METAL
EXTRACTION
Name :- Somdatta Bhattacharya
Branch :- Kurmannapalem
Admin No :- 2274557
Class :- N120
INDEX
1. Definition of extraction of metals
Definition of
Extraction of metals
The process of extracting metal ores buried deep
underground is called mining. The metal ores are
found in the earth’s crust in varying abundance.
The extraction of metals from ores is what allows
us to use the minerals in the ground. The ores are
very different from the finished metals that we see
in buildings and bridges. Ores consist of the
desired metal compound and the impurities and
earthly substances called gangue.
The extraction of metals and their isolation occurs
over a few major steps:
• Concentration of Ore – Here the ore is
separated from earthy impurities.
• Isolation of metal from concentrated Ore – Here
the ore is converted to its oxide form and then
reduced. The steps involved are either calcination
or roasting and then heating with a reducing
agent.
• Purification of the metal – Here the metal is
purified for practical purposes.
TYPES OF ORES
Oxide Ores-
In this particular ore, the metals are present in the oxidised
form. Obtaining metals from this ore is much easier. For
example, Haematite ore ( Iron) and Bauxite ore (Aluminium)
Sulphide Ores-
In this particular ore, the metals are present in the sulphide
form. Since it is difficult to extract metals from this ore, they
are usually converted to oxides with the process of
metallurgy. For example, Zinc Blende ( Zinc) and Lead
(Galena)
Carbonate Ores-
In this ore, carbonate ions are present. Since it is difficult to
extract metals from these ores, they are also converted to
oxide ores first. For example, Calamine (Zinc)
Sulphate Ores-
They are generally found underground and have sulphur
ions present in them. For example, Anglesite (Lead)
Important metal ores
found in INDIA
Aluminium :-
Bauxite- AlOx(OH)3-2x
KAOLINITE(a form of clay)- [Al2(OH)4 Si2O5]
IRON :-
Haematite – Fe2O3
Magnetite- Fe3O4
Siederite- FeCO3
Iron Pyrites- FeS2
Copper:
• Copper pyrites- CuFeS2
• Malachite- CuCO3.Cu(OH)2
• Cuprite- Cu2O
• Copper glance- Cu2S
Zinc:
• Zinc blend/Sphalerite- ZnS
• Calamine- ZnCO3
• Zincite- ZnO
BASIC STEPS OF
EXTRACTING
METALS
1. Grinding and Crushing
The bigger chunks of the ore extracted are crushed and ground in ball mills
and crushers. It helps to increase the surface area of the chunks for better
chemical actions later. In technical terms, it is called pulverisation.
2. Concentrating the Ore
This step concentrates the ore by performing the removal of impurities. It is
also called ore dressing. This process is quite elaborate and is named according
to the equipment or technique used. Let us take a quick look.
Hydrolytic Method:
In this method, the ground ore particles are poured over a vibrating table with
a slope or inclination. A water jet is used to flow on the ground particles. The
impurities are lighter than the metal-containing ore particles. They wash down
while the heavier particles settle down on the grooves of the inclined table. This
is generally used when the metal ore is much heavier than the impurities.
Magnetic Separation:
The name of the concentration process is enough to explain. This technique is
used to separate the ferromagnetic metal ore from the impurities after
pulverizing. The ground ore particles are carried on a conveyor belt with two
wheels. One of these wheels is magnetic. The ferromagnetic ore particles will
then get attracted and separated from the impurities easily.
Froth Floatation:
This is one of the methods of extraction of metals from ores by using
two mediums together. Both oil and water are used to separate
impurities. It can only be done when the ore forms froth when
compressed air is passed in this medium. The frothed ore collects on
the oil section whereas the impurities settle down in the water
medium.
Chemical Separation:
One way of concentrating the ore is by chemical separation. For
example, the separation of aluminium (Al) from the bauxite ore. This
process of separating aluminium from the bauxite ore is also termed
Bayer’s Process. Hot NaOH reacts with the bauxite ore which leads to
the formation of sodium aluminate which is water-soluble. The
solution of sodium aluminate is then diluted with water which when
cooled, gives aluminium hydroxide. This is then further washed and
filtered to get the pure aluminium oxide called the alumina.
3. Calcination and Roasting
Once the ore is concentrated using the above methods, it is then
either heated in the presence or absence of air. It all depends on the
element and its chemical properties. For instance, sulphide ores are
heated in the presence of oxygen. It is called roasting. On the other
hand, carbonated metal ores are heated in a vaccum for easy
extraction of metals. This is called calcination. This is how a
concentrated ore is again refined to gather purer metals.
This is a gist of how the extraction of metals ores and minerals
is performed based on the physical and chemical properties of
the impure ores. This concept page will also describe how
metals in the lower part of the activity series can be extracted
from their ores.
