Effect of Phyllosilicate Minerals on the Rheology, Colloidal and ...

<strong>Effect</strong> <strong>of</strong> <strong>Phyllosilicate</strong> <strong>Minerals</strong> on the Rheology,
Colloidal and Flotation Behaviour <strong>of</strong> Chalcopyrite
Mineral
Saeed. Farrokhpay* and Bulelwa Ndlovu
JKMRC, University <strong>of</strong> Queensland, 40 Isles Road, Indooroopilly, QLD 4068, Australia
* Email: s.farrokhpay@uq.edu.au
Abstract- The effects <strong>of</strong> phyllosilicate minerals, namely
illite, muscovite, talc, kaolinite and montmorillonite, on the
flotation <strong>of</strong> chalcopyrite were investigated. For this
purpose, the effect <strong>of</strong> these phyllosilicate minerals on the
froth stability, rheological properties, zeta potential as well
as copper flotation grade and recovery was investigated. It
was found that various phyllosilicate minerals behave
differently when added to the chalcopyrite slurries,
however, they all caused the flotation grade to be reduced,
albeit at different levels.
The effect <strong>of</strong> different phyllosilicate minerals on the froth
stability <strong>of</strong> chalcopyrite slurry followed the order <strong>of</strong>
montmorillonite> muscovite >illite > kaolinite, talc. The
effect on the rheology <strong>of</strong> chalcopyrite slurries was more or
less negligible, except for montmorillonite where the
suspension behaviour shifted from near Newtonian to
pseudoplastic.
The effect <strong>of</strong> phyllosilicate minerals on the zeta potential <strong>of</strong>
chalcopyrite particles was also varied. While 30%
montmorillonite and kaolinite had a very minimal effect,
addition <strong>of</strong> 30% muscovite to the chalcopyrite slurry
resulted in the zeta potential values being closer to the
pure muscovite suggesting full surface coverage <strong>of</strong>
chalcopyrite particles.
Montmorillonite and talc had the most deleterious effect
on chalcopyrite flotation. The deleterious effect <strong>of</strong>
montmorillonite is attributed to both rheology and froth
stability. The deleterious effect <strong>of</strong> muscovite is also
attributed to the surface coatings <strong>of</strong> the chalcopyrite
particles.
Keywords: <strong>Phyllosilicate</strong> minerals, chalcopyrite, flotation,
clays
I. INTRODUCTION
The difficulty <strong>of</strong> treating ores in the presence <strong>of</strong> clay minerals
is well known in the mineral processing industry [1, 2]. Clay
minerals have been named as one <strong>of</strong> the main problems in
leaching and milling processes due to their small size, which
causes a higher viscosity in grinding and also blocks the
leaching path [3]. The situation is hardly better in froth
flotation. For example, bentonite can greatly depress coal
flotation by reducing the froth stability [4]. The effect <strong>of</strong> clay
minerals on froth stability in flotation has been recently
reviewed [2].
The various deleterious roles <strong>of</strong> clay minerals in froth flotation
have been investigated by a number <strong>of</strong> authors [5-7]. The
effects include i) surface coating <strong>of</strong> the mineral surfaces [8],
ii) increasing reagent consumption due to their high surface
area [9], iii) transferring large quantities <strong>of</strong> clay minerals into
the concentrate during the flotation process, iv) increasing
pulp viscosity [4], and v) changing froth stability (decreasing
or increasing) [5, 10]. Even so, there is still no clear
understanding <strong>of</strong> the specific effects <strong>of</strong> different phyllosilicate
minerals on froth flotation. This is perhaps due to the
complexity that arises when dealing with multicomponent ore
systems as has <strong>of</strong>ten been the case in the mentioned studies.
Moreover, different phyllosilicate minerals are likely to
present dissimilar effects on flotation, due to varying inherent
hydrophobic or rheological properties.
Froth stability is a key parameter in controlling and optimising
the mineral grade and recovery in flotation. It not only
depends on the frother type and concentration, but also on the
amount and nature <strong>of</strong> the suspended particles (particle
hydrophobicity and size) [11]. These are then inherent
properties <strong>of</strong> the minerals and mineral type in the slurry. Other
parameters which could influence froth stability include the
quality <strong>of</strong> process water, gas dispersion, particle contact angle,
conditioning <strong>of</strong> flotation feed particles with various chemical
reagents, froth height, temperature, salt concentration, particle
size and froth retention time [11, 12]. The froth stability <strong>of</strong>
mineral slurries has been successfully investigated at
laboratory scale using a “froth column” [13, 14]. The effect <strong>of</strong>
phyllosilicate minerals on froth stability can be examined in a
similar manner.

