Iron Extraction by Blast Furnace Metallurgy

Define Iron Extraction by Blast Furnace Metallurgy?

Iron, when extracted from iron ore such as haematite containing iron(III) oxide, Fe2O3, in a blast furnace is called iron extraction blast furnace metallurgy. In this reduction reaction, oxygen is removed from the iron(III) oxide to leave behind iron.

Generally, the extraction of metals and their isolation are based on three major procedures. The steps are:

1. Concentration of Ore 

2. Extraction of metal from concentrated ore and 

3. Purification of the metal 

In the following article extraction of iron from its ore in the blast furnace is described in light of these three quintessential steps. Extracted iron is used in several ways like building a bridge, house etc. The process is very important in the domain of Metallurgy. 


What is The Procedure of Extraction of Iron From its Ore?

Extraction of iron is lengthy process which commences from Concentration through calcination roasting. Water and other volatile impurities like sulphur and carbonates are removed by the process of Concentration. The concentrated ore is blended with limestone (CaCO3) and Coke and fed into blast furnace from the top. Extraction of iron happens in the blast furnace. It is a very lengthy and submissive procedure. The above process helps in separating the useful ingredients from the waste materials like slag. 


What is Calcination?

Calcination is the procedure of converting an ore into an oxide by heating it strongly. The heating of ore is materialised below its melting point either in absence of air or in a controlled supply. The carbonates and hydroxides are converted into their respective oxides by this process. Calcination also separates the moisture and volatile impurities. Calcination may also be termed as a thermal process which is used to convert ores and other solid materials by providing thermal decomposition. The word calcination came from a Latin word ‘calcinare’ which means ‘to burn lime’. Therefore, decomposition of limestone (calcium carbonate) to lime (calcium oxide) and carbon dioxide takes place by the method of calcination. The products from calcination are termed as calcines. 

CaCO3 = CaO + CO2


What is Roasting?

Roasting is a method of Metallurgy. It converts an ore into its oxide by heating it above the melting point in the presence of excess air. While roasting is a process that is used for converting sulphide ores, calcination is generally used in the oxidation of carbonates. Moisture and non-metallic impurities in the volatile gases are extracted during the process of roasting. Oxidation, reduction, sulfation, chlorination and pyrohydrolysis are included in the solid-gas thermal reaction which is an important part of roasting. 

The major drawback of the process is that roasting involves sulphides which are the main source of air pollution. Apart from that, the process of releasing a large amount of metallic as well as toxic and acidic compounds results in harm to the environment. When Zinc sulphide is converted into zinc oxide, that will be an example of roasting.

2ZnS + 3O2 = 2ZnO + CO2


What are The Differences Between Calcination and Roasting?

The major differences between the Calcination and Roasting are given in the following table:

Calcination

Roasting

An ore is heated in the absence of air or air might be supplied in controlled way during the process of Calcination

An ore is heated to higher than its melting point in the presence of air or oxygen during the process of Roasting

Thermal decomposition of carbonate ores occur in Calcination

Sulphide minerals are formed at the time of Roasting 

Moisture is driven out from ore at the time of Calcination

Roasting does not engross in any dehydrating an ore

Carbon dioxide is extracted at the time of Calcination

A large amount of toxic, metallic and acidic compounds are released at the time of roasting

     

 What Happens In The Blast Furnace?

The concentrated ore is reduced to its liquid metal state in a chemical method in Blast Furnace. A Blast Furnace is a giant, steel stack parallel with refractory brick where the concentrated ore, coke and limestone are dumped from the top and a blast of steamy air is blown into the bottom. All the three components are crushed into small round pieces and blended and put on a hopper which regulates the input. 

Hot steamy air is blown from the underneath and coke is burned to capitulate temperatures up to 2200K. The maximum portion of heat for this process is produced by burning coke. Coke reacts with the oxygen in the hot air to generate Carbon Monoxide (CO) at such high temperature. After that, the CO and heat move in the upward direction to meet the raw material coming down from the top. The temperature in the upper portion of the Blast Furnace is eventually lower than the 2200K at the lower portion. Ferrous Oxide (FeO) is generated by reducing Haematite (Fe2O3) and Magnetite (Fe3O4).

