Important General Principles & Process of Isolation of Metals Formulas for JEE and NEET

 Page 1


  
METALLURGY
The compound of a metal found in nature is called a mineral. The minerals
from which metal can be economically and conveniently extracted are
called ores. An ore is usually contaminated with earthy or undesired
materials known as gangue.
(a) Native ores contain the metal in free state. Silver, gold, platinum etc,
occur as native ores.
(b) Oxidised ores consist of oxides or oxysalts (e.g. carbonates, phosphates,
sulphates and silicates ) of metals.
(c) Sulphurised ores consist of sulphides of metals like iron, lead, zinc,
mercury etc.
(d) Halide ores consist of halides of metals.
Metal Ores Composition
Aluminium Bauxite AlO
X
(OH)
3?2X  
[where 0 < X < 1] Al
2
O
3
Diaspore Al
2
O
3
.H
2
O
Corundam Al
2
O
3
Kaolinite (a form of clay) [Al
2
 (OH)
4
 Si
2
O
5
]
Iron Haematite Fe
2
O
3
Magnetite Fe
3
O
4
Siderite FeCO
3
Iron pyrite FeS
2
Limonite Fe
2
O
3
.3H
2
O
Copper Copper pyrite CuFeS
2
Copper glance Cu
2
S
Cuprite Cu
2
O
Malachite CuCO
3
.Cu(OH)
2
Azurite 2CuCO
3
.Cu(OH)
2
Zinc Zinc blende or Sphalerite ZnS
Calamine ZnCO
3
Zincite ZnO
Lead Galena PbS
Anglesite PbSO
4
Cerrusite PbCO
3
Magnesium
Carnallite KCl.MgCl
2
 6H
2
O (K
2
MgCl
4 
.6H
2
O)
Magnesite MgCO
3
Dolomite MgCO
3
 CaCO
3
Epsomsalt (Epsomite) MgSO
4
 7H
2
O
Langbeinite K
2
Mg
2
(SO
4
)
3
Tin
Cassiterite (Tin stone) SnO
2
Silver
Silver glance (Argentite) Ag
2
S
Chlorargyrite (Horn silver) AgCl
Page 2


  
METALLURGY
The compound of a metal found in nature is called a mineral. The minerals
from which metal can be economically and conveniently extracted are
called ores. An ore is usually contaminated with earthy or undesired
materials known as gangue.
(a) Native ores contain the metal in free state. Silver, gold, platinum etc,
occur as native ores.
(b) Oxidised ores consist of oxides or oxysalts (e.g. carbonates, phosphates,
sulphates and silicates ) of metals.
(c) Sulphurised ores consist of sulphides of metals like iron, lead, zinc,
mercury etc.
(d) Halide ores consist of halides of metals.
Metal Ores Composition
Aluminium Bauxite AlO
X
(OH)
3?2X  
[where 0 < X < 1] Al
2
O
3
Diaspore Al
2
O
3
.H
2
O
Corundam Al
2
O
3
Kaolinite (a form of clay) [Al
2
 (OH)
4
 Si
2
O
5
]
Iron Haematite Fe
2
O
3
Magnetite Fe
3
O
4
Siderite FeCO
3
Iron pyrite FeS
2
Limonite Fe
2
O
3
.3H
2
O
Copper Copper pyrite CuFeS
2
Copper glance Cu
2
S
Cuprite Cu
2
O
Malachite CuCO
3
.Cu(OH)
2
Azurite 2CuCO
3
.Cu(OH)
2
Zinc Zinc blende or Sphalerite ZnS
Calamine ZnCO
3
Zincite ZnO
Lead Galena PbS
Anglesite PbSO
4
Cerrusite PbCO
3
Magnesium
Carnallite KCl.MgCl
2
 6H
2
O (K
2
MgCl
4 
.6H
2
O)
Magnesite MgCO
3
Dolomite MgCO
3
 CaCO
3
Epsomsalt (Epsomite) MgSO
4
 7H
2
O
Langbeinite K
2
Mg
2
(SO
4
)
3
Tin
Cassiterite (Tin stone) SnO
2
Silver
Silver glance (Argentite) Ag
2
S
Chlorargyrite (Horn silver) AgCl
  
