Chemistry Metallurgy charts

GAURAV SONI
IIT ROORKEE
 The isolation and extraction of metals from their ores involve the following major steps:

(A) Crushing of the ore.

Metallurgy
(B) Dressing or concentration of the ore.
(C) Isolation of the crude metal from its ore
(D) Purification or refining of the metal.

Crushing
The ore is first crushed by jaw crushers and ground to a powder (pulverization of the
&
ore) in equipment’s like ball mills and stamp mills.
Grinding

(i) Hydraulic washing or Gravity separation or Levigation method:

1. It is based on the difference in the densities of the gangue and ore particles.
2. In this, the powdered ore is agitated with water or washed with a upward stream of running water, the
lighter particles of sand, clay etc are washed away leaving behind heavier ore particles. For this either
hydraulic classifier or Wilfley table is used.
3. This method is generally used for the concentration of oxide and native ores.

(ii) Electromagnetic separation:

1. It is based on differences in magnetic properties of the ore components.
2. It is used when either the ore or the impurities associated with it are magnetic in nature.
3. A magnetic separator consists of a belt (of leather or brass) moving over two rollers, one of which is
magnetic.
4. When the powdered ore is dropped on the belt at the other end, magnetic component of the ore is
attracted by the magnetic roller and falls nearer to the roller while the non-magnetic impurities fall
away from it.
5. Examples :
Chromite ore (FeO.Cr2O3) is separated from non–magnetic silicious impurities and cassiterite ore (SnO2)
is separated from magnetic Wolframite (FeWO4 +MnWO4).
 Froth contains sulphide ore Generally used for sulphide ore (ZnS, PbS, CuS,
Process: FeS2)

Powdered ore + H2O + frother + collector 

Water contains impurities Based on difference in wettability of ore particle

and impurities with pine oil and H2O.

Some definitions:
Frother: used to make stable froth (pine oil)
Concept: ore particle are prefencially wetted by Collector: which is attached to the ore particle and
pine oil and impurities are prefencially wetted Froth floatation process make them water repellant, so ore particle pass into
by H2O. froth. (ex Na or K , xanthalate)
Activators: actives the particle of ore to pass through
into froth.
Depressing agent: deactivates tendency of ore
particle to pass into froth.

Ex. Extraction of PbS from PbS + ZnS + FeS2 + impurity

(Ore + impurity) + (add H2O + froth + collector)  froth (PbS + ZnS + FeS2) ------------> froth PbS + (mix of H2O + ZnS + FeS2) -------------> froth ZnS
+ (mix of H2O + FeS2)
Example: leaching of Ag/Au Concept
(Mac-arther forest process- hydrometallurgy) 1. This process is used where ore particle are soluble in
Ore (Ag/Au) + KCN (excess)  Soluble somplex some reagent leaving behind impurities undissolved
2. Used for Al, Ag, Au, Cu, Sn
( [Ag(CN)2]- / [Au(CN)2]- )
Soluble complex + Zn  Ag/Au + [Zn(CN)4]-

Leaching

Example: leaching of bauxite ore (Al)

Three methods:
A) Baeyer’s Process
(Al2O3 + imp) + conc NaOH ------------> NaAlO2 -------------> Al(OH)3 ----------> Al2O3 (pure)
(40 atm, 500K) (CO2/NH4Cl) (1470k)
B) Hall’s Process
Bauxite ore + Na2CO3 ------------------> NaAlO2
(fusion at high T)
C) Serpecks process
Bauxite ore + N2 gas + C --------------------------> AlN + CO
(electric furnace 18000C)

AlN + H2O ----> NH3+ (Al(OH)3) -------->Al2O3 (pure)

(1470k)
Conversion to oxide:
Oxide are easier to reduce into metal so (oxosalts & sulphide) are converted to
oxide before reduction to metal.

Calcination Roasting
1. It is the process of heating ore in limited It is process of heating ore in presence of
supply of air or in absence of air is air known as roasting.
known as calcination.
2. This is used for oxosalts. This is used for sulphide ores
3. Oxosalts -------> oxide Roasting at moderate temperature.
(heat) Some portion of sulphide + O2  oxide + SO2
FeCO3  FeO + CO2
PbCO3  PbO + CO2 Remaining portion of sulphide + O2 
ZnCO3  ZnO + CO2 sulphates
CaCO3.MgCO3  MgO + CaO + CO2
(dolomite) 2PbS + 3O2  2PbO + 2SO2
PbS + O2  PbSO4
Cu(OH)2CuCO3  CuO + H2O + CO2
ZnS + O2  ZnO + SO2
ZnS + O2  ZnSO4
4. Oxide containing water of crytalisation At high T
becomes anhydrous on heating. Sulphide + O2  oxide + SO2

Fe2O3.3H2O  Fe2O3 + 3H2O At high T in some cases oxide and sulphide

react with each other to form metal. Process
Al2O3.XH2O  Al2O3 + XH2O is known as auto reduction or self-reduction.

