In mineral flotation the challenge is to maximize the recovery of desired minerals while rejecting unwanted components.

Depressants are required to give a low affinity to active sites on valuable mineral surfaces and a high affinity for minerals and some sulfides. Typically, depressants prevent collector adsorption or bubble attachment to unwanted mineral surfaces. This increases the selectivity of flotation, rendering certain minerals hydrophilic and preventing them floating to the surface.

Dispersing reagents are surface charge modifiers. When processing complex ores their purpose is to prevent aggregation of fine and gangue particles. The dispersant controls the charge density at the solid-liquid interface or the electrical charges of fine and ultrafine particles so they remain as discrete, stabilized particles in solution. By selectively targeting gangue surfaces and rendering them hydrophilic (water-avid), gangue is therefore less likely to float or be entrained in the froth phase.