CHAPTER 7 Extraction of metals from sulphide ores.pdf

DEFENCE ENGINEERING COLLEGE
Metallurgical And Materials Engineering
Present By:
Weldebrhan Hadush (Maj.)
Nov., 2019

Content
Introduction
Winning of metals from sulphide ores
Extraction of Copper
a. Hydro - metallurgy of copper
b. Pyro - metallurgical extraction of copper
c. Newer process for copper extraction
d. Energy concepts in copper smelting
Extraction of metals from oxide members
d. Energy concepts in copper smelting
Extraction of Lead
i. Treatments of ores of lead and its production
ii. Modern developments in lead smelting
Extraction of Zinc
a. Pyro - metallurgical extraction
b. Hydro – metallurgical extraction
c. Imperial smelting process
d. Production of other metals by ISP
e. Zinc from lead slags by slag fuming
Extraction of Nickel
Pyro – metallurgical process

INTRODUCTION
 Several common non ferrous metals such as copper, lead, zinc and nickel are
found in nature as sulphide minerals. The minerals are beneficiated through mineral
dressing methods such as flotation, to obtain concentrates rich in one of the metal
sulphides. Such sulphide concentrate are subjected to a pretreatment process of
roasting in the range of 500 – 800 °C.
 During roasting, sulphur is oxidized to SO and sulphides of metal are partly or
Extraction of metals from sulphide ores
 During roasting, sulphur is oxidized to SO2 and sulphides of metal are partly or
completely oxidized to oxides.
 The extent of sulphur removal desired depends on the metal. In the case of lead,
the sulphur is completely oxidized to PbO.
 For copper and nickel, only the iron sulphide impurity is oxidized partly and the
other sulphides are retained as such.
 The hot exhaust gases from roaster, containing SO2 and SO3 are utilized in the
manufacture of sulphuric acid.
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Metallurgy of Copper (Cu)
Atomic number of Copper is 29 and its atomic weight is 63.55 and denoted by
symbol Cu. Density of copper is 8.93 g/cm3.
Copper is found as native (pure) form or combined with other elements that is good
conductor of heat and electricity , resistant to corrosion, can be alloyed to make bronze
and brass, reddish-orange bright metallic luster, ductile and malleable .
and brass, reddish-orange bright metallic luster, ductile and malleable .
Occurrence
Copper is most commonly present in the earth’s crust as coppereironesulfide and copper
sulfide minerals, such as pyrite/chalcopyrite (CuFeS2) and chalcocite (Cu2S). Copper
also occurs to a lesser extent in oxidized minerals (carbonates, oxides, hydroxy-silicates,
sulfates) such as Malachite green [CuCO3.Cu (OH)2]. Azurite blue [2CuCO3.Cu (OH)2].
Bornite (3Cu2S.Fe2S3) or peacock ore. Melaconite (CuO) etc.
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EXTRACTION OF COPPER
HYDROMETALLURGICAL EXTRACTION OF COPPER
About 80% of copper-from-ore is obtained by flotation, smelting, and refining. The
other 20% is obtained hydro-metallurgically.
Hydrometallurgical extraction entails:
i. Sulfuric acid leaching of Cu from broken or crushed ore to produce impure aqueous solution
(leaching)
ii. Transfer of Cu from this impure solution to pure, high-Cu electrolyte via solvent extraction
iii. Electroplating pure cathode copper from this pure electrolyte.
The ores most commonly treated this way are:
a. Oxide copper minerals, including carbonates, hydroxy-silicates, sulfates, and
b. Chalcocite (Cu2S).
The leaching is mostly done by dripping dilute sulfuric acid on the crushed ore
Extract and purify Cu from oxide ores, usually in three steps: Leaching, Solvent extraction and
Electrowinning 3
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Cont’d
Oxidized minerals are rapidly dissolved by sulfuric acid by reactions like:
CuO (s) + H2SO4 (l) → Cu2+ (aq) + SO4
2- (aq) + H2O (l) @ 30 °C
ore acid prenant leach solution
Sulfide minerals, on the other hand, require oxidation, schematically:
CuS (s) + 2.5O2 (g) + H2SO4 (l) → 2Cu2+ (aq) + SO4
2- (aq) + H2O (l) @ 30 °C
ore in air acid prenant leach solution
Solvent Extraction
These solutions are too dilute in Cu and too impure for direct electroplating of pure
copper metal. Their Cu must be transferred to pure, high-Cu electrolyte.
The solvent extraction process is represented by the reaction:
Cu2+ (aq) + SO4
2- (aq) + 2RH → R2Cu + H+ (aq) + SO4
2- (aq) @ 30 °C
In prenant leach solution in organic solvent in organic solvent
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Cont’d
Electrowinning
The Cu in the above electrolytes is universally recovered by electroplating pure metallic
cathode copper. This electrowinning is similar to electrorefining except that the anode is
inert (usually lead)
The cathode reaction is:
Cu2+ (aq) + 2e- → Cu(s) @ 60 °C
sulfate electrolyte electrons from external power pure metal deposite on cathode
The anode reaction is:
H2O (l) → 0.5O2(g) + H+ (aq) + 2e- @ 60 °C
in electrolyte involve in anode in electrolyte electrons from external power
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Electrowinning of copper
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PYRO-METALLURGICAL EXTRACTION OF COPPER
About 80% of copper-from-ore is obtained by flotation, smelting, and refining. Ores
containing 4% or more copper are treated by smelting process. Very poor ores are treated
by hydro-metallurgical process. Large amount of copper are obtained from copper
pyrite or chalcopyrite (CuFeS2) by smelting.
CONCENTRATION
CONCENTRATION
 The finely crushed ore is concentrated by Froth-Floatation process.
 The finely crushed ore is suspended in water containing a little amount of pine oil. A
blast of air is passed through the suspension.
 The particles get wetted by the oil and float as a froth which is skimmed. The gangue
(unwanted materials) sinks to the bottom then removed.
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Froth floatation process DUC 2019/20

