Principles of Non Ferrous

Extraction MetallurgyExtraction Metallurgy

Date 13th Aug, 2014

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

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

Metals like Lead, Zinc, copper, Aluminium,

Magnesium, Sodium, Antimony are produced using

pyrometallurgical processespyrometallurgical processes

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

+ =

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

Cu ore, Cu matte, Cu Slag, Cu cathode

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

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

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

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

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

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

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)

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?

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

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??

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

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?

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)

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?

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

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??