Australia is the world’s sixth largest producer of aluminium and has 4 operating smelters. As electricity is a key input in aluminium smelting, smelters are usually located in areas with reliable, historically low-cost electricity.
The Australian industry continuously focuses on improving electricity efficiency, while also leading the global industry in controlling direct greenhouse gas emissions.
The Hall- Héroult process is the main method of smelting aluminium used today and consists of five steps:
- adding bath and alumina;
- tapping; and
- primary casting.
Adding Bath and Alumina
Inside a pot, alumina is dissolved in a “bath” of molten cryolite (sodium aluminium fluoride) and other materials.
A pot is a large rectangular cell, lined with carbon blocks and insulating bricks. This lining forms the “cathode”.
A potline is a long building, or collection of buildings, which contain a series of “pots”, or large electrolytic cells, in which aluminium is made.
Anodes are used to conduct electricity into the smelting cells/pots in the pot room. Anodes are consumed in the smelting process and the remaining portions (known as butts) are recycled.
Anodes are attached to rods and suspended into the electrolytic cells in the pot room where they are slowly consumed in the aluminium smelting process.
Carbon anodes, made from petroleum coke and pitch, are often manufactured on site.
A high electric current is passed through pots via the anode. The current flows continuously from the anode (positive) through alumina/cryolite mix to the lining of the pot (negative) and then onto the next pot.
Electricity maintains the temperature of the process at about 950°C and enables the alumina to split into aluminium and oxygen.
At regular intervals the molten aluminium is tapped from the pots and transported to the casthouse.
The molten aluminium is cast at a temperature of just over 700°C to form ingots, slabs, billots and t-bars.