How is aluminium extracted using electrolysis?

Aluminium is extracted from its ore, bauxite, through a process called electrolysis in a cell known as a Hall-Héroult cell.

In more detail, the extraction of aluminium involves several steps. Firstly, the bauxite ore is purified to produce aluminium oxide, a white powder from which aluminium can be extracted. This is done through a process called the Bayer process. The aluminium oxide is then dissolved in molten cryolite, an aluminium compound with a lower melting point than aluminium oxide. The mixture is heated to around 950°C, which is still below the melting point of aluminium, but enough to dissolve the aluminium oxide.

The molten mixture is then subjected to electrolysis in a cell known as a Hall-Héroult cell. This cell consists of a steel container lined with carbon, which acts as the cathode (negative electrode). Carbon anodes (positive electrodes) are dipped into the molten mixture. When electricity is passed through the cell, the aluminium ions are attracted to the cathode, where they gain electrons and are reduced to aluminium atoms. These atoms then pool at the bottom of the cell, where they can be tapped off as pure aluminium.

The oxygen ions move towards the carbon anodes, where they lose electrons and are oxidised to form oxygen gas. This reaction is exothermic and helps to maintain the high temperature needed for the process. The oxygen gas reacts with the carbon anodes to form carbon dioxide, which is released into the atmosphere. This is one of the environmental issues associated with the extraction of aluminium.

Overall, the extraction of aluminium is a complex process that involves several stages, including the purification of bauxite, the dissolution of aluminium oxide in molten cryolite, and electrolysis in a Hall-Héroult cell.