9.3 Metals, Ores and Extraction
You should remember studying the reactivity series of metals in Year 8.
The most reactive metals are placed at the top. These metals react vigorously with
water, acid and oxygen. Metals in the middle react moderately with acids and
oxygen, whilst those at the bottom don't even react with acids and react very
slowly, if indeed at all, with oxygen in the air.
The more reactive a metal is the more likely it is to form a compound. The more
reactive a metal, the more stable its compound.
Therefore, the more reactive a metal, the more difficult it is to extract.
This is because the more reactive a metal, the more strongly it combines with
another non-metallic element like oxygen or sulphur and the more energy is needed
to separate the metal.
Although most metals occur as compounds, some metals are so unreactive
that they do not readily combine with oxygen in the air or any other
element present in the Earth's crust, and so can be found as the metal
itself (sometimes referred to as a 'native' metal).
For example, a metal, most frequently found ‘native’ is gold (and sometimes copper
and silver) and no chemical separation or extraction is needed. In fact all the metals
below hydrogen can be found as the 'free' or 'native' element, although they occur
mainly as compounds combined with non-metals like oxygen or sulphur, or the
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carbonate ion in their ores. Therefore, for most metals, their naturally occurring
compounds require processing via chemical reactions to obtain the free metals.
9.3.1 Displacement reactions
A metal will displace (take the place of) a less reactive metal in a metal salt solution.
For example,
iron + copper sulphate  iron sulphate + copper
Fe(s) + CuSO4 (aq)

(blue)
FeSO4 (aq) + Cu(s)
(pale green)
(brown)
Copper sulphate is blue while iron sulphate is a very pale green solution. During the
reaction the blue solution loses its colour and the iron metal is seen to turn brown as
the displaced copper becomes deposited on it.
If a less reactive metal is added to a metal salt solution there will be no reaction nothing will happen! For example, iron is less reactive than magnesium.
iron + magnesium sulphate  no reaction
In these displacement reactions the metals are competing for the non-metal negative
ion or anion. In the above examples the non-metal anion is sulphate, SO42-. Reactions
using anions such as chlorides or nitrates can also be used. The order of the metals in
the reactivity series can be worked out by using these types of reaction.
For example tin would be seen to displace lead from lead chloride but would not react
with iron chloride.
tin + lead chloride  tin chloride + lead
Sn (s) +
PbCl2 (aq) 
SnCl2 (aq) + Pb (s)
But…
tin + iron chloride  no reaction
Sn(s) +
FeCl2(aq)  no reaction
Therefore tin must be above lead but below iron in the reactivity series.
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9.3.2 Ores
Most metals are found as metal compounds in rocks and minerals in the Earth’s crust.
If there is enough metal in the rock to make it economically worth extracting, then
the rock is called an ore.
Aluminium, for example, is the most common metal in the Earth's crust. The usual
ore that aluminium is extracted from is called bauxite - which contains mostly
aluminium oxide, Al2O3.
Copper is much rarer, but fortunately can be found in high-grade ores (ones containing
a high percentage of copper) in particular places. Because copper is a valuable metal,
it is also worth extracting it from low-grade ores as well.
Metals ores are commonly oxides, for example bauxite (Al2O3), haematite (Fe2O3)
and rutile (TiO2)
Ores can also be sulphides, for example pyrite (FeS2) and chalcopyrite (CuFeS2)
Reducing the metal compound to the metal
Why is this called ‘reduction’?
At its simplest, where you are starting from metal oxides, the ore is being reduced
because oxygen is being removed.
This is the opposite of a process called oxidation which is the gain of oxygen.
Fe2O3
Al2O3
Removal of oxygen = reduction
Removal of oxygen = reduction
Fe
Al
The substance that reduces the metal oxide to the metal is called the reducing
agent
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9.3.3 Extracting metals from their ores
There are various economic factors you need to think about in choosing a method of
reduction for a particular ore. These are all covered in detail on other pages in this
section under the extractions of particular metals. What follows is a quick summary.
You need to consider:

the cost of the reducing agent (e.g. carbon, a common reducing agent, is cheap)

energy costs (for example, electrical energy for electrolysis is expensive)

the purity of the metal (sometimes carbon is left in the metal as an impurity,
which affects the properties of the metal).

