Extracting iron and copper

Ores

Unreactivemetals such as gold are found in the Earth's crust as the uncombined elements. However, most metals are found combined with other elements to form compounds.

An ore is a rock that contains enough of a metal or a metal compound to make extracting the metal worthwhile:

  • low-grade ores contain a small percentage of the metal or its compound
  • high-grade ores contain a larger percentage

Most metals are extracted from ores found in the Earth's crust. It is more expensive and wasteful to extract a metal from a low-grade ore, but most high-grade ores have already been used.

Extraction methods

The extraction method used depends upon the metal's position in the reactivity series. In principle, any metal could be extracted from its compounds using electrolysis. However, large amounts of electrical energy are needed to do this, so electrolysis is expensive.

If a metal is less reactive than carbon, it can be extracted from its compounds by heating with carbon.

Metal oxide + carbon → metal + carbon dioxide

For example, molten copper can be produced from copper oxide by heating with carbon:

Copper oxide + carbon → copper + carbon dioxide

2CuO(s) + C(s) → 2Cu(l) + CO2(g)

Copper oxide is reduced as carbon is oxidised, so this is an example of a redox reaction.

Remember:

  • oxidation is the gain of oxygen by a substance
  • reduction is the loss of oxygen by a substance
  • a redox reaction involves the loss and gain of oxygen

Note: the impure copper is purified by electrolysis.

The table summarises the extraction methods used for different metals.

Table of metals in order of ease of extraction and the methods used.

Extracting iron

As iron is below carbon in the reactivity series it can be displaced from its compounds by heating with carbon. Iron is extracted from iron ore in a large container called a blast furnace. Iron(III) oxide is reduced to molten iron when it reacts with carbon. The overall reaction is:

Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)

The iron oxide is reduced and the carbon is oxidised.

These reactions happen because carbon is more reactive than iron, so it can displace iron from iron compounds. Extracting a metal by heating with carbon is cheaper than using electrolysis.

Question

Write a balanced equation for the reaction between tin(IV) oxide and carbon, forming molten tin and carbon dioxide.

SnO2(s) + C(s) → Sn(l) + CO2(g)