Bauxite → Bayer's process → pure Al2O3 → Hall-Heroult electrolysis. Al2O3 is dissolved in molten cryolite Na3AlF6 (lowers m.p. from 2345 K to ~1240 K). Some CaF2 added for fluidity. Cathode (carbon lining): $Al^{3+}$ + 3$e^-$ → Al(l) (collected at bottom). Anode (graphite rods): 2$O^{2-}$ → O2 + 4$e^-$; then O2 + C → CO/CO2 (graphite anode is consumed — must be replaced periodically). Cryolite is essential: (1) lowers melting point, (2) increases conductivity, (3) acts as solvent for Al2O3. The process is extremely energy-intensive (~15 kWh/kg Al) — aluminium smelters are located near cheap hydroelectric power.