Metallurgy
The branch of chemistry deals with the method of extraction of metals from their ores.
Most abundent metal in earth crust is AA.
(1)
(2)
(3)
(4)
Minerals
Ores
Flux
Gangue or Matrix
Elements or
other substances
obtained from
earth crust
Minerals from
which metal
can be
extracted easily
+ profitably
Compounds which are used to remove non
volatile impurities
acidic flux (used to remove basic impurities)
basic flux (used to remove acidic impurities)
Impurity present in
ores
All ores are mineral but all minerals are not an ores
Types of Metallurgy
(1)
Pyro metallurgy
(2)
Hydro metallurgy
(3)
Electro metallurgy
Different steps are used in pyro metallurgy
(a)
Crushing & grinding of ore
(b)
Concentration of ore
It is done by different methods
(1)
Froth floatation method used for sulphideore
(2)
Froth floation method (water soluble impurities remove)
(3)
G
r
av
it
y
s
e
p
a
r
a
ti
on m
e
t
ho
d
(
H
eav
y
/
l
i
g
h
t
i
m
p
u
riti
e
s
r
e
mo
ve
)
(4)
Magnetic separation method (Magnetic/non-magnetic impurities remove)
(5)
Leaching method (In this method chemicals are used which react with pure metal)
(c)
Calcination (done in absence or controlled air)
(d)
Roasting (Done in exess of air) (sulphide ore convert to oxide ore and SO
2
, P
2
O
5
, As
2
O
5
evolve out)
(e)
Main advantage of roasting is to convert sulphide or into oxide ore because oxide ore easily reduced than
sulphide.
(f)
Smelting (non volatile impurities remove)
(g)
Bessemerisation
(h)
Purification of metal (by Electrolysis)
Hydro metallurgy
Cyanidation method
(a)
Crushing ore
(b)
Concentration of ore
(c)
Complex formation
(d)
Metal displacement
2 2 4
2 2 2 2 4
[Extration of Ag from Ag
2
S]
(a)
Curshing of ore
(b)
Ore reacts with excess of NaCN in presence of excess of air.
Ag S + 4NaCN + 2O —→ 2Na[Ag(CN) ] + Na SO
Use of oxygen is to convert reversible reaction into irreversible
(c)
Displacement of Ag by Zn
Zn + 2Na[Ag(CN) ] —→ Na [Zn(CN) ] + 2Ag
Here Zn acts as reducing agent.
(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
Hopper
Suspended
ore
Gangue
particles
Water
Ore
particles
Concentrated
ore
Hydraulic classifier
(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
and oil. The gangue preferentially wetted by water and the ore by oil.
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.
(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
ores which then become water repellent and pass on into the froth.
Example: sodium ethyl xanthate, pine oil and fatty acid.
(c) Froth stabilisers : To stabilise froth.
Ex. Cresol, Aniline etc.
(d) Depressants : These reagents activate or depress the floatation property and help in the
separation of different sulphide ores present in a mixture.
e.g. NaCN.
Impurity of ZnS in PbS ore removed by NaCN
NaCN+ [PbS + ZnS] Na [Zn(CN) ] + PbS form froth
Powdered Ore + Oil + Water
Compressed air
Light ore particle
in froth
Concentrated Ore
[Froth floatation process]
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)
Gangue
2 4 4
2
2
2 3 2 2
3
2
—————→
2 3
2
2
COT
H
O
3
2 2
2
2
2 2 2 2
3
Finely ground ore
Magnetic roller
Magnetic particles
• SnO having the impurities of FeWO + MnWO (Wolframite)
FeO.Cr O having the impurities of SiO .
Non-magnetic particles
2.
CHEMICAL SEPARATION (LEACHING) : In this process we use suitable agent which react with ore to form
water soluble complex while impurities remain insoluble. Applicable for Al, Ag,Au.
J
Re d Bauxite Al
2
O
3
.2H
2
O
+
Fe
2
O
3
(
Major impurity
)
(a)
Aluminium :
|
White Bauxite Al O .2H O + SiO (
Major impurity
)
(I)
RED BAUXITE :
Two processes
(i) Baeyer's process : NaOH is used.
