Antimony

Don’t get any ideas. I’m not here to hold your hand or explain things in a way that makes them palatable for your evidently limited comprehension. If you want information, you’ll get it, but don’t expect me to sugarcoat anything. This is what it is.

Antimony

This isn’t about some philosophical paradox or a contradictory chant. This is about a chemical element. Specifically, the one with the atomic number 51, bearing the symbol Sb. Don’t confuse it with antinomy or antiphony , though frankly, the confusion might be understandable given the general lack of clarity in most things. For other uses, consult the Antimony (disambiguation) page. This, however, is about the element itself.

Chemical Element with Atomic Number 51 (Sb)

Antimony. Pronounced, depending on your dialect, as either /ˈæntɪməni/ (UK) or /ˈæntəmoʊni/ (US). It’s a silvery, lustrous gray metal. Or perhaps a metalloid. The distinction, while important to some, is likely irrelevant to your immediate needs. Its standard atomic weight is approximately 121.760 ± 0.001. Don’t get too attached to the precision; it’s a number, much like any other.

It resides in the periodic table , specifically in group 15 , among the pnictogens . It occupies period 5 and resides in the p-block . Its electron configuration is a rather tidy Kr 4d¹⁰ 5s² 5p³. The electrons are arranged as 2, 8, 18, 18, 5. A neat little package, wouldn’t you agree?

Appearance

Antimony presents itself as a silvery, lustrous gray solid. It’s stable in air at room temperature, which is more than can be said for most things. However, if you decide to introduce heat, it will react with oxygen to form antimony trioxide , Sb₂O₃. It’s also susceptible to oxidizing acids. So, not entirely impervious.

The stable form of antimony crystallizes in a trigonal cell, sharing an isomorphic structure with bismuth and the gray allotrope of arsenic . There’s also a yellow allotrope, supposedly analogous to yellow arsenic, which forms when stibine (SbH₃) is oxidized by air or oxygen at extremely low temperatures (−90 °C). It’s fleeting, though, transforming into the more stable black allotrope at ambient temperatures and light. And then there’s the rare, supposedly “explosive” form. It’s generated from the electrolysis of antimony trichloride , but it’s never truly pure, always retaining some chlorine. It’s more of a theatrical display than a true allotrope.

Elemental antimony’s structure is layered, with fused, ruffled six-membered rings. The atoms are arranged in an irregular octahedral complex. This arrangement leads to a high density (6.697 g/cm³) but also makes it brittle. Weak bonds between the layers, you see. A perfect metaphor for many relationships, if you ask me.

Isotopes

Antimony has two stable isotopes :

• ¹²¹Sb, which constitutes 57.21% of the natural abundance.
• ¹²³Sb, making up the remaining 42.79%.

Beyond these, there are 37 artificial radioactive isotopes known, with mass numbers ranging from 104 to 142. The longest-lived among these is the fission product ¹²⁵Sb, with a half-life of 2.758 years. Numerous meta states exist, the most stable being ¹²⁰m¹Sb, with a half-life of 5.76 days. Isotopes lighter than ¹²³Sb tend to decay via β⁺, while those heavier undergo β⁻ decay, with a few exceptions. It’s all very predictable, really.

Occurrence

Antimony isn’t exactly common. Its abundance in the Earth’s crust is estimated at a mere 0.2 parts per million . That’s comparable to thallium and more than silver . It ranks as the 63rd most abundant element. Despite its scarcity, it’s found in over 100 mineral species.

It can be found in its native state, though this is rare. More commonly, it appears as the sulfide mineral stibnite (Sb₂S₃). This is its primary ore. Other sulfide minerals include pyrargyrite (Ag₃SbS₃), zinkenite , jamesonite , and boulangerite . Antimony also forms antimonide compounds with metals, like indium antimonide (InSb) and silver antimonide (Ag₃Sb).

Compounds

Antimony compounds are typically categorized by their oxidation states: Sb(III) and Sb(V). The +5 state is more prevalent.

