Cryolite

The chemical name of cryolite is sodium hexafluoroaluminate and its chemical formula is Na3AlF6. It's a rare mineral associated with the once-large deposit at Ivittuut on Greenland's west coast, which was depleted by 1987. Cryolite, sodium aluminium fluoride, is a colourless to white halide mineral. It's found in large quantities in Ivigtut, Greenland, and in small amounts in Spain, Colorado, and other places. 

It is used as a solvent for bauxite in the electrolytic production of aluminium and has various other metallurgical applications, and it is used in the glass or ceramic industries and enamel factories, inbounded abrasives as filtering membranes, and in the manufacture of insect-killing chemicals (insecticides). A huge amount of synthetic or artificial cryolite is made from fluorite.

On this page, we have covered all the important topics related to cryolite like cryolite meaning, its uses, properties, and its ore. Let us discuss the cryolite meaning, cryolite meaning indicates that it is a mineral of aluminium and fluoride.

Properties of Cryolite

• Cryolite occurs in a monoclinic crystal state.

• The cryolite is whitish glassy in colour.

• The hardness of cryolite in the moh scale is 2.5 to 3.

• The specific gravity of cryolite is 2.95 to 3.

• Cryolite is transparent to translucent to transparent in nature due to which its refractive index is very low.

• Cryolite is invisible in nature, due to a similar refractive index.

• Cryolite as the essential component of the electrolyte (85 – 90 %) decreases the temperature of the smelting flux electrolysis.

Cryolite Lattice Structure

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The above figure represents the cryolite unit cell structure. In the above-shown figure, the arrangement of sodium atoms is shown by the purple colour. Fluorine atoms are shown by pale green colour. Fluorine atoms are arranged in an octahedral form around the sodium metal ion.

What are the Cryolite Ores?

Cryolite is a salt of sodium aluminium hexafluoride. It is represented as Na3AlF6. It consists of Aluminium, Sodium and Fluorine. It can be synthesized by the given reaction.

H2SiF6 + 6 NH3 + 2H20 → 6NH4F + SiO2

6NH4F + 3NaOH + Al(OH)3 → Na3AlF6+ 6NH3 + 6 H2O

Cryolite ores are the chief ore of aluminium. These cryolite ores are associated with the earthy material, these earthy materials are known as gangue.  

Cryolite Uses

• Cyolite plays an important role in the metallurgy of cryolite. It helps in making alumina a good conductor of electricity. 

• It helps in lowering the melting point of alumina.

• Cryolite is used in manufacturing aluminium waste.

• Cryolite is used as a flux in steel aluminization and in welding technology.

• Cryolite is used as additives in abrasives.

• Cryolite is used in the remelting of metals.

What is Synthetic Cryolite?

Synthetic cryolite is a crystalline white powder made of hydrofluoric acid, sodium carbonate, and aluminium. Since it essentially lowers the melting point of alumina, synthetic cryolite is mainly used as a flux in the electrolytic processing of aluminium. Cryolite is used in the ceramic industries and enamel coating industries as a filler, in compounded abrasives as a filler, in the synthesis of sodium salts and aluminium salts, porcelaneous glass, and pesticides and insecticides. Cryolite is a relatively safe insecticide for fruits and vegetables. Many iron, calcium, and magnesium-containing enzymes are inhibited by fluoride.

Types of Synthetic Cryolite

1. Sodium cryolite

2. Potassium cryolite

Let us discuss these synthetic cryolites one by one.

Sodium Cryolite

Sodium Cryolite salts are used as a solvent for bauxite in the electrolytic processing of aluminium; other metallurgical uses include foundry additives for aluminium foundries, sleeves, and cover flux; filler for bonded abrasives in the glass and enamel industries; and insecticide manufacturing.

Potassium Cryolite

Potassium Cryolite (K3AIF6) is utilised for the synthesis of welding agents, blasting agents (a large amount of energy-producing agents), pyrotechnics, and abrasives materials. KAlF4 and K3AlF6 are the chemical formulas for potassium cryolite. Potassium fluoroaluminate, Potassium tetrafluoroaluminate, Potassium Cryolite, Kalium Aluminium Fluoride, KAlF, KAlF4, and K3AlF6 are some of the other names for potassium cryolite.

Extraction of Aluminium Using Cryolite 

The Hall–Héroult process is the most popular industrial smelting method for aluminium. It entails dissolving aluminium oxide (alumina) in molten cryolite aluminium and electrolysing the molten salt bath, usually in a purpose-built cell, which is obtained most often from bauxite, aluminium's chief ore, via the Bayer process. At 940–980 °C, the Hall–Héroult process produces 99.5–99.8 percent pure aluminium on an industrial scale. Since recycled aluminium does not require electrolysis, it is not used in this process. By emitting carbon dioxide, this process contributes to climate change. 

Sodium cryolite is a key component of the HallHeroult process, which uses an electrolyte to produce aluminium (Na3AlF6). Al2O3 has a very high melting point and is very soluble. Any addition to the molten sodium cryolite (typically AlF3, CaF2, MgF2) lowers the electrolyte liquidus temperature as well as the alumina solubility. Despite this, the operating temperature of aluminium electrolysis remains high (950-960 °C), which is a critical factor in increased fluoride corrosion operation. The inability to use new constructional materials in conventional sodium electrolytes, such as non-consumable anodes, piques interest in finding new low-melted electrolytes.

Did You Know?

• Cryolite is a scarce mineral. It consists of sodium fluoride bonds and aluminium fluoride bonds.

• On immersing it in water, it becomes invisible. Due to its similar refractive properties with water, it becomes invisible, although it does not dissolve.

• Cryolite minerals are found in vast quantities in Greenland.

• Nowadays, cryolite mineral is manufactured artificially from the fluorite.