Classification of flotation frothers based on their foam generation ability under dynamic and static conditions

Abstract

Frothers are widely used in flotation to primarily generate air bubbles, aid gas dispersion, and form a stable froth that provides a selective separation of particles. The current frother classification approaches are based on only three characteristics of the frothers. A number of studies have reported the use of characteristics of frothers including critical coalescence concentration and the ability to create an effective foam under dynamic conditions, as well as foam stability to group frothers. Moreover, the majority of studies are based on a two-phase system, ignoring to some extent the effect of particles, which is relevant to flotation. This thesis explores the effect of frother type on foam stability under dynamic and static conditions and provides a framework to classify frothers based on their foam generation ability. Three foam stability variables, dynamic foam stability index, static foam stability index, and decay rate index are quantified for eighteen different frothers. Four more frothers characteristics reported in the literature, MW, HLB, CCC, DL were defined. The hierarchical cluster analysis was conducted to group frothers based on similarity and provide a category system. Based on the similarities, frothers were grouped into four categories as opposed to the binary frother classification reported in the literature. The selectivity of frothers increases from Group 1 to Group 4, whereas frothers decrease their powerfulness from Group 1 to Group 4. To complement the proposed frother classification and assess the relevance to flotation, the effect of particles on the foam generation under dynamic conditions was explored for four frothers from different families. In terms of froth stability, the three-phase system showed a similar frother ranking to the two-phase system, except that TPG behaved as a more powerful frother in the presence of hydrophobic particles than MIBC. It was also found that the proposed frother classification system in a two-phase system translates well to the three-phase system as frothers were clustered in the same groups. Further insight into the changes of foam stability was gained by simulating the coalescence of two air bubbles at various frother concentrations using the volume of fluid method (VOF). It was observed that an increase in frother concentration damped the oscillation of coalesced bubbles by the surface elasticity, suggesting that the bubble surface area moves at a lower velocity, which may reduce the motion of particles attached to the interface and consequently, their detachment during the merging of two bubbles.