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I. PRINCIPLES OF EXTRACTIVE METALLURGY
R AKES H KUM AR
Em ail : rakesh@ ninlindia.org
Extractive m etallurgy as a discipline deals with the ex traction of metals from naturally occurring
and man m ade resources. Separation is the essence of metal extraction. Dev elopment of efficient
separation schem es calls for a through un derstanding of extractive metallurgy p rinciples in
terms of p hysical chemistry (thermodynamics & kinetics); materials and energy flow/balance,
transport phenomena, reactor and reactor engineering, instrumentation and process control,
and environment and w aste management. (Slide 1-4)
In general, metallurgical separation processes invo lves chem ical reactions, and classified as
pyrometallurgical, hydrometallurgical, and electrometallurgical. The processes are also
classified as ferrous [dealing with iron and steel] and nonferrous [dealing with all other metals,
e.g. base metals (like Cu , Pb, Zn, N i, ...), light metals (Al, M g, Ti), precious metals (Au , Ag,
Pt, Pd, ...), rare earth (Ce, N d, Sm , ...), nuclear m etals (U, T h, ...), rare metals (Os, R u, ...)
etc]. (Slide 6)
Various pyrometallurgical unit processes are: calcination, roasting, smelting, converting,
refining, distillation etc. Eac h of these processes serves a sp ecific purp ose from the po int of
view of separation. They require specialized reactor depending upo n the ph ases (solid/liquid/
gases) involved, mode of co ntact, temperature, environmental measu res etc Calcination and
roasting are used as pre-treatment prior to other pyro- and hy dro- metallurgical operations.
(Slide 7, 8) Smelting is the most common of pyrometallurgical operations. Reduction smelting
is carried out for ox ides. During the smelting, metal compou nd (e.g. oxide of metal) is reduced
to metallic form, and the undesirable impurities gangue)
combine w ith f lux to form slag.
Imm iscibility of metal and slag together w ith density difference forms the b asis for separation.
Ellingham Diagrams (AG vs. T plots), w hich are available for ox ides, sulphides, chlorides etc
serve as a fundamental guide in predicting the relative stability of compounds. Based on these
diagrams, selection o f reduc tion, reduction temp erature, equilibrium partial pressures, can b e
indicated. Similarly, slag atlases are available for most com mo n slag systems. M atte (liquid
mixture of sulphides) smelting, which ex ploits the imm iscibility betw een slag and m atte, is
used for metal extraction from sulph ide ores.
Slide 9-14)
The w ord hydro- is derived from a Greek w ord wh ich means water. Separation steps involved
in hydrom etallurgy are: leaching, pu rification and/or conc entration, and precipitation/metal
production.
(Slide 15)
Leaching
involves preferential dissolution through water solvation,
acid/alkali attack, base-exchange reaction, complex ion formation and oxidation/reduction
reaction. The variables affecting leaching are pH, Eh, concentration, temperature, pressure,
prcomp lexing ion etc. Eh-pH diagrams are thermodynam ic plots that give an idea of the stability
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of various solution and solid species in equilibrium under different acidity (pH) and reduction
potential (Eh) conditions (ex. Cu-H20-S system). Bacteria assisted leaching (bacteria leaching)
is also used for the leaching/upgradation of ores (ex. U, Cu, bauxite etc). Depending upon
nature of leaching system (means mode of contact of solid-liquid, pressure, temperature,
stirring), wide variety of leaching systems are available to carry out leaching reaction, e.g.
heap, colum n, stirred tank and autoclave. Leaching gives rise to a metal solution
leach liquor)
and solid residue
leach residue). Leach liquor and residue are separated using filtration. A\
number of techniques are available for the purification of leach liquor. These include
precipitation, liquid-liquid and solid-liquid ion-exchange (solvent extraction, ion exchange)
and adsorption. Basic thermodynamic data are available in literature to predict the efficacy of
various separation systems. Metal/metal compound can be precipitated from the purified
solution through concentration, temperature adjustment, etc. Cementation exploits difference
in standard reduction potential of metal ions.
(Slide 16-22)
Electrometallurgy
is the process of obtaining metals through electrolysis. Starting materials
may be: (a) molten salt, and (b) aqueous solution. The separation is based on difference in
Standard electrode potential and it is used for Electrowinning or Electrorefining purpose.
Aluminium extraction is based on the fuse salt electrolysis.
(Slide 23-31)
While 'separation is the essence of metal extraction'. The scope extends beyond separation.
Number of issues that require attention includes:
Plant Size -
transportation, materials handling
Reactor - Size, Mixing, Materials flow, Heat transfer (engineering skills), material
selection, energy ...
Alloying -
Metals are generally used
in
the form of alloys
Waste disposal -
Huge quantity of waste is generated
Recycling - Resource conservation, Energy saving, Waste mininimisation
Manufacturing -
large scale manufacturing, many techniques.
