Metals that are more reactive than carbon are extracted using electrolysis. One example is aluminium, which is a low-density metal and is extracted on a large scale using electrolysis.
To extract aluminium from its ore (bauxite), the ore is first purified to produce aluminium oxide (Al2O3).
For the electrolysis process, electrolytes must be either dissolved in water or in an ionic state. However, aluminium oxide is insoluble in water and has a very high melting point. So instead, powdered aluminium oxide is dissolved in a compound called cryolite, which produces an electrolyte with a lower melting point.
This significantly reduces the amount of energy required for the process, which reduces costs. However, it still takes a large amount of energy to melt the cryolite.
The electrodes are made of graphite, which is a form of carbon. Graphite is a great conductor of electricity and it has a high melting point. This allows us to use it at high temperatures without it melting.
During the process:
So, the overall equation for the reaction is:
2Al2O3 (l) ⟶ 4Al (l) + 3O2 (g)
Some of the oxygen reacts with the graphite (carbon) anode to form carbon dioxide.
C (s) + O2 (g) ⟶ CO2 (g)
If you’re taking a Higher paper, it’s important to remember the half equations involved in the process of aluminium extraction.
The overall equation for the process of aluminium extraction is 4Al³⁺ + 6O²⁻ → 4Al + 3O2. This shows that aluminium ions and oxide ions combine to produce aluminium metal and oxygen gas.
While electrolysis is a useful method for extracting certain metals, it does have some disadvantages. The main disadvantage is that it requires large amounts of electricity to extract metals from their ores. As a result, the costs of electricity can be very high, making the process expensive.
Another issue is that the ores need to be in a molten form to conduct electricity for electrolysis. This means that the ores must be melted, which can be a costly process. However, for the extraction of aluminium, the use of molten cryolite helps to reduce the melting point of aluminium oxide (Al2O3). This helps to reduce energy consumption costs.
The reduction method of extracting metals using carbon is much cheaper. Carbon is a cheap and readily available material that also acts as a fuel to provide the energy (heat) needed for metal extraction. This makes the process of metal extraction more affordable.
Metals that are lower in the reactivity series are generally cheaper to extract than metals that are higher in the series. This is because they require less energy and resources to extract.