ANTIMONY(III) SULFIDE

Chemical Properties

Antimony trisulfide is soluble in alkalies and in concentrated, but not dilute, hydrochloric acid. It also goes into solution if it is boiled in alkali carbonate solutions. However, it precipitates as a reddish-brown powder, of nondefinite oxygen content (kermesite), when the solution is cooled. It forms thioantimonates if it is dissolved in alkali-metal sulfides. Antimony trisulfide is a starting material for the production of antimony and antimony compounds.

Physical properties

Natural stibnite is black orthorhombic crystal; or grayish-black powder; the compound also exists as an amorphous substance in yellow-red modification; distorted octahedral arrangement; density 4.64 g/cm³ for the natural stibnite and 4.12 g/cm³ for the red modification; melts at 550°C; vaporizes around 1150°C; insoluble in water (1.75mg/L at 18°C) and acetic acid; soluble in hydrochloric acid and caustic soda solution; also, soluble in alcohol, ammonium hydrosulfide and potassium sulfide.

Occurrence

Antimony trisulfide occurs in nature primarily as the mineral, stibnite, which consists of two parallel Sb4S6 chains linked together. It is used in fireworks; in certain types of safety matches; as a pigment in paints; and in the manufacture of ruby glass.

Uses

Antimony(III) sulfide is used as a red dye in rubber vulcanization. It is used as catalyst, additive, anti- blushing agent, heat stabilizer and used in the production of ruby-colored glass and in plastics as a flame retardant.

Uses

In pyrotechnics, Bengal fires; manufacture of ruby glass, matches, explosives; as a pigment in paints.

Uses

Antimony trisulfide is better known as the mineral stibnite and is used as a yellow paint pigment and in the manufacture of ruby glass, fireworks, and matches. It is also used to make percussion caps that set off explosives.

Preparation

The pure sulphide is obtained from its ore. Stibnite is separated from other ores by grinding and flotation. The ore is then heated to 550-600°C in a perforated vessel. The pure molten material is collected and cooled. It is also prepared by passing hydrogen sulfide into a solution of antimony trichloride:
2 SbCl₃ + 3 H₂S → Sb₂S₃ + 6 HCl
or treating antimony trichloride solution with sodium thiosulfate.
Alternatively, heating antimony metal or antimony trioxide with sulfur forms antimony trisulfide:2 Sb + 3 S → Sb₂S₃
2 Sb₂O₃ + 9 S → 2 Sb₂S₃ + 3 SO₂
All these above preparative methods yield amorphous antimony trisulfide.

Production Methods

Ores with more than 40 – 60 % Sb2S3 and free from lead and arsenic often are beneficiated by heating. Because stibnite, Sb2S3, has an unusually low melting point, 546 – 548 ℃, it can be separated from the gangue by melting (liquation). Stibnite more than 90 % pure is obtained and is referred to as crude antimony. It can be sold as such for producing antimony compounds, or it can be converted to antimony metal.
The commercial product should have a striated crystalline structure and a metallic gloss, and its color should be that of graphite. These properties are attained only if the molten antimony(III) sulfide is cooled very slowly. Ores with less than 40 – 45% Sb2S3 are unsuitable for liquation because the large amount of gangue interferes and too much antimony is retained in the residue.
The ore is best fed in the form of walnutsized lumps (1 – 4 cm). If the ore is too fine, the molten Sb2S3 does not flow. The most suitable temperature range is 550 – 660 ℃ because the volatilization of the Sb2S3 (bp 1000 ℃) is prevented, and liquation is successful. Liquation is carried out in a reducing atmosphere in crucibles or in reverberatory furnaces. The main impurities in crude antimony are arsenic, lead, and iron sulfide.

Hazard

Explosion risk in contact with oxidizing materials. Questionable carcinogen.

Flammability and Explosibility

Non flammable

Safety Profile

Poison by intraperitoneal route. Human blood and gastrointestinal system effects by inhalation. Questionable carcinogen. See also ANTIMONY COMPOUNDS and SULFIDES. Spontaneously flammable when exposed to strong oxidizers. Flammable when exposed to heat or flame. Moderately explosive by spontaneous reaction with chlorates, perchlorates, Cl0, thallic oxide. When heated to decomposition or on contact with acid or acid fumes it emits highly toxic fumes of oxides of sulfur and antimony. Will react with water or steam to produce toxic and flammable vapors.