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Extraction of Aluminium.
The principal or of aluminium,bauxite usually contains silicon dioxide(SiO2  ),iron oxides and titanium oxide(TiO2 ) as impurities .Concentration is carried out by digesting the powdered ore with a concentrated solution of sodium hydroxide at 473 -523 K and 35-36 bar pressure .This way Al2O3 is leached out as sodium aluminate leaving the impurities behind


The aluminate in solution is neutralised by passing CO2  gas and hydrated Al2O3 is precipitated .At this stage ,the solution is seeded with freshly prepared samples of hydrated Al2O3 which includes the precipitation .

   
The sodium silicate remains in the solution and hydrated alumina is filtered,dried and heated to give back pure Al2O .


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