2722 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Firouzi, M., Howes, T., &Nguyen, A. V. (2015). A quan-
titative review of the transition salt concentration for
inhibiting bubble coalescence. Advances in Colloid and
Interface Science 222, 305–318.
Galvin, K. P., &Dickinson, J. E. (2014). Fluidized bed
desliming in fine particle flotation – Part II: Flotation.
Chemical Engineering Science 108, 299–309.
Galvin, K. P., Harvey, N. G., &Dickinson, J. E. (2014).
Fluidized bed desliming in fine particle flotation -
Part III flotation of difficult to clean coal. Minerals
Engineering 66-68, 94–101.
Jeldres, R. I., Forbes, L., &Cisternas, L. A. (2016). Effect
of Seawater on Sulfide Ore Flotation: A Review.
Mineral Processing and Extractive Metallurgy Review 37,
369–384.
Laskowski, J. S., Castro, S., &Gutierrez, L. (2019).
Flotation in Seawater. Mining, Metallurgy &Exploration
36, 89–98.
Marrucci, G., &Nicodemo, L. (1967). Coalescence of gas
bubbles in aqueous solutions of inorganic electrolytes.
Chemical Engineering Science 22, 1257–1265.
Massinaei, M., Kolahdoozan, M., Noaparast, M.,
Oliazadeh, M., Yianatos, J., Shamsadini, R., &
Yarahmadi, M. (2009). Hydrodynamic and kinetic
characterization of industrial columns in rougher cir-
cuit. Minerals Engineering 22, 357–365.
Parkes, S., Wang, P., &Galvin, K. P. (2022). Investigating
the System Flotation Kinetics of Fine Chalcopyrite
in a REFLUX ™ Flotation Cell using a Standardised
Flotation Cell Reference Method. Minerals Engineering
178.
Romero, C. P., Jeldres, R. I., Quezada, G. R., &Concha, F.
(2018). Zeta potential and viscosity of colloidal silica
suspensions: Effect of seawater salts, pH, flocculant
and shear rate. Colloids and Surfaces A, 210–218.
Schwarz, S., &Alexander, D. (2006). Gas dispersion
measurements in industrial flotation cells. Minerals
Engineering 19, 554–560.
Wang, B., &Peng, Y. (2014). The Effect of Saline Water
on MIneral Flotation -A Critical Review. Minerals
Engineering 66‑68, 13–24.
Wills, B. A., &Finch, J. A. (2016). Wills’ Mineral Processing
Technology. Montreal: Elsevier.
Wu, B., Ribeiro, A. S., Firouzi, M., Rufford, T. E., &
Towler, B. (2020). Use of pressure signal analysis to
characterise counter-current two-phase flow regimes in
annuli. Chemical Engineering Research and Design 153,
547–561.

Previous Page Next Page

Extracted Text (may have errors)

2722 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
Firouzi, M., Howes, T., &Nguyen, A. V. (2015). A quan-
titative review of the transition salt concentration for
inhibiting bubble coalescence. Advances in Colloid and
Interface Science 222, 305–318.
Galvin, K. P., &Dickinson, J. E. (2014). Fluidized bed
desliming in fine particle flotation – Part II: Flotation.
Chemical Engineering Science 108, 299–309.
Galvin, K. P., Harvey, N. G., &Dickinson, J. E. (2014).
Fluidized bed desliming in fine particle flotation -
Part III flotation of difficult to clean coal. Minerals
Engineering 66-68, 94–101.
Jeldres, R. I., Forbes, L., &Cisternas, L. A. (2016). Effect
of Seawater on Sulfide Ore Flotation: A Review.
Mineral Processing and Extractive Metallurgy Review 37,
369–384.
Laskowski, J. S., Castro, S., &Gutierrez, L. (2019).
Flotation in Seawater. Mining, Metallurgy &Exploration
36, 89–98.
Marrucci, G., &Nicodemo, L. (1967). Coalescence of gas
bubbles in aqueous solutions of inorganic electrolytes.
Chemical Engineering Science 22, 1257–1265.
Massinaei, M., Kolahdoozan, M., Noaparast, M.,
Oliazadeh, M., Yianatos, J., Shamsadini, R., &
Yarahmadi, M. (2009). Hydrodynamic and kinetic
characterization of industrial columns in rougher cir-
cuit. Minerals Engineering 22, 357–365.
Parkes, S., Wang, P., &Galvin, K. P. (2022). Investigating
the System Flotation Kinetics of Fine Chalcopyrite
in a REFLUX ™ Flotation Cell using a Standardised
Flotation Cell Reference Method. Minerals Engineering
178.
Romero, C. P., Jeldres, R. I., Quezada, G. R., &Concha, F.
(2018). Zeta potential and viscosity of colloidal silica
suspensions: Effect of seawater salts, pH, flocculant
and shear rate. Colloids and Surfaces A, 210–218.
Schwarz, S., &Alexander, D. (2006). Gas dispersion
measurements in industrial flotation cells. Minerals
Engineering 19, 554–560.
Wang, B., &Peng, Y. (2014). The Effect of Saline Water
on MIneral Flotation -A Critical Review. Minerals
Engineering 66‑68, 13–24.
Wills, B. A., &Finch, J. A. (2016). Wills’ Mineral Processing
Technology. Montreal: Elsevier.
Wu, B., Ribeiro, A. S., Firouzi, M., Rufford, T. E., &
Towler, B. (2020). Use of pressure signal analysis to
characterise counter-current two-phase flow regimes in
annuli. Chemical Engineering Research and Design 153,
547–561.

