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Ore: Hematite( Limestone): Contains more that 60 % iron.
Hematite contains mostly iron (III) oxide.
Limestone is a mineral that largely contains calcium carbonate
Container: Blast furnace
Temperature: Bottom of furnace:15000C
Top of the furnace:2500C
Temperature of hot air: 550-8500C
Raw materials: Coke (C)/iron ore/limestone
Two functions of coke in the blast furnace are
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Iron extraction
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1. To provide heat ( to burn)
2. To form carbon monoxide.
Diagram:
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Formation of reducing
agent:
This CO 2 is reduced to carbon
monoxide as it reacts with coke .
CO 2 (g) +C(s) -----> 2CO(g)
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Reduction of Fe 2 O 3:
By CO
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At the bottom of the furnace
the coke ( C) burns in hot blast
of air and forms carbon dioxide.
The reaction is exothermic and
the temperature rises to
20000C.
C(s) +O 2 (g)--------> CO 2 (g)
Fe 2 O 3 (s) + 3CO(g)-----<> 2Fe(l) + 3CO 2 (g)
Most iron is produced in this way.
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By C
Coke (C) reduces Fe 2 O 3 in the hotter parts of the furnace
Fe 2 O 3 (s) + 3C(g)-----<> 2Fe(l) + 3CO(g)
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The hot gases that escape are used to heat the air going into the furnace.
thus energy costs are reduced.
SiO 2 - Sand is the major impurity in the hematite ore. This impurity is
removed by adding Limestone-CaCO 3.
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Decomposition of limestone:
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Removal of impurities(Silica):
heat
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CaCO 3 (s)---------->CaO(s) + CO 2 (g)
CaO(s) + SiO 2 (s)-----> CaSiO 3 (l)
The liquid slag runs down and forms a layer on the top of the liquid iron
because its density is less than that of iron. The slag is run off.
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----------------------------------------------Use of slag(waste product):
Solid slag is used as a building material and to build
roads.
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Impurities present in the iron:
• Mainly Carbon
• Sulfur, silicon and phosphorous
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Effect of impurities on iron:
Impurities make the iron very brittle.
Pure iron facts:
Pure iron with no impurities in it is very soft. Hence molding this pure
iron is very easy.
As pure iron is very soft, so it does not have many uses.
Pure iron rusts easily.
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The equations taking place in the blast furnace can be categorised
as:
Redox equations
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Acid -base equations
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