Pre-Medical : Chemistry
ALLEN
METALLURGY
4.1 INTRODUCTION
Metallurgy : The branch of chemistry which deals with the method of extraction of metals from their ores by
profitable means.
Metal : The element which tends to form positive ion is called a metal.
Minerals : The various compounds of metals which occur in the earth's crust and are obtained by mining are called
minerals. In earth crust order of abundance of elements is. O > Si > Al > Fe
A mineral may be single compound or a mixture.
Ore : The mineral from which a metal can be extracted profitably and easily is called an ore.
All ores are minerals but all minerals are not ores. (T/F)
Type of Ores :
(I) Combined Ore : Metals placed above H in electrochemical series are generally reactive i.e. why they
generally found in combined state.
N
(a) Halide ore / Sulphate ore / Oxy ore : Metals are highly reactive (Li ® Mg)
(b) Oxide ore : Reactive metal (Al to Sn)
(c) Sulphide ore : Metal placed near H or below H. (Pb, Hg, Cu, Ag)
0
(II) Native Ore : Metal placed below H in electrochemical series are generally found in native state.
-2
E (Ag, Au, Cu, Pt etc.)
Gangue or matrix : The undesirable impurities present in an ore are called gangue.
19
Types of metallurgy
20
LL
Pyrometallurgy Hydrometallurgy Electro metallurgy
Temp. is involved Solution is involved
n
Electricity involved
io
For heavy metals According to E.C.S. IA, IIA, Al
ss
Fe, Zn, Cu, Hg, For metals placed below H
Sn, etc
Se
Cu, Ag, Au
A
4.2 STEPS INVOLVED IN THE EXTRACTION OF METALS
Z:\NODE02\B0AI-B0\TARGET\CHEM\ENG\MODULE-5\4-METALLURGY\1.THEORY.P65
The extraction of a metal from its ore is completed in the following four steps.
(A) Concentration of the ore (B) Conversion of concentrated ore into oxide form.
(C) Reduction of the metal (D) Refining of the metal.
(A) Concentration of the ore or dressing or benefaction
The removal of impurities from the ore is called its concentration or to increase the concentration of ore in ore
sample. Two process – (1)Physical (2) Chemical
(1) PHYSICAL :
(i) Gravity separation (Levigation) : This method of concentration of the ore is based on the difference
in the specific gravities of the ore and the gangue particles.Powdered ore is agitated with a running stream
of water. The lighter gangue particles are taken away by water while heavier ore particles settle down.
Ex. Oxygenated ore
E 141
,Pre-Medical : Chemistry
ALLEN
Hopper
Gangue
Suspended particles
ore
Ore
Water particles
Concentrated
ore
Hydraulic classifier
N
(ii) Froth Floatation method
This method is mainly employed for the concentration of sulphide ores.
The method is based on the different wetting characteristics of the gangue and the sulphide ore with water
0
and oil. The gangue preferentially wetted by water and the ore by oil.
-2
The crushed ore along with water is taken in a floatation cell. Various substances are added depending
on the nature of the ore and a current of air is blown in. The substances added are usually of three types.
E
19
(a) Frothers :–They generate a stable froth which rises to the top of the tank.
Example of frother is pine oil, Eucalyptus oil, fatty acids etc.
(b) Collectors or floating agents :– These attach themselves by polar group to the granules of the
20
ores which then become water repellent and pass on into the froth.
LL
Example: sodium ethyl xanthate, pine oil and fatty acid.
(c) Froth stabilisers : To stabilise froth.
n
Ex. Cresol, Aniline etc.
io
(d) Depressants :– These reagents activate or depress the floatation property and help in the
separation of different sulphide ores present in a mixture.
ss
e.g. NaCN.
Impurity of ZnS in PbS ore removed by NaCN
Se
NaCN + [PbS + ZnS] ®Na2[Zn(CN)4] + PbS ® form froth
A
Powdered
Z:\NODE02\B0AI-B0\TARGET\CHEM\ENG\MODULE-5\4-METALLURGY\1.THEORY.P65
Ore + Oil + Water
Compressed air Light ore particle
in froth
Concentrated Ore
Gangue
[Froth floatation process]
142 E
, Pre-Medical : Chemistry
ALLEN
• Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using
‘depressants’.