Al O
+ NaOH
NaAlO
excess H O
2
Al(OH)
+ NaOH
FeO + NaOH —→inso lub le
Basic
(ii) Hall's process : Na CO is used.
Al O
+ Na CO
—→
2NaAlO
H
O
H
A
l
(
O
H
)
+ Na CO
2 3 2 3
2
CO
2
3 2 3
(II)
WHITE BAUXITE :
One process.
Serpeck's process : (C+N ) is used
Al O + N
——
180
0
°
C
A
l
N
2
Al(OH)
+ NH T [not in NCERT]
C + SiO —→ CO T + SiT .
(b)
Ag and Au (CYANIDE PROCESS)
(I) A
g
A
g
S
+
4
N
a
C
N
——
2
O
2
2
N
a
[
A
g
(
C
N
)
]
+
N
a
S
O
2 2 2
4
[in absence of O
2
, reaction become reversible]
2Na[Ag (CN) ] + Zn —→ Na [Zn (CN) ] + 2Ag
2 2 4
(II)
Au
Au + KCN + H O
O
2
K
[
A
u
(
C
N
)
]
+
K
O
H
K[Au (CN) ] + KOH + Zn K ZnO + KCN + H O + Au
(B)
Conversion of concentrated ore into oxide form
Calcination and roasting
(a) Calcination : Calcination is a process in which ore is heated, generally in the absence of air, to expel
water from a hydrated or hydroxide ore and oxide or carbon dioxide from a carbonate ore at temperature
below their melting points.
3
2
3
3
2
3 2
3 2
3 2
3 2
2 3 2 2 3 2
2
2 2
2 4 3
2
For Example: All carbonates, hydrated ore and hydroxide ore
Bauxite Al O . 2H O Al O
+ 2H O, 2Al(OH)
Al
O
+ 3H O
2 3 2
2 3 2
3 2 3 2
Haematites
2Fe O . 3H O 2Fe O + 3H O
Limestone CaCO CaO + CO
Siderite FeCO FeO + CO
Calamine
ZnCO ZnO + CO
Cerussite PbCO PbO + CO
Malachite green
CuCO ·Cu(OH) CuO + CO + H O
3 2 2 2
Advantages of Calcination :
(i)
Moisture is removed.
(ii)
Organic matter is destroyed
(iii)
The hydroxide and carbonates ores are converted into their oxides.
(iv)
The ore become porous and easily workable
(b) Roasting : The removal of the excess sulphur contained in sulphide ores in the form of SO by heating in
an excess of air is called roasting.
The concentrated sulphide ore is heated in reverberatory furnace, below its melting point in the presence of an
excess of air with or without the addition of an external substance.
2ZnS + 3O 2ZnO + 2SO T
ZnS + 2O ZnSO ZnO + SO T
PbS + O
R
o
a
s
ti
n
g
Pb
O
+
S
O
T
2
2 3
3
2
3 2
2
2
Thermal reduction
Some less stable metal oxide further decompose into metal and oxygen.
A
g
S
+
O
——
R
o
a
s
ti
n
g
A
g
O
——
300
°
C
2A
g
+
1
O
T
2 2
SO
2
T
2
2
2
H
g
S
+
O
——
R
o
a
s
ti
n
g
H
g
O
——
400
°
C
H
g
+
1
O
2
Partial roasting
SO
2
T
2
2
2
C
u
FeS
2
+
O
2
C
u
2
S
+
2
FeS
+
S
O
2
T
C
u
2
O
2
Fe
O
after roasting
Roasting in Fe metallurgy
Fe O + FeO
Haematite
Fe O
Magnetite
= Fe O
+ FeO
F
e
C
O
——
A
F
e
O
+
C
O
T
Siderite
Roasting to prevent wastage of Fe as slag in reduction step
2FeO +
1
O Fe O
(It does not form slag)
2
2 2 3
In reduction step
FeO + SiO = FeSiO
(Flux) (Impurity) (Slag)
Advantages of Roasting :
(i)
Excess of sulphur is removed as volatile oxide.
S + O
2
SO
2
T
(air)
(ii)
The metal sulphide is converted into metal oxide.
