How metals are extracted depends on their position in the reactivity series. The table below shows the reactivity series of metals and the method of extraction for each metal.
Reactive metals readily form compounds with other elements in the Earth’s crust. An ore is a rock that contains enough metal to make it economically viable to extract the metal. Many ores contain metal oxides, while metal sulfides and metal carbonates are also common.
The process of extracting a metal often involves removing the oxygen to obtain the pure metal. This is reduction, as it involves the loss of oxygen. So, metal oxides are often reduced to obtain pure metals.
Two common examples of oxide ores are:
The extraction of metals depends on their reactivity. A metal that is less reactive than carbon can be extracted by heating it with carbon. As carbon is more reactive, it will displace the metal from the oxide. This process forms a pure metal.
For example, heating copper(II) oxide with carbon will produce molten copper and carbon dioxide, as shown in the equation:
Copper oxide + Carbon → Copper + Carbon dioxide
2CuO (s) + C (s) → 2Cu (l) + CO2 (g)
Another key example is the extraction of pure iron from iron(III) oxide by heating it with carbon. The iron(III) oxide solids are reduced to molten iron, and the reaction also forms carbon monoxide, as shown in the equation:
Iron(III) oxide + Carbon → Iron + Carbon monoxide
Fe2O3 (s) + 3C (s) → 2Fe (l) + 3CO (g)
The carbon monoxide (CO) can be oxidised further to produce carbon dioxide, which is less harmful when inhaled.
Extracting metals by heating them with carbon is more cost-effective than using electrolysis. However, if a metal is more reactive than carbon, it cannot be reduced by carbon. In this case, the metal has to be extracted using electrolysis.
Unreactive metals, such as gold and silver, are found in the Earth’s crust as pure metals. This is because they do not easily react with other substances, so they can be mined directly from the Earth’s crust.