Extraction of metals

Question 1

Where and how is iron extracted from?

Answer 1

Hematite in a blast furnace

Question 2

Where and how is aluminium extracted from?

Answer 2

Bauxite using electrolysis

Question 3

Describe the process of extracting iron in a blast furnace.

Answer 3

Raw materials:

Iron ore (hematite), coke (impure form of carbon), limestone

Raw materials are added into the top of the blast furnace
Hot air is blown into the bottom

Reactions:

1. Carbon + Oxygen -> Carbon Dioxide
   C(s) + O2(g) -> CO2(g)

Complete combustion of carbon from the coke, using oxygen from the air blast. Reaction is exothermic; generates the heat needed to bring the furnace to correct temperature.

2. Carbon Dioxide + Carbon -> Carbon Monoxide
   CO2(g) + C(s) -> 2CO(g)

Reduction of CO2 to CO due to incomplete combustion of carbon

3. Iron (III) Oxide + Carbon Monoxide -> Iron + Carbon Dioxide
   Fe2O3(s) + 3CO(g) -> 2Fe (l) + 3CO2 (g)

Reduction of iron (III) oxide by CO to become molten iron. Liquid iron flows downwards; collected at bottom.

4. Calcium carbonate -> Calcium oxide + Carbon dioxide
   CaCO3(s) -> CaO(s) + CO2 (g)

Thermal decomposition of calcium carbonate (limestone) to produce calcium oxide

5. Calcium oxide + Silicon dioxide -> Calcium silicate (slag)
   CaO(s) + SiO2(s) -> CaSiO3(l)

Calcium oxide formed reacts with silicon dioxide, which is an impurity in the iron ore; forms calcium silicate. Melts and collects molten slag on top of the molten iron, which is tapped off seperately.

Question 4

Describe the process of extracting aluminium by electrolysis.

Answer 4

Bauxite purified to produce Al2O3 (Aluminium Oxide)
Al2O3 dissolved in molten cryolite:
- This is because Al2O3 has a melting point of 2000 degrees C; use a lot of energy and can be very expensive
- Resulting mixture has lower melting point without interfering with the reaction
Mixture placed in electrolysis cell, which is made from steel, lined with graphite
Graphite lining acts as cathode, several large graphite blocks as cathodes

Note:

Cryolite (Na3AlF6) has 3 functions:
Lowers melting point of aluminium oxide, which reduces operating cost
Acts as solvent which can also increase conductivity

Question 5

Describe the reactions during the process of extracting aluminium by electrolysis.

Answer 5

At the anode:
Oxide ions lose electrons (oxidation)
Oxygen is produced
2O2 2- -> O2 + 4e