HallsHéroultprosessen

The Halls Héroult process is the primary method used for the industrial production of aluminum. It was independently developed by Charles Martin Hall in the United States and Paul Héroult in France in 1886. The process relies on the electrolysis of alumina (aluminum oxide) dissolved in molten cryolite (sodium aluminum fluoride). Alumina is first purified from bauxite ore through the Bayer process.

In the Halls Héroult process, alumina is dissolved in a cryolite bath at temperatures around 950-1000 degrees Celsius. This molten mixture is contained within large steel cells lined with carbon. Carbon anodes, also made from baked carbon, are submerged into the molten cryolite. A strong electric current is passed through the cell. At the cathode (the carbon lining of the cell), aluminum ions are reduced to molten aluminum metal, which collects at the bottom of the cell. At the anode, oxide ions react with the carbon anodes, producing carbon dioxide gas and consuming the anodes over time.

The molten aluminum is periodically siphoned from the cells and cast into ingots. The carbon anodes are replaced as they are consumed. The energy requirements for the Halls Héroult process are substantial, making electricity cost a significant factor in aluminum production. Despite its energy intensity, the process remains the most economically viable and widely used method for producing primary aluminum due to its efficiency and the abundance of bauxite.