Oxides and Hydroxides

When antimony is burned in air, it forms antimony trioxide . In the gas phase, this compound exists as Sb₄O₆ molecules, but it polymerizes upon condensation. Antimony pentoxide , Sb₄O₁₀, requires oxidation with concentrated nitric acid for its formation. A mixed-valence oxide, antimony tetroxide (Sb₂O₄), also exists, containing both Sb(III) and Sb(V). Unlike their phosphorus and arsenic counterparts, these oxides are amphoteric . They don’t form well-defined oxoacids , instead reacting with acids to produce antimony salts.

Antimonous acid, Sb(OH)₃, is not directly observed, but its conjugate base, sodium antimonite ([Na₃SbO₃]₄), can be formed by fusing sodium oxide with Sb₄O₆. Transition metal antimonites are also known. Antimonic acid exists solely as the hydrate HSb(OH)₆, forming salts with the antimonate anion, Sb(OH)⁻₆. Dehydration of solutions containing this anion yields precipitates of mixed oxides.

Antimony pentasulfide is a non-stoichiometric substance containing antimony in the +3 oxidation state and S–S bonds. Various thioantimonides are known, such as [Sb₆S₁₀]²⁻ and [Sb₈S₁₃]²⁻.

Halides

Antimony forms two distinct series of halides : SbX₃ and SbX₅. The trihalides—SbF₃, SbCl₃, SbBr₃, and SbI₃—are all molecular compounds with a trigonal pyramidal molecular geometry . Antimony trifluoride, prepared by reacting antimony trioxide with hydrofluoric acid , is Lewis acidic and readily accepts fluoride ions to form complex anions like SbF⁻₄ and Sb₂F⁻₅. Molten antimony trifluoride is a weak electrical conductor . The trichloride is synthesized by dissolving stibnite in hydrochloric acid . This method is useful as arsenic sulfides are not easily dissolved by HCl, providing a way to obtain antimony free from arsenic.

In the gas phase, pentahalides like SbF₅ and SbCl₅ exhibit trigonal bipyramidal molecular geometry . However, in the liquid state, SbF₅ becomes polymeric , while SbCl₅ remains monomeric. Antimony pentafluoride is a potent Lewis acid, crucial in the creation of the superacid fluoroantimonic acid (H₂F⁺·SbF⁻₆). Oxyhalides are more common for antimony than for arsenic and phosphorus. Antimony trioxide dissolves in concentrated acids to yield oxoantimonyl compounds, such as SbOCl and (SbO)₂SO₄.

Antimonides, Hydrides, and Organoantimony Compounds

These compounds are generally considered derivatives of Sb³⁻. Antimony forms antimonides with metals, including indium antimonide (InSb) and silver antimonide (Ag₃Sb). Alkali metal and zinc antimonides, like Na₃Sb and Zn₃Sb₂, are more reactive. Treating these antimonides with acid liberates the highly unstable gas stibine (SbH₃). Stibine can also be produced by reacting Sb³⁺ salts with hydride reagents such as sodium borohydride . Stibine is spontaneously unstable at room temperature due to its positive heat of formation . This thermodynamic instability explains why antimony does not react directly with hydrogen .

Organoantimony compounds are typically synthesized by alkylating antimony halides with Grignard reagents . A wide array of compounds are known, featuring both Sb(III) and Sb(V) centers, including mixed chloro-organic derivatives, anions, and cations. Notable examples include triphenylstibine (Sb(C₆H₅)₃) and pentaphenylantimony (Sb(C₆H₅)₅).

History

Antimony sulfide (Sb₂S₃) was known and used as an eye cosmetic, kohl , in predynastic Egypt as early as 3100 BC. Artifacts suggest its use dates back to approximately 3000 BC in Chaldea and between 2500 and 2200 BC in Egypt , where copper objects were plated with antimony. Some speculate this indicates a lost method for rendering antimony malleable, though the evidence is debated.