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2723
Role of Surface Forces in the Kinetics of Film Thinning and
Contact Angle Formation
Mohit Gupta, Kaiwu Huang, Roe-Hoan Yoon
Center for Advanced Separation Technologies, Virginia Tech, Blacksburg, VA
ABSTRACT: When an air bubble approaches a flat surface in water, a thin liquid film (TLF) is formed in
between. Its stability is controlled by the surface forces, which in turn determine the disjoining pressure (Π)
in units of N/m2. If Π 0, the film ruptures at a critical film thickness (hc), forming a finite contact angle (θ).
In the present work, we have measured the surface forces by monitoring the changes in bubble curvature and
analyzing the results using the Young-Laplace equation. We have studied the role of different surface forces,
particularly that of EDL force, on the kinetics of film thinning and contact angle formation.
INTRODUCTION
During the early part of his career, Professor D.W.
Fuerstenau of U.C. Berkely focused on the adsorption of
surfactant and/or collector molecules to mineral surfaces.
His work showed that the adsorption mechanisms are
closely related to the structure of the electrical double lay-
ers (EDLs) formed around mineral particles suspended in
the aqueous phase. His work helped the industry develop
powerful and selective collectors for more efficient flotation
separation (Fuerstenau and Pradip, 2005). While his work
in this area of research may be characterized as microscopic,
there was another part of his work that had not received as
much attention, i.e., the macroscopic interaction between
bubbles and particles. He showed that flotation recover-
ies of quartz and molybdenite reached the maxima at the
points of zero charge (PZCs) of the minerals (Fuerstenau,
1957 Chander and Fuerstenau, 1972). The authors attrib-
uted this finding to the role of the EDL around air bubbles
playing a role in bubble-particle interactions in flotation.
Derjaguin and Dukhin (1961) modeled bubble-particle
interactions using the DLVO theory, which considers the
EDL and van der Waals (vdW) forces. The authors thought
that flotation is controlled by the attractive vdW force and
the repulsive EDL force and developed a flotation criterion,
A
d}
C 1
2 f
m (1)
in which ε is the dielectric permittivity of the solution, d
is the double-layer thickness, ψ1 is the doublelayer poten-
tial, and A represents the attractive force due to the van
der Waals interaction. For small particles C" is equal to
1. In the absence of any information on the hydrophobic
force at the time, the authors thought that bubble-particle
interaction was driven by the vdW force, which is repul-
sive in bubble-particle interactions. Regardless, Derjaguin
and Dukhin (1961) were the first to recognize that flota-
tion kinetics is controlled by the surface forces involved in
bubble-particle interactions.
The authors of the present investigation have been
measuring surface forces using the atomic force microscope
(AFM) and the surface force apparatus (SFA) with particu-
lar interest in the forces between hydrophobic surfaces in
water. However, the subject matter has been controversial
as many investigators detected the formation of nano-scale
air bubbles during the measurement, while others reported

Previous Page Next Page

Extracted Text (may have errors)

2723
Role of Surface Forces in the Kinetics of Film Thinning and
Contact Angle Formation
Mohit Gupta, Kaiwu Huang, Roe-Hoan Yoon
Center for Advanced Separation Technologies, Virginia Tech, Blacksburg, VA
ABSTRACT: When an air bubble approaches a flat surface in water, a thin liquid film (TLF) is formed in
between. Its stability is controlled by the surface forces, which in turn determine the disjoining pressure (Π)
in units of N/m2. If Π 0, the film ruptures at a critical film thickness (hc), forming a finite contact angle (θ).
In the present work, we have measured the surface forces by monitoring the changes in bubble curvature and
analyzing the results using the Young-Laplace equation. We have studied the role of different surface forces,
particularly that of EDL force, on the kinetics of film thinning and contact angle formation.
INTRODUCTION
During the early part of his career, Professor D.W.
Fuerstenau of U.C. Berkely focused on the adsorption of
surfactant and/or collector molecules to mineral surfaces.
His work showed that the adsorption mechanisms are
closely related to the structure of the electrical double lay-
ers (EDLs) formed around mineral particles suspended in
the aqueous phase. His work helped the industry develop
powerful and selective collectors for more efficient flotation
separation (Fuerstenau and Pradip, 2005). While his work
in this area of research may be characterized as microscopic,
there was another part of his work that had not received as
much attention, i.e., the macroscopic interaction between
bubbles and particles. He showed that flotation recover-
ies of quartz and molybdenite reached the maxima at the
points of zero charge (PZCs) of the minerals (Fuerstenau,
1957 Chander and Fuerstenau, 1972). The authors attrib-
uted this finding to the role of the EDL around air bubbles
playing a role in bubble-particle interactions in flotation.
Derjaguin and Dukhin (1961) modeled bubble-particle
interactions using the DLVO theory, which considers the
EDL and van der Waals (vdW) forces. The authors thought
that flotation is controlled by the attractive vdW force and
the repulsive EDL force and developed a flotation criterion,
A
d}
C 1
2 f
m (1)
in which ε is the dielectric permittivity of the solution, d
is the double-layer thickness, ψ1 is the doublelayer poten-
tial, and A represents the attractive force due to the van
der Waals interaction. For small particles C" is equal to
1. In the absence of any information on the hydrophobic
force at the time, the authors thought that bubble-particle
interaction was driven by the vdW force, which is repul-
sive in bubble-particle interactions. Regardless, Derjaguin
and Dukhin (1961) were the first to recognize that flota-
tion kinetics is controlled by the surface forces involved in
bubble-particle interactions.
The authors of the present investigation have been
measuring surface forces using the atomic force microscope
(AFM) and the surface force apparatus (SFA) with particu-
lar interest in the forces between hydrophobic surfaces in
water. However, the subject matter has been controversial
as many investigators detected the formation of nano-scale
air bubbles during the measurement, while others reported

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

Previous Page Next Page

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