In the previous section, we saw the various stages in the production of metals. In this section, we will see how these stages are applied in the case of iron.
1. Haematite is the principal ore of iron.
• As we have seen in the previous sections, which ever be the metal, the ore has to be powdered.
• The 'concentration of the powdered ore' is the first stage.
2. In the case of haematite, we use the levigation method for the concentration.
• As iron is heavier than the impurities, it will settle to the bottom of the tank.
• The impurities will be washed away.
• So first stage is over
3. The second stage is the extraction of the metal from the concentrated ore.
• We have seen that there are two steps to be completed for this. They are:
(a) Conversion of the ore into it's oxide.
(b) Reduction of the oxide
4. Let us see how they are accomplished in the case of iron:
(a) First we have to convert the iron into iron oxide. There are two methods available.
(i) Calcination and (ii) roasting.
• In the case of iron, roasting is used.
• Haematite is Fe2O3. So it already contains the oxide of iron. Even then, it is subjected to roasting.
• During roasting, impurities like sulphur, arsenic, phosphorus etc., are removed as their gaseous oxides. Water is also expelled.
5. Next, we have to reduce the oxide.
• The haematite obtained after roasting will contain large quantities of silicon dioxide (sand). So we have to remove it to get the pure iron. The following procedure is used:
6. A mixture of roasted haematite, coke and lime stone (CaCO3) is fed into a blast furnace. See fig.13.7 below:
• Blast furnace is a huge steel furnace.
• Steel cannot withstand the high temperature produced inside the furnace.
• So the inner side of the furnace is lined with a refractory material.
7. A blast of hot air is sent into the furnace from the bottom.
• At the same time, the mixture containing haematite falls from the top.
• Because of the heat, chemical reactions will take place. Let us see each of those reactions:
• The calcium carbonate (in the form of limestone) which is supplied along with the haematite, will decompose into calcium oxide and carbon dioxide.
The equation is: CaCO3 (s) ➙ CaO (s) + CO2 (g)
8. The calcium oxide (CaO) thus formed will combine with silicon dioxide (SiO2).
• This SiO2 is the main impurity. It is sand.
• The reaction between sand and CaO converts the sand into calcium silicate.
• The equation is: CaO (s) + SiO2 (s) ➙ CaSiO3 (s)
• Thus the sand is removed.
9. Now we are left with the iron oxide Fe2O3
• It will soon be reduced to iron. Let us see:
10. At the bottom of the furnace, coke combines with the oxygen. This oxygen is obtained from the hot blast of air.
• The equation of the reaction is: C (s) + O2 (g) ➙ CO2 (g) + heat
• From the equation, we can see that it is an exothermic reaction. So the temperature rises upto 1800o C.
• The CO2 thus produced rises to the upper parts of the furnace. It will get reduced by coke.
• The equation is: CO2 (g) + C (s) + heat ➙ 2CO (g)
11. The temperature in these upper parts is lower than the temperature at the bottom parts. This is because, the reaction here is endothermic.
• Note that, the 'heat' is on the left side of the arrow. So there is an 'absorption of heat'
• The fig.13.7 above indicates that the lower parts are 'white hot'. While upper parts are 'red hot'.
♦ 'White hot' is much hotter than 'red hot'.
♦ There is a gradation from white to red as we go upwards
• The carbon monoxide reaches the middle portion of the furnace and reacts with the iron oxide.
• The iron oxide gets reduced to iron.
• The equation is: Fe2O3 (s) +3CO (g) ➙ 2Fe (s) + 3CO2 (g)
12. The iron thus formed moves downwards.
• Due to the high temperatures in the lower parts, it will melt into liquid form.
• This liquid gets collected at the bottom of the furnace. From there it can be taken out. This is shown in fig.13.7 above
Thus we successfully produce iron. Now we have to learn some technical terms involved in the above process.
■ The impurity in the ore is called gangue.
• See step (5) above. In our present case, sand (SiO2) is the gangue.
■ The chemical that is used to remove the gangue is called the flux.
• In step (8), we see that the calcium oxide (CaO) combines with sand to form calcium silicate.
• So in our present case, CaO is the flux
■ The product formed as a result of the reaction between gangue and flux is called the slag.
• The only way to remove the sand is by converting it to 'another material'.
