INTRODUCTION

Iron is extracted from its oxideore called HAEMATITE (Fe2O3).

PRINCIPLE OF EXTRACTION

Extraction of iron is based on the reduction of HAEMATITE (Fe2O3) with carbon..

DETAILS OF EXTRACTION

The process of the extraction of iron is carried out by the following steps:

Concentration of oreCalcination or Roasting of oreReduction of ore

Concentration of ore:In this metallurgical operation, the ore is concentrated by removing impurities like soil etc. Theprocess involves the crushing and washing of ore.

Calcination orRoasting of ore:The concentrated ore is now heated in the presence of air. The process of roasting is performed to remove moisture,CO2, impurities of sulphur, arsenic. Ferrousoxide is also oxidized to ferric oxide.

Reduction of ore

The process of reduction is carried out in a blast furnace.

Blast Furnace

The blast furnace is a cylindrical tower like structure about 25m to 35m high. It has an outer shell of steel. Inside of furnace is lined with fire bricks. The top of the furnace is closed by a cup-cone feeder.

The charge

The charge consists of :roasted oreCokeLimestone

Details of reduction

The charge is fed into the furnace from its top. A preheated blast of air at 1500OC, is blown into the furnace under pressure near to the bottom. The blast oxidizes carbon to CO2.

C + O2CO2+ heat

Formation of CO2is an exothermic reaction in which a huge amount of heat is liberated which rises the temperature to 1900OC in this region. As the CO2passes upwards, it reacts more coke to form carbon monoxide.

CO2+ C2CO+ heat

Formation of CO is an endothermic reaction and the temperature in this region falls to 1100OC. COis the main reducing agent in the upper portion of blast furnace.

Reactions in blast furnace

Fe2O3+ 3C2Fe + 3COFe3O4+ 4CO3Fe + 4CO2CO2+ C2CO

Overall reaction

Fe2O3+ 3CO2Fe + 3CO2

The liquid iron runs downward to the bottom of the furnace and is withdrawn through tap hole.

Slag formation

Lime stone on heating decomposes to CaO and CO2.

CaCO3CaO + CO2

CaO now reacts the impurities of ore called GANGUE to form slag. Slag is the mixture of CaSiO3and Ca(AlO2)2. The slag floats over the top of molten iron. Slag is a useful byproduct. It is usedin road making, cement manufacturing a light weight building materials.

Flux + GangueSlagCaO + SiO2CaSiO3CaO + Al2O3Ca(AlO2)2