Meaningful contact angles in flotation systems: critical analysis and recommendations

Froth flotation was invented in the nineteenth century. Since then, many laboratories have been committed to both fundamental and applied research on the collection of particles by dispersed gas bubbles in aqueous solutions of electrolytes, in particular those working on the processing of natural resources. However, despite the tremendous progress made in the characterization of particles and their surfaces and understanding particle–bubble interactions, supported by detailed recordings of gas bubble attachments to both bulk specimens and particles, the flotation process remains poorly correlated with the wetting characteristics of particle surfaces. In fact, the contact angles used frequently to describe the wettability of mineral surfaces remain among the most controversial, misunderstood and misinterpreted values in mineral processing literature. Contrary to wide-ranging beliefs, it is the authors’ position that neither the methodology of contact angle measurements nor the selection of contact angles important to the particle flotation process is properly executed when analyzing the flotation process. In this paper, the authors provide a brief personal perspective on some of the misconceptions on contact angles and the importance of additional fundamental studies in the area of mineral particle flotation.