What is the role of collector and depressants in froth flotation process?

Depressants are chemicals that inhibit the flotation of minerals.  They are used to improve the selectivity of a flotation process.  They often make it feasible to separate minerals that were initially floated together.

The response of many minerals to the flotation process is often dramatically affected by pH.  Flotation circuits are often operated at a pH range of 7.5 to 11.5.  The exact range at any given plant is optimized for the ore at that site.  Lime is often used to raise the pH of the pulp and also reduce the flotation of iron pyrite.