Aluminium by Hall–Héroult Electrolysis: Alumina in Molten Cryolite

Aluminium is won from alumina by electrolysis. Dissolve alumina in molten cryolite with a little aluminium fluoride at 940–980 °C and pass a low-voltage direct current from carbon anodes. Molten aluminium sinks to the bottom and is siphoned off; the anodes burn away as carbon dioxide. The cell also gives off hydrogen fluoride. The picture: our diagram of the cell.