Discuss the method of extraction of iron from its ore with the help of equations and diagram. Also discuss the thermodynamic principle of the reduction of its oxide into metal

iron is extracted from its oxide ore 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 ore
Calcination or Roasting of ore
Reduction of ore
Concentration of ore:
In this metallurgical operation, the ore is concentrated by removing impurities like soil etc. The
process 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 ore
Coke
Limestone


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 + O2 ------ CO2+ 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+ C ----- 2CO+ heat
Formation of CO is an endothermic reaction and the temperature in this region falls to 1100OC. CO
is the main reducing agent in the upper portion of blast furnace.
Reactions in blast furnace

Fe2O3+ 3C--- 2Fe + 3CO
Fe3O4+ 4CO----- 3Fe + 4CO2
CO2+ C ------ 2CO
Overall reaction

Fe2O3+ 3CO----- 2Fe + 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The liquid iron runs downward to the bottom of the furnace and is withdrawn through tap hole.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.
CaCO3 ----- CaO + CO2
CaO now reacts the impurities of ore called GANGUE to form slag. Slag is the mixture of CaSiO3
and Ca(AlO2)2. The slag floats over the top of molten iron. Slag is a useful byproduct. It is used
in road making, cement manufacturing a light weight building materials.
Flux + Gangue Slag
CaO + SiO2 ---- CaSiO3
CaO + Al2O3 ----- Ca(AlO2)2


(2)
The direct reduction process for making iron rests firmly on the guidance of Ellingham diagrams, which show that hydrogen can alone reduce iron oxides to the metal.

Iniron ore smelting,haematitegets reduced at the top of the furnace, where temperature is in the range 600 – 700°C. The Ellingham diagram indicates that in this range carbon monoxide acts as a stronger reducing agent than carbon since the process

2 CO + O2→ 2CO2

has a more-negative free energy change than the process:

2 C +O2→ 2 CO.

In the upper part of the blast furnace, haematite is reduced by CO (produced by oxidation of coke lower down, at higher temperatures) even in the presence of carbon – though this is mainly because the kinetics for gaseous CO reacting with the ore are better.