minerals
Article
Study of the Effect of Sodium Sulfide as a Selective
Depressor in the Separation of Chalcopyrite
and Molybdenite
Huiqing Peng 1 , Di Wu 1, *, Mohamed Abdalla 1,2 , Wen Luo 1 , Wenya Jiao 1 and Xuexiang Bie 1
1
2
*
School of Resource and Environmental Engineering, Wuhan University of Technology, 122 Luoshi Road,
Wuhan 430070, China; [email protected] (H.P.); [email protected] (M.A.);
[email protected] (W.L.); [email protected] (W.J.); [email protected] (X.B.)
Mining Engineering Department, University of Khartoum, Khartoum 11111, Sudan
Correspondence: [email protected]
Academic Editor: Massimiliano Zanin
Received: 19 December 2016; Accepted: 27 March 2017; Published: 30 March 2017
Abstract: Two kinds of collectors, sodium butyl xanthate and kerosene, and a depressor, sodium
sulfide, were used in this research. The study applied flotation tests, pulp potential measurements,
contact angle measurements, adsorption calculations, and Fourier Transform Infrared Spectroscopy
(FTIR) analyses to demonstrate the correlation between reagents and minerals. For xanthate collectors,
the best flotation responses of chalcopyrite and molybdenite were obtained at pH = 8, and, for
kerosene, these were obtained at pH = 4. The flotation of molybdenite seemed to be less influenced
by xanthate than by kerosene, while that of chalcopyrite showed the opposite. The optimum
concentration of sodium sulfide for separation was 0.03 mol/L, which rejected 83% chalcopyrite and
recovered 82% molybdenite in the single mineral flotation. Pulp potential measurements revealed that
the dixanthogen and xanthate were decomposed and desorbed, respectively, from the mineral surface
in a reducing environment. The contact angle measurement and adsorption calculation conformed
to the flotation response, indicating that few functions of the xanthate and sodium sulfide on the
molybdenite flotation were due to their low adsorption densities. The FTIR results further clarified
that the xanthate ion was adsorbed on chalcopyrite by forming cuprous xanthate and dixanthogen;
however, on molybdenite the adsorption product was only dixanthogen. After conditioning with
sodium sulfide, the chalcopyrite surface became clean, but the molybdenite surface still retained
slight peaks of dixanthogen. Meanwhile, the possible mechanism was expounded in this research.
Keywords: chalcopyrite-molybdenite separation; sodium sulfide; pulp potential; contact angle;
adsorption; FTIR
1. Introduction
Molybdenite (MoS2 ), the main occurrence state of molybdenum resources, is generally associated
with chalcopyrite (CuFeS2 ) [1,2]. Since molybdenite is a valuable mineral, its collection and purification
are of crucial importance, which requires more attention to research on the collector and depressor [3].
Molybdenite is a natural hydrophobic mineral, cleaved by the rupture of the weak bond of
S–S [4], exposing a large slice of the sulfur hydrophobic face, which interacts with water only via
dispersion forces [5]. However, the element distribution on the chalcopyrite surface accords to its
chemical formula [6]. Cuprous/copper and ferric ions are known as the hydrophilic [7], resulting in
less hydrophobicity of chalcopyrite surfaces. Due to the big difference between these two minerals,
molybdenite can be recovered from a copper-bearing molybdenite ore by removing 99% of the copper [8].
Minerals 2017, 7, 51; doi:10.3390/min7040051
www.mdpi.com/journal/minerals
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Common sulfide mineral collectors such as xanthates and thiophosphates are known to adsorb
onto molybdenite but are not necessarily effective for molybdenite flotation. In molybdenite flotation,
the collector generally used is non-polar oil obtained from petroleum [9], such as kerosene and diesel
oil. From this, one can conclude that molybdenite must have different surface properties with other
sulfide minerals [10]. Therefore, the collector’s selection may provide an auxiliary way to separate
molybdenite from chalcopyrite.
As molybdenite has better inherent floatability, most beneficiation plants prefer to float
molybdenite and reject chalcopyrite to tailings. Lots of mineral treatment operations have paid
attention to the depressants of chalcopyrites, such as the reductant (e.g., sodium sulfide, sodium
hydrosulfide, Nokes, and sodium cyanide) [11–13], the oxidant (e.g., potassium permanganate
and potassium dichromate) [14–16], and some organic depressors (e.g., chitosan and thioglycolic
acid) [17,18]. The reductant is demonstrated to desorb the collector from the mineral surface in
a reduced condition or even form hydrophilic species. The oxidant generally oxidizes the mineral
surface and causes it to be hydrophilic. These organic depressors are declared to be hydrophilic
and cover the mineral surface to prevent the adsorption of collectors. Although these reagents have
a universal depression to sulfide minerals, molybdenite and chalcopyrite can successfully be separated
due to their different surface properties, which determine the sensitivities of minerals to the depressor.
In this study, two collectors, sodium butyl xanthate and kerosene, were tested to find their different
behaviors in the flotation of molybdenite and chalcopyrite under various conditions. Sodium sulfide,
a simple depressor, was also applied in this investigation to report the optimum dosage for the selective
flotation. Pulp potential and contact angle measurements were combined to demonstrate the flotation
response. The Brunauer-Emmett-Teller (BET) measurement, ultraviolet spectrophotometer (UV), and
inductively coupled plasma-optical emission spectrophotometry (ICP-OES) were used to calculate
the reagent ion adsorption capacity and density on the mineral surface. The surface properties before
and after conditioning with reagents were also analyzed by Fourier Transform Infrared Spectroscopy
(FTIR) measurements.
2. Experimental
2.1. Minerals and Reagents
Pure minerals of chalcopyrite (Cp) and molybdenite (Mot), both obtained from Guangxi, China,
were employed as experimental samples in this study. To ensure high-purity samples, large pieces
of the chalcopyrite and molybdenite were individually broken, and unwanted substances (gangue
minerals) were removed by tweezers under an optical microscope. X-ray diffraction (XRD) analyses
indicated that most impurities in chalcopyrite were quartz, while the impurities in molybdenite were
undetected (Figure 1). Chemical analyses showed that chalcopyrite contained 32.02% Cu, 29.13%
Fe, 33.16% S, and 3.63% SiO2 and that molybdenite contained 58.88% Mo and 40.03% S. In addition,
the chemical analysis method for Cu, Fe, S, and Si was titration, while for Mo it was carried out
with UV. The mineral samples were ground and powdered manually in an agate mortar, which had
high hardness, and it was difficult to contaminate the sample surface. Then they were screened to
−100 + 45 µm for flotation tests and adsorption measurements. The BET specific surface areas of these
size fractions of chalcopyrite and molybdenite were 0.31 and 0.57 m2 /g, respectively, determined by
an Autosorb-iQ analyzer (Quantachrome, Boynton Beach, FL, USA).
The collectors used in this investigation were sodium butyl xanthate (SBX) and kerosene, and the
forther used was terpenic oil. Sodium chloride was added to maintain the ionic strength of the solution
constant at 5 × 10−3 mol/L. Sodium sulfide (Na2 S·9H2 O) was used as the depressor. Hydrochloric
acid and sodium hydroxide were added for pH adjustments. Sodium butyl xanthate, kerosene, and
terpenic oil were industrial grade chemicals. Other reagents mentioned were of analytical grade.
Stock aqueous solutions of sodium sulfide and sodium butyl xanthate were prepared daily. De-ionized
water was used throughout this research work.
Minerals 2017, 7, 51
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3 of 17
10000
10000
C-Chalcopyrite
Q-Quartz
M
C
8000
6000
Intensity (counts)
8000
Intensity (counts)
M-Molybdenite-2H
C
4000
C
2000
Q
Q
CQ
C
Q
6000
4000
M
2000
20
30
40
50
o
2Theta ( )
(a)
60
70
M
M
MM
0
10
M
M
C
Q
0
M
10
20
30
MM
40
50
M
60
70
o
2Theta ( )
(b)
Figure
and (b)
(b) molybdenite.
molybdenite.
Figure 1.
1. X-ray
X-ray diffraction
diffraction (XRD)
(XRD) analyses
analyses of
of pure
pure minerals,
minerals, (a)
(a) chalcopyrite
chalcopyrite and
2.2. Laboratory Flotation Tests
2.2. Laboratory Flotation Tests
All flotation tests were conducted at 5% solids by weight in a 100 mL microflotation cell.
All flotation tests were conducted at 5% solids by weight in a 100 mL microflotation cell.
Mineral suspensions were prepared by single minerals at 22 °C
in the presence of air. The flotation
Mineral suspensions were prepared by single minerals at 22 ◦ C in the presence of air. The flotation
machine (Rock, Hanging Cell, Wuhan, China) operated at 1200 rpm and a flow rate of 0.6 dm33 per
machine (Rock, Hanging Cell, Wuhan, China) operated at 1200 rpm and a flow rate of 0.6 dm per
minute. Surface treated plexiglass cell walls and the impeller could effectively reduce the material
minute. Surface treated plexiglass cell walls and the impeller could effectively reduce the material
loss by adhesion during high-speed stirring. Five minutes was allowed for the conditioning of each
loss by adhesion during high-speed stirring. Five minutes was allowed for the conditioning of each
reagent. After 5 min flotation, both the concentrates and tailings were collected and dried to
reagent. After 5 min flotation, both the concentrates and tailings were collected and dried to calculate
calculate mineral recovery (weighed by an analytical balance for which sensitivity is 0.0001 g). All
mineral recovery (weighed by an analytical balance for which sensitivity is 0.0001 g). All tests were
tests were carried out in triplicate, and the average was taken to draw the figure. Obviously, if the
carried out in triplicate, and the average was taken to draw the figure. Obviously, if the result was not
result was not as expected or had big error compared to others, it would have been discarded.
as expected or had big error compared to others, it would have been discarded.
