Write the three main reactions of purification of alumina.
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When finely divided bauxite is treated with strong caustic soda then bauxite is converted into sodium aluminate
Al2O3.nH2O +2NAOH - 2NaAlO2 +2nH2O
The sodium is filtered to remove Fe2O3
The fused mass is extracted with water leaving behind both impurities. Sodium aluminate is then heated up to 50°C to 60°C in the presence of CO2
The precipitates of aluminum hydroxide are formed
2NaAlO2 +3H2O +CO2 - 2Al(OH)3 +Na2CO3
The precipitates of Al(OH)3 are washed to remove sodium carbonate dried and ignited at about 1500°C to get pure alumina
2Al(OH)3 - Al2O3 +3H2O
Al2O3.nH2O +2NAOH - 2NaAlO2 +2nH2O
The sodium is filtered to remove Fe2O3
The fused mass is extracted with water leaving behind both impurities. Sodium aluminate is then heated up to 50°C to 60°C in the presence of CO2
The precipitates of aluminum hydroxide are formed
2NaAlO2 +3H2O +CO2 - 2Al(OH)3 +Na2CO3
The precipitates of Al(OH)3 are washed to remove sodium carbonate dried and ignited at about 1500°C to get pure alumina
2Al(OH)3 - Al2O3 +3H2O
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