Flotation is a complex process with many variables

(Harris, C C, 1975. Flotation Machines, in Flotation, ed. M.C. Fuerstenau, pp 753-815 AIME: New York)

Particle shape is one of the affecting variables on the particle-bubble attachment   

Ore grinding in froth flotation is an important step to liberate the valuable mineral particles from the gangue (Forssberg et al., 1993). When considering particle shape in minerals processing, comminution is of particular interest as this is the process where the particles attain their shape which in turn affects classification and separation stages downstream. Studying the shape characteristics of progeny particles can also be used to interpret breakage mechanisms within milling devices and in some instances, can even be related to the degree of liberation (Leroy et al., 2011). Particle shape can have an impact on numerous processes through its effect on drag coefficients, rheology, and particle bubble interactions.

Froth flotation is a separation process which plays a major role in the mining industry. The flotation process essentially relies on the attachment of solid particles on the surface of gas bubbles immersed in water. The attachment of a solid particle on the surface of a gas bubble can be divided into three successive stages: the particle approach, the collision with the bubble and the sliding down the gas–bubble interface (Schulze, 1989; Albijanic et al., 2010). The downward sliding motion of the particle is caused by the gravity and also by the hydrodynamic forces arising from the local water flow around the rising bubble. Should the particle approach the bubble surface within the range of attractive surface forces, a thin intervening liquid film between the gas–liquid interface and the solid–liquid interface forms. The liquid film eventually drains, leading to a critical thickness at which rupture occurs (Ralston et al., 1999). The rupture of the liquid film results in the formation of a stable three-phase contact (Schulze, 1992).

Figure 1. The fact that the recovery of particles by true flotation is influenced by also particle shape has been widely reported by some researchers (Koh et al., 2009; Vizcarra et al., 2011; Ulusoy and Yekeler, 2005).

Figure 2. Flotation rate as a function of particle size for angular and spherical particles (Adapted from Koh et al. (2009).

Koh, P.T.L., Hao, F.P., Smith, L.K., Chau, T.T. and Bruckard, W.J., 2009. The effect of particle shape and hydrophobicity in flotation. International Journal of Mineral Processing 93(2), 128-134.