2866 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
aligns with our understanding of frothers as surface-active
agents. Cappuccitti and Nesset (2010) and Nesset et al.
(2006) reported minimum bubble sizes ranging between 1
and 0.5 mm, while in our study, we observed bubble sizes
ranging from 0.37 to 0.45 mm. These values are consistent
with other studies of bubble size distributions in fluidised
bed flotation (K. Demir et al., 2023). The difference in min-
imum bubble size between conventional and fluidised bed
flotation systems could be attributed to the distinctly differ-
ent bubble generation mechanisms used in the two devices.
However, the currently available evidence is insufficient to
demonstrate this definitively. Despite this variation, the
consistent trends in bubble size highlight the robust influ-
ence of hydrodynamics in both studies, emphasising their
significance in conventional flotation and novel fluidised
bed flotation technologies such as the HydroFloat ®.
It is also evident from the results that hydrodynam-
ics, in particular the superficial gas velocity, significantly
affect both the critical coalescence concentration (CCC)
and the minimum attainable bubble size. Notably, this
influence is independent of the specific bubble generation
mechanism used within the system. This trend is similar to
that observed in conventional flotation by Cappuccitti and
Nesset (2010), as shown in Figure 1.
Further comparison of the work by Cappuccitti and
Nesset (2010) and the data obtained in this study (Figures
6 and 7) shows that even though the minimum Jg value in
the conventional flotation work is comparable to the maxi-
mum Jg value in this study using fluidised bed flotation,
the overall trends in bubble size and bubble surface area
flux behaviour are very similar to those observed in conven-
tional flotation.
However, even though the trends are similar, the abso-
lute values of CCC are vastly different. In conventional
flotation, CCC values for MIBC range between 10 and
30 ppm (Figure 1). However, in fluidised bed flotation,
the CCC values were estimated to range between approxi-
mately 100 and 200 ppm, a nearly 10-fold increase.
In addition, it is important to remember that in flui-
dised bed flotation, water is used as both the medium and
mechanism for suspension (fluidisation). This means that
HydroFloat ® makes us use significantly more water than
conventional flotation. The 10-fold increase in the CCC,
coupled with a significant increase in the volume of water
required to run the flotation system, means that the over-
all frother consumption (on a mass or g/ton basis) will
increase even further.
The substantial difference in frother dosage, in terms
of concentration (solution-based, measured in ppm) and
frother demand (solids-based, measured in g/ton), can be
clearly illustrated by simple mass balance calculation. Both
this study and the one performed by Cappuccitti and Nesset
(2010) were conducted in the absence of solids. However,
one can use some “typical” solids concentration values for
both conventional and fluidised bed flotation to enable the
calculation.
When we compare the estimated frother dosages for
critical coalescence concentration (CCC) values, consider-
ing the maximum airflow in a conventional flotation cell
(30 ppm) and the minimum CCC value in HydroFloat ®
(100 ppm), distinct differences can be seen (Table 2).
In conventional flotation, a typical solids concentration
is approximately 40%. In this case, 30 ppm frother solu-
tion concentration translates to the consumption of 45 g
of frother per ton of solid material. On the other hand, the
HydroFloat ® tends to operate with a solids concentration
of approximately 20%. In this case, the concentration of
100 ppm frother solution corresponds to the consumption
of 400 g of frother per ton of solid material. This repre-
sents a roughly 100-fold increase in frother consumption
to achieve the minimum bubble size. MIBC is a relatively
weak alcohol-based frother that requires high concen-
trations to reach CCC (Zhang, Nesset, Rao et al., 2012
Pawliszak, Bradshaw-Hajek, Skinner et al., 2024). Stronger
frother formulations that contain long-chained polygly-
col molecules are characterised by much lower CCC val-
ues in conventional flotation. A similar trend will hold for
fluidised bed flotation, where the increase in frother con-
sumption will likely be proportionally smaller for stronger
frother chemistries.
Overall, it is apparent that to reach the lower required
frother solution concentration for a CCC value at low linear
gas velocities, fluidised bed flotation requires a significantly
higher frother consumption. However, it is still not clear
if fluidised bed flotation requires operation at a minimum
bubble size to achieve optimum performance. The effect of
smaller bubbles on the buoyancy limitations of the larger
particles have yet to be studied and fully understood. The
Table 2. Frother consumption comparison in conventional vs. fluidised bed flotation systems
Parameters Conventional Flotation HydroFloat®
%Solids 40% 20%
Frother concentration at CCC, ppm 30 100
Frother consumption, g/t of solids 45 400
aligns with our understanding of frothers as surface-active
agents. Cappuccitti and Nesset (2010) and Nesset et al.
