Froth Flotation

    Particles attached to bubbles

    Particles attached to bubbles

    Froth Flotation is a surface-chemistry process of separation of fine solids that takes advantage of the differences of wettability at solids particle-surfaces. Solid surfaces are often naturally wettable by water and termed hydrophilic. A surface that is non-wettable is water repelling and termed hydrophobic. If a surface is hydrophobic, it is also typically air attracting termed aerophilic, and is strongly attracted to an air interface, which readily displaces water at the solid's surface. In froth Flotation, separation of a binary solids mixture may be accomplished by the selective attachment of hydrophobic solid particles to gas bubbles (typically air). The other hydrophobic solid particles remain in the liquid (typically water). The difference in the density between the air bubbles and water provides buoyancy that preferentially lift the hydrophobic solids particles to the surface where they remain entrained in a froth which can be drain off or mechanically skimmed away, thus, effecting the separation. Froth Flotation if often used to separate solids of similar densities and sizes, which prevent other types of separations based upon gravity that might other wise be employed. It is especially useful for particles below 100 µm, which are typically too small for gravity separation using jigging and tabling. The lower size limit for flotation separation is approximately 35 µm; although particles as small as 1 µm can be separated. At these small particles sizes, it may be difficult take advantage of surface properties differences to induce selective hydrophobicity. On the other hand particle greater than 200 µm tend to be readily sheared from the bubble surfaces by collision with other particles or vessel walls. However, relativity low density materials, such as coal may be successfully separated up to 1600 µm in some systems.