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Class 10, Science, Chapter-3, Lecture-3, Metallurgy (Notes)


MINERALS: 

The inorganic metal-bearing compounds that occur naturally in the earth’s crust are known as minerals.

Contents of minerals-
1.    Metal in combined state
2.    Gangue or Matrix – The unwanted material contained in the mineral are called gangue or matrix

ORE:   

 The minerals from which metals can be extracted easily and profitably are called ores.

METALLURGY: 

The extraction of metals from their ores and refining them for use is called metallurgy.

Steps Involved in Metallurgy-
1.    Preliminary Treatment
        (i)    Concentration to ore    (ore dressing).
        (ii)   Conversion of Concentrated ore into metal oxide.
2.    Reduction of metal oxide to metal.
3.    Refining of impure metal.

ORE CONCENTRATION: 

The process of removal of unwanted impurities from the ore is called ore concentration or ore dressing.

Methods of Converting Ores to Oxide:

1. Calcination:
    The process of heating the concentrated ore in the absence of air is called calcination.
    Calcination is used for CARBONATE ORES     

2. Roasting:
    The process of heating the concentrated ore in the presence of air is called roasting
    Roasting is used for SULPHIDE ORES.         

DIFFERENCES BETWEEN:  

CALCINATION      ROASTING

1. It is the process of heating in the absence of air.

1. It is the process of heating in the presence of air.

2. It is used for converting carbonate ores.

2. It is used for converting Sulphide ores.

3. In the process CO2 is evolved.

3. In the process SO2 is evolved.

4. It can be used for removing water from hydrated ores.   

4. It cannot be used for removing water from hydrated ore.

REDUCTION: 

The conversion of metal oxide into metal is called reduction.
Three types –        
   1.  Thermal Reduction      
   2.  Chemical Reduction        
   3.  Electrolytic Reduction.

Thermal Reduction:

The conversion of metal oxide into metal by heating alone is called thermal reduction. (For Less Reactive Metals)

Chemical Reduction:

The conversion of metal oxide into metal by using reducing agents is called chemical Reduction.
1. Reduction by carbon         
2. Reduction by Aluminium (THERMIT PROCESS)     
    •  These are Highly exothermic reactions
    •  Reaction of iron with Aluminium is used for welding railway tracks

ELECTROLYTIC REDUCTION (For Highly Reactive Metals)

The conversion of metal oxides into metal by electrolysis of the fused metal oxide is called electrolytic reduction.

In the process:

  1. Carbon rods act as anode            (+ve)
    Carbon lining acts as cathode      (–ve)
    Fused metal oxide acts as electrolyte
  2. During electrolysis, Metal deposits at cathode (–ve)

REFINING OF METALS:

The process of purification of impure metals is known as refining of metals.

Examples of methods of refining: Liquation, Distillation, Electrolytic refining

Factors on which the Method used for Refining depend: 

  1. The nature of the element     
  2. The nature of impurities present in the element.

ELECTROLYTIC REFINING:

The purification of impure metal by electrolysis of metal salt in which impure metal acts as anode and pure metal acts as cathode is called electrolytic refining.  (used for copper, gold, zinc, chromium, nickel)

In the process:

  1. Impure metal acts as anode  (+ve)
    Pure metal acts as cathode   (–ve)
    Metal salt solution acts as electrolyte
  2. Pure metal is deposited at cathode
  3. More reactive metals pass into the solution.
  4. Less reactive metals fall at the bottom as ANODE MUD

Carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc.

Reason:
These metals are highly reactive and their affinity towards oxygen is greater than that of carbon.
So, carbon cannot reduce the oxides of these metals.