The Roman scholar Pliny the Elder , in his Natural History around 77 AD, described methods for preparing antimony sulfide for medicinal purposes. He distinguished between “male” and “female” forms of antimony, with the latter, heavier and less friable , suspected to be native metallic antimony. The Greek naturalist Pedanius Dioscorides also noted that roasting antimony sulfide could produce metallic antimony.

Antimony was a subject of interest in alchemical manuscripts, including the Summa Perfectionis attributed to Pseudo-Geber around the 14th century. Procedures for isolating antimony were detailed by Vannoccio Biringuccio in his 1540 book De la pirotechnia , predating the more famous De re metallica by Georg Agricola in 1556. Agricola is often mistakenly credited with its discovery. The book Currus Triumphalis Antimonii (The Triumphal Chariot of Antimony), published in 1604, described the preparation of metallic antimony. While purportedly written by a 15th-century Benedictine monk named Basilius Valentinus , historical consensus suggests it was authored later, likely by Johann Thölde .

German chemist Andreas Libavius documented obtaining antimony in 1615 through a process involving iron and a molten mixture of antimony sulfide, salt, and potassium tartrate , resulting in a crystalline or starred surface. As the phlogiston theory was challenged, antimony began to be recognized as an element, similar to other metals, forming sulfides and oxides.

The discovery of naturally occurring pure antimony in the Earth’s crust is credited to the Swedish scientist Anton von Swab in 1783, with the type-sample originating from the Sala Silver Mine in Sweden. Coins made of antimony were briefly issued in China’s Guizhou province in 1931 but were discontinued due to the metal’s softness and toxicity.

Etymology

The name “antimony” originates from the medieval Latin antimonium. Its etymology is uncertain, with various theories proposed, none entirely satisfactory. A popular but likely inaccurate explanation suggests it derives from Greek anti (“not”) and monos (“alone”), implying it’s not found alone in nature. Another popular etymology points to Greek antimonos (“against aloneness”), referencing its tendency to alloy. However, the more plausible origin likely lies in Arabic. Medieval Latin adopted terms like ithmid or athmar, which referred to antimony sulfide used as kohl. The Greek word στίμμι (stimmi), used by Attic tragic poets, is possibly a loanword from Arabic or Egyptian stm. The standard chemical symbol Sb was established by Jöns Jakob Berzelius , derived from the Latin stibium.

Production

The extraction of antimony from its ores is dictated by the ore’s quality and composition. Most antimony is mined as sulfide ore. Lower-grade ores undergo froth flotation for concentration, while higher-grade ores are heated to 500–600 °C, causing the stibnite to melt and separate from gangue minerals. Crude antimony sulfide can be reduced with scrap iron:

Sb₂S₃ + 3 Fe → 2 Sb + 3 FeS

Alternatively, the sulfide is roasted to form an oxide, which is then purified by vaporization and recovery of volatile antimony(III) oxide. This sublimate is often used directly, with impurities like arsenic being removed. Antimony is then isolated from the oxide via carbothermal reduction:

2 Sb₂O₃ + 3 C → 4 Sb + 3 CO₂

Lower-grade ores are processed in blast furnaces , while higher-grade ores are treated in reverberatory furnaces .

World Production and Reserves

In 2022, China was the dominant producer, accounting for 54.5% of global antimony output, followed by Russia (18.2%) and Tajikistan (15.5%). Chinese production is projected to decrease due to government-imposed pollution controls and stricter environmental regulations. Myanmar also faces supply disruptions due to political instability.

World reserves are substantial, with China and Russia holding the largest known deposits, followed by Bolivia, Kyrgyzstan, and Myanmar.

Supply Risk

Antimony is considered a critical mineral for industrial manufacturing in regions like Europe and the U.S., posing a risk of supply chain disruption. The heavy reliance on a few producing countries, primarily China, makes it vulnerable. The European Union, for instance, imports 100% of its antimony, mainly from Turkey, Bolivia, and Guatemala. The United Kingdom’s Geological Survey ranked antimony high on its supply risk index. In the U.S., antimony is deemed critical for economic and national security , yet no domestic mining occurred in 2021. Recent geopolitical developments, including potential export bans from China, further heighten supply concerns.

