Explain the froth flotation process.

(N/A) Principle: The process is based on the difference in wetting properties of ore and impurities in the presence of water and a frothing agent. The following components are used in the process:
$(i)$ Frothers: These substances create froth. Examples: Pine oil,turpentine oil,etc.
$(ii)$ Collectors: Collectors help in the adhesion of ore particles to air bubbles in the froth. Example: Sodium ethyl xanthate.
$(iii)$ Froth stabilizers: These substances stabilize the froth. Examples: Aniline,cresol,etc.
$(iv)$ Depressants: These substances prevent the formation of froth with air bubbles for specific minerals. Example: $NaCN$ (sodium cyanide).
Process: In this process,a suspension of the powdered ore is made with water. The mineral particles become wet by oils,while gangue particles are wetted by water. $A$ rotating paddle agitates the mixture and draws air into it. As a result,froth is formed which carries the mineral particles. The froth is light and is skimmed off. It is then dried for the recovery of ore particles.
Role of depressants: Sometimes,it is possible to separate two sulphide ores by adjusting the proportion of oil to water or by adding depressants. For example,in the case of an ore containing $ZnS$ and $PbS$,the depressant used is $NaCN$. $NaCN$ forms a layer of zinc complex $Na_2[Zn(CN)_4]$ on the surface of $ZnS$,thereby preventing it from froth formation and allowing $PbS$ to come with the froth.
Conclusion: The sulphide ores,being lighter and easily wetted by oils,come to the surface,leaving behind the gangue. Hence,this method is used for the concentration of sulphide ores.