Metallurgy :
The scientific and technological process used for the extraction/isolation
of the metal from its ore is called as metallurgy.
The isolation and extraction of metals from their ores involve the following
major steps:
(A) Crushing and Grinding  :  The ore is first crushed by jaw crushers and
ground to a powder.
(B) Concentration :
The removal of  unwanted useless impurities from the ore is called dressing,
concentration or benefaction of ore.
(i) Hydraulic washing or Gravity separation or Levigation method :
It is based on the difference in the densities of the gangue and ore particles.
This method is generally used for the concentration of oxide and native
ores.
(ii) Electromagnetic separation :
It is based on differences in magnetic properties of the ore components.
Chromite ore(FeO.Cr
2
O
3
) is separated from non?magnetic silicious
impurities and cassiterite ore(SnO
2
) is separated from magnetic Wolframite
(FeWO
4
 + MnWO
4
).
(iii) Froth floatation process. This method is commonly used for the concentration
of the low grade sulphide ores like galena, PbS (ore of Pb); copper pyrites
Cu
2
S.Fe
2
S
3
 or CuFeS
2
 (ore of copper) ; zinc blende, ZnS (ore of zinc) etc.,
and is based on the fact that gangue and ore particles have different degree
of wettability with water and pine oil; the gangue particles are preferentially
wetted by water while the ore particles are wetted by oil. In this process
one or more chemical frothing agents are added.
(iv) Leaching : Leaching is often used if the ore is soluble in some suitable
solvent, e.g, acids, bases and suitable chemical reagents.
(C) Extraction of crude metal from concentrated ore :
The isolation of metals from concentrated ore involves two major steps as
given below.
(i) Conversion to oxide :
Calcination. It is a process of heating the concentrated ore strongly in a
limited supply of air or in the absence of air. The process of calcination
brings about the following changes :
(a) The carbonate ore gets decomposed to form the oxide of the metal.
(b) Water of crystallisation present in the hydrated oxide ore gets lost as
moisture.
(c) Organic matter, if present in the ore, gets expelled and the ore becomes
porous. Volatile impurities are removed.
Page 3


  
METALLURGY
The compound of a metal found in nature is called a mineral. The minerals
from which metal can be economically and conveniently extracted are
called ores. An ore is usually contaminated with earthy or undesired
materials known as gangue.
(a) Native ores contain the metal in free state. Silver, gold, platinum etc,
occur as native ores.
(b) Oxidised ores consist of oxides or oxysalts (e.g. carbonates, phosphates,
sulphates and silicates ) of metals.
(c) Sulphurised ores consist of sulphides of metals like iron, lead, zinc,
mercury etc.
(d) Halide ores consist of halides of metals.
Metal Ores Composition
Aluminium Bauxite AlO
X
(OH)
3?2X  
[where 0 < X < 1] Al
2
O
3
Diaspore Al
2
O
3
.H
2
O
Corundam Al
2
O
3
Kaolinite (a form of clay) [Al
2
 (OH)
4
 Si
2
O
5
]
Iron Haematite Fe
2
O
3
Magnetite Fe
3
O
4
Siderite FeCO
3
Iron pyrite FeS
2
Limonite Fe
2
O
3
.3H
2
O
Copper Copper pyrite CuFeS
2
Copper glance Cu
2
S
Cuprite Cu
2
O
Malachite CuCO
3
.Cu(OH)
2
Azurite 2CuCO
3
.Cu(OH)
2
Zinc Zinc blende or Sphalerite ZnS
Calamine ZnCO
3
Zincite ZnO
Lead Galena PbS
Anglesite PbSO
4
Cerrusite PbCO
3
Magnesium
Carnallite KCl.MgCl
2
 6H
2
O (K
2
MgCl
4 
.6H
2
O)
Magnesite MgCO
3
Dolomite MgCO
3
 CaCO
3
Epsomsalt (Epsomite) MgSO
4
 7H
2
O
Langbeinite K
2
Mg
2
(SO
4
)
3
Tin
Cassiterite (Tin stone) SnO
2
Silver
Silver glance (Argentite) Ag
2
S
Chlorargyrite (Horn silver) AgCl
  