Applications

Antimony finds its way into numerous applications, with flame retardants and lead-acid batteries being the largest consumers.

Flame Retardants

Antimony trioxide is predominantly used as a flame retardant , typically in conjunction with halogenated compounds. It functions by forming halogenated antimony compounds that interfere with the combustion process. These flame retardants are found in products ranging from children’s clothing and toys to aircraft components and automotive upholstery. They are also incorporated into polyester resins for fiberglass composites , providing self-extinguishing properties. Antimony trioxide also acts as a synergist with brominated flame retardants in electronic equipment casings to meet flammability standards like UL 94.

Alloys

Antimony forms crucial alloys with lead, enhancing hardness and mechanical strength. Its addition improves the fluidity of lead melts and reduces shrinkage during solidification. In lead–acid batteries , antimony alloys strengthen the plates and improve charging capabilities. It’s also used in antifriction alloys like Babbitt metal , bullets, lead shot , electrical cable sheathing, type metal for printing, some “lead-free ” solders, pewter , and in alloys for hardening low-tin content in organ pipes.

Other Applications

Other significant uses include:

• As a stabilizer and catalyst in the production of polyethylene terephthalate (PET).
• As a fining agent in glass manufacturing, particularly for TV screens, to remove microscopic bubbles and prevent discoloration.
• In pigments, and to maintain color stability and surface smoothness in ceramics and enamels.
• As a dopant in semiconductor devices , especially in n-type silicon wafers for diodes, infrared detectors, and Hall-effect devices. Indium antimonide (InSb) is used for mid-infrared detectors.
• The material Ge₂Sb₂Te₅ is employed in phase-change memory .

Antimony has limited use in biology and medicine. Antimony compounds, known as antimonials , have been used as emetics and antiprotozoal agents . Potassium antimonyl tartrate (tartar emetic) was an early anti-schistosomal drug, later replaced by praziquantel . Antimony compounds like meglumine antimoniate are still used to treat leishmaniasis , though resistance is a growing concern. Antimony-based veterinary preparations are used for skin conditioning in ruminants.

Antimony(III) sulfide is found in the heads of some safety matches and helps stabilize friction coefficients in brake pads. It’s also used in bullets, bullet tracers, paints, glass art, and as an opacifier in enamel . Antimony-124, in combination with beryllium , serves as a neutron source .

The powdered antimony sulfide, kohl , has been used for millennia as an eye cosmetic, believed to treat eye infections. This practice persists in some regions.

Precautions

Antimony and many of its compounds are toxic , with effects similar to arsenic poisoning , though generally less severe. Antimony poisoning primarily affects the cardiovascular system, potentially causing cardiotoxicity and myocarditis , and in severe cases, Adams–Stokes syndrome . Inhalation of antimony dust is hazardous, leading to headaches, dizziness , depression, dermatitis, and potential kidney and liver damage with prolonged exposure.

Antimony is incompatible with strong oxidizing agents , strong acids , halogen acids , chlorine , and fluorine . It must be kept away from heat.

Antimony can leach from polyethylene terephthalate (PET) bottles into beverages. While levels in bottled water are typically below guidelines, fruit juice concentrates have shown higher concentrations, exceeding EU limits for tap water. Various international bodies have established drinking water guidelines for antimony, with the U.S. Environmental Protection Agency, Health Canada, and the Ontario Ministry of Environment setting a limit of 6 μg/L. The tolerable daily intake (TDI) proposed by the WHO is 6 μg/kg of body weight.

Toxicity

Specific antimony compounds, such as antimony trioxide and antimony potassium tartrate, are particularly toxic. Occupational exposure can lead to respiratory irritation, pneumoconiosis , skin lesions, gastrointestinal issues, and cardiac arrhythmias. Antimony trioxide is also considered potentially carcinogenic to humans. Adverse health effects have been documented in humans and animals following various exposure routes. The role of antimony in dental decay is also under investigation.