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  • Which among the following reactions does not take place during leaching for concentration of bauxite?Option: 1 <img alt="\begin{aligned} & \mathr

Which among the following reactions does not take place during leaching for concentration of bauxite?

Option: 1

\begin{aligned} & \mathrm{Al}_2 \mathrm{O}_3(\mathrm{~s})+2 \mathrm{NaOH}(\mathrm{aq})+3 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{Na}\left[\mathrm{Al}(\mathrm{OH})_4\right](\mathrm{aq}) \\ \end{aligned}


Option: 2

2 \mathrm{Na}\left[\mathrm{Al}(\mathrm{OH})_4\right](\mathrm{aq})+\mathrm{CO}_2(\mathrm{~g}) \rightarrow \mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{xH}_2 \mathrm{O}(\mathrm{s})+2 \mathrm{NaHCO}_3(\mathrm{aq}) \\


Option: 3

\mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{xH}_2 \mathrm{O}(\mathrm{s})+\mathrm{Heat} \rightarrow \mathrm{Al}_2 \mathrm{O}_3(\mathrm{~s})+\mathrm{xH}_2 \mathrm{O}(\mathrm{g}) \\


Option: 4

\mathrm{Al}_2 \mathrm{O}_3(\mathrm{~s})+\text { Heat } \rightarrow 2 \mathrm{Al}+3 \mathrm{O}_2


Answers (1)

best_answer

In leaching, a suitable reagent (not water) dissolves the ore but not the impurities. Thus, leaching is a chemical method of concentration of the ore. 

Leaching is used in extraction of aluminium from bauxite.

\mathrm{Al}_2 \mathrm{O}_3(\mathrm{~s})+2 \mathrm{NaOH}(\mathrm{aq})+3 \mathrm{H}_2 \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{Na}\left[\mathrm{Al}(\mathrm{OH})_4\right](\mathrm{aq})

Sodium Aluminate is filtered. The filtrate is neutralised by passing \mathrm{CO_{2}} gas.

2 \mathrm{Na}\left[\mathrm{Al}(\mathrm{OH})_4\right](\mathrm{aq})+\mathrm{CO}_2(\mathrm{~g}) \rightarrow \mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{xH}_2 \mathrm{O}(\mathrm{s})+2 \mathrm{NaHCO}_3(\mathrm{aq})

The sodium silicate remains in the solution and hydrated alumina is filtered, dried and heated to about 1200?C to get pure Alumina \mathrm{ (Al_{2}O_{3}).}

\mathrm{Al}_2 \mathrm{O}_3 \cdot \mathrm{XH}_2 \mathrm{O}(\mathrm{s})+\text { Heat } \rightarrow \mathrm{Al}_2 \mathrm{O}_3(\mathrm{~s})+\mathrm{xH}_2 \mathrm{O}(\mathrm{g})

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