The following reactions occur in the blast Furnace at 500-800K in the upper portion with lower temperatures:

3Fe2O3 + CO = 2Fe3O4 + CO2

Fe3O4 + 4CO = 3Fe + 4CO2

Fe2O3 + CO = 2FeO + CO2

In the lower portion of the Blast Furnace (at 900-1500K)

C + CO2 = 2 CO

3FeO + CO2 = Fe + CO2

The limestone is also decomposed to CaO that separates the silicate impurity of the ore in the form of Slag. It can be easily removed from the molten iron. Approximately 3-4% of Carbon and little quantities of many other impurities like sulphur, Silicon etc are contained in the iron manufactured in the Blast Furnace. The same is termed as Pig Iron. The strength is acutely hampered by the impurities. Carbon plays a pivotal role in influencing the brittleness and hardness balance in iron. The above component is melted again with scraps of iron and coke to further reduce the carbon content in Pig iron. It is also subject to the blast of hot air. The above kind of iron is termed as cast iron and contains slightly lower carbon content (2-3%). Cast iron is harder than pig iron. 


What is Wrought Iron/Malleable Iron?

The purest form of iron commercially available is the Wrought Iron. It is made by heating cast iron in a furnace lined with Haematite (Fe2O3). Carbon is reacted with Haematite to produce pure iron and carbon monoxide gas which escapes.

Fe2O3 +3C = 2Fe + 3 CO

After that limestone is added as flux and slag is created. Various impurities like S, Si pass into the slag and later on slag can be easily removed to produce pure iron.

The above procedure describes the Extraction of Iron in the Blast Furnace. It is one of the most important phenomenons in the context of Metallurgy. The extracted iron can be utilized in several sectors. 

FAQ (Frequently Asked Questions)

1. What is Metallurgy?

Metallurgy is the method that is used for the extraction of metals in their pure form. The components of metals blended with soil, limestone, sand and rocks are termed as minerals. The commercial extraction of metals from minerals at low cost and minimum effort is the main motto of Metallurgy. The minerals are called ores. Flux is the substance that is added to the charge in the furnace to separate the gangue (impurities). Process of purification of metals and the formation of alloys are the basic areas of Metallurgy.

2. What are the Various Steps of Metallurgy?

The various Metallurgical processes can be classified as the following:

1. Crushing and grinding: The crushing of ores into a fine powder in a crusher or ball mill is the first step of Metallurgy.

2. The concentration of ores: The next process of Metallurgy to separate impurities from ore is known as a concentration of minerals or ore dressing. 

3. Hydrolytic method: The ore is poured over a sloping, vibrating corrugated table with grooves in this process.

4. Magnetic separation: The crushed ore is placed on a conveyor belt which rotates around two wheels in which one of the wheels in magnetic in this method.

5. Froth floatation: The crushed ore is taken into a large tank which contains oil and water.

6. Roasting and Calcination: Calcination is nothing but the procedure of converting an ore into an oxide by heating it strongly. Roasting is a method of Metallurgy. It converts an ore into its oxide by heating it above the melting point in the presence of excess air.  

3. What are the Ores of Various Metals?

Aluminium: Bauxite: AIOx (OH)3-2x (where 0<x<1)

                      Kaolinite: Al2(OH)4 Si2O5 (a form of clay)


Iron: Haematite: Fe2O3

          Magnetite: Fe3O4

          Siderite: FeCO3

          Iron Pyrites: FeS2


Copper: Copper Pyrites: CuFeS2

                Malachite: CuCO3, Cu(OH)2

                Cuprite: Cu2O

                 Copper Glance: Cu2S


Zinc: Zinc blend/Sphalerite: ZnS

          Calamine: ZnCO3

           Zincite: ZnO

4. What are The Classifications of Matter?

The Matter is classified into three parts namely Elements, Compounds and Mixtures. The simplest chemical substances in which all the atoms are exactly the same are called elements. When two or more elements are chemically bound together in a fixed ratio then it is called compounds. The mixture is the perfect blending of various compounds which play a very crucial role in the field of Chemistry. All matters fall in one of these three categories.