Iron naturally exists in ores. Iron ores are usually hematite, Fe2O3. To extract pure iron metal from hematite, several method can be used.
Electrolysis can be used to extract pure iron by passing through high voltage of electricity through hematite. Electricity will overcome the electrostatic forces of attraction between oppositely iron and oxygen electrons and iron will be obtained in solid state.
However, this method is very expensive so iron, which has a large demand, is usually extracted using blast furnaces in industries.
At
first, a mixture of limestone (calcium carbonate, CaCO3),
coke (carbon, C) and hematite is added at the top of the blast furnace.
Then,
hot air will be blasted into the blast furnace at the bottom to raise the
temperature within the blast furnace.
High
temperature causes carbon in coke burns in hot air to produce carbon dioxide.
Since this is an exothermic process, a lot of heat will be produced.
C (s)
+ O2 (g) CO2 (g)
Limestone
will also be decomposed by heat to form carbon dioxide and calcium oxide.
CaCO3(s) CaO (s) +
CO2 (g)
The coke will react with carbon dioxide formed previously to
produce carbon monoxide.
C (s) + CO2 (g)
2CO (g)
The carbon monoxide formed reduces the hematite to form iron
and carbon dioxide. Molten iron is formed and it runs to the bottom of the
blast furnace. Waste gases like nitrogen and carbon dioxide escape from the top
of the blast furnace.
Fe2O3 (s) +3CO (g)
2Fe (l) + 3CO2 (g)
Impurities
like sand will be removed using limestone.
CaCO3
(s) CaO (s) + CO2 (g)
The
basic calcium oxide will react with acidic impurities like silica to form slag
which is less dense than iron and it floats on top of molten iron at the
bottom. The molten slag can be tapped off at intervals.
CaO
(s) + SiO2 (s) CaSiO3 (l)
The process of using blast furnace has a big problem: it
creates waste gases like carbon monoxide and sulfur dioxide. Carbon monoxide is
lethal for human body as its molecules bind with heamoglobin in red blood cells
to give carboxyhaemoglobin. This causes haemoglobin unable to carrty oxygen
molecules, leading to suffocation. Sulfur dioxide will react with water
molecules in the atmosphere to produce sulfuric acid, which causes acid rains
that speed up corrosions of metals on earth.
Harmful gases must be treated so that they cannot be released
into the atmosphere. Carbon monoxide can be heated strongly to decompose the
compound into carbon and oxygen gas. Carbon obtained can be reused as coke for
extraction of iron while oxygen gas can be safely released in to the
atmosphere. Sulfur dioxide is an acidic gas. It can be removed by passing the gas through a column
containing lumps of calcium carbonate. Calcium carbonate will react with
sulphur dioxide to produce calcium sulphate and safe carbon dioxide gas.
Source:
http://uk.answers.yahoo.com/question/index?qid=20100105101641AAmlSf4
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