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  Inorganic Chemistry

Aluminum :

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(1) Ores of Aluminum : Bauxite ( AI2O3.2H2O) Cryolite ( Na3AIF6, Felspar (KAISi3O8 ), Kaolinite (AI2O3. 2SiO2.2H2O ), Mica ( K2O.3AI2O3.6SiO2.2H2O), Corundum ( AI2O3) , Diaspore (AI2O3.H2O) Alunite or alum stone [ K2SO4. AI2(SO4)3. 4AI(OH)3]

(2) Extraction : Aluminum is obtained by the electrolysis of the oxide (alumina) dissolved in fused cryolite. This involves following steps,

Purification of ore

(i)Baeyer's process

                  Roasted                      + Caustic soda solution
Bauxite———→Roasted ore ——————→
Finely powdered          FeO→Fe2o3             high pressure (150oc, 80atm)
(red)                                                            filtered, Fe2O3 asresidue
                     Filtered                                 Heat
FiItrate ———→ Pure AI2O3 ——→ AI(OH)3
(Sod. Aluminate) CO2

(ii) Hall's process

                                +Na2CO3                                CO2
Bauxite ——————→ Solution ———→
(Finely powdered)      Fused, extracted with       50 - 60oC and filtered.
(red)                           water.Residue Fe2O3        Filtrate (Na2CO3)

                                                      Heat
Precipitate Al (OH)3 ————→ Pure Al2O3

(iii) Serpek's process

                    + Coke +N2
Bauxite ————→ Silicareduced to + Alumina form AIN
(Finely powdered)   Heated to      Si which volatalises   aluminium           nitride
(white)                     1800oC

Hydrolysis                                 Heated
————→Pure AI2O3 ————AI(OH)3

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