Cryolite is also known as sodium hexafluoroaluminate or sodium aluminum fluoride. Its molecular formula is Na3AlF6. It is a small white crystal with no smell. Its solubility is greater than that of natural cryolite. Its specific gravity is 3, hardness is 2-3, melting point is 1000 ℃, and it is easy to absorb water and moisture.

Cryolite is mainly used as flux for aluminum electrolysis, wear-resistant filler for rubber and grinding wheel, enamel opal, glass shading agent and metal flux, pesticide for crops, etc.

At present, cryolite production at home and abroad mainly includes the following processes:

Hydrofluoric acid method: it can be divided into dry method and wet dry method. The gaseous hydrofluoric acid reacts with aluminum hydroxide at 400 ~ 700 ℃ to produce fluoroaluminic acid (h3alf6), and then reacts with soda ash at high temperature. The wet method is prepared by reacting 40 ~ 60% hydrofluoric acid with aluminum hydroxide and then adding soda ash.

Fluorosilicic acid method: it can be divided into ammonium fluoride intermediate product method and sodium fluorosilicate intermediate product method. The former is formed by ammoniating fluorosilicic acid with ammonia and reacting with sodium aluminate. The latter is prepared by recovering sodium fluosilicate from the fluorine-containing waste gas in the production of phosphate fertilizer, and then ammoniating and synthesizing.

Carbonation method: cryolite can also be prepared by adding carbon dioxide in sodium aluminate and sodium fluoride solution.

Aluminum industry recovery method: the dilute hydrofluoric acid recovered from the waste gas of aluminum smelting production reacts with sodium aluminate to recover cryolite.

Alkali method: it is obtained by reacting soda ash, fluorspar and silica sand with aluminum sulfate after roasting, crushing and leaching. It is rarely used in industry.