Choosing the Method of Extraction
- The position of the metal on the reactivity series determines the method of extraction.
- Higher placed metals (above carbon) have to be extracted using electrolysis as they are too reactive and cannot be reduced by carbon.
- Lower placed metals can be extracted by heating with carbon which reduces.
- The process is very expensive as large amounts of energy are required to melt the ores and produce the electrical current.
- The reactivity series of metals is shown below with the corresponding method of extraction.
The Extraction of Aluminium
Extraction of Aluminium by Electrolysis
Diagram Showing the Extraction of Aluminium by Electrolysis
Aluminium Ore (Bauxite)
The bauxite is first purified to produce aluminium oxide Al2O3. Aluminium Oxide has a very high melting point so it is first dissolved in molten cryolite producing an electrolyte with a lower melting point, as well as a better conductor of electricity than molten aluminium oxide. This reduces expenses considerably making the process more efficient.
The electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000 °C. The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell. The cell operates at 5-6 volts and with a current of 100,000 amps. The heat generated by the huge current keeps the electrolyte molten. A lot of electricity is required for this process of extraction which is a major expense.
The overall equation is:
2Al2O3(l) ⟶ 4Al(l) + 3O2(l)
Reaction at the Negative Electrode:
The Aluminium melts and collects at the bottom of the cell and is then tapped off:
Al3+ + 3e– ⟶ Al
Reaction at the Positive Electrode:
2O2- – 4e– ⟶ O2Some of the oxygen produced at the positive electrode then reacts with graphite (Carbon) electrode to produce carbon dioxide gas:
C(s) + O2(g) ⟶ CO2(g)This causes the carbon anodes to burn away, so they must be replaced regularly.
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Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.