(iii)
Impurities of arsenic, antimony & phosphorous are removed as their volatile oxides.
Sb
4
+ 3O
2
2Sb
2
O
3 T
As
4
+ 3O
2
2As
2
O
3
T
P
4
+ 3O
2
2P
2
O
3
T
For PbS, CuS and HgS partial roasting is carried out because these sulphide ore easily convert into metal by
auto reduction process.
Reduction of metal oxide to metal
Different methods are used to convert metal oxide to metal
(a)
Reduction by Carbon - Oxide of less reactive metal can be convert to metal on strongly heating with coke.
Eg. PbO + C —→ Pb + CO
Fe O
+ 3C 2Fe + 3CO
ZnO + C —→ Zn + CO
Note :- Some metal oxides like AA
2
O
3
Cr
2
O
3
, Mn
3
O
4
, MnO
2
are not reduced by coke.
Note :- CO is better reducer but not for Zn.
(b)
Self reduction
Compounds of certain metals are reduced to metal without using any additional reducing agent. ores of Cu,
Pb, Hg etc.
Their sulphide ores are partially roasted to give some oxide. This oxide is now reduced to the metal by the
remaining sulphide ore at elevated temperatures in the absence of air. The process is known as self reduction.
C
u
2
S
+
FeS
+
C
u
2
O
+
Fe
O
4
3
3
3
S
e
l
f
r
e
du
c
t
i
o
n
f
o
r
C
u
(
E
x
t
r
a
c
t
i
o
n
o
f
C
U
f
r
o
m
c
o
pp
e
r
g
l
a
n
c
e
.
)
2
C
u
2
O
+
C
u
2
S
A
6
C
u
+
S
O
2
(c)
Metal displacement method
In this method, a water soluble compound is obtained from the ore. The aqueous solution of the compound is
reacted with a more electropositive metal which displaces, the metal from the solution.
Ex.
(i)
Extraction of Cu fro low grade (lean) ore
C
u
C
O
3
.
C
u
(
O
H
)
2
+
di
l
u
t
e
a
c
id
—→
C
u
+
2
——
S
c
r
a
p
e
F
e
C
u
+
F
e
+
2
Malachite
(aq) (s)
(aq)
Ex.
(ii)
Separation of Ag by Complex formation (Cyanide process).
2Na[Ag(CN)
2
] + Zn Na
2
[Zn(CN)
4
+ 2Ag
(d)
Electrolytic reduction
This process is mainly used for the extraction of highly electropositive metals.
Electrolysis is carried out in large cells and a small amount of another suitable electrolyte is added which:
(i)
Lowers the melting point of the main electrolyte
(ii)
Enhances its conductivity
(iii)
Reduces corrosion troubles
Ex.
Na, K, Mg, Ca, Al, etc.
e.g. Manufacture of metallic sodium (Down's process)
Molten NaCl containing a little CaCl
2
is electrolysed between graphite anode and iron cathode. The
various reactions that take place are
On Fusion : NaCl
Na
+
+ Cl
(Ions become mobile)
On Electrolysis : At Cathode :
Na
+
+ e
Na (reduction)
(Metallic sodium)
At Anode : 2Cl
Cl
2
(g) + 2e
Note : Hall heroult process :
This process is used for extraction of Al from alumina. The extraction of Al from
Al
2
O
3
is quite difficult because
(i)
Fusion temperature of Alumina is quite high (2050°C). Even more than boilling point of Al (1150°C).
(ii)
It is a bad conductor of electricity.
To overcome these difficulties we mix some amount of neutral flux [Na
3
AlF
6
+ CaF
2
]. Neutral flux provide free
ions to the solution which decreases the fusion temperature of Alumina from 2050°C to 950°C.
(e)
Alumino thermite process :
In this process those metal oxide will be reduced which required high temperature
and at high temperature carbon react with metal to from metal carbide.
In this process we use aluminium as a reducing agent due to
(i)
Al has greater affinity towards oxygen as it forms most stable oxide (Al
2
O
3
)
(ii)
This reaction is highly exothermic in nature and once it starts it will continue till all the metal oxide reduces
to metal.
