Metallurgy class 10 notes - ICSE CHEMISTRY

Metallurgy Important points for Final exam ICSE BOARD

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Notes of Metallurgy Chemistry ICSE

Mineral: Naturally occurring compounds of metals along with the earthly impurities.

Ore: The mineral from which metals are extracted easily and profitably.

Metallurgy: The process in which metals are extracted from their minerals.

Matrix (or) Gangue: The impurities that associated with an ore.

 

Metallurgy involves the following steps:

Step -I - Concentration of Ore-Removal of impurities.

Step - II - Conversion of ore to metal oxide.

Step - III - Reduction of the metal oxide to the metal.

Step - IV - Refining impure metal to pure metal.

 

 

Extraction of Aluminium from Bauxite ore:

Ore : Bauxite – Al₂O₃.2H₂O – Hydrated Aluminium oxide

 

Step I: Concentration of ore

            The matrix is removed by chemical method.

            Chemical used : Conc. Sodium hydroxide solution

            Process name: Baeyer’s process

 

æ      Al₂O₃.2H₂O + 2NaOH --> 2NaAlO₂ + 3H₂O

The amphoteric nature of Aluminium oxides makes it react with NaOH where as other impurities like Fe₂O₃ and SiO₂ do not react and will be separated out.

           

æ      NaAlO₂ + 2H₂O -->  NaOH + Al(OH)₃

Al(OH)₃ crystals are added to the dil. NaAlO₂ solution to further precipitate out Al(OH)₃ crystals this process is called seeding.

 

æ      2Al(OH)₃  --> Al₂O₃ + 3H₂O

                                                      Alumina

Step II : This step is not necessary as the pure ore is an oxide.

 

Step III : Reduction of pure Alumina to Aluminium.

            Aluminium oxide (Alumina) is not reduced by reducing agents because it is highly stable hence Alumina is reduced by electrolysis in Hall Heroult’s process.

 

Hall Heroult’s process

 

Electrolyte                   : Fused mixture of Alumina (Al₂O₃) , Cryolite (Na₃AlF₆) and

                                    Fluorspar (CaF₂) in the ratio 1:3:1.

Reason: Cryolite lowers the fusion point of Alumina (2050⁰C to 950⁰C)and enhances the conductivity of the electrolyte.

Electrolytic cell           : Steel tank with Carbon lining acts as cathode.

Electrodes                   : Anode – A series of Graphite electrodes

                                    Cathode – The electrolytic cell with Carbon lining

Graphite rods connected in a series is taken as anode instead of one Graphite rod because the Oxygen released at anode will oxidize them to CO and CO₂.

Precaution:

Coke powder is sprinkled on the surface of fused electrolyte.

Reason: It prevents the oxidation of anode by the atmospheric Oxygen and heat loss by radiation.

 

Electrolytic reaction involves the following steps:

Na₃AlF₆ --> 3Na⁺ + Al³⁺ + 6F ^–

CaF₂ --> Ca²⁺ + 2F ^–

Al₂O₃ --> 2Al³⁺ + 3O^{2 –}

at cathode : 2Al³⁺ + 6e ^–  --> 2Al                  product: pure Aluminium metal

at anode : 6O^{2 –} - 12e ^–  -->  3O₂                           product: Oxygen gas (CO and CO₂)

 

Step IV is not necessary because the Aluminium metal obtained in Hall Heroult’s process is 99.5% pure. (Further purification can be done by Hoope’s process.)