• For example, in case of an ore containing ZnS and PbS, the depressant used is NaCN. It selectively prevents
ZnS from coming to the froth but allows PbS to go along with the froth.
(iii) Magnetic separation:-
If either the ore or the gangue (one of these two) is capable of being attracted by a magnetic field, then
such separations are carried out (e.g. in case of iron ores)
e.g. • SnO2 having the impurities of FeWO4 + MnWO4(Wolframite)
• FeO.Cr2O3 having the impurities of SiO2.
Finely ground ore
N
Magnetic roller
0
Magnetic particles
-2
E Non-magnetic particles
19
2. CHEMICAL SEPARATION (LEACHING) : In this process we use suitable agent which react with ore to
20
form water soluble complex while impurities remain insoluble. Applicable for Al, Ag,Au.
LL
é Re d Bauxite ® Al2 O3 .2H2O + Fe 2O 3 ( Major impurity)
n
(a) Aluminium : ê
io
ë White Bauxite ® Al O .2H O + SiO ( Major impurity)
2 3 2 2
ss
(I) RED BAUXITE : Two processes
(i) Baeyer's process : NaOH is used.
Se
excess H O
Al2O3 + NaOH ¾® NaAlO2 ¾¾¾¾¾® 2 Al(OH)3 + NaOH
A
Z:\NODE02\B0AI-B0\TARGET\CHEM\ENG\MODULE-5\4-METALLURGY\1.THEORY.P65
FeO + NaOH ¾® inso lub le
¯
Basic
(ii) Hall's process : Na2CO3 is used.
HOH
Al2O3 + Na2CO3 ¾® 2NaAlO2 ¾¾¾¾
CO2
® Al(OH) + Na CO
3 2 3
(II) WHITE BAUXITE : One process.
Serpeck's process : (C+N2) is used
1800°C H2 O
Al2O3 + N2 ¾¾¾¾
- CO
® AlN ¾¾¾ ® Al(OH)3 + NH3 [not in NCERT]
¾ T]
C + SiO2 ¾® CO2 + Si .
E 143
ALLEN
METALLURGY
4.1 INTRODUCTION
Metallurgy : The branch of chemistry which deals with the method of extraction of metals from their ores by
profitable means.
Metal : The element which tends to form positive ion is called a metal.
Minerals : The various compounds of metals which occur in the earth's crust and are obtained by mining are called
minerals. In earth crust order of abundance of elements is. O > Si > Al > Fe
A mineral may be single compound or a mixture.
Ore : The mineral from which a metal can be extracted profitably and easily is called an ore.
All ores are minerals but all minerals are not ores. (T/F)
Type of Ores :
(I) Combined Ore : Metals placed above H in electrochemical series are generally reactive i.e. why they
generally found in combined state.
N
(a) Halide ore / Sulphate ore / Oxy ore : Metals are highly reactive (Li ® Mg)
(b) Oxide ore : Reactive metal (Al to Sn)
(c) Sulphide ore : Metal placed near H or below H. (Pb, Hg, Cu, Ag)
0
(II) Native Ore : Metal placed below H in electrochemical series are generally found in native state.
-2
E (Ag, Au, Cu, Pt etc.)
Gangue or matrix : The undesirable impurities present in an ore are called gangue.
19
Types of metallurgy
20
LL
Pyrometallurgy Hydrometallurgy Electro metallurgy
Temp. is involved Solution is involved
n
Electricity involved
io
For heavy metals According to E.C.S. IA, IIA, Al
ss
Fe, Zn, Cu, Hg, For metals placed below H
Sn, etc
Se
Cu, Ag, Au
A
4.2 STEPS INVOLVED IN THE EXTRACTION OF METALS
Z:\NODE02\B0AI-B0\TARGET\CHEM\ENG\MODULE-5\4-METALLURGY\1.THEORY.P65
The extraction of a metal from its ore is completed in the following four steps.
(A) Concentration of the ore (B) Conversion of concentrated ore into oxide form.
(C) Reduction of the metal (D) Refining of the metal.
