Iron Extraction Manufacturing Process - Blast Furnace Method

Iron is extracted from different ores exist in the world. Hematite (Fe₂O₃) is reduced to iron metal in the blast furnace under several steps. Limestone and coke are used as other raw materials to generate heat and reducing agents. Iron extraction is one of the largest chemical industry in the world because iron is a very useful metal to manufacture lot of things in our daily life.

Reducing iron oxides | Ferric oxide (Fe₂O₃) and Ferrous oxide (FeO)

Iron is located in the middle part of the electrochemistry series. Therefore Ferric oxide and Ferrous oxide can be reduced to iron by reducing agents such as carbon monoxide or coke.

Fe₂O₃ - Iron(III) oxide
FeO - Iron(II) oxide

What is ore?

When a mineral is available for using a metal in useful way, it is defined as ore.

Types of ores containing Iron

Following ores contain iron. But according to the amount of existing iron amount, ability of extraction is depend. If iron percentage is high, it is a good for extraction because it will give good yield. When other metals exist with those ores they make problems in iron extraction.

Hematite - Fe₂O₃
Siderite - FeCO₃
Copper pyrites - CuFeS₂
Magnetite - Fe₂O₃FeO
Limonite - Fe₂O₃.xH₂O
Iron Pyrites - FeS₂
Ilmenite - Feo.TiO₂

How iron is extracted?

Iron is fairly reactive element. Because of that it does not exist as a free substance in the world (iron reacts with oxygen to form oxides).

Iron locates at middle part in the activity series. Hence oxides of Iron can be reduced by carbon monoxide and coke.

Extraction of Iron using Blast Furnace

Raw Materials for Iron extraction

A mineral which contains iron (Hematite - Fe₂O₃)
Limestone (CaCO₃)
Coke - C

Hematite - Fe₂O₃

SiO₂, Al₂O₃ is mixed with hematite.

Why we use limestone in iron extraction?

to make slag
Amount of CaCO₃ depends on amount of silicate materials.

Why we use coke in iron extraction?

To produce heat and increase the temperature in burst furnace.

Complete iron extraction process

Mixture is smashed into tiny parts and heated into high temperature.
Hot air is entered from bottom of the furnace. Heat is generated by burning coke. Also carbon monoxide gas is produced by burning coke.
In the furnace, bottom and top temperatures are about 1500⁰C and 200⁰C respectively.
Fe₂O₃ is reduced to iron mainly by carbon monoxide and to some extent by coke.

Reactions of iron extraction

Fe₂O₃ reduction to iron is done step by step. Temperature variation along the blast furnace will help to occur these reactions. Now, we can study what are the reactions occurring inside the blast furnace at different temperatures.

at 400⁰C

Reduction of Ferric oxide by carbon monoxide | Fe₂O₃ + CO

Ferric oxide (Fe₂O₃) is reduced Fe₃O₄ by carbon monoxide. Fe₃O₄ contains FeO and Fe₂O₃.

Fe₃O₄ = FeO.Fe₂O₃

at 500⁰C - 600⁰C

CO is reduced to carbon and oxidized CO₂.

at 800⁰C

FeO is reduced liquid Fe by CO. CO is oxidized to CO₂.

at 900⁰C

Limestone decomposes to CaO and CO₂.

at 1000⁰C

FeO is again reduced to liquid Fe at this temperature. Also, CO₂ combines with C to give CO.

at 1800⁰C

Slag is produced at this temperature. It exists as a liquid. Mixture of liquid CaSiO₃ and liquid Ca(AlO₂)₂ is the slag.

Melting pointof pure Iron is 1015⁰C. But including impurities will reduce the melting point to 1015⁰C.

CaO reacts with SiO₂ and Al₂O₃. It produce slag which is CaSiO₃ and Ca(AlO₂)₂. Slag exist in liquid state. Liquid slag floats on liquid iron bottom of the blast furnace. Therefore oxidization of iron is prevented by entering air.

Environmental Pollution in Iron Production

Iron manufacturing process makes a lot of environmental pollution problems.

CO is emitted to the atmosphere. CO causes to breathing problems, deadly diseases, increasing green house effect (increase global temperature).
CO₂ also increases the global temperature.
SO₂ can be released to atmosphere due to use of ores which contains sulfur. It also contribute to increasing green house effect and acid rains.
Releasing slag pollutes soil and water.
High heat, dust also pollute environment.

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