Using Electrolysis to Extract Metals (AQA GCSE Chemistry)

• 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
• Electrolysis 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

Metal Extraction Methods Summary Table

• Aluminium is extracted on a large scale using electrolysis:

Diagram showing the extraction of aluminium by electrolysis

Raw Materials:

• Aluminium Ore (bauxite)
• Cryolite (sodium aluminium fluoride)

Explanation:

• 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 the costs 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 (g)

• Some of the oxygen produced at the positive electrode then reacts with the 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