Ninety percent of all mining of metallic ores is for the extraction of iron. Industrially, iron production involves iron ores, principally hematite (nominally Fe2O3) and magnetite (Fe3O4) in 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 silicon dioxide impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a massive blast of heated air, about 4 tons per ton of iron, is forced into the furnace at the bottom.
Iron output in 2005
In the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:
2 C + O2 → 2 CO
The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:
Fe2O3 + 3 CO → 2 Fe + 3 CO2
Some iron in the high-temperature lower region of the furnace reacts directly with the coke:
2 Fe2O3 + 3 C → 4 Fe + 3 CO2
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 (calcium-magnesium carbonate). 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 (also known as quicklime):
CaCO3 → CaO + CO2
Then calcium oxide combines with silicon dioxide to form a liquid slag.
CaO + SiO2 → CaSiO3
The slag melts in the heat of the furnace. In the bottom of the furnace, the molten slag floats on top of the denser 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
This heap of iron ore pellets will be used in steel production.
In 2005, approximately 1,544 million metric tons of iron ore were produced worldwide. According to the British Geological Survey, China was the top producer of iron ore with at least one quarter world share, followed by Brazil, Australia and India.
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