ROASTING
The concentrated ore is then roasted in a furnace between 500 °C and 700 °C in the
presence of a current of air. Sulphur is oxidized to SO2 and impurities of As and Sb are
removed as volatile oxides. The following reaction takes place.
2CuFeS2 + O2 → Cu2S+ 2FeS +SO2
S + O2 → SO2
4As + 3O2 → As2O3
4Sb + 3O2 → 2Sb2O3
4Sb + 3O2 → 2Sb2O3
Cuprous sulphide and ferrous sulphide are further oxidized into their oxides.
2Cu2S + 3O2 → 2Cu2O + 2SO2
2FeS + 3O2 → 2FeO + 2SO2
SMELTING
The roasted ore is mixed with coke and silica (sand) SiO2 and is introduced in to a blast
furnace with 1200 °C. The hot air is blasted and FeO is converted in to ferrous silicate
(FeSiO3).
FeO + SiO2 → FeSiO3
Cu2O + FeS → Cu2S + FeO
FeSiO3 (slag) floats over the molten matte of copper. (If no enough SiO2, CaO added to lower M.P and
increase fluidity of slag good for phase separation .
9

BESSEMERIZATION
Copper metal is extracted from molten matte through bessemerization.
The matte is introduced in to Bessemer converter which uphold by tuyeres. The air is
blown through the molten matte. Blast of air converts Cu2S partly into Cu2O which
reacts with remaining Cu2S to give molten copper.
2Cu2S + 3O2 → 2Cu2O + 2SO2
2Cu O + Cu S → 6Cu + SO
2Cu2O + Cu2S → 6Cu + SO2
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Impurities in blister copper and their effects
Blister copper is 99% pure. It contains impurities mainly iron but little amount of As,
Zn, Pb, Ag and Au may also be present. These impurities adversely affect the
electrical as well as mechanical properties of copper. Therefore, they must be
removed.
REFINING OF COPPER
REFINING OF COPPER
Blister copper is refined by electrolysis. Blocks of blister copper are casted to use as
anodes and thin sheets of pure copper act as cathodes. The cathode plates are coated
with graphite in order to remove depositing copper. The electrolyte is copper sulphate
(CuSO4) mixed with a little amount of H2SO4to increase the electrical conductivity.
Optimum potential difference is 1.3 volt for this electrolytic process.
During electrolysis, pure copper is deposited on the cathode plates and impurities
which are soluble and fall to the bottom of the cell as anode mud or sludge. 11