The suspension rheology is also important in determining the
hydrodynamics and dispersion properties within the pulp
phase. This, in turn, affects the minerals reporting to the
concentrate. The rheological properties <strong>of</strong> mineral slurries are
<strong>of</strong> great practical importance in many mineral processing
applications as they are useful indicators <strong>of</strong> the degree <strong>of</strong>
aggregation and dispersion <strong>of</strong> particles within that suspension
[15, 16]. For example, the design and operation <strong>of</strong> pumping
systems <strong>of</strong> particulate suspensions is based on the viscosity
and yield stress values. In such an application, knowledge <strong>of</strong>
the yield stress is significant in ensuring the successful start-up
<strong>of</strong> a pumping system from a static shut down condition. The
viscosity is an indication <strong>of</strong> the pumping requirements and
ease <strong>of</strong> flow thereafter. Studies linking the mineralogical
content and rheological response have identified phyllosilicate
gangue minerals as major contributors towards ore flow
behaviour [17, 18]. This is supported by fundamental studies
which have been conducted on pure phyllosilicate mineral
suspensions, reporting significantly higher viscosities and
yield stresses in the presence <strong>of</strong> phyllosilicate minerals
(particularly swelling clays and serpentine minerals) compared
to non-phyllosilicate mineral suspensions (e.g. quartz) [19,
20]. The importance <strong>of</strong> rheology in mineral processing has
also recently been reviewed [21].
This study seeks to investigate the effects <strong>of</strong> different
phyllosilicate minerals (namely illite, muscovite, talc,
kaolinite and montmorillonite) on the flotation <strong>of</strong> chalcopyrite
mineral. By using such a simplified model mineral system,
rather than an ore comprising multicomponent mineral
systems, the effects <strong>of</strong> the different phyllosilicate minerals can
be better elucidated.
II.
A. Material
MATERIAL AND EXPERIMENTALS METHODS
Pure chalcopyrite, illite, talc, kaolinite, montmorillonite and
muscovite were used in this study. Chalcopyrite single
mineral, with a purity <strong>of</strong> more than 98%, was obtained from
Ward’s Science (USA). Kaolinite Q38 (pre-ground) was
provided by Unimin Australia Limited. All other phyllosilicate
samples were obtained in a pre-ground form Ward’s Science.
Potassium amyl xanthate (PAX) and MIBC, were used as
collector and frother, respectively, in copper flotation.
Brisbane tap water was used throughout the study.
B. Flotation
200g <strong>of</strong> chalcopyrite was ground to P80 <strong>of</strong> 75 microns and
suspended in a 1L bottom driven flotation cell. The flotation
tests were conducted at 20% solid (by weight) at a pH <strong>of</strong> 8.
This is within the pH range at which most industrial flotation
runs are conducted. 100 g/t sodium alkyl xanthate (PAX) and
40 ppm MIBC were used as collector and frother, respectively.
The pH was monitored and adjusted if needed using KOH and
HCl. Three concentrates were collected at 10 seconds intervals
over 1, 3 and 5 minutes (cumulative).
C. Froth stability tests
Chalcopyrite was ground to P80 <strong>of</strong> 75 microns for froth
stability tests. Varying concentrations <strong>of</strong> each phyllosilicate
were added to the pure chalcopyrite and the froth stability <strong>of</strong>
each slurry was assessed (at laboratory scale) using a specially
designed froth stability column [22, 23]. The froth column
consists <strong>of</strong> a 100 cm high acrylic column, with square 10 cm ×
10 cm section, in which pulp samples are introduced for
testing foaming proprieties. The column is provided with an
impeller to ensure sufficient pulp agitation and a porous plate
at the bottom for uniform air diffusion. Air flow is regulated
by means <strong>of</strong> a flow-meter, and the same Jg as in flotation
(1 cm/s) was maintained during the tests. A 2 L sample was
conditioned with the collector and frother and placed into the
apparatus. Once the pulp sample was introduced into the
column, the stirrer was turned on, in order to ensure sufficient
agitation and avoid settling <strong>of</strong> particles. At time t = 0, air was
turned on, and froth height against time was measured, until
an equilibrium value for the froth height H f0 was reached. At
this point, air was turned <strong>of</strong>f, and froth decay measured. The
half-life <strong>of</strong> the froth, i.e. the time needed for the froth to
collapse to half its equilibrium height, was taken as an
indicator for froth stability.
