Extraction of Iron

Raw materials used

The blast furnace

The iron is extracted from its ore in the blast furnace by reduction of iron (II) oxide.

Reactions in the blast furnace

1. A blast of hot air is sent in near the bottom of the furnace through holes (tuyères) which makes the ‘charge’ glow, as the coke burns in the preheated air.

C(s) + O₂(g) →     CO₂(g)

1. The carbon dioxide gas produced reacts with more hot coke higher up in the furnace, producing carbon monoxide in an endothermic reaction: carbon dioxide + coke → carbon monoxide CO₂(g) + C(s) → 2CO(g).
2. Carbon monoxide is a reducing agent. it rises up the furnace and reduces the iron (III)oxide ore. This takes place at a temperature of around 700 °C: iron (III) oxide + carbon monoxide _→ iron + carbon dioxide

Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)

The molten iron trickles to the bottom.

3. Because of high temperatures in the furnace the limestone (CaCO₃) decomposes.

Calcium carbonate → calcium oxide + carbon dioxide

CaCO₃(s) → CaO(s) + CO₂(g)

4. Calcium oxide reacts with impurities such as silicon(iv) oxide in the iron, to form a slag which is mainly calcium silicate. calcium oxide + silicon(iv) oxide → calcium silicate

CaO(s) +SiO₂(s) → CaSiO₃(l)

• The slag trickles to the bottom of the furnace, but because it is less dense than the molten iron, it floats on top of it.
• The molten iron, as well as the molten slag, may be tapped off (run off) at regular intervals.
• The waste gases, mainly nitrogen and oxides of carbon, escape from the top of the furnace. They are used in a heat exchange process to heat incoming air and so help to reduce the energy costs of the process. Slag is the other waste material. It is used by builders and road makers for foundations.
• The iron obtained by this process is known as ‘pig’ or cast iron and contains about 4% carbon (as well as some other impurities

Heating Iron Oxide on a charcoal block

• A hole was made on the side of the charcoal block and a spatula full of iron oxide was placed in the hole.
  
• A burner was lit and the burner flame directed at the iron oxide in the hole by blowing into the blowpipe for some time.
  
• A small bead of greyish metal was seen at the end of the experiment, when the charcoal block had cooled.
  
• The iron (III) oxide was reduced to iron by carbon in the charcoal block.
  

  Iron (III)oxide + Carbon → Iron + Carbon dioxide
  
  

ALLOYS OF IRON

• An alloy is a mixture of metals or metals and non-metals to improve its properties.
• They are harder, more resistant to corrosion and have a more attractive appearance than the metals they are formed from.