Extracting Metals
Applied Science: BTEC Level 3 National Extended Diploma, topic 4.2.5
Extraction of Metals
Most metals are only found as compounds because the metal has reacted with other elements in the past. Because of this, the metal has to be extracted from the ore (rock) where the metal compound is found.
Carbon - why
- Metals that are less reactive than carbon can be extracted from their oxides (compounds with oxygen) by reducing with carbon.
- Carbon is used because it is cheap and abundant.
Carbon - how
- In the reduction, the metal oxide loses oxygen to form a pure metal.
- Reduction with carbon normally involves heating the metal oxide in the presence of the carbon, which is often used in the form of coal.
Electrolysis - Extracting Metals
Electrolysis is used to extract reactive metals from molten ores (melted materials containing metals). It is used to extract metals such as aluminium, which are more reactive than carbon.
Process
- Powdered aluminium ore (Al2O3) is first mixed with another aluminium salt called cryolite.
- This mixture has a lower melting point than pure Al2O3. This makes it cheaper as less energy is needed to melt the powder.
- Once molten, a large voltage is applied.
At the cathode (negative electrode)
- The aluminium is formed at the cathode.
At the anode (positive electrode)
- Carbon dioxide is formed at the anode.
- The anode is usually made of carbon because it is a good conductor and is cheap.
Disadvantages
- Lots of energy is needed to:
- Melt the solid ionic compound to allow the ions to flow.
- To produce the electrical current.
- All this energy costs money, and a lot of it!
Test yourself on Extracting Metals
What type of reaction is used when extracting metals using carbon?
Why is carbon used to extract metals from their oxides?
Why are zinc, iron, and copper commonly extracted from their oxides by reduction with carbon?
Why can't potassium be extracted from its compounds by reduction with carbon?
What aspects of using electrolysis to extract metals need lots of energy?