Iron oxide is an ore of iron. It contains oxygen in addition to iron. The oxygen is removed by heating the ore with charcoal or coke. At high temperatures, the oxygen combines with carbon to form carbon monoxide and carbondioxide.
Other impurities are removed as slag and iron is obtained.
Smelting consists of two main processes.
Roasting
Roasting is the process in which the ore is thermally decomposed into simpler compounds, usually oxides of the metal.
Reduction
This is the process in which oxygen is removed from the oxide are removed to obtain the elemental metal.