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Chemistry

Baeyer's process is used to concentrate bauxite ore to alumina. Give balanced chemical equations for the reaction taking place for it's conversion from bauxite to alumina.

Metallurgy

ICSE 2020

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Answer

Conversion of impure bauxite to sodium aluminate:

Al2O3.2H2[Impure bauxite]Amphoteric oxide+2NaOH [conc. soln]Base150200°C2NaAlO2[sodium aluminate]Salt+3H2OWater\underset{\text{Amphoteric oxide}}{\underset{\text{[Impure bauxite]}}{\text{Al}2\text{O}3.2\text{H}2\text{O }}} + \underset{\text{Base}}{\underset{\text{[conc. soln]}}{2\text{NaOH }}} \xrightarrow{150 - 200 \degree\text{C}} \underset{\text{Salt}}{\underset{\text{[sodium aluminate]}}{2\text{NaAlO}2}} + \underset{\text{Water}}{ \text{3H}_2\text{O}}

Conversion of sodium aluminate to aluminium hydroxide:

NaAlO2[sodium aluminate]+2H2O5060°CNaOH[sodium hydroxide]+Al(OH)3[aluminium hydroxide]\underset{\text{[sodium aluminate]}}{\text{NaAlO}2} + 2\text{H}2\text{O} \xrightarrow{50 - 60 \degree\text{C}} \underset{\text{[sodium hydroxide]}}{\text{NaOH}} + \underset{\text{[aluminium hydroxide]}}{\text{Al(OH)}_3}

Conversion of Al(OH)3 - to pure alumina - heat on Al(OH)3:

2Al(OH)3[aluminium hydroxide]1100°CAl2O3[pure alumina]+3H2O\underset{\text{[aluminium hydroxide]}}{\text{2Al(OH)}3} \xrightarrow{1100\degree\text{C}} \underset{\text{[pure alumina]}}{\text{Al}2\text{O}3} + \text{3H}2\text{O}

Precipitated Al(OH)3 is ignited to give pure alumina [Al2O3]

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