Metals can be extracted by using a suitable reducing agent such as carbon or for the more reactive metals by using electrolysis. Electrolysis requires a lot of energy so is a more costly method than reduction with carbon.

Extraction of iron

Iron is extracted in a structure called a blast furnace where raw materials are continually added and the extracted product and waste materials are removed. The raw materials are as follows:

Raw Materials

Calcium carbonate (limestone)

Coke (a form of carbon)

Iron III oxide (haematite)

The calcium carbonate or limestone reacts with silica, an impurity in the iron ore, to produce calcium silicate which floats to the top and can easily be removed. If allowed to build up it would clog up the furnace which would then have to be turned off and cleaned. This would be a time consuming process and increase the cost of production. The coke is a cheap and readily available form of carbon that acts as the reducing agent but also provides energy in the form of heat as it burns. The haematite is the iron ore from which iron is extracted.

The calcium silicate which rises to the top can be skimmed off and is sometimes referred to as slag. The iron produced is only 96% iron and 4% carbon which is more accurately called cast iron. This is very hard due to the presence of a high percentage of carbon. It is however very brittle but can be used for specific applications as given in the list below.

Chemical equations

Carbon in the blast furnace burns in hot air to produce carbon dioxide

C + O 2 → CO 2

The high temperatures produced by the reaction brings about the next reaction at the bottom of the blast furnace where carbon reacts with carbon dioxide:

C + CO 2 → 2CO

Carbon monoxide acts as the main reducing agent which is responsible for reduction of iron III:

Fe 2O 3 + 3CO → 2Fe + 3CO 2 

The limestone gets broken down to calcium oxide and carbon dioxide in a thermal decomposition reaction:

CaCO 3 → CaO + CO 2 

​

Calcium oxide reacts with the main impurity in iron ore called silicon dioxide or sand to produce calcium silicate:

​CaO + SiO 2  → CaSiO 3​ 

Uses of cast iron

Car engines

Wood burning stoves

Manhole covers 

Exercise 1

1. State the uses of the 3 following raw materials in the extraction of iron:

a) Calcium carbonate

b) Coke

c) Iron III oxide

2. Removing oxygen from iron III oxide can be described as reduction but how can

this reduction be described in terms of electrons? 

3. Iron produced from a blast furnace is called cast iron. State:

a) the % of iron to carbon

b) the physical properties of cast iron

c) the uses of cast iron