Question

How is Bauxite purified by Serpeck's process?

Answer 1

Finely powdered bauxite $\left(A{l}_2{O}_3\right)$ is heated with coke and $N_2$ to 2000 K. Alumina forms aluminium nitride and silica is reduced to Si which is volatile. The hydrolysis of aluminium nitride gives aluminium hydroxide which on heating gives pure alumina.
$A{l}_2{O}_3\cdot 2H_{2}O+N_2+3C\stackrel{2000K}{\to }2AlN+3CO\uparrow +2H_{2}O$
$Si{O}_2+2C\to Si\uparrow +2CO\uparrow$
$AlN+3H_{2}O\to Al(OH{)}_3\downarrow +N{H}_3$