Chemistry in Industry and Technology

1. Chemistry in Industry and Technology Option C

3. The Blast Furnace

4. This follows closely from IGCSE work. If you can’t remember the work you did at IGCSE then you need to revise! • You will learn about some different sources of iron, and you will learn more detail about the chemical reactions that happen in a blast furnace.

5. Syllabus Statements • C1.1 State the main sources of iron. • C1.2 Describe the main reactions that occur in the blast furnace.

6. Tuyere

7. The Iron Ore fed into the blast furnace may be a number of different compounds: • Haematite Fe2O3(this is the one you learnt at IGCSE) • Magnetite Fe3O4 • Iron Pyrites FeS2(Fool’s gold!) FeS2 must be converted to the oxide: 4FeS2 + 11O2 2Fe2O3 + 8SO2

8. Coke is also fed in at the top. • This provides a source of carbon to reduce the iron oxide. • Fe2O3 + 3C  2Fe + 3CO • This DOES happen to a small extent – but from IGCSE you know its not really that simple!

9. Most of the reduction is done by Carbon Monoxide CO. • C + O2 CO2 • CO2 + C  2CO

10. This carbon monoxide then reduces the iron ore. • Either • Fe2O3 + 3CO  2Fe + 3CO2 • Or • Fe3O4 + 4CO  3Fe + 4CO2

11. Both these reactions are exothermic. • The iron produced is molten because of the high temperature. (Iron melts at 1536 °C or 2797 °F (1811 K). It boils at 2862 °C or 5182 °F (3134 K).) • It sinks to the bottom of the furnace where it can be “tapped”

12. There are 2 more possible reaction mechanisms that you need to learn: • If methane (“natural gas”) is blown into the furnace, then incomplete combustion can take place. • 2CH4 + O2 2CO + 4H2 • Then either the CO can act as the reducing agent as before, or the H2 can act as the reducing agent. • Write balanced equations for hydrogen reducing both the forms of iron oxide present.

13. Fe3O4 + 4H2 3Fe + 4H2O • Fe2O3 + 3 H2  2Fe + 3H2O

14. Getting rid of impurities • The iron ore fed into the blast furnace is NOT a pure chemical. • It contains impurities such as silicon (IV) oxide and aluminium oxide. • These come from the rocks which contain the iron compounds.

15. Relative abundance of elements in the Earth’s crust • Oxygen 46.6% • Silicon 27.7% • Aluminum8.1% • Iron 5.0% • Calcium 3.6% • Potassium 2.6% • Magnesium 2.6%

16. The third raw material added at the top of the blast furnace is powdered limestone. • This decomposes at the high temperatures involved. • CaCO3 CaO + CO2 • Calcium oxide is “quicklime” • Quicklime is very basic and reacts with the impurities we have mentioned.

17. CaO + SiO2 CaSiO3 • CaO + Al2O3  CaAl2O4 • Silicon oxide is a non-metal oxide and is therefore acidic. • Aluminium oxide is amphoteric!!

18. Both the compounds formed are liquids. • We call them “slag” • They float on top of the molten iron and can be removed through a second outlet. • They are used for roads and making cement. • Because they can be easily removed the blast furnace can be run continuously for a number of years (good economics!). • Eventually the lining of the furnace breaks down and we have to let the whole thing cool down so we can replace it.

19. Reminder . . . • C1.1 State the main sources of iron. • C1.2 Describe the main reactions that occur in the blast furnace.

20. Summary . . .

21. Tuyere