To fully understand the mineral flotation responses in different pHs and different collectors,
To fully understand the mineral flotation responses in different pHs and different collectors,
flotation tests were carried out at various pHs from 2 to 13 with SBX or kerosene. 100 g/t SBX or 40
flotation tests were carried out at various pHs from 2 to 13 with SBX or kerosene. 100 g/t SBX or 40 g/t
g/t kerosene and 25 g/t terpenic oil were added in sequence before adjusting the pH values. The
kerosene and 25 g/t terpenic oil were added in sequence before adjusting the pH values. The dosages
dosages were chosen by flotation tests, which are not presented in this paper. The dosages are 100 g/t
were chosen by flotation tests, which are not presented in this paper. The dosages are 100 g/t SBX
SBX and 40 g/t kerosene, which could get full recoveries of chalcopyrite and molybdenite,
and 40 g/t kerosene, which could get full recoveries of chalcopyrite and molybdenite, respectively,
respectively, in these microflotation tests. Although terpenic oil has certain floatability to sulfide
in these microflotation tests. Although terpenic oil has certain floatability to sulfide minerals, this
minerals, this dosage of 25 g/t is insufficient for it to be an effective collector but enough to improve
dosage of 25 g/t is insufficient for it to be an effective collector but enough to improve the solution
the solution surface activity. Flotation kinetic tests were carried out at pH 11 with or without
surface activity. Flotation kinetic tests were carried out at pH = 11 with or without collectors during
collectors during the flotation time from 0 to 5 min. The reagent addition steps were the same as with
the flotation time from 0 to 5 min. The reagent addition steps were the same as with the former.
the former. The aeration purged was air in these flotation tests.
The aeration purged was air in these flotation tests.
Selective flotation tests and pulp potential measurements were carried out at various sodium
Selective flotation tests and pulp −1
potential measurements were carried out at various sodium
sulfide concentrations from 10−−66 to 10−
with different collectors. After adding the mineral
1mol/L
sulfide concentrations
from
10
to
10
mol/L with different collectors. After adding the mineral
−3 mol/L NaCl aqueous solution, the collector (SBX or kerosene), the depressor
sample to a 5 × 10−
sample to a 5 × 10 3 mol/L NaCl aqueous solution, the collector (SBX or kerosene), the depressor
(sodium sulfide), and the frother (terpenic oil) were added in sequence then adjusted the pH to 11.
(sodium sulfide), and the frother (terpenic oil) were added in sequence then adjusted the pH to 11.
During the condition of each reagent, the mineral suspensions were opened to the atmosphere. After
During the condition of each reagent, the mineral suspensions were opened to the atmosphere.
that, in the beginning of the flotations and measurements, the suspensions were purged with
After that, in the beginning of the flotations and measurements, the suspensions were purged with
nitrogen. The pulp potential was measured by a smooth platinum electrode relative to a saturated
nitrogen. The pulp potential was measured by a smooth platinum electrode relative to a saturated
calomel electrode and recorded during the flotation time. The results were reported on a hydrogen
calomel electrode and recorded during the flotation time. The results were reported on a hydrogen
scale by adding 0.2415 V. Since sulfide ions are well known to poison Pt electrodes. causing a
scale by adding 0.2415 V. Since sulfide ions are well known to poison Pt electrodes. causing a sluggish
sluggish response and erroneous readings [19], electrodes were cleaned with 10% diluted
response and erroneous readings [19], electrodes were cleaned with 10% diluted hydrochloric acid and
hydrochloric acid and deionized water. The electrode system was calibrated using a standard
deionized water. The electrode system was calibrated using a standard ferric-ferrous solution [20].
ferric-ferrous solution [20].
Minerals 2017, 7, 51
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2.3. Contact Angle Measurements
The bulk molybdenite and chalcopyrite crystals used in this research were cut along with the
cleavage plane as flat shapes using a scalpel and a stainless steel saw, then exposed for polishing with
#800 to #2000 emery paper. Contact angle measurements were carried out at various concentrations of
sodium sulfide from 10−6 to 10−1 mol/L with or without collectors. After conditioning with various
concentrations of sodium sulfide for 5 min, the solution advancing and receding contact angle of the
flat mineral surfaces was immediately measured by the sessile drop method [21]. All measurements
were performed in triplicate.
2.4. Adsorption Measurements
The adsorption components in the flotation were butyl xanthate ions, kerosene, and sulfide ions.
Kerosene is an oily collector, and it was very easy to adhere to the vessel surface in this research,
whether the vessel was made of glass, plexiglass, or plastic. Therefore, the adsorption of kerosene was
not presented because of its big error.
An ultraviolet spectrophotometer was used to measure the concentration of SBX remaining in
the solution before and after contact with the sample. The characteristic peak of xanthate appears
at a wavelength of 301 nm [22]. Standard solutions of various concentrations of SBX, 0.5, 1, 2, 3, 4
and 5 g/L, were used to attain the standard linear equation, then referred to the absorption intensity
of the solution to calculate the concentration of xanthate remaining in the solution. An inductively
coupled plasma-optical emission spectrometer (Perkin Elmer, Model Optima 4300 DV, Waltham, MA,
USA) was used to quantify the element S in the solution before and after contact with the sample.
Since few sulfur-containing anions are released from mineral samples and the oxidization of the sulfide
reagent is maintained at a lower level, the total element S can be regarded as S2− from sodium sulfide.
The solution was then introduced into the plasma formed in the quartz torch by an alumina injector
(1.2 mm internal diameter (ID)). The formulas for calculating the adsorption capacity and adsorption
density are listed below.
AC = (Cb − Ca )V
(1)
AD =
AC
SBET ·m
(2)
AC—The adsorption capacity, mg.
Cb —The ion concentration in the solution before contact with the sample, mg/L.
Ca —The ion concentration in the solution after contact with the sample, mg/L.
V—The volume of the solution measured, L.
SBET —The BET specific surface area, m2 /g.
m—The mass of the sample, g.
AD—The adsorption density, mg/m2 .
2.5. FTIR Measurements
For the measurements of SBX adsorbed on mineral surfaces without contact with sodium sulfide,
5 g each pure sample and 100 g/t SBX were filled with deionized water to keep the final volume at
100 mL; the pH was adjusted to 11 and then stirred for 5 min using a magnetic stirrer. Similarly, for the
measurements of SBX adsorbed on mineral surfaces with sodium sulfide added, 5 g of each pure
sample and 100 g/t SBX were filled with 0.1 mol/L sodium sulfide solution to keep the final volume at
100 mL; the pH was also adjusted to 11, then stirred for 5 min using a magnetic stirrer. All reacted
solid samples were filtered out and water-washed to get rid of the remainder solution on the mineral
surface and dried using a vacuum pump with a Buchner funnel.
The adsorption of the chemical agent was assessed by utilizing attenuated total reflection (ATR)
Fourier transforms infrared (FTIR) spectroscopy. The ATR accessory was outfitted with a diamond
Minerals 2017, 7, 51
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Minerals 2017, 7, 51
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crystal as the reflection component. The spectrometer was supplied with a purgative system employing
reading.
spectra was
by spreading
solid sample
onto
crystal,
dried
airThe
to minimize
themeasured
consequence
of the labthe
wetness
causeddirectly
by water
on the
thediamond
sample reading.
which
required
a small
amount ofthe
sample.
Samplesdirectly
did notonto
undergo
any treatment
before
The
spectra
was only
measured
by spreading
solid sample
the diamond
crystal, which
measurement;
the
samples
were
more
sensitive
to
the
adsorbent
component.
required only a small amount of sample. Samples did not undergo any treatment before measurement;
the samples were more sensitive to the adsorbent component.
3. Results and Discussion
3. Results and Discussion
3.1. Laboratory Flotation Tests
3.1. Laboratory Flotation Tests
Figure 2 presents the flotation response of chalcopyrite and molybdenite as a function of pH by
Figure
presents
the With
flotation
molybdenite
as a function
of pH
adding
SBX2or
kerosene.
the response
addition of chalcopyrite
kerosene as aand
collector,
the flotation
recoveries
of
by
adding
SBX
or
kerosene.
With
the
addition
of
kerosene
as
a
collector,
the
flotation
recoveries
of
chalcopyrite and molybdenite both increased and then decreased as the pH increased. Their
chalcopyrite
and molybdenite
both
increased
and
then
maximum recoveries
appeared
at pH
3–4. This
can
be decreased
explained as
bythe
thepH
zetaincreased.
potentialTheir
of themaximum
minerals.
recoveries
at pH prefer
= 3–4. This
can beon
explained
by strength
the zeta potential
ofdepending
the minerals.
Non-polarappeared
oily collectors
to adsorb
zero field
materials,
onNon-polar
the value
oily
collectors
prefer
to adsorboronclusters
zero field
strength
materials,
depending
onbe
thepredicted
value assigned
to
assigned
to water
molecules
at the
interface
[23]. Thus
it could
that best
water
molecules
or clusters
at the
Thus
it could appeared
be predicted
flotation
recoveries
flotation
recoveries
of these
twointerface
minerals[23].
using
kerosene
at that
theirbest
points
of zero
charge
of
these The
two PZC
minerals
using kerosene
appeared
at their
points
of zero
charge
(PZCs).zeta
Thepotential
PZC of
(PZCs).
of chalcopyrite
is in the
low acidic
pH 2–3
region
[24,25].
However,
chalcopyrite
is in
low acidic give
pH =very
2–3 negative
region [24,25].
zeta potential
measurements
for
measurements
forthe
molybdenite
valuesHowever,
over the whole
pH range
[26,27]. It is due
molybdenite
give very
negative
values over the
[26,27].
