1. The document examines the effect of water salinity on gold ore treated with flotation reagents using atomic force microscopy. 2. It finds that pyrite treated with copper sulfate activator and potassium amyl xanthate collector in non-saline solutions forms large masses on its surface believed to be dixanthogen, increasing the surface's attractive adhesive force due to hydrophobic interaction. 3. However, pyrite treated in saline solutions did not show the same trend and instead displayed a larger repulsive force with copper sulfate and a minor attractive force with potassium amyl xanthate, believed to be due to hydrated cations and salts interfering with surface forces.

1. 10.6Appendix F: Draft Manuscriptfor Publication
The effect of water salinity on gold ore treated with flotation
reagents on the forces contributing to mineral hydrophobicity
using Atomic Force Microscopy (AFM)
Zachary Hearne
Department of Chemical Engineering, Curtin University of Technology, Western Australia, Australia
Submitted 14 November 2014
Abstract
Atomic forcemicroscopyhas been used to observethetransition in surfacestructureand surfaceadhesion of pyrite
within polished samples of sulphidic gold oreover acourseof treatmentwith 6 x 10-5 M Copper Sulphate(CuSO4)
activator and 6 x 10-5 M Potassium Amyl Xanthate(PAX) collectorin solutions of varyingsalinity at pH 5.9. Copper
activated pyritetreated with PAX showed theformation of largemasses on themineral surfacebelieved to betheproduct
of reaction of thesurfacewith xanthate resultingin theaccumulation of dixanthogen. Thesurfacedensity of thesemasses
was consistent with an increasingattractiveforceof adhesion that has been observed with residencetimein solution.
Adhesion forcemeasurements showed an attractiveadhesiveforcethat has been attributed to thehydrophobic
interaction of thesurfacelayer of dixanthogen with thecantilever dueto thehydrophobic forcegenerated by the
interaction of dixanthogen with theaqueous environment. Pyritetreated in salt solutions did not showthesametrend in
growth and adhesion that has been characterized by alargerepulsiveforcewhen treated with CuSO4 followed bythe
recovery of aminor attractiveforcewith PAX. This phenomenon is believed to arisefrom theonset of repulsivehydration
forces dueto excessivehydrated cationsin solution bound tothemineral surface, and ionized salts in solution interfering
with Van der Waals forces between molecules of water. From thedatarecovered on surfaceadhesion and images of
surfacetopography, theformation of dixanthogen is evidentlyresponsiblefor thedevelopmentof ahydrophobic surface,
and that salts in solution limit thedevelopment of ahydrophobicsurfaceas aresult of thedisruption of theforcesof
interaction between theaqueous layer and mineral surface, and restricted collector adsorption of xanthates.
1. Introduction
Gold mining operations within the
Eastern Goldfields of Western Australia use
hypersaline water within their process
circuitry due to its abundance within the
local area, long-term availability due to
natural recharge, and local water
stringencies restricting the use of potable
water on site. KCGM, Australia’s largest
producer of gold, mines and processes
golden miledolerite from the Fimiston open
pit operation located within the Eastern
Goldfields where the gold exists
predominately as tellurides and inclusions
within pyrite. Mineral flotation is a major
component of its operations in the recovery
of gold as a sulphide mineral froth
concentrate. Mineral surface hydrophobicity
is justifiably the most important factor in
the selective recovery of the valuable
mineral constituent from host gangue
within mineral flotation. Within an industry
facing greater competitiveness, higher
operations costs and commodity price
volatility, there is a need for better flotation
efficiency, and therefore a need to
understand the implications of salts
contained within process water.
An extensive number of studies have been
conducted on selective sulphide recovery.
Most of the studies reviewed recognized
that the recovery of sulphides is achieved by
the selective chemical adsorption of
xanthates (RX) to the mineral surface
forming metal xanthates (MX) and
eventuating to dixanthogen (X2) that
hydrophobizes the surface [4,6,11,14], and
through mineral-bubble adherence by
hydrophobic interaction selectively
hydrophobised solids can be recovered.