• In step (8) we see that this 'another material' is calcium silicate (CaSiO3). It is formed as a result of the reaction between the gangue and the flux.
• So in our present case, CaSiO3 is the slag.
■ CaO is chosen as the flux because it is basic in nature. It will react with the gangue (SiO2) which is acidic in nature
13. The slag formed in our present case will melt due to the high temperature. So like the molten iron, it also becomes a liquid and gets collected at the bottom of the furnace
• But the two liquids do not mix together. This is because, the slag is lighter.
• So it floats above the molten iron. So it can be removed easily. This is shown in the fig.13.7 above
• The formation of the separate 'slag layer' above the 'molten iron layer' has the following advantages:
♦ The two can be removed from the furnace easily
♦ Contact between molten iron and oxygen is avoided, thus preventing the formation of iron oxide.
14. The iron produced in this way has 4% carbon.
• That is., if we take 100 grams of this iron, 4 grams will be carbon
• This much carbon is not allowable. It will prevent the iron from acquiring it's unique properties.
• This iron has other impurities also like manganese, silicon, phosphorus etc.,
• This iron is called pig iron. Images can be seen here. It has only limited use and is an intermediate product of the iron industry.
15. The pig iron is taken to another special furnace (The electric arc furnace is used in modern days).
• There, it is mixed with scrap iron and coke and again melted.
• The product obtained is called cast iron. It contains 3% carbon
• When molten cast iron cools and solidifies, there will be an increase in volume.
• So the molten cast iron is poured into moulds to make various shapes. Some products can be seen here.
• The shapes thus obtained are very hard. But they will break if subjected to bending.
16. The cast iron can be purified further.
• The product obtained will contain only 0.2 - 0.5% carbon.
• It will also contain some traces of phosphorus and silicon. This is called wrought iron.
• Some products using wrought iron can be seen here.
17. So we can write:
Pig iron ➙ Cast iron ➙ Wrought iron
Following are some of the processes done on steel:
■ Annealing:
• Heat the steel to high temperature
• And then allow it to cool slowly.
• This will make the steel ready to be shaped into different forms
■ Hardening:
• Heat the steel to high temperature
• And then cool it rapidly by dipping in water or oil
• This will make the steel very hard. But it will be brittle
■ Tempering:
• Heat the hardened steel until it becomes blue in colour
• And then allow it to cool slowly.
• This will make the hardened steel less brittle, while maintaining the hardness
We will now see 3 alloys in which iron is a component:
1. Name: Stainless steel
Components: Iron (Fe), Chromium (Cr), Nickel (Ni) and Carbon (C)
Properties: Strong, will not rust.
Uses: For the manufacture of utensils, parts of vehicles
2. Name: Alnico
Components: Iron (Fe), Nickel (Ni), Aluminium (Al) and Cobalt (Co)
Properties: Magnetic in nature
Uses: For the manufacture of permanent magnets
3. Name: Nichrome
Components: Iron (Fe), Nickel (Ni), Chromium (Cr), and Carbon (C)
Properties: High resistance
Uses: For the manufacture of heating coils
■ If we examine the above alloys, we can note an interesting point:
• Stainless steel and nichrome have the same components. But their properties are different.
• Why is that so?
Ans: The difference in properties is achieved by increasing or decreasing the quantity of each component of the alloys. For example:
• Take 100 grams of stainless steel
Let the amount of chromium contained in it be x1 grams
• Take 100 grams of nichrome
Let the amount of chromium contained in it be x2 grams
• Then x1 will not be equal to x2
• In other words, the 'percentage of chromium' in stainless steel and nichrome are different
• Same is applicable for the other components iron, nickel and carbon
■ We can make different alloys by:
• Combining appropriate metals and also by
• Changing the percentage content of each metal or element
In the next section, we will see the industrial production of aluminium and copper.
Industrial production of iron
We will write it in steps:1. Haematite is the principal ore of iron.
• As we have seen in the previous sections, which ever be the metal, the ore has to be powdered.
• The 'concentration of the powdered ore' is the first stage.
2. In the case of haematite, we use the levigation method for the concentration.
• As iron is heavier than the impurities, it will settle to the bottom of the tank.
• The impurities will be washed away.
