Welcome to histalu.orgThe site for the history of aluminium
Primary aluminium is obtained by electrolysis of alumina according to the process discovered in 1886, at the same time but independently of each other, by the American Charles Martin Hall and the French scientist Paul Héroult.
It remains today the only process used in the world. While the principles of its operation have not changed, its qualitative and quantitative performance has increased dramatically.
The process consists in reducing alumina through electrolysis, whereby it is dissolved in a bath of cryolite (double fluoride of aluminium and sodium – AlF3, 3NaF) molten at around 950°C, in a tank through which a high-intensity electric current passes.
When subjected to the action of the direct electric current (where the electrical current always travels in the same direction), the ions are transported to the two electrodes.
The positive electrode, the anode, where the current enters, attracts negative ions, oxygen (O--). The anode is placed at the top of the crucible where the electrolysis takes place; oxygen can thus be released in the form of gaseous CO2, after having burned the carbon which constitutes the anode.
The negative electrode, the cathode, through which the current leaves, attracts the positive ions, the aluminium (Al+++). The cathode is located at the bottom of the crucible where the aluminium heavier than the bath is deposited and remains in the form of a liquid layer.
The global phenomenon results in the reaction: 2 Al 2 O 3 + 3 C = 4 Al + 3CO 2
The liquid aluminum metal settles at the bottom of the tank during electrolysis. It is regularly removed by siphoning into a ladle and taken to the foundry to be treated and shaped.
From there, it will be transported to processing plants
Discover the aluminium transformation process
