Extracting Metals

Many objects we use in our everyday lives are made of metal. These metals are found trapped in rocks. So, we need to take the metals out from the rocks in order to use them to make useful objects.

As metals are stored in rocks within the Earth’s crust, we first need to dig up the rock in order to extract the metal.

  • It is important to note that the extraction of metal from rocks leads to environmental damage. This is partly because it involves the set up of large quarries, which can result in habitat loss. The machinery used also in the quarrying process contributes to global warming.

We must first extract a metal from an ore, which are rocks that contain extractable metals. You can’t actually see the metal in the ore as the metal has bonded to another element to form a compound.

Therefore, a chemical reaction is require to extract the metal from the ore. A method of extracting the metal from the compound is through a displacement reaction.

When looking at displacement reactions, it is important to remember the reactivity series, you can see this below:

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In black are the metals in order of most reactive at the top and least reactive at the bottom, while the non-metals are in red. Reactivity series are useful when looking at extracting metals.

Extracting Metals using Carbon

If you wanted to extract lead from lead oxide, you could react lead oxide with carbon, using carbon. This is possible because lead is less reactive than carbon.

Carbon and lead oxide would be heated in a heat chamber. You can see the equation below:

Lead oxide + carbon → Lead + Carbon dioxide

The lead that was initially within lead oxide swapped with carbon and is now separate from a compound. Lead is now on its own to be used and carbon dioxide is a product.

However, displacement reactions with carbon can only be used to extract metals that are less reactive with carbon. For example:

  • Zinc
  • Iron
  • Tin
  • Copper
  • Silver

The displacement reactions for these metals are:

  • Zinc oxide + carbon → Zinc + Carbon dioxide
  • Iron oxide + carbon → Iron + Carbon dioxide
  • Tin oxide + carbon → Tin + Carbon dioxide
  • Copper oxide + carbon Copper + Carbon dioxide
  • Silver oxide + carbon → Silver + Carbon dioxide

The metal oxide is in green and the separated metal is in red.

To extract gold, we don’t need a displacement reaction, as it is an unreactive metal. Gold is not found in a compound, you can find it by itself naturally.

Metals More Reactive than Carbon

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 instance, 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 reduced by reacting with. However, this does not work with all metals. If the metal is higher than carbon in the reactivity series (such as calcium), then a method called electrolysis will have to be used.

The metal will have to be less reactive than carbon, to use to carbon to extract the metal.