2786 XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3
seconds to several hours, whereas 30 µm galena particles can
only increase the froth lifetime to 60 seconds (Pugh et al.
2005). There are several mechanisms by which particles can
influence the stability of particle-laden froths. For example,
particles can increase the viscosity of the aqueous phase in
the froth lamella, which in turn can slow down the drain-
age of the liquid and increase the froth stability (Horozov
2008). Particles can also form a layered structure within the
thinning film and stabilize it through the so-called oscilla-
tory structural forces that arise when spherical particles are
confined in the gap between two surfaces (Basheva et al.
2007). In addition, particles can adsorb at the interfaces,
preventing the coalescence of bubbles in the froth phase
by providing a mechanical barrier to coalescence. The pres-
ence of adsorbed particles can also change the curvature
of the gas-liquid interface, reducing the pressure difference
between the plateau borders and the three films associated
with it, which can increase the stability of the foam phase
(Horozov 2008 Dickinson et al. 2010).
So far in this introduction, ultrafine particles have been
considered to have a negative impact on the flotation pro-
cess. However, in some cases, ultrafine particles are specifi-
cally designed and added to the cell to increase the efficiency
of the froth flotation. Yang et al. (Yang et al. 2011) have used
nanoparticles (NPs) as collectors to increase the hydropho-
bicity of coarser particles and improve their recovery. They
reported on laboratory-scale flotation experiments using
glass beads (GBs), a model particle for minerals, and two
different sizes (46 and 120 nm) of polystyrene NPs as col-
lectors. According to Yang et al., NP collectors are likely to
influence two important steps in the sequence of flotation
mechanisms: the attachment of the mineral particle to the
air bubble surface after collision, and the unwanted detach-
ment of the mineral particles from the bubbles. According
to Yang et al. (Yang et al. 2011), NP collectors can facili-
tate attachment by increasing the rupture thickness of the
water film, i.e., less film drainage is required before rupture
occurs, thus increasing its probability. Furthermore, it is
argued that during the dewetting process, the three-phase
contact line (TPCL) can jump from hydrophobic site to
hydrophobic site, facilitating the expansion of the TPCL
from the critical radius to form a stable wetting perimeter.
In this paper, we study the dynamics of particles attach-
ment to a single bubble using a modeled stirred cell. The
setup allows for precise control of the bubble size and direct
observation of the bubble surface, providing the potential
to study packing density, packing structure, and selectivity.
Using this approach, we study the attachment of GBs with
mean diameters of 66 µm micron and 176 µm micron to
a single bubble in the presence of ultrafine particles. We
show that our approach can provide valuable insights into
the dynamics of the attachment process in which ultrafine
and fine particles co-exist.
MATERIALS AND METHODS
Materials
Hexadecyltrimethylammonium bromide (CTAB) is used as
the cationic surfactant to hydrophobicize the GBs. CTAB
has a molecular weight of 364.45 g.mol–1, a hydrophilic-
lipophilic balance (HLB) of 10, and a critical micelle con-
centration of 0.91 mM (Maestro et al. 2012). Two different
sizes of spherical soda-lime GBs with a mean diameter of
D50 =66 ± 3 µm and D50 =176 ±3 µm (uncertainty range
from three repeated laser diffraction measurements), and a
specific density of 2.5 g.cm–3 were purchased from Merck
and used as model particles for model flotation experiments.
The particle size distribution of the GBs was measured
using a HELOS/KR-Vario laser diffractometer (HELOS/
BR, Sympatec, Germany). For the zeta potential of the
GBs, a value of –40 mV at pH 9 is given in the literature
(Ata 2008). A commercially available colloidal dispersion
of silica NPs, Levasil 300/30 (with a stock concentration
of 30 wt%, Nouryon, Germany), was used as the stock NP
dispersion. The nominal particle size of Levasil was 9 nm,
but due to electrostatic discharge of the particles caused by
CTAB adsorption on them, the mean diameter increased
to 0.3 µm. Ultrapure water (from a Milli-Q ELGA appara-
tus, United Kingdom) with 18.2 MΩ.cm resistivity and less
than 2 ppb organic content is used to prepare the aqueous
solutions.
The GBs were conditioned according to Ata (Ata
2008). That is, 1 gr of GBs is added to a beaker containing
15 ml of CTAB solution of the desired concentration and
stirred with a magnetic stirrer for about 15 minutes. The
volume of the surfactant solution is proportionally adjusted
for different mass concentrations of GBs, to provide the
same ratio of surfactant molecules to GB particles. The GBs
were then drained and thoroughly rinsed with clean water
to remove any remaining free surfactants.
Dynamic Coating
The experimental setup shown in Figure 1 is designed to
study the dynamics of particles attachment to a single bub-
ble. The setup consists of an attachment chamber with a
cross-sectional area of 32 mm × 32 mm filled with ultrapure
water and a defined amount of hydrophobized GBs, with
seconds to several hours, whereas 30 µm galena particles can
only increase the froth lifetime to 60 seconds (Pugh et al.
