Question

what is the role of depressant in froth floatation process?

Answer 1

Depressants are added to prevent certain type of particles from forming the froth with the air bubbles.
For example -  to separate zinc sulphide(ZnS) ore from lead sulphide(PbS) ore,sodium cyanide is used as adepressant which acts as adepressant for ZnS but does not prevent PbS from the formation of froth.
Thus, the two ores can easily be separated.