For Cr, Mn, Fe :
Cr
2
O
3
+ Al —— Al
2
O
3
+ 2Cr
Fe
2
O
3
+ Al ——→ Al
2
O
3
+
2Fe
Commercial use of this method is in aluminothermite weldings.
Note :-
(Fe
2
O
3
: Al) mixture in 3 : 1 is used.
REFINING OF METALS
Depending upon the nature of the metal and impurities, the following methods are used for purification of the
metals.
(1)
Distillation
Metals having low boiling point are refined by this method, for example, zinc, cadmium and mercury.
(2)
Liquation
This method is used for the refining of metals having low melting point and are associated with high melting
impurities.
Ex.
Pb, Sn, Sb, Bi and Hg.
The impure metal is heated on the sloping hearth of a furnace.
The pure metal flows down leaving behind the non- fusible material on the hearth.
(3)
Electrorefining of Metals
Metals such as Cu, Ag, Zn, Sn, Pb, Al, Ni, Cr are refined by this method.
Anode mud - Deposition of noble metals like Au Y Pt below anode.
Anode - made of impure metal
Cathode - made of pure metal
Electro refining of Copper
Anode
: Blister copper (98%)
Cathode
: Pure copper
Electrolyte
:
An aqueous solution of CuSO
4
(15%) + 5% dil H
2
SO
4
Electro refining of Pb (Bett's process)
Anode
: Impure lead.
Cathode
: Pure lead.
Electrolyte
: A mixture of PbSiF
6
and H
2
SiF
6
(4)
Zone refining or fractional crystallisation
Metals of very high purity are obtained by zone refining.
This refining method is based on the fact that impurities tend to remain dissolved in molten metal than solid.
Ge, Si and Ga
used as semiconductors are refined in this manner.
(5)
Vapour phase refining
(i)
Van - Arkel process
Employed for purification of metals like
titanium(Ti)
and
zirconium(Zr)
.
T
i
(
s
)
+
2
I
2
(
g
)
523
k
T
i
I
4
(
g
)
Impure
T
i
I
4
(
g
)
1
70
0
k
T
i
(
s
)
+
2
I
2
(
g
)
AG vs T
T
higher T
(ii)
Mond's process
Nickel is purified by using CO gas. This involves the formation of nickel tetracarbonyl.
Ni
(Impure)
+ 4CO
——
A
[
N
i
(
C
O
)
4
]
——
A
N
i
(
p
u
r
e
)
+
4
C
O
T
(6)
Some chemical processes
(i)
Cupellation :
This process is used to purify silver containing the impurities of Pb.
This process is used when impurity have greater affinity towards O
2
while metal does not have.
(ii)
Polling : Used to purify Cu, Pb.
This process is used for the metal having the impurity of their own oxide. In this process a wooden pole
is heated with molten metal, which provide C and H to metal oxide which reduces impurity of metal oxide
to metal .
CuO + H
2
——→ Cu + H
2
O T
CuO + C ——→ Cu + CO T
(iii)
Bessemerisation :
Impure metal is heated in a furnace and a blast of compressed air is blown which
oxidises the impurity into their oxides and that can be removed in the form of slag .
2Mn + O
2
——→ 2MnO
Si + O
2
——→ SiO
2
THERMODYNAMICS OF REDUCTION PROCESSES (ELLINGHAM DIAGRAM)
It is explanation of the feasibility of pyrometallurgical process by using gibbs equation
If AG = ve Process is stable or Spontaneous
AG = + ve or Less ve then process is Unstable or non-Spontaneous
When pyrometallurgical process contains more than one type of reaction then spontanity of reaction can be
explain by Ellingham diagram. Ellingham diagram contains plot .
(I)
400
300
200
100
0
300
500
A
700
800
900
1000
1100
1200
0 400 800 1200 1600 2000
T
A
AG = AH TAS
2 3
AG = Ve
Ca +
AG = +Ve
Cr +
CaO +
C
r
2
O
3
+
According to Ellingham diagram, the below metal can reduce the oxide of metal above it in the curve, as affinity
of metal below for oxygen is more.
Example Al Metal can reduce Cr O but can not reduce MgO & CaO.
At very high T after 'A' Point Al' metal can reduce MgO because Formation of MgO contains
less ve AG.
