Question

Observe the following statements regarding purification of bauxite
I. During Hall's process, silica is removed as Si (vapour).
II. Bauxite ore contaminated with $F{e}_2{O}_3$ is purified in Baeyer's process.
III. During Serpeck's process, $AlN$ is formed.
The correct answer is

• A. I, II and III are correct
• B. Only I and II are correct
• C. Only I and III are correct
• D. Only II and III are correct

Answer 1

Answer: (D)

Red bauxite which contains $F{e}_2{O}_3$ as the main impurity, is refined either by Baeyer's process or by Hall's process. White bauxite containing $Si{O}_2$ impurity is refined by Serpeck's method. In Serpeck's method, following reactions take place.
$A{l}_2{O}_3\cdot 2H_{2}O+3C+N_2\stackrel{1800^{\circ }\mathrm{C}}{\to }2AlN+3CO+2H_{2}O$
$AlN+3H_{2}O⟶Al(OH{)}_3+N{H}_3$
$2Al(OH{)}_3⟶A{l}_2{O}_3+3H_{2}O$