Question

Complete the  statement using every given option.
During the extraction of aluminium..............

Chemical reaction of transformation of bauxite into alumina by Hall’s process.

Answer 1

In the Hall’s process the bauxite is in powdered form and then leached by heating with aqueous sodium carbonate in the digester to form water soluble sodium aluminate. Then the insoluble impurities are filtered out. The filtrate is warmed and neutralised by passing carbon dioxide gas through it. This results in the precipitation of aluminium hydroxide.

\[A l_2 O_3 2 H_2 O (s) + N a_2 C O_3 (aq) \to 2NaAl O_2 (aq) + C O_2 + 2 H_2 O (l)\]
\[ 2NaAl O_2 (aq) + 3 H_2 O + C O_2 (g) \to 2Al(OH )_3 + N a_2 C O_3 \]

The precipitate of Al(OH)₃ obtained in both, Bayer’s and Hall’s processes is filtered, washed, dried and then calcined by heating at 1000⁰C to obtain alumina.

\[2Al(OH )_3 \to A l_2 O_3 + 3 H_2 O\]