(II)
A
710° T
According to diagram at high T (710°C or above 710°C) Oxidation of C contains more ve AG so at high T 'C'
is good Reducing agent.
At Low T (below 710°C) Oxidation of CO contains more ve AG so at Low T, CO is good Reducing agent.
Types of Iron
Pig iron
Cast iron
Steel iron
Wrought iron
(i)
Cast iron and pig iron
It is most impure form of Iron and contains the highest proportion of carbon (2.5 - 4 % ) along with traces of
S, P, Mn and Si. Cast iron contain 2.5 to 4.3 & pig contain 2.5 to 5%.
(ii)
Wrought iron (Fibrous iron) or malleable iron
It is the purest form of iron and contains minimum amount of carbon (0.12 - 0.25%) and less than 5% of other
impurities.
(iii)
Steel
It is the most important form of iron and finds extensive applications. As far as carbon content (impurity) is
concerned it is mid-way between cast iron and wrought iron, it contains 0.25- 2% carbon. Thus all the three
forms of iron differ in their carbon contents, both iron and steel are obtained from cast iron.
Order of M.P. :- Wrought iron > Steel > Cast iron or Pig iron
2
C
+
2
O
2
2
C
O
2
(
I
)
MgO
A
l
2
O
3
C
r
2
O
3
Mg
Al
Cr
CaO
MgO
A
l
2
O
3
Al
Mg
Ca
2
2 2 2 2
2 2 2 2
2
2 3
2
2
Heat Treatment of Steel
(a)
Quenching or hardening :
Steel is heated to red hot temp. and is then cooled suddenly by plunging into
either cold water or oil. It makes steel hard and brittle.
(b)
Annealing :
The steel is heated to red hot temp. and then cooled slowly. It makes steel soft.
(c)
Tempering :
If quenched steel is heated to temp. between 500 to 575 K and then cooled slowly, it
becomes quite hard but brittleness disappears. The process is called tempering.
Extraction of Cu
Ore - CuFeS copper pyrites
Coke
(only fuel)
+ CaO
Slag
Self
reduction
Bassemerisation
in bessemer
Slag
CaSiO
3
Reaction involved :
(a) Roasting step
Electrorefining
E CuSO
4(aq)
+ dil.H
2
SO
4
C Pure Cu
A Impure Cu
CuFeS
+
O
C
u
S
+
FeS
+
S
O
T
FeS + O
Fe
O
+
S
O
T
Very less
C
u
S
+
O
C
u
O
+
S
O
T
(b)
Smelting step :-
Cu S remain unaffected again becoz carbon reduction occurs only for oxide and not for sulphide.
Fe
O
+
S
i
O
FeS
i
O
Slag FeS + Cu O FeO + Cu S
C
a
O
+
S
i
O
C
aS
i
O
2 2
copper Matte
(c)
Bassemer convertor reaction :-
FeS
+
O
2
Fe
O
+
S
O
2
T
Fe
O
+
S
i
O
2
FeS
i
O
3
s
l
a
g
C
u
2
S
+
O
2
C
u
2
O
+
S
O
2
T
C
u
2
O
+
O
2
C
u
+
S
O
2
T
Blister Cu
Cu
2
S + FeS + Cu
2
O + FeO
less
less
99.99%
Pure Cu
Pure Cu
Cu
2
S + FeS
2
3
Finely
divided
Ore
CuFeS
2
Froath floatation
Conc. ore
+
Little SiO
2
Roasting at
Cu
2
S+FeS
+FeO+Cu
2
O
+SiO
2
Smelting
Filteration
moderate temp.
convertor
Copper matte
Cu
2
S + FeS
+ SiO
2
Blister Cu
Poling
Extraction of Aluminium
Short chart of Al from Al
2
O
3
.2H
2
O (Bauxite)
BAUXITE
Concentration of Bauxite ore
(a)
Baeyer's process :
(Used for red bauxite in which main impurity is iron oxide)
B
au
x
i
t
e
o
r
e
R
o
a
s
t
e
d
a
s
t
o
c
o
n
v
e
r
t
F
e
O
i
n
t
o
F
e
2
O
3
Roasted ore + NaOH
150°C
8 atm
N
a
A
l
O
2
H
yd
r
o
l
y
s
i
s
Al(OH)
3
+ NaOH
solution
in presence ppt.