It isfaces
due and
to theofanisotropic
to the anisotropic
surfaces
of molybdenite
thatwhole
both pH
the range
charges
of the
the edges
surfaces
of molybdenite
that
both
the charges
of the faces and
of the edges
contribute
to the overall
zeta
contribute
to the overall
zeta
potential
of molybdenite
particles.
Parreira
and Schulman
[28] used
potential
molybdenite
particles.
Parreira
and
Schulman [28]
very
wax instead
very pureofparaffin
wax instead
of the
face of
molybdenite
andused
found
thatpure
the paraffin
PZC of molybdenite
of
the face of molybdenite
thataround
the PZC
of4.molybdenite
hydrophobic
seemed
to be
hydrophobic
faces seemed and
to befound
situated
pH
Therefore, the
maximum faces
recovery
conforms
situated
around
pH
=
4.
Therefore,
the
maximum
recovery
conforms
to
the
PZC
of
the
mineral.
to the PZC of the mineral.
100
Recovery (%)
90
80
70
Chalcopyrite with SBX
Chalcopyrite with Kerosene
Molybdenite with SBX
Molybdenite with Kerosene
60
50
0
2
4
6
8
10
12
14
pH
Figure 2.
2. Flotation
of chalcopyrite
chalcopyrite and
and molybdenite
molybdenite as
as aa function
function of
of pH
pH by
by adding
adding sodium
sodium
Figure
Flotation recoveries
recoveries of
butyl
xanthate
(SBX)
(100
g/t)
or
kerosene
(40
g/t)
and
opening
to
the
atmosphere.
butyl xanthate (SBX) (100 g/t) or kerosene (40 g/t) and opening to the atmosphere.
With the increasing pH, the zeta potentials of chalcopyrite and molybdenite became more and
With the increasing pH, the zeta potentials of chalcopyrite and molybdenite became more and
more negative, and hydrophilic metal hydroxides began to generate on the mineral surfaces, causing
more negative, and hydrophilic metal hydroxides began to generate on the mineral surfaces, causing
the recovery decrease. The recovery of molybdenite was 20%–30% higher than that of chalcopyrite,
the recovery decrease. The recovery of molybdenite was 20%–30% higher than that of chalcopyrite,
with kerosene used as a collector in the whole pH range. This indicates that kerosene is a better
with kerosene used as a collector in the whole pH range. This indicates that kerosene is a better
collector for molybdenite, compared with chalcopyrite. When the collector addition was SBX, with
collector for molybdenite, compared with chalcopyrite. When the collector addition was SBX, with
increasing pH, chalcopyrite recoveries were raised to the maximum at pH 8, then were prominently
increasing pH, chalcopyrite recoveries were raised to the maximum at pH = 8, then were prominently
reduced in high alkaline conditions. However, molybdenite recoveries showed different tendencies.
reduced in high alkaline conditions. However, molybdenite recoveries showed different tendencies.
Two peaks of the recovery curve appeared at pH = 3 and 8, and the maximum recovery was obtained
Two peaks of the recovery curve appeared at pH = 3 and 8, and the maximum recovery was obtained at
at the latter. The low recoveries refer to the instability and weak hydrolysis of SBX in acidic
the latter. The low recoveries refer to the instability and weak hydrolysis of SBX in acidic environments.
environments. Under this condition, sodium butyl xanthate can react with hydrogen ions to form
butyl xanthate acid, which can easily be decomposed to carbon disulfide and butanol [29]. Once the
pH increases to alkaline, butyl xanthate ions (BX−) become relatively stable in the solution and react
Minerals 2017, 7, 51
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Under this condition, sodium butyl xanthate can react with hydrogen ions to form butyl xanthate
acid, which can easily be decomposed to carbon disulfide and butanol [29]. Once the pH increases
to alkaline, butyl xanthate ions (BX− ) become relatively stable in the solution and react with the
mineral surfaces to form hydrophobic species [30]. In high alkaline conditions, however, hydroxide
species can block the adsorption process of xanthate with metal ions [31]. The maximum recoveries
of both minerals appeared at pH = 8 and confirmed those mechanisms. Additionally, the peak of
molybdenite recoveries at pH = 3 was responsible for the PZC of the hydrophobic face. The recoveries
of molybdenite were also shown to be 0%–5% higher than those of chalcopyrite using SBX in whole pH
ranges but still 3%–10% lower than those of molybdenite using kerosene as a collector. The collector
contrast test indicates that the SBX is a better collector for chalcopyrite flotation, while kerosene is
better for molybdenite.
Figure 3 presents the flotation behavior of chalcopyrite and molybdenite as a function of flotation
time treated with different collectors at pH = 11. As shown in Figure 3a, chalcopyrite recoveries
increased dramatically from 0 to 2 min flotation and tended to be stable after 4 min flotation,
indicating that 5 min flotation is enough to get full chalcopyrite recoveries. Under these conditions,
chalcopyrite flotation using SBX as a collector showed the best recovery at 80% compared with the use
of kerosene (63% recovery) or collectorless (44% recovery). It indicates that both SBX and kerosene can
significantly improve chalcopyrite flotation. Kerosene can only physically adsorb on the chalcopyrite
surface because it has no active group. BX− can react with cuprous and copper ions exposed on
chalcopyrite surfaces to form CuBX and Cu(BX)2 [32], which refers to chemical adsorption. Moreover,
the dispersibility of SBX is better than kerosene in an aqueous solution; it has more opportunities
to contact chalcopyrite particles. Thus, chalcopyrite showed a better flotation response using SBX
as a collector. In the case of molybdenite flotation, shown in Figure 3b, 5 min flotation could reach
maximum recoveries by adding kerosene or none of the collectors but is almost insufficient when using
SBX. This is because xanthates are weak collectors for molybdenite and molybdenite is commonly
floated with the addition of non-polar oily collectors [33]. Castro and Mayata [34] have found that
fine particles of molybdenite (6.8 µm) practically do not respond to an increase in xanthate doses, but
with coarse particles (51.7 µm) flotation recoveries are significantly enhanced. The results suggest that
xanthate effectively improves the flotation of molybdenite only in large particle sizes, which have a
higher degree of inherent hydrophobic given by the large faces/edges ratio. Moreover, Castro [33]
has summarized that no insoluble metal xanthate has been detected on molybdenite, indicating that
xanthate ions cannot chemically adsorb on molybdenite surfaces. However, in the presence of dissolved
oxygen, semi-conducting minerals (sulfides) are able to electro-catalytically oxidize xanthate ions to
form non-polar dimmer molecules (dixanthogen), which adsorb on the faces sites of minerals [35,36].
Therefore, the effective flotation response is mainly attributed to non-polar oily collectors (i.e., kerosene
and dixanthogen). As the oxidation reaction of xanthate needs time to complete, 5 min for molybdenite
flotation with the addition of SBX as a collector was not enough to meet the maximum recovery.
Although SBX and kerosene both improve molybdenite floatability, kerosene is a better collector for
molybdenite flotation. Comparing the results from Figure 3a,b, molybdenite had stronger inherent
floatability, regardless of the collector used in the flotation, and the recovery of molybdenite always
showed a better response than that of chalcopyrite, which is consistent with the result in Figure 2.
7 of 17
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100
100
80
80
Molybdenite Recovery (%)
Chalcopyrite Recovery (%)
Minerals 2017, 7, 51
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60
40
Collectorless
Kerosene
SBX
20
0
60
40
Collectorless
Kerosene
SBX
20
0
0
1
2
3
4
5
0
1
2
3
Time (min)
Time (min)
(a)
(b)
4
5
Figure 3.
3. Flotation
(a) chalcopyrite
chalcopyrite and
(b) molybdenite
molybdenite at
at pH
pH =
= 11
11 as
as aa function
function of
of
Figure
Flotation recoveries
recoveries of
of (a)
and (b)
flotation
time
open
to
atmosphere
with
a
collector:
SBX
(100
g/t),
kerosene
(40
g/t),
or
collectorless.
flotation time open to atmosphere with a collector: SBX (100 g/t), kerosene (40 g/t), or collectorless.
The flotation behavior and the pulp potential of chalcopyrite treated with different dosages of
The flotation behavior and the pulp potential of chalcopyrite treated with different dosages of
sodium sulfide and 100 g/t SBX or 40 g/t kerosene used as the collector at pH = 11 are plotted in
sodium sulfide and 100 g/t SBX or 40 g/t kerosene used as the collector at pH = 11 are plotted in
Figure 4. According to the hydrolytic equilibrium of sodium sulfide in aqueous solution, the main
Figure 4. According to the hydrolytic equilibrium of sodium sulfide in aqueous solution, the main role
role of sulfur-containing anions is hydrosulfide. Optimum chalcopyrite flotation was obtained with
of sulfur-containing anions is hydrosulfide.
