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 $Fe _{2} O _{3}$ 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 $Fe _{2} O _{3}$ as the main impurity, is refined either by Baeyer's process or by Hall's process. White bauxite containing $SiO _{2}$ impurity is refined by Serpeck's method. In Serpeck's method, following reactions take place.
$Al _{2} O _{3} \cdot 2 H _{2} O +3 C + N _{2} \ce{->[{1800^{\circ} C }]} 2 AlN +3 CO +2 H _{2} O $
$AlN +3 H _{2} O \longrightarrow Al ( OH )_{3}+ NH _{3} $
$2 Al ( OH )_{3} \longrightarrow Al _{2} O _{3}+3 H _{2} O$