Froth Flotation

Froth Flotation has been used in mineral processing industry since the mid of the XIX century with many of its broad-based applications to mineral recovery extensively developed at the beginning of the last century. Today, hundred of minerals, including almost all the world's copper, lead, zinc, nickel, silver, molybdenum, manganese, chromium, cobalt, tungsten, and titanium, are processed using froth flotation. Another major use of froth flotation is by the coal industry for desulphurization and the recovery of fine coal, once discarded as waste.

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.

Analysis of flotation is best approach through consideration of the overall process first, and then of its components. An ideal system would be a circuit in a steady state, supplied at a constant rate with ore having constant initial properties, a fixed optimum size distribution and its mineral surfaces pretreated to yield optimum floatability. The feed would flow through machines and circuits selected, designed, and adjusted to give an optimum separation, resulting in production of concentrates at a fixed rate and grade, and with an associated recovery. The optimum combination would have been determined by economic criteria, and could be changed according to market conditions. With such ideal conditions maintained, no operation of the circuit would be required except to compensate for wear and other mechanical considerations. Real systems obviously do not fulfill these ideal conditions, mainly because of feed variations or disturbances. These originate outside the flotation system and are not under its direct control. However when their effects on flotation performance are identified, they can be compensated for by adjustment of the control variables which are available within the system.

Flotation control depends on the interactions among multiple effects which originate broadly in three areas: ore and mineral properties; pretreatment by size reduction and by surface chemistry modification; and flotation cell and circuits characteristics. The most important of these properties influencing the results will have been taken into account in test work and in circuit design through their average values and through provision of control capabilities. Other factors usually have minor effects, are not controlled, and are responsible for random variations in results. They are not controlled either because control methods are not available, or they are not justifiable economically.