What happens to aluminium oxide when it is dissolved in cryolite?

When aluminium oxide is dissolved in cryolite, one of the primary effects is a reduction in the melting point of the resulting mixture. This is significant for industrial processes, particularly in aluminium smelting.

Aluminium oxide, by itself, has a very high melting point, making it difficult and energy-intensive to extract aluminium metal from its ore via electrolysis when using only pure aluminium oxide. Cryolite (Na3AlF6) is added because it acts as a solvent, allowing aluminium oxide to dissolve and thereby creating a lower melting point mixture. This means that the process can occur at much more manageable temperatures, improving efficiency and reducing energy costs.

This lowering of the melting point is crucial for the Hall-Héroult process, which is the primary method for extracting aluminium. It enables the electrolytic reduction of aluminium oxide to occur more easily, as the mixture becomes molten at a temperature that is feasible for current industrial technology.