Metallurgy of Aluminium.pptx

Metallurgy of Aluminium
Occurence of Aluminium
Ores of Aluminium
Extraction of Aluminium from bauxite

1. Metallurgy of Aluminium Chapter 4 p block elements XII CHM

2. Occurrence Aluminium is the 7% of earth crust Third most abundant element after Oxygen and Silicon

3. Important ores of Aluminium Silicates Kaolin Al 2 O 3. 2SiO 2 .2H 2 O Potash felspar K 2 O.Al 2 O 3 .6SiO 2 Potash mica K 2 O.3Al 2 O 3 .6SiO 2 .2H 2 O Fluoride Cryolite Na 3 AlF 6 Sulphate Alunite K 2 SO 4 .Al 2 (SO 4 ) 3 .4Al(OH) 3 Oxides Bauxite Al 2 O 3 .nH 2 O Gibbisite Al 2 O 3 .3H 2 O Diaspore Al 2 O 3 .H 2 O Corundum Al 2 O 3

4. Bauxite Occurrence : Near Muzaffarabad, Margalla hills, Attock, THarparkar and Dadu

5. Corundum Emerald (Green = Panna) Swat region Ruby (Red = Yaqoot) Hunza, Gilgilt, Kashmir Sapphire (Blue = Neelum) Kashmir Topaz (Yellow = Pukhraj) Chitral

6. Extraction of Aluminium Aluminium is extracted from Bauxite The extraction involves three steps: Purification of Bauxite Electrolysis of pure alumina Refining of Aluminium

7. Purification of Bauxite Impurities: Fe 2 O 3 SiO 2 Three methods are used: Hall’s method Baeyer’s method Serpeck’s method

8. Hall’s method Used when Fe 2 O 3 and SiO 2 impurities are present. Bauxite is fused with sodium carbonate to form soluble sodium illuminate Al 2 O 3 nH 2 O + Na 2 CO 3 → 2NaAlO 2 + CO 2 + nH 2 O Filtration is done to remove impurities and CO 2 is passed to get aluminium hydroxide 2NaAlO 2 + 3H 2 O + CO 2 → 2Al(OH) 3 + Na 2 CO 3 The precipitate of Al(OH) 3 are washed, dried and ignited to get pure alumina 2Al(OH) 3 → Al 2 O 3 + 3H 2 O

9. Baeyer’s Method Used when excess Fe 2 O 3 is present as impurity Bauxite is dissolved in NaOH at 150 o C Impurities are left behind which are removed by filtration Al 2 O 3 nH 2 O + 2NaOH → 2NaAlO 2 + 2 nH 2 O NaAlO 2 + 2H 2 O → Al(OH) 3 + NaOH 2Al(OH) 3 +Heat → Al 2 O 3 + 2H 2 O

10. Serpeck’s method Used when SiO 2 is present in excess as impurity Bauxite is heated with C and N to form aluminium nitride Al 2 O 3 nH 2 O + 3C + N 2 → 2AlN + 3CO + nH 2 O SiO 2 + 2C → Si + 2CO Aluminium nitride upon hydrolysis produces aluminium hydroxide precipitates AlN + 3H 2 O → Al(OH) 3 + NH 3 2Al(OH) 3 + Heat → Al 2 O 3 + 3H 2 O

11. 2. Electrolysis of Alumina Construction of Electrolytic cell Steel tank lined with graphite which act as cathode Anode is suspended carbon rods Electrolyte is molten alumina dissolved in fused Cryolite Na 3 AlF 6 and fluorspar CaCl 2 Cryolite decreases the Melting point about 950 o C Fluorspar increases the fluidity of metal

12. Working of cell Upon electrolysis, Al is collected at cathode at the bottom of tank from where it is removed periodically Oxygen is collected at carbon anode which forms CO 2

13. 3. Refining of Aluminium - Hoop’s electrolytic method Impurities such as Cu, Si and Fe are removed at this stage The electrolysis cell is an iron tank which has three layers or different specific gravity

14. Hoop’s electrolytic cell - Layers Top layer contains pure Al which acts as cathode Middle layer contains cryolite Na 3 AlF 6 and BaF 2 Bottom layer contains impure Al

15. Hoop’s electrolytic cell - Working When Current is passed Al +3 ions from middle layer go to top layer (cathode) and discharged there as pure Al - 99.9% purity Equivalent amount of Al from Bottom layer is passed into middle layer The impurities settle down at the bottom of tank

16. Hoop’s Electrolytic method - cell reactions Na 3 AlF 6 → 3NaF + AlF 3 AlF 3 → Al +3 + 3F - Al +3 + 3e - → Al (Cathode) Al → Al +3 + 3e - (Anode) Over all reaction: Al +3 + Al → Al + Al +3

17. Physical properties of Aluminium Bluish white metal with brilliant silvery luster which is destroyed by formation of oxide Light and cheap Malleable and ductile Resistant to corrosion Good conductor of heat and electricity Density 2.7 gm/ml M.P 658 o C B.P 1800 o C

18. Uses of Aluminium Electrical transmission wires Foil is used for wrapping food items, medicines, cigarettes , photographic films Cooking utensils, cans Mixture of aluminium powder and Aluminium nitrate is called ammonal is used in explosive bombs

19. Alloys of Aluminium - Aluminium Bronze 10% Al and 90% Cu Golden in color Light and tough Resistant to corrosion Used in manufacture of coins, jewellery and statues

20. Alloys of Aluminium - Dura Lumin 95% Al 4% Cu 0.5% Mg and 0.5% Ni Light, tough, ductile, tensile Resistant to corrosion Used in making aircrafts