Effect of platy gangue minerals in sulfide flotation: Part 2: Mechanisms

Abstract

The presence of the usually unwanted, hydrophilic ore particles (gangue) in a mineral flotation froth plays a critical role. While they reduce the grade of the concentrate, they are also an important influence on the dynamical structure of the froth and its ability to transport value particles into the launder for ultimate recovery. This paper discusses how the shape and size of these gangue particles affect their transport through the froth zone under conditions typical of commercial sulfide flotation, but without hydrophobic ore particles present.Advective transport of gangue particles via entrainment depends on slurry drag due to the upward motion of air bubbles and the drainage effects of gravity on the liquid and solid phases confined in the network of fluid channels in the froth. In a companion paper (Bhambhani et al., 2023a) a significant increase in gangue transport rates through the froth zone was observed when a copper sulfide ore was mixed with platy mica (higher aspect ratio) compared to when the same ore was mixed with globular (lower aspect ratio) silica. It was hypothesized that this increased upwards transport rate was related to the greater upward drag experienced by the platy mica particles as compared to the lower aspect-ratio silica particles of comparable size. This hypothesis was tested by conducting froth sampling experiments, reported here, under increased upward drag conditions for the suspension and thus increased upward advective forces on the particles. It was observed that the entrainment vs particle size curves shifted upwards for the coarser sizes for both mica and silica. This was unexpected. It was additionally hypothesized that as the particle size approached the size of the channels (Plateau borders), through which settling particles must pass if they are to move downward, the particles become more confined and on average experience less downward motion. Platy mica particles of a certain sieve size are more susceptible to confinement in the channels than their lower aspect-ratio counterparts due to their reduced mass per particle. This was suggested from froth sampling experiments where drag and drainage were balanced in one case, and more drag dominated in the other.