2782 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Figure 12 shows the stabilities of foams in a pilot-
scale flotation column. The experimental setup shown in
Figure 7 was used to identify the preferred location of the
loudspeaker for improving foam stability. The frother used
was polypropylene glycol (PPG) with an average molecu-
lar weight of 425 g/mol. The PPG solutions were prepared
using local tap water. The loudspeaker (Monarcor AR-50)
was used with the frequency set at 400 Hz. The foam stabil-
ity was indicated by the flowrate of the overflowing foam,
which should be somehow proportional to the air recovery,
an indicator for foam/froth stability (Hadler and Cilliers,
2009). Use of the sound systematically improved foam
stability, at any given frother concentration tested and any
location of the loudspeaker installed. It was observed that
the location of the loudspeaker would be preferably 5 cm
below the foam surface if the speaker was positioned less
than 4cm below the foam surface, it would tend to reduce
the foam stability if the speaker was located 15 cm (or
more) below the foam surface, the improvement of foam
stability would become smaller.
Effect of Sound on the Stability of Foam Films
(Representing Bubble-Bubble Interaction) and Wetting
Film (Representing Bubble-Particle Interaction)
Figure 13a shows that with sound at a certain frequency
and amplitude, the stability of foam films could be signifi-
cantly improved, with evolution of the foam films being
associated with vigorous liquid flows within the films. The
presence of vigorous liquid flows indicates a relatively high
kinetic energy and thus a relatively low pressure within the
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
5cm 10cm 15cm
Speaker's distance to foam top
a) 10 ppm PPG
Blank Sound
3.00
3.20
3.40
3.60
3.80
4.00
5cm 10cm 15cm
Speaker's distance to foam top
b) 50 ppm PPG
Blank Sound
Figure 12. Effect of sound (at 400 Hz) on foam stability (represented by the overflowing froth flowrate) with the loudspeaker
immersed in the foam at different positions. The tests were conducted at two frother concentrations using the setup shown in
Figure 7
Source: Ng et al., 2020b, Yang, 2023.
Figure 13. Characteristic images of liquid film evolution: a) foam film, b) wetting film
Overflowflowrate
(liter/min)
Overflow
flowrate
(liter/min)
Figure 12 shows the stabilities of foams in a pilot-
scale flotation column. The experimental setup shown in
Figure 7 was used to identify the preferred location of the
loudspeaker for improving foam stability. The frother used
was polypropylene glycol (PPG) with an average molecu-
lar weight of 425 g/mol. The PPG solutions were prepared
using local tap water. The loudspeaker (Monarcor AR-50)
was used with the frequency set at 400 Hz. The foam stabil-
ity was indicated by the flowrate of the overflowing foam,
which should be somehow proportional to the air recovery,
an indicator for foam/froth stability (Hadler and Cilliers,
2009). Use of the sound systematically improved foam
stability, at any given frother concentration tested and any
location of the loudspeaker installed. It was observed that
the location of the loudspeaker would be preferably 5 cm
below the foam surface if the speaker was positioned less
than 4cm below the foam surface, it would tend to reduce
the foam stability if the speaker was located 15 cm (or
more) below the foam surface, the improvement of foam
stability would become smaller.
Effect of Sound on the Stability of Foam Films
(Representing Bubble-Bubble Interaction) and Wetting
Film (Representing Bubble-Particle Interaction)
Figure 13a shows that with sound at a certain frequency
and amplitude, the stability of foam films could be signifi-
cantly improved, with evolution of the foam films being
associated with vigorous liquid flows within the films. The
presence of vigorous liquid flows indicates a relatively high
kinetic energy and thus a relatively low pressure within the
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
5cm 10cm 15cm
Speaker's distance to foam top
a) 10 ppm PPG
Blank Sound
3.00
3.20
3.40
3.60
3.80
4.00
5cm 10cm 15cm
Speaker's distance to foam top
b) 50 ppm PPG
Blank Sound
Figure 12. Effect of sound (at 400 Hz) on foam stability (represented by the overflowing froth flowrate) with the loudspeaker
immersed in the foam at different positions. The tests were conducted at two frother concentrations using the setup shown in
Figure 7
Source: Ng et al., 2020b, Yang, 2023.
Figure 13. Characteristic images of liquid film evolution: a) foam film, b) wetting film
Overflowflowrate
(liter/min)
Overflow
flowrate
(liter/min)