Optimum chalcopyrite flotation was obtained with sodium
sodium sulfide added at about
10−4 mol/L, indicating that a small amount of sodium sulfide addition
−
4
sulfide added at about 10 mol/L, indicating that a small amount of sodium sulfide addition could
could improve chalcopyrite flotation. It seems that hydrosulfide prefers to react with metal ions
improve chalcopyrite flotation. It seems that hydrosulfide prefers to react with metal ions dissolved
dissolved from chalcopyrite or its oxidized species, resulting in xanthate to more effectively float
from chalcopyrite or its oxidized species, resulting in xanthate to more effectively float chalcopyrite
chalcopyrite particles [37], and it also can be explained by the sulfur induced flotation of
particles [37], and it also can
be explained by the sulfur induced flotation of chalcopyrite, i.e., the HS−
chalcopyrite, i.e., the HS− ion is0 oxidized to hydrophobic S0 by redox reactions and adsorbs on
ion is oxidized to hydrophobic S by redox reactions and adsorbs on chalcopyrite surface to make it
chalcopyrite surface to make it more floatable [38,39]. As Chander [40] reveals that platinum
more floatable [38,39]. As Chander [40] reveals that platinum electrodes respond to changes in the
electrodes respond to changes in the hydrosulfide ion concentration in solution, the pulp potential in
hydrosulfide ion concentration in solution, the pulp potential in this study changed a little in the low
this study changed a little in the low sodium sulfide addition (Figure 4b). Chalcopyrite flotation
sodium sulfide addition (Figure 4b). Chalcopyrite flotation drastically
fell with the addition of sodium
drastically fell with−3the addition
of sodium sulfide from 5 × 10−3 to 3 × 10−2 mol/L. The edge of the
−
2
sulfide from 5 × 10 to 3 × 10 mol/L. The edge of the depression coincides with the drop in pulp
depression coincides with the drop in pulp potential. The poor flotation response when the sulfide
potential. The poor flotation−3 response when the sulfide added is greater than 5 × 10−3 mol/L and
added is greater than 5 × 10 mol/L and is directly related to a cathodic shift in potential below the
is directly related to a cathodic shift in potential below the value required for copper butyl xanthate
value required for copper butyl xanthate formation. Under reducing conditions, the mineral surface
formation. Under reducing conditions, the mineral surface is free of exchangeable oxide species
is free of exchangeable oxide species and highly negatively charged as a result of a high adsorption
and highly negatively charged as a result of a high adsorption density of hydrosulfide ions [41].
density of hydrosulfide ions [41]. These phenomena were generated by the competitive adsorption
These phenomena were generated by the competitive adsorption of hydrosulfide ions and butyl
of hydrosulfide ions and butyl xanthate ions with cuprous/copper ions on the chalcopyrite surface.
xanthate ions with cuprous/copper ions on the chalcopyrite surface. Figure 4b also shows a difference;
Figure 4b also shows a difference; the flotation response with kerosene added was still at a lower
the flotation response with kerosene added was still at a lower level, even though its pulp potential
level, even though its pulp potential was higher. According to the results in Figure 3, kerosene is not
was higher. According to the results in Figure 3, kerosene is not a suitable collector for chalcopyrite;
a suitable collector for chalcopyrite; its efficiency is astricted by the dispersibility in aqueous solution.
its efficiency is astricted by the dispersibility in aqueous solution. Further, kerosene does not show
Further, kerosene does not show the oxidation-reduction quality in this condition; it seems not to be
the oxidation-reduction quality in this condition; it seems not to be affected by the change of Eh.
affected by the change of Eh. This opinion agrees with the flotation behavior in large doses of
This opinion agrees with−1 the flotation behavior in large doses of sodium sulfide. With 10−1 mol/L
sodium sulfide. With 10 mol/L sodium sulfide added, the pulp potential was mainly controlled by
sodium sulfide added, the pulp potential was mainly controlled by the hydrosulfide ion, resulting in
the hydrosulfide ion, resulting in the similar Eh (about −390 mV) value for different collectors, but
the similar Eh (about −390 mV) value for different collectors, but their recoveries were against their
their recoveries were against their effectiveness shown in the high Eh lever. It can be clarified by the
effectiveness shown in the high Eh lever. It can be clarified by the physical motion of collector shapes,
physical motion of collector shapes, i.e., the kerosene drop and the butyl xanthate ion. During
i.e., the kerosene drop and the butyl xanthate ion. During violent stirring, the drop has a greater kinetic
violent stirring, the drop has a greater kinetic energy to break through the electrical double layer,
energy to break through the electrical double layer, and it directly contacts with particles or cocoons
and it directly contacts with particles or cocoons the particle, leading to more floatable chalcopyrite
the particle, leading to more floatable chalcopyrite (see Figure 5).
(see Figure 5).
Minerals 2017, 7, 51
Minerals 2017, 7, 51
Minerals 2017, 7, 51
8 of 17
8 of 17
8 of 17
CCh ha alco
lcop pyrite
yriteSSu uspspe en nsio
sion ns sEEh h(m(mVV) )
CCh ah lco
a lcop yrite
p yriteSSu sp
u spe ne sio
n sion sn sRRe co
e coveveryry(%(%) )
100
100
80
80
60
60
40
40
20
20
200
200
0
0
-200
-200
SBX
SBX
Kerosene
Kerosene
SBX
SBX
Kerosene
Kerosene
-400
-400
0
0
-6
-6
-4
-4
-2
-2
Log Sodium Sulfide Added (mol/L)
Log Sodium Sulfide Added (mol/L)
(a)
(a)
0
0
-6
-6
-4
-4
-2
-2
Log Sodium Sulfide Added (mol/L)
Log Sodium Sulfide Added (mol/L)
0
0
(b)
(b)
Figure4.
4.(a)
(a)The
Theflotation
flotationrecovery
recoveryofofchalcopyrite
chalcopyriteat
pH=11
11
as
function
ofadded
addedsodium
sodiumsulfide
sulfide
Figure
4.
(a)
11as
asaaafunction
functionof
of
added
sodium
sulfide
Figure
chalcopyrite
atatpH
pH
−3−mol/L
3
NaCl;
(b)
The
Eh
of
the
system
under
the
with
100
g/t
SBX
or
40
g/t
kerosene
added
in
5
×
10
−3
with 100
100 g/t
g/tSBX
SBXor
or40
40g/t
g/tkerosene
keroseneadded
addedinin55××
mol/L
NaCl;
(b) The
Ehthe
of system
the system
under
NaCl;
(b) The
Eh of
under
the
with
1010 mol/L
same
conditions.
the same
conditions.
same
conditions.
− ions
Figure 5.
Physicalmotions
motions
of
the
kerosene
drop
and
BX− −ions
ions meeting
meeting
with
the mineral
mineral
particle
Figure
5.5.Physical
ofof
the
kerosene
drop
andand
BX
meeting
with with
the
mineral
particleparticle
during
Figure
Physical
motions
the
kerosene
drop
BX
the
during
violent
stirring.
violent
stirring.
during violent stirring.
Actually,the
thebreakthrough
breakthroughphenomenon
phenomenonrarely
rarelyoccurs
occurssince
sincethe
thechalcopyrite
chalcopyriterecovery
recoveryisis
isstill
still
Actually,
Actually,
the
breakthrough
phenomenon
rarely
occurs
since
the
chalcopyrite
recovery
still
verylow.
low.The
Thehard
hardbreakthrough
breakthroughmay
maybe
becaused
causedby
bythe
themultilayer
multilayeradsorption
adsorptionof
ofhydrosulfide
hydrosulfideions
ions
very
very
low.
The
hard
breakthrough
may
be
caused
by
the
multilayer
adsorption
of
hydrosulfide
ions
on
mineral
surfaces,
which
were
thick
and
strongly
charged
negatively,
to
prevent
chalcopyrite
on
on mineral
mineral surfaces,
surfaces, which
which were
were thick
thick and
and strongly
strongly charged
charged negatively,
negatively, to
to prevent
prevent chalcopyrite
chalcopyrite
particles
from
contacting
with
collectors.
Hence,
depression
began
due
to
the
negatively
charged
particles
from
contacting
with
collectors.
Hence,
depression
began
due
to
the
negatively
particles from contacting with collectors. Hence, depression began due to the negatively charged
charged
surface,multilayer
multilayeradsorption
adsorptionof
ofhydrosulfide
hydrosulfideions,
ions,and
andreducing
reducingpotentials,
potentials,all
allof
ofwhich
whichimpede
impede
surface,
surface,
multilayer
adsorption
of
hydrosulfide
ions,
and
reducing
potentials,
all
of
which
impede
collector
adsorption.
collector
collector adsorption.
adsorption.
The
flotationresponse
responseof
ofmolybdenite
molybdenite(a)
(a)and
andits
itsEh
Eh(b)
(b)at
pH=11
11
under
various
concentrations
The
Eh
(b)
atatpH
pH
The flotation
flotation
response
11under
undervarious
variousconcentrations
concentrations
of sodium
sodium sulfide
sulfide with
withthe
theaddition
additionof
of100
100 g/t
g/t SBX
SBX
or 40
40 g/t
g/t kerosene
kerosene
as
collector are
are given
given in
in
of
of
sodium
sulfide
with
the
addition
of
100
g/t
SBXor
or
40
g/t
keroseneas
asaaacollector
collector
are
given
in
Figure
6.
The
molybdenite
recovery
seemed
unchangeable
in
a
low
dose
of
added
sodium
sulfide
Figure
Figure 6.
6. The
Themolybdenite
molybdeniterecovery
recoveryseemed
seemedunchangeable
unchangeablein
inaalow
low dose
dose of
of added
added sodium
sodium sulfide
sulfide
−4 mol/L), and a sharp drop occurred when the added sulfide concentration was more
(less
than
10
−
4
−4
(less
(less than
than 10 mol/L),
mol/L),and
anda asharp
sharpdrop
dropoccurred
occurredwhen
whenthe
theadded
addedsulfide
sulfideconcentration
concentrationwas
was more
more
−3 mol/L. This is similar to the flotation response of chalcopyrite, but the descent rate of
than 555××
×10
10
3 mol/L.
than
This
is similar
to the
flotation
response
of chalcopyrite,
butbut
thethe
descent
raterate
of
than
10−3−mol/L.
This
is similar
to the
flotation
response
of chalcopyrite,
descent
molybdenite
was
much
less
than
that
of
chalcopyrite.
The
pulp
potential
also
showed
the
same
trend.
molybdenite
was
much
less
than
that
of
chalcopyrite.