Ex; Cu, Pb, Hg

2Cu2S + 3O2  2Cu2O + 2SO2
Cu2S + 2Cu2O  6Cu + SO2

PbS + O2  PbO + SO2

PbS + PbO  Pb + SO2

HgS + O2  HgO
HgS + HgO  Hg
5. Organic metal being volatile escape Nonmetallic impurities after oxidation being
from the ore and the ore becomes volatile and escape from the ore.
pores.
Smelting (flux & slag)
Concept:
During roasting as well as reduction some compounds (flux) are added to remove
impurities and the mixture is melted. Flux form slag with impurity which can be removed
easily.
The principle of slag formation is essentially the following:
Nonmetal oxide (acidic oxide) + Metal oxide (basic oxide) ------> Fusible (easily melted) slag
Properties of a slag:
 Slag is a fusible mass.
 It has low melting point.
 It is lighter than and immiscible with the molten metal. It is due to these impurities
that the slag floats as a separate layer on the molten metal and can thus be easily
separated from the metal. The layer of the slag on the molten metal prevents the
metal from being oxidized.

Acidic flux Basic flux

D) Acidic flux + basic imp  slag I) Acidic imp + basic flux  slag
E) It is oxide of nonmetal J) oxide of metal
F) Ex. SiO2, P4O10 K) Ex. MnO, CaO
G) Cao + SiO2  CaSiO3
Imp flux slag
H) Reduction of Sn
Electrolytic reduction:
ΔGo = -nFE0cell Reduction by coupling with more spontaneous reaction
For the ore of more electropositive (low MO  M + ½ O2 ΔGo = 100kJ .........(1)
SRP value) elements use electrolytic
reduction because they are difficulty to be N + ½ O2  NO ΔGo = -200kJ ........(2)
reduced. Principle involved From 1 and 2
Anode -> oxidation occurs in reduction of MO + N  NO + M ΔGo = -100Kj (spontaneous reaction)
Cathode-> reduction occurs (metal)
ore into metal
Where N -> like carbon or coke
Example: extraction of Na from M -> metal to be reduced
electrolysis of fused NaCl
A: 2Cl-  Cl2 + 2e-
C: Na+ + e-  Na

Reduction of metal oxide into metal (application of Ellingham diagram)

1. Carbon reduction method ( C or CO )
2. Reduction by other metal
3. Self-reduction method
4. Hydrogen as a reducing agent
Ellingham diagram
1. Ellingham diagram is formed by plotting standard gibbs free energy of formation of
metallic oxide per mole of oxygen.
2. 2xM(s) + O2 ---> 2MXO (s)
ΔH0 => -VE = -X
ΔG0 => -VE = -Y
ΔG0 = ΔH0 - T ΔS0
-X + TY

3. M(s) + O2  MXO (s)

Slop of some lines increases sharply at a point. This is due to more entropy change
associated with the boiling of metal, so the turning point represent boiling point of
metal.

Ex: Hg-HgO line changes its slop at 3560C (boiling point of Hg) and Mg-MgO line
changes its slope at 11200C.
4. ΔG0f -ve reflect the spontaneous formation of oxide so that oxide is stable.
+ve value of ΔG0f reflects non spontaneous formation of oxide so oxide is unstable.
5. Due to +ve slope of ΔG0f line eventually all the line cross ΔG0f = 0 line. So theoretically
all metallic oxide converted to metal by heating strongly.
But due to practical difficulties associated with high T this method of reduction is
limited use only for only very less electropositive metal like Ag, Hg, Au etc
6. MxO + N  NYO + M (ΔG0f < 0 )
So NyO is more stable than MxO.
Ex: Zn, Al, Mg etc are used to reduce iron, copper oxides to respective metals.
7. Hydrogen line is not widely used due to its high slop and less intercept.
 A metal which lies below in Ellingham diagram can be used to reduce oxide of other
metal which lie above in Ellingham diagram.
Ex: Zn, Al, Mg etc are used to reduce iron, copper oxides to respective metals.
 Hydrogen line is not widely used due to its high slop and less intercept.
2H2 + O2  H2O (l)  H2O (g)
For ex oxides of less electropositive elements like Cu, Co, Mo etc are reduced by
Hydrogen to metal.
 Carbon reduction method
C(s) + ½ O2 (g) ---------> CO (g) ΔS0 = +ve
C(s) + O2 ----------> CO2 (g) ΔS0 = 0
CO(g) + ½ O2 --------> CO2 (g) ΔS0 = -ve

