General Principles and Processes of the Isolation of Elements

General Principles & Process of Isolation of Elements

Important Points :

1. The chemical substances in the earth’s crust obtained by mining are called Minerals.

2. Minerals, which act as source for metal, are called Ore. From ore metal can be obtained economically.

3. The unwanted impurities present in ore are called Gangue.

4. The entire process of extraction of metal from its ore is called Metallurgy.

5. Removal of gangue from ore is called Concentration, Dressing or Benefaction of ore.

6. Concentration by Hydraulic washing is based on the difference in gravities of ore and gangue particles.

7. Concentration by Magnetic separation is based on differences in magnetic properties of ore components. If either of ore or gangue is capable of attracted by a magnet field, then such separation is carried out.

8. Concentration by Froth Flotation Process is based on the facts that sulphide ore is wetted by oil & gangue particles are wetted by water.

9. Concentration by Leaching is based on the facts that ore is soluble in some suitable reagent & gangue is insoluble in same reagent. e.g. Bauxite ore contains impurities of silica, iron oxide & TiO₂ .The powdered ore is treated with NaOH which dissolve Al & impurities remains insoluble in it.

Al₂O₃ +2NaOH + 3H₂O → 2Na [Al(OH)₄].

10. Calcination involves heating of ore in absence of air below melting point of metal. In this process volatile impurities escapes leaving behind metal oxide.

Fe₂O₃.xH₂O → Fe ₂O₃ + xH₂O

ZnCO₃ → ZnO + CO₂

CaCO₃.MgCO₃ → CaO + MgO + 2CO ₂

11. Roasting involves heating of ore in presence of air below melting point of metal in reverberatory furnace. In this process volatile impurities escapes leaving behind metal oxide and metal sulphide converts to metal oxide.

2 ZnS + 3O₂ → 2ZnO +2 SO₂

2 PbS + 3O₂ → 2 PbO +2 SO₂

2 Cu₂S + 3O₂ → 2Cu₂O + 2 SO₂

12. Reduction of metal oxide involves heating of metal in presence of suitable reagent Coke or CO₂.

13. Reactions taking place at different zones of blast furnace in extraction of iron:-

(i) Zone of reduction:- Temperature range 250^oC-700^oC

3Fe₂O₃ + CO → 2Fe₃O ₄ + CO₂

Fe₃O₄ + CO → 3FeO + CO₂

FeO + CO → Fe + CO₂

(ii) Zone of slag formation:- Temperature range 800^oC-1000 ^oC

CaCO₃ → CaO+CO₂

CaO + SiO₂ → CaSiO₃, P₄O ₁₀ + 10C → 4P + 10CO,

SiO₂ + 2C → Si + 2CO, MnO₂ + 2C → Mn + 2CO

(iii) Zone of fusion: - Temperature range 1150^oC-1350 ^oC

CO₂ + C → 2CO

(iv) Zone of fusion: - Temperature range 1450^oC-1950^o C

C + O₂ → CO₂

14. Vapour phase refining is used for extraction of Nickel (MOND PROCESS) and Zirconium &Titanium

(VAN ARKEL PROCESS).

15. Zone refining is used for extraction of Si, Ge, Ga, etc.

16. Chromatography method is based on selective distribution of various constituents of a mixture between

two phases, a stationary phase and a moving phase. The stationary phase can be either solid or liquid on

solid support.

17. Column chromatography is based on adsorption phenomenon. This method is useful for those elements,

which are available in small amounts and the impurities are not much different in chemical properties from

the element to be purified

FLOW SHEET FOR EXTRACTION OF IRON:-

[Figures and tables are omitted from this preview.]

Pig Iron: - It contains Fe 93-95%, Carbon 2.5-5%, and Impurities 3%.

Cast Iron: - It contains Fe 99.5-99.8%, Carbon 0.1-0.2% Impurities 0.3%.

Spongy iron: - Iron formed in the zone of reduction of blast furnace is called spongy iron. It contains impurities of C, Mn , Si, etc.

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