Frothers refer to a class of surfactants capable of lowering the surface tension of water to generate foam, thereby enabling air bubbles within an aerated flotation pulp to adhere to mineral particles selected for flotation.
The molecular structure of frothers bears similarities to that of collectors; most are amphipathic surfactants composed of both polar and non-polar functional groups.
One end of the molecule features a polar group, while the other end features a non-polar group. In the case of collectors, the polar group is affinic toward solids (minerals), whereas the non-polar group is affinic toward air.
Conversely, the polar groups of frothers are hydrophilic (water-loving), while their non-polar groups are aerophilic (air-loving). By orienting themselves specifically at the water-air interface, they reduce the surface tension of the water, thereby exerting a foaming effect. These compounds are further categorized into non-ionic and ionic types; among them, non-ionic surfactants generally demonstrate superiority in terms of variety, functional efficacy, and overall performance. Non-ionic frothers typically lack collecting properties, whereas ionic frothers often possess collecting capabilities in addition to their foaming function.
Frothers exhibit strong adsorption capabilities at the gas-water interface; ideally, superior frothers do not adsorb onto mineral surfaces. Most frothers significantly reduce the surface tension of water, enhancing the dispersion of air within the pulp and influencing the size of the air bubbles formed therein; specifically, as the size and density of the mineral particles undergoing flotation increase, the required size of the air bubbles must correspondingly increase. Furthermore, these bubbles remain relatively stable, preventing bubble coalescence and facilitating the formation of the mineralized foam layer required for effective flotation at the surface of the pulp.
The generation of air bubbles within a flotation pulp relies primarily on the various types of aeration and agitation mechanisms incorporated into the flotation equipment, as well as the addition of an appropriate amount of frothers to the pulp.
Frothers are, by definition, surfactants; their molecular structure consists of non-polar, lipophilic (hydrophobic) functional groups and polar, hydrophilic (lipophobic) functional groups, thereby forming a so-called "amphiphilic structure"-a molecule possessing affinity for both water and oil. The lipophilic group may be an aliphatic, alicyclic, or aromatic hydrocarbon group-or such a group containing heteroatoms such as oxygen or nitrogen. The hydrophilic group typically consists of moieties such as carboxyl, sulfonic acid, sulfuric acid, phosphonic acid, amino, nitrile, thiol, halogen, or ether groups.
When a foaming agent is added to water, the hydrophilic groups insert themselves into the aqueous phase while the lipophilic groups insert themselves into the oil phase (or orient themselves toward the air), thereby forming an ordered arrangement at the interface or surface; this arrangement results in a reduction of the interfacial or surface tension. Generally speaking, an aqueous solution containing even a minute amount of foaming agent will exhibit foaming properties.
