Journal of Minerals & Materials Characterization & Engineering, Vol. 5, No.1, pp 21-45, 2006
jmmce.org
Printed in the USA. All rights reserved
21
XPS & FTIR Study of Adsorption Characteristics Using
Cationic and Anionic Collectors on Smithsonite
Hosseini S. Hamid
*
and Forssberg Eric
Division of Mineral Processing,
Department of Chemical Engineering and Geosciences
Luleå University of Technology,
SE –971 87 Luleå, Sweden
*Corresponding author: Tel.:+46-920- 491784; fax: +46-920-97364
E-mail address: hamid.hosseini@ltu.se
ABSTRACT
The adsorption of cationic and anionic collectors on the surface of smithsonite was
studied using diffuse reflectance FTIR (DRIFT) and X-ray photoelectron spectroscopy
(XPS or ESCA) techniques.
The FT-IR spectra studies of smithsonite conditioned using DDA (dodecylamine)
show the presence of RNH
2
on the surface of smithsonite and accordingly the adsorption
of DDA. XPS results show the presence of a ZnS layer on the surface after sulphidising in
amine adsorption. The appearance of the N (1s) signal of the amine groups and
S (2p)
signal of ZnS which increased in the intensity of the signal of C (1s) peak by adsorption
of DDA on smithsonite. The presence of COO
-
on the surface of smithsonite after oleic
acid treatment confirmed the adsorption of OA (oleic acid) onto the surface. The most
adsorption occurs at around pH 10, when RCOO
-
is predominant in solution and has
ample opportunities for interaction with the mineral surface.
The appearance of CS
2
on the surface of smithsonite exposes the adsorption of KAX
(potassium amyl xanthate) onto surface. XPS results confirm the presence of ZnS layer on
the surface after sulphidising in amine adsorption and also the transferring the surface to
CuS in KAX adsorption. It is suggested that copper cations exchange with those of zinc
during copper activation of smithsonite such as activation of sphalerite.
Keywords: Smithsonite; Anionic collector; Cationic collector; FTIR; XPS
INTRODUCTION
A large investigation was devoted to finding the best collector for the recovery of
smithsonite. Several amines were tested and a dodecylamine derived from vegetable oil
proved to be the most suitable [1]. However, there is no complete analogy between the
properties of metal ions in solution and on mineral surfaces, due to the various degrees of
coordination saturation caused by surrounding anions. In the case of carbonate minerals
22 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
such as smithsonite, the surface activity of the mineral in water increases, and the
adsorption of water molecules resemble chemisorption. This high activity to water
dipoles is one of the main reasons for the low natural floatability of smithsonite compared
with sphalerite. Hence, there is a lower possibility of effective adsorption of flotation
reagent molecules on the smithsonite surface [2].
The design of reagent regimes for a selective hydrophobization of mineral surfaces by
means of collectors is still an important subject in flotation research. The ionic surfactants
are used with different structures for the selective flotation due to hydrophobization of
the minerals. These collectors are adsorbed through electrostatic interaction of the polar
group of the surfactant molecules with ions of the minerals’ surface [3].
The most important sources of zinc ore have been the oxidised zinc minerals e.g.
smithsonite (ZnCO
3
), willemite (Zn
2
SiO
4
), hydrozincite (2ZnCO
3
3Zn(OH)
2
), zincite
(ZnO) and hemimorphite (Zn
2
SiO
3
H
2
O). The flotation of oxidised lead and zinc, in
particular oxidized zinc minerals, is much more difficult than the flotation of
corresponding sulphide minerals [4].
Many researchers suggested that the oxidised zinc ores can be collected by flotation
with long chain primary amines as collector after sulphidizing with sodium sulphide.
They stressed that hexyl and amyl xanthate can be used for collecting smithsonite, but in
practice the process is not selective enough. The amount of sulphidizing reagent and pH
of the pulp must be carefully controlled. Sodium sulphide is a preferred soluble sulphide
in comparison to other sulphides e.g. calcium sulphide, barium sulphide and ammonium
polysulphide [5-8].
The activating effect of sodium sulphide is strongly time dependent. An increase in
sulphidisation leads to an increase in the hydrophobicity of the mineral surface. Excess of
sodium sulphide acts as a depressant for oxidised lead and zinc minerals because the
adsorption of divalent sulphide ions on the surface of lead oxide minerals increases the
negative charge which prevents the adsorption of collector [9]. XPS and FTIR have been
found to be useful techniques for elucidating the surface properties of solids, which may
be relevant in applied aspects of mineral processing [10].
