Aluminium is the most plentiful metal in the earth’s crust. It is found in the form of aluminium oxide in an ore called bauxite. Alumina and bauxite are the two main raw materials in the aluminium making process. Aluminium is obtained by the electrolysis of alumina which extracts pure aluminium metal from alumina.
The production process:
- Aluminium production starts with the raw material bauxite, a clay-like soil. It is mined in Queensland and the Northern Territory.
- Alumina, or aluminium oxide, is extracted from the bauxite through refining.
Alumina is separated from the bauxite by using a hot solution of caustic soda and lime. The alumina mixture is heated and filtered and the remaining alumina dried to a white powder. Alumina is transported by ship to the specially designed berth in the Port of Newcastle before being taken to the smelter to be made into aluminium metal. Australia is the world’s leading producer of both Bauxite and Alumina, accounting for approximately 20%
- of global Alumina and 30% of global Bauxite.
- At the aluminium plant like Tomago, three different raw materials are needed to make aluminium – alumina, electricity and carbon.
The aluminium production takes place in the potlines. Tomago Aluminium has three enormous pot lines on site with 840 pots in total. A substation on-site supplies electricity to the pots which are connected electrically so a current flows through one pot onto the next. The electricity reacts with the anodes (a black carbon block that lines each pot) and causes the alumina to separate into its constituent elements – aluminium and oxygen.The liquid aluminium is then siphoned from the pots using a method called tapping. The liquid metal is carried to the casthouse in ladles on top of specially designed vehicles.
At the casthouse impurities are removed and alloying elements such as magnesium and silicon are added according to its final use. Properties such as strength, corrosion resistance and surface quality are manipulated by this final chemical composition.
The liquid aluminium is cast into extrusion ingots, sheet ingots or foundry alloys, depending on what it will be used for.