Draw a flow chart of classification of mettalurgy
all process name and method
for ICSE board
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Answers
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Mineral
The naturally occurring substances in the form of which the metals occur in the earth’s crust are called minerals.
Ore
The mineral from which a metal can be extracted profitably and conveniently is called an ore.
Gangue
The earthy impurities like sand, rock, etc., that surround the worthy mineral in a ore, are called called gangue.
Metallurgy
The scientific and technological process used for separating metal from its ore is known as metallurgy.
Extraction of metals
The extraction of metals involves three major steps:
(i) Concentration of the ore
(ii) Isolation of the metal from its concentrated ore
(iii) Purification of the metal
Concentration of ores
The process of removal of unwanted materials from the ore is called concentration or benefaction of the ore.
It can be carried out by various steps as stated below:
Hydraulic washing: In this method, the lighter earthy impurities are washed away from the heavier ore particles. Thus this method of concentration of ore is based on the difference in specific gravities of the ore and gangue particles.
Magnetic separation: This method is based on the magnetic and non-magnetic properties of the ore components.
Froth flotation: This method is quite useful for the purification of the sulphide ores. The mineral particles are wetted by oils and the gangue particles by water. As a result. the ore particles become light and rise to the top in the form of froth while the gangue particles become heavy and settle down. The froth can be stabilised by the addition of stabilisers like aniline or cresols.
Extraction of crude metal from concentrated ore
Concentrated ore is usually converted to oxide before reduction, as oxides are easier to reduce. Thus, extraction of crude metal from concentrated ore involves two major steps:
(i) Conversion to oxide.
(ii) Reduction of the oxides to metal
Conversion to oxide
It can be carried out by following two methods:
Calcination: It is the process of converting an ore into its oxide by heating it in a limited supply of air or in absence of air, below its melting point. The volatile matter is burnt away and the oxide of the metal is obtained. This process is useful for metal carbonates and hydroxides. For example: CaCO3 → CaO + CO2 and Al2O3.2H2O → Al2O3 + 2H2O.
Roasting: It is the process of converting an ore into its oxide by heating the ore in excess of oxygen (air). This process is commonly used for suiphide ores.
For example: 2PbS + 3O2 → PbO + 2 SO2 and 2 Cu2S + 3O2 → 2 Cu2O + 2 SO2
Reduction of metal oxides to metal
The metal present in metal oxide can be converted from cationic form to free by supplying electrons, i.e., by reduction of metal oxide. The nature of reducing agent used depends upon the activity of metal.
For example: If the metal is very reactive like Na, K, electrolytic reduction method is used whereas the less reactive metals like Cu, Sn, Fe can be reduced by chemical reducing agents like CO, H2, etc.
Reduction by carbon (Smelting):
The process of using carbon in form of coke, charcoal, CO to reduce metal oxides to respective metals, is termed as smelting.
For example: Fe2O3 + 3 CO → 2 Fe + 3CO2
Reduction by hydrogen:
Because of highly inflammable nature of H2 it is used as a reducing agent especially for oxides of Tungsten (W) and Molybdenum (Mo).
For example: MO3 + 3H2 → M + 3H2O
Reduction by Aluminium:
Reduction of metal oxides to respective metals by using aluminium is known as alumino thermite or Gold Schmidt thermite process. It is mainly used to reduce Cr2O3 or Fe2O3
For example: Cr2O3 + 2Al → Al2O3 + 2Cr
Electrolytic refining:
This method is used for Cu, Au, Ag, Pb, zinc, aluminium etc. The impure metal is made anode and pure metal is cathode. The following reaction takes place:
Anode: M → Mn+ + ne‒
Cathode: Mn+ + ne‒ → M
The impurities are collected at the bottom of anode and are called anode mud.
Zone refining method:
It is the method used to get elements of very high purity like Ge, Si, B, Ga. The method is based on the principle that the impurities are more soluble in the melt than in the pure metal. The method is specially useful for producing semiconductors of very high purity.
Distillation:
This method of purification is useful for low boiling metals. Examples are purification of zinc and mercury. Liquation In this method of purification, a low melting metal like tin can be made to flow on a sloping surface and thus separated from higher melting impurities.