The ore obtained after mining contains iron in the form of iron oxide. Pure iron is obtained, therefore, by the reduction of this ore. This process is carried out in the blast furnace. Temperature is different at different heights in the furnace. Mixture of iron ore, lime stone and coke is introduced the furnace from the top and a blast of burning gases is blown with pressure from an inlet near the bottom. Temperature of these gases is 1500°C. Falling mixture and up going blast of hot gases first meet near the base. Aerial oxygen present in the blast of gases combines with coke and forms carbon dioxide with huge amount of heat energy. As this reaction is exothermic, so the temperature in this zone of furnace reaches up to 1900°C. When this carbon dioxide rises up it reacts with more carbon and forms carbon monoxide this reaction is endothermic, so temperature in this region falls up to 1100°C. CO is very good reducing agent. It reduces iron oxide to free iron which is obtained in molten form due to high temperature. Calcium oxide (CaO) obtained by the decomposition of calcium carbonate combines with the impurities of ore i.e. Silicate and aluminate. Most of calcium silicate and calcium aluminate is called slag. It is lighter than iron floats over iron. Slag is obtained from the upper out let and is used in building material. Iron obtained from blast furnace is called pig iron. It contains 96 percent iron, 4 percent carbon and traces of sulphur, silicon, phosphorus and manganese.
