Question

In the extraction of aluminium Process X : employed for red bauxite to remove iron oxide (main impurity)

Process Y: (Serpeck`s process) : used for white bauxite to remove Z (main impurity) then,

Select correct option for the process X and impurity Z.

• A. X = Hall and Heroult`s process and Z = SiO2
• B. X = Bayer`s process and Z = SiO2
• C. X = Serpeck`s process and Y = iron oxide
• D. X = Bayer`s process and Y = iron oxide

Answer 1

Answer: (B)

X = Bayer`s process and Z = SiO2

Answer 2

(X) Red bauxite contains the impurities of oxides of iron and silicates. In Bayer process, alumina is dissolved by reacting sodium hydroxide solution leaving behind the insoluble oxide of iron.

(Y) White bauxite contains the impurity of silica which is removed by Serpeck's method.

Al2O3 + N2 + 3C $\overset{\quad 1800^{0}C\quad}{\rightarrow}$ 2AlN + 3CO ; SiO2 + 2C $\overset{\quad 1800^{0}C\quad}{\rightarrow}$ Si + 2CO

AlN + 3H2O $\longrightarrow$ Al(OH)3 + NH3 ; 2Al(OH)3 $\overset{\quad\Delta\quad}{\rightarrow}$ Al2O3 + 3H2O.