XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 477
and Carpick, 2005] while DMT considers “attractive inter-
actions acting at all separations between the sphere and
the plane.” [Grierson, Flater and Carpick, 2005] The work
of Sansao (non-AFB based) [Sansao et al., 2021a, 2021b,
2022, 2023] used JKR mechanics, while the AFM work
performed for this work used DMT mechanics.
EXPERIMENTAL PROCEDURES
For this work silica glass discs and mica discs were pur-
chased from Electron Microscope Sciences and the silica
discs were 8 mm in diameter and 0.19 mm thick and mica
disks were V-1 quality, 8.5 mm in diameter and 0.2 mm
thick. Surface treatments of the disks included cleaning
the as-received materials in a Harrick Plasma Asher, and
when required treating the disks with silane coupling agent
treatments using trichlorooctadecyl silane (TCOD) or
n1-(3-trimethoxysilylpropyl) diethylene triamine (TMPA.)
These coupling agent treatments were performed in the
same manner as previous work in our group [Sansao et al.,
2021a, 2021b, 2022]. A Bruker Multimode 8 was used
for atomic force microscopy (AFM) measurements. The
experiments were performed using the Peak Force TUNA
software and performed according to the manufacturers
recommended procedures. Two different types of AFM tips
were used to collect force-displacement curves. The first
is a Bruker ScanAsyst-Air silicon tip with an approximate
0.4 N/m cantilever spring constant. The second type of tip
was manufactured using our Focused Ion Beam (FIB) facil-
ity (ThermoScientific Helios 5 CX gallium FIB-SEM) to
manufacture our own silica tips. Silicon and silica tips were
considered to be similar as the silicon tip will likely have
oxide coating on its surface.
Focused Ion Beam (FIB) Tip Manufacture
As mentioned above, AFM tips were produced by focused
ion beam (FIB) milling. Inspiration for the technique
came from Wang et al.’s work (Wang and Butte, 2014).
A bulk silica mineral chosen from silica provided by the
Department of Geology and Geological Engineering at
South Dakota Mines was mounted on an SEM stub.
Once a region of interest was identified, the FIB was used
to trench out a sub-volume of the mineral approximately
10 × 10 × 10 microns, which was then extracted from the
bulk mineral with a nanomanipulator needle. This subvol-
ume was then mounted to the AFM cantilever by tungsten
deposition and subsequent removal of the nanomanipula-
tor. From this point, the sub-volume was milled at several
rotational angles with the FIB to produce a sharp tip suit-
able for AFM use. Throughout this process the FIB was
operated at 30 keV, with trenching currents of 9 nA, and
tip shaping currents of 70 pA. Final FIB polishing of the tip
was performed at 8 keV and 70 pA to remove amorphized
surface material typically produced by FIB processes at
30 keV. Figure 1 shows the AFM tip manufactured by FIB.
RESULTS AND DISCUSSION
There has been considerable interest recently within the
mineral processing field with respect to sustainable prac-
tices, particularly practices reducing water usage in min-
eral processing as evidenced by recent books such as Dry
Mineral Processing [Chelgani and Neisiani, 2022] and
Recent Advances in Mineral Processing Plant Design
[Malhotra et al., 2009].
Our research group has also been working in this
area [Sansao et al., 2021a, 2021b, 2022, 2023] and have
developed and patented a humidity-controlled, adhesion-
force-based technique for mineral processing [Sansao et al.,
2023]. The results of this initial work have been to show
that the adhesion of model particles can be measured by a
variety of techniques, including contact angle goniometry
and a modified drop test. In addition, a separation win-
dow occurs between ~45% and 75% relative humidity for
10–100 µm hydrophobic and hydrophilic silica particles
with a hydrophilic surface that was modified with a cleaned,
stainless steel, 325 × 2300 mesh Dutch-weave screen. Some
water would be needed to generate the humidity in the gas
phase, but far less would be used than is used in froth flota-
tion, for example.
In this research adhesion measurements using atomic
force microscopy (AFM) have been performed. Two types
of tip materials were used. The first material type were
standard silicon tips purchased from Bruker. The second
tip type was manufactured in-house from quartz mineral
pieces utilizing our focused ion beam system. A tip of this
second type is shown in Figure 1.
In AFM adhesion measurements the tip on a canti-
lever measures the interaction force between the tip and
the substrate. The force is measured from the cantilever
bending resulting in a force-displacement curve as shown
in Figure 2. The cantilever vibrates and as the tip moves
toward the surface eventually the interaction force over-
whelms the cantilever spring constant and the tip snaps into
contact with the surface. The tip is subsequently retracted
from the surface and the adhesion force is determined from
the force as the tip leaves the surface, see Figure 2. Both
the tip and the substrate can have their surfaces modified,
although this was only performed for the substrates in
this work. In many previous works, the tip is modified by
securing a particle to the tip and measuring the adhesion
of the particle to the substrate [Dorobantu et al., 2009 Jin
and Carpick, 2005] while DMT considers “attractive inter-
actions acting at all separations between the sphere and
the plane.” [Grierson, Flater and Carpick, 2005] The work
of Sansao (non-AFB based) [Sansao et al., 2021a, 2021b,
2022, 2023] used JKR mechanics, while the AFM work
performed for this work used DMT mechanics.
