what is the chemical process involved in production of steel from haematite. some books has given ans: "oxidation followed by reduction" while some books say reverse. please explain.

what is the chemical process involved in production of steel from haematite.

some books has given ans: "oxidation followed by reduction" while some books say reverse. please explain.


2 Answers

879 Points
11 years ago

Dear student,

Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, deep purple, to rusty red.  It almost always consists of iron oxides, the primary forms of which are magnetite (Fe3O4) and hematite (Fe2O3).Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel. 98% of the mined iron ore is used to make steel.

The production of iron or steel is a process unless the desired final product is cast iron. The first stage is to produce pig iron in a blast furnace. The second is to make wrought iron or steel from pig iron by a further process.

Blast furnace
Blast furnace is a type of metallurgical furnace used for smelting to produce metals, generally iron.

90% of all mining of metallic ores is for the extraction of iron. Industrially, iron is produced starting from iron ores, principally hematite and magnetite 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.

Image of Blast furnaceIn the furnace, the coke reacts with oxygen in the air blast to produce carbon monoxide:

  • 2C + O2 → 2CO

The carbon monoxide reduces the iron ore (hematite) to molten iron, becoming carbon dioxide in the process:

  • 3CO + Fe2O3 → 2Fe + 3CO2

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 (CaCO3.MgCO3). 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):

  • 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. 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.

Further processes
Pig iron is not pure iron. It has 4-5% carbon dissolved in it with small amounts of other impurities like sulfur, phosphorus, magnesium and manganese.

As the carbon is the major impurity, pig iron becomes brittle and hard. This form of iron is used to cast articles in foundries such as stoves, pipes, radiators, lamp-posts and rails.

Pig iron can be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including finery forges, open hearth furnaces, puddling furnaces, Bessemer converters, basic oxygen furnaces, etc. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels.

29 Points
11 years ago

oxidation is dine first to remove extra carbon then reduced to elemental iron and carbon is furter added to get steel of desired quality

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