On the Interpretation of Floatability Using the Bubble Load

Flotation models describe the separability of mineral particles using a loosely defined term known as floatability or probability of collection, a response of particles in the pulp zone of a flotation vessel, unrelated to events in the froth phase. The Bubble Load measurement samples the particles that have attached to bubbles in the pulp zone and, thus, should give an indication of floatability. This thesis investigates the role of floatability in flotation models, and assesses the Bubble Load measurement as a direct estimate of floatability. Towards these ends, continuous pilot-scale flotation tests were carried out in which collector addition rate was varied. This allowed the floatability of mineral particles to be back-calculated on a size-by-liberation basis and be compared to the measured Bubble Load. Contrary to expectations it was found that, with increasing collector addition rate, the “floatability” of a majority of galena particle classes did not increase after 5 mg/kg of collector, while the measured Bubble Load actually decreased. This was found to be due to the stability of the froth increasing with collector addition rate, causing more galena to reach the concentrate, and less to drop-back to the pulp phase to be reattached. Conversely, there were other particle classes (such as sphalerite and coarse galena) where the expected trends were found, namely increasing floatability and Bubble Load with collector addition rate. These results indicate a high level of interdependence between the pulp and froth zones of the studied flotation cell through the flow of material between them (internal reflux). In the case of galena, the flow of material returning via drop-back from the froth had a greater impact on the Bubble Load than the galena in the feed made sufficiently hydrophobic to attach to bubbles. This means that, for the system studied here, the Bubble Load measurement does not provide a direct estimate of mineral particle floatability, defined as a sole consequence of pulp phase events. Moreover, for the current case, it appears that this definition of floatability is not sufficient to capture the interactions between the pulp and the froth. It is recommended that pulp and froth zone flotation models be developed in concert, recognising the interaction between the two zones, and that flotation models be formulated with due allowance for the material transport paths within a flotation vessel. It should be recognised that “floatability” is an aid for the imagination; a term for a process, rather than a particle “property” to be measured. An extension of the kinetic chemical reaction analogue, incorporating flotation sub-processes, is suggested/revived, to give some phenomenological basis to kinetic flotation models