In many teaching exams including REET, UTET & DSSSB Exams etc. Science may be an interesting subject having and 30 questions of Science content and 30 questions of Science Pedagogy in REET, UTET and other State TET Exams. Science comprising of various branches of studies like chemistry, physical science, and life science.
The process of obtaining a pure metal from its ores is called metallurgy and various steps involved in the extraction are called metallurgical operations.
These operations depend upon the activity of metals. A more reactive metal (like Na, K, Mg, Ca, Al etc.) is obtained by the electrolysis of its salt in molten state, e.g., sodium is obtained by the electrolysis of fused sodium chloride. Following steps are involved in case of moderately and less reactive metals.
- Ore Concentration:
The removal of impurities from the ore is called its concentration.
It is carried out by the following methods:
(a) Gravity separation or hydraulic washing: This method is generally used for the concentration of oxide ores. Powdered ore is agitated with a running stream of water. The lighter gangue particles are taken away by water while heavier ore particles settle down.
(b) Froth floatation process: This method is generally used for the concentration of sulphide ores. In this process, powdered ore is put in a tank containing a mixture of water and pine oil. When compressed air is blown into the mixture, it gets agitated and forms froth. The ore particles stick to the froth which floats on the top and can be separated easily. The gangue particles are left behind.
(c) Magnetic separation: This method is used when one component either the ore or the impurity is magnetic in nature e.g., Wolframite (magnetic) is separated from the non-magnetic ore cassiterite (SnO2) by this method.
(d) Leaching: In this method, concentration is done by chemical methods, i.e., by using chemical reagents, gold and silver are concentrated by this method. Aluminium is also obtained by this method.
(e) Roasting: In this method, concentrated ore is heated in excess of air. It involves conversion of sulphide ores into oxides and oxidation of impurities. e.g.
(f) Calcination In this method, the concentrated ore is heated in a reverberatory furnace below its melting point, in the absence of air without addition of any external substance calcination is mainly done in case or carbonate of hydroxide ores.
The wasting away of metals layer-by-layer due to the formation of metal compounds on the surface is called Corrosion. Corrosion in case of iron is called rusting. The presence of air (oxygen) and water is essential for rusting.
Corrosion of metals can be prevented by painting, greasing, galvanization (coating with zinc), electroplating and alloying.
- Alloys: A mixture of two more metals is called alloy. Some important alloys and their uses are tabulated below.
Some Important Alloys and Their uses
|1.||Alloys of copper
iii. German silver
iv. Sterling silver
|Copper and zinc
Copper and tin
Copper, zinc and nickel
Copper and silver
|Screw wires, cooking utensils, machine parts, ornaments, musical instruments Coins, cooking utensils, ornaments, medals etc.
Silver ware, electroplating etc. Jewellery, silver ware etc.
|2.||Alloys of iron
vi. Stainless steel
|Iron and carbon
Iron, chromium, nickel and carbon
|Construction of railway lines, ships, bridges, machines etc.
Cutlery, cooking utensils, surgical instruments etc.
|3.||Alloys of aluminium
|Aluminium, copper, magnesium, manganese
Aluminium, nickel, cobalt, iron
|Making the aircraft parts, space satellite
|4.||Alloy of lead
|Lead and tin||Soldering joints etc.|
|5.||Alloy of nickel
|Nickel, iron, chromium and manganese||Electrical heating elements|
|6.||Alloy of mercury Amalgam||Mercury, silver, tin and zinc||Teeth filling|