Covalent bonding Cryolite

The metal is produced on a massive scale by the Hall-Heroult method in which alumina, a non-electrolyte, is dissolved in molten cryolite and electrolyzed. The bauxite contains iron, which would contaminate the product, so the bauxite is dissolved in hot alkali, the iron oxide is removed by filtration, and the pure alumina then precipitated by acidification. Molten aluminum is tapped off from the base of the cell and oxygen evolved at the anode. The aluminum atom is much bigger than boron (the first member of group 3) and its ionization potential is not particularly high. Consequently aluminum forms positive ions AP. However, it also has non-metallic chemical properties. Thus, it is amphoteric and also has a number of covalently bonded compounds. 

Under the action of the mechanical forces developed during cryolitic treatment, the covalent or ionic chemical bonds suffer the mechano-cracking process, generating radicals, ions or combined particles... 

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