Many objects that we use in our everyday lives are made of metal. These metals are found trapped in rocks within the Earth’s crust. Mining techniques are used to extract the metal containing the desired metal. After this, the metals are extracted from the rocks. This process is called quarrying.
Extracting metals from rocks can lead to environmental damage. It involves the set-up of large quarries, which can result in the loss of natural habitats. The machinery used in the quarrying process also contributes to global warming.
An ore is a naturally occurring rock that contains a valuable metal or mineral that can be extracted. To extract a metal from its ore, a chemical reaction is necessary to separate the metal from other elements present in the ore.
One method of achieving this is through a displacement reaction. The reactivity series arranges elements by their relative reactivity. It is important to consider the reactivity series when using displacement reactions to extract metals, which is shown in the diagram below.
In black are a series of metals in order, with the most reactive at the top and the least reactive at the bottom. The non-metals are in red.
To extract lead from lead oxide, you can react lead oxide with carbon in a heat chamber. This is possible because lead is less reactive than carbon.
Lead oxide + carbon → Lead + Carbon dioxide
The lead oxide went through a process in which it exchanged its lead atoms with carbon atoms. This separated lead from the compound and produced carbon dioxide.
However, displacement reactions with carbon can only be used to extract metals that are less reactive with carbon. For example:
The displacement reactions for these metals are:
The metal oxide is in green and the separated metal is in red.
As gold is unreactive, it can be found naturally in its pure form, instead of in a compound. So it does not require a displacement reaction for extraction.
As outlined above, metals have to be separated from their oxides.
For example, iron may need to be separated from iron oxide. This process is also called reduction, which is carried out using carbon. In this case, the oxide is reacted with carbon to form the metal required, as well as carbon dioxide.
If the element is below carbon in the reactivity series (such as zinc and iron), then it can be extracted by reacting its compound with carbon. However, this does not work with all metals. If the metal is higher than carbon in the reactivity series (such as calcium), then it will require electrolysis for extraction.