The
pulp
potential
also
showed
the
same
trend.
of molybdenite was much less than that of chalcopyrite. The pulp potential also showed the same
However,
there is
is aa remarkable
remarkable
difference
between
thethe
kerosene
and
SBX
molybdenite
flotation
However,
there
difference
between
the
kerosene
and
SBX
trend.
However,
there
is a remarkable
difference
between
kerosene
and
SBXmolybdenite
molybdeniteflotation
flotation
recoveries,
using
kerosene
as
a
collector,
were
stable
(about
87%)
in
the
sulfide
dose
range
from
10−4−4
recoveries,
collector,
were
stable
(about
87%)
in the
sulfide
dosedose
range
fromfrom
10
recoveries,using
usingkerosene
keroseneasasa a
collector,
were
stable
(about
87%)
in the
sulfide
range
−3 mol/L but decreased by about 5% when using SBX. These results may be caused by the
to−
10
to
554××to
10
mol/L
decreased
by about
when
These
be may
caused
by the
10
5−3 ×
10−3 but
mol/L
but decreased
by5%
about
5%using
whenSBX.
using
SBX.results
These may
results
be caused
unique
structure
of molybdenite
molybdenite
crystals.
According
to the
thethe
literature
[33],
molybdenite
has
unique
structure
of
crystals.
According
to
literature
by the unique
structure
of molybdenite
crystals.
According
to
literature[33],
[33],molybdenite
molybdenite has
has
anisotropic
surface
properties,
i.e.,
(1)
hydrophobic
faces
formed
by
the
break
of
weak
S–S
bonds
anisotropic
anisotropic surface
surface properties,
properties, i.e.,
i.e., (1)
(1) hydrophobic
hydrophobicfaces
faces formed
formedby
by the
the break
break of
of weak
weak S–S
S–S bonds
bonds
and
(2)
hydrophilic
edges
generated
by
the
rupture
of
strong
covalent
Mo–S
bonds,
which
resulted
and (2) hydrophilic edges generated by the rupture of strong covalent Mo–S bonds, which resulted
inthe
thelarge
largefaces/edges
faces/edgesratio.
ratio.Non-polar
Non-polaroil,
oil,such
suchas
askerosene
keroseneand
anddixanthogen,
dixanthogen,can
canadsorb
adsorbon
onthe
the
in
Minerals 2017, 7, 51
9 of 17
and
(2)2017,
hydrophilic
edges generated by the rupture of strong covalent Mo–S bonds, which resulted
Minerals
7, 51
9 of 17
in the large faces/edges ratio. Non-polar oil, such as kerosene and dixanthogen, can adsorb on the
faces to enhance its hydrophobicity.
hydrophobicity. The edges that contain Mo atoms could not react with collectors,
but only
or HMoO44−−ininaqueous
aqueoussolution.
solution.The
The main
main hydrosulfide
hydrosulfide ion consumption
only release
releaseMoO
MoO4422−− or
must have taken place at
the
Mo
atom
on
the
edges.
In
this
case,
molybdenite
still shows better
at the Mo atom on the edges.
recoveries
in the
condition.
Moreover,
the dixanthogen
oxidized by
xanthates
recoveries than
thanchalcopyrite
chalcopyrite
in same
the same
condition.
Moreover,
the dixanthogen
oxidized
by
is
decomposed
when the when
Eh is decreased
lower than
its formation
potentialpotential
value (about
mV
xanthates
is decomposed
the Eh is decreased
lower
than its formation
value180
(about
at
= 11
a certain
of sodium
resulting
in the
lower molybdenite
180pH
mV
at [42])
pH =by11adding
[42]) by
addingamount
a certain
amountsulfide,
of sodium
sulfide,
resulting
in the lower
recovery
compared
with
the usewith
of kerosene.
the recovery
in curves
Figuresin4 Figures
and 6, it4 and
can
molybdenite
recovery
compared
the use ofFrom
kerosene.
From thecurves
recovery
−2 mol/L,
−2
be
concluded
that
the
optimum
dose
of
sodium
sulfide
added
is
3
×
10
which
not
only
6, it can be concluded that the optimum dose of sodium sulfide added is 3 × 10 mol/L, which not
depresses
chalcopyrite
flotation
effectively
but also
reduces
the losses
molybdenite
recovery
greatly.
only depresses
chalcopyrite
flotation
effectively
but
also reduces
the of
losses
of molybdenite
recovery
Further,
the best the
reagent
condition
for molybdenite-chalcopyrite
flotation
and separation
is using
greatly. Further,
best reagent
condition
for molybdenite-chalcopyrite
flotation
and separation
is
kerosene
in
the
bulk
flotation
to
obtain
high
molybdenite
recovery
and
applying
xanthate
with
sodium
using kerosene in the bulk flotation to obtain high molybdenite recovery and applying xanthate with
sulfide
the selective
flotationflotation
to reject more
chalcopyrite.
sodiuminsulfide
in the selective
to reject
more chalcopyrite.
400
M o ly b d e n ite S u s p e n s io n s E h (m V )
M o ly b d e n ite S u s p e n s io n s R e c o v e ry (% )
100
80
60
SBX
Kerosene
200
0
-200
SBX
Kerosene
-400
40
-6
-4
-2
Log Sodium Sulfide Added (mol/L)
(a)
0
-6
-4
-2
0
Log Sodium Sulfide Added (mol/L)
(b)
Figure 6.
6. (a).
(a). The
The flotation
flotation recovery
recovery of
ofmolybdenite
molybdeniteatatpH
pH=11
sulfide
Figure
11as
asaa function
function of
of added
added sodium
sodium sulfide
−3−
3
with
100
g/t
SBX
or
40
g/t
kerosene
added
in
5
×
10
mol/L
NaCl;
(b)
The
Eh
of
the
system
under
the
with 100 g/t SBX or 40 g/t kerosene added in 5 × 10 mol/L NaCl; (b) The Eh of the system under
same
conditions.
the same conditions.
3.2. Contact
Contact Angle
Angle Measurements
Measurements
3.2.
Figure 77 presents
presents the
the contact
contactangles
angles of
ofchalcopyrite
chalcopyrite (a)
(a) and
and molybdenite
molybdenite faces
faces (b)
(b) at
at pH
pH =1111asasa
Figure
concentrationswith
withororwithout
without
collectors.
shown
in Figure
7a,contact
the contact
afunction
functionofofsulfide
sulfide concentrations
collectors.
As As
shown
in Figure
7a, the
angle
−4 mol/L, then
angle
of
chalcopyrite
increased
a
little
when
the
sulfide
concentration
was
10
−
4
of chalcopyrite increased a little when the sulfide concentration was 10 mol/L, then dramatically
−2 mol/L, and at last slowly decreased to a
dramatically
dropped
in the10range
10−−32 to
3 × 10and
−3 to from
dropped
in the
range from
3 × 10
mol/L,
at last slowly decreased to a relatively
relatively
stable
at which
0.1 mol/L,
which
with the
flotation
4a.angle
The
stable
value
at 0.1value
mol/L,
agreed
withagreed
the flotation
responses
in responses
Figure 4a. in
TheFigure
contact
contact
angle
conditioned
with
kerosene
was
lower
in
the
beginning
and
higher
in
the
end
with
the
conditioned with kerosene was lower in the beginning and higher in the end with the sulfide dose
sulfide dose
increase,to
inthe
contrast
to the
contact
angle conditioned
SBX,
which conformed
to the
increase,
in contrast
contact
angle
conditioned
with SBX, with
which
conformed
to the result
in
result
in
Figure
4a.
The
untreated
chalcopyrite
sample
has
a
contact
angle
at
73°,
in
accordance
with
◦
Figure 4a. The untreated chalcopyrite sample has a contact angle at 73 , in accordance with the test
by
the test by
Tsuyoshi
Hirajima
[16], which
reveals
that the measurement
reliable andObviously,
reproducible.
Tsuyoshi
Hirajima
[16],
which reveals
that the
measurement
is reliable and is
reproducible.
the
Obviously, the
chalcopyrite
contact angle
conditioned
with SBX wasequal
approximately
equal
to that of
chalcopyrite
contact
angle conditioned
with
SBX was approximately
to that of the
collectorless
the collectorless
sample
in the sulfide
of 0.1
mol/L.
It indicates
xanthate
ions
sample
in the sulfide
concentration
of 0.1 concentration
mol/L. It indicates
that
xanthate
ions mustthat
be fully
desorbed
must
fully desorbed
thethe
aqueous
solutionsurface
from the
chalcopyrite
surface
order
them not
to
the be
aqueous
solution to
from
chalcopyrite
in order
for them
not to in
affect
thefor
adsorption
to
affect
the
adsorption
density
of
hydrosulfide.
As
shown
in
Figure
7b,
the
contact
angle
curves
of
density of hydrosulfide. As shown in Figure 7b, the contact angle curves of molybdenite faces by
molybdenite
faces
by
adding
amounts
of
collectors
were
constant
at
a
lower
sulfide
concentration
adding amounts of collectors were constant at a lower sulfide concentration (<10−3 mol/L) but were
(<10−3 mol/L) but were vastly reduced when the sulfide concentration continuously increased,
which showed the same trend with molybdenite flotation (Figure 6a). The contact angle of
untreated molybdenite faces is 81°, which is consistent with the measurement of Arbiter et al. [43];
molybdenite faces have a contact angle from 70° to 90° by different polishing operations. In contrast
Minerals 2017, 7, 51
10 of 17
vastly reduced when the sulfide concentration continuously increased, which showed the same trend
◦
with
molybdenite
Minerals
2017, 7, 51 flotation (Figure 6a). The contact angle of untreated molybdenite faces is 81 , which
10 of 17
is consistent with the measurement of Arbiter et al. [43]; molybdenite faces have a contact angle
◦ to 90◦ bywithout
to the70condition
molybdenite
faces reaction
with SBXwithout
had bigger
contact
from
differentcollector,
polishingthe
operations.
