Question

Role of concentrrated sodium hydroxide in leaching of aluminum from bauxide

Answer 1

$\bold{Use \: of \: Sodium\: hydroxide}$

▶In electrometallurgy of aluminium sodium hydroxide is used in Baeyer's process, to first convert it to sodium aluminate at 150- 200 temperature since,

◼Bauxite is reacted with NaOH under 2 Atmospheric pressure for obtaining pure $\bold{Al_2O_3}$

◼Bauxite have impurities like $\bold{Fe_2O_3}$ and $\bold{SiO_2}$ , since they arent amphoteric they didnt react.

▶Bauxite is amphoteric so it reacts to form salt and water $\bold{Al(OH)_3}$ .

▶Further in process , water and crystals of aluiminium hydroxide are reacted together to obtain aluminium hydroxide by process of seeding.

▶At last , aluminium hydroxide is heated at high temperature to obtain pure alumina.

EQUATION :--

▶${Al_2O_3.H_2O + 2NaOH \longrightarrow 2NaAlO_2 + 3H_2O}$ .

▶${NaAlO_2 + 2H_2O \longrightarrow 2NaOH + Al(OH)_3}$ .

▶${2Al(OH)_3 \longrightarrow Al_2O_3 + 3H_2O}$ .