Question

The process by which lighter earthy particles are freed from the heavier particles using water is/are__________(This question has multiple correct answers)
A.Gravity separation
B.Levigation
C.Hydraulic washing
D.leaching

Answer 1

Gravity separation, levigation, hydraulic washing and leaching are different methods of concentrating an ore, in order to extract the crude metal from it.

Complete step by step answer:
Let us try to understand each option in detail. This will help us in choosing the most suitable set of correct options for the above asked question.
Metallurgy is the process of extraction of a metal in a pure state from its respective ore. A mineral can be defined as a naturally occurring substance obtained by mining which contains the metal in free state or combined state (form). An ore is the mineral, from which the metal can be economically and conveniently extracted. Depending upon the nature of metal, nature of ore and the impurities present in it, there can be different methods used in the extraction of metals. The common steps that are involved in the extraction of metals are as follows-
Step 1- crushing and grinding of ore
Step 2- concentration of ore
Step 3- extraction of crude metal from extracted ore
Step 4- purification of crude metal
The process by virtue of which unwanted impurities such as sand, clay, etc., are removed from the ore is termed as concentration of ore. It can be carried out by following methods-
Gravity separation or levigation or hydraulic washing: This method is based on the differences in gravities of the ore particles and the gangue particles. When the powdered ore is fed into a stream of running water, due to differences in their specific gravities, heavier ore particles are retained while lighter impurities are washed away.
Magnetic separation: This method is based on the differences in magnetic properties of the ore components. It has been found out to be useful when either an ore or the gangue (but not both) exhibit attraction by a magnet.
Leaching: This is a chemical method of concentration of ore. In this method, a soluble material is extracted from the ore, by dissolving it in a suitable solvent. This method is useful for concentrating ores of aluminium, silver, gold, etc.

Among all these methods of concentration of ores, gravity separation, levigation, hydraulic washing methods are based on methods based on the difference in densities of the metallic ore and gangue particles. In these three methods, powdered ore is first treated with a stream of running water, and because of this the lighter gangue particles are washed away and heavier ore particles are left behind. But, leaching follows a different mechanism. In this method, ore is made to dissolve in a suitable reagent (not water) but not the impurities.

So, the correct options are A, B and C.

Note:
Hydraulic washing can be carried out in two ways- hydraulic washing by Wilfley table and hydraulic classifier method/Levigation. Out of these two methods, Wilfley table method is used for concentration of native gold ore or ore of tin and the later one is used for concentration of ores of iron, gold, chromium, etc.