In contrast
to the condition
collector,
the
angles, even faces
though
the sulfide
concentration
increased
to 0.1even
mol/L,
which
different
from the
molybdenite
reaction
with SBX
had bigger contact
angles,
though
the is
sulfide
concentration
behavior of
It indicates
thatfrom
certain
ions It
still
exist orthat
adsorb
on
increased
to chalcopyrite.
0.1 mol/L, which
is different
theamounts
behaviorof
ofxanthate
chalcopyrite.
indicates
certain
molybdenite
surfaces.
capacity
and density
wereThe
calculated
tocapacity
clarify and
the
amounts
of xanthate
ionsThe
still adsorption
exist or adsorb
on molybdenite
surfaces.
adsorption
phenomenon
in the nexttopart.
density
were calculated
clarify the phenomenon in the next part.
150
M o lyb d e n ite F a ce s C o n ta ct A n g le (°)
C h a lco p yrite C o n ta ct A n g le (°)
140
100
50
SBX
Kerosene
Collectorless
120
100
80
SBX
Kerosene
Collectorless
60
40
0
-6
-4
-2
Log Sodium Sulfide Added (mol/L)
(a)
0
-6
-4
-2
0
Log Sodium Sulfide Added (mol/L)
(b)
Figure 7.
7. (a)
(a) The
The contact
contact angles
angles of
ofchalcopyrite
chalcopyriteand
and(b)
(b)molybdenite
molybdenitefaces
facesatatpH
pH=11
of
Figure
11as
as aa function
function of
added sodium
sodium sulfide
sulfide with
with 100
100 g/t
g/t SBX,
added
SBX, 40
40 g/t
g/tkerosene
keroseneor
orcollectorless.
collectorless.
3.3. Adsorption
3.3.
Adsorption Measurements
Measurements
Figure 88 exhibits
exhibits the
the adsorption
adsorption capacities
capacitiesofofBX
BX−− and
and SS22−− on
chalcopyrite and
and molybdenite
molybdenite
Figure
on chalcopyrite
surfaces
treated
with
different
dosages
of
sodium
sulfide.
The
left
axle
belongs
to
the
butyl
xanthate
surfaces treated with different dosages of sodium sulfide. The left axle belongs to the butyl xanthate
− ions completely adsorbed on molybdenite and
ion
adsorption
capacity,
which
showed
that
BX
ion adsorption capacity, which showed that BX− ions completely adsorbed on molybdenite and
−
chalcopyrite surfaces
surfaces at
at 10
10−−55 mol/L
residual
chalcopyrite
mol/Lsulfide,
sulfide,i.e.,
i.e., almost
almost no
no BX
BX−ions
ionswere
were detected
detected in
in the
the residual
− on chalcopyrite dropped faster than on molybdenite with the sulfide
solution.
After
that,
the
BX
solution. After that, the BX− on chalcopyrite dropped faster than on molybdenite with the sulfide
− still remained in small amounts on molybdenite but
concentration increase.
increase.Finally,
Finally,
concentration
BX−BX
still remained
in small amounts on molybdenite but disappeared
disappeared
on These
chalcopyrite.
These performances
prove
thatsulfide
high sodium
sulfidecould
concentration
on
chalcopyrite.
performances
prove that high
sodium
concentration
seriously
could
seriously
destroy
the
adsorption
of
xanthate
on
sulfide
minerals,
especially
on
chalcopyrite.
destroy the adsorption of xanthate on sulfide minerals, especially on chalcopyrite. The complete
The complete
desorption on
chalcopyrite
at 0.1
mol/L
sulfide
agreesangle
with results
the contact
angle
desorption
on chalcopyrite
at 0.1
mol/L sulfide
agrees
with
the contact
in Figure
7a.results
Thus,
in
Figure
7a.
Thus,
the
incomplete
desorption
on
molybdenite
may
be
due
to
the
larger
specific
the incomplete desorption on molybdenite may be due to the larger specific surface area, the better
surface area, the better inherent floatability, or the unique layered structure. BET measurements
inherent floatability, or the unique layered structure. BET measurements showed that molybdenite
showed that molybdenite samples were about twice the surface area of chalcopyrite samples, which
samples were about twice the surface area of chalcopyrite samples, which suggested that molybdenite
suggested that molybdenite had stronger adsorbability, according to the concept of higher
had stronger adsorbability, according to the concept of higher adsorption capacities occurring on
adsorption capacities occurring on larger surface areas [44]. The better inherent floatability of
larger surface areas [44]. The better inherent floatability of molybdenite predicts that it would be
molybdenite predicts that it would be more attractive to the non-polar group of chemicals [45]. The
more attractive to the non-polar group of chemicals [45]. The unique layered structure of molybdenite
unique layered structure of molybdenite may allow the collector or its branch to diffuse as
may allow the collector or its branch to diffuse as molybdenite is a layered modified material [46].
molybdenite is a layered modified material [46]. The sulfide (hydrosulfide) ion adsorption capacity
The sulfide (hydrosulfide) ion adsorption capacity marked in the right axle showed that sulfide
marked in the right axle showed that sulfide completely adsorbed on chalcopyrite and molybdenite
completely adsorbed on chalcopyrite and molybdenite and obtained the same absorption capacities
and obtained the same absorption capacities when the sulfide concentration was less than 0.01
when the sulfide concentration was less than 0.01 mol/L. Then molybdenite had a little more sulfide
mol/L. Then molybdenite had a little more sulfide coating than chalcopyrite in the sulfide
coating than chalcopyrite in the sulfide concentration range from 0.01 to 0.04 mol/L, while having
concentration range from 0.01 to 0.04 mol/L, while having fewer sulfide coverages than chalcopyrite
fewer sulfide coverages than chalcopyrite when the sulfide was added to 0.1 mol/L. It seems that
when the sulfide was added to 0.1 mol/L. It seems that sulfide (hydrosulfdie) does not tend to
adsorb on molybdenite in high sulfide concentrations. The BX− and S2− adsorption densities are also
calculated and presented in Figure 9. The density of butyl xanthate adsorbed on molybdenite is
much less than that of chalcopyrite in a sulfide dosage lower than 0.02 mol/L. In contrast, with the
sulfide dosage continuously increasing, the BX− adsorption density on molybdenite was shown to
Minerals 2017, 7, 51
11 of 17
sulfide (hydrosulfdie) does not tend to adsorb on molybdenite in high sulfide concentrations. The BX−
and S2− adsorption densities are also calculated and presented in Figure 9. The density of butyl
xanthate adsorbed on molybdenite is much less than that of chalcopyrite in a sulfide dosage lower than
Minerals 2017,
7, 51
11 of 17
0.02 mol/L.
In contrast,
with the sulfide dosage continuously increasing, the BX− adsorption
Minerals 2017,
7, 51
11 of density
17
on molybdenite was shown to be a little higher than that of chalcopyrite, which clearly explained the
be a little higher than that of chalcopyrite, which clearly explained the flotation responses of
be a responses
little higher than
that of chalcopyrite,
which clearlySBX
explained
the flotation
responses of
flotation
chalcopyrite
and
molybdenite
in the high
in
chalcopyrite andofmolybdenite
with
SBX
in the high with
sulfide concentration,
insulfide
which concentration,
molybdenite
− adsorption
2− density
chalcopyrite
andretains
molybdenite
with SBX Different
in the− high
sulfide
concentration,
in density,
which molybdenite
which
molybdenite
its
floatability.
from
the
BX
the
S
2−
retains its floatability. Different from the BX adsorption density, the S density adsorbed on
retainsonits
floatability. was
Different
from
the BX− adsorption
density, the the
S2− same
density
adsorbed on and
adsorbed
chalcopyrite
always
higher
on the molybdenite
concentrations,
chalcopyrite
was always higher
than
on thethan
molybdenite
in the same in
concentrations,
and the gap
chalcopyrite was always higher than on the molybdenite in the same concentrations, and the gap
the gap
between
these
adsorption
densities
became
greater
assulfide
the sulfide
dosage
increased.
between
these
twotwo
adsorption
densities
became
greater
as the
dosage
increased.
It alsoIt also
between these two adsorption densities became greater as the sulfide dosage increased. It also
indicated
depression
sodiumsulfide
sulfideon
onmolybdenite.
molybdenite.
indicated
less less
depression
of of
sodium
indicated less depression of sodium sulfide on molybdenite.
180
180
150
150
0.4
0.4
120
120
0.3
0.3
90
90
0.2
0.2
0.1
0.1
0.0
0.0 -6
-6
-
60
60
BX- on Chalcopyrite
BX - on Chalcopyrite
BX- on Molybdenite
BX2- on Molybdenite
S2- on Chalcopyrite
S 2- on Chalcopyrite
S2- on Molybdenite
S on Molybdenite
-5
-5
-4
-4
30
30
-3
-3
-2
-2
Log Sodium Sulfide Added (mol/L)
Log Sodium Sulfide Added (mol/L)
−
-1
-1
S 2-S 2-Adsorption
AdsorptionCapacity
Capacity(mg)
(mg)
- BXBX
Adsorption
AdsorptionCapacity
Capacity(mg)
(mg)
0.5
0.5
0
00
0
−
2− chalcopyrite
Figure
8. The
adsorptioncapacities
capacities of
of BX
BX −and
S2 Son
and molybdenite
surfaces surfaces
at pH
Figure
8. The
adsorption
and
on chalcopyrite
and molybdenite
at
Figure 8. The adsorption capacities of BX− and S2− on chalcopyrite and molybdenite surfaces at pH
11
as
a
function
of
various
dosages
of
sodium
sulfide
added
in
the
presence
of
100
g/t
SBX
and
40SBX
g/t and
pH =1111asasa function
a function
of
various
dosages
of
sodium
sulfide
added
in
the
presence
of
100
g/t
of various dosages of sodium sulfide added in the presence of 100 g/t SBX and 40 g/t
kerosene,
respectively,
and and
opened
to the atmosphere.