of little Al(OH)
3
(b)
Hall's Process :
(Red bauxite)
B
au
x
i
t
e
o
r
e
+
N
a
2
C
O
3
Fu
s
e
d
N
a
A
l
O
2
extracted with water
Solution
warmed 50° 60° C
CO
2
is circulated
Al(OH)
3
+ Na
2
CO
3
(c)
Serpeck's process :
(Used for white bauxite in which main impurity is silica)
Bauxite ore + coke
1
800
°
C
A
l
N
H
2
O
A
l
(
O
H
)
3
+
N
H
3
+ ppt.
(Nitrogen) N
2
C + SiO
2
(gangue)
CO
2
A
+ Si
CALCINATION
Al(OH)
3
1
500
°
C
A
l
2
O
3
Electrolytic Reduction
Electrolyte Al
2
O
3
dissolved in Na
3
AlF
6
and CaF
2
Cathode
Carbon lining
Anode Graphite rods
Al O
E
l
e
c
tr
o
ly
s
i
s
A
l
+
O
2 3
950°C
2
99.8% pure
Electrolytic Refining
(Hoop's process)
Pure Al (99.98 % pure)
3 4
2 3 2 3
2
2
2 3 2
2 3 2 2
Molten slag
Molten iron
Extraction of Fe
Gravity separation
S
i
O
2
Calcination
and
Roasting
Carbon reduction
Blast
Furnace
Ore (8) part
+Coke (4) part
+
C
a
CO
3
(
1
)
p
a
rt
Reaction involved :
(1) Roasting step :-
(Pudding process)
Molten iron taken in
Mn
S
i
O
3
Fe
3
(
P
O
4
)
2
Slag
C
aS
i
O
3
Fe
O
A
Fe
O
+
Fe
O
Fe
O
r
eac
t
s
w
it
h
S
i
O
t
o
g
i
ve
FeS
i
O
a
s
s
l
a
g
.
Fe
C
O
A
Fe
O
+
C
O T
H
e
n
ce
t
o
p
r
eve
n
t
t
h
e
f
o
r
m
a
ti
on o
f
FeS
i
O
.
3
FeO + O
2
A
Fe
O
FeO is converted into Fe O
3
which does not
Fe O .3H O
A
Fe
O
+
3
H
OT
r
eac
t
w
it
h
S
i
O
du
e
t
o h
i
g
h
L.
E
.
Reduction by carbon (Smelting)
"Reduction of the oxide with carbon at high temperature is known as smelting".
The oxides of less electropositive metals like Pb, Zn, Fe, Sn, Cu etc. are reduced to metal by strongly
heating them with coal or coke, in the blast furnace.
Metal Oxide + Coke + flux Metal + CO
2
T
+Slag.
(Blast Furnace)
Fe
2
O
3
+
l
itt
l
e
S
i
O
2
Conc. ore
+
Litt
l
e
S
i
O
2
Finely divided ore
m
a
g
n
e
tit
e
Fe
3
O
4
h
ae
m
a
tit
e
Fe
2
O
3
l
i
mon
it
e
Fe
2
O
3
.3
H
2
O
S
i
d
e
rit
e
Fe
CO
3
2
3
3
Wrought iron
Fe + 0.1 to
0.25%C + 0.3 to
0.45%S,Mn,Si,P
a furnace which
is lined with Haematite
Pig Iron or
Cast Iron
CO
2
S
O
2
Fe + C, S,
Mn, Si, P
2
2
2 2
2 3 2
eg. ZnO + C —→ Zn + COT
PbO + C —→ Pb + COT
These reactions are carried out at high temperature
SnO
+ 2C —→ Sn + 2COT
because at high temp. C is better reducing agent.
Fe O
+ 3C 2Fe + 3COT
Fe O + 3CO 2Fe + 3CO T
PbO + CO Pb + CO T
SnO + 2CO Sn + 2CO T
These reactions are carried out at low temperature
because at low temp. CO is better reducing agent.
2
3