Question

Purification of alumina takes place by ______.
(A) Bosch process
(B) Hall’s process
(C) Hoope’s process
(D) Quartation process

Answer 1

We know that alumina is aluminium oxide. Alumina is obtained from bauxite which is an ore of aluminium. Alumina is purified by fusing bauxite ore with sodium carbonate. To solve this we must know the process to purify alumina.

Complete Answer:
We know that alumina is aluminium oxide. Alumina is obtained from bauxite which is an ore of aluminium. Bauxite is an impure form of alumina i.e. aluminium oxide. Bauxite ore contains impurities like ferric oxide and silica. Bauxite ore is crushed and pulverized first. The impurities like ferric oxide are removed by magnetic separation. The bauxite ore is then concentrated by Hall’s process.

The steps involved in bauxite ore are as follows:
Step 1: Conversion of bauxite to sodium aluminate: In this step, bauxite ore is fused with sodium carbonate and sodium aluminate is produced. The reaction is as follows:
${\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}} \cdot {\text{2}}{{\text{H}}_{\text{2}}}{\text{O}} + {\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}} + {\text{Heat}} \to {\text{2NaAl}}{{\text{O}}_{\text{2}}} + {\text{2}}{{\text{H}}_{\text{2}}}{\text{O}} + {\text{C}}{{\text{O}}_{\text{2}}}$

Step 2: Conversion of sodium aluminate to aluminium hydroxide: In this step, sodium aluminate is converted to aluminium hydroxide by allowing it to react with water and carbon dioxide. The reaction is as follows:
${\text{2NaAl}}{{\text{O}}_{\text{2}}} + {\text{3}}{{\text{H}}_{\text{2}}}{\text{O}} + {\text{C}}{{\text{O}}_{\text{2}}} \to {\text{N}}{{\text{a}}_{\text{2}}}{\text{C}}{{\text{O}}_{\text{3}}} + {\text{2Al}}{\left( {{\text{OH}}} \right)_{\text{3}}}$

Step 3: Conversion of aluminium hydroxide to pure alumina: In this step, aluminium hydroxide is heated at ${1100^ \circ }{\text{C}}$ and converted to alumina i.e. aluminium oxide. The reaction is as follows:
${\text{2Al}}{\left( {{\text{OH}}} \right)_{\text{3}}} + {1100^ \circ }{\text{C}} \to {\text{A}}{{\text{l}}_{\text{2}}}{{\text{O}}_{\text{3}}} + {\text{3}}{{\text{H}}_{\text{2}}}{\text{O}}$
Thus, purification of alumina takes place by Hall’s process.

Thus, the correct option is (B) Hall’s process.

Note: Aluminium is a highly reactive metal. Aluminium belongs to group 13 of the periodic table. Naturally, aluminium is found in the form of oxides. The common ores of aluminium are bauxite, corundum, cryolite, etc.