Metallurgy :
The scientific and technological process used for the extraction/isolation
of the metal from its ore is called as metallurgy.
The isolation and extraction of metals from their ores involve the following
major steps:
(A) Crushing and Grinding  :  The ore is first crushed by jaw crushers and
ground to a powder.
(B) Concentration :
The removal of  unwanted useless impurities from the ore is called dressing,
concentration or benefaction of ore.
(i) Hydraulic washing or Gravity separation or Levigation method :
It is based on the difference in the densities of the gangue and ore particles.
This method is generally used for the concentration of oxide and native
ores.
(ii) Electromagnetic separation :
It is based on differences in magnetic properties of the ore components.
Chromite ore(FeO.Cr
2
O
3
) is separated from non?magnetic silicious
impurities and cassiterite ore(SnO
2
) is separated from magnetic Wolframite
(FeWO
4
 + MnWO
4
).
(iii) Froth floatation process. This method is commonly used for the concentration
of the low grade sulphide ores like galena, PbS (ore of Pb); copper pyrites
Cu
2
S.Fe
2
S
3
 or CuFeS
2
 (ore of copper) ; zinc blende, ZnS (ore of zinc) etc.,
and is based on the fact that gangue and ore particles have different degree
of wettability with water and pine oil; the gangue particles are preferentially
wetted by water while the ore particles are wetted by oil. In this process
one or more chemical frothing agents are added.
(iv) Leaching : Leaching is often used if the ore is soluble in some suitable
solvent, e.g, acids, bases and suitable chemical reagents.
(C) Extraction of crude metal from concentrated ore :
The isolation of metals from concentrated ore involves two major steps as
given below.
(i) Conversion to oxide :
Calcination. It is a process of heating the concentrated ore strongly in a
limited supply of air or in the absence of air. The process of calcination
brings about the following changes :
(a) The carbonate ore gets decomposed to form the oxide of the metal.
(b) Water of crystallisation present in the hydrated oxide ore gets lost as
moisture.
(c) Organic matter, if present in the ore, gets expelled and the ore becomes
porous. Volatile impurities are removed.
  
Roasting :
It is a process of heating the concentrated ore (generally sulphide ore)
strongly in the excess of air or O
2
 below its melting point. Roasting is an
exothermic process once started it does not require additional heating.
Smelting :
Slag formation : In many extraction processes, an oxide is added
deliberately to combine with other impurities and form a stable molten
phase immiscible with molten metal called a slag. The process is termed
smelting.
The principle of slag formation is essentially the following :
Nonmetal oxide (acidic oxide) + Metal oxide (basic oxide)  ?? Fusible
(easily melted) slag
Removal of unwanted basic and acidic oxides: For example, FeO is the
impurity in extraction of Cu from copper pyrite.
2CuFeS
2
 + 4O
2
 ??   Cu
2
S + 2FeO   +  3SO
2
Cu
2
S    +   FeO +   SiO
2
 ??????  FeSiO
3
 (Fusible slag)    +   Cu
2
S (matte)
? ? ? ? ? ? ? ? ?
) pyrite roasted (
(upper layer) (lower layer)
Matte also contains a very small amount of iron(II) sulphide.
To remove unwanted acidic impurities like sand and P
4
O
10
, smelting is
done in the presence of limestone.
CaCO
3
 ?? CaO + CO
2
CaO + SiO
2
 ?? CaSiO
3
 (fusible slag)
6CaO + P
4
O
10
 ?? 2Ca
3
(PO
4
)
2
 (fusible slag - Thomas slag)
(ii) Reduction of a metal oxide :
The free metal is obtained by reduction of a compound, using either a
chemical reducing agent or electrolysis.
Chemical reduction method :
Reduction with carbon :
PbO + C ?? Pb + CO (extraction of lead)
Reduction with CO : In some cases CO produced in the furnace itself is
used as a reducing agent.
Fe
2
O
3
 + 3CO ?? 2Fe + 3CO
2
Reduction by other  metals :
Metallic oxides (Cr and Mn) can be reduced by a highly electropositive
metal such as aluminium  that liberates a large amount of energy (1675
kJ/mol) on oxidation to AI
2
O
3
. The process is known as Goldschmidt or
Page 4


