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The Emergence of Techniques and Methodologies for
Measuring Bubble–Particle Attachment
Lisa October, Malibongwe Manono, Kirsten Corin
Centre for Minerals Research, Department of Chemical Engineering, University of Cape Town, South Africa
ABSTRACT: Understanding the effects various parameters have on the separation efficiency in flotation
has been topical for many years, particularly at the bubble-particle level. Many experimental techniques
emerged to measure the interaction between bubble and particle. The induction timer is a popular choice for
measuring bubble-particle interactions and has transformed over the years not only in physical form but in how
measurements are conducted. This work initially considers the various techniques for assessing bubble-particle
interactions, then goes on the journey of how the induction timer has evolved. This work concludes with results
from the Automated Contact Time Apparatus (ACTA) which is a recently developed technique which is aimed
at being a quick diagnostic tool to determine bubble-particle attachment probability under various conditions.
INTRODUCTION
In froth flotation, the attachment of mineral particles to
air bubbles causes the separation of hydrophobic valuable
particles from hydrophilic gangue particles. As a result, the
bubble-particle attachment sub-process is crucial in achiev-
ing efficient separation in froth flotation. Understanding
bubble-particle attachment under various conditions,
therefore provide insights into the dynamics of the interac-
tions between bubbles and particles and assists in designing
more efficient flotation processes.
The process of bubble-particle attachment occurs in
three steps and is illustrated in Figure 1.
Bubble-particle attachment starts when a bubble and
particle are in close proximity to each other, a liquid film
then develops at the air-water and solid-water interfaces.
This film thins until it reaches critical thickness. The bubble
and particle are now even closer when the second step occurs
– the liquid film becomes unstable and ruptures resulting
in a three-phase contact line, upon which bubble-particle
attachment occurs. In the final step the bubble-particle
contact line spreads across the surface, resulting in a stable
wetting perimeter where the contact angles are in equilib-
rium (Albijanic et al., 2010). The total time it takes for
these three steps to occur is termed the attachment time.
The faster the liquid film at the air-water and solid-
water interfaces thin, the higher the chance of that particle
floating. The induction time is often used to predict the
particles susceptibility to float, which is the time it takes for
the first step of the attachment process to occur.
For bubble-particle attachment to occur, the time
it takes for a particle to attach to an air bubble must be
shorter than the time in which the particle is brought in
contact with the air bubble, known as the contact time.
t t
attachment contact #(1)v
The collision contact time and sliding contact time theo-
ries were both formulated to measure the bubble-particle
attachment in flotation cells. The collision contact time
theory caters for high momentum bubble-particle interac-
tions this generally occurs with particles of large diameter