In the present investigation, the adsorption behaviour effects of various amounts of
cationic and anionic collectors on pure smithsonite surfaces was verified using diffuse
reflectance FT-IR and XPS studies.
MATERIALS AND METHODS
Materials
The crystalline smithsonite samples (90% purity) were obtained from the Angooran
zinc deposit, Iran. The XRF chemical analysis showed the pure sample contains 58.50 %
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 23
ZnO, 0.26 % Fe
2
O
3
, 0.29 % SiO
2
, 0.84 % CaO, 3.41 % Na
2
O, 1.06 % PbO, 0.34 %
others, 35.30% L.O.I (Loss of ignition). The mineral samples were wet ground in a
porcelain mill to obtain -5 µm size fractions. This final product (-5 µm) was employed
for FT-IR and XPS measurements.
Reagents
Dodecylamine (99% purity) was obtained from Fluka Chemie, Switzerland.
Potassium amyl xanthate with 90% purity was purchased from Shandong Qixia Flotation
Reagent Co., Ltd, China and was purified by recrystallization from acetone. Oleic acid
(99.9% purity), sodium sulphide and copper sulphate anhydrous (99% purity) was
procured from Merck KGaA, Germany. Analytic grade HCl and NaOH were used for pH
adjustment in all experiments. Deionised water (specific conductance, 0.4-0.7 µS cm
-1
)
was used in all experiments.
Diffuse Reflectance FTIR Measurements
The mineral suspensions of smithsonite with -5 µm particle size and 1% solid ratio
were first conditioned for 2-4 minutes together with NaOH or HCl as pH regulating
reagent in the presence of various activators. Sodium sulphide and copper sulphate were
used in KAX treatment whereas sodium sulphide as sulphidising agent was used in amine
treatment. Then the samples were conditioned for 5-10 minutes with different reagents
such as dodecylamine, oleic acid and KAX. The infrared spectra were obtained for all
pure samples on the air dried -5 µm mineral powders before recording the DRIFT
infrared spectrum.
The FTIR spectra were registered with a Perkin Elmer Spectrum 2000 FTIR-Diffuse
reflectance spectrometer. This instrument is capable of data collection over a wave
number range of 370-7800 cm
-1
and can be configured to run in single-beam, ratio or
interferogram modes. About 10 % by weight of the solid samples were mixed with
spectroscopic grade KBr with a refractive index of 1.559 and a particle size of 1-5 µm.
These spectra were recorded with 200 scans measured at 4 cm
-1
resolution.
X-ray Photoelectron Spectroscopy (XPS) Measurements
X-ray photoelectron spectroscopy (XPS) is one of the major techniques in basic
research of flotation-related surface studies of different minerals. The advantages of the
method, in general, are good surface sensitivity, rather straightforward elemental and
chemical state analysis and reliable quantification of the data.
The XPS spectra were obtained with an Axis Ultra electron spectrometer
manufactured by Kratos Analytical. Ltd, UK. The vacuum in the sample analysis
chamber was 10
-9
Torr. A value of 285.0 eV was adopted as standard C (1s) binding
energy. The measurements were performed on the samples used in FTIR measurement.
24 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
RESULTS AND DISCUSSION
FT-IR Studies of Pure Smithsonite
The smithsonite spectrum displays several bands in the region 4000-400 cm
-1
, Table 1
shows the assignment of pure smithsonite bands according to literature and experimental
data. When smithsonite is immersed in water there are carbonate, hydroxyl carbonate,
and hydroxide. H
2
O group physically adsorbs on the surface of the mineral. The amount
of physically adsorbed water decreased by Na
2
S treatment which transforms into ZnS.
Marabini and Rinelli stressed that there are no significant variations after sulphidization
and this is expected because the ZnS and ZnCO
3
bands are very similar. The ZnCO
3
species disappears after sulphidization and completely forms the ZnS coating in the case
of very high Na
2
S concentrations as a form of one monolayer or a little more [11]. The
reference DRIFT spectra of smithsonite, dodecylamine, KAX, sodium oleate, copper sulphate
and sodium sulphide
are shown in Fig. 1.