  
METALLURGY
The compound of a metal found in nature is called a mineral. The minerals
from which metal can be economically and conveniently extracted are
called ores. An ore is usually contaminated with earthy or undesired
materials known as gangue.
(a) Native ores contain the metal in free state. Silver, gold, platinum etc,
occur as native ores.
(b) Oxidised ores consist of oxides or oxysalts (e.g. carbonates, phosphates,
sulphates and silicates ) of metals.
(c) Sulphurised ores consist of sulphides of metals like iron, lead, zinc,
mercury etc.
(d) Halide ores consist of halides of metals.
Metal Ores Composition
Aluminium Bauxite AlO
X
(OH)
3?2X  
[where 0 < X < 1] Al
2
O
3
Diaspore Al
2
O
3
.H
2
O
Corundam Al
2
O
3
Kaolinite (a form of clay) [Al
2
 (OH)
4
 Si
2
O
5
]
Iron Haematite Fe
2
O
3
Magnetite Fe
3
O
4
Siderite FeCO
3
Iron pyrite FeS
2
Limonite Fe
2
O
3
.3H
2
O
Copper Copper pyrite CuFeS
2
Copper glance Cu
2
S
Cuprite Cu
2
O
Malachite CuCO
3
.Cu(OH)
2
Azurite 2CuCO
3
.Cu(OH)
2
Zinc Zinc blende or Sphalerite ZnS
Calamine ZnCO
3
Zincite ZnO
Lead Galena PbS
Anglesite PbSO
4
Cerrusite PbCO
3
Magnesium
Carnallite KCl.MgCl
2
 6H
2
O (K
2
MgCl
4 
.6H
2
O)
Magnesite MgCO
3
Dolomite MgCO
3
 CaCO
3
Epsomsalt (Epsomite) MgSO
4
 7H
2
O
Langbeinite K
2
Mg
2
(SO
4
)
3
Tin
Cassiterite (Tin stone) SnO
2
Silver
Silver glance (Argentite) Ag
2
S
Chlorargyrite (Horn silver) AgCl
  
