The Hall- Heroult process is an example of Aluminium smelting process and is used industrially.Aluminium cannot be produced by an aqueous electrolytic process because hydrogen is electrochemically much nobler than aluminium. Thus, liquid aluminium is produced by the electrolytic reduction of alumina (Al2 O3) dissolved in an electrolyte (bath) mainly containing Cryolite (Na3AlF6).
Aluminium is formed at about 900°C, but once formed has a melting point of only 660°C. In some smelters this spare heat is used to melt recycled metal, which is then blended with the new metal. Recycled metal requires only 5 percent of the energy required to make new metal. Blending recycled metal with new metal allows considerable energy savings, as well as the efficient use of the extra heat available. When it comes to quality, there is no difference between primary metal and recycled metal.
The smelting process required to produce aluminium from the alumina is continuous, the potline is usually
kept in production for 24 hours a day year around. A smelter cannot be easily stopped and restarted. There are two basic technology- Prebaked Technology and Soderberg Technology. In prebaked technology the anodes used are termed as prebaked anodes which are made from a mixture of petroleum coke, aggregate and coal tar pitch binder moulded into blocks and baked in separate anode
baking furnace at about 1120 °C. An aluminium rod with iron studs is then cast or rammed into grooves in the top of the anode block in order to support the anode and conduct the electric current to the anode when it has been positioned in the cell.