To extract the iron out of their ores, the iron ores are reduced in Blast Furnaces which are nearly 40metres high with each unit costing millions of dollars.
These furnaces are made out of steel which is line with a special refractory firebrick which can be made of Magnesium Oxide which is an ionic compound which has a high melting point, allowing it to withstand high temperatures that happen in the blast furnaces.
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 and makes use of the reduction by carbon method to reduce the iron ores. Inside these blast furnaces, temperatures easily reach above 1600 degrees Celsius.
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)
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. The silicon is present
as acidic oxide. This will react with the calcium oxide to form calcium
silicate(slag)
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.
Done
By: Ling Zihui –Researcher on Diagrams, Iron Extraction and Processes
Wan Xinyu- Iron Extraction and
Processes
Brendan Ng-Iron Extraction and
Processes+ Minor details
Marc- Researcher on Videos , Diagrams,
Uses of Iron
Source:
Chemistry-
A Course for ‘O’level
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