Table 1- Assignment of pure smithsonite bands according to literature and experimental
data (Wave number in cm
-1
)
FT-IR experiment data
Reference data
744.01 743 [12], 742.9 [13], 744 [14], 745 [15]
840.0 841 [13]
868.7 870 [13-15], 874.1 [12]
1089.88 1093 [12], 1096 [15]
1175 1170 [15]
1435.46 1427 [14-15],1440 [12-13]
1812.03 1830-1790 [13], 1816 [15], 1810 [14]
2492 2493 [14-15]
2850 2850 [15]
2920 2924 [15]
Adsorption of Dodecylamine
Since the functional groups of the collector absorption region closely match to the
strong absorption region of smithsonite, it is difficult to identify any bands under mono
layer adsorption. The absorption bands are often highly coupled and therefore it is not
always possible to assign them to one specific vibration.
Figure 2 shows the spectra of pure smithsonite treated with sodium sulphide solution
(2.6×10
-2
M)
at pH 11.5 with increasing initial concentration of dodecylamine.
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 25
0
1
2
3
4
5
6
7
8
9
10
60010001400180022002600300034003800
Wavenumber(cm
-1
)
Absorbance C/
S
Smithsonite
Dodecylamine
Potassium Amylxanthate
Sodium oleate
Copper Sulphate
Sodium sulphide
Fig. 1- Reference DRIFT IR-spectra of smithsonite, dodecylamine,
KAX, sodium oleate, copper sulphate and sodium sulphide
The spectra exhibit intense absorption band corresponding to υ (NH
2
) in
dodecylamine solution (1.6×10
-3
M) after sulphidising with sodium sulphide (2.6×10
-2
M). The reagent may be linked with Zn
2+
ions through coordination bonds formed by N
atoms and adsorbs to the smithsonite surface in the form of Zn-amine complexes or
perhaps the hydroxyl ions presents as zinc hydroxyl species on the surface of smithsonite
[16-17].
26 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
260027002800290030003100320033003400
Wavenumber(cm
-1
)
Absorbance C/S
a
b
c
d
Fig. 2- FT-IR spectra of pure smithsonite treated with sodium sulphide solution
(2.6×10
-2
M) at pH 11.5 with increasing initial concentration of dodecylamine
(a) 10
-5
M (b) 5.3×10
-4
M (c) 1.1×10
-3
(d) 1.6×10
-3
M
Generally at the flotation pH of around 10 the RNH
3+
is effectively absent and it can
be assumes that the RNH
2
becomes attached to the zinc on the surface in ZnS form
through complexation bonds as follows [11]:
n
n
OHSorCO
ZnSorCO
RNHSorCO
)(
|
|
)(
3
3
23
O
N
(1)
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 27
The area under the alkyl chain bands (3000-2800 cm-1) and the adsorption density of
DDA as a function of DDA concentrations are shown in Fig. 3. The adsorption density
was calculated according the measured specific surface area of smithsonite (0.43 m
2
/g).
The results of DDA adsorption study by means of DRIFT IR-spectra show the increasing
DDA adsorption density with increasing initial concentration of dodecylamine from 0.63
mg/m
2
(10
-5
M) to 5.95 mg/m
2
(1.62×10
-3
M).
0
1
2
3
4
5
6
7
8
9
10
0.00E+005.00E-041.00E-031.50E-032.00E-03
DDA concentration (mol/l)
Alkyl groups Area( cm
-1
)
0
1
2
3
4
5
6
7
8
9
10
Adsorption density (mg/ m
2
)
DDA Area
DDA+Na2S Area
Adsorption Density DDA
Adsorption Density DDA+Na2S
0
5×10
-4
10
-3
1.5×10
-3
2×10
-3
Fig. 3- Adsorption density and area under alkyl chain bands (2990-2800 cm
-1
) of DRIFT
IR-spectra of smithsonite as a function of dodecylamine concentration at pH 11.5 in the
presence or absence of sodium sulphide
28 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
Adsorption of Oleic Acid
The peaks at 2924 and 2852 cm
-1
[18-19] show that long alkyl chain is present in
oleic acid treated smithsonite samples (Fig. 4). The appearance of peak 3411 cm
-1
shows
that -OH on the surface of smithsonite has not reacted completely.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
100014001800220026003000
a
b
c
d
e
Absorbance C/S
Fig. 4- DRIFT IR-spectra of pure smithsonite at pH 10 with increasing initial
concentration of oleic acid (a) 4.42×10
-5
M (b) 1.77×10
-4
M
(c) 3.54×10
-4
M (d) 5.31×10
-5
M (e) 1.1×10
-3
M
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 29
It is known that RCOOH
(l)
and RCOOH
(aq)
are the predominant species, whereas
species such as RCOO
-
, (RCOO)
-2
2
and a lesser extent [(RCOO)
2
H]
-
exist in the
basic region.