o In many metallurgical extraction carbon reduction is used because at low T

3rd line is useful and at High T 1st line is useful. (due to its negative slop)
o Below 7100C, 3rd line i.e. carbon monoxide is better reducing agent and
above 7100C carbon is reducing agent.
o Reduction of metal is genrally carried out from oxide not from sulphide ore
due to the absence of 1st and 3rd line. [CS is unstable and due to less
thermodynamic stability of CS2 2nd line not very useful.]
 1. Carbon reduction method
Carbon can reduce a number of oxides and other compounds because of low cost. It is
carried out in blast furnace.

2. R

Disadvantages:
5. High T needed
6. Some metallic oxide like CaO gives metallic carbides instead of metals
CaO + 3C  CaC2 + CO
7. During cooling of products, in many cases reformation of oxides and carbon
may takesplace.
8. MgO + C <----> Mg + CO
2. Reduction by other metal
1. In carbon reduction T required is very high so reduction is done by other metal.
2. Also certain metallic oxide cannot reduce by carbon (like CaO) because affinity of
oxygen for metal is greater than its affinity for carbon.
3. such metallic oxides (Cr, Mn) can be reduced by highly electropositive metal such as
Al that liberates large amount of energy on oxidation to Al2O3.

1. Cr2O3 is mixed with some amount of Al powder and placed in large fire clay
crucible
2. An intimate mixture of Na2O2 or BaO2 and Mg powder (called ignition mix or
igniter) is placed in small depression made in thermite mixture.
3. The crucible is surrounded by sand which prevent lose of heat by radiation.
4. A piece of Mg ribbon is struck into ignition mixture and charge is covered by layer
of CaF2 (fluorspar) which acts as a heat insulator.
5. Now Mg ribbon is ignited so that ignition mixture cataches fire and flame is
produced leading to a violent reaction b/w Mg and BaO2 with evolution of large
amount of heat.
Mg + BaO2  BaO + MgO + Heat
Heat produced makes Cr2O3 and Al powder react together
Cr2O3 + Al  2Cr(l) + Al2O3
Molten metal formed settles down at bottom of crucible
6. This process is used for joining broken pieces of iron(welding).
 Concept:
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 oxides or sulphates which
react with remaining part of sulphide ore to give the metal.

3. Self-reduction method
(Auto reduction)

Cu2S + O2  Cu2O + SO2 HgS + O2  HgO + SO2

Cu2O + Cu2S  Cu + SO2 HgS + HgO  Hg + SO2

PbS + O2  PbSO4
PbS + O2  PbO + SO2
OR PbSO4 + PbS  Pb + SO2
PbO + PbS  Pb + SO2

4. Hydrogen as a reducing agent

1. Not very effective
2. ΔS is –ve for
2H2(g) + O2(g)  2H2O (g)
3. H2 reduces oxides such as Cu(I) oxide, Cu(II) oxide, W, Mo, Co oxides (since
ΔG is above that of H2O)
4. Can not reduce Al, Mg, Ca
5. Oxides of iron ore reduced with difficulty.
Purification of impure metal

Metallic impurity (due to simultaneous

reduction of other metal)
Impure
Nonmetallic impurity (already present in
metal
the ore P, As, S etc)

Compounds (oxides and sulphides)

Physical method Chemical method

1. Liquation 1. Oxidation
Two types of method 2. Fractional distillation 2. Reduction
3. Zone refining 3. Electrolytic refining
4. Chromatography
Liquation Fractional distillation Zone refining
1. This method is used when melting 1. This method is used 1. Used for semiconductors mainly
point of metal is considerably less when B.P. of metal is 2. This method is used when metal is
than impurities. less. required in high purity
2. Concept: heat the impure metal 2. Concept: On heating 3. For example Si and Ge are required
above melting point of metal on impure metal upto B.P. in high purity for semiconducting
the slopping Hurth of reverberatory of metal, metal is device.
furnace so that the molten metal collected in vapour 4. Concept: this method is based on
flows down leaving impurities on phase while impurities the fact that impurities are more
the Hurth. are left behind in soluble in liqvid metal than that in
3. Example: furnace. solid metal.
Purification of Sn 3. Example: 5. Using moving heater soft zone of
Zn, Cd, Hg metallic rod shifted from one end
Sn impure ------------> molten tin to other, so the impurities will be
(pig tin) + impurities are left behind collected at one end of the rod
on the hurth known as dross. which will be cut off and the metal
becomes ultra-pure.
 It is used for elemental (metallic + nonmetallic) impurities