Electrochemical changes during electrolysis
Cu → Cu+2 + 2e- (at the anode)
Cu+2+2e- → Cu (at the cathode)
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Application of copper
 Copper is used for electric wires due to the nature of very good conductor of
electricity, used for electrical components ductile,
 Copper is used in water pipes because copper is non-poisonous, strong, malleable and
ductile, corrosion resistant, used in
ductile, corrosion resistant, used in
 Copper used for cooking utensils because it is excellent conductor of heat,
nonpoisonous, strong, malleable, corrosion resistant
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Metallurgy of Lead (Pb)
Atomic number of Lead is 82 and its atomic weight is 207.2 and denoted by
symbol Pb. Density of lead is 11.34 g/cm3. It is a soft, malleable, ductile, bluish-white,
dense metallic element.
Health effects of lead:
 Damage most organs: kidney , hepatic
 Death can occur at extremely high levels,
 Cognitive development in children
Occurrence
Lead rarely found pure in nature an mainly occurs as galena (PbS), and Other common
varieties include cerussite (PbCO3) and angelsite (PbSO4).
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EXTRACTION OF LEAD
Crushing and Ore Dressing
The processes of size reduction involve the breakage or fracture of particles where as
For small ore, crushing and grinding doesn’t need because losing of energy, then fine
grinding can be allowed for small ore in size.
EXTRACTION OF LEAD
Ore dressing is the process of separating commercially valuable minerals from
their ores. Flotation Process is generally used in ore dressing process. A substance is
added that wets the zinc ore, allowing it to sink to the bottom, but does not wet the
galena, allowing it to be caught up in a foam that floats on the surface of the water.
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Cont’d
Lead smelting
The standard method for lead production is roast-reduction. Due to the sulfur content, carbon
from the coke will not be able to reduce lead. Therefore, the mineral must be roasted to
oxidize sulfur and create a metal oxide out of galena.
2PbS +3O2 → 2PbO + 2SO2 * gelena is roasted to remove sulfer
EXTRACTION OF LEAD
2PbO + C → 2Pb + 2CO2
An alternative method is the roast-reaction that is raw ore is then added to the products and is
heated further.
2PbO + PbS → 3Pb + SO2
The standard Gibbs free energy change for this reaction is nagative above 900 °C, but is less
so that the corresponding copper reaction, Further more PbS, PbO and Pb are rather volatile,
Which sets as upper limit to the temperature which can be used with out excessive vapor losses.
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Cont’d
The result is not just lead sulphide, but also the sulphides of copper, iron, zinc,
antimony and arsenic. The enriched ore is then roasted in ovens to drive off as much
of the sulphur as possible. The roasted ore must be ground and sintered to put it in the
form of porous chunks that allow gases to pass through freely, and will not collapse
into a thick, impervious layer in the blast furnace.
EXTRACTION OF LEAD
into a thick, impervious layer in the blast furnace.
Lead ores are such that these two operations are best combined into one simultaneous
roasting-sintering process that produces a sinter ready for the lead blast furnace.
Sintering : The lead(II) oxide is heated and made into lumps, a process known as
sintering. The lumps (the sinter) are crushed and sorted to a suitable size for
subsequent treatment in a blast furnace, similar in construction to those for making iron
but smaller.
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EXTRACTION OF LEAD
Fig: Sintering Machine
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Cont’d
The second stage of smelting can take place in an ore hearth, or a larger blast furnace.
The sintered ore is charged, with coke, limestone flux, and other additives
depending on the impurities present.
The products that accumulate at the bottom are lead, matte (containing iron and
copper), speiss (containing iron and arsenic), and slag (containing the silicates, zinc,
EXTRACTION OF LEAD
copper), speiss (containing iron and arsenic), and slag (containing the silicates, zinc,
iron and calcium). Cold air is blown in at the bottom, and flue dust and gases come