40 g/t
kerosene,
respectively,
opened
the atmosphere.
kerosene,
respectively,
and opened
to the to
atmosphere.
120
120
100
100
0.2
0.2
80
80
60
60
-
0.1
0.1
0.0
0.0 -6
-6
BX- on Chalcopyrite
BX - on Chalcopyrite
BX- on Molybdenite
BX2- on Molybdenite
S2- on Chalcopyrite
S 2- on Chalcopyrite
S2- on Molybdenite
S on Molybdenite
-4
-4
40
40
20
20
-2
-2
0
00
0
2
2S2-SAdsorption
Density
(mg/m
Adsorption
Density
(mg/m) 2)
- 2
BX
Density
(mg/m
BXAdsorption
Adsorption
Density
(mg/m) 2)
0.3
0.3
Log Sodium Sulfide Added (mol/L)
Log Sodium Sulfide Added (mol/L)
Figure 9. The adsorption densities of BX− and S2− on chalcopyrite and molybdenite surfaces at pH 11
Figure
9. The
adsorption
densities of BX
andSS22−
chalcopyrite
and
molybdenite
surfaces
at pH
11
− −and
− on
Figure
The
adsorption
densities
onadded
chalcopyrite
and
molybdenite
surfaces
at pH
as 9.
a function
of various
dosagesofofBX
sodium
sulfide
in the presence
of 100 g/t SBX
and 40
g/t = 11
as a function of various dosages of sodium sulfide added in the presence of 100 g/t SBX and 40 g/t
as a function
various dosages
of sodium
sulfide added in the presence of 100 g/t SBX and 40 g/t
kerosene, of
respectively,
and opened
to the atmosphere.
kerosene, respectively, and opened to the atmosphere.
kerosene, respectively, and opened to the atmosphere.
Minerals 2017, 7, 51
12 of 17
Minerals 2017, 7, 51
12 of 17
3.4. FTIR Measurements
3.4. FTIR Measurements
Figure 10 demonstrates the FTIR spectrum of sodium butyl xanthate, which is industrial grade.
Figure 10 is
demonstrates
FTIR
sodium
butyl xanthate,
which
is industrial
grade.
The spectrum
enlarged to the
reveal
thespectrum
details ofofthe
characteristic
peaks of
xanthate
in the range
of
−
1
−
1
The
spectrum
is
enlarged
to
reveal
the
details
of
the
characteristic
peaks
of
xanthate
in
the
range
of
1400–800 cm . According to the literatures [47,48], the spectral peak at 1069.18 cm assigns to the
−1 assigns to the
1400–800
cm−1. vibration
According
theThe
literatures
[47,48],
the spectral
peak at 1069.18
C=S stretching
of to
SBX.
intense peak
at 1112.40
cm−1 symbolizes
to thecm
C–O–C
symmetric
−
1
−1 symbolizes to the C–O–C
C=S
stretching
vibration
of SBX.
The intense
peaktoat
stretching
vibration,
and that
at 1162.52
cm refers
the1112.40
C–O–Ccm
asymmetric
stretching vibration
1 are
−1 refers to the C–O–C asymmetric stretching
symmetric
vibration,
and that
at 1040
1162.52
of SBX. Thestretching
peaks detected
at 1021.64
and
cm−cm
attributed to the C=S stretching vibration
−
1
vibration
of SBX.
The
peaks detected
at 1021.64
1040
cm−1 symmetric
are attributed
to the C=S
stretching
in (BX)2 . The
peak
at 1212.42
cm also
assigns and
to the
C–O–C
stretching
vibration,
and
−1 peaks
vibration
(BX)
2. The cm
peak
at 1212.42
cm−1 also
assigns
to the C–O–C
symmetric
stretching
the 1260.92inand
1245.07
correspond
to C–O–C
asymmetric
stretching
vibration
in (BX)2 .
−1 peaks correspond to C–O–C asymmetric stretching
vibration,
andC=S
thevibration
1260.92 peak
and 1245.07
Evidently, the
of (BX)2 cm
shifted
toward lower wavenumbers as the C–O–C vibrations
vibration
in (BX)
2. Evidently,
the C=S compared
vibration peak
of (BX)
2 shifted
towardthat
lower
as
moved toward
higher
wavenumbers,
to those
of SBX.
It indicates
the wavenumbers
SBX collector has
the
C–O–C
vibrations
moved
toward
higher
wavenumbers,
compared
to
those
of
SBX.
It
indicates
been oxidized and contains (BX)2 [49]. Although the SBX was partly oxidized, it did not influence
− in
that
the SBX collector
has been
oxidized
and contains
(BX)the
2 [49].
Although
thereact
SBX with
was BX
partly
the adsorption
measurement.
In the
chalcopyrite
suspension,
copper
ion could
oxidized,
did not
influence
the2 , adsorption
measurement.
In the
chalcopyrite
solution toitform
unstable
Cu(BX)
which in turn
dissociated into
CuBX
and (BX)2 , suspension,
as shown in the
−
copper
ionequation
could react
following
[31]:with BX in solution to form unstable Cu(BX)2, which in turn dissociated into
CuBX and (BX)2, as shown in the following equation [31]:
(3)
2Cu2+ + 4BX − → 2Cu( BX )2 → 2CuBX + ( BX )2
(3)
2
+4
→2 ( ) →2
+( )
20
1400
1300
1200
1100
769.98
903.74
1021.64
994.44
40
1112.40
1069.18
1040.80
60
1162.52
Reflectance(%)
80
1260.92
1245.07
1212.42
SBX
1000
900
800
-1
Wavenumbers (cm )
The Fourier
Fourier transforms
transforms infrared
infrared (FTIR)
(FTIR) spectrum
spectrum of
of sodium
sodium butyl
butyl xanthate
xanthate powder
powder in
Figure 10. The
room temperature.
The
FTIRspectrum
spectrumof of
chalcopyrite
before
and conditioning
after conditioning
with
Na2S is
The FTIR
chalcopyrite
before
and after
with SBX
andSBX
Na2 Sand
is presented
presented
in
Figure
11.
No
vibration
peak
was
found
in
the
FTIR
spectrum
of
the
unprocessed
in Figure 11. No vibration peak was found in the FTIR spectrum of the unprocessed chalcopyrite
chalcopyrite
After conditioning
5 min,
five visible
absorption
peakson
were
sample. Aftersample.
conditioning
with SBX for with
5 min,SBX
fivefor
visible
absorption
peaks
were detected
the
detected
on
the
chalcopyrite
surface.
The
weak
intensities
of
these
peaks
may
be
due
to
the
less
chalcopyrite surface. The weak intensities of these peaks may be due to the less reagent dosage and
reagent
dosage time.
and limited
time.
The
C=S vibration
peaklower
of CuBX
shifts toward
lower
limited reaction
The C=Sreaction
vibration
peak
of CuBX
shifts toward
wavenumbers,
while
the
wavenumbers,
while
the
C–O–C
vibration
shifts
toward
higher
wavenumbers,
compared
with
those
C–O–C vibration shifts toward higher wavenumbers, compared with those of butyl xanthate, due
of
xanthate, due
to the coordinated
structure
of CuBX
[47]. Itcm
reveals
cm−1stretching
is due to
−1 is that
to butyl
the coordinated
structure
of CuBX [47].
It reveals
that 1043.95
due 1043.95
to the C=S
−1
the
C=S stretching
of CuBX,
from 1069.18
to 1043.95
cm at
. Also,
the cm
peak
1211.50
cm−1
−1 at
of CuBX,
which shifts
from which
1069.18shifts
to 1043.95
cm−1 . Also,
the peak
1211.50
and
the broad
−1
and
broad peak
containing
1260.94cm
and
1245.31
cm are
the C–O–Cand
symmetric
and
−1 are
peakthe
containing
1260.94
and 1245.31
attributed
to attributed
the C–O–Ctosymmetric
asymmetric
asymmetric stretching of (BX)2, respectively. The peak at 1020.86 cm−1 corresponds to the C=S
stretching vibration in (BX)2. No obvious shift (less than 20 cm−1) occurring during the adsorption of
(BX)2 indicates that (BX)2 physically adsorbs on the chalcopyrite surface [50]. After conditioning
Minerals 2017, 7, 51
13 of 17
stretching of (BX)2 , respectively. The peak at 1020.86 cm−1 corresponds to the C=S stretching vibration
in (BX)2 . No obvious shift (less than 20 cm−1 ) occurring during the adsorption of (BX)2 indicates that
Minerals
2017, 7, 51
13 of 17
(BX)
2 physically adsorbs on the chalcopyrite surface [50]. After conditioning with Na2 S for 5 min, all
absorption peaks disappeared, indicating that sodium sulfide could decompose the products, CuBX
with(BX)
Na2S
for 5 min, all absorption peaks disappeared, indicating that sodium sulfide could
and
2 , on the chalcopyrite surface. Two equations can be used to explain the mechanism.
decompose the products, CuBX and (BX)2, on the chalcopyrite surface. Two equations can be used to
explain the mechanism.
(4)
2CuBX + S2− → Cu2 S + 2BX −
2
+
→
+2
( BX )2 + S2− → S0 + 2BX −
( ) +
→
+2
(4)
(5)
(5)
Cp+SBX+Na2S
1400
1300
1043.95
1020.86
Cp
1211.50
1260.94
1245.31
Reflectance (%)
Cp+SBX
1200
1100
1000
900
800
-1
Wavenumbers (cm )
Figure 11.