Metallurgy :
The scientific and technological process used for the extraction/isolation
of the metal from its ore is called as metallurgy.
The isolation and extraction of metals from their ores involve the following
major steps:
(A) Crushing and Grinding  :  The ore is first crushed by jaw crushers and
ground to a powder.
(B) Concentration :
The removal of  unwanted useless impurities from the ore is called dressing,
concentration or benefaction of ore.
(i) Hydraulic washing or Gravity separation or Levigation method :
It is based on the difference in the densities of the gangue and ore particles.
This method is generally used for the concentration of oxide and native
ores.
(ii) Electromagnetic separation :
It is based on differences in magnetic properties of the ore components.
Chromite ore(FeO.Cr
2
O
3
) is separated from non?magnetic silicious
impurities and cassiterite ore(SnO
2
) is separated from magnetic Wolframite
(FeWO
4
 + MnWO
4
).
(iii) Froth floatation process. This method is commonly used for the concentration
of the low grade sulphide ores like galena, PbS (ore of Pb); copper pyrites
Cu
2
S.Fe
2
S
3
 or CuFeS
2
 (ore of copper) ; zinc blende, ZnS (ore of zinc) etc.,
and is based on the fact that gangue and ore particles have different degree
of wettability with water and pine oil; the gangue particles are preferentially
wetted by water while the ore particles are wetted by oil. In this process
one or more chemical frothing agents are added.
(iv) Leaching : Leaching is often used if the ore is soluble in some suitable
solvent, e.g, acids, bases and suitable chemical reagents.
(C) Extraction of crude metal from concentrated ore :
The isolation of metals from concentrated ore involves two major steps as
given below.
(i) Conversion to oxide :
Calcination. It is a process of heating the concentrated ore strongly in a
limited supply of air or in the absence of air. The process of calcination
brings about the following changes :
(a) The carbonate ore gets decomposed to form the oxide of the metal.
(b) Water of crystallisation present in the hydrated oxide ore gets lost as
moisture.
(c) Organic matter, if present in the ore, gets expelled and the ore becomes
porous. Volatile impurities are removed.
  
Roasting :
It is a process of heating the concentrated ore (generally sulphide ore)
strongly in the excess of air or O
2
 below its melting point. Roasting is an
exothermic process once started it does not require additional heating.
Smelting :
Slag formation : In many extraction processes, an oxide is added
deliberately to combine with other impurities and form a stable molten
phase immiscible with molten metal called a slag. The process is termed
smelting.
The principle of slag formation is essentially the following :
Nonmetal oxide (acidic oxide) + Metal oxide (basic oxide)  ?? Fusible
(easily melted) slag
Removal of unwanted basic and acidic oxides: For example, FeO is the
impurity in extraction of Cu from copper pyrite.
2CuFeS
2
 + 4O
2
 ??   Cu
2
S + 2FeO   +  3SO
2
Cu
2
S    +   FeO +   SiO
2
 ??????  FeSiO
3
 (Fusible slag)    +   Cu
2
S (matte)
? ? ? ? ? ? ? ? ?
) pyrite roasted (
(upper layer) (lower layer)
Matte also contains a very small amount of iron(II) sulphide.
To remove unwanted acidic impurities like sand and P
4
O
10
, smelting is
done in the presence of limestone.
CaCO
3
 ?? CaO + CO
2
CaO + SiO
2
 ?? CaSiO
3
 (fusible slag)
6CaO + P
4
O
10
 ?? 2Ca
3
(PO
4
)
2
 (fusible slag - Thomas slag)
(ii) Reduction of a metal oxide :
The free metal is obtained by reduction of a compound, using either a
chemical reducing agent or electrolysis.
Chemical reduction method :
Reduction with carbon :
PbO + C ?? Pb + CO (extraction of lead)
Reduction with CO : In some cases CO produced in the furnace itself is
used as a reducing agent.
Fe
2
O
3
 + 3CO ?? 2Fe + 3CO
2
Reduction by other  metals :
Metallic oxides (Cr and Mn) can be reduced by a highly electropositive
metal such as aluminium  that liberates a large amount of energy (1675
kJ/mol) on oxidation to AI
2
O
3
. The process is known as Goldschmidt or
  
aluminothermic process and the reaction is known as thermite reaction.
Cr
2
O
3
 + AI ? 2Cr (?) + AI
2
O
3
Magnesium reduction method : Magnesium is used in similar way to
reduce oxides. In certain cases where the oxide is too stable to reduce,
electropositive metals are used to reduce halides.
TiCI
4
 + 2 Mg 
C º 1150 ? 1000
rocess p Kroll
? ? ? ? ? ? ? Ti + 2 MgCI
2
TiCI
4
 + 4Na  ? ? ? ? ? ? ?
? ? rocess p M
 Ti + 4 NaCI
Self-reduction method :
This method is also called auto-reduction method or air reduction method.
If the sulphide ore of some of the less electropositive metals like Hg, Cu,
Pb, Sb, etc. are heated in air, a part of these is changed into oxide or
sulphate then that reacts with the remaining part of the sulphide ore to
give its metal and SO
2
.
Cu
2
S + 3O
2
 
?? ?
 
