The document discusses three key processes related to the extraction of aluminium: 1) The Bayer process extracts aluminium from bauxite ore by crushing it, heating it with sodium hydroxide, and filtering out impurities to produce aluminium hydroxide. 2) In the Hall-Héroult process, aluminium oxide is mixed with calcium fluoride or sodium aluminium fluoride and electrolyzed to produce oxygen and molten aluminium. 3) The Bayer process is preferred over the Hall-Héroult process for extracting aluminium as it allows for purification based on aluminium oxides' amphoteric nature, since aluminium must be reduced from its compounds in ores.

1. Extraction of
Aluminium
- Extraction of Bauxite ore
- Hall Heroult’s process
- Bayer process

2. Extraction of metal

3. What is
meant by
extraction of
metal?
It simply means purifying the
metal according to reactivity
series. Carbon is used to
reduce oxides of metals below
it in the reactivity series. e.g,
oxides of zinc, lead, and iron
can be reduced by carbon.

5. Hall Heroult’s
process
In Hall-Heroult’s process, pure Al2O3 is mixed with CaF2 or
Na3AlF6.
This results in lowering of the melting point of the mixture and
increases its ability to conduct electricity.
A steel vessel with the lining of carbon and graphite rods is used.
The carbon lining acts as cathode and graphite act as an anode.
When electricity is passed through the electrolytic cell which
consists of carbon electrodes, oxygen is formed at the anode.
This oxygen formed reacts with the carbon of the anode to form
carbon monoxide and carbon dioxide.
In this method of production of aluminium for every 1 kg of Al
produced, approximately 0.5 Kg of carbon anode is burnt.

7. Bayer’s
process
1) Bayer process, bauxite ore is crushed, milled and then heated
with sodium hydroxide at the temperature of around 150-200
degree Celsius. In the Bauxites, aluminium compounds are
present as gibbsite (Al (OH) 3), boehmite (AlOOH) and
diaspore (α-AlO (OH)).
2) Filtration: In this step the mixture is clarified to remove
impurities. Other than alumina and silica, all other components
present in Bauxite do not get dissolved. The solids which are
not dissolved get settled down at the bottom forming red mud.
This red mud is then discarded from the solution commonly by
using rotary sand trap.
3) The filtration process converts the aluminium oxide to soluble
sodium aluminates, 2NaAlO2, as per the equation:
4) Al2O3 + 2NaOH → 2NaAlO2 + H2O.
5) Precipitation: The clear remaining mixture is added to
precipitators by using heat exchangers, which turns the
mixture from heat to cool liquor. Silica is precipitated from the
mixture because heating. Crystals of aluminium hydroxide are
discovered in this step.

8. Bayer’s
process
6) 90 percentage of the gibbsite manufactured is converted into
alumina by washing, drying.
7) Then Although the carbon lining of the cell is labelled as the
cathode, the effective cathode is mainly the molten aluminium
that forms on the bottom of the cell.
8) Molten aluminium is syphoned out of the cell from time to time,
and new aluminium oxide added at the top.
9) The cell operates at a low voltage of about 5 - 6 volts, but at
huge currents of 100,000 amps or more. The heating effect of
these large currents keeps the cell at a temperature of about
1000°C.
10)Aluminium is released at the cathode. Aluminium ions are
reduced by gaining 3 electrons.
11)Al3+ + 3e-  Al
12)Oxygen is produced initially at the anode.

10. Why Bayer’s
process is
relevant than the
Hall Heroults’s
process?
The purification process of aluminium is
based on the amphoteric nature of
aluminium oxides. Since aluminium is
found in compounds with other elements
it needs to be reduced. The Bayer
process is essentially referring to the
refining of bauxite, the most important
aluminium ore, to produce alumina. From
here, the intermediate alumina must be
smelted into metallic aluminium through
the Hall-Heroult Process.

11. Some uses of
Aluminium
Aluminium is used for aircraft because light,
strong, resists corrosion
Other transport such as ships'
superstructures, container vehicle bodies,
tube trains (metro trains) because light,
strong, resists corrosion
Overhead power cables (with a steel core to
strengthen them) because light, resists
corrosion, good conductor of electricity
Saucepans because light, resists corrosion,
good appearance, good conductor of heat

12. Thankyou