Environmental considerations - some of which will have economic costs.
9.3.4 Iron
Metals below carbon (such as iron) can be extracted by heating the oxide with carbon
or carbon monoxide. The non-metallic elements carbon will displace the metals less
reactive than carbon in a smelter or Blast Furnace, e.g. iron or zinc and metals lower in
the series. Therefore metals like iron, copper, tin, lead, zinc can readily be extracted
by reaction-reduction of their oxides using coke.
Environmental problems in mining and transporting the raw material
 Loss of landscape due to mining, processing and transporting the iron ore, coke
and limestone.
 Noise and air pollution (greenhouse effect, acid rain) involved in these
operations.
Extracting iron from the ore
 Loss of landscape due to the size of the chemical plant needed.
 Noise.
 Atmospheric pollution from the various stages of extraction. For example:
carbon dioxide (greenhouse effect); carbon monoxide (poisonous); sulphur
dioxide from the sulphur content of the ores (poisonous, acid rain).
 Disposal of slag, some of which is just dumped.
 Transport of the finished iron.
Recycling
 Saving of raw materials and energy by not having to first extract the iron
from the ore.
 Avoiding the pollution problems in the extraction of iron from the ore.
 Not having to find space to dump the unwanted iron if it wasn't recycled.
 (Offsetting these to a minor extent) Energy and pollution costs in collecting
and transporting the recycled iron to the steel works.
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The Blast Furnace
The basic set-up of the Blast Furnace is shown in the diagram below. The top part is
where the three solid ingredients are added (iron ore, coke and limestone). Hot air is
blown in at the bottom, and this reacts with the carbon in the coke to produce carbon
dioxide. The carbon dioxide reacts with more carbon to form carbon monoxide. The
carbon monoxide then reduces the iron oxide to iron. The temperature of the furnace
is higher than the melting point of iron, so iron is produced as a liquid and collects at
the bottom of the furnace. Impurities called slag are lighter than liquid iron, so they
float on the surface and are removed separately.
There are three key chemical reactions that happen in the Blast Furnace which
convert iron oxide into iron are:
Carbon + oxygen  carbon dioxide
C (s) + O2 (g) 
CO2 (g)
Carbon dioxide + carbon  Carbon monoxide
CO2 (g) + C (s) 
2CO (g)
Iron oxide + carbon monoxide  iron + carbon dioxide
Fe2O3 (s) +
3CO (g)
 2Fe (l) +
3CO2 (g)
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Cast iron
The molten iron from the bottom of the furnace can be used as
cast iron. Cast iron is very runny when it is molten and doesn't
shrink much when it solidifies. It is therefore ideal for making
castings - hence its name. However, it is very impure, containing
about 4% of carbon. This carbon makes it very hard, but also
very brittle. If you hit it hard, it tends to shatter rather than
bend or dent. Cast iron is used for things like manhole covers,
guttering and drainpipes, cylinder blocks in car engines, Agatype cookers, and very expensive and very heavy cookware.
Steel
Most of the molten iron from a Blast Furnace is used to make one of a number of types
of steel. There isn't just one substance called steel - they are a family of alloys
(mixtures of iron with carbon or various metals).
Mild steel
Mild steel is iron containing up to about 0.25% of carbon. The presence of the carbon
makes the steel stronger and harder than pure iron. The higher the percentage of
carbon, the harder the steel becomes.
Mild steel is used for lots of things - nails, wire, car
bodies, ship building, girders and bridges amongst
others.
High-carbon steel
High-carbon steel contains up to about 1.5% of carbon.
The presence of the extra carbon makes it very hard,
but it also makes it more brittle. High-carbon steel is
used for cutting tools and 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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Special steels
These are iron alloyed with other metals. For example:
Type of
steel
Iron mixed
with
Special
properties
Uses
Stainless
steel
Chromium
and nickel
Resists corrosion
Cutlery, cooking utensils, kitchen
sinks, industrial equipment for
food and drink processing
Titanium
steel
Titanium
Withstands high
temperatures
Gas turbines, spacecraft
Very hard
Rock-breaking machinery, some
railway track (e.g. points), military
helmets
Manganese
steel
Manganese
9.3.5 Copper
Copper can be extracted from copper-rich ores by heating the ores in a furnace
(smelting). The copper produced by smelting is too impure to use, so it is purified by
electrolysis. However, the supply of copper-rich (high grade) ores is limited, hence
they are very valuable, and production costs are quite high.
Because of its position in the reactivity series of metals, copper can be extracted
using carbon in a smelting furnace.
Copper is below carbon in the Reactivity Series (it’s less reactive), and so can be
displaced by carbon from its compounds, e.g. copper oxides or sulfides.
However, in practice, modern copper smelters can actually manage the extraction
without using carbon (coke) and then electrolysis is usually used to purify the impure
copper from the smelter.
Ores that are rich in copper are becoming scarce so new methods of extracting
copper are being developed to exploit low-grade ores. A low-grade ore is one with
low concentrations of copper, and research is going on to try and exploit waste
material left over from processing high-grade ores.
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Purification of copper using electrolysis
The purification uses an electrolyte of copper(II) sulphate solution (CuSO4), impure
copper anodes (positive electrodes), and strips of high purity copper for the
cathodes (negative electrodes). The diagram shows a very simplified view of a cell.
At the cathode, copper(II) ions (Cu2+) are deposited as copper metal.
Cu2+(aq) + 2e- → Cu (s)
At the anode, copper goes into solution as copper(II) ions (Cu2+).
Cu (s) → Cu2+(aq) + 2eFor every copper ion that is deposited at the cathode, in principle another one goes
into solution at the anode. The concentration of the solution should stay the same.
All that happens is that there is a transfer of copper from the anode to the
cathode. The cathode gets bigger as more and more pure copper is deposited; the
anode gradually disappears.
In practice, it isn't quite as simple as that because of the impurities involved.
What happens to the impurities?
Any metal in the impure anode that is below copper in the electrochemical series
(reactivity series) doesn't go into solution as ions. It stays as a metal and falls to
the bottom of the cell as an "anode sludge", together with any unreactive material
left over from the ore. The anode sludge will contain valuable metals such as silver
and gold.
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Uses of copper
Amongst other things copper is used for:





Electrical wiring. It is a very good conductor of electricity and is easily drawn
out into wires.
Domestic plumbing. It doesn't react with water, and is easily bent into shape.
Boilers and heat exchangers. It is a good conductor of heat and doesn't react
with water.
Making brass. Brass is a copper-zinc alloy. Alloying produces a metal harder
than either copper or zinc individually. Bronze is another copper alloy - this
time with tin.
Coinage. In the UK, as well as the more obvious copper-coloured coins, "silver"
coins are also copper alloys - this time with nickel. These are known as
cupronickel alloys. UK pound coins and the gold-coloured bits of euro coins are
copper-zinc-nickel alloys.
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9.3.6 Aluminium
Metals above carbon in the reactivity series cannot usually be extracted with carbon
or carbon monoxide. So, metals more reactive than carbon are usually extracted by
electrolysis of the purified molten ore or other suitable compound.
Electrolysis is the process of breaking down a compound using electrical energy. The
process of electrolysis uses of large amounts of energy in the extraction of these
reactive metals and makes them expensive to produce.
The electrolysis cell
The diagram shows a very simplified version of an electrolysis cell used to extract
aluminium from aluminium oxide.
The electrode reactions
The aluminium ore used to extract aluminium is BAUXITE which contains aluminium
oxide (Al2O3). It is dissolved at high temperature in a substance called CRYOLITE in
the electrolysis cell.
Aluminium is released at the cathode (negative electrode). Aluminium ions are
reduced by gaining 3 electrons to form the neutral aluminium atoms.
Al3+ + 3e- → Al
The oxide ions (O2-) travel to the anodes (positive electrodes) and produce oxygen
gas.
2O2- → O2 + 4eHowever, at the temperature of the cell, the carbon anodes burn in this oxygen to
give carbon dioxide and carbon monoxide. Thus, continual replacement of the anodes
is a major expense.
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Although the carbon lining of the cell is labelled as the cathode, the effective
cathode is mainly the molten aluminium that forms on the bottom of the cell.
Molten aluminium is siphoned out of the cell from time to time, and new aluminium
oxide added at the top. The cell operates at a low voltage of about 5–6 volts, but at
huge currents of 100,000 amps or more. The heating effect of these large currents
keeps the cell at a temperature of about 1000°C.
Economic considerations



The high cost of the process because of the huge amounts of electricity used.
Energy and material costs in constantly replacing the anodes.
Energy and material costs in producing the cryolite, some of which gets lost
during the electrolysis.
Uses of aluminium
Aluminium is usually alloyed with other elements such as silicon, copper or
magnesium. Pure aluminium isn't very strong, and alloying it adds to it strength.
Aluminium is especially useful because it:





has a low density
is strong when alloyed
is a good conductor of electricity
has a good appearance
resists corrosion because of the strong thin layer of aluminium oxide on its
surface. This layer can be strengthened further by anodising the aluminium.
Aluminium is used for
Reason
Aircraft
Light, strong, resists corrosion.
Other transport such as ships'
superstructures, container vehicle bodies,
tube trains.
Light, strong, resists corrosion.
Overhead power cables
(with a steel core to
strengthen them).
Light, resists corrosion, good
conductor of electricity.
Saucepans
Light, resists corrosion, good
appearance, good conductor of heat.
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9.3.7 Titanium
Other extraction methods are used in special cases. A more reactive metal can be
used to displace and extract a less reactive metal but these are costly processes as
the more reactive metal also has to be produced in the first place! Titanium is
another very useful metal but expensive to produce.
Titanium extraction
The extraction of titanium takes place in a couple of steps.
The first stage involves converting titanium(IV) oxide, TiO2, into titanium(IV)
chloride, TiCl4. The ore rutile (impure titanium(IV) oxide) is heated with chlorine and
coke (a cheap source of carbon) at a temperature of about 900°C.
Reduction of the titanium chloride by sodium metal then takes place.
Titanium chloride + sodium  titanium + sodium chloride
TiCl4 + 4Na  Ti + 4NaCl
Uses of titanium
Titanium is corrosion resistant, very strong and has a high melting point. It has a
relatively low density (about 60% that of iron). It is also the tenth most commonly
occurring element in the Earth's crust. That all means that titanium should be a
really important metal for all sorts of engineering applications. In fact, it is very
expensive and only used for rather specialised purposes.
Titanium is used, for example:



in the aerospace industry - for example
in aircraft engines and air frames
for replacement hip joints
for pipes, etc, in the nuclear, oil and
chemical industries where
corrosion is likely to
occur.
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Why is titanium so expensive?
Titanium is very expensive because it is awkward to extract from its ores - for
example, from rutile, TiO2, and you can't use carbon reduction.
As we have seen, titanium can't be extracted by reducing the ore using carbon as a
cheap reducing agent. This is not because titanium is more reactive than carbon but
because titanium forms a carbide, TiC, if it is heated with carbon, so you don't get
the pure metal that you need. The presence of the carbide makes the metal very
brittle.
That means that you have to use an alternative reducing agent. In the case of
titanium, the reducing agent is either sodium or magnesium. Both of these would, of
course, first have to be extracted from their ores by expensive processes.
Other problems


The titanium is produced by reacting titanium(IV) chloride, TiCl4 - NOT the
oxide - with either sodium or magnesium. That means that you first have to
convert the oxide into the chloride. That in turn means that you have the
expense of the chlorine as well as the energy costs of the conversion.
High temperatures are needed in both stages of the reaction.
With titanium, however, you make it one batch at a time. Titanium(IV) chloride is
heated with sodium or magnesium to produce titanium. The titanium is then
separated from the waste products, and an entirely new reaction is set up in the
same reactor. This is a slow and inefficient way of doing things.
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Summary
When metals are placed in a list showing the trend in their chemical reactivity we
call it The ____________________________.
The metals at the top include the Group ____ metals p___________,
s__________ and l____________.
These react vigorously with _____________, oxygen and _____________.
Metals at the ___________ of the list react __________ or not at all.
The more reactive a metal the more ______________ its compound.
Therefore, the more reactive a metal, the more _____________ it is to extract, ie
more ______________ is needed to separate the metal from the other elements in
the compound. A chemical ________________ is required to separate the
elements.
Those metals that are so unreactive that they occur as the element itself are known
as _____________ metals, eg ______________.
Reactions where a metal will take the place of a less reactive metal in a metal
compound are called ____________________ reactions.
For example (complete the eqns)
magnesium + copper sulphate  ____________ + ___________
Mg(s)
+
CuSO4 (aq)

____________ + ___________
(blue)
If a less reactive metal is added to a metal salt solution there will be
____________________________ eg.iron and sodium chloride.
The __________ of the metals can be worked out by using these types of reaction.
The metal that is displaced must lie _________ the metal that displaced it.
When metals are found in a rock at an appreciable level that makes it worth extracting
we call the rock an __________.
Aluminium ore is called _________________, iron ore is ________________ and
titanium ore is _____________.
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The process of extracting the metal is called ___________________ because it
involves removing ________________.
The substance that reduces the metal oxide to the metal is called
the______________________.
The method used needs to consider ___________, purity and effects on the
___________________________.
Iron is extracted using ____________________ as a reducing agent in a
_____________ furnace.
Aluminium is more reactive than iron and needs _____________________ to extract
it from its ore. This is more expensive as it uses a lot of
_______________________ energy.
Copper is also extracted in a furnace by smelting but is impure so needs electrolysis to
__________ it.
purify
blast
stable
electrolysis
reactivity series
reducing agent
difficult
reaction
displacement
reactivity
potassium
MgSO4
below
water
native
energy
cost
Cu
bottom
electrical
haematite
bauxite
environment
carbon monoxide
sodium
TOPIC 9.3 METALS, ORES AND EXTRACTION
slowly
oxygen
acid
15
lithium
1
reduction
rutile
no reaction
ore
magnesium sulphate
gold
copper