3Cu
2
O + 2 SO
2
2Cu
2
O + Cu
2
S 
?? ?
 6Cu + SO
2
Electrolytic reduction :
It presents the most powerful method of reduction and gives a very pure
product. As it is an expensive method compared to chemical methods, it
is used either for very reactive metals such as magnesium or aluminum or
for production of samples of high purity.
1. In aqueous solution : Electrolysis can be carried out conveniently and
cheaply in aqueous solution that the products do not react with water.
Copper and zinc are obtained by electrolysis of aqueous solution of their
sulphates.
2. In fused melts : Aluminum is obtained by electrolysis of a fused mixture
of AI
2
O
3
 and cryolite Na
3
[AIF
6
].
Extraction of Aluminium : It involves the following processes
(a) Purification of bauxite :
Page 5


  
METALLURGY
The compound of a metal found in nature is called a mineral. The minerals
from which metal can be economically and conveniently extracted are
called ores. An ore is usually contaminated with earthy or undesired
materials known as gangue.
(a) Native ores contain the metal in free state. Silver, gold, platinum etc,
occur as native ores.
(b) Oxidised ores consist of oxides or oxysalts (e.g. carbonates, phosphates,
sulphates and silicates ) of metals.
(c) Sulphurised ores consist of sulphides of metals like iron, lead, zinc,
mercury etc.
(d) Halide ores consist of halides of metals.
Metal Ores Composition
Aluminium Bauxite AlO
X
(OH)
3?2X  
[where 0 < X < 1] Al
2
O
3
Diaspore Al
2
O
3
.H
2
O
Corundam Al
2
O
3
Kaolinite (a form of clay) [Al
2
 (OH)
4
 Si
2
O
5
]
Iron Haematite Fe
2
O
3
Magnetite Fe
3
O
4
Siderite FeCO
3
Iron pyrite FeS
2
Limonite Fe
2
O
3
.3H
2
O
Copper Copper pyrite CuFeS
2
Copper glance Cu
2
S
Cuprite Cu
2
O
Malachite CuCO
3
.Cu(OH)
2
Azurite 2CuCO
3
.Cu(OH)
2
Zinc Zinc blende or Sphalerite ZnS
Calamine ZnCO
3
Zincite ZnO
Lead Galena PbS
Anglesite PbSO
4
Cerrusite PbCO
3
Magnesium
Carnallite KCl.MgCl
2
 6H
2
O (K
2
MgCl
4 
.6H
2
O)
Magnesite MgCO
3
Dolomite MgCO
3
 CaCO
3
Epsomsalt (Epsomite) MgSO
4
 7H
2
O
Langbeinite K
2
Mg
2
(SO
4
)
3
Tin
Cassiterite (Tin stone) SnO
2
Silver
Silver glance (Argentite) Ag
2
S
Chlorargyrite (Horn silver) AgCl
  
