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Chapter 13
The extraction of metals…read more

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The extraction of metals
· The properties of metals include strength,
thermal and electrical conductivity. They
are also one of the most useful materials
known to mankind. Most of metals are
usually found in ores containing minerals,
in which metals are combined with oxygen
or sulfur. Therefore, in order to obtain the
metal, the oxygen or sulfur has to be
· This is a reduction reaction as oxides and
sulphides have positive oxidation states. As
elements metals have oxidation states of 0.
· As well as the metal-containing compound,
ores contain unwanted materials such as
clay and rock that have to be removed.
These materials are called gangue. An ore
must contain enough metal for it to be
economically worth extracting. However, if
the metal is very valuable it may be worth
mining even if there is very little metal in
the ore.…read more

Slide 3

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Converting sulphide ores to oxides
· Before reduction, sulphide ores
are usually converted to oxides by
heating them in air, this is called
­ ZnS(s) + 1 ½ O (g) ZnO(s) + SO
­ The by product, sulfur dioxide, is an
acidic gas which if it is allowed to
escape, it is converted to sulphuric
acid by reaction with water and
oxygen in the atmosphere, it is a
contributor to acid rain.
­ Fortunately sulfur dioxide can be
collected and converted to sulfuric
­ SO (g) + H O(g) + ½ O H SO4…read more

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Choosing a reducing agent
· Coke (an impure form of carbon) is
chosen as a reducing agent for the
extraction of metals. It is cheaply
obtained by heating coal without air.
However , for some metals the
temperature required for the reaction
with carbon is so high that the process
in uneconomic. Also at high
temperatures, reactive metals react
with carbon to form carbides
· Hydrogen is another reducing agent
(made from methane, CH4 and water
H2O) This method is used to extract
· Metals higher up the reactivity series,
such as sodium and aluminium, may be
reduced by electrolysis
· A more reactive metal as a reducing
agent.…read more

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Iron (and steel) is by far the most
commonly used metal, over ½ q
billion tonnes are produced each
year worldwide.
· The iron itself is usually found as
the ores magnetite, Fe3O4 and
· The major impurity is silica SiO2…read more

Slide 6

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Iron- reduction by carbon in the blast furnace
· Extraction of iron from its oxide ores is done
using coke in tall brick towers called blast
furnaces that are up to 70 m high. A typical blast
furnace can produce up to 10 000 tonnes of iron
per day
· These run continuously for years at a time. The
hopper is charged with a mixture of iron ore,
coke and calcium carbonate (limescale)
Inside the blast furnace
· At the base of the furnace the coke burns in a
blast of hot air. Heat is generated by this
exothermic process so that the temperature is
around 2000K.(the melting point of iron is 1800
K). Carbon dioxide is formed which then reacts
with more carbon to form carbon monoxide.
­ C(s) +O2(g) CO2
· Then...
­ C02(g) + C(s) 2CO(g)
· The carbon monoxide is the reducing agent. It
reacts with the iron oxide to produce molten
­ Fe2O3(s) + 3CO(g) 2Fe(l) + 3CO2(g)…read more

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