Leppinen [4] using FTIR-ATR spectroscopy
evidenced the co-formation of ferric-
xanthate and dixanthogen on pyrite. These
results have been corroborated by Vucinic,
Popov and Tomanec [11] using ATR-IR
spectrometry, and Wang, Forssberg and
Bolin [14] with the use of developed
Pourbaix diagrams. Proposed within

2. Napier-Munn and Wills [7], the reaction of
metal sulphide with collector follows:
2𝑀𝑆 + 4𝑋−
+ 3𝐻2 𝑂
→ 2𝑀( 𝑋)2 + 𝑆2 𝑂3
2−
+ 6𝐻+
+ 8𝑒−
(1)
Similarly, Wang, Forssberg and Bolin [14]
proposed the following for the co-reduction
of xanthate and ferric ion to dixanthogen:
𝐹𝑒3+
+ 2𝑋−
→ 𝐹𝑒2+
+ 0.5(𝑋)2 + 2𝑒−1
(2)
And within Subasinghe’ Mineral Processing
562 Handbook [9], the following was
proposed:
0.5𝑂2 ( 𝑔) + 𝐻2 𝑂( 𝑙) + 2𝑅𝑂𝐶𝑆𝑆( 𝑎𝑞)
−
↔ 𝑅𝑂𝐶𝑆 − 𝑆𝑆 − 𝑆𝐶𝑂𝑅(𝑎𝑞) + 2𝑂𝐻(𝑎𝑞)
−
(3)
Most studies however were conducted in
controlled, high purity environments,
raising the question of how such systems
would respond within environments of high
salt content. The literature has provided
little information about the impact of salts
on the formation of hydrophobic surfaces,
presenting an opportunity to research what
implications salt has in process water on the
forces contributing to mineral
hydrophobicity.
Studies on mineral hydrophobicity are
commonly conducted using the surface
contact angle method or using the
Hallimond tube technique. Atomic Force
Microscopy has become a versatile imaging
tool that possesses the capacity to
distinguish, quantify and characterize the
detectable mechanical material properties
of a sample surface at the nano-scale. A
number of studies have successfully
exploited the functionality of AFM to
quantify hydrophobic forces and infer
mineral hydrophobicity [3,5,8,12,13].
AFM is particularly useful in allowing the
user to observe at the nano-scale the
transition in surface structure of the sample
over the course of treatment, and deriving
from force-distance data measurements of
adhesion, warranting its use to capture the
transition in surface topography and
adhesion when looking at the treatment of a
mineral surface to flotation reagents, and to
study the outcome of treatment over time
on mineral surface hydrophobicity.
This present paper looks to understand the
fundamental principles controlling the
surface behavior of pyrite within saline
environments using Atomic Force
Microscopy surface adhesion
measurements. The transition of surface
topography and surface adhesion has been
monitored by AFM over the course of
treatment with flotation reagents. Adhesion
force measurements have been used to
indicate a level of surface hydrophobicity.
2. Experimental Methods
2.1 Materials
Purified water treated by Reverse
osmosis of unspecified resistivity was used
in the makeup of all reagent solutions
within this work. Milli-Q water of resistivity
18.2 MΩ was used during work with AFM.
Dry Potassium Amyl Xanthate (PAX)
collector and Copper Sulphate Pentahydrate
crystal (CuSO4.5H2O) collector were
provided by the university. The pH
adjustments to solutions were made using
solutions of dissolved Sodium Hydroxide
salt (NaOH) and Hydrochloric Acid (HCl)
provided by the university. Artificial salt
solutions were created dissolvingvarying
amounts of Sodium Chloride (NaCl) salt and
Magnesium Sulphate (MgSO4) salts in store.
2.2 Sample and Sample Preparation
Hand selected samples of crushed
gold ore were obtained from KCGM’
Fimiston ore stockpile. Samples of the ore
were cut to provide slides of size 1cm x1cm
x 0.5cm and set into an epoxy resin forming
a circular mold and leaving the surface
exposed. The surface roughness was
reduced to 1µm by preliminary coarse
sanding followed by fine sanding using
siliconcarbide sandpaper of grits in the
order of 240, 320, 400, 600, 800, 1000 and
finally 1200. Polishing of the surface was
carried out using a rotary sander with 9µm,
6µm, 3µm and 1µm diamond pastes,
between each stage in polishing the surface
cleaned in an ultrasonic bath. Sample
surfaces were blown with nitrogen gas and
washed with Mill-Q water prior to use
within the AFM to remove any residual
polishing material and foreign material.
