For each substance listed below, explain its significance in extraction of aluminium.

Bauxite

• Extraction of Aluminium is done from its main ore Bauxite $({\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O})$. It is done by the electrolytic reduction technique.
• There is about $40-60\%$ alumia $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$ in bauxite ore.
• It also contains some impurities like Iron oxide(${\mathrm{Fe}}_2{\mathrm{O}}_3$), Silicon oxide(${\mathrm{SiO}}_2$) and Titanium oxide(${\mathrm{TiO}}_2$).
• These impurities are removed first to obtain alumina. Baeyer's process is used for this purpose.