The maximum adsorption of oleic acid on smithsonite around pH 10 may be attributed
to interaction between RCOO
-
and zinc on the smithsonite surface and can be assumed
that the adsorption of oleic acid takes place by an ion exchange mechanism as
represented below:
OH RCOO Zn RCOO Zn(OH)
-- -
(surf)
2
+⇔+
+
(2)
Accordingly, the frequencies of the bands of carboxylate ion should show
intermediate values between υ
C=O
and υ
C-O.
Bands between 1538-1650 cm
-1
and 1360-
1470 cm
-1
were assigned due to asymmetric and symmetric stretching vibrations of
carboxylate ion [20]. The asymmetric carboxylate vibration band may be attributed to
chemisorbed oleate [21-22].
If the oleate is present in the form of undissociated oleic acid (-COOH) ,the mean
frequency of υ
C=O
stretching vibration should appear around 1690 cm
-1
for dimmer
and
1718 cm
-1
for monomer. In the present investigation, the band around 1690 cm
-1
and
1718 cm
-1
was absent. It means that there is no dimmer adsorption. The broad band
around 3411 cm
-1
may be assigned to intermolecular hydrogen bonding of H
2
O molecules
thus formed during adsorption.
The area under the alkyl chain bands (3000-2800 cm
-1
) and the adsorption density of
oleic acid as a function of oleic acid concentrations are shown in Fig. 5. The results of
oleic acid adsorption studies by means of DRIFT IR-spectra show the increasing oleic
acid adsorption density with increasing initial concentration of oleic acid from 0.63
mg/m
2
(4.42×10
-5
M) to 13.1 mg/m
2
(1.1×10
-3
M).
Adsorption of KAX
Figure 6 shows the FTIR spectra of smithsonite treated with different concentrations
of KAX in the presence of sodium sulphide and copper sulphate solutions.
Clearly in all
obtained spectra the surface, the dixanthogen (AX)
2
(1270-1240 cm
-1
) bands are missing.
For all surface coverage values, the spectra exhibit absorption bands at 1041 cm
-1
,
assigned to C=S stretching mode [3,18] and 1137 cm
-1
, characteristics of C-O-C
stretching in dixanthogen [3]. The bands related to the hydrocarbon chain assigned at
2855, 2955 cm
-1
[18-19].
30 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
0
5
10
15
20
25
00.00020.00040.00060.00080.0010.0012
Oleic acid concentration(mol/l)
Alkyl group area (cm
-1
)
0
4
8
12
16
20
Adsorption density( mg/m
2
)
Alkyl group area
Adsorption density
0
2×10
-4
4×10
-4
6×10
-4
8×10
-4
10
-3
1.2×10
-3
Fig. 5- Adsorption density and area under alkyl chain bands (2990-2800 cm
-1
) of DRIFT
IR-spectra of smithsonite as a function of oleic acid concentration at pH 10
The interaction of amylxanthate with the surface of smithsonite may be represented by
the following reaction:
CO ZnAX 2AXZnCO
(aq)
-2
32(s)
-
(aq)3(s)
+⇔+ (4)
It is pointed out that the similar equation was suggested for adsorption of xanthate on
the cerussite surface by some researchers [23-24]. This ion-exchange reaction produces
solid zinc xanthate at the mineral surface and releases carbonate ions to the solution. The
area under the alkyl chain bands (3000-2800 cm
-1
) and the adsorption density of KAX as
a function of KAX concentrations are shown in Fig.7.
The adsorption density was calculated according the measured specific surface area of
smithsonite (0.43 m
2
/g). The results of KAX adsorption study by means of DRIFT IR-
spectra show the increasing KAX adsorption density with increasing initial concentration
of potassium amylxanthate from 0.35 mg/m
2
(4.94×10
-4
M) to 9.26 mg/m
2
(2.96×10
-3
M).
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 31
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
9001200150018002100240027003000
a
b
c
d
e
Wavenumber (cm
-1
)
Absorbance C/S
Fig.6- FT-IR spectra of pure smithsonite treated with sodium sulphide (2.6×10
-2
M)
and copper sulphate (9.4×10
-3
M) at pH 10.5 with increasing initial concentration
of KAX (a) 4.94×10
-4
M (b) 1.48×10
-3
M(c) 1.98×10
-3
M
(d) 2.47×10
-3
M
(e) 2.96×10
-3
M
X-ray Photoelectron Spectroscopy (XPS) Measurements
XPS Spectra of Pure Smithsonite
The XPS spectral results of pure smithsonite demonstrate the appearance of the Zn
(2p), C (1s) and O (1s). The Zn (2p) and C (1s) spectra of the smithsonite are presented in
Fig. 8.