out the top.
Zinc, incidentally, does not dissolve in molten lead, and can be added to extract
impurities by differential solubility.
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Cont’d
When the lead has been sufficiently refined, it is cooled and cast into blocks which may
weigh as much as a ton. This is the finished product. Lead alloys may also be produced at
the smelter plant.
EXTRACTION OF LEAD
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Application of lead
 Widely used in batteries,
 Cable and iron rod sheaths for corrosives,
 Soldering,
 Bullets
EXTRACTION OF LEAD
EXTRACTION OF LEAD
 Bullets
 Used with other compounds in manufacturing of paints and pigments
 Shipbuilding, light industry,
 Lead oxide,
 Radiation protection/ radiation shielding and other industries.
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Metallurgy of Zinc (Zn)
Atomic number of Zinc is 30 and its atomic weight is 66.39 and denoted by
symbol Zn. Density of zinc is 7.13 g/cm3 . It is has white silver color with Tm: 4200c.
Occurrence
EXTRACTION OF ZINC
Zinc occurs in nature mainly as Sphalerite (ZnS), Zincite (ZnO) , Calamine
(Zn2 (OH)2SiO3 ), Smithsone(ZnCO3), and Franklinite( ZnO(Fe,Mn)2O4)
Typical zinc ores generally contain about 5-15 % metals.
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EXTRACTION OF ZINC
Zinc can be extract in both pyro-metallurgy and hydro-metallurgy these follows electrochemical
treatment.
Pyrometallurgical treatment
In iron and copper during reduction process vapor pressure of metal is negligible whereas, in zinc
metal the vapor pressure is appreciable in the pyro-matllurgy production, the metal is obtained as a
EXTRACTION OF ZINC
metal the vapor pressure is appreciable in the pyro-matllurgy production, the metal is obtained as a
gas rather than as a liquid.
The vapor pressure of pure metal is given by:
RT ln PMetal =-ΔGVapor =-ΔHVapor + TΔSVapor
Particlarly there are no phase transformation in the condensed phase of Zn then ΔHVapor and
ΔSVapor are independent with temperature and vapor pressure varies with the temperature according
the relation : log Pmetal =A/T +B
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Crushing and ore dressing
 The zinc blende (sphalerite: zinc sulphide) is first crushed to powder, wet grinding
and then treated by froth flotation.
 Froth floatation has been used with aid of CuSO4 to collect Zinc ore.
Roasting
Roasting was done to convert sulphide Zinc ores to its oxide, by O2 flow & removal of
EXTRACTION OF ZINC
SO2 at 700-800 °C. This reaction is exothermic, which increases the temperature up to
1000 °C.
ZnS + 3/2O2 → ZnO + SO2 (Pyro-Metallurgy)
ZnS + 2O2 → ZnSO4 (Hydro-Metallurgy)
Soluble in water & dilute acids
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EXTRACTION OF ZINC
Zinc sulphide
ores
Crushing and
grinding
Flotation
Acid
Flotation
Concentrated
sulfide ore
Roasting
ZnO (<1% S)
Smelting
SO2
Acid
plant
Air blow
700-600 °C
Fig: Production Zinc 27
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Smelting
The zinc oxide is then reduced to the metal using either a thermal or an electrolytic
process.
ZnO is treated in blast furnace, reduction done with carbon & limestone at 500 °C as
a preheating, then O2 supplied from top furnace to produce carbon monoxide (CO) at
1300 °C.
EXTRACTION OF ZINC
Reduction smelting reaction as follows:
C+ ½O2 → CO
C + O2 → CO2
CO2 +C → 2CO
ZnO +CO → Zn (g) + CO2 PCO2/PCO =K1/PZn
Zn in Vapor
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Cont’d
Zn vapor is drawn at 1000 °C then cooled rapidly to 550 °C in molten lead bath to
produce condensate zinc (contain small amount of Cd) which is denser than other
component (Zn sink to the bottom), then tapped of, while slug (lighter) tapped from above.
Two layers will form as follows:
1. Zinc contains 1wt% Pb → drawn to more refining by distillation to produce pure Zn.
EXTRACTION OF ZINC
1. Zinc contains 1wt% Pb → drawn to more refining by distillation to produce pure Zn.
2. Pb contains 2.25wt% Zn → return to condenser.
Then Redistillation at T =765 0c to vaporize Cd off.
Zinc produced by this process is about 98.5% pure and can be further refined if required.
Around 15% of the world's zinc is produced this way.
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EXTRACTION OF ZINC
Fig: Blast furnace used in zinc process
30

