W. Richard Bowen and Nidal Hilal 4

100 3. QUANTIFICATION OF PARTICLE–BUBBLE INTERACTIONs
Normalised force, F/R (mN/m)
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Velocity
Force
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Separation distance, D (nm)
FIGurE 3.8 The relative velocity V and the measured (points) and hydrodynamic
forces (line), for a piezo-movement speed of 48.8 �m s �1 . Reprinted from [12], Copyright
2004, with permission from Elsevier.
3.8 ConCLuSIonS
The AFM-based colloid probe technique has been used to investigate the
interactions between single particles and air bubbles in aqueous solution
with the aim of increasing the basic understanding of processes dependent
upon this type of interaction. The effect of such particle properties as the
degree of hydrophobicity has been examined in relation to properties such
as particle–bubble adhesion, the favourability of long-range interaction
forces to particle–bubble attachment, as well as measured contact angles
in a number of studies. Measurements have also begun to characterise
the effect of force and approach speed on these interactions. As froth flotation
is a dynamic process, an understanding of the forces and kinetics
involved in particle–bubble attachment may be necessary to marry AFMbased
measurements to what is happening in the flotation chamber or
other related industrial processes. The body of literature which now exists
is not yet complete enough to give a full insight into how particle–bubble
interactions on the single interaction level mediate the bulk process of
froth flotation. In addition, measurements so far utilise micro-spheres with
an idealised geometry. Particles used in mineral separation are more likely
to be rough and irregular and quite likely more heterogeneous, leading to
more complexity in their attachment to bubbles. In the industrial processes,
there are a large number of different surfactants and other chemicals used
to modulate mineral separation, depending upon the properties of the
minerals of interest. In the AFM-based literature, only a small number of
commonly available surfactants have been used. On the whole, the use of
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Relative velocity, U (µm/s)