The process of extraction of metal in the free state from its ore is called Metallurgy.Some common steps involved in the metallurgical operations are:
1. Crushing and grinding of the ore.
2. Concentration or benefication of the ore.
3. Production of metal from the ore.
4. Purification of the crude metal.
Here,we shall be discussing in detail about "concentration of the ore"
Benefication of ore concentration:
The ore obtained from the earth's crust is associated with rocky and silicon impurities.It is essential to get rid of these impurities so that they may not interfere in the process of extraction.The removal of impurities from the pulverised ore is called concentration or benefication of ore.The benefication of the ore is carried out by any of the following methods depending upon the nature of the ore and also the impurities present in the ore.
Process of ore concentration:
(i)Levigation or gravity separation method:This method is usually applicable to oxide ores in which the ore particles are heavier than the impurities.The powdered ore is washed with running stream of water.The lighter impurities are washed away leaving behind the heavier ore particles.
(ii)Froth floatation process:This process is generally used for the concentration of sulphide ores.The finely powdered ore is taken in a mixture of water and pine oil.The oil acts as a frothing agent.The contents are kept agitated by a blast of air.As a result of agitation,the froth is produced.The ore particles are preferentially wet by the oil and are carried to the surface by the foam. The gangue material which is preferentially wet by water sinks to the bottom of the tank.The foam at the surface is transferred to another tank where it is washed with water to recover the ore particles.
(iii) Magnetic separation of impurities:This method is usually employed for the separation of magnetic impurities from non -magnetic ore.For example,tungstates of iron and manganese from tin stone are separated by this method.The powdered ore is dropped over a belt revolving around the rollers,one of which is magnetic.The magnetic rollers attract the magnetic part of the ore and they are collected in a heap in front of it.
(iv) Leaching: It is a chemical method for the concentration of the ore.In this process,the powdered ore is dissolved selectively in certain acids,bases or other suitable reagents.The impurities remain undissolved as sludge.The solution of the ore is filtered and the ore is recovered by precipitation or crystallisation.
Besides these methods,other methods of concentration of ores are also used which are based on specific properties.Some of these are:electrostatic separation,amalgamation,liquation and optical separation etc.
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