The majority of metals do not occur native and, instead, are compounds like sulphides or oxides. These compounds are called minerals and a rock which contains a mineral is known as an ore.

Metals can be extracted from ores using a range of methods. The best technique to use depends on:

• if the method will extract the metal successfully (which depends on how reactive the metal is)
• the cost of the reactants (which varies widely)
• the level of purity required and the cost of purification methods
• the amount of energy used by the process (with high temperatures and electrolysis using high amounts)
• the efficiency with which the metal can be produced and the amounts involved
• the environmental considerations involved

Methods include:

• Extraction of iron: reduction of metal oxides with carbon.
• Extraction of titanium: reduction of metal halides with other more reactive metals.
• Extraction of aluminium: electrolysis of the metal ore.
• Extraction of tungsten: reduction of the metal oxide with hydrogen.

All these methods involve expensive extraction processes and the ore supply is finite. This is why metal recycling is essential.

——————————————————

Sulphide Ores

Sulphide ores need to be converted into their oxide first because they cannot be converted into a metal directly. This is carried out by roasting them in air:

• 2ZnS + 3O₂(g) ? 2ZnO(s) + 2SO₂(g)
• 2PbS + 3O₂(g) ? 2PbO(s) + 2SO₂(g)

The problem with this method is that a lot of sulphur dioxide is created: a major cause of acid rain. However, it is possible to contain the sulphur dioxide before it is released and then using it to produce sulphuric acid.