EXTRACTION OF IRON:

Important Ores of Iron:

SN	Ores	Formula
1	Haematite (Red)	Fe2O3
2	Magnetite	Fe3O4
3	Siderite or Spathic	FeCO3
4	Iron Pyrite (fool’s Gold)	FeS2
5	Goethite	FeO(OH)
6	Limonite	2Fe3O4.3H2O
	Others Ores
7	Ilmenite  (FeO+TiO2)	FeTiO3
8	Chromite (FeO+Cr2O3)	FeCr2O4

Extraction process of iron: Iron is extracted from if oxide ores especially form the magnetite, Haematite, and Limonite ores. The extraction involves the following process.

(1) Enrichment of concentration of ores:

(A)Dressing or Benefaction of the ore: After mining, Iron ore is first broken into small pieces of 3 – 5 cm in size.

(B)Magnetic and Gravity Separation: Use due to the presence of metal carbonate

(2) Conversion of ores into oxide ores:

(A) Calcination: Heating ore in the absence of oxygen below melting point moisture and CO2 are removed.

(B) Roasting: Heating of ore in the presence of oxygen below melting point. During roasting P, S, C, As, Sb etc. are oxidized to the respective oxides and removed.

(i) Fe₃O₄ is decomposed to ferrous oxide (FeO) and ferric oxide (Fe₂O₃).

(ii) Ferrous oxide reacts with silica to form ferrous silicate at high temperature.

(ii) The conversion of FeO into Fe₂O₃ will prevent the formation of FeSiO₃ Thus mass of the ore becomes porous causing the increase in the effective surface area.

(3) Smelting: The calcined ore is mixed with Limestone (Flux) and Coke (a reductant) and smelted in Blast furnace.

Reaction in Blast furnace: A blast furnace is used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. The blast furnace is a huge, steel stack lined with refractory brick, where iron ore, coke and limestone are dumped into the top, and pre heated air is blown into the bottom.

 (1) Zone of combustion: (900 -1500 K): This is the higher temperature range found at lower part of blast furnace

(2)  Zone of reduction: (500 – 800 K): This is lower temperature range found at upper part of blast furnace.

(3)  Zone of slag formation: (1070-1270 K): Middle part of blast furnace:

Other impurities like P₄O₁₀ and SiO₂ and MnO₂ also reduced

(4) Zone of fusion:  (1570 – 2170 K): lower part of furnace.

Molten iron is heavier than molten slag. The two liquids are periodically tapped off and solidified into blocks called pigs. And thus Iron obtained from blast furnace is also called pig Iron.

Type of Iron:

(1) Pig Iron: Composition:

                                

SN	Impurities	%
1	Carbon (C)	3- 4.3
2	Silicon (Si)	1-2.0
3	Manganese (Mn)	0.5-2.0
4	Phosphorous (P)	0.05-2.0
5	Sulphure (S)	0.05-1.0

(2) White Cast Iron: When re molted pig iron is suddenly cooled, white cast iron is results. In this form of cast iron carbon is found to be combined form as cementite (Fe₃C).

(3) Grey Cast Iron: However when re molted pig iron is slowly cooled, Grey cast iron is results. In this form of cast iron carbon is found to be combined form of Graphite.

(4) Wrought iron:

This is done by heating cast iron with haematite (Fe₂O₃) which oxidises C to CO, S to SO₂ Si to SiO₂, P, P₄O₁₀ and Mn to MnO . Where CO and SO₂ escapes, manganese oxide (MnO) and Silica (SiO₂) combine to form slag.

Similarly phosphorus pentoxide combines with haematite to form ferric phosphate slag.

Manufacturing Process:

Casts iron takes in Puddling furnace and melted by hot blast of air. The chemical reactions which occur are:-

On removing impurities, the melting point rises and it becomes a semi solid mass. The metal is taken out of the furnace in the form of balls which are then beaten under hammer to separate out the slag. The product thus formed is thus called wrought iron.