(2006) reported minimum bubble sizes ranging between 1
and 0.5 mm, while in our study, we observed bubble sizes
ranging from 0.37 to 0.45 mm. These values are consistent
with other studies of bubble size distributions in fluidised
bed flotation (K. Demir et al., 2023). The difference in min-
imum bubble size between conventional and fluidised bed
flotation systems could be attributed to the distinctly differ-
ent bubble generation mechanisms used in the two devices.
However, the currently available evidence is insufficient to
demonstrate this definitively. Despite this variation, the
consistent trends in bubble size highlight the robust influ-
ence of hydrodynamics in both studies, emphasising their
significance in conventional flotation and novel fluidised
bed flotation technologies such as the HydroFloat ®.
It is also evident from the results that hydrodynam-
ics, in particular the superficial gas velocity, significantly
affect both the critical coalescence concentration (CCC)
and the minimum attainable bubble size. Notably, this
influence is independent of the specific bubble generation
mechanism used within the system. This trend is similar to
that observed in conventional flotation by Cappuccitti and
Nesset (2010), as shown in Figure 1.
Further comparison of the work by Cappuccitti and
Nesset (2010) and the data obtained in this study (Figures
6 and 7) shows that even though the minimum Jg value in
the conventional flotation work is comparable to the maxi-
mum Jg value in this study using fluidised bed flotation,
the overall trends in bubble size and bubble surface area
flux behaviour are very similar to those observed in conven-
tional flotation.
However, even though the trends are similar, the abso-
lute values of CCC are vastly different. In conventional
flotation, CCC values for MIBC range between 10 and
30 ppm (Figure 1). However, in fluidised bed flotation,
the CCC values were estimated to range between approxi-
mately 100 and 200 ppm, a nearly 10-fold increase.
In addition, it is important to remember that in flui-
dised bed flotation, water is used as both the medium and
mechanism for suspension (fluidisation). This means that
HydroFloat ® makes us use significantly more water than
conventional flotation. The 10-fold increase in the CCC,
coupled with a significant increase in the volume of water
required to run the flotation system, means that the over-
all frother consumption (on a mass or g/ton basis) will
increase even further.
The substantial difference in frother dosage, in terms
of concentration (solution-based, measured in ppm) and
frother demand (solids-based, measured in g/ton), can be
clearly illustrated by simple mass balance calculation. Both
this study and the one performed by Cappuccitti and Nesset
(2010) were conducted in the absence of solids. However,
one can use some “typical” solids concentration values for
both conventional and fluidised bed flotation to enable the
calculation.
When we compare the estimated frother dosages for
critical coalescence concentration (CCC) values, consider-
ing the maximum airflow in a conventional flotation cell
(30 ppm) and the minimum CCC value in HydroFloat ®
(100 ppm), distinct differences can be seen (Table 2).
In conventional flotation, a typical solids concentration
is approximately 40%. In this case, 30 ppm frother solu-
tion concentration translates to the consumption of 45 g
of frother per ton of solid material. On the other hand, the
HydroFloat ® tends to operate with a solids concentration
of approximately 20%. In this case, the concentration of
100 ppm frother solution corresponds to the consumption
of 400 g of frother per ton of solid material. This repre-
sents a roughly 100-fold increase in frother consumption
to achieve the minimum bubble size. MIBC is a relatively
weak alcohol-based frother that requires high concen-
trations to reach CCC (Zhang, Nesset, Rao et al., 2012
Pawliszak, Bradshaw-Hajek, Skinner et al., 2024). Stronger
frother formulations that contain long-chained polygly-
col molecules are characterised by much lower CCC val-
ues in conventional flotation. A similar trend will hold for
fluidised bed flotation, where the increase in frother con-
sumption will likely be proportionally smaller for stronger
frother chemistries.
Overall, it is apparent that to reach the lower required
frother solution concentration for a CCC value at low linear
gas velocities, fluidised bed flotation requires a significantly
higher frother consumption. However, it is still not clear
if fluidised bed flotation requires operation at a minimum
bubble size to achieve optimum performance. The effect of
smaller bubbles on the buoyancy limitations of the larger
particles have yet to be studied and fully understood. The
Table 2. Frother consumption comparison in conventional vs. fluidised bed flotation systems
Parameters Conventional Flotation HydroFloat®
%Solids 40% 20%
Frother concentration at CCC, ppm 30 100
Frother consumption, g/t of solids 45 400