1. 1
Lecture 16-17
Occurrence, extraction &
uses of some important
metals

2. Uses of Metals
A. Properties of metals as related to their uses
1. Density - generally have high densities.
2. Melting point - generally high melting points
3. Thermal (heat) conductivity - good conductors of heat
4. Electrical conductivity - good conductors of electricity
5. Strength - high tensile strength, i.e. metals can support a heavy
load without breaking.
6. Malleability – malleable (can be hammered and bent into
different shapes without breaking)
7. Ductility – ductile (can be drawn into wires without breaking)
8. Lustre - lustrous and shiny 3

3. Uses of Metals
B. Choosing a metal for a particular use
☺ The decision to choose a certain metal for a particular use depends on
its properties as well as its price.
☺ Here are some questions to be answered before choosing a metal.
1. Does the metal have to be strong?
E.g. in building ships
2. Does the metal need to be light?
E.g. metals used for building aircraft need to be both light & strong
3. Does it have to be attractive in appearance?
E.g. in jewellery
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4. Uses of Metals
B. Choosing a metal for a particular use
4. Does it have to be cheap?
Nails are made of iron although there are metals which are
equally strong or even stronger than iron, but they are much
expensive.
5. Does it require to be corrosion resistant?
E.g. cans for soft drink
6. Sometimes, we have to choose a certain metal even if it has some
undesirable properties.
E.g. iron is used for building ships because it is strong & cheap
even though it rusts.
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5. Uses of Metals
C. Uses of some metals
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Metal Uses Reasons for choice
Iron Making bridges
and ships
Hard, strong, malleable and ductile
Price: cheap
Magnet Magnetic
Copper Electrical wires Very good conductor of electricity, very ductile,
corrosion resistant
Price: quite expensive
Water pipes Very malleable and ductile, corrosion resistant,
non-poisonous, strong,
Cooking utensils Very good conductor of heat, very malleable,
non-poisonous, strong, corrosion resistant,

6. Uses of Metals
C. Uses of some metals
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Metal Uses Reasons for choice
Aluminium Overhead
electricity cables
Very good conductor of electricity, low density,
ductile,
Price: quite expensive
(Compare with copper: Al is lighter & cheaper
than copper)
Aircraft body Light but strong, corrosion resistant
Cooking foils Very malleable, very good conductor of heat,
non-poisonous, corrosion resistant
Soft drink cans Non-poisonous, low density (hence convenient
to carry), very malleable, corrosion resistant,
Window frames Corrosion resist, strong

7. Uses of Metals
C. Uses of some metals
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Metal Uses Reasons for choice
Zinc Galvanizing iron More reactive than iron
Protective paints &
electroplating
More reactive than iron
Lead Car batteries
Petrol additive

8. Occurrence
☺ About 25% of the earth's crust consists of metals.
 Al (8%) & iron (6%) are the two most abundant metals.
☺ In nature, only a few metals exist as free, uncombined element.
Most other metals exist as compounds in nature.
1) Elemental Form
 e.g. Ag, Au, Pt – noble metals.
2) Aluminosilicates and Silicates (Hard to extract metals).
 Metal + Al, Si, O
• e.g. Beryl = Be
3) Nonsilicate Minerals
 Oxides – Al2O3, TiO2, Fe2O3
 Sulphides – PbS, ZnS,
 Carbonates – CaCO3
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9. Occurrence
☺ The rocks or minerals which contain a high proportion of useful
metals or their compounds from which the constituent metals can be
profitably extracted are called metal ores.
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Ore Main constituent Metal extracted
Haematite Fe2O3 Iron
Bauxite Al2O3 Aluminium
Copper pyrite copper(II) iron(II) sulphide
(CuFeS2)
Copper
Galena lead(II) sulphide (PbS) Lead
Zinc blende zinc sulphide (ZnS) Zinc
Argentite silver sulphide (AgS) Silver
Cinnabar mercury(II) sulphide Mercury

10. Metallurgy
☺ The entire scientific & technological process used for isolation of the
metal from its ores is known as metallurgy
☺ The extraction and isolation of metals from ores involve the following
major steps:
1. Mining
2. Concentration of the ore,
• Floatation.
• Magnetic separation
3. Isolation of the metal from its concentrated ore
• Chemically or electrochemically,
– Hydrometallurgy – leaching.
– Pyrometallurgy – roasting, smelting.
– Electrometallurgy.
4. Purification of the metal.
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11. Concentration of an Ore
by Flotation
In the flotation method, the ore is ground into a powder
and mixed with water and additives.
Particles of ore
are attached to
air bubbles and
rise to the top.
Undesired waste
rock, called gangue,
falls to the bottom.