• So first stage is over
3. The second stage is the extraction of the metal from the concentrated ore.
• We have seen that there are two steps to be completed for this. They are:
(a) Conversion of the ore into it's oxide.
(b) Reduction of the oxide
4. Let us see how they are accomplished in the case of iron:
(a) First we have to convert the iron into iron oxide. There are two methods available.
(i) Calcination and (ii) roasting.
• In the case of iron, roasting is used.
• Haematite is Fe2O3. So it already contains the oxide of iron. Even then, it is subjected to roasting.
• During roasting, impurities like sulphur, arsenic, phosphorus etc., are removed as their gaseous oxides. Water is also expelled.
5. Next, we have to reduce the oxide.
• The haematite obtained after roasting will contain large quantities of silicon dioxide (sand). So we have to remove it to get the pure iron. The following procedure is used:
6. A mixture of roasted haematite, coke and lime stone (CaCO3) is fed into a blast furnace. See fig.13.7 below:
 |
| Fig.13.7 |
• Steel cannot withstand the high temperature produced inside the furnace.
• So the inner side of the furnace is lined with a refractory material.
7. A blast of hot air is sent into the furnace from the bottom.
• At the same time, the mixture containing haematite falls from the top.
• Because of the heat, chemical reactions will take place. Let us see each of those reactions:
• The calcium carbonate (in the form of limestone) which is supplied along with the haematite, will decompose into calcium oxide and carbon dioxide.
The equation is: CaCO3 (s) ➙ CaO (s) + CO2 (g)
8. The calcium oxide (CaO) thus formed will combine with silicon dioxide (SiO2).
• This SiO2 is the main impurity. It is sand.
• The reaction between sand and CaO converts the sand into calcium silicate.
• The equation is: CaO (s) + SiO2 (s) ➙ CaSiO3 (s)
• Thus the sand is removed.
9. Now we are left with the iron oxide Fe2O3
• It will soon be reduced to iron. Let us see:
10. At the bottom of the furnace, coke combines with the oxygen. This oxygen is obtained from the hot blast of air.
• The equation of the reaction is: C (s) + O2 (g) ➙ CO2 (g) + heat
• From the equation, we can see that it is an exothermic reaction. So the temperature rises upto 1800o C.
• The CO2 thus produced rises to the upper parts of the furnace. It will get reduced by coke.
• The equation is: CO2 (g) + C (s) + heat ➙ 2CO (g)
11. The temperature in these upper parts is lower than the temperature at the bottom parts. This is because, the reaction here is endothermic.
• Note that, the 'heat' is on the left side of the arrow. So there is an 'absorption of heat'
• The fig.13.7 above indicates that the lower parts are 'white hot'. While upper parts are 'red hot'.
♦ 'White hot' is much hotter than 'red hot'.
♦ There is a gradation from white to red as we go upwards
• The carbon monoxide reaches the middle portion of the furnace and reacts with the iron oxide.
• The iron oxide gets reduced to iron.
• The equation is: Fe2O3 (s) +3CO (g) ➙ 2Fe (s) + 3CO2 (g)
12. The iron thus formed moves downwards.
• Due to the high temperatures in the lower parts, it will melt into liquid form.
• This liquid gets collected at the bottom of the furnace. From there it can be taken out. This is shown in fig.13.7 above
Thus we successfully produce iron. Now we have to learn some technical terms involved in the above process.
■ The impurity in the ore is called gangue.
• See step (5) above. In our present case, sand (SiO2) is the gangue.
■ The chemical that is used to remove the gangue is called the flux.
• In step (8), we see that the calcium oxide (CaO) combines with sand to form calcium silicate.
• So in our present case, CaO is the flux
■ The product formed as a result of the reaction between gangue and flux is called the slag.
• The only way to remove the sand is by converting it to 'another material'.
• In step (8) we see that this 'another material' is calcium silicate (CaSiO3). It is formed as a result of the reaction between the gangue and the flux.
• So in our present case, CaSiO3 is the slag.
■ CaO is chosen as the flux because it is basic in nature. It will react with the gangue (SiO2) which is acidic in nature
13. The slag formed in our present case will melt due to the high temperature. So like the molten iron, it also becomes a liquid and gets collected at the bottom of the furnace
• But the two liquids do not mix together. This is because, the slag is lighter.