If the oxides are volatile they

will be volatilized off
Metal
Impure metal +
Hot O2 is passed
+ Impurities get
in molten metal If oxides form scum over the
Elemental impurities oxidized which can molten metal, removed by
be removed as skimming

Some oxides form slag with the

Oxidative linings of the furnace which can
method be removed easily

EX. Manufacturing of steel from cast

iron
Cast iron Molten metal + SO2 + CO + CO2 + SiO2 + P4O10 + MnO
Melt in bassimer
+ (Escapes from
converter and pass (Form slag)
Imp S, Si, C, P, Mn mouth of the
Hot O2 gas
furnace)

SiO2 + CaO  CaSiO3

P4O10 + CaO  Ca3(PO4)2
MnO + SiO2  MnSiO3
EX. Purification of Pb (softening process) [combination of parks and cupellation]
1. Due to presence of these impurities lead is hard and brittle. So removal of these impurities is known as softening
process.

2. PbS -----------> Pb + ( Cu, Fe, S, Bi, P, As, Ag etc)

(Self-reduction)

Impure lead ----------------------> impurities are oxidized and can be removed + Pb-Ag
(Melt in an iron pot & pass hot air) (Argentite ferrous lead)

3. Parks process:

Pb-Ag (alloy) -----------------------> Ag is 300 times more soluble in Zn than that in Pb (two layer)
(Melt in iron pot & add 1 % Zn)
Upper layer  contains Zn-Ag alloy with Pb as impurity
Lower layer  contains almost pure lead (0.0004% Ag) which is further purified by battis electrolytic method
 This method is used to reduce oxide & sulphide of metal in impure metal. It is followed after oxidation
method.
1. Poling method
in this method molten metal ( with impurities) is stirred by green stem with some carbon which reduces
oxide of metal.

Ex: purification of Cu and Sn by poling

Cu2O + Cu ------------------------------------------------------> molten Cu
(melt in furnace and stirred with green stem)

Green stem + C  Hydrocarbon (CH4) etc

Reductive Cu2O + CH4  Cu + CO2 + H2O

method (99.5% ) (Pitch copper)

2. Vapour Phase decomposition

1. Mond’s process (for Ni)

Ni (impure) + CO -----------> Ni(CO)4 (g) ---------------------> Ni(g) + 4CO (g)

(500C) (collect it separately
& then heat upto 2000C to 3000C)

2. Van-Arbel De Doer process

(used for Ti, Zr , Bi)

Ti + 2 I2 ------> TiI4 (g) + imp (s) ----------------------> Ti (pure) + 2I2

(150 – 2500C) (collect it separately & heat it upto 14000C over W filament)
 Extraction of iron from Hematite ore
Ore (oxide, carbonate + water of crystallization)

[Concentration by gravity separation &

electromagnetic separation]

Concentrated ore

[Calcination and roasting in reversible furnace

1. To decompose carbonate
2. To evaporate water]

Oxide ore

[Mixed with coke and lime ston(flux)

and fed into blast furnace with O2 gas.]

Low temperature 900 – 1500K

CaCO3  CaO + CO2
500-800 k
C + O2  CO2
Fe2O3 + CO  Fe3O4 + CO2
High temperature C + CO2  2CO
Fe3O4 + CO  Fe + CO2
SiO2 + CaO  CaSiO3
Fe2O3 + C  Fe + CO
Imp flux slag

Slag (molten metal)

[(Pig iron), Melting pig iron with scrap

iron + coke + hot air blast]
Cast iron

[Which can be casted into different

Fe2O3 + C  Fe + CO + CO2
shapes (extremely hard and brittle)]

Wrought iron (meleable)

(Purest form of commercial iron)
 Extraction of Au and Ag
(Mac-arther forest process)
(Hydrometallurgy)

Ore

4Au + 8CN- + O2 + 2H20  4Au(CN)2-1 + 4OH-

[Ore is passed through excess of KCN solution
Ag + 2CN- + O2 + H2O  Ag(CN)2-1 + 4OH- to form soluble complex]
If Ag2S + 4KCN + O2  2Ag(CN)2-1 + 2K+ + K2SO4

Soluble complex

[Solution is filtered off to remove impurity]

Filterate
Complex

Au(CN)2-1 + Zn  2Au + Zn(CN)42- [Soluble complex is passed through Zn dust]

(metal displacement reaction occurs)
Ag(CN)2-1 + Zn  Ag + Zn(CN)42-

Pure Ag/Au
 Extraction of Mg from carnallite and magnesite ore

Ore

KCl.MgCl2.6H2O ------ > MgCl2

(carnallite) (Heat)

