Trivalent metal salts such as iron(III) salts and aluminum salts are mostly used as flocculants, but other hydroxide-forming agents such as milk of lime, soda or sodium aluminate are also used. Flocculants form larger micro-flocs from the colloids, which can be easily removed by filtration. | If solids removal by sedimentation or flotation is desired, a flocculation aids is used in addition to the flocculant, which forms larger macro-flakes from the micro-flakes.