• So it floats above the molten iron. So it can be removed easily. This is shown in the fig.13.7 above
• The formation of the separate 'slag layer' above the 'molten iron layer' has the following advantages:
♦ The two can be removed from the furnace easily
♦ Contact between molten iron and oxygen is avoided, thus preventing the formation of iron oxide.
14. The iron produced in this way has 4% carbon.
• That is., if we take 100 grams of this iron, 4 grams will be carbon
• This much carbon is not allowable. It will prevent the iron from acquiring it's unique properties.
• This iron has other impurities also like manganese, silicon, phosphorus etc.,
• This iron is called pig iron. Images can be seen here. It has only limited use and is an intermediate product of the iron industry.
15. The pig iron is taken to another special furnace (The electric arc furnace is used in modern days).
• There, it is mixed with scrap iron and coke and again melted.
• The product obtained is called cast iron. It contains 3% carbon
• When molten cast iron cools and solidifies, there will be an increase in volume.
• So the molten cast iron is poured into moulds to make various shapes. Some products can be seen here.
• The shapes thus obtained are very hard. But they will break if subjected to bending.
16. The cast iron can be purified further.
• The product obtained will contain only 0.2 - 0.5% carbon.
• It will also contain some traces of phosphorus and silicon. This is called wrought iron.
• Some products using wrought iron can be seen here.
17. So we can write:
Pig iron ➙ Cast iron ➙ Wrought iron
• We often hear the word steel. Words 'iron' and 'steel' are sometimes used interchangeably.
• But they are not the same. Let us see the difference:
■ Iron is an element in the periodic table. It's symbol is Fe
• We try to make pure iron in the blast furnace.
• But the product obtained contain some carbon and other impurities.
• It is not possible to completely avoid the 'presence of some impurities'.
• However pure iron can be prepared in specially equipped labs
■ Steel is an alloy.
• We know that alloy is:
♦ a combination of two or more metals
♦ or a combination of a metal and another element
• Steel is an alloy of 'the metal iron' and 'the element carbon'.
• It should not contain any other element
• Also, the amount of carbon should not exceed 2%
• By varying the content of carbon within the 2%, steels having various properties can be obtained.
♦ Low carbon steels have carbon less than 0.3%
♦ Medium carbon steels have carbon from 0.3% to 0.6%
♦ High carbon steels have carbon more than 0.6%
■ Annealing:
• Heat the steel to high temperature
• And then allow it to cool slowly.
• This will make the steel ready to be shaped into different forms
■ Hardening:
• Heat the steel to high temperature
• And then cool it rapidly by dipping in water or oil
• This will make the steel very hard. But it will be brittle
■ Tempering:
• Heat the hardened steel until it becomes blue in colour
• And then allow it to cool slowly.
• This will make the hardened steel less brittle, while maintaining the hardness
We will now see 3 alloys in which iron is a component:
1. Name: Stainless steel
Components: Iron (Fe), Chromium (Cr), Nickel (Ni) and Carbon (C)
Properties: Strong, will not rust.
Uses: For the manufacture of utensils, parts of vehicles
2. Name: Alnico
Components: Iron (Fe), Nickel (Ni), Aluminium (Al) and Cobalt (Co)
Properties: Magnetic in nature
Uses: For the manufacture of permanent magnets
3. Name: Nichrome
Components: Iron (Fe), Nickel (Ni), Chromium (Cr), and Carbon (C)
Properties: High resistance
Uses: For the manufacture of heating coils
■ If we examine the above alloys, we can note an interesting point:
• Stainless steel and nichrome have the same components. But their properties are different.
• Why is that so?
Ans: The difference in properties is achieved by increasing or decreasing the quantity of each component of the alloys. For example:
• Take 100 grams of stainless steel
Let the amount of chromium contained in it be x1 grams
• Take 100 grams of nichrome
Let the amount of chromium contained in it be x2 grams
• Then x1 will not be equal to x2
• In other words, the 'percentage of chromium' in stainless steel and nichrome are different
• Same is applicable for the other components iron, nickel and carbon
■ We can make different alloys by:
• Combining appropriate metals and also by
• Changing the percentage content of each metal or element
In the next section, we will see the industrial production of aluminium and copper.
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