A mineral, from which a metal is economically, easily, extracted, is called the Ore
Concentration of ore
The process of removing impurities from the ore obtained from the earth’s crust.
Depending on the nature of the ore and impurities, there are different methods of
Levigation or Hydraulic washing
When the impurities are lighter and the ore particles are heavier, the lighter
impurities are removed by washing in a current of water.
Eg: concentration of gold.
This process is used when the impurities are heavier and the ore particles are lighter,
a mixture of powdered ore, water and pine oil is strongly agitated by compressed air.
As a result the ore particles stick to the froth of the oil formed during the mixing
process and floats on the surface of water. The heavier impurities are sink to the
bottom. The ore is separated from the ore.
Eg: concentration of copper pyrites
If either the ore or the impurity is magnetic in nature, this method is used. The
powdered ore is fed to the conveyor belt moving over a magnetic wheel to separate
the magnetic substance.
Eg: concentration of the ore of iron.
On adding the ore to the suitable solution, a chemical reaction takes place and the
ore dissolves in the solution. The insoluble impurities are filtered off. The pure ore is
separated from the filtrate by chemical reaction.
Eg: concentration of Bauxite
- Extraction of metal from concentrated ore
a. Conversion of concentrated ore in to its oxide
b. Reduction of the oxide
Conversion of concentrated ore in to its oxide
The process of heating the concentrated ore at a temperature below its melting point to
remove the volatile impurities. Oxygen will not take Part in this reaction.
Eg: ZnCO3 is converted to ZnO by Calcination
The process of heating the concentrated ore at a temperature below its melting point in a
current of air. Impurities like sulphur, phosphorous and other organic matter are oxidised
Eg: Cu2S is converted to Cu2O by roasting.
Reduction of the oxide
The process of extraction of metal from the oxide .suitable reducing agents are use for this
purpose. CO is used as the reducing agent to extract iron from haematite, and C is used to
extract zinc from zinc oxide.
Electricity is used to extract highly reactive metals like sodium, potassium etc
from their ores.
Refining of Metals
The metal obtained by reduction may contain other metals, metal oxides and small
quantities of non metal as impurities.
Refining is the process of removal of these impurities to get the pure metal.
There are different methods are used to for the refining of metals based on the nature
of metal and impurities.
Low melting metals like tin and lead may contain other high melting metals or metal oxides
as impurities. On heating such on the inclined surface of the furnace, the pure metal melts
and flows down leaving the impurities behind
This method is used for the refining of metals with low boiling points such as zinc, cadmium
and mercury. When the impure metal is heated in a retort, the pure metal alone
vapourises.the vapours are condensed to get the pure metal.
It is the process of refining of a metal by the electrolysis of a solution of the salt of the
metal, using a small piece of pure metal as –ve electrode and impure metal as +ve electrode.
By electrolysis the pure metal from the +ve electrode dissolves in the electrolyte and get
deposited on the –ve electrode. Copper and silver are refined using this method.
INDUSTRIAL PREPARATION OF IRON
Blast furnace is the huge steel furnace with a blast of hot air in the bottom.
A mixture of roasted Haematite, coke, lime stone (CaCO3) are falls into the Blast furnace.
Here the CaCO3 decomposes at high temperature
CaCO3→ CaO + CO2
The formed CaO is combined is here combines with silicon dioxide (SiO2) the main impurity of ore.
Flux +Gangue → Slag
The impurities in the metal are known as Gangue.
The material used to remove gangue and to convert it as separable molten material is known as Flux.
The gangue and flux combines to form Slag. ( Flux +Gangue →Slag)
Here CaO is the flux, SiO2 is the Gangue and CaSiO3 is the slag.
If gangue is acidic then the flux is basic and vice versa.
Here the Gangue (SiO2) is Acidic so the Flux is Basic (CaO)
The coke combines with oxygen in the hot air.
The CO in the middle of the furnace reacts with iron oxide to produce iron.
The iron obtained from the blast furnace contains impurities like 4% carbon silicon manganese, phosphorous
this iron is called Pig iron.
Pig iron+ Scrap iron +Coke→ Cast iron.
By purifying the cast iron, comparatively pure raw iron is obtained this is known as Wrought iron
EXTRACTION OF ALUMINIUM
· Ore of aluminium is Bauxite.
· The main impurity in aluminium is SiO2
Aluminium is extracted using electricity, because Aluminium is highly reactive
· The alumina (Al2O3) obtained by concentration of bauxite is mixed with cryolite (Na3AlF6)
and subjected to electrolysis.
· Cryolite is added to alumina to reduce melting point and increase its electrical conductivity.
· When electricity is passed through this mixture, its get heated, cryolite melts and alumina
dissolves in it.
Al3++3e → Al (Pure aluminium is produced at cathode)
2O2- → O2+4e