2.3 Atomic Force Microscopy
Sample surfaces were analysed
with a Bruker Dimension FastScan AFM
using Bruker’ PeakForce Tapping ModeTM in
a fluid operated with ScanAsyst® to image

3. the change in surface topography and
adhesion over the course of treatment with
reagents. All AFM images were taken using
Peak Force Quantitative Nano-Mechanical
mapping in fluid using a ScanAsyst® Fluid
Probe sharpened triangular-shaped silicon-
tipped nitride cantilever with a nominal
spring constant of 0.7N/m. Default image
settings were accepted for all experimental
work (1.95Hz scanning rate, 256
samples/line x 256 lines/image, 250 mV
amplitude setpoint). All images were taken
immersed in solution that focused on a
singular point on the polished sample
surface, typically a grain of pyrite within the
mineral complex imaged over a 500nm x
500nm cross-sectional area.
2.4 Data Analysis
Data recovered as force-distance
data from AFM measurements have been
analyzed and interpreted using Gwyddion
software to provide 2- and 3-dimensional
maps of surface topography and tabulated
data on adhesion measurements. Imaging
correction tools have been applied to
remove AFM imaging errors.
2.5 Experimental Procedure
Polished samples were secured to
the base of a shallow open cylindrical glass
dish using a heat-activated adhesive and
placed onto the platform beneath the AFM
scanner head. Primary experiments
involved treating the sample surface with a
weakly acidic solution of water of pH 5.9
and immediately treating with 6 x 10-5 M
CuSO4 activator solution allowing a sitting
time of 5 minutes. 6 x 10-5 M PAX was added
to the sample surface and allowed to sit up
to 20 minutes. Secondary experiments
involved treating the sample surface with
weakly-acidified saline solutions containing
50% equivalent (11.58 g MgSO4 + 69.08g
NaCl) and 100% equivalent (23.15 g MgSO4
+ 138.17g NaCl) salts contents of salts found
in local bore water sourced for KCGM’
Fimiston operation, and similarly treating
afterwards with 6 x 10-5 M CuSO4 and 6 x 10-5
M PAX. All throughout treatment the sample
surfaces were analyzed with AFM. Solutions
were injected in controlled amounts using a
micropipette between the face of the sample
surface and the AFM scanner forming a film
bridging both faces.
Prior to imaging, the slides were wetted
with additive-free Milli-Q water for
calibration of the AFM for imaging in a fluid.
3. Results and Discussion
3.1 AFM Surface Topography Observations
Images in figure 2 show the change
in surface topography of pyrite with time
over the course of treatment with varying
reagents and concentrations of salts in
solution. Figure 2c for copper-activated
pyrite with PAX in salt-free water at pH 5.9
shows the formation of large masses
immediately after treatment with PAX that
continues to grow with time in treatment.
Surfaces treated in salt did not show the
same growth, showing almost no change in
surface topography. A surface anomaly was
identified on figure 2e that is likely some
foreign material that has been introduced
into the system. The growth observed is
believed to be dixanthogen accumulating on
the surface. Figure 1 below is a rudimentary
illustration of the process of copper
activation and xanthate adsorption and
dixanthogen accumulation according to
equations (1), (2) and (3):
Figure 1: (top) Copper activation of pyrite(middle)
deposition and adsorption of collector with surface
sites of iron and copper (bottom) dixanthogen
formation and accumulation
AuAu
Fe S Fe S Fe S Fe S Fe S Fe S
FeS S S Fe S SS- - - - - -
- - - - - -
2+2+2+ 2+
2+
2+ 2+
Cu2+
Cu2+
Fe
2+
Fe2+
Cu
2+
Fe2+
Cu2+
SO2-
4
SO2-
4
SO2-
4
Cu
2+
P-28
AuAu
Fe S Fe S Fe S Fe S Fe S Fe S
S S S Fe S SS- - - - - -
- - - - - -
2+ 2+
2+
2+
Fe
2+
Cu
2+
Cu
Cu
2+
Cu
2+
2+2+ 2+
S
S
C
O
R
-
2+
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C O R
-
S
S
C O R
-
S
S
C O R
S
C
O
R
S
S C
O
R
-
-
AuAu
Fe S Fe S Fe S Fe S Fe S Fe S
S S S Fe S SS- - - - - -
- - - - - -
2+
2+
2+
Fe
2+
Cu
2+
Fe
Cu
2+
Fe
2+
2+ 2+
2+
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S
C
O
R
-
S
S C O R
S
S
COR
-
S
S C O R
S
S
COR

4. 11.8 nm
Figure 2: AFM surfacetopography falsecolorimages of pyritegrains within theFimiston gold oresamplesurfacein fluid.