11. The
of chalcopyrite
chalcopyrite surface
surface under
under different
different conditions:
conditions: untreated
untreated
Figure
The FTIR
FTIR spectrum
spectrum of
chalcopyrite,
chalcopyrite
with
100
g/t
SBX,
and
chalcopyrite
with
100
g/t
SBX
in
the
presence
of 0.1
chalcopyrite, chalcopyrite with 100 g/t SBX, and chalcopyrite with 100 g/t SBX in the presence
mol/L
sodium
sulfide.
of 0.1 mol/L sodium sulfide.
The FTIR spectrum of the molybdenite surface before and after conditioning with SBX and Na2S
The FTIR spectrum of the molybdenite surface before and after conditioning with SBX and Na2 S is
is shown in Figure 12. Similarly, no vibration peak was detected by the FTIR spectrum for the
shown in Figure 12. Similarly, no vibration peak was detected by the FTIR spectrum for the untreated
untreated molybdenite sample. After conditioning with SBX, the characteristic peaks of (BX)2 were
molybdenite sample. After conditioning with SBX, the characteristic
peaks of (BX)2 were exposed on
exposed on the mineral surface. However, peaks of BX− were not found, maybe due to its low
the mineral surface. However, peaks of BX− were not found, maybe due to its low intensity. Then, after
intensity. Then, after conditioning with sodium sulfide, the intensities of these peaks were reduced
conditioning with sodium sulfide, the intensities of these peaks were reduced but did not disappear,
but did not disappear, suggesting the difference with chalcopyrite [51]. The (BX)2 physically
suggesting the difference with chalcopyrite [51]. The (BX)2 physically adsorbed on the surface of
adsorbed on the surface of molybdenite, and it was very easy for it to be desorbed by sodium
molybdenite, and it was very easy for it to be desorbed by sodium sulfide. This was surprising because
sulfide. This was surprising because (BX)2 is relative stable on molybdenite surfaces. Probably it
(BX)2 is relative stable on molybdenite surfaces. Probably it happened as a result of the larger specific
happened as a result of the larger specific surface area, the better inherent floatability, or the unique
surface area, the better inherent floatability, or the unique layered structure of molybdenite, which
layered structure of molybdenite, which have been illustrated in Figure 8.
have been illustrated in Figure 8.
Minerals 2017, 7, 51
Minerals 2017, 7, 51
14 of 17
14 of 17
1400
1300
1020.90
1021.86
Mot
1260.03
1244.83
1212.72
Reflectance (%)
Mot+SBX
1212.94
1260.25
Mot+SBX+Na2S
1200
1100
1000
900
800
-1
Wavenumbers (cm )
FTIR
spectrum
of molybdenite
surface under
untreated molybdenite,
Figure 12.
12.The
The
FTIR
spectrum
of molybdenite
surfacedifferent
under conditions:
different conditions:
untreated
molybdenite
with
100
g/t
SBX,
molybdenite
with
100
g/t
SBX
in
the
presence
of
0.1
mol/L
sodium
molybdenite, molybdenite with 100 g/t SBX, molybdenite with 100 g/t SBX in the presencesulfide.
of 0.1
mol/L sodium sulfide.
4. Conclusions
4. Conclusions
Flotation tests in various pHs showed that molybdenite had better floatability than chalcopyrite
in The
various
pHskerosene,
showedhad
that
molybdenite
hadatbetter
than
in theFlotation
whole pHtests
range.
collector,
an optimal
condition
pH = 4floatability
to get maximum
chalcopyrite
in the
whole which
pH range.
The collector,
an optimal
at pHfor
= SBX
4 to
mineral flotation
recovery,
was determined
by kerosene,
the PZC ofhad
the mineral.
Thecondition
best condition
get maximum
mineral
recovery,
determined
by the surface
PZC ofproperty.
the mineral.
The
was
at pH = 8, which
wasflotation
responsible
for the which
stabilitywas
of SBX
and the mineral
Flotation
best
condition
for SBX
was at
pH = 8, which
wasthe
responsible
for the stability
of SBX
the mineral
kinetics
indicated
that SBX
efficiently
improved
mineral flotation,
and it was
notand
directly
to float
surface
property.
Flotation
kinetics
indicatedfirst.
thatKerosene
SBX efficiently
improved
theofmineral
flotation,
molybdenite
instead
of forming
dixanthogen
gave a high
recovery
molybdenite
but
and
it was
directly
to for
float
molybdenite
instead
dixanthogen
first. surface
Kerosene
gave a
seemed
notnot
to be
effective
chalcopyrite
because
of of
itsforming
less inherent
hydrophobic
area.
high The
recovery
of response,
molybdenite
seemed
not dosages
to be effective
for sulfide,
chalcopyrite
because
of itstrend
less
flotation
afterbut
adding
various
of sodium
presented
the same
inherent
hydrophobic
surface area. The recovery remained unchanged or slightly increased under the
with
chalcopyrite
and molybdenite.,
The flotation of
response,
after adding
various
sulfide,
presented
thesulfide
same
low concentration
sodium sulfide
(less than
0.001dosages
mol/L) of
andsodium
then sharply
dropped
as the
trend
with chalcopyrite
and molybdenite.,
TheDifferently,
recovery remained
unchanged
or slightly
increased
concentration
became higher
than 0.01 mol/L.
the molybdenite
showed
less sensitivity
to
under
low concentration
of sodium
(less
thanchalcopyrite
0.001 mol/L)was
andfully
thendepressed.
sharply dropped
as
sodiumthe
sulfide
and still reported
a highsulfide
recovery
when
The pulp
the sulfide
concentration
became
higher than
0.01 mol/L.
Differently,
thethe
molybdenite
less
potential
measured
by a smooth
Pt/calomel
electrode
system
revealed that
depression showed
occurring
at
sensitivity
sodium sulfide
still
a highenvironment;
recovery when
chalcopyrite
was
high sulfideto
concentrations
was and
due to
thereported
strong reducing
the mineral
surface
wasfully
free
depressed.
The pulp
measured
by a smooth
Pt/calomel
electrode
revealed that
the
of exchangeable
oxidepotential
species and
highly charged
negatively
as a result
of thesystem
high adsorption
density
depression
occurring
at
high
sulfide
concentrations
was
due
to
the
strong
reducing
environment;
of hydrosulfide ions. Kerosene, as a non-polar oil, still renders a little floatability to chalcopyrite in
the
was
free of exchangeable
oxidemeasurement
species and highly
charged
negatively
a result
highmineral
sulfide surface
dosages.
Moreover,
the contact angle
completely
agreed
with theasflotation
of
the highAs
adsorption
density
hydrosulfide
ions. Kerosene,
as a non-polar
oil, still
renders
a little
response.
a consequence,
theofoptimum
concentration
for separation
chalcopyrite
and
molybdenite
floatability
to
chalcopyrite
in
high
sulfide
dosages.
Moreover,
the
contact
angle
measurement
was 0.03 mol/L. The bulk flotation using kerosene as a collector could achieve high molybdenite
completely
agreed
with
the flotation
response.
a consequence,
thereject
optimum
concentration for
recovery, while
using
xanthate
and high
doses of As
sodium
sulfide could
more chalcopyrite.
− and
separation
chalcopyrite
and molybdenite
was
0.03
mol/L.
bulk flotation
using kerosene
a
The adsorption
capacities
and densities
of BX
S2− The
on minerals
were calculated,
and it as
was
collector
could
high
molybdenite
whilebut
using
xanthate
high doses
sodium
found that
moreachieve
xanthate
ions
adsorbed onrecovery,
molybdenite
showed
fewerand
densities
due toofthe
large
sulfide
couldarea.
rejectFurther,
more chalcopyrite.
BET surface
the S2− prefered to adsorb on the chalcopyrite surfaces in multiple layers,
The
adsorption
capacities
and
densities
of BX− and
S2− on minerals
were
and it was
which
always
had a larger
density
than
S2− adsorbtion
on molybdenite.
The
FTIRcalculated,
results corresponded
−
foundthe
that
more xanthate
ions adsorbed
on molybdenite
but showed
fewer densities
due to the
with
adsorption
measurement,
indicating
that BX chemically
adsorbed
on chalcopyrite
to large
form
2− prefered to adsorb on the chalcopyrite surfaces in multiple layers,
BET
area.
Further,
the
S
CuBXsurface
and (BX)
but
physically
adsorbed
on
molybdenite
and
only
formed
(BX)
.
After
reaction
with
2
2
2− adsorbtion on molybdenite. The FTIR results
which
always
had
a
larger
density
than
S
sodium sulfide, all xanthate peaks disappeared on chalcopyrite but remained in part on molybdenite
− chemically adsorbed on
corresponded
with
the surface
adsorption
indicating
that or
BXthe
due to the larger
specific
area,measurement,
the better inherent
floatability,
unique layered structure
chalcopyrite
to form CuBX and (BX)2 but physically adsorbed on molybdenite and only formed (BX)2.
of molybdenite.
After reaction with sodium sulfide, all xanthate peaks disappeared on chalcopyrite but remained in
Minerals 2017, 7, 51
15 of 17
Acknowledgments: The authors are grateful for the support of the Resource and Environmental Engineering
School, Wuhan University of Technology (WUT), China.
Author Contributions: Huiqing Peng supported the experiment; Di Wu conceived, designed, and performed
the experiment and analyzed the data; Wen Luo, Xuexiang Bie, and Wenya Jiao contributed reagents/materials/
analysis tools; and Di Wu and Mohamed Abdalla wrote the paper.
Conflicts of Interest: The authors declare no conflict of interest.
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