MgCO3 ------> CO2 + MgO ------>MgCl2 + H2O

(Magnesite) (dry HCl)

Sea water + Ca(OH)2  Mg(OH)2  MgCl2.6H2O --- > MgCl2

(0.13% Mg) (HCl) (dry HCl)

MgCl2

MgCl2 is electrolyzed using

Anode : 2Cl-  Cl2
Iron – cathode
Cathode: Mg2+ + 2e-  Mg
Graphite - anode
Overall : MgCl2  Mg + Cl2

Mg

[Further purification by distillation

under reduced pressure]

Pure Mg
 Extraction of Sn from Cassiterite Ore

Ore

[Concentration of ore by gravity separation

and electromagnetic separation]

Concentrated Ore

S + O2  SO2
Si + O2  SiO2 GAS [Roasting in presence of air in rev. furnace
As + O2  As2O3 then mixture is leached with water. Sulphates
of Cu and Fe are dissolved in water]
CuS + O2 CuSO4
FeS + O2  FeSO4

60-70 % SnO2 (black tin)

SnO2 + C  SnO + CO
SnO + SiO2  SnSiO3 Smelting:
CaO + SiO2  CaSiO3 [Black Tin + anthracite coal + silica + lime
CaO + SnSiO3 + C  CaSiO3 + Sn + CO stone]
Flux slag
(CaO prevents the formation of slag of tin)

Impure tin

[Purification by liquation and poling]

99% Sn (Pig Tin)

[Further purification by electrolytic refining]

Sn pure
 Extraction of Zn from Zinc blende (ZnS)

Ore

[Concentration by froth floatation method]

Concentrated ore

ZnS + O2  ZnO + SO2

[Roasting at high temperature in reverberatory
ZnS + O2  ZnSO4  ZnO + SO2 + O2
12000C
furnace at 1200K]

ZnO

[Add coke and heat upto 4000C]

ZnO + C  Zn + CO
(Carbon reduction method)

Impure Zn

[Zn is purified by liquation and fractional distillation]

Pure Zn
 Extraction of Cu by hydro metallurgy
(used for low grade copper ore=> cuprite + malachite)

Ore

CuCO3.Cu(OH)2  CuO + C  Cu + CO
[concentration by leaching
Cu2O + H2SO4 + O2  CuSO4 + H2O
with dil. H2SO4 + O2 pure]
CuCO3.Cu(OH)2 + H2SO4  CuSO4 + H2O + CO2

CuSO4

Electrolytic reduction By treatment with scrap iron

Fe + Cu+2  Fe+2 + Cu
(further purification by electrolytic refining)
 Extraction of copper from copper glance(Cu2S) and copper
pyrite(CuFeS2)

Ore

[Concentration by froth floatation process]

Concentrated ore

CuFeS2 + O2  Cu2S + FeO + SO2

[Ore is heated in reversible furnace + SiO2 (silica)]
FeO + SiO2  FeSiO3

Slag + copper matte

(Cu2S + FeS)

FeS + O2  FeO + SO2

[1. Taken in silica lined blister converter + hot
FeO + SiO2  FeSiO3 (slag) air blast (self reduction)
Cu2S + O2  Cu2O + 3O2 2. here slag is formed during both roasting
Cu2S + Cu2O  Cu + SO2 and smelting and bassimerization ]
(blister copper)

[It has blistered appearance due to

BLISTER COPPER evolution of SO2]

[Purification of blister Cu by poling process]

99.5% Pure copper

(pitch copper)

Impure Cu at anode  pure Cu at cathode

[Further purification by electrolyte refining]
Electrolyte => CuSO4

Pure copper
 Extraction of lead from galena

Ore

[Concentration by froth floatation]

Concentrated ore

PbS + O2  PbO + SO2 [Heat the ore at moderate T in reverberatory

PbS + O2  PbSO4 furnace in supply of air (roasting)]

PbO + PbS + PbSO4

PbS + PbO  Pb + SO2

PbS + PbSO4  Pb + SO2 [Temperature is increased to melt the
charge and lime stone is added and
CaCO3  CaO + CO2
air supply is cut off]
CaO + SiO2  CaSiO3
(Self-reduction method)
Flux impurity slag
(CaO prevents the formation of slag of Pb) (Hard and brittle)
PbO + SiO2  PbSiO3

Impure LEAD

PbSiO3 + CaO  CaSiO3 + PbO [Purified by liquation (parks process)]

Pb
(desilverised lead)

[Further purified by battle’s

electrolytic refining]

Pure Pb