Extraction of iron

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Iron is the second-most abundant metal in the Earth's crust after aluminium. It is one of the most commonly used metals in the modern world. Iron as a metal in elemental form is rarely used on its own. Most of the iron extracted today is converted to steel, an alloy of iron and carbon, which proves to be more useful than iron. Steel has good domestic as well as industrial use, mainly because it does not corrode easily, and because of its high tensile strength. It is far less brittle than iron.

The common ores of iron are hematite [Fe₂O₃], limonite [Fe₂O₃].xH₂O, magnetite [Fe₃O₄] and siderite [FeCO₃]. Iron from hematite is usually extracted through the carbon reduction process.

Representation of blast furnaces and other ironmaking processes from the 19th century

The iron ore with carbon in the form of coke (once charcoal) and limestone are added to a blast furnace (temperatures of at least 1300°C, but now usually 2000°C). The product of the blast furnace process is not pure iron, but pig iron which contains 4-5% carbon and silicon, which must be removed in further processes. An earlier process (which did produce fairly pure wrought iron used a bloomery, where the iron was kept in the solid state throughout, but this was gradually abandoned because it could not easily be scaled up.

The steps in the extraction of iron by carbon reduction method are:

1. Hot air is pumped into the blast furnace through the bottom. The carbon reacts with the oxygen to produce carbon dioxide:

C + O₂ → CO₂

2. After carbon dioxide is formed, excess carbon reacts with it to form carbon monoxide - the main reducing reagent in the furnace.

CO₂ + C → 2CO +

Δ

3. The carbon monoxide in the blast furnace reacts with the hematite (iron(III) oxide). This occurs since carbon monoxide reacts with the oxygen, and with this compound forms carbon dioxide. This effectively reduces the iron oxide as the iron gains three electrons in the process and becomes iron atoms:

Fe₂O₃ + 3CO → 2Fe + 3CO₂

4. While the iron is being extracted, the limestone flux reacts with the impurities in the ore and melts them to form slag, which effectively prevents the impurities from affecting the reduction of the iron ore:

CaCO₃ → CaO + CO₂

CaO + SiO₂ → CaSiO₃