Main function of roasting is

General Principles And Processes Of Isolation Of Metals (Metallurgy)

1. Metallurgy: The entire scientific and technological process used for extraction of pure metal from its ore is known as metallurgy.

2. Mineral is a naturally occurring chemical substance obtained by mining from the earth’s crust that contains metal in its native state or combined state.

3. Ore: A mineral from which metal can be extracted conveniently and economically is called an ore.

4. All the ores are minerals but all minerals cannot be ores.

5. Gangue or matrix: The earthly and undesired impurities associated with the ore is known as gangue or matrix.

6. Concentration: The process of removal of earthly and unwanted impurities from the ore is called concentration, dressing or benefaction of ore.

7. Some of the important procedures for concentration of ores are Hydraulic washing, magnetic separation, froth floatation method and leaching, roasting.

8. Calcination: It is the process of heating the ore in a limited supply of air below its melting point. This process is used for oxide ores and carbonate ores.

9. Roasting: It is the process of heating the ore in the excess supply of air below its melting point. This process is used for sulphide ores.

10. Smelting: In this process, the roasted or calcined ore is mixed with suitable quantity of coke or charcoal (which acts as a reducing agent) and is heated to a high temperature above its melting point. During reduction, an additional reagent (flux) is also added to the ore to remove the impurities still present in the ore. The flux combines with the impurities to form a fusible product known as slag.

11. Electrolytic reduction: The highly electropositive metals such as alkali metals, alkaline earth metals and aluminium are extracted by electrolysis of their fused salts.

12. The extraction of metals by process of electrolysis is called electrometallurgy.

13. Hydrometallurgy: Certain metals, such as silver and gold, are extracted by dissolving the concentrated ore in some suitable reagent and then recovering the metal from the solution by treatment with some more electropositive metal. Such process in which metal is recovered from aqueous solution is referred to as hydrometallurgy.

14. Ellingham diagram: The graphical representation of the variation of Gibbs energy of formation of oxides with temperature.

15. Distillation: Metals having low boiling points, such as mercury and zinc, can be purified by distillation.

16. Liquation process is applied for purification of metals having low melting points, such as tin and lead.

17. Electrolytic refining: Metals such as copper, silver, aluminium and gold are refined by process of electrolysis. In this method impure metal is made to act as anode, while a thin strip of pure metal is made cathode and solution of some salt of the metal is used as electrolyte.

18. Zone refining: This method is used when metals are required in very high degree of purity. This method is used in purification of germanium, gallium, silicon, etc., which are used in semiconductors.

19. Vapour phase refining: In this method, the metal is converted into its volatile compound which is collected and decomposed to give pure metal.

20. Van Arkel method: Small amounts of very pure titanium and zirconium are obtained by this method

    $\underset{\mathrm{Impure}}{\mathrm{Ti}}+2{\mathrm{I}}_2\stackrel{325-525\mathrm{K}}{\to }\underset{\mathrm{Volatile}}{{\mathrm{TiI}}_4}\stackrel{1700\mathrm{K}}{\underset{\mathrm{ }\mathrm{Volatile}\mathrm{ }\mathrm{Tungsten}\mathrm{ }}{\to }}\mathrm{Ti}+2{\mathrm{I}}_2$

21. Iron is the second most abundant metal in the earth’s crust. The important ores of iron are:

(i) Haematite, ${\mathrm{Fe}}_2{\mathrm{O}}_3$ (red oxide of iron),

(ii) Magnetite, Fe3O4 (Magnetic oxide of iron)

(iii) Siderite, FeCO3

(iv) Iron pyrites, FeS2

     22. The common ore of copper is Copper pyrite, ${\mathrm{CuFeS}}_2$.

(i) Zinc does not occur in native state. In combined state it occurs as:

(ii) Zinc blende: $\mathrm{ZnS}$ (principal ore)

(iii) Calamine: ${\mathrm{ZnCO}}_3$

(iv) Zincite: $\mathrm{ZnO}$

     23. Aluminium is the most abundant metal in the earth’s crust.

     24. Its most important ore is bauxite (Al2O3.2H2O).

     25. Bauxite is concentrated by leaching process. Aluminium is obtained by electrolysis of pure alumina dissolved in molten cryolite. The process is known as Hall-Heroult process.