Froth flotation is a physico-chemical mineral separation process that selectively concentrates valuable minerals from gangue (waste) minerals by exploiting differences in the surface wettability (hydrophobicity) of mineral particles in an aerated slurry. It is one of the most widely used and economically important mineral processing operations in the global mining industry and is fundamental to the processing of gold sulfide ores, iron ore, base metal ores, and to a lesser extent, bauxite and diamond recovery operations.
The flotation process involves grinding the ore to a fine particle size sufficient to liberate individual mineral grains, conditioning the pulp with specific reagents, and then introducing the conditioned slurry into flotation cells where air is dispersed as fine bubbles. Hydrophobic mineral particles, rendered so by the selective adsorption of collector reagents (such as xanthates, dithiophosphates, fatty acids, or thionocarbamates), attach to the rising air bubbles and are carried to the surface of the cell, where they accumulate in a mineral-rich froth that overflows into concentrate launders. Hydrophilic gangue minerals remain in the pulp and are discharged as tailings.
Frother reagents (such as MIBC — methyl isobutyl carbinol — or pine oil) stabilize the froth and control bubble size to optimize particle–bubble collision efficiency. Depressant reagents are used to prevent specific minerals from floating — for example, lime (CaO) depresses pyrrhotite in gold circuits, and sodium cyanide is used to depress iron sulfides in copper flotation. Activators are used to make specific minerals more amenable to collector adsorption.
In gold processing, flotation is used to pre-concentrate sulfide minerals hosting refractory gold prior to biological oxidation (BIOX), pressure oxidation (POX), or roasting, significantly reducing the mass and volume of material requiring high-cost treatment. In iron ore processing, reverse flotation is used to float silica (quartz) away from iron oxide minerals, producing a high-grade iron concentrate. Froth flotation performance is typically measured by concentrate grade and metal recovery, and is continuously optimized through real-time process control and regular metallurgical sampling and mass balancing.