Hall's process is based on the electrolysis of

The production of aluminium by Hall's process was one of the earliest applications of electrolysis on a large scale, and is still the major method for obtaining that very useful metal. The process was discovered in 1886 by Charles M. Hall. Aluminium  is very reactive and therefore difficult to reduce from its compounds by chemical means. On the other hand, electrolysis of a molten aluminium salt or oxide is difficult because the salts are hard to obtain in anhydrous (dry) form and the oxide, Al₂O₃, does not melt until 3,762°F (2,072°C). Hall discovered that Al₂O₃, in the form of the mineral bauxite, dissolves in another aluminium mineral called cryolite, Na₃AlF₆, and that the resulting mixture could be melted fairly easily. When an electric current is passed through this molten mixture, the aluminium ions migrate to the cathode, where they are reduced to metal. At the anode, oxide ions are oxidised to oxygen gas.