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CBSE Class-12 Chemistry Quick Revision NotesChapter-06: General Principles and Processes of Isolation of Elements
• Minerals:
The naturally occurring chemical substances in the earth’s crust which are obtained by
mining are known as minerals.
• Metals may or may not be extracted profitably from them.
• Ores:
The rocky materials which contain sufficient quantity of mineral so that the metal can be
extracted profitably or economically are known as ores.
• Gangue:
The earthy or undesirable materials present in ore are known as gangue.
• Metallurgy:
• The entire scientific and technological process used for isolation of the metal from its
ores is known as metallurgy.
• Chief Ores and Methods of Extraction of Some Common Metals:
Sodium metal
a) Occurrence: Rock salt (NaCl), Feldspar (Na3AlSi3O8)
b) Extraction method: Electrolysis of fused NaCl or NaCl/ CaCl2
c) Inference: Sodium is highly reactive and hence, it reacts with water.
Copper metal
a) Occurrence: Copper pyrites (CuFeS2), Malachite (CuCO3.Cu(OH)2), Cuprite ( Cu2O)
Copper glance (Cu2S)
b) Extraction method: Roasting of sulphide partially and reduction.
2 Cu2O + Cu2S → 6 Cu +SO2
c) Inference: It is self-reduction in a specially designed converter. Sulphuric acid
leaching is also employed.
Aluminium metal
a) Occurrence: Bauxite:(AlOx(OH)3-2x where 0 < x < 1), Cryolite (Na3AlF6), Kaolinite
(Al2(OH)4Si2O5 )
b) Extraction method: Electrolysis of Al2O3 dissolved in molten cryolite or in Na3AlCl6
c) Inference: A good source of electricity is needed in the extraction of Al
Zinc metal
a) Occurrence: Zinc blende or Sphalerite (ZnS), Zincite (ZnO), Calamine (ZnCO3)
b) Extraction method: Roasting and then reduction with carbon.
c) Inference: The metal may be purified by fractional distillation.
Lead metal
a) Occurrence: Galena (PbS)
b) Extraction: Roasting of the sulphide ore and then reduction of the oxide.
c) Inference: Sulphide ore is concentrated by froth floatation process.
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, Silver metal
a) Occurrence: Argentite (Ag2S)
b) Extraction method: Sodium cyanide leaching of the sulphide ore and finally
replacement of Ag by Zn.
c) Inference: It involves complex formation and displacement.
Gold metal
a) Occurrence: Native, small amounts in many ores such as those of copper and silver
b) Extraction method: Cyanide leaching, same as in case of silver
c) Inference: Gold reacts with cyanide to form complex
Iron metal
a) Occurrence: Haematite (Fe2O3), Magnetite (Fe3O4), Siderite (FeCO3), Iron pyrites
(FeS2)
b) Extraction method: Reduction with the help of CO and coke in blast furnace.
c) Inference: Limestone is added as flux which removes SiO2 as calcium silicate (slag)
floats over molten iron and prevents its oxidation. Temperatures approaching 2170
K is required.
• Steps of metallurgy:
a) Concentration of ore
b) Conversion of concentrated ore to oxide
c) Reduction of oxide to metal
d) Refining of metal
• Concentration of ore:
The process of removal unwanted materials like sand, clay, rocks etc from the ore is
known as concentration, ore – dressing or benefaction. It involves several steps which
depend upon physical properties of metal compound and impurity (gangue). The type of
metal, available facilities and environmental factors are also taken into consideration.
• Hydraulic washing (or gravity separation):
It is based on difference in densities of ore and gangue particles. Ore is washed with a
stream of water under pressure so that lighter impurities are washed away whereas
heavy ores are left behind.
• Magnetic separation:
This method is based on the difference in magnetic and non – magnetic properties of two
components of ore (pure and impure). This method is used to remove tungsten ore
particles from cassiterite (SnO2). It is also used to concentrate magnetite (Fe3O4),
chromite (FeCr2O4) and pyrolusite (MnO2) from unwanted gangue.
• Froth floatation process:
It is based on the principle that sulphide ores are preferentially wetted by the pine oil or
fatty acids or xanthates etc., whereas the gangue particles are wetted by the water.
Collectors are added to enhance the non-wettability of the mineral particles.
Froth stabilizers such as cresols, aniline etc., are added to stabilize the froth.
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