The overall design of a metallurgical plant may involve optimization from the point of view
of process (energy, recovery, separation efficiency, productivity etc), cost of production and
environmental factors. (Slide 32-35)
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Principles of
Extractive Metallurgy
Training Course on
Mineral Processing and
Nonferrous Extractive Metallurgy
June 30 - July 5, 2008
Rakesh Kumar
National Metallurgical Laboratory
Jamshedpur - 831 007
Resources for metals
Natural Resources
Gold is found in native state
Agg regates of m inerals (or ores)
mostly oxides and sulphides, example Al, Fe (oxide
ores), Cu, Pb, Zn, Ni etc (sulphide ores).
(a)
land-based (comm on)
(b) shallow sea (beach sand)
(c)
deep-sea (Ferromanganese nod ules)
Seawater and natural brines, Ex. Mg and Li
Man Made Resources
Metallic form - Consumer goods and process scrap
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/
Batteries
Natural ore
Recyclables
Natural vs. Man Made Resources
Elcolron ir scrap
2
Separation Ore to Metal
Iron ore
Hem atite (Fe2 03
)
Si0
2
, A12 0
, P, S b earing minerals
Aluminium ore (bauxite)
What to
separate?
AliO3 .x H
2
0 (x=1,3)
[F
e
2
0
, FeOOH, Si02
, TiO,, FeTiO
3 (gangue).
Copper Or
Chalcopy rite (Cti
uFeS2 )
\Sulphides of m etal such Fe, Pb, Zn and silicates
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it -
ess
Wet treatment*
Sizing (0.06-2.0)
Gravity concentration (0.06-2M)
Magnetic separation (0.015-1.8)
Flotation (0.007-0.3)
Dry treatment*
Sizing (0.06-2.0)
Gravity c oncentration (0.15-0.18)
M agnetic separation (0.1-2)
Electrical separation (0. I -1.2)
* values are only indicative
4
Mineral Processing -
Limits
Focus of lecture
Exploration
Mining
1
Ore
Mineral Processing
Concentrate
Metal Production
4 ,
etal
Extraction
Metal Refinement
Base ma terial
Metal Processing
i
onsumer m aterial
Commercial Good
Production
Focus is generic
Separation
0)
0
0
C C
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* The word pyro- is
derived from a greek
word w hich means fire.
* A pyrometallurgical
process may be defined
as one involving the
application of heat
energy
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Metallurgical Separation Processes
Most often involves chemical reactions
Pyro-metallurgical
Hydro-metallurgical
Electro-metallurgical
Classification based on metals
Ferrous
dealing with iron and steel
Non Ferrous
includes all other metals
Base metals (Pb,
Zn, Cu, and Ni),
Light metals
(Mg, Al, Sn, and Ti),
Precious metals
(Au and Ag
and the Pt group metals), Refractory metals (W,
Nb, Ta) etc.
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Smelting
Reduction
Matte
Converting
Fire refining
metal oxide to metal, chemical reduction,
slag/metal separation
Matte and slag, oxidation, matte/slag
separation
metal sulphide to metal, selective conversion
of matte into metal and slag
selective oxidation of impurities, slag-metal,
gas-metal separation
Zone refining
Distillation
purification, solubility
purification/separation, difference in boiling
point
8
I
Pyrometallurgy
Operation, purpose and basis of separation
Calcination emoval of H2 0/CO2 decomposition
Roasting onversion of form, chemical reaction
Hematite (Fe
2
0
3 )
Si0
2
, A1
2
0
3
, P, S bearing minerals
Oxygen removal
Fe2
03(s)+3 C(s) = Fe(1)+3 CO (g)
Fe
2
03(s)+3 CO(s) = Fe(1)+3 CO
2
(g)
Carbon forms stronger bond with
oxygen at the reaction temperature
Key Words
Stability of
Oxides
Stability is
temperature
dependent
9
Iron ore
Pyrometallurgy
Iron Making
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AGc: vs. T
AG = AHo T .AS
0
Ellingham
Diagram
(for oxides)
oc
Similar
5
diagrams for
o
sulphides
o chlorides
o
carbides
o
nitrides
04
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et
,
40.40
mlo
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er
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AO
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. . . . .
,
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er
too
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p a
y
p.
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r
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me
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allor
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m
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m-
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e
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0 19 tO IC
1
10.0
D o .
10
10.
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00
Reduction in BF
Ore, Cole hamster*
GiS 010 eloaneap
00%
Fe
F
eO
Fe4
Smell
balF
tame
bet
Steel
sheF
g
150'C
Mact ',nog
FehaCiOry
t.
G a s
B...le -
Bosh P P'
e
Tuyer0S-
0 1 0
trth S.109
1MP
1 1 0 . . v
9000c
Temperature
lAcislare demo Mt
ndaterrec
CaC00
--,-CaO
G O :
nd:germ