Flotation, also termed froth flotation, is a physicochemical separation process used in mineral and rock processing to selectively separate valuable minerals from gangue material based on differences in surface hydrophobicity. Hydrophobic particles attach to rising air bubbles and are carried to the surface of a pulp suspension, where they form a mineral-laden froth that is skimmed off, while hydrophilic particles remain in the pulp and report to the tailings stream.
Principle of Separation
The process relies on conditioning the surface chemistry of mineral particles so that target minerals become water-repellent (hydrophobic) while gangue minerals stay wettable (hydrophilic). This is achieved through the addition of chemical reagents: collectors adsorb onto the target mineral surface to induce hydrophobicity, frothers stabilize the air bubbles at the pulp surface to form a persistent froth layer, and modifiers such as depressants, activators, or pH regulators control selectivity between mineral species. Pulp pH is a critical control variable and is typically adjusted with lime or soda ash depending on the ore system.
Feed Preparation
Flotation requires the ore to be ground to a liberation size at which the target mineral is physically separated from gangue. Typical flotation feed particle sizes range from approximately 10 µm to 150 µm, with finer grinds required for disseminated or fine-grained ore bodies. Oversize or undersize particles reduce flotation efficiency: coarse particles may detach from bubbles due to gravitational forces, while ultrafine particles can report to froth indiscriminately through entrainment.
Equipment
Flotation is carried out in flotation cells or flotation columns. Mechanical flotation cells use an impeller to disperse air and suspend solids, with industrial cell volumes ranging from a few cubic meters up to approximately 300 m³ in large-scale copper and iron ore operations. Flotation columns rely on counter-current contact between rising air bubbles and descending slurry without mechanical agitation, commonly used for cleaner stages requiring higher selectivity. Air bubble diameters in flotation systems typically range between 0.5 mm and 2 mm, influencing collision efficiency with particles.
Applications
Flotation is widely applied in the beneficiation of sulfide ores such as copper, lead, zinc, and nickel, as well as in processing of coal, phosphate, potash, and industrial minerals. It is also used in the recovery of precious metals when associated with sulfide gangue. In aggregate and quarry operations, flotation is less common than gravity or magnetic separation methods, but it is applied where fine-grained ore bodies require chemical surface differentiation for economic recovery.
Flotation in Coverage of This Publication
In the context of mobile construction equipment, this publication has used the term "flotation" in a distinct technical sense, referring to the ability of a machine to distribute weight and reduce ground pressure on soft terrain. The article "Articulated Dump Truck Drivetrain and Differential Lock Systems Explained" discusses how the articulated chassis structure of ADTs improves flotation in soft or muddy conditions by distributing weight more evenly across both axle sets (read more). This usage should not be confused with froth flotation as a mineral processing method described above.
