Question

Describe the role played by Sodium hydroxide in the extraction of aluminium.

Answer 1

The role played by sodium hydroxide in the extraction of Aluminium:
Two major roles are played by sodium hydroxide in the extraction of aluminium,

1. Sodium aluminate is produced by heating finely ground bauxite under pressure with $\mathrm{NaOH}$ a solution for 2-4 hours at $140°\mathrm{C}-150°\mathrm{C}$.
2. $$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3.2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{l}\right)\to 2{\mathrm{NaAlO}}_2\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Bauxite}\mathrm{Sodium}\mathrm{hydroxide}\mathrm{Sodium}\mathrm{Aluminate}\mathrm{Water} \end{gathered}$$
3. Aluminium hydroxide precipitate is obtained by hydrolyzing sodium aluminate solution by diluting it with water and cooling it to $50°\mathrm{C}$. The impurities get dissolved in sodium hydroxide solution.