Antimony(III) oxide is the
inorganic compound with the
formula Sb
2O
3. It is the most important commercial compound of
antimony
Antimony is a chemical element with the symbol Sb (from la, 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 t ...
. It is found in nature as the minerals
valentinite
Valentinite is an antimony oxide mineral with formula Sb2 O3. Valentinite crystallizes in the orthorhombic system and typically forms as radiating clusters of euhedral crystals or as fibrous masses. It is colorless to white with occasional shad ...
and senarmontite. Like most polymeric
oxides, Sb
2O
3 dissolves in aqueous solutions with
hydrolysis
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolys ...
. A mixed arsenic-antimony oxide occurs in nature as the very rare mineral stibioclaudetite.
Production and properties
Global production of antimony(III) oxide in 2012 was 130,000 tonnes, an increase from 112,600 tonnes in 2002. China produces the largest share followed by US/Mexico, Europe, Japan and South Africa and other countries (2%).
As of 2010, antimony(III) oxide was produced at four sites in EU27. It is produced via two routes, re-volatilizing of crude antimony(III) oxide and by oxidation of antimony metal.
Oxidation of antimony metal dominates in Europe. Several processes for the production of crude antimony(III) oxide or metallic antimony from virgin material. The choice of process depends on the composition of the ore and other factors. Typical steps include mining, crushing and grinding of ore, sometimes followed by
froth flotation
Froth flotation is a process for selectively separating hydrophobic materials from hydrophilic. This is used in mineral processing, paper recycling and waste-water treatment industries. Historically this was first used in the mining industry, wher ...
and separation of the metal using pyrometallurgical processes (smelting or roasting) or in a few cases (e.g. when the ore is rich in precious metals) by hydrometallurgical processes. These steps do not take place in the EU but closer to the mining location.
Re-volatilizing of crude antimony(III) oxide
Step 1) Crude stibnite is oxidized to crude antimony(III) oxide using furnaces operating at approximately 500 to 1,000 °C. The reaction is the following:
:2 Sb
2S
3 + 9 O
2 → 2 Sb
2O
3 + 6 SO
2
Step 2) The crude antimony(III) oxide is purified by sublimation.
Oxidation of antimony metal
Antimony metal is oxidized to antimony(III) oxide in furnaces. The reaction is exothermic. Antimony(III) oxide is formed through sublimation and recovered in bag filters. The size of the formed particles is controlled by process conditions in furnace and gas flow. The reaction can be schematically described by:
:4 Sb + 3 O
2 → 2 Sb
2O
3
Properties
Antimony(III) oxide is an
amphoteric oxide. It dissolves in aqueous
sodium hydroxide solution to give the meta-antimonite NaSbO
2, which can be isolated as the trihydrate. Antimony(III) oxide also dissolves in concentrated
mineral acids
A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water.
Ch ...
to give the corresponding salts, which hydrolyzes upon dilution with water.
With
nitric acid
Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available nitri ...
, the trioxide is oxidized to
antimony(V) oxide
Antimony pentoxide (molecular formula: Sb2O5) is a chemical compound of antimony and oxygen. It contains antimony in the +5 oxidation state.
Structure
Antimony pentoxide has the same structure as the ''B'' form of niobium pentoxide and can be der ...
.
When heated with
carbon
Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
, the oxide is reduced to
antimony
Antimony is a chemical element with the symbol Sb (from la, 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 t ...
metal. With other reducing agents such as
sodium borohydride
Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula Na BH4. This white solid, usually encountered as an aqueous basic solution, is a reducing agent that finds applica ...
or
lithium aluminium hydride, the unstable and very toxic gas
stibine is produced. When heated with
potassium bitartrate
Potassium bitartrate, also known as potassium hydrogen tartrate, with formula K C4 H5 O6, is a byproduct of winemaking. In cooking, it is known as cream of tartar. It is processed from the potassium acid salt of tartaric acid (a carboxylic ac ...
, a complex salt potassium antimony tartrate, KSb(OH)
2•C
4H
2O
6, is formed.
Structure
The structure of Sb
2O
3 depends on the temperature of the sample. Dimeric Sb
4O
6 is the high temperature (1560 °C) gas.
Sb
4O
6 molecules are bicyclic cages, similar to the related oxide of phosphorus(III),
phosphorus trioxide
Phosphorus trioxide is the chemical compound with the molecular formula P4O6. Although the molecular formula suggests the name tetraphosphorus hexaoxide, the name phosphorus trioxide preceded the knowledge of the compound's molecular structure, a ...
.
The cage structure is retained in a solid that crystallizes in a cubic habit. The Sb-O distance is 197.7 pm and the O-Sb-O angle of 95.6°. This form exists in nature as the
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...
senarmontite.
Above 606 °C, the more stable form is
orthorhombic, consisting of pairs of -Sb-O-Sb-O- chains that are linked by oxide bridges between the Sb centers. This form exists in nature as the mineral
valentinite
Valentinite is an antimony oxide mineral with formula Sb2 O3. Valentinite crystallizes in the orthorhombic system and typically forms as radiating clusters of euhedral crystals or as fibrous masses. It is colorless to white with occasional shad ...
.
Uses
The annual consumption of antimony(III) oxide in the United States and Europe is approximately 10,000 and 25,000
tonne
The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...
s, respectively. The main application is as
flame retardant
The term flame retardants subsumes a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an ignition source and ...
synergist in combination with halogenated materials. The combination of the halides and the antimony is key to the flame-retardant action for polymers, helping to form less flammable chars. Such flame retardants are found in electrical apparatuses, textiles, leather, and coatings.
Other applications:
*Antimony(III) oxide is an
opacifying agent for
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
es,
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
s and
enamels.
*Some specialty
pigments
A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compoun ...
contain antimony.
*Antimony(III) oxide is a useful
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
in the production of
polyethylene terephthalate (PET plastic) and the
vulcanization
Vulcanization (British: Vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to includ ...
of rubber.
Safety
Antimony(III) oxide has suspected carcinogenic potential for humans.
[ Its TLV is 0.5 mg/m3, as for most antimony compounds.] No other human health hazards were identified for antimony(III) oxide, and no risks to human health and the environment were identified from the production and use of antimony trioxide in daily life.
References
Further reading
* Institut national de recherche et de sécurité (INRS), ''Fiche toxicologique nº 198 : Trioxyde de diantimoine'', 1992.
* The Oxide Handbook, G.V. Samsonov, 1981, 2nd ed. IFI/Plenum,
External links
International Antimony Association
Antimony Market And Price
Société industrielle et chimique de l'Aisne
{{DEFAULTSORT:Antimony Trioxide
Antimony(III) compounds
Oxides
Inorganic pigments
IARC Group 2B carcinogens
Sesquioxides
Adamantane-like molecules