EXPERIMENTAL PROCEDURES
For this work silica glass discs and mica discs were pur-
chased from Electron Microscope Sciences and the silica
discs were 8 mm in diameter and 0.19 mm thick and mica
disks were V-1 quality, 8.5 mm in diameter and 0.2 mm
thick. Surface treatments of the disks included cleaning
the as-received materials in a Harrick Plasma Asher, and
when required treating the disks with silane coupling agent
treatments using trichlorooctadecyl silane (TCOD) or
n1-(3-trimethoxysilylpropyl) diethylene triamine (TMPA.)
These coupling agent treatments were performed in the
same manner as previous work in our group [Sansao et al.,
2021a, 2021b, 2022]. A Bruker Multimode 8 was used
for atomic force microscopy (AFM) measurements. The
experiments were performed using the Peak Force TUNA
software and performed according to the manufacturers
recommended procedures. Two different types of AFM tips
were used to collect force-displacement curves. The first
is a Bruker ScanAsyst-Air silicon tip with an approximate
0.4 N/m cantilever spring constant. The second type of tip
was manufactured using our Focused Ion Beam (FIB) facil-
ity (ThermoScientific Helios 5 CX gallium FIB-SEM) to
manufacture our own silica tips. Silicon and silica tips were
considered to be similar as the silicon tip will likely have
oxide coating on its surface.
Focused Ion Beam (FIB) Tip Manufacture
As mentioned above, AFM tips were produced by focused
ion beam (FIB) milling. Inspiration for the technique
came from Wang et al.’s work (Wang and Butte, 2014).
A bulk silica mineral chosen from silica provided by the
Department of Geology and Geological Engineering at
South Dakota Mines was mounted on an SEM stub.
Once a region of interest was identified, the FIB was used
to trench out a sub-volume of the mineral approximately
10 × 10 × 10 microns, which was then extracted from the
bulk mineral with a nanomanipulator needle. This subvol-
ume was then mounted to the AFM cantilever by tungsten
deposition and subsequent removal of the nanomanipula-
tor. From this point, the sub-volume was milled at several
rotational angles with the FIB to produce a sharp tip suit-
able for AFM use. Throughout this process the FIB was
operated at 30 keV, with trenching currents of 9 nA, and
tip shaping currents of 70 pA. Final FIB polishing of the tip
was performed at 8 keV and 70 pA to remove amorphized
surface material typically produced by FIB processes at
30 keV. Figure 1 shows the AFM tip manufactured by FIB.
RESULTS AND DISCUSSION
There has been considerable interest recently within the
mineral processing field with respect to sustainable prac-
tices, particularly practices reducing water usage in min-
eral processing as evidenced by recent books such as Dry
Mineral Processing [Chelgani and Neisiani, 2022] and
Recent Advances in Mineral Processing Plant Design
[Malhotra et al., 2009].
Our research group has also been working in this
area [Sansao et al., 2021a, 2021b, 2022, 2023] and have
developed and patented a humidity-controlled, adhesion-
force-based technique for mineral processing [Sansao et al.,
2023]. The results of this initial work have been to show
that the adhesion of model particles can be measured by a
variety of techniques, including contact angle goniometry
and a modified drop test. In addition, a separation win-
dow occurs between ~45% and 75% relative humidity for
10–100 µm hydrophobic and hydrophilic silica particles
with a hydrophilic surface that was modified with a cleaned,
stainless steel, 325 × 2300 mesh Dutch-weave screen. Some
water would be needed to generate the humidity in the gas
phase, but far less would be used than is used in froth flota-
tion, for example.
In this research adhesion measurements using atomic
force microscopy (AFM) have been performed. Two types
of tip materials were used. The first material type were
standard silicon tips purchased from Bruker. The second
tip type was manufactured in-house from quartz mineral
pieces utilizing our focused ion beam system. A tip of this
second type is shown in Figure 1.
In AFM adhesion measurements the tip on a canti-
lever measures the interaction force between the tip and
the substrate. The force is measured from the cantilever
bending resulting in a force-displacement curve as shown
in Figure 2. The cantilever vibrates and as the tip moves
toward the surface eventually the interaction force over-
whelms the cantilever spring constant and the tip snaps into
contact with the surface. The tip is subsequently retracted
from the surface and the adhesion force is determined from
the force as the tip leaves the surface, see Figure 2. Both
the tip and the substrate can have their surfaces modified,
although this was only performed for the substrates in
this work. In many previous works, the tip is modified by
securing a particle to the tip and measuring the adhesion
of the particle to the substrate [Dorobantu et al., 2009 Jin