D. Rheology measurements
The rheology <strong>of</strong> suspensions <strong>of</strong> the chalcopyrite-phyllosilicate
mixtures was analysed using an Anton Paar DR301 rheometer.
In each case, 60 mL <strong>of</strong> slurry was taken from the flotation cell.
Each suspension was stirred using a magnetic stirrer, ensuring
homogeneity and suspension <strong>of</strong> particles prior to rheology
testing. Measurements were conducted in triplicate for each
slurries using a cup and bob geometry. The shear rate was
adjusted from 2 to 300 s -1 , and then reverse from 300 to 2 s -1
and no significant hysteresis observed. The same tests were
conducted on the flotation tailings. Different equivalent
concentrations <strong>of</strong> pure chalcopyrite suspensions were also
tested to determine if changes in rheological behaviour were
due to either increasing total solid concentration or to the
effect <strong>of</strong> clay addition.
E. Zeta potential measurements
The zeta potential <strong>of</strong> the chalcopyrite and phyllosilicate mineral
samples was measured as a function <strong>of</strong> pH using a Colloidal
Dynamics ZetaProbe. 100 grams <strong>of</strong> chalcopyrite was ground to
obtain P80 <strong>of</strong> 38 µm. The suspension was prepared and in
0.001M NaCl solution. The pH was reduced from 10.5 to 4.5,
using 0.2 M HCl and NaOH solutions to adjust the pH
accordingly during measurement.
III.
RESULTS AND DISCUSSIONS

A. Flotation
Figure 1 shows the changes in Cu grade <strong>of</strong> chalcopyrite upon
the addition <strong>of</strong> varying concentrations <strong>of</strong> each phyllosilicate.
The Cu flotation recovery was unchanged at about 90%, with
or without addition <strong>of</strong> phyllosilicate minerals. However, the
Cu grades were lower in the presence <strong>of</strong> all tested
phyllosilicate minerals. The Cu grade <strong>of</strong> pure chalcopyrite
flotation is 34.8% (calculated based on Cu in CuFeS 2 ). Figure
1 shows that with the addition <strong>of</strong> the maximum tested amount
<strong>of</strong> illite, kaolinite and muscovite, the Cu grade decreases (from
34.8%) to about 30%, 28% and 26.5%, respectively. The Cu
grade decreases dramatically to 22% when 30% <strong>of</strong> talc or 15%
<strong>of</strong> montmorillonite was added to the chalcopyrite flotation.
Talc is known to be hydrophobic and one may expect it to
float during mineral flotation. Therefore, it is <strong>of</strong>ten depressed
in industry by using a depressant such as CMC or guar gum
[24].
the froth stability results may need further validation as talc
had a strong tendency to stick to the froth column walls during
testing, making analysis particularly difficult.
Figure 2: <strong>Effect</strong> <strong>of</strong> phyllosilicate minerals (illite , kaolinite ■, muscovite ▲,
montmorillonite ●, and talc x) on the froth stability (half-life) <strong>of</strong> chalcopyrite
suspension
Figure 1: <strong>Effect</strong> <strong>of</strong> phyllosilicate minerals (illite , kaolinite ■, muscovite ▲,
montmorillonite ●, and talc x) on the copper grade in chalcopyrite flotation
(Cu flotation recovery unchanged at about 90%).
C. Rheology
Figure 3 shows the rheograms <strong>of</strong> pure chalcopyrite
suspensions at increasing solid concentration. These tests were
conducted to gauge whether any changes in rheology could be
attributed to chalcopyrite or to the added phyllosilicate
minerals. The results show a similar rheological trend for
chalcopyrite concentrations between 20 to 30%. However,
there is a considerable increase in the slurry viscosity at 40%
solid by weight. These results suggest that in the range <strong>of</strong> total
solids concentration up to 30% (by wt.), any change in the
chalcopyrite slurry rheology, after addition <strong>of</strong> phyllosilicate
minerals is indeed due to the phyllosilicate addition and not a
result <strong>of</strong> the increased solid concentration <strong>of</strong> the chalcopyrite.
In order to understand the effect <strong>of</strong> phyllosilicate minerals on
the chalcopyrite flotation, froth stability, rheology and zeta
potential measurements were conducted, which are discussed
in the following sections.
