Na3AlF6

Na3AlF6, commonly known as cryolite, is a fluoride compound that occurs both as a natural mineral and as a synthetic material. Its formula is Na3AlF6. In nature cryolite forms as a rare halide mineral and was historically mined in Greenland; industrially it serves as a flux and electrolyte in aluminum production because it lowers the melting point of alumina and improves the conductivity of the molten salt.

Natural cryolite deposits were once a major source of aluminum ore, notably at Ivittuit in Greenland. Today, virtually all cryolite used in industry is synthetic, produced to provide a stable and impurity-controlled electrolyte for aluminum smelting.

Physically, cryolite has a relatively low melting point for a fluoride compound, around 1012 C for the pure substance. In an alumina-containing bath, cryolite-based electrolytes melt at roughly 900–1000 C and enable dissolution of alumina for electrolysis in the Hall-Héroult process. The presence of cryolite lowers both the operating temperature and the electrical resistance of the bath, reducing energy consumption.

Safety and handling: fluoride compounds are toxic and corrosive. Handling cryolite requires appropriate engineering controls, personal protective equipment, and good hygiene to avoid inhalation or ingestion hazards and skin contact.

Synthesis: since the early 20th century, most industrial cryolite is synthesized rather than mined from natural deposits, produced by processes that combine fluoride sources with aluminum-containing materials to yield Na3AlF6 for use as an electrolyte.