2005). There are several mechanisms by which particles can
influence the stability of particle-laden froths. For example,
particles can increase the viscosity of the aqueous phase in
the froth lamella, which in turn can slow down the drain-
age of the liquid and increase the froth stability (Horozov
2008). Particles can also form a layered structure within the
thinning film and stabilize it through the so-called oscilla-
tory structural forces that arise when spherical particles are
confined in the gap between two surfaces (Basheva et al.
2007). In addition, particles can adsorb at the interfaces,
preventing the coalescence of bubbles in the froth phase
by providing a mechanical barrier to coalescence. The pres-
ence of adsorbed particles can also change the curvature
of the gas-liquid interface, reducing the pressure difference
between the plateau borders and the three films associated
with it, which can increase the stability of the foam phase
(Horozov 2008 Dickinson et al. 2010).
So far in this introduction, ultrafine particles have been
considered to have a negative impact on the flotation pro-
cess. However, in some cases, ultrafine particles are specifi-
cally designed and added to the cell to increase the efficiency
of the froth flotation. Yang et al. (Yang et al. 2011) have used
nanoparticles (NPs) as collectors to increase the hydropho-
bicity of coarser particles and improve their recovery. They
reported on laboratory-scale flotation experiments using
glass beads (GBs), a model particle for minerals, and two
different sizes (46 and 120 nm) of polystyrene NPs as col-
lectors. According to Yang et al., NP collectors are likely to
influence two important steps in the sequence of flotation
mechanisms: the attachment of the mineral particle to the
air bubble surface after collision, and the unwanted detach-
ment of the mineral particles from the bubbles. According
to Yang et al. (Yang et al. 2011), NP collectors can facili-
tate attachment by increasing the rupture thickness of the
water film, i.e., less film drainage is required before rupture
occurs, thus increasing its probability. Furthermore, it is
argued that during the dewetting process, the three-phase
contact line (TPCL) can jump from hydrophobic site to
hydrophobic site, facilitating the expansion of the TPCL
from the critical radius to form a stable wetting perimeter.
In this paper, we study the dynamics of particles attach-
ment to a single bubble using a modeled stirred cell. The
setup allows for precise control of the bubble size and direct
observation of the bubble surface, providing the potential
to study packing density, packing structure, and selectivity.
Using this approach, we study the attachment of GBs with
mean diameters of 66 µm micron and 176 µm micron to
a single bubble in the presence of ultrafine particles. We
show that our approach can provide valuable insights into
the dynamics of the attachment process in which ultrafine
and fine particles co-exist.
MATERIALS AND METHODS
Materials
Hexadecyltrimethylammonium bromide (CTAB) is used as
the cationic surfactant to hydrophobicize the GBs. CTAB
has a molecular weight of 364.45 g.mol–1, a hydrophilic-
lipophilic balance (HLB) of 10, and a critical micelle con-
centration of 0.91 mM (Maestro et al. 2012). Two different
sizes of spherical soda-lime GBs with a mean diameter of
D50 =66 ± 3 µm and D50 =176 ±3 µm (uncertainty range
from three repeated laser diffraction measurements), and a
specific density of 2.5 g.cm–3 were purchased from Merck
and used as model particles for model flotation experiments.
The particle size distribution of the GBs was measured
using a HELOS/KR-Vario laser diffractometer (HELOS/
BR, Sympatec, Germany). For the zeta potential of the
GBs, a value of –40 mV at pH 9 is given in the literature
(Ata 2008). A commercially available colloidal dispersion
of silica NPs, Levasil 300/30 (with a stock concentration
of 30 wt%, Nouryon, Germany), was used as the stock NP
dispersion. The nominal particle size of Levasil was 9 nm,
but due to electrostatic discharge of the particles caused by
CTAB adsorption on them, the mean diameter increased
to 0.3 µm. Ultrapure water (from a Milli-Q ELGA appara-
tus, United Kingdom) with 18.2 MΩ.cm resistivity and less
than 2 ppb organic content is used to prepare the aqueous
solutions.
The GBs were conditioned according to Ata (Ata
2008). That is, 1 gr of GBs is added to a beaker containing
15 ml of CTAB solution of the desired concentration and
stirred with a magnetic stirrer for about 15 minutes. The
volume of the surfactant solution is proportionally adjusted
for different mass concentrations of GBs, to provide the
same ratio of surfactant molecules to GB particles. The GBs
were then drained and thoroughly rinsed with clean water
to remove any remaining free surfactants.
Dynamic Coating
The experimental setup shown in Figure 1 is designed to
study the dynamics of particles attachment to a single bub-
ble. The setup consists of an attachment chamber with a
cross-sectional area of 32 mm × 32 mm filled with ultrapure
water and a defined amount of hydrophobized GBs, with