B. Froth stability
Figure 2 shows the changes in froth half-life (froth stability)
upon the addition <strong>of</strong> different phyllosilicate minerals. It can be
seen that montmorillonite and muscovite have a noticeable
effect on the froth stability <strong>of</strong> chalcopyrite suspension. The
froth height increases by 20-25% with the addition <strong>of</strong>
montmorillonite and muscovite to the mineral suspension. On
the other hand, illite has less effect, and both kaolinite and talc
have a negligible effect. Therefore, the effect <strong>of</strong> different
phyllosilicate minerals on the froth stability <strong>of</strong> chalcopyrite
suspension follows the order <strong>of</strong> montmorillonite> muscovite>
illite> kaolinite and talc. Montmorillonite demonstrated the
most noticeable effect on froth stability and, at the same time,
it has a major deleterious effect on chalcopyrite flotation
(Figure 1). Talc, on the other hand, which has the same effect
on the copper flotation grade seems to have a very minimal
effect on the froth stability. It should be noted, however, that
Figure 3: Rheology <strong>of</strong> chalcopyrite slurry as a function <strong>of</strong> solid%; for 20%▲,
30% □, and 40% ○.
Figures 4 and 5 also show the rheograms <strong>of</strong> suspensions
containing chalcopyrite and varying concentrations <strong>of</strong> each
phyllosilicate. The results show that there is no marginal
rheological effect observed for all phyllosilicate minerals other
than montmorillonite.
Figure 5 shows that montmorillonite considerably affects the
chalcopyrite slurry rheology. Addition <strong>of</strong> 5 to 10%
montmorillonite causes a slight change in the rheology <strong>of</strong>

chalcopyrite slurry. However, a different rheological
behaviour with a yield stress is observed by addition <strong>of</strong> 15%
montmorillonite. The significant change in the rheology can
be related to the considerable effect montmorillonite had on
the froth stability, compared to the other four phyllosilicate
minerals tested in this study. In fact, when the effects <strong>of</strong> the
phyllosilicate minerals on the rheology <strong>of</strong> chalcopyrite slurry
are compared to each other, the prominent effect <strong>of</strong>
montmorillonite is very clear.
The extreme rheological effects observed for montmorillonite
are in agreement with the results <strong>of</strong> Ndlovu et al. [25], which
demonstrated a ‘critical’ concentration <strong>of</strong> < 4% by volume for
pure montmorillonite, while this occurs at much higher
concentrations for the other minerals in their pure form (>
15% solids by volume).
Figure 4: <strong>Effect</strong> <strong>of</strong> kaolinite, illite, talc and muscovite on the chalcopyrite
slurry (20 wt%) rheology as a function <strong>of</strong> solid% <strong>of</strong> phyllosilicate minerals
(0% +, 10% □, 20%▲ and 30% ●).

Figure 7 shows the zeta potential curves <strong>of</strong> suspensions <strong>of</strong>
each phyllosilicate and chalcopyrite-phyllosilicate mixtures (at
varying mixture concentrations). The results show that the zeta
potential <strong>of</strong> chalcopyrite with 30% montmorillonite and
kaolinite is very close to that <strong>of</strong> pure chalcopyrite particles.
However, addition <strong>of</strong> 30% muscovite to the chalcopyrite
suspension results in zeta potential values closer to the pure
muscovite, which may suggest full surface coverage <strong>of</strong>
chalcopyrite particles with muscovite. Addition <strong>of</strong> 30% talc
and illite to the chalcopyrite suspension also results in zeta
potential values shifting between that <strong>of</strong> chalcopyrite and
these phyllosilicate minerals, as one may expect from partial
surface coatings <strong>of</strong> chalcopyrite particles. A similar behaviour
can be seen when 10% <strong>of</strong> all phyllosilicate minerals is added
to the chalcopyrite suspension.
Figure 5: <strong>Effect</strong> <strong>of</strong> Montmorillonite (0% +, 5% □, 10%▲, and 15% ●) on the
chalcopyrite slurry (20 wt%) rheology.
