2702 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
then transferred to the cell. The superficial gas velocity of
0.002 m/s and the superficial water velocity of 0.01 m/s
were maintained for every experiment. Tap water was used
for the experiment and to adjust the pulp level in the cell.
Concentrates were collected at one-minute intervals dur-
ing each flotation test for a duration of three minutes. The
concentrates were dried and weighed, and the recovery was
calculated according to the mass of the particles recovered
in the concentrated.
RESULTS AND DISCUSSION
Effect of Particle Size on Froth Characteristics
The physical characteristics of the froth observed at various
conditions are shown in Figure 2. Figure 2(a) illustrates the
development of the froth phase. Note that this experiment
was carried out in the absence of particles. The yellow mark
in the column indicates the water level. As can be seen, air
bubbles rising from the pulp enter the froth phase, clearly
forming two phases: the pulp phase and the froth phase.
Figure 2(b) shows the development of the froth phase
with the coarse particles. It was observed that the bubble
clusters or even a single bubble with multiple attached par-
ticles reached the top of the pulp they were accumulating
and gradually developing below the pulp surface. Almost all
the particles were hydrophobic, so after 50 seconds, all the
particles were buoyed to the froth phase by bubbles and the
froth reached a steady state.
Figure 2(c) illustrates the development of the froth
phase with fine particles. Initially, a similar observation was
seen with the fine particles as well that the clusters reach-
ing the top of the pulp started accumulating, packing, and
developing below the pulp surface. However, gradually
with time, the froth phase began to rise above the initial
liquid level. This phenomenon of froth development was
not observed with the coarse particles. After 120 seconds, it
can be clearly observed that the top section of the froth has
more big bubbles and is expanded. In contrast, the bottom
section appears more compact, with smaller bubbles mostly
below the pulp level. While with the coarse particles, after
all the particles reached the froth phase, the height of the
froth remained constant and did not grow with time.
Fine particles have more surface area and provide better
coverage on the bubble surface (Dankwah et al., 2022). This
leads to formating of a protective layer on the bubble sur-
face, enhancing their ability to stabilize bubbles in the froth.
Also, it is possible that fine particles (contact angle 90°) at
the liquid-gas interface stabilize the films through a capil-
lary mechanism, causing a capillary rise of liquid between
the particles. This mechanism opposes drainage and results
in an increase in the resistance to bubble coalescence and
rupturing (Sutherland, 1955 Pugh, 2005 Farrokhpay,
2011). In contrast, coarse particles are typically less effec-
tive in providing stability to froth due to their inability to
form a uniform and well-attached coating on the bubble
surface. Their larger size poses a challenge in achieving even
distribution at the gas-liquid interface, leading to rapid
thinning, and rupturing of the bubble film. Consequently,
this results in a decrease in froth stability (Johansson and
Pugh, 1992 Morris et al., 2015 Norori-McCormac et
al., 2017). Several studies have shown experimentally that
froth stability is higher for fine particles compared to coarse
particles. For example, Pugh (2005) reported that froth life
can be extended for several hours using 100 µm galena par-
ticles, whereas it can only sustain up to 60 seconds using
300 µm particles.
It was observed that the cluster initially reached the
top of the pulp level but remained below the pulp surface.
This could be attributed to the presence of air above the
pulp, which has a significantly lower density compared to
the pulp. When a bubble carrying particles reaches the air-
pulp interface, it stays beneath the pulp boundary possibly
due to insufficient buoyancy to rise above the pulp surface.
Interestingly, this phenomenon was not observed in the
first case, where the bubble rose and entered the froth phase
because the bubble was unloaded. It is possible that with
very fine particles (10 µm), bubble aggregates do not accu-
mulate below the pulp surface due to their lower weight
and have sufficient buoyancy to move into the froth. This
hasn’t been studied but can be explored in future investi-
gations to understand the froth formation with very fine
particles. Also, note that the pulp level rises with an increase
in gas volume within the pulp phase.
Figure 2(d) illustrates the development of the froth
phase when a blend of 50% fine and 50% coarse particles
was present. Clusters initially formed below the pulp sur-
face, but over time, the froth phase began to grow, like in
the case of fine particles. This shows that the presence of fine
particles plays a crucial role in this development, as fine par-
ticles arrange onto the bubble surfaces, hindering the film
drainage and stabilizing the bubbles (meaning the ability of
the bubble in the froth to resist coalescence and bursting).
As a result, when air bubbles from the pulp phase consis-
tently flow into the froth phase (Schramm and Wassmuth,
1994), the air volume in the froth increases because the
bubbles in the froth are stable and do not coalesce. This
causes the froth phase to expand, carrying coarse particles
with it (Pugh, 2005). It was observed that the froth below
the pulp level was less significant.
