Raw Materials for Aluminium
Bauxite is a mixture of aluminium oxide and iron oxide and it is the primary source of aluminium. When mixed with Caustic Soda and heated under pressure (Bayer process) it becomes Aluminium Hydroxide, which after washing and heating (calcining) converts into pure aluminium oxide called Alumina. Electrolysis transforms alumina into aluminium; this is a smelting process that involves two metal electrodes being submerged into a molten material containing positive and negative ions, one electrode is a positive terminal (anode) and the other electrode is a negative terminal (cathode). Baked Anodes are made from the mixture of Calcined Petroleum Coke (made by calcination of Green Petroleum Coke ) and binding material called Coal Tar Pitch. Alumina is dissolved into molten cryolite at 1,000 degrees C. Cryolite (Crushed Bath) and Aluminium Fluoride are added to lower the temperature of the electrolysis and to increase the conductivity of the molten material in the cell (pot). When electrical current passes through the molten material at the cathode end aluminium ions are reduced to aluminium metal and at the anode end carbon is oxidized to form carbon dioxide gas. Finally molten aluminium sinks to the bottom of the pot and is drained through a plug.