Metallurgy :
The scientific and technological process used for the extraction/isolation
of the metal from its ore is called as metallurgy.
The isolation and extraction of metals from their ores involve the following
major steps:
(A) Crushing and Grinding  :  The ore is first crushed by jaw crushers and
ground to a powder.
(B) Concentration :
The removal of  unwanted useless impurities from the ore is called dressing,
concentration or benefaction of ore.
(i) Hydraulic washing or Gravity separation or Levigation method :
It is based on the difference in the densities of the gangue and ore particles.
This method is generally used for the concentration of oxide and native
ores.
(ii) Electromagnetic separation :
It is based on differences in magnetic properties of the ore components.
Chromite ore(FeO.Cr
2
O
3
) is separated from non?magnetic silicious
impurities and cassiterite ore(SnO
2
) is separated from magnetic Wolframite
(FeWO
4
 + MnWO
4
).
(iii) Froth floatation process. This method is commonly used for the concentration
of the low grade sulphide ores like galena, PbS (ore of Pb); copper pyrites
Cu
2
S.Fe
2
S
3
 or CuFeS
2
 (ore of copper) ; zinc blende, ZnS (ore of zinc) etc.,
and is based on the fact that gangue and ore particles have different degree
of wettability with water and pine oil; the gangue particles are preferentially
wetted by water while the ore particles are wetted by oil. In this process
one or more chemical frothing agents are added.
(iv) Leaching : Leaching is often used if the ore is soluble in some suitable
solvent, e.g, acids, bases and suitable chemical reagents.
(C) Extraction of crude metal from concentrated ore :
The isolation of metals from concentrated ore involves two major steps as
given below.
(i) Conversion to oxide :
Calcination. It is a process of heating the concentrated ore strongly in a
limited supply of air or in the absence of air. The process of calcination
brings about the following changes :
(a) The carbonate ore gets decomposed to form the oxide of the metal.
(b) Water of crystallisation present in the hydrated oxide ore gets lost as
moisture.
(c) Organic matter, if present in the ore, gets expelled and the ore becomes
porous. Volatile impurities are removed.
  
Roasting :
It is a process of heating the concentrated ore (generally sulphide ore)
strongly in the excess of air or O
2
 below its melting point. Roasting is an
exothermic process once started it does not require additional heating.
Smelting :
Slag formation : In many extraction processes, an oxide is added
deliberately to combine with other impurities and form a stable molten
phase immiscible with molten metal called a slag. The process is termed
smelting.
The principle of slag formation is essentially the following :
Nonmetal oxide (acidic oxide) + Metal oxide (basic oxide)  ?? Fusible
(easily melted) slag
Removal of unwanted basic and acidic oxides: For example, FeO is the
impurity in extraction of Cu from copper pyrite.
2CuFeS
2
 + 4O
2
 ??   Cu
2
S + 2FeO   +  3SO
2
Cu
2
S    +   FeO +   SiO
2
 ??????  FeSiO
3
 (Fusible slag)    +   Cu
2
S (matte)
? ? ? ? ? ? ? ? ?
) pyrite roasted (
(upper layer) (lower layer)
Matte also contains a very small amount of iron(II) sulphide.
To remove unwanted acidic impurities like sand and P
4
O
10
, smelting is
done in the presence of limestone.
CaCO
3
 ?? CaO + CO
2
CaO + SiO
2
 ?? CaSiO
3
 (fusible slag)
6CaO + P
4
O
10
 ?? 2Ca
3
(PO
4
)
2
 (fusible slag - Thomas slag)
(ii) Reduction of a metal oxide :
The free metal is obtained by reduction of a compound, using either a
chemical reducing agent or electrolysis.
Chemical reduction method :
Reduction with carbon :
PbO + C ?? Pb + CO (extraction of lead)
Reduction with CO : In some cases CO produced in the furnace itself is
used as a reducing agent.
Fe
2
O
3
 + 3CO ?? 2Fe + 3CO
2
Reduction by other  metals :
Metallic oxides (Cr and Mn) can be reduced by a highly electropositive
metal such as aluminium  that liberates a large amount of energy (1675
kJ/mol) on oxidation to AI
2
O
3
. The process is known as Goldschmidt or
  
