalate. It removes microscopic bubbles from glass, mostly for TV screens, and prevents discolouration. It is also used in pigments.

  In the 1950s, tiny beads of lead-antimony alloy doped the emitters and collectors of n-p-n alloy-junction transistors. By the 1990s, antimony was increasingly a dopant in n-type silicon wafers for diodes and infrared detectors. Indium antimonide serves in mid-infrared detectors, and antimony is used in phase-change computer memory.

  Antimony-124 combined with beryllium makes a neutron source. Its gamma rays trigger the photodisintegration of beryllium, and the emitted neutrons average 24 keV.

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• 8. Medicine and Poison

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  In 1919, potassium antimonyl tartrate, called tartar emetic, began to be used as an anti-schistosomal drug. Praziquantel later replaced it. Biology and medicine have few uses for antimony. Treatments containing it, called antimonials, serve as emetics, and antimony compounds are used as antiprotozoan drugs.

  In 1922, Upendranath Brahmachari invented a much safer antimony(V) drug for leishmaniasis. Earlier treatments used trivalent antimony. Pentavalent antimonials, such as meglumine antimoniate, have been the standard first-line treatment since. Leishmania strains in Bihar and neighboring regions have developed resistance. An antimony pill was once used as medicine, and it could be reused by others after ingestion and elimination. In veterinary preparations, antimony compounds serve as a skin conditioner for ruminants.

  Antimony poisoning resembles arsenic poisoning, but antimony is far less toxic. That may reflect differences in uptake, metabolism and excretion. At most 20 percent of antimony(III) or antimony(V) is taken up from the gastrointestinal tract. Biomethylation of antimony does not occur, so antimony(V) leaves mainly in urine.

  The most serious effect of acute poisoning is cardiotoxicity and the resulting myocarditis. Antimony can also cause Adams-Stokes syndrome, which arsenic does not. A reported case involving 90 milligrams of antimony potassium tartrate dissolved from enamel showed only short-term effects. An intoxication with 6 grams of that compound resulted in death after three days. Inhaled dust can be fatal in certain cases, and small doses cause headaches, dizziness and depression. Antimony trioxide is potentially carcinogenic to humans.

  Antimony also leaches from PET bottles into liquids. Bottled water stays below drinking water guidelines. The World Health Organization sets a guideline of 20 micrograms per litre, Japan 15, and the US Environmental Protection Agency 6. The EU and the German Federal Ministry of Environment set 5. The WHO proposes a tolerable daily intake of 6 micrograms per kilogram of body weight. Fruit juice concentrates produced in the UK contained up to 44.7 micrograms per litre, well above the EU limit for tap water.

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