Metallurgy of iron

                                                                       
                                                 METALLURGY OF IRON

•        Symbol : Fe
•         Colour : Greyish white
•         Atomic mass : 55.9
•         Atomic number: 26
•         Valency : 2 & 3
•         Electronic
•         configuration : 2, 8, 14, 2

Occurrence:

Iron is the second most abundant metal after aluminium. It occurs in nature

as oxides, sulphides and carbonates.

Ores of iron Formula

•        Haematite Fe2O3
•        Magnetite Fe3O4
•        Iron pyrites FeS2

     

   Extraction of Iron from haematite ore (Fe2O3)

Concentration by gravity separation

        The powdered ore is washed with stream of water. As a result, the lighter

sand particles and other impurities are washed away and heavier ore particles

settle down.

Roasting and calcination

        The concentrated ore is strongly heated in a limited supply of air in a reverberatory furnace. As a result, moisture is driven out and sulphur, arsenic, phosphorus impurities are oxidised off.

Smelting (in Blast furnace)

        The charge consisting of roasted ore, coke and limestone in the ratio 8 : 4 : 1 is smelted in a blast furnace by introducing

it through the cup and cone arrangement at the top. There are three important regions in the furnance.

   The lower region(combustion zone)- temperature is at 1500° C. In this region, coke burns with oxygen to form CO2 when the charge comes in contact with the hot blast of air.

C + O2→ CO2 + heat

It is an exothermic reaction since heat is liberated.

  The middle region (fusion zone)-The temperature prevails at 10000C.In this region CO2 is reduced to CO.

CO2 + C → 2CO

Limestone decomposes to calcium oxide and CO2.

                                                                                              ▲

CaCO3→ CaO + CO2

These two reactions are endothermic due to the absorption of heat. Calcium oxide combines with silica to form calcium silicate slag.

CaO + SiO2 → CaSiO3

  The upper region (reduction zone)- temperature prevails at 4000C. In this region carbon monoxide reduces ferric oxide to form a fairly pure spongy iron.

400°C

Fe2O3 + 3CO → 3Fe + 3CO2

The molten iron is collected at the bottom of the furnace after removing the slag.

Physical properties

• It is a heavy metal of specific gravity 7.9

• It is a lustrous metal and greyish white in colour.

• It has high tensility, malleability and ductility.

• It is a good conductor of heat andelectricity.

Chemical properties

Reaction with air or oxygen: 

   Only on heating in air, iron forms magnetic oxide.

3Fe + 2O2 → Fe3O4 (black)

Reaction with moist air: 

    When iron is exposed to moist air, it forms a layer of brown hydrated ferric oxide on its surface. This compound is known as rust and the phenomenon of forming this rust is known

as rusting.

4Fe + 3O2 + 3H2O → 2Fe2O3.3H2O(Rust)

    

Reaction with steam: 

 When steam is passed over red hot iron,magnetic oxide

of iron is formed.

3Fe + 4H2O(steam) → Fe3O4 + 4H2↑

Reaction with chlorine:

  Iron combines with chlorine to form ferric chloride.

2Fe + 3Cl2 → 2FeCl3(ferric chloride)

Reaction with acids: 

•  With dilute HCl and dilute H2SO4 it evolves H2 gas.

Fe + 2HCl → FeCl2 + H2↑

Fe + H2SO4 → FeSO4 + H2↑

• With conc. H2SO4 it forms ferric sulphate

2Fe + 6H2SO4 → Fe2(SO4)3 + 3SO2 + 6H2O

•  With dilute HNO3 in cold condition it gives ferrous nitrate

4Fe + 10HNO3 → 4Fe(NO3)2 + NH4NO3 + 3H2O

  When iron is dipped in conc. HNO3 it becomes chemically inert or passive due to the formation of a layer of iron oxide (Fe3O4) on its surface.

Uses of iron

•  Pig iron is used in making stoves, radiators, railings, man hole covers and drain pipes.
• Steel is used in the construction of buildings, machinery, transmission and T.V towers and in making alloys.
• Wrought iron is used in making springs, anchors and electromagnets