Metals - Chemistry - page 158

Table 10.6 Some common ores.

Metal Name of ore Chemical name of

compound in ore

Formula Usual method of extraction

Aluminium Bauxite Aluminium oxide Al 2 O 3 .2H 2 O Electrolysis of oxide dissolved in molten cryolite

Copper Copper pyrites Copper iron sulfide CuFeS 2 The sulfide ore is roasted in air

Iron Haematite Iron( iii ) oxide Fe 2 O 3 Heat oxide with carbon

Sodium Rock salt Sodium chloride NaCl Electrolysis of molten sodium chloride

Zinc Zinc blende Zinc sulfide ZnS Sulfide is roasted in air and the oxide produced is heated with carbon

Extraction of reactive metals
Because reactive metals, such as sodium, hold on
to the element(s) they have combined with, they
are usually difficult to extract. For example, sodium
chloride (as rock salt) is an ionic compound with the
Na + and Cl − ions strongly bonded to one another.
The separation of these ions and the subsequent
isolation of the sodium metal is therefore difficult.
Electrolysis of the molten, purified ore is the
method used in these cases. During this process, the
metal is produced at the cathode while a non-metal
is produced at the anode. As you might expect,
extraction of metal by electrolysis is expensive. In
order to keep costs low, many metal smelters using
electrolysis are situated in regions where there is
hydroelectric power (Chapter 6, p. 94).
For further discussion of the extraction of
aluminium, see Chapter 5, pp. 74-76.

Figure 10.12 A blast furnace.

hot waste gases -
these are used to heat
air going into the
blast furnace

Extraction of fairly reactive metals
Metals towards the middle of the reactivity series,
such as iron and zinc, may be extracted by reducing
the metal oxide with the non-metal carbon.

skip dumps charge of
iron ore, coke and
limestone into hopper

Iron
Iron is extracted mainly from its oxides, haematite
(Fe 2 O 3 ) and magnetite (Fe 3 O 4 ), in a blast furnace
(Figures 10.12 and 10.13). These ores contain
at least 60% iron. The iron ores used are a blend
of those extracted in Australia, Canada, Sweden,
Venezuela and Brazil. The blast furnace is a steel
tower approximately 50 m high lined with heat-
resistant bricks. It is loaded with the 'charge' of iron
ore (usually haematite), coke (made by heating coal)
and limestone (calcium carbonate).
A blast of hot air is sent in near the bottom of the
furnace through holes (tuyères) which makes the
'charge' glow, as the coke burns in the preheated air.
carbon
C( s )

hopper

50 rows of
water-cooled
copper coolers
in the lining
of the furnace

height
approximately
90 m

650 C

heat-resistant
brick

hot air
blown
through
tuyère

1000 C

50 m

1100 C

slag notch

molten slag

molten iron tap hole

firebrick pad

+
+

oxygen
O 2 ( g )

carbon dioxide
CO 2 ( g )

→ ●
→

Figure 10.13 Cross-section of a blast furnace.