HallHéroultprosessin

The HallHéroult process is the primary industrial method for producing aluminum. It was developed independently by Charles Martin Hall in the United States and Paul Héroult in France in 1886. This electrolytic process involves dissolving alumina (aluminum oxide) in molten cryolite (sodium aluminum fluoride) and then passing an electric current through the solution.

Alumina is first purified from bauxite ore. The purified alumina is then mixed with molten cryolite, which acts as a solvent, lowering the melting point of alumina and allowing for a more energy-efficient electrolysis. The mixture is contained within a large steel or carbon-lined cell, which serves as the cathode. Carbon anodes are suspended in the molten electrolyte.

When a strong direct electric current is passed through the cell, the alumina ($Al_2O_3$) is decomposed. Aluminum ions ($Al^{3+}$) are attracted to the cathode (the cell lining), where they gain electrons and are reduced to molten aluminum metal. Oxygen ions ($O^{2-}$) are attracted to the anodes, where they react with the carbon anodes to form carbon dioxide ($CO_2$) gas, which escapes. This reaction consumes the carbon anodes over time, requiring their periodic replacement. The molten aluminum, being denser than the electrolyte, collects at the bottom of the cell and is periodically tapped off. The HallHéroult process is highly energy-intensive due to the large amounts of electricity required for electrolysis.