aluminothermic process and the reaction is known as thermite reaction.
Cr
2
O
3
 + AI ? 2Cr (?) + AI
2
O
3
Magnesium reduction method : Magnesium is used in similar way to
reduce oxides. In certain cases where the oxide is too stable to reduce,
electropositive metals are used to reduce halides.
TiCI
4
 + 2 Mg 
C º 1150 ? 1000
rocess p Kroll
? ? ? ? ? ? ? Ti + 2 MgCI
2
TiCI
4
 + 4Na  ? ? ? ? ? ? ?
? ? rocess p M
 Ti + 4 NaCI
Self-reduction method :
This method is also called auto-reduction method or air reduction method.
If the sulphide ore of some of the less electropositive metals like Hg, Cu,
Pb, Sb, etc. are heated in air, a part of these is changed into oxide or
sulphate then that reacts with the remaining part of the sulphide ore to
give its metal and SO
2
.
Cu
2
S + 3O
2
 
?? ?
 
3Cu
2
O + 2 SO
2
2Cu
2
O + Cu
2
S 
?? ?
 6Cu + SO
2
Electrolytic reduction :
It presents the most powerful method of reduction and gives a very pure
product. As it is an expensive method compared to chemical methods, it
is used either for very reactive metals such as magnesium or aluminum or
for production of samples of high purity.
1. In aqueous solution : Electrolysis can be carried out conveniently and
cheaply in aqueous solution that the products do not react with water.
Copper and zinc are obtained by electrolysis of aqueous solution of their
sulphates.
2. In fused melts : Aluminum is obtained by electrolysis of a fused mixture
of AI
2
O
3
 and cryolite Na
3
[AIF
6
].
Extraction of Aluminium : It involves the following processes
(a) Purification of bauxite :
  
(b) Electrolytic reduction (Hall-Heroult process) :
2Al
2
O
3
 + 3C ?? ? 4Al + 3CO
2
Cathode : Al
3+
  (melt) + 3e
? 
?? ? Al(l)
Anode : C(s) + O
2?
 (melt) ?? ? CO(g) + 2e
?
C(s) + 2O
2?
 (melt) ?? ? CO
2
 (g) + 4e
?
Metallurgy of some important metals
1. Extraction of iron from ore haematite :
Reactions involved :
At 500 ? 800 K (lower temperature range in the blast furnace)
3 Fe
2
O
3
 + CO 
?? ?
 2 Fe
3
O
4
 + CO
2
Fe
3
O
4
 + CO 
?? ?
 3Fe + 4 CO
2
Fe
2
O
3
 + CO 
?? ?
 2FeO + CO
2
At 900 ? 1500 K (higher temperature range in the blast furnace):
C + CO
2
 ?? ? 2 CO ; FeO + CO ?? ? Fe + CO
2
Limestone is also decomposed tom CaO which removes silicate impurity
of the ore as slag. The slag is in molten state and separates out from iron.
CaCO
3
  ?? ? CaO + CO
2 
 ; CaO + SiO
2
 ?? ? CaSiO
3
2. Extraction of copper :
From copper glance / copper pyrite (self reduction) :
2CuFeS
2
 + 4O
2
 ??   Cu
2
S + 2FeO + 3SO
2
Cu
2
S + FeO + SiO
2
 ?? FeSiO
3
 (fusible slag) + Cu
2
S (matte)
2FeS + 3O
2
 
?? ?
 2FeO + 2SO
2           
; FeO + SiO
2
 
?? ?
 FeSiO
3
2Cu
2
S + 3O
2
 
?? ?
 2Cu
2
O + 2SO
2 
 ;
2Cu
2
O + Cu
2
S 
?? ?
 6Cu + SO
2  
(self reduction)
3. Extraction of lead :
(i)  2PbS(s)  + 3O
2
 (g) ?? ?
?
 2PbO (s) 
?
?
? ?? ?
C
 2Pb(?) + CO
2
 (g)
(ii) 3PbS(s)  
air
in heat
? ? ? ? ? PbS (s) + 2PbO (s) 
air of absence
in Heat
? ? ? ? ?
 3Pb(?) + SO
2
 (g)