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Transcript of 13-08-14
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Principles of Non Ferrous
Extraction MetallurgyExtraction Metallurgy
Date 13th Aug, 2014
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Pyrometallury
We found pyrometallurgical process is
adopted for large scale production. This is
reason in classification of different process
steps we found Pyrometallurgical operationssteps we found Pyrometallurgical operations
are dominated in comparison to
hydrometallurgical and electrometallurgical
process
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Advantages of Pyrometallurgical
process
Reaction rates are greatly accelerated at higher
temperatures.
Question: What type of reactor must be use, Big or
SmallSmall
Some reaction which are not thermodynamically
possible at lower temperature become active at
higher temperature
The greater ease with which metal can be
separated from gangue
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Metals like Lead, Zinc, copper, Aluminium,
Magnesium, Sodium, Antimony are produced using
pyrometallurgical processespyrometallurgical processes
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Smelting Production of metal or metal rich phase (matte)
Metal oxide to metal, carbon is used as
reducing agent
During smelting gangue is removed using flux
Design of flux is big area of research and Design of flux is big area of research and
business
Gangue + Flux = Slag
+ =
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Meaning of terms in relation to metal
extraction
Matte : A mixture (impure fused material) of a metal with its sulfides, produced by smelting the sulfide ores of copper, lead, or nickel.
Gangue: The waste material in the ore is called ganguegangue
Flux: in metallurgy is like a chemical agent which softens gangue mineral to form slag
Slag : waste left over after after reduction of metal
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Cu ore, Cu matte, Cu Slag, Cu cathode
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Matte
Metal rich phase
If extraction of metal from matte is cost consuming than people leave it.
If some precious metal is present in matte If some precious metal is present in matte than they process it via matte smelting
Matte may also contain gangue which can be selectively combined with flux to produce slag leaving behind crude metal
Matte form a separate layer with slag because of difference in specific gravity
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Matte
Matte has higher electrical conductivity ??
Density of Matte is between metal and slag
phases
Matte is insoluble in metal and slag phases Matte is insoluble in metal and slag phases
Matte is excellent solvent for some impurity
metal, especially for traces of precious metals
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Smelting
But Matte is not rich source of bulk metal
Why carbon as reducing agent? Easily available at low cost
Carbon (non volatile) Carbon (non volatile)
(a) results in volatile oxide CO2Or (b) results in volatile oxide CO
If CO2 or CO is volatile than they are automatically removed from system
CO is only stable at higher temperature
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Smelting
Theoretically speaking carbon can reduce any metal oxide provided temperature is sufficiently high
MO (s,l) + C (s) = M (s,l)+ CO (g)
MO (s,l) + CO (g) = M (s,l)+ CO (g)MO (s,l) + CO (g) = M (s,l)+ CO2 (g)
If stability of MO is high, than temperature required for reduction has to be high
If temperature is too high than Carbon may dissolve into metal to make metal carbides which is detrimental towards properties..unintentional carbides are impurity
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Metallothermic reduction
Reduction of metal compound using carbon is
carbothermic reduction (different from
Metallothermic reduction)
Cr O (s) + 2 Al (l) = 2 Cr (l) + Al O (l), example Cr2O3 (s) + 2 Al (l) = 2 Cr (l) + Al2O3 (l), example
for metallothermic reduction
Many oxides are also reduced by calcium
because calcium form stable oxide and
reduction is called calciothermic reduction
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Metallothermic reduction
Many metal halides can be reduced by
another metal which form most stable halides
TiCl4 (l) + 2Mg(l) = MgCl2(l) + Ti (s)
Most halides have lower melting point. Most halides have lower melting point.
If metal produced is in liquid form than liquid-
liquid separation can be used to separate
metal and slag
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Solid state reduction of oxides
Smelting is above fusion point
What about if metal has high MP and ore is
very poor grade?
A case of Tungsten (MP 3400 deg C) A case of Tungsten (MP 3400 deg C)
Tungsten ore contain 2% WO3 and rest
constitute the gangue
If gangue is large than you require large
quantity of flux (which is costly)
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Strategy for W
First produce pure WO3 using extensive ore dressing
Than hydrometallurgical operation at 800 to 1000 deg C1000 deg C
WO3 (s) + 2 H2 (g) = W (s) + H2O (g)
Now W obtained can shaped in desired form by powder metallurgical route like CIP followed by sintering or HIP at 3200 deg C.
Is and Why W in power form in above reaction?
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Pyrometallurgical process under low
and high temperature
We have seen nature of pyrometallurgical
process
We understand Low temp and high temp
process from themodynamic and kinetic view process from themodynamic and kinetic view
point??
If we say process is favorable at high temp,
means equilibrium will shift towards product a
speed of reaction will proceed towards
product
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Pyrometallurgical process under low
and high pressure
Thermal reduction
R (s,l) + MA (s,l) = RA (s,l) + M (g)
R (s,l) + MA (s,l) = RA (g) + M (s,l)
Thermal DissociationAre this example
Thermal Dissociation
MA (s,l) = M (g) + A (s,l)
MA (s,l) = M (s,l) + A (g)
Sublimation or distillation
M(s,l) = M(g)
M (in solution)= M (g)
Are this example
of high pressure
or low pressure
process??
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High pressure or low pressure
In the previous slide, thermodynamic equilibrium can be shifted by manipulating pressure parameter
Say low pressure. How to achieve? By vacuum Say low pressure. How to achieve? By vacuum
Vacuum helps to eliminate one of the reaction production and thus driving reaction towards completion
Thus vacuum found it application in distillation, thermal reduction and thermal dissociation
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Other example
Take thermal decomposition of oxide. Can we
have solution from Vacuum? Answer
Do thermal decomposition of oxides under
vacuum offer possibility of metal extraction vacuum offer possibility of metal extraction
from oxides?
Do you see solution of high vaccum with high
temperature?
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Thermal decomposition of oxides?
If we say thermal decomposition of oxides can be done under vacuum than such oxides are unstable oxides (Hg or Ag)
Hg and Ag has high vapor pressure at temperature of decomposition, chance of back temperature of decomposition, chance of back reaction is highly probable
Vacuum proves successful if volatile phases comes out of reaction chamber for reaction of nature say
MA (s,l) + R (s,l)=RA (g) + M (s,l)
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Another example for Vacuum
(1) ZnS + Fe = Zn + FeS (under vacuum, at 1000
deg C)
(2) ZnS roasted to ZnO, ZnO reduce to Zinc
Reaction (1) is feasible provided ZnS is without Reaction (1) is feasible provided ZnS is without
impurity
Another example is high temperature reduction of oxide by carbon: Low pressure or high Pressure?
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Problem
Nb2O5 (c) + 5 C(c) = 2Nb (c) + 5 CO (g)
G = 68.85 kcal Positive free energy indicate forward reaction
is not favourable at 1 atmis not favourable at 1 atm
G =-RTlnK pco=3x10
-3atm or 2.28mm of Hg
This means reaction is feasible using vacuum
better than 2.28mm of Hg
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Test yourself
WO3 (c) + 3H2 (g) = W (c) + 3H2O (g)
Now what is role of vacuum here???
Do you think vacuum will influence here??
FeO (s) + CO (g) = Fe (c) + CO2(g)
Now what is role of vacuum here???
Do you think vacuum will influence here??