These experimental observations make it clear that the
characteristics of the froth phase depend strongly on the
then transferred to the cell. The superficial gas velocity of
0.002 m/s and the superficial water velocity of 0.01 m/s
were maintained for every experiment. Tap water was used
for the experiment and to adjust the pulp level in the cell.
Concentrates were collected at one-minute intervals dur-
ing each flotation test for a duration of three minutes. The
concentrates were dried and weighed, and the recovery was
calculated according to the mass of the particles recovered
in the concentrated.
RESULTS AND DISCUSSION
Effect of Particle Size on Froth Characteristics
The physical characteristics of the froth observed at various
conditions are shown in Figure 2. Figure 2(a) illustrates the
development of the froth phase. Note that this experiment
was carried out in the absence of particles. The yellow mark
in the column indicates the water level. As can be seen, air
bubbles rising from the pulp enter the froth phase, clearly
forming two phases: the pulp phase and the froth phase.
Figure 2(b) shows the development of the froth phase
with the coarse particles. It was observed that the bubble
clusters or even a single bubble with multiple attached par-
ticles reached the top of the pulp they were accumulating
and gradually developing below the pulp surface. Almost all
the particles were hydrophobic, so after 50 seconds, all the
particles were buoyed to the froth phase by bubbles and the
froth reached a steady state.
Figure 2(c) illustrates the development of the froth
phase with fine particles. Initially, a similar observation was
seen with the fine particles as well that the clusters reach-
ing the top of the pulp started accumulating, packing, and
developing below the pulp surface. However, gradually
with time, the froth phase began to rise above the initial
liquid level. This phenomenon of froth development was
not observed with the coarse particles. After 120 seconds, it
can be clearly observed that the top section of the froth has
more big bubbles and is expanded. In contrast, the bottom
section appears more compact, with smaller bubbles mostly
below the pulp level. While with the coarse particles, after
all the particles reached the froth phase, the height of the
froth remained constant and did not grow with time.
Fine particles have more surface area and provide better
coverage on the bubble surface (Dankwah et al., 2022). This
leads to formating of a protective layer on the bubble sur-
face, enhancing their ability to stabilize bubbles in the froth.
Also, it is possible that fine particles (contact angle 90°) at
the liquid-gas interface stabilize the films through a capil-
lary mechanism, causing a capillary rise of liquid between
the particles. This mechanism opposes drainage and results
in an increase in the resistance to bubble coalescence and
rupturing (Sutherland, 1955 Pugh, 2005 Farrokhpay,
2011). In contrast, coarse particles are typically less effec-
tive in providing stability to froth due to their inability to
form a uniform and well-attached coating on the bubble
surface. Their larger size poses a challenge in achieving even
distribution at the gas-liquid interface, leading to rapid
thinning, and rupturing of the bubble film. Consequently,
this results in a decrease in froth stability (Johansson and
Pugh, 1992 Morris et al., 2015 Norori-McCormac et
al., 2017). Several studies have shown experimentally that
froth stability is higher for fine particles compared to coarse
particles. For example, Pugh (2005) reported that froth life
can be extended for several hours using 100 µm galena par-
ticles, whereas it can only sustain up to 60 seconds using
300 µm particles.
It was observed that the cluster initially reached the
top of the pulp level but remained below the pulp surface.
This could be attributed to the presence of air above the
pulp, which has a significantly lower density compared to
the pulp. When a bubble carrying particles reaches the air-
pulp interface, it stays beneath the pulp boundary possibly
due to insufficient buoyancy to rise above the pulp surface.
Interestingly, this phenomenon was not observed in the
first case, where the bubble rose and entered the froth phase
because the bubble was unloaded. It is possible that with
very fine particles (10 µm), bubble aggregates do not accu-
mulate below the pulp surface due to their lower weight
and have sufficient buoyancy to move into the froth. This
hasn’t been studied but can be explored in future investi-
gations to understand the froth formation with very fine
particles. Also, note that the pulp level rises with an increase
in gas volume within the pulp phase.
Figure 2(d) illustrates the development of the froth
phase when a blend of 50% fine and 50% coarse particles
was present. Clusters initially formed below the pulp sur-
face, but over time, the froth phase began to grow, like in
the case of fine particles. This shows that the presence of fine
particles plays a crucial role in this development, as fine par-
ticles arrange onto the bubble surfaces, hindering the film
drainage and stabilizing the bubbles (meaning the ability of
the bubble in the froth to resist coalescence and bursting).
As a result, when air bubbles from the pulp phase consis-
tently flow into the froth phase (Schramm and Wassmuth,
1994), the air volume in the froth increases because the
bubbles in the froth are stable and do not coalesce. This
causes the froth phase to expand, carrying coarse particles
with it (Pugh, 2005). It was observed that the froth below
the pulp level was less significant.
These experimental observations make it clear that the
characteristics of the froth phase depend strongly on the