The dynamic behaviour of coarse particles in flotation froths. Part II: Density tracer tests

A novel flotation cell was used in which hydrophobic particles act as film breakers and sink through the froth as concentrate, while hydrophilic particles are supported by the upward flow of froth and are recovered as a top product tailings. Experimental results on density tracers showed that the behaviour of particles (within the size range tested) in the froth phase of the cell is primarily dependent on the mass of a particle. In general, the higher the mass, the steeper is the trajectory of the particle in the froth, i.e., an increase in particle mass results in an increased recovery to the concentrate. The contact angle on the particle surface has only a secondary influence on the overall particle trajectory, in that an increase in the equilibrium contact angle will result in an increased recovery. However, the particle contact angle has very little influence on the behaviour of large, high-density particles, as well as small, low-density particles.Particles will therefore only separate on the basis of contact angle as long as their mass is between an upper and lower critical value. Any particle with a mass greater than the critical value will fall through the froth irrespective of the contact angle. Similarly, the upward force component acting on a particle with mass less than the lower critical value will dominate the force balance. The particle will therefore remain supported by the froth, irrespective of the particle contact angle and bubble film rupture time. For particles within these mass limits, the effect of the contact angle increases with a decreased mass.It was further concluded that these mass limits are dependent on the operating conditions of the cell as well as the particle shape. The particle shape determines the mass to cross-sectional surface area ratio (M/A₀). Where particles therefore have the same mass, the M/A₀ ratio would govern the particle trajectory. The higher the M/A₀ ratio, the more particles would be recovered to the concentrate, while a decrease in the M/A₀ ratio would result in flatter particle trajectories in the froth, thereby increasing the probability of a particle reporting to the tailings. A mathematical model provides an understanding of the interrelationship between the various parameters.