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General Principles and Processes of Isolation of Elements

We all are very well aware of the fact that all metals are obtained from the earth crust through mining. This is not a one step process and involves number of steps like

  • Mining or minerals are ores,  

  • Purification of ores (concentration of ores)

  • Extraction of metals from ore and finally  

  • Purification of the extracted ore (Refining)

Each of these steps involves application of some special type of techniques and processes depending of number of factors which we will discuss in detail later in this chapter.

All the chemical and physical processes used from obtaining the pure metal from its ore/mineral are collectively known as metallurgy.

The branch of science that deals with the extraction of metals from their respective ores and the preparation of alloys is called metallurgy.

The metallurgy of each metal is an individual problem and the line of treatment depends upon the nature of ore and the chemical properties of the metal. Some common steps involved in the metallurgical operations are

  • Crushing and grinding of the ore

  • Concentration or dressing of ore

  • Extraction of crude metal from concentrated ore

  • Reduction of ore to the metallic form and

  • Purification of metal

Occurrence of Metals

  • The earth’s crust is the biggest source of metals besides some soluble salts of metals found in sea water.

  • The mode of occurrence of a metal is largely dependent on its chemical nature.

  • Those metals, which are relatively inert, occur in free or native state (i.e. in uncombined state) but most of the metals are reactive and hence are found in combined state.

  • The naturally occurring inorganic substances, which are obtained by mining, are known as minerals.

  • The mineral has a definite composition. It may be a single compound or a complex mixture.

  • The minerals from which the metals can be conveniently and economically extracted are known as ores.

  • All ores are minerals, but all minerals are not ores, e.g. cinnabar (HgS) is an ore as well as mineral of mercury but iron pyrites (FeS2) is a mineral of iron but not an ore.

  • The valuable mineral contained in an ore is an ore mineral. The other minerals contained in the mixture, which ordinary are waste materials, constituted the gangue of the ore.

Ore = Ore mineral + Gangue 

  • The chief ores in the ores of economic importance are : 
    • Oxides

    • Sulphides

    • Carbonate

    • Sulphates

    • Halides and

    • Silicates.

Native Ores:

These ores contain metal in free state. For example : Silver, gold, platinum, mercury, copper etc. Sometime lumps of pure metals are found known as nuggets. 

Combined Ores:

These ores contain metal in combination with oxygen or sulphur or halides etc. The ores & minerals of various metals are

Metals

Minerals/ores with their chemical formula

 

 

1.

 

 

Iron

Iron pyrite; FeS2 (as sulphide)

Siderite; FeCO3 (as carbonate)

Red haematite; Fe2O3 (as oxide)

Magnetite; Fe3O4 (as oxide)

Limonite or brown haematite; 2Fe2O3.3H2O (as oxide)

 

 

2.

 

 

 

Copper

 

Cuprite; Cu2O (as oxide)

Copper pyrites; CuFeS2 (as sulphides)

Copper glance; Cu2S (as sulphides)

malachite; CuCO3.Cu(OH)2

Azurite;2CuCO3.Cu(OH)2

3.

Tin

Cassiterite or Tin stonel SnO2 (as oxide)

Stannite; Cu2S.FeS.SnS2 (as sulphide)

 

4.

 

Lead

Galena; PbS (as sulphide)

Cerussite; PbCO3 (as carbonate)

Anglessite; PbSO4 (as sulphate)

White lead; 2Pb(OH)2.PbCO3 (as carbonate)

 

 

5.

 

 

Magnesium

Carnalite; KCI.MgCI2.6H2O (as chloride)

Dolomite; MgCO3.CaCO3 (as carbonate)

Magnesite; MgCO3 (as carbonate)

Epsomite; MgSO4.7H2O (as sulphate)

Kiesserite; MgSO4.H2O (as sulphate)

Asbestos; CaMg(SiO3)4

 

 

 

6.

 

 

 

Aluminium

Bauxite; AI2O.2H2O (as oxide)

Corundum; AI2O3 (as oxide)

Feldspar; KAISi3O6 (as oxide)

Clay silicate; AI2O3.2SiO2.2H2O (as oxide)

Cryolite; 3NaF.AIF3.(Na3AIF6) (as halide)

Alum; K2O.3AI2(SO4)3.24H2O (as sulphate)

Diaspore; AI2O3.H2O (as oxide)

Mica; K2O.3AI2O3.6SiO2.2H2O (as oxide)

 

 

7.

 

 

Zinc

Zinc blende; ZnS (as sulphide) or sphalerite

Zincite; ZnO (as oxide)

Smithsonite, ZnCO3 (as carbonate)

Hemimorphite or Calamine, Zn2SiO4.H2O (as silicate)

 

8.

 

Silver

Horn silver (Chlorapatite); AgCI (as halide)

Lunar caustic; AgNO3 (as nitrate)

Silver glance or argentite; Ag2S (as sulphide)

Ruby silver or pyrogyrite; 3Ag2S.Sb2S3

Crushing or Grinding of the Ore

The ores occur in nature as huge lumps. They are broken to small pieces with the help of crushers. This process is called comminution of ores. Comminution is done in any of the following crushers.

  • Jaw crusher

  • Gyratory crusher

  • Symons cone crusher

  • Roll crusher 

These pieces are then reduced to fine powder with the help of a ball mill or stamp mill. This process is called pulverization. Pulverisation is done in any of the following mills. 

  • Ball mill

  • Rod mill

  • Flint Pebble mill

Question 1: A mineral is called ore if

a. The metal present in the mineral is costly

b. A metal can be extracted from it

c. A metal can be extracted profitably from it.

d. A metal cannot be extracted from it.

Question 2: Which of the following is an ore of Fe?

a. Malachite

b. Calamine

c. Stellite

d. Limonite

Question 3: Which of the following minerals is not an ore of Cu?

a. Cuprite

b. Malachite

c. Copper Pyrites

d. Diaspore;

Question 4: The formula of copper pyrites is

a. Cu2O

b. CuFeS2

c. Cu2S

d. CuCO3.Cu(OH)2

Q.1

Q.2

Q.3

Q.4

c

d

d

b

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