Flotation, or froth flotation, is one of the most important and widely used mineral processing techniques for the selective separation and concentration of valuable mineral particles from their gangue (waste rock) based on differences in the surface chemistry and hydrophobicity (water repellency) of the mineral surfaces. The process was developed in the early twentieth century and has since become the dominant concentration technology for sulfide minerals, and is also widely applied in the processing of non-sulfide minerals, industrial minerals, and coal. In mining, flotation is a critical unit operation in the treatment of gold ore (refractory and free-milling), copper, nickel, zinc, and lead ores, and has emerging applications in iron ore and phosphate processing.
In the flotation process, finely ground ore slurry is conditioned with chemical reagents that modify the surface properties of the target minerals. Collector reagents adsorb onto the surface of the target mineral, rendering it hydrophobic. Frother reagents reduce surface tension at the air-water interface to produce a stable, persistent froth layer at the top of the flotation cell. Modifier reagents — including pH regulators (lime, sulfuric acid), activators, and depressants — control the selectivity of the collector, enhancing recovery of the target mineral while suppressing the flotation of unwanted minerals. Air is introduced into the conditioned slurry, and hydrophobic mineral particles attach to the rising air bubbles, are carried to the froth layer, and overflow into a concentrate launder, while hydrophilic gangue particles remain in the pulp and are discharged as tailings.
In gold mining, flotation is used to produce a gold-bearing sulfide concentrate that is either shipped to a smelter or treated by pressure oxidation (POX) or roasting prior to cyanide leaching to liberate refractory gold. In iron ore processing, reverse flotation is used to remove silica and other gangue minerals from iron ore slurries, improving the iron grade of the final product. Flotation circuit design, reagent selection, and operational parameter optimization (pH, air flow, froth depth, pulp density) are critical determinants of metallurgical recovery and concentrate grade.