(A) Concentration of the ore or dressing or benefaction
The removal of impurities from the ore is called its concentration or to increase the concentration of ore in ore
sample. Two process – (1)Physical (2) Chemical
(1) PHYSICAL :
(i) Gravity separation (Levigation) : This method of concentration of the ore is based on the difference
in the specific gravities of the ore and the gangue particles.Powdered ore is agitated with a running stream
of water. The lighter gangue particles are taken away by water while heavier ore particles settle down.
Ex. Oxygenated ore
E 141
,Pre-Medical : Chemistry
ALLEN
Hopper
Gangue
Suspended particles
ore
Ore
Water particles
Concentrated
ore
Hydraulic classifier
N
(ii) Froth Floatation method
This method is mainly employed for the concentration of sulphide ores.
The method is based on the different wetting characteristics of the gangue and the sulphide ore with water
0
and oil. The gangue preferentially wetted by water and the ore by oil.
-2
The crushed ore along with water is taken in a floatation cell. Various substances are added depending
on the nature of the ore and a current of air is blown in. The substances added are usually of three types.
E
19
(a) Frothers :–They generate a stable froth which rises to the top of the tank.
Example of frother is pine oil, Eucalyptus oil, fatty acids etc.
(b) Collectors or floating agents :– These attach themselves by polar group to the granules of the
20
ores which then become water repellent and pass on into the froth.
LL
Example: sodium ethyl xanthate, pine oil and fatty acid.
(c) Froth stabilisers : To stabilise froth.
n
Ex. Cresol, Aniline etc.
io
(d) Depressants :– These reagents activate or depress the floatation property and help in the
separation of different sulphide ores present in a mixture.
ss
e.g. NaCN.
Impurity of ZnS in PbS ore removed by NaCN
Se
NaCN + [PbS + ZnS] ®Na2[Zn(CN)4] + PbS ® form froth
A
Powdered
Z:\NODE02\B0AI-B0\TARGET\CHEM\ENG\MODULE-5\4-METALLURGY\1.THEORY.P65
Ore + Oil + Water
Compressed air Light ore particle
in froth
Concentrated Ore
Gangue
[Froth floatation process]
142 E
, Pre-Medical : Chemistry
ALLEN
• Sometimes, it is possible to separate two sulphide ores by adjusting proportion of oil to water or by using
‘depressants’.
• For example, in case of an ore containing ZnS and PbS, the depressant used is NaCN. It selectively prevents
ZnS from coming to the froth but allows PbS to go along with the froth.
(iii) Magnetic separation:-
If either the ore or the gangue (one of these two) is capable of being attracted by a magnetic field, then
such separations are carried out (e.g. in case of iron ores)
e.g. • SnO2 having the impurities of FeWO4 + MnWO4(Wolframite)
• FeO.Cr2O3 having the impurities of SiO2.
Finely ground ore
N
Magnetic roller
0
Magnetic particles
-2
E Non-magnetic particles
19
2. CHEMICAL SEPARATION (LEACHING) : In this process we use suitable agent which react with ore to
20
form water soluble complex while impurities remain insoluble. Applicable for Al, Ag,Au.
LL
é Re d Bauxite ® Al2 O3 .2H2O + Fe 2O 3 ( Major impurity)
n
(a) Aluminium : ê
io
ë White Bauxite ® Al O .2H O + SiO ( Major impurity)
2 3 2 2
ss
(I) RED BAUXITE : Two processes
(i) Baeyer's process : NaOH is used.
Se
excess H O
Al2O3 + NaOH ¾® NaAlO2 ¾¾¾¾¾® 2 Al(OH)3 + NaOH
A
Z:\NODE02\B0AI-B0\TARGET\CHEM\ENG\MODULE-5\4-METALLURGY\1.THEORY.P65
FeO + NaOH ¾® inso lub le
¯
Basic
(ii) Hall's process : Na2CO3 is used.
HOH
Al2O3 + Na2CO3 ¾® 2NaAlO2 ¾¾¾¾
CO2
® Al(OH) + Na CO
3 2 3
(II) WHITE BAUXITE : One process.
Serpeck's process : (C+N2) is used
1800°C H2 O
Al2O3 + N2 ¾¾¾¾
- CO
® AlN ¾¾¾ ® Al(OH)3 + NH3 [not in NCERT]
¾ T]
C + SiO2 ¾® CO2 + Si .
E 143
