These notes for CBSE Class 12 Chemistry, Chapter 6, cover the General Principles and Processes of Isolation of Elements. Metallurgy, the process of extracting metals from ores, involves three main steps: concentration of the ore, isolation of the metal from the concentrated ore, and purification of the metal. The chapter details various methods for ore concentration like hydraulic washing, magnetic separation, froth flotation, and leaching. It explains the extraction of crude metal through conversion to oxide (calcination and roasting) and subsequent reduction using thermodynamic principles, including Ellingham diagrams, and electrochemical principles. Finally, the notes discuss refining techniques for crude metals such as distillation, liquation, electrolytic refining, zone refining, vapour phase refining, and chromatographic separation. These notes are ideal for students to revise the key concepts of metal extraction and purification for their exams.
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The entire scientific and technological process used for isolation of the metal from it‘s ore.
The extraction involves 3 major steps
(i) concentration of the ore
(ii) isolation of the metal from it‘s concentrated ore
(ii) purification of the meta
| Metal | Important ores |
| Aluminium | Bauxite(Al2O3. xH2O) |
| Zinc | Zinc blend (ZnS), calamine (ZnCO3) |
| Iron | Haematite (Fe2O3) & magnetite (Fe3O4) |
| Copper | copper pyrites (CuFeS2) , copper glance (Cu2S) |
Concentration: Removal of the unwanted materials from the ore.
(i) Hydraulic washing :– It is based on the differences in gravities of the ore & the gangue particles.
(ii) Magnetic separation :– It is based on the differences in magnetic properties of the ore components.
(iii) Froth floatation :– It is used for removing gangue from sulphide ores. Collectors (e. g., pine oils) enhance non-wettability of the mineral particles. Froth stabilisers (e. g., cresols, aniline) stabilise the froth.
(iv) Leaching :- It is often used if the ore is soluble in some suitable solvent.
(i) Conversion to oxide Calcinaton:- It involves heating when the volatile matter escapes leaving behind the metal oxide.
Eg :- ZnCO3 (s) ? ZnO(s) + CO2(g)
Roasting : The ore is heated in a regular supply of air at a temperature below the melting point of the metal
Eg :- 2ZnS + 3O2 ? 2ZnO + 2SO2
(ii) Reduction of the oxide to metal - It involves heating metal oxide with a reducing agent (C or CO or even another metal).
MxOy + yC ? xM + y CO
The metal oxide is reduced to the metal by reducing agent . This is a redox reaction and it is feasible only at a temperature at which ?G0 value is negative .
?G0= ?H0 -T?S0
This is a graph which represents the variation of standard Gibb‘s energy with temperature for the formation of oxides of various elements . (refer fig. 6.4 of NCERT text book ) From the Ellingham Diagram it is evident that (a) Any metal oxide with lower ?G0 value is more stable than the metal oxide with higher?G0 (b) The element (or metal) involved in the formation of oxide placed lower in the diagram can reduce the oxide of the element (or metal ) placed higher in the diagram .
When aqueous solution or molten form of a metal oxide /halide is electrolyzed , the metal with higher value of reduction potential will get reduced (molten metal will be deposited ) and the metal with the lower value of reduction potential will undergo oxidation .
(i) Distillation :- In this method the impure metal is evaporated to obtain the pure metal as distillate. (ii) Liquation :-In this method a low melting metal is separated from higher melting impurities. (iii)Electrolytic refining :– In this method, the impure metal is made as anode , a strip of the same metal in the pure form is used as cathode . The electrolyte is aqueous solution of a suitable soluble salt of the same metal . (iv)Zone refining :- This method is based on the principle that the impurities are more soluble in the melt than in the solid state of the metal (v) Vapour phase refining :- In this method the following requirements are needed. (a) The metal should form a volatile compound (b) The volatile compound should be easily decomposable. (vi) Chromatographic separation :- This method is based on the principle that different components of a mixture are differently adsorbed on an adsorbent
Metallurgy is the entire scientific and technological process used for the isolation of a metal from its ore.
The three major steps are: concentration of the ore, isolation of the metal from its concentrated ore, and purification of the metal.
Froth flotation is used for removing gangue from sulphide ores.
It is based on the principle that a metal oxide is reduced to metal by a reducing agent only at a temperature where the standard Gibbs energy change (?G°) is negative.
An Ellingham Diagram represents the variation of standard Gibbs energy with temperature for the formation of oxides of various elements.
In electrolytic refining, the impure metal is made the anode, a pure strip of the same metal is the cathode, and an aqueous solution of a soluble salt of the metal is the electrolyte.
Zone refining is based on the principle that impurities are more soluble in the molten state than in the solid state of the metal.
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