Electrolytic refining (Hydrometallurgy)
Zinc refining included; leaching, purification, electrolysis, and melting & casting.
The crude zinc oxide is dissolved in dilute sulphuric acid (H2SO4) to produce a solution
of Zinc sulphate after filtration and purification the solution.
ZnO + H2SO4 → ZnSO4 + H2O
EXTRACTION OF ZINC
ZnO + H2SO4 → ZnSO4 + H2O
ZnSO4 electrolysed using a (Pb -1%Ag) anode and an aluminum cathode.
O2 is released at anode, while Zinc is deposited on the cathode. H2SO4 is regenerated at
the anode and can be used again.
31
Fig; Electrolytic refining of zinc

Application of Zinc
 Protective coating for steel (Galvanizing)
 Used to coat steel to protect it from corrosion at room temperature and for
decorative finish.
 Fabrication of alloys such as Cu-Zn brasses
EXTRACTION OF ZINC
EXTRACTION OF ZINC
 Rolled zinc plates are used in dry cell batteries
 formability of the metal makes it ideal for forging and extrusion
 Used with other compounds in manufacturing of paints and pigments
DUC 2019/20 33

Metallurgy of Nickel (Ni)
Atomic number of nickel is 28 and its atomic weight is 58.69 and denoted by
symbol Ni. Density of Nickel is 7.13 g/cm3 . A silvery metal that resists corrosion
even
at high temperatures.
EXTRACTION OF NICKEL
Occurrence
Nickel occurs in nature mainly as Nickel-iron sulfides (FeNi4S4
+3 ) and
laterite (Hydrous nickel silicate ). Both of them typically contain 1-3% of nickel.
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Extraction of nickel
Crushing and ore dressing
 The nickel sulfide is first crushed to powder, wet grinding and then treated by
froth flotation.
 Froth floatation has been used to separat of the nickel sulfide mineral from the
gangue. This operation is conducted in a flotation chamber where the ground ore
gangue. This operation is conducted in a flotation chamber where the ground ore
mixed with water is treated by air bubbles which move upward and cause flotation
of the mineral particles to the top of the chamber.
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Smelting
At this stage the concentrate is smelted in the Bessemer converter to produce a
mixture of nickel, copper and other metals called matte. The gangue is absorbed by
the slag and removed.
Extraction of nickel from the laterite ores
Extraction of nickel from the laterite ores is carried out by either pyrometallurgical or
hydrometallurgical process:
Hydrometallurgical process involves ammoniacal or sulfuric acid leaching followed
by nickel precipitatation.
pyrometallurgical process the ore is dried and calcined in a rotary kiln and then
smelted in an electric furnace with addition of carbon. 37

Cont’d
Mond process
The Mond process, sometimes known as the carbonyl process, is a technique created
by Ludwig Mond in 1890, to extract and purify nickel. This process converts nickel
oxides into pure nickel.
This process involves the fact that carbon monoxide combines with nickel readily and
This process involves the fact that carbon monoxide combines with nickel readily and
reversibly to give nickel carbonyl. No other element forms a carbonyl compound under
the mild conditions used in the process.
Mond process:
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Mond process has three steps:
1. Nickel oxide reacts with Syngas at 200°C to give nickel, together with impurities
including iron and cobalt.
NiO(s) + H2(g) → Ni(s) + H2O(g)
2. The impure nickel reacts with carbon monoxide at 50–60°C to form the gas nickel
carbonyl, leaving the impurities as solids.
carbonyl, leaving the impurities as solids.
Ni(s) + 4 CO(g) → Ni(CO)4(g)
3. The mixture of nickel carbonyl and Syngas is heated to 220–250°C, resulting in
decomposition back to nickel and carbon monoxide:
Ni(CO)4(g) → Ni(s) + 4 CO(g)
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Application of Nickel
 Used for alloying elements (stainless steel ),
 Coatings,
 In kitchen wares,
 Medical equipment,
 Transport, buildings,
 Transport, buildings,
 Power generation and jewellery.
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EXTRACTION OF Sulfides
EXTRACTION OF Sulfides
Reaction Gibb’s free energy
41

“The future can not be predicted,
but it can be made !”

CHAPTER 7 Extraction of metals from sulphide ores.pdf

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CHAPTER 7 Extraction of metals from sulphide ores.pdf