Question

12. Write then process of extraction of aluminium metal from natural impure bauxite by concentration
and subsequent electrolytic method.​

Answer 1

Answer:

SORRY bro my notebook is at my friends house otherwise I will help you with that.

But now u have to understand from this.

Aluminium is the most abundant metal in the earth’s crust. Aluminium does not occur free in nature, but its compounds are numerous and widely distributed.

The chief and important ore from which aluminium is exclusively and profitably obtained is Bauxite, AI2O3.2H2O. The extraction of the metal from bauxite involves the three main steps.

Purification of Bauxite

Electrolytic reduction of Alumina, (AI2O3)

Purification of AI.

1. Ores of Aluminium

Name of Ore

Formula of Ore

Bauxite

Al2O3×2H2O

Cryolite

Na3AlF6

Feldspar

K2Oal2O3×6SiO2 or KalSi3O8

Mica

K2O×3Al2O3×6SiO2×2H2O

Corundum

Al2O3

Aluminium is mainly extracted from bauxite ore.

2. Extraction of Aluminium

Purification of Bauxite

By Bayer’s process comercially it is being carried out (for red bauxite not for the white bauxite).

Flow sheet of Bayer’s process for the preparation of pure Al2O3

Purification of Bauxite

Hall’s process

Crude bauxite at 1100°C reacts with Na2CO3, little CaCO3 when CaSiO3, NaSiO2, NaFeO2 etc. form

Al2O3 + Na2CO3 → 2NaAlO2 + CO2­

Fe2O3 + Na2CO3 → 2NaFeO2 + CO2­

SiO2 + Na2CO3 → Na2SiO3 + CO2­

CaO + SiO2 → CaSiO3

Then at 50° – 60°C CO2is passed through NaAlO2 solution and produces thereby Al(OH)3

2NaAlO2 + CO­2 + 3H2O ¾® 2Al(OH)3¯ + Na2CO3

2Al(OH)3 \overset{100^{o}c}{\rightarrow}Al2O3 + 3H2O­

Serpeck’s Process

Bauxite containing high percentage of silica can be purified by Serpeck’s process. In this process finely powdered bauxite is mixedf with coke and the mixture is heated to 1800°C in a current of nitrogen. The AlN thus obtained is reacted with hot and dilute NaOH, produced NaAlO2 and excess AlN is hydrolysed and Al(OH)3 is formed.

Al2O3 + 3C + N2 → 3AlN + 3CO­

SiO2 + 2C → Si­ + 2CO­

AlN +NaOH → NaAlO2 + NH2+

NaAlO­2 + 2H2O → Al(OH)3¯ + NaOH

AlN + 3H2O → Al(OH)3¯ + NH3­

2Al(OH)3 \overset{100^{o}c}{\rightarrow}Al2O3 + 3H2O­

Electrolytic Reduction of Al2O3

Pure alumina melts at about 2000°C and is a bad conductor of electricity. If fused cryolite AlF3.3NaF and CaF2 (Fluorspar) is added the mixture melts at 900°C and Al­2O3 becomes a good conductor of electricity. Metallic Al is liberated at the cathode

Electrolytic Reduction of Al2O3

Alumina is mixed with cryolite (Na3AIF3), fluorspar (CaF2) in the ratio 20 : 60 whereby, it not only becomes good conductor but also fuses at about 900oC which is much below the b.p. of aluminium.

The electrolysis of the fused mass is carried out in an iron box, which lined with gas carbon. The lining serves as the cathode, the anode consists of carbon rods dipped in the fused mass. The fused electrolyte is kept covered with a layer of powdered coke to prevent any action of air. The voltage employed in the electrolysis is 5.3 volts. The current passed (about 50,000 amperes) serves to purposes: (i) heating and (ii) electrolysis. Thus the fused mass is automatically kept at 900oC during electrolysis.

Aluminium is obtained at the cathode and being heavier than the electrolyte sinks to the bottom and is tapped off periodically from the tap hole. Oxygen liberated at the anode attacks carbon rods and forms CO and CO2. During electrolysis the concentration of the electrolyte goes on falling thereby increasing the resistance of the cell which is indicated by the glowing of a lamp placed parallel. Much of the alumina is then added and the process is made continuous.

Electrolysis of molten mixture

Cathode: Carbon

Anode: Graphite rods

Electrolyte: 60 parts cryolite + 20 parts fluorspar + 20 parts pure Al2O3

Temperature: 900°C

Reactions

According to the 1st theory the following reaction occurs

Al2O3 \rightleftharpoons 2Al+3 + 3O–2

At cathode : 2Al+3 + 6e → 2Al

At anode : 3O–2 – 6e → 3O2­

As cryolite has greater electrochemical stability it does not dissociate. It only increases the dissociation of Al2O3

But the second theory states that, cryolite undergoes electrolytic dissociation first then Al+3 goes to the cathode, produced F2 at anode then reacts with Al2O3 produces AlF3.

AlF3.3NaF ------->Al+3 + 3Na+ + 6F–

At cathode : Al+3 + 3e → Al

At anode : 6F– – 6e → 3F2

Overall Reaction : Al2O3 + 6F­2 → 4AlF3 + 3O2­

Answer 2

Scandium and Germanium