Images from top to bottom: Salt freewater;50% equivalent salts; 100%equivalent salts
Images from left to right: immediately in mildly acidic water; 5 minutes CuSO4 treatment; 5 minutes PAX treatment
3.2 AFM Surface Adhesion Observations
Trends in adhesion over the course
of treatment are shown in figures 3, 4 and 5
that reflect the interaction of the cantilever
with the mineral surface. A negative value of
adhesion corresponds to an overall
repulsive force that opposes the approach of
the cantilever tip which is being pressed
towards the surface, and a positive value of
adhesion corresponds to an attractive force
acting on the cantilever tip that maintains
tip to surface contact against the retractive
action of the cantilever. Pyrite treated in
salt-free water was characterized by an
attractive force of adhesion that increased
(a) (b) (c)
(d) (e) (f)
(g) (h) (i)
17.2 nm 16.3 nm 23.4 nm
15.8 nm 21.3 nm 12.2 nm
10.3 nm 12 nm
0 nm 0 nm 0 nm
0 nm0 nm0 nm
0 nm0 nm0 nm

5. with each stage in treatment and time in
treatment to reach a peak force of 1.04nN at
ten minutes in PAX and steadying within a
5% variance thereafter (figures 3). This
phenomenon is explained by the formation
of surface xanthate compounds and
accumulation of dixanthogen, and the
hydrophobic interaction of the surface with
the cantilever tip as a result of the
hydrophobic force generated by the re-
structuring of water molecules within the
vicinity of the hydrophobised surface such
that the cohesive energy of the hydrated
layer increases to permit solid-to-solid
contact [7,10,13]. The attractive force of
adhesion suggests that pyrite treated with
PAX becomes hydrophobic.
Figure 3: Averageadhesion forceof imaged pyritearea
in salt-freepH-modified water throughoutstages of
treatment
Pyrite in salt solutions was characterized by
a large repulsive force followed by the
recovery of a minor attractive force. Pyrite
in 50% equivalent salts observed a
repulsive force of -0.2204nN at fiveminutes
in CuSO4 treatment (figure 4), and similarly
in 100% equivalent salts a repulsive force of
-0.5739nN (figure 5) that recovers to a
more-or-less neutral state when treated
with PAX. The repulsive force can be
explained by the onset of hydration forces
due to the elevated presence of cations in
solution that bind to the mineral surface
through electrostatic attraction becoming
hydrated in solution, that at the expense of
the system to try and dehydrate those
cations at the approach of the cantilever to
the mineral surface a repulsive force is
generated (figure 6) [1,2]. These findings
are consistent with that of Butt [1] and
Pashley and Israelachvilli (1983) (cited
within Butt [1]) who tested the interaction
of mica surfaces with a siliconnitride
cantilever using divalent salts, measuring a
repulsive force. The addition of diluted
CuSO4 solution may have to a greater extent
hydrated the cations bound to the mineral
surface.
Figure 4: Averageadhesion forceof imaged pyritearea
in salinepH-modified water (50% equivalent salts)
throughout stages of treatment
Figure 5: Averageadhesion forceof imaged pyritearea
in salinepH-modified water (100% equivalent salts)
throughout stages of treatment
Cappella and Diteler [2] evidenced the
interference salts create on the electrostatic
forces of interaction in solution. The
deposition of salts and in solution interferes
with the surface electrostatic charge carried
by the mineral surface in solution that
would impact the effectiveness of CuSO4 and
PAX addition to solution. Teschke and Souza
[10] similarly suggested that the adsorption
of ionic species in solution to the mineral
surface modifies the surface interfacial ionic
charge and the Debye length.
