Barium sulfate (or sulphate) is an inorganic compound with the chemical formula BaSO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs naturally as the mineral barite, which is the primary commercial source of barium and materials derived from it. It occurs naturally as the mineral barite or baryte, which is abundant and found all over the world.
Barium sulfate is useful in a variety of industries. Its main applications make use of its white opaque appearance and high density. It is chemically stable under normal conditions and does not react with most chemicals.
Properties
- Chemical formula: BaSO4
- Molar mass: 233.39 g/mol
- Appearance: white crystalline
- Odor: odorless
- Density: 4.49 g/cm3
- Melting point: 1,580 °C (2,880 °F; 1,850 K)
- Boiling point: 1,600 °C (2,910 °F; 1,870 K) (decomposes)
- Solubility in water: 0.2448 mg/100 mL (20 °C); 0.285 mg/100 mL (30 °C)
- Solubility product (Ksp): 1.0842 × 10−10 (25 °C)
- Solubility: insoluble in alcohol, soluble in concentrated, hot sulfuric acid
Production
Almost all of the barium consumed commercially is obtained from barite, which is often highly impure. Barite is processed by thermo-chemical sulfate reduction (TSR), also known as carbothermal reduction (heating with coke) to give barium sulfide:
BaSO4 + 4 C → BaS + 4 CO
In contrast to barium sulfate, barium sulfide is soluble in water and readily converted to the oxide, carbonate, and halides. To produce highly pure barium sulfate, the sulfide or chloride is treated with sulfuric acid or sulfate salts:
BaS + H2SO4 → BaSO4 + H2S
This type of barium sulfate is known as blanc fixe, which translates to “permanent white” in French. Blanc fixe barium is the type of barium found in consumer products such as paints.
Barium sulfate is created in the laboratory by combining solutions of barium ions and sulfate salts. Due to the insolubility of barium sulfate, the least toxic salt of barium, wastes containing barium salts are sometimes treated with sodium sulfate to immobilize (detoxify) the barium. One of the most insoluble salts of sulfate is barium sulfate. Its low solubility is used as a test for Ba2+ ions as well as sulfate in qualitative inorganic analysis.
Applications
- Medical Imaging: It is commonly used in medical imaging, such as barium meals, barium enemas, and barium swallow tests.
- Oil and Gas Industry: It is used as a weighting agent in drilling fluids in the oil and gas industry.
- Paints and Coatings: It is used as a filler in some paints and coatings to enhance opacity and provide a smooth finish.
- Plastics: It is used as a filler in certain plastics to improve mechanical properties.
- Pigment Extender: It is used as a pigment extender in the production of certain pigments.
- Paper Industry: It is used in the paper industry to improve brightness and smoothness.
Toxicity
While barium sulfate itself is relatively non-toxic, ingestion of large amounts of soluble barium compounds can be harmful. However, the low solubility of barium sulfate makes it less toxic compared to other barium compounds.
