Zone 1
Coke, C reacts with oxygen, \(O_2\) from the hot air to form carbon dioxide, \(CO_2\).
\(C(s) + O_2(g) \rightarrow CO_2(g)\)
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This is a redox exothermic reaction that makes the temperature of the blast furnace reach 1600 °C. |
Zone 2
The produced carbon dioxide, \(CO_2\) reacts with the remaining coal.
\(C(s) + CO_2(g) \rightarrow 2CO(g)\)
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Carbon monoxide, \(CO\) is the reducing agent for the subsequent reaction.
This is an endothermic reaction that lowers the temperature in Zone 2.
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Zone 3
Coke, C and carbon monoxide, \(CO\) function as reducing agents and reduce iron(III) oxide, \(Fe_2O_3\) or iron ore to molten iron.
\(2Fe_2O_3(s) + 3C(s) \rightarrow 4Fe(l) + 3CO_2(g)\)
\(Fe_2O_3(s) + 3CO(s) \rightarrow 2Fe(l) + 3CO_2(g)\)
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Iron(III) oxide, \(Fe_2O_3\) is reduced by carbon monoxide, \(CO\).
Iron deposits are formed at the bottom of the blast furnace.
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At high temperature, calcium carbonate, \(CaCO_3\) decomposes to form calcium oxide, \(CaO\) (quicklime) and carbon dioxide, \(CO_2\).
\(CaCO_3(s) \rightarrow CaO(s) + CO_2(g)\)
Impurities in the iron ore like silicon(IV) oxide, \(SiO_2\) react with calcium oxide to form slag or calcium silicate, \(CaSiO_3\).
\(CaO(s) + SiO_2(s) \rightarrow CaSiO_3(l)\)
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Calcium oxide, CaO is a base and can neutralise the acidic silicone(IV) oxide, \(SiO_2\).
This reaction is important to separate the impurities from molten iron.
The difference in density causes the slag to be at the top layer of the molten iron, which makes the separation process easier.
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