Figure 6: Hydrated cationic speciesat themineral
surface, and theeffect of hydration forces on the
cantilever tip
AuAu
Fe S Fe S Fe S Fe S Fe S Fe S
FeS Fe Fe S Fe S Fe S Fe S FeS- - - - - -
- - - - - -
2+ 2+ 2+ 2+ 2+ 2+
2+ 2+ 2+ 2+ 2+ 2+
Mg
2+
Na
+Na
+
Mg
2+ Mg
2+
Water

6. The recovery of the surface force with PAX
to a margin above zero suggested two likely
scenarios: the displacement of salts at the
surface bound by weak electrostatic forces
by injected PAX solution, or the deposition
of PAX creating a composite layering of
salts, water and PAX. Wang, Yoon and
Morris [13] found that with flushing salt
solution with pure water between two
hydrophobised surfaces the hydrophobic
force was restored, suggesting that salt in
fact does not retard the surface products
responsible for hydrophobic force but
interferes with the forces at play, citing
Zhang et al. [15] that foreign electrolyte
species in solution disrupts the organized
hydrogen-bonding structure of water
molecules between two surfaces, reducing
the cohesive energy of water and reducing
the hydrophobic force. From their work, we
can establish that the interactions of
excessive ionic species in solution impede
the Van der Waals intermolecular forces
between water molecules and disorganizing
the structure of water between surfaces. In
the absence of surface characterizing
products to influence the structure of water,
extremely low values of adhesion are
yielded when the surface is partially cleared
of salts.
4. Conclusions
AFM has been successfully applied
to imaging the transition in surface
topography and surface adhesion of pyrite
throughout the stages of treatment in
solutions of differing salinity. A number of
authored works have been referenced to
assist in explaining the findings.
The topographical images in salt-free water
showed the formation of large masses with
PAX treatment insinuated to be dixanthogen
on the surface that grew with time in
treatment. This growth saw a corresponding
increase in the attractive force of adhesion
which was inferred to a more hydrophobic
surface as a result of dixanthogen formation.
Tests in salts showed no distinctive growth
on the surface. Adhesion measurements
were characterised by a large repulsive
force with treatment in activator believed to
be overriding hydration forces, followed by
the recovery of a marginal attractive force
with collector due to salt displacement
rather than collector adsorption. Mineral
hydrophobicity has been attributed to the
orientation of water molecules within the
volume of water between two surfaces, and
the response of the aqueous layer to factors
affecting the intermolecular interactions of
water including solubilised ionic species,
surface products and surface charge.
Findings from both topographical and
adhesion measurements using AFM suggest
that salts in solution will inhibit the
formation of a hydrophobic mineral surface
as a result of the disruption of forces of
interaction between the surfaces and the
aqueous layer, where mineral
hydrophobicity on pyrite is induced by the
formation of surface xanthate compounds
and accumulation of dixanthogen on the
surface.
The information gathered can only provide
an indication of flotation response within
salt environments. Mineral surface
hydrophobicity has been inferred from
adhesion measurements within a static
environment that is not representative of
the behaviour of particles that would be
observed within an agitated aerated mineral
pulp. As salts are bound to the surface only
by weak electrostatic forces of attraction,
agitation would see the surface is constantly
replenished. Within an agitated vessel, the
film layer on the mineral surface would be
constantly replaced due to agitation, and
collector chemical adsorption would be
observed to a degree in such an
environment.
5. Consequences
The accuracy of representation of samples is
dependent on how the surface has been
prepared. Unfortunately during sample
preparation the sample has been exposed to
air and polishing material that has likely
oxidised the surface forming surface
inhibiting products restricting activator and
collector adsorption. Though each slidewas
purged in nitrogen gas and washed in Mill-Q
water, oxidised products will always be
present giving a less accurate
representation of the true response of the
mineral surface to the solution conditions.
Also, tip microasperities unavoidably
formed during the manufacturing process
have not been taken into account during
measurements. Tip roughness, etch pits and
sharpness will have a minor impact on the
accuracy of the measurements recorded.

7. Acknowledgements
The author would like to express
his gratitude for the support received by the
various members of staff at Curtin
University including Dr. Chi Phan, Dr.
Thomas Becker and Mr. Andy Viereckl, and
Mr. Joe Morgan on behalf of KCGM for
providing the ore samples used for this
research.
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