The curve fitting unveiled that the Zn (2p) spectra consist of two components, at
1022.1 and 1045.1 eV which the both components are assigned to zinc in ZnO bond [25].
The C (1s) spectra shows the signal at 285, 290 eV which is assigned to carbon in C-O
32 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
and C=O in carbonate groups [26]. According to Fig. 8, the O (1s) spectra at 532 eV
which is relevant to C-O and C=O in carbonate groups [27]. The atomic percentage of
XPS spectral results shows the element percent of Zn 17.11%, C 6.65 %, and O 56.19 %.
0
2
4
6
8
10
12
14
16
0.00E+001.00E-032.00E-033.00E-034.00E-03
KAX concentration (mol/l)
Adsorption density (mg/m
2
)
0
2
4
6
8
10
12
14
16
Alkyl groups area(cm
-1
)
Adsorption density
Alkyl groups area
0
10
-3
2
×
10
-3
3
×
10
-3
4
×
10
-3
Fig. 7- Adsorption density and area under alkyl chain bands (2990-2800 cm-1) of IR-
spectra of smithsonite as a function of KAX concentration at pH 10.5 in sodium sulphide
(2.6×10
-2
M) and copper sulphate (9.4×10
-3
M) solutions
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 33
Fig. 8- XPS Zn (2p), C (1s) and O (1s) spectra of pure smithsonite
34 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
Adsorption of Dodecylamine
XPS analysis of samples treated with DDA shows nitrogen to be present on the
surface of sulphidised sample and this shows that DDA is present with the formation of
DDA layer on the smithsonite surface. The C(1s), N(1s), S(2p) spectra of the smithsonite
treated with DDA (1.62×10
-3
M ) are presented in Fig. 9.
The curve fitting unveiled that the C (1s) spectra consists of two components, at 285
(reference peak) and 288.1 eV. The first component is assigned to carbon in C-(C, H)
bond and second one to the carbon in the C-N [28].
The N (1s) signal of the amine groups at 399.6 eV can be assigned to nitrogen in R-
NH
2
bond and confirms the existent of DDA on the surface of mineral [29]. The S (2p)
spectra of pure sample conditioned with 1.62×10
-3
M DDA show the broad peak at
around 162.1 eV confirms that ZnS is present on the mineral surfaces [30].
The XP spectra results of pure smithsonite conditioned with Na
2
S (2.6×10
-2
M) and
DDA (1.62×10
-3
M) demonstrate the appearance of the N(1s) signal of the amine groups
and
S(2p) signal of ZnS which increased in the intensity of the signal of C(1s) peak by
adsorption of DDA on smithsonite with a simultaneous decrease in the peak intensities
of oxygen.
Figure 10 shows the atomic percent of elements at the mineral surface. As it can be
seen, there is increasing the carbon atomic percent after conditioning the pure mineral
which show increasing the adsorption of DDA on the surface of mineral. The maximum
adsorption occurs at the DDA concentration (1.62×10
-3
M). The N (1s) spectra and also
the nitrogen atomic percent show the same total atomic concentrations of nitrogen at
higher concentration of DDA.
Figure 11 shows the effect of dodecylamine conditioned on sulphidised smithsonite
with 2.6× 10
-2
M of sodium sulphide.
The large increase in O/Zn and N/Zn values is noted with increasing the reagent
concentration. There is always an excess of oxygen compared with that attributed to the
smithsonite (ZnCO
3
), as a result of both reagents used together. Initially the S/Zn value
decreases and then increases, which may be attributed to substitution of a pre-existing
sulphide species. The small increase in S/Zn may be due to the adsorption of
dodecylamine.
Adsorption of Oleic Acid
The XPS C (1s) and O (1s) spectra of pure smithsonite conditioned in solution of oleic
acid at pH 10 are shown in Fig. 12. The C (1s) spectra consist of peaks 285 eV (reference
peak) and 290.2 eV, corresponding to alkyl and carboxylate carbon respectively.
