Production
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Industrially, iron is produced starting from iron ores, principally haematite (nominally Fe2O3) and magnetite (Fe3O4) by a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000°C. In a blast furnace,
iron ore, carbon in the form of coke, and a flux such as limestone (which is used to remove impurities in the ore which would
otherwise clog the furnace with solid material) are fed into the top of the furnace, while a blast of heated air is forced
into the furnace at the bottom.
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In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:
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6C + 3O2 6CO
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The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:
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6CO + 2Fe2O3 4Fe + 6CO2 |
The flux is present to melt impurities in the ore, principally silicon dioxide sand and other silicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (CaMg(CO3)2). Other fluxes may be used depending on the impurities that need to be removed from the ore. In the heat of the furnace the
limestone flux decomposes to calcium oxide (quicklime):
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CaCO3 CaO + CO2 |
Then calcium oxide combines with silicon dioxide to form a slag. |
CaO + SiO2 CaSiO3 |
The slag melts in the heat of the furnace, which silicon dioxide would not have. In the bottom of the furnace, the molten slag floats on top of the more dense molten iron, and apertures
in the side of the furnace are opened to run off the iron and the slag separately. The iron once cooled, is called pig iron,
while the slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.
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Pig iron is not pure iron, but has 4-5% carbon dissolved in it. This is subsequently reduced to steel or commercially pure iron, known as wrought iron, using other furnaces
or converters.
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In 2005, approximately 1,544Mt (million tons) of iron ore was produced worldwide. China was the top producer of iron ore with atleast one-fourth world share followed by Brazil, Australia and India, reports the British Geological Survey. |
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