Does hemimicelle concentration (HMC) coincide with critical aggregation concentration (CAC) in flotation?

Flotation recoveries of oxide, silicate, and salt-type minerals when plotted against collector concentration exhibit a break point followed by a sharp increase. This threshold point called hemimicelle concentration (HMC) has been traditionally characterized by the formation of two-dimensional surfactant patches on the solid surface. The condensed phases have been identified by a variety of techniques since their inception in the early 1960s. Conversely, in another hypothesis, this breakthrough point was ascribed to surface precipitation of collector species on the mineral surface. Despite these controversies, a clear understanding of this issue has not been agreed upon. In fact, both occurrences are thermodynamically indistinguishable as they represent a similar property of surfactant deposition on the surface. In this context, the same researchers have stated that surface precipitation occurs way below the appearance of bulk precipitates. This issue of threshold point is a logical phenomenon and well documented in flotation literature. However, the alternatives discussed above have been usually taken for granted due to a lack of sufficient evidence. The objective of this paper is to present an alternative vision to the flotation literature. In this paper, we are proposing a third mechanism in which the threshold point is shown to correspond to the critical aggregation concentration (CAC) of particles in the bulk. Micro-flotation, zeta potential, and aggregation studies along with Fast-Cam recordings illustrate that aggregation of particles from this critical breakthrough point onward accelerates due to the formation of both hemimicelles and surface precipitates and particles undergo more intensive assemblage leading to higher flotation kinetics. The XDLVO calculations also confirm these findings.