12. The Metallurgy of Iron
☺ Iron is present in the earth’s crust in many types of minerals.
 Iron pyrite (FeS) : widely distributed but not suitable for
production of metallic iron and steel because it is almost
impossible to remove the last traces of sulfur. The presence of
sulfur makes the resulting steel too brittle to be useful.
 Siderite (FeCO) is a valuable iron mineral that can be converted
to iron oxide by heating.
 The iron oxide minerals are hematite(Fe2O3 ), the more
abundant, and magnetite (Fe3O4 )
 Taconite ores contain iron oxides mixed with silicates and are
more difficult to process than the others.
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13. Concentration of the ore
☺ To concentrate the iron in
iron ores, advantage is taken
of the natural magnetism of
Fe3O4 (hence its name,
magnetite).
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☺ The Fe3O4 particles can be separated from the gangue by magnets.
The ores that are not magnetic are often converted to Fe3O4;
 hematite is partially reduced to magnetite, while siderite is first
converted to FeO thermally, then oxidized to Fe2O3, and then
reduced to Fe3O4 :

14. Extraction of iron
☺ The most commonly used reduction process for iron takes place in
the blast furnace.
☺ Raw materials: concentrated iron ore, coke, & limestone (which
serves as a flux to trap impurities).
☺ The furnace, which is approximately 25 feet in diameter, is charged
from the top with a mixture of iron ore, coke, and limestone.
☺ A very strong blast (,350 mi/h) of hot air is injected at the bottom,
where the oxygen reacts with the carbon in the coke to form CO, the
reducing agent for the iron.
☺ The temperature of the charge increases as it travels down the
furnace, with reduction of the iron to iron metal occurring in steps:
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15. Essential chemistry
2C(s) + O2(g)  2CO(g)
3Fe2O3 (s) + CO(g)  2Fe3O4 (s) + CO2(g)
Fe3O4 (s) + CO (g)  3FeO(s) + CO2(g)
FeO (s) + CO(g)  Fe(s) + CO2(g)
☺ Iron can reduce carbon dioxide,
Fe + CO2  FeO + CO
☺ so complete reduction of the iron occurs only if the carbon dioxide is
destroyed by adding excess coke:
CO2 + C  2CO
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16. 18

17. Essential chemistry
☺ Why is CaCO3 added?
☺ CaCO3 in the charge loses CO2, in the hot furnace and combines with
silica & other impurities to form slag, which is mostly molten calcium
silicate, CaSiO3,
CaCO3  CaO + CO2
CaO + SiO2 CaSiO3 (slag)
☺ Limestone (CaCO3 removes SiO2) (and other) impurities
☺ slag floats on Fe(l); protects it from oxidation by O2
☺ Slag: cement, building materials
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18. ☺ The iron collected from the blast furnace, called pig iron or cast
iron, is quite impure.
☺ It contains ,90% Fe, ,5% C, ,2% Mn, ,1% Si, ,0.3% P, and ,0.04% S
(from impurities in the coke).
☺ The production of 1 ton of pig iron requires approximately 1.7 tons of
iron ore, 0.5 ton of coke, 0.25 ton of limestone, and 2 tons of air
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19. Production of Steel
☺ Steel is an alloy and can be classified as carbon steel, which
contains up to about 1.5% carbon, or alloy steel, which contains
carbon plus other metals such as Cr, Co, Mn, and Mo.
☺ The wide range of mechanical properties associated with steel is
determined by its chemical composition & by the heat treatment of
the final product.
☺ The production of iron from its ore is fundamentally a reduction
process, but the conversion of iron to steel is basically an oxidation
process in which unwanted impurities are eliminated.
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20. ☺ Impurities in the iron from the Blast Furnace include carbon, sulphur,
phosphorus and silicon. These have to be removed.
Removal of sulphur
☺ Mg powder is blown through the molten iron and the sulphur reacts
with it to form MgS. This forms a slag on top of the iron and can be
removed.
Mg + S  MgS
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21. Removal of carbon etc
☺ The still impure molten iron is mixed with scrap iron (from recycling)
and oxygen is blown on to the mixture. The oxygen reacts with the
remaining impurities to form various oxides.
 The C forms CO. Since this is a gas it removes itself from the
iron! This CO can be cleaned and used as a fuel gas.
 Elements like P and Si react with the O2 to form acidic oxides.
These are removed using quicklime (calcium oxide) which is
added to the furnace during the oxygen blow.
• They react to form compounds such as calcium silicate or
calcium phosphate which form a slag on top of the iron.
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22. Types of iron and steel
☺ Cast iron: impure iron from blast furnace
☺ Wrought iron: when all the C is removed from iron (high purity iron),
 quite soft & has little structural strength.
 It was once used to make decorative gates and railings, but these
days mild steel is normally used instead.
☺ Mild steel: iron containing up to about 0.25% of C.
 The presence of the C makes the steel stronger & harder than pure
Fe. The higher the % of C, the harder the steel becomes.
 Uses: nails, wire, car bodies, ship building, girders and bridges
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23. Types of iron and steel
☺ High carbon steel: High C steel contains up to about 1.5% of C.
 The presence of the extra carbon makes it very hard, but it also
makes it more brittle.
 Uses: for cutting tools & masonry nails (nails designed to be driven
into concrete blocks or brickwork without bending). You have to be
careful with high carbon steel because it tends to fracture rather
than bend if you mistreat it.
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24. Special steels
☺ These are iron alloyed with other metals. For example:
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iron mixed
with
special
properties
uses include
stainless
steel
Cr and Ni
resists
corrosion
cutlery, cooking utensils, kitchen
sinks, industrial equipment for food
and drink processing
titanium
steel
titanium
withstands
high temp
gas turbines, spacecraft
mangane
se steel
manganese very hard
rock-breaking machinery, some
railway track (e.g. points), military
helmets

