1. Chemsheets AS006 (Electron arrangement)
21/04/2017
METAL EXTRACTION
© AS Jul-12

2. 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

3. EARTH’S CRUST
Metals have to be extracted by chemical reactions from compounds found in the crust.

4. 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
© AS Jul-12

5. 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)
© AS Jul-12

6. ACID RAIN
Damages plants

7. Branches from a tree in Germany's Black Forest show needle loss and yellowed boughs caused by acid rain

8. Kills fish

9. Damages some stones (e.g. limestone)

10. 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)
© AS Jul-12

11. BLAST FURNACE 1) C + O2 → CO2 2) C + CO2 → 2 CO
Fe2O CO → 2 Fe CO2
Fe2O C → 2 Fe CO
4) CaCO3 → CaO + CO2
5) CaO + SiO2 → CaSiO3

12. BLAST FURNACE Pollution issues 1) CO2 formed – greenhouse gas
2) CO formed – toxic
3) SO2 formed (roasting of sulphide ores) – acid rain
© AS Jul-12

13. 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
© AS Jul-12

14. REDUCTION WITH CARBON Mn MnO2 + C  Mn + CO2 Cu 2 CuO + C  2 Cu + CO2
Malachite ore
CuCO3  CuO + CO2

15. ELECTROLYSIS OF MELTS
© AS Jul-12

16. ACTIVE METAL REDUCTION
Titanium is
Low density
Strong
Corrosion resistant
Replacement hip joints
Nuclear reactors
Aircraft

17. ACTIVE METAL REDUCTION
Titanium must be very pure.
Reduction with C forms TiC which is brittle.
Electrolysis does not make it pure enough.
© AS Jul-12

18. Ti EXTRACTION 1) TiO2 + 2 Cl2 + 2 C → TiCl4 + 2 CO
2) Purify TiCl4 by fractional distillation
TiCl Na → Ti NaCl
TiCl Mg → Ti MgCl2
Expensive due to:
High temperatures (high energy)
Use of Ar
Cost of Na/Mg (made by electrolysis)
© AS Jul-12

19. Wolframite (contains WO3)
HYDROGEN REDUCTION
Wolframite (contains WO3)
Tungsten
WO H2  W H2O
C reduction would form WC (tungsten carbide)

20. RECYCLING METALS Advantages Disadvantages Lower energy cost
Saves resources
Less waste
Less pollutants (e.g. CO2, SO2, CO)
Preventing people throwing away
Transport cost
© AS Jul-12

21. 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