D. Zeta potential
Figure 6 shows the zeta potential curves <strong>of</strong> pure
chalocopyrite. The results show that the zeta potential <strong>of</strong>
chalcopyrite is about -25 mV at pH above 8.5. However below
pH <strong>of</strong> 8.5, the zeta potential becomes less negative, reaching
the iso electric point (iep) at pH about 5.5. Therefore, it is
negatively charged across the pH examined in this project (pH
8). The iep <strong>of</strong> non-oxidized chalcopyrite in different salt
solutions has been reported to be between pH 4-5 [12]. The
observed zeta potential is then within the range <strong>of</strong> previously
reported values. However, Peng and Zhang [26] have reported
the iep <strong>of</strong> chalcopyrite, after grinding with peroxide, exhibited
at around pH 8.5, indicating strong oxidation. Sulfide minerals
get oxidised quickly and therefore the zeta potential does vary.
Figure 6: Zeta potential <strong>of</strong> chalcopyrite (repeated 4 times with 95%
confidence).
CONCLUSIONS
Various phyllosilicate minerals were found to behave
differently when added to the chalcopyrite slurry, however,
they all caused the flotation grade to be reduced. Addition <strong>of</strong>
the maximum tested amount <strong>of</strong> illite, kaolinite and muscovite
caused the Cu grade to decrease (from 34.8%) to about 30%,
28% and 26.5%, respectively (at the same flotation recovery).
The Cu grade was also decreased dramatically to about 22%
when 30% talc or 15% montmorillonite was added to the
chalcopyrite flotation. Therefore, the effect <strong>of</strong> phyllosilicate
minerals on the flotation <strong>of</strong> chalcopyrite can be ranked as talc,
montmorillonite> muscovite> kaolinite> illite.
The ranking for different phyllosilicate minerals on the froth
stability <strong>of</strong> chalcopyrite slurry followed the order <strong>of</strong>
montmorillonite > muscovite >illite > kaolinite, talc.
An increase in the concentration <strong>of</strong> each phyllosilicate mineral
resulted in more complex suspension rheology, but the effect
was negligible except for montmorillonite where the
suspension behaviour shifted from near Newtonian to
pseudoplastic.
The effect <strong>of</strong> phyllosilicate minerals on the zeta potential <strong>of</strong>
chalcopyrite particles was varied. While 30% montmorillonite
and kaolinite had a very minimal effect, addition <strong>of</strong> 30%
muscovite to the chalcopyrite slurry resulted in the zeta
potential values being closer to the pure muscovite suggesting
full surface coverage <strong>of</strong> chalcopyrite particles. Addition <strong>of</strong>
30% talc and illite to the chalcopyrite suspension also resulted
in zeta potential values shifting between that <strong>of</strong> chalcopyrite
and these phyllosilicate minerals, as one may expect from
partial surface coverage.
Montmorillonite and talc were found to have the most effect
on chalcopyrite flotation. From this study, the deleterious
effect <strong>of</strong> montmorillonite can be related to both rheology and
froth stability. The deleterious effect <strong>of</strong> muscovite can also be
related to the surface coatings <strong>of</strong> the chalcopyrite particles (as
observed in the zeta potential results) which also affect the
froth stability. There is no evidence in this study to support the

Kaolinite
Illite
Talc
deleterious effect <strong>of</strong> talc, however, one may relate it to the
ability <strong>of</strong> talc to float and decrease the concentration grade, as
it is a naturally hydrophone phyllosilicate mineral.
Montmorillonite and talc were found to have the most effect
on chalcopyrite flotation. From this study, the deleterious
effect <strong>of</strong> montmorillonite can be related to both rheology and
froth stability. The deleterious effect <strong>of</strong> muscovite can also be
related to the surface coatings <strong>of</strong> the chalcopyrite particles (as
observed in the zeta potential results) which also affect the
froth stability. There is no evidence in this study to support the
deleterious effect <strong>of</strong> talc, however, one may relate it to the
ability <strong>of</strong> talc to float and decrease the concentration grade, as
it is a naturally hydrophone phyllosilicate mineral.
The study undertaken here was conducted in a simplistic
manner. Indeed, the phyllosilicate minerals behave differently
with different effects on flotation performance. While not
underpinning the specific effects <strong>of</strong> the minerals, this study
has aided in better understanding the exact effects <strong>of</strong> each
mineral. More rigorous analysis would be required for in
depth understanding.
ACKNOWLEDGMENT
The authors would like to acknowledge Yang Jiang, Annie
Nguyen and Elisheba Radke for practical testwork during their
summer vacation project at the JKMRC.
Muscovite
Montmorillonite
Figure 7: Zeta potential <strong>of</strong> chalcopyrite (●), phyllosilicate (as marked) (■),
and chalcopyrite/ phyllosilicate mixed suspensions (10% ▲; and 30% ◊
phyllosilicate).
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