25. Metallurgy of aluminum
Properties of Al
☺ the lightest of the common metals (except with Mg) with density
= 2.7 g/cc.
☺ soft & malleable at ordinary temperature (becomes brittle when
heated to above 150oC).
☺ silvery white in color
☺ an amphoteric metal
☺ good conductor of heat & electricity
☺ an active metal but it does not corrode
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26. Occurrence of Al
☺ Aluminum is the most abundant and the 3rd plentiful element
on the earth’s crust. The elemental form does not occur in
nature, its principal ore is bauxite. The major sources of
aluminum are:
 bauxite, Al2O3
.H2O
 cryolite, Na3AlF6
 corundum, Al2O3
 orthoclase, KalSi3O8
 beryl, Be3Al2Si6O18

27. Uses of Al
☺ its chief use is in automobile and aircraft
construction.
☺ kitchen utensils, aluminum foil and beverage cans
☺ high voltage transmission line
☺ used as solid propellant for rockets
☺ in the welding of iron and steel.

28. Hydrometallurgy of Al
☺ Ore: Bauxite – Al2O3.xH2O, impurities: SiO2, Fe2O3
☺ Bayer Process
☺ Bayer process: bauxite (~ 50 % Al) is concentrated to produce Al
☺ Dissolve bauxite in strong base (NaOH) at high T, P
☺ Filter out solids
 Fe2O3, SiO2 do not dissolve
☺ Lower pH, Al(OH)3 precipitates
 Take advantage of amphoteric nature of Al
☺ The aluminate hydroxide is heated to produce the aluminum oxide.

29. Electrometallurgy of Al
☺ Electrometallurgy: process of obtaining metals through electrolysis.
☺ The aluminum oxide from bauxite is melted with cryolite to form 5%
solution. The oxide dissociates as follows:
Al2O3  2Al+3 + 3O-2
☺ The mixture is electrolyzed to produce aluminum and oxygen gas:
Anode : 3 [2O-2 - 4e-  O2]
Cathode : 4 [Al+3 + 3e-  Al]
☺ The overall reaction is:
2Al2O3  4Al + 3O2
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30. Electrometallurgy of Al
☺ O2 gas reacts with the C anodes to form CO & CO2, which escapes
as a gas.
☺ The liquid Al metal (m.p. 660.2oC) sinks to the bottom of the vessel
from which it can be drawn from time to time.
 This way for each kg of aluminium produced, about 0.5 kg of
carbon anode is burnt away
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31. Economic considerations
☺ The high cost of the process because of the huge amounts of
electricity it uses.
☺ This is so high because to produce 1 mole of Al which only
weighs 27 g you need 3 moles of electrons. You are having to
add a lot of electrons (because of the high charge on the ion)
to produce a small mass of aluminium (because of its low
relative atomic mass).
☺ Energy & material costs in constantly replacing the anodes.
☺ Energy & material costs in producing the cryolite, some of
which gets lost during the electrolysis.
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32. Environmental problems in mining &
transporting the bauxite
☺ Loss of landscape due to mining, processing and transporting the
bauxite.
☺ Noise and air pollution (greenhouse effect, acid rain) involved in
these operations.
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33. Extracting aluminium from the bauxite
☺ Loss of landscape due to the size of the chemical plant needed, and
in the production and transport of the electricity.
☺ Noise.
☺ Atmospheric pollution from the various stages of extraction.
 E.g.: CO2 from the burning of the anodes (greenhouse effect);
CO(poisonous); fluorine (and fluorine compounds) lost from the
cryolite during the electrolysis process (poisonous).
☺ Pollution caused by power generation (varying depending on how
the electricity is generated.)
☺ Disposal of red mud into unsightly lagoons.
☺ Transport of the finished aluminium.
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34. Recycling
☺ Saving of raw materials and particularly electrical energy by not
having to extract the aluminium from the bauxite. Recycling
aluminium uses only about 5% of the energy used to extract it from
bauxite.
☺ Avoiding the environmental problems in the extraction of aluminium
from the bauxite.
☺ Not having to find space to dump the unwanted aluminium if it
wasn't recycled.
☺ (Offsetting these to a minor extent) Energy and pollution costs in
collecting and transporting the recycled aluminium.
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35. ☺ http://www.chemguide.co.uk/inorganic/extraction/aluminium.html#to
p
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