Q.What is the role of cryolite in the metallurgy of aluminium?

In aluminium metallurgy cryolite (Na3AlF6) lowers the fusion temperature of alumina and increases the conductivity of the melt.

Aluminium is extracted by the Hall-Heroult process, which is the electrolysis of purified alumina (Al2O3). Pure alumina melts at a very high temperature (about 2050 C), which is impractical and costly to maintain for electrolysis.

To overcome this, alumina is dissolved in molten cryolite (Na3AlF6), usually along with some fluorspar (CaF2). The roles of cryolite are:

1. It lowers the melting point of the electrolyte mixture to about 950 C, so a much lower operating temperature is possible.
2. It makes the fused mass a good conductor of electricity, allowing electrolysis to proceed efficiently. …