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 35
Fig. 9- XPS spectra of pure smithsonite conditioned in solution of DDA (pH 11)
36 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
0
20
40
60
80
100
Pure mineral0.1g/l0.2 g/l0.3 g/l
%Zinc
%Sulphur
%Nitrogen
%Carbon
%Oxygen
Pure mineral
5.4×10
-4
M1.1×10
-3
M1.6×10
-3
M
Fig. 10- Atomic percent elements on to smithsonite of surface after adsorption of DDA
The O (1s) spectra measured consist of the peak 533.5 eV, corresponding to O (1s) in
carboxylate group [31]. It is obvious that the most adsorption occurs at around pH 10 and
this is because of the existence of RCOO
-
is predominant in solution and has interaction
with mineral surface.
Figure 13 shows the atomic percent of elements at the mineral surface. As it can be
seen, there is increasing the carbon atomic percent after conditioning the pure mineral
which show increasing the existence of alkyl chain at the surface and conclusively
increasing the adsorption of oleic acid on the surface of mineral. The maximum
adsorption occurs for the OA concentration of 1.1× 10
-3
M at pH 10. The XPS analysis of
samples treated with oleic acid shows that OA is present with the formation of OA layer
on the smithsonite surface. Fig. 14 shows the effect of oleic acid conditioned on pure
smithsonite with 1.1× 10
-3
M of oleic acid.
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 37
0
1
2
3
4
5.00E-049.00E-041.30E-031.70E-03
DDA concentration(mol/l)
O/Zn or S/Zn
0
0.5
1
1.5
N/Zn
O/Zn
S/Zn
N/Zn
5×10
-4
9×10
-4
1.3×10
-3
1.7×10
-3
Fig. 11- The effect of DDA treatment on sulphidized smithsonite
with 2.6× 10
-2
M of Na
2
S
The increase in O/Zn and C/Zn values with increasing the reagent concentration at pH
10 shows the increasing of carbon content regarding carbon chain in reagent. There is
always an excess of oxygen compared with that attributed to the smithsonite (ZnCO
3
), as
a result of reagent used and the increasing of Zn content in media.
38 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
Fig. 12- XPS C (1s) and O (1s) spectra of pure smithsonite conditioned in solution of
oleic acid (pH 10)
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 39
0
20
40
60
80
100
Pure
mineral
pH 8pH 9pH 10pH 11
% Zinc%Carbon
%Oxygen
Fig. 13- Atomic percent elements on smithsonite surface after treatment with
oleic acid (1.1×10
-3
M)
40 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
0
10
20
30
40
50
60
7.588.599.51010.51111.5
pH
O/Zn
0
20
40
60
80
100
120
140
C/Zn
O/Zn
C/Zn
Fig. 14- The effect of oleic acid (1.1× 10
-3
M) treatment on pure smithsonite
at different pH
Adsorption of KAX
The XPS C (1s), S (2p), O (1s) and Cu (2p) spectral results of pure smithsonite
conditioned in solution of KAX (2.96 × 10
-3
M) at pH 10.5 are illustrated in Fig. 15.
The C (1s) spectra consists of peaks 285 eV (reference peak), 286.4 and 288.4 eV,
corresponding to alkyl, CS
2
and
CO carbon respectively [32-33]. The intensity of
characteristic peak in spectra for alkyl group (285.0) shows the increasing peak intensity
in comparison to C (1s) spectra in pure smithsonite. It shows that there is adsorption to
form a film at the surface of mineral.
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 41
Fig. 15- XPS spectra of pure smithsonite conditioned in solution of KAX
(2.96 × 10
-3
M) at pH 10.5
The S (2p) spectra measured consists of the peak 161.6 eV, corresponding to S (2p) in
ZnS layer onto the mineral surface [34].
The changes in the C1s and O1s emissions during the adsorption treatment show that
the adsorption of xanthate occurs. The detailed mechanism by which the exchange takes
place is not clear and obviously cannot be concluded from the above observations. Slight
changes in the positions and shapes of the components due to the xanthate group are
observed during the adsorption process.
42 Hosseini S. Hamid and Forssberg Eric Vol. 5, No. 1
The Cu (2p) spectra measured consist of the peak 932.1 eV, corresponding to Cu (2p)
in CuS [34] and 952.3 eV, corresponding to Cu
2
O layer on the mineral surface [25]. The
atomic concentration of the Cu peaks shows the more concentration for CuS in
comparison of Cu
2
O. It may be suggested that copper cations exchange with those of
zinc during copper activation of smithsonite