© www.chemsheets.co.uk
AS 080
10-Jul-12
ORES
• Most metals are found in compounds in the
Earth’s crust.
• A rock containing enough of the metal for
extraction to be profitable is called an ore.
iron ore
haematite
Fe2O3
copper ore
malchite
CuCO3
titanium ore
rutile
TiO2
aluminium ore
bauxite
Al2O3
lead ore
galena
PbS
EARTH’S CRUST
Metals have to be extracted
by chemical reactions from
compounds found in the
crust.
EXTRACTION METHODS
Methods
1) Reduction by heating with carbon
2) Reduction by electrolysis of melt
3) Reduction by active metal
4) Reduction by hydrogen
Which method is used depends on
1) Energy requirements (heat, electricity)
2) Cost of reductants (C / active metal / electricity)
3) Purity of metal required
© www.chemsheets.co.uk
AS 080
10-Jul-12
ROASTING SULPHIDE ORES
Ore is roasted in air
e.g.
ZnS +
3/
2
O2  ZnO + SO2
Produces SO2 – causes acid rain
To prevent this, SO2 is collected to stop it entering
the atmosphere (and then used to make some
H2SO4)
© www.chemsheets.co.uk
AS 080
10-Jul-12
ACID RAIN
Damages plants
Branches from a tree in Germany's Black Forest show
needle loss and yellowed boughs caused by acid rain
Kills fish
Damages some stones (e.g. limestone)
REDUCTION WITH CARBON
Most metals can be extracted by heating with carbon. Many
are not because:
1) Metal carbides may be formed (e.g. with Ti, W, Al)
2) Temperature required is excessively high (energy costs)
© www.chemsheets.co.uk
AS 080
10-Jul-12
BLAST FURNACE
1)
C + O2 → CO2
2)
C + CO2 → 2 CO
3)
Fe2O3 + 3 CO → 2 Fe + 3 CO2
Fe2O3 + 3 C → 2 Fe + 3 CO
4)
CaCO3 → CaO + CO2
5)
CaO + SiO2 → CaSiO3
BLAST FURNACE
Pollution issues
1)
CO2 formed – greenhouse gas
2)
CO formed – toxic
3)
SO2 formed (roasting of sulphide ores) – acid rain
© www.chemsheets.co.uk
AS 080
10-Jul-12
STEEL MAKING
Impurities: C, P, S, Si
1)
Inject powdered Mg to remove S (forms MgS –
floats on surface and scraped off)
2)
Scrap steel added to recycle
3)
O2 blown through molten metal (converts C, P, Si to
oxides, CO2 bubbles off)
4)
Limestone added (decomposes to CaO) which
reacts with P4O10 and SiO2 to form slag
5)
Other metals and/or C added to make steel
© www.chemsheets.co.uk
AS 046
10-Jul-12
REDUCTION WITH CARBON
Mn
MnO2 + C  Mn + CO2
Cu
2 CuO + C  2 Cu + CO2
Malachite ore
CuCO3  CuO + CO2
ELECTROLYSIS OF MELTS
g ra p h ite p o s itiv e e le c tro d e
2 O
2-
- 4 e
-
 O2
(th e n C + O 2  C O 2 )
m o lte n m ixtu re o f
a lu m in iu m o xid e
a n d c ryo lite
g ra p h ite n e g a tiv e e le c tro d e
Al
3+
+ 3 e
-
 Al
m o lte n a lu m in iu m
© www.chemsheets.co.uk
AS 046
10-Jul-12
ACTIVE METAL REDUCTION
Titanium is
Replacement
hip joints
• Low density
• Strong
• Corrosion resistant
Nuclear reactors
Aircraft
ACTIVE METAL REDUCTION
• Titanium must be very pure.
• Reduction with C forms TiC which is brittle.
• Electrolysis does not make it pure enough.
© www.chemsheets.co.uk
AS 080
10-Jul-12
Ti EXTRACTION
1)
TiO2 + 2 Cl2 + 2 C → TiCl4 + 2 CO
2)
Purify TiCl4 by fractional distillation
3)
TiCl4 + 4 Na → Ti + 4 NaCl
TiCl4 + 2 Mg → Ti + 2 MgCl2
Expensive due to:
• High temperatures (high energy)
• Use of Ar
• Cost of Na/Mg (made by electrolysis)
© www.chemsheets.co.uk
AS 080
10-Jul-12
HYDROGEN REDUCTION
Wolframite (contains WO3)
Tungsten
WO3 + 3 H2  W + 3 H2O
C reduction would form WC (tungsten carbide)
RECYCLING METALS
Advantages
• Lower energy cost
• Saves resources
• Less waste
Disadvantages
• Preventing people
throwing away
• Transport cost
• Less pollutants
(e.g. CO2, SO2, CO)
© www.chemsheets.co.uk
AS 080
10-Jul-12
COPPER RECYCLING & EXTRACTION
1) Covert waste Cu to Cu2+(aq) – add H2SO4 or enzyme
2) Extract Cu from solution with Fe:
Cu2+(aq) + Fe(s)  Cu(s) + Fe2+(aq)
Useful for
recycling scrap
extraction from low grade ores