Question

What is meant by non-wettability of the mineral particles?

Answer 1

Hint: Froth floatation method for concentration of ore in metallurgy is based on this property of non-wettability of mineral particles by water. It occurs in the solid-liquid interface. The capacity of solute to get wetted by a solvent is known as wettability. So, non-wettability is when solute does not mix with the solvent. The minerals particles such as metallic sulphides are wetted by oil and not water.

Complete answer:
In froth floatation method we have preferential wetting of solid by a particular liquid. The finely divided ore is put in water to which a small quantity of oil is added. The water is agitated which will cause froth formation. The ore is wetted by the oil and thus will be in the froth whereas the impurities are wetted by water which will eventually settle down.
Another example that deals with non-wettability of a particle is when we consider water droplets on the surface of paraffin. The drop will not wet the paraffin but in turn forms spherical drops that roll off the surface. But the same water can actually wet the surface of a mineral such as quartz. This capacity of a material to be wetted by water is termed as wettability.

Note:
Adhesive forces and cohesive forces can be used to explain the phenomenon of wetting. Adhesive forces cause water to wet a surface whereas cohesive force tend water to form droplets and act as non-wetting agents
The contact angle also plays an important role in wetting a surface. A contact angle of less than 90 degrees is usually an indicator of wetting property.