Extraction of Metals

Most metals are too reactive to exist pure in nature, so they are found combined with oxygen or sulfur as ores. Getting the metal out means removing the oxygen - this is reduction. Only very unreactive metals like gold and platinum are found native (already pure).

Where a metal sits in the reactivity series decides how hard it is to free. Metals below carbon can be reduced by heating with carbon - cheap and common. Metals above carbon hold their oxygen too tightly for carbon, so they need electrolysis.

Iron oxide is reduced by carbon monoxide in a blast furnace. Coke burns to carbon monoxide, which strips the oxygen from the ore: Fe2O3 + 3CO gives 2Fe + 3CO2. Limestone removes sandy impurities as slag.

Aluminium is above carbon, so it must be extracted by electrolysis of molten aluminium oxide. The oxide is dissolved in molten cryolite to lower the melting point and save energy. Aluminium forms at the negative cathode; oxygen at the positive anode.