2720 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
&Nguyen, 2014 Firouzi &Nguyen, 2017 Marrucci &
Nicodemo, 1967), which accounts for the larger propor-
tion of larger bubbles in the scenario lacking both wash
and salt.
The bubble surface flux data shown in Figure 6(B) con-
firms the inhibition effect of both wash water and salt on
the bubble coalescence. A key feature of the RFC is the
ability to generate high bubble surface area fluxes. As such
the reported values are greater than what can be typically
expected from conventional flotation cells, ranging from
30–60 s–1 (Massinaei, et al., 2009).
Gas Holdup
Throughout every run, the pressure drop in the vertical sec-
tion of the cell was recorded. This was converted to a gas
holdup over time using the relationship presented in equa-
tion 1.
1
G f tsgDx
DP =-(1)
where εG is the gas holdup, P is the pressure gradient, ρs is
the slurry density, g is the gravitational acceleration, and Δx
is the distance between the pressure transducers. The
Figure 6. (A) Bubble size distribution and (B) bubble surface flux in the presence and absence of salt and
counter-current wash

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Extracted Text (may have errors)

2720 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
&Nguyen, 2014 Firouzi &Nguyen, 2017 Marrucci &
Nicodemo, 1967), which accounts for the larger propor-
tion of larger bubbles in the scenario lacking both wash
and salt.
The bubble surface flux data shown in Figure 6(B) con-
firms the inhibition effect of both wash water and salt on
the bubble coalescence. A key feature of the RFC is the
ability to generate high bubble surface area fluxes. As such
the reported values are greater than what can be typically
expected from conventional flotation cells, ranging from
30–60 s–1 (Massinaei, et al., 2009).
Gas Holdup
Throughout every run, the pressure drop in the vertical sec-
tion of the cell was recorded. This was converted to a gas
holdup over time using the relationship presented in equa-
tion 1.
1
G f tsgDx
DP =-(1)
where εG is the gas holdup, P is the pressure gradient, ρs is
the slurry density, g is the gravitational acceleration, and Δx
is the distance between the pressure transducers. The
Figure 6. (A) Bubble size distribution and (B) bubble surface flux in the presence and absence of salt and
counter-current wash

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XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2721
average gas holdup for with and without wash water and
NaCl is presented in Figure 7.
Figure 7 shows that the addition of wash increased the
gas holdup for both with and without NaCl. The addition
of wash water reduces the rise velocity of bubbles in the
vertical section of the column. This increases the average
residence time of the bubbles, allowing for a denser accu-
mulation of bubbles in the cell. The effect of salt on the gas
holdup is negligible when wash water is used however, a
marginal increase in gas holdup is observed in cases with-
out wash. This effect can be linked to the inhibition of
bubble coalescence, as demonstrated in Figure 6. The pres-
ence of the salt concentration leads to smaller bubbles due
to reduced coalescence. These smaller bubbles rise more
slowly, which contributes to their increased accumulation
and, therefore, a higher gas holdup. In conventional flota-
tion gas holdup typically ranges from 3% to 20% (Schwarz
&Alexander, 2006), whereas the RFC, as demonstrated,
achieves much higher values. As shown in Figure 6(B), this
results in a significantly higher bubble surface flux, which is
a key parameter in flotation.
CONCLUSIONS
This work demonstrates the effectiveness of counter-cur-
rent washing on the removal of hydrophilic silica particles
in the presence of salt in a Reflux Flotation Cell. The find-
ings offer promising prospects for the use of saline water
in mineral processing plants, potentially contributing to
global efforts in addressing freshwater scarcity through
water recycling. To further elucidate the implications of
these findings, additional research involving various salts at
higher concentrations is recommended.
ACKNOWLEDGMENTS
The authors would like to acknowledge the financial sup-
port from the Australian Research Council (ARC) through
the ARC Centre of Excellence for Enabling Eco-efficient
Beneficiation of Minerals, grant number CE200100009.
REFERENCES
Castro, S., &Laskowski, J. S. (2011). Froth Flotation
in Saline Water. KONA Powder and Particle Journal
No.29, 4–15.
Crompton, L. J., Islam, T. M., &Galvin, K. P. (2022).
Investigation of Internal Classification in Coarse
Particle Flotation of Chalcopyrite Using the CoarseAIR.
Minerals.
Dickinson, J. E., &Galvin, K. P. (2014). Fluidized bed
desliming in fine particle flotation – Part I. Chemical
Engineering Science 108, 283–298.
Firouzi, M., &Nguyen, A. V. (2014). On the effect of van
der Waals attractions on the critical salt concentration
for inhibiting bubble coalescence. Minerals Engineering
58, 108–112.
Firouzi, M., &Nguyen, A. V. (2017). The Gibbs-Marangoni
stress and nonDLVO forces are equally important for
modeling bubble coalescence in salt solutions. Colloids
and Surfaces A: Physicochemical and Engineering Aspects
515, 62–68.
Figure 7. Gas Holdup for each NaCl feed concentration and wash rate

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2721
average gas holdup for with and without wash water and
NaCl is presented in Figure 7.
Figure 7 shows that the addition of wash increased the
gas holdup for both with and without NaCl. The addition
of wash water reduces the rise velocity of bubbles in the
vertical section of the column. This increases the average
residence time of the bubbles, allowing for a denser accu-
mulation of bubbles in the cell. The effect of salt on the gas
holdup is negligible when wash water is used however, a
marginal increase in gas holdup is observed in cases with-
out wash. This effect can be linked to the inhibition of
bubble coalescence, as demonstrated in Figure 6. The pres-
ence of the salt concentration leads to smaller bubbles due
to reduced coalescence. These smaller bubbles rise more
slowly, which contributes to their increased accumulation
and, therefore, a higher gas holdup. In conventional flota-
tion gas holdup typically ranges from 3% to 20% (Schwarz
&Alexander, 2006), whereas the RFC, as demonstrated,
achieves much higher values. As shown in Figure 6(B), this
results in a significantly higher bubble surface flux, which is
a key parameter in flotation.
CONCLUSIONS
This work demonstrates the effectiveness of counter-cur-
rent washing on the removal of hydrophilic silica particles
in the presence of salt in a Reflux Flotation Cell. The find-
ings offer promising prospects for the use of saline water
in mineral processing plants, potentially contributing to
global efforts in addressing freshwater scarcity through
water recycling. To further elucidate the implications of
these findings, additional research involving various salts at
higher concentrations is recommended.
ACKNOWLEDGMENTS
The authors would like to acknowledge the financial sup-
port from the Australian Research Council (ARC) through
the ARC Centre of Excellence for Enabling Eco-efficient
Beneficiation of Minerals, grant number CE200100009.
REFERENCES
Castro, S., &Laskowski, J. S. (2011). Froth Flotation
in Saline Water. KONA Powder and Particle Journal
No.29, 4–15.
Crompton, L. J., Islam, T. M., &Galvin, K. P. (2022).
Investigation of Internal Classification in Coarse
Particle Flotation of Chalcopyrite Using the CoarseAIR.
Minerals.
Dickinson, J. E., &Galvin, K. P. (2014). Fluidized bed
desliming in fine particle flotation – Part I. Chemical
Engineering Science 108, 283–298.
Firouzi, M., &Nguyen, A. V. (2014). On the effect of van
der Waals attractions on the critical salt concentration
for inhibiting bubble coalescence. Minerals Engineering
58, 108–112.
Firouzi, M., &Nguyen, A. V. (2017). The Gibbs-Marangoni
stress and nonDLVO forces are equally important for
modeling bubble coalescence in salt solutions. Colloids
and Surfaces A: Physicochemical and Engineering Aspects
515, 62–68.
Figure 7. Gas Holdup for each NaCl feed concentration and wash rate

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2719
As shown in Figure 4, the application of wash water
greatly reduced the silica retained in the product stream.
Operating at 3 wt.% feed solids concentration, the system
is already significantly dilute. When wash water is applied
to the upper vertical section, it becomes extremely dilute.
With a product flux of 0.31 cm/s ±0.02 cm/s, and wash
water flux at 0.83 cm/s, a bias flux of 0.52 cm/s down the
column is generated. At these conditions, the upper zone of
the cell acts as a reverse fluidized bed, generating a highly
permeable bubbly/foam flow. This condition facilitates the
stripping of bulk solids away from the rising bubbles. The
reduction in particle entrainment, whether through bubble
swarms or in the wake of rising bubbles, consequently, leads
to decreased silica yield in the presence of wash water.
The addition of NaCl appears to slightly increase the
recovery of silica in the absence of wash water. This effect
can be attributed to the salt-induced aggregation of par-
ticles, as it screens the surface charge of silica particles.
This leads to less electrostatic double layer (EDL) repulsion
between particles as shown in Figure 5, allowing particles to
come closer, with finer particles more inclined to aggregate
with larger ones. With the introduction of counter-current
washing, these aggregate particles are more likely to be
washed into the tailings. Consequently, fewer fine particles
are expected to report to the product at higher salt concen-
tration in the presence of wash water.
Zeta Potential
The addition of NaCl changes the silica particle surface
charge, as shown in the work of Romero et al. (2018). The
zeta potential of the silica particles used, was measured at
different NaCl concentrations, and presented in Figure 5.
From Figure 5, the addition of NaCl salt significantly
lowered the negative surface charge of the silica particles.
Reducing the surface charge, lowers the EDL repulsion
between silica particles, increasing the aggregation of these
particles within the thin liquid film between bubbles prior
to entering the wash zone. In the highly permeable bubbly
zone, these particles are carried away by the strong bias flux.
Bubble Size
Upon applying the Stardist code to the extracted frames,
between 519 and 9685 bubbles were measured for each con-
dition. The quantity of bubbles measured was constrained
not by any inherent limit but by the quality of the captured
video. A number distribution was generated, presented in
Figure 6. From these distributions, the Sauter mean diam-
eter was determined and subsequently determined the bub-
ble surface flux which is presented in Figure 6.
In Figure 6(A) the distinct distribution observed is for
the conditions without wash and without NaCl, where the
curve shows a secondary peak at 1.15 mm size. This sug-
gests potential bubble coalescence. The introduction of the
counter-current washing increases the fluid flow between
the bubbles, decreasing the rise velocity and establishing a
more robust separation between the bubbles. This reduced
rise velocity, along with the thicker liquid film encasing each
bubble, mitigates bubble coalescence, thereby eliminating
the secondary peak in bubble size distribution noted in the
absence of counter-current washing. Moreover, the pres-
ence of salt is known to inhibit bubble coalescence (Firouzi
Figure 5. Zeta potential of silica particles (at 0.1 wt% solids) as a function of NaCl concentration

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Extracted Text (may have errors)

XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2719
As shown in Figure 4, the application of wash water
greatly reduced the silica retained in the product stream.
Operating at 3 wt.% feed solids concentration, the system
is already significantly dilute. When wash water is applied
to the upper vertical section, it becomes extremely dilute.
With a product flux of 0.31 cm/s ±0.02 cm/s, and wash
water flux at 0.83 cm/s, a bias flux of 0.52 cm/s down the
column is generated. At these conditions, the upper zone of
the cell acts as a reverse fluidized bed, generating a highly
permeable bubbly/foam flow. This condition facilitates the
stripping of bulk solids away from the rising bubbles. The
reduction in particle entrainment, whether through bubble
swarms or in the wake of rising bubbles, consequently, leads
to decreased silica yield in the presence of wash water.
The addition of NaCl appears to slightly increase the
recovery of silica in the absence of wash water. This effect
can be attributed to the salt-induced aggregation of par-
ticles, as it screens the surface charge of silica particles.
This leads to less electrostatic double layer (EDL) repulsion
between particles as shown in Figure 5, allowing particles to
come closer, with finer particles more inclined to aggregate
with larger ones. With the introduction of counter-current
washing, these aggregate particles are more likely to be
washed into the tailings. Consequently, fewer fine particles
are expected to report to the product at higher salt concen-
tration in the presence of wash water.
Zeta Potential
The addition of NaCl changes the silica particle surface
charge, as shown in the work of Romero et al. (2018). The
zeta potential of the silica particles used, was measured at
different NaCl concentrations, and presented in Figure 5.
From Figure 5, the addition of NaCl salt significantly
lowered the negative surface charge of the silica particles.
Reducing the surface charge, lowers the EDL repulsion
between silica particles, increasing the aggregation of these
particles within the thin liquid film between bubbles prior
to entering the wash zone. In the highly permeable bubbly
zone, these particles are carried away by the strong bias flux.
Bubble Size
Upon applying the Stardist code to the extracted frames,
between 519 and 9685 bubbles were measured for each con-
dition. The quantity of bubbles measured was constrained
not by any inherent limit but by the quality of the captured
video. A number distribution was generated, presented in
Figure 6. From these distributions, the Sauter mean diam-
eter was determined and subsequently determined the bub-
ble surface flux which is presented in Figure 6.
In Figure 6(A) the distinct distribution observed is for
the conditions without wash and without NaCl, where the
curve shows a secondary peak at 1.15 mm size. This sug-
gests potential bubble coalescence. The introduction of the
counter-current washing increases the fluid flow between
the bubbles, decreasing the rise velocity and establishing a
more robust separation between the bubbles. This reduced
rise velocity, along with the thicker liquid film encasing each
bubble, mitigates bubble coalescence, thereby eliminating
the secondary peak in bubble size distribution noted in the
absence of counter-current washing. Moreover, the pres-
ence of salt is known to inhibit bubble coalescence (Firouzi
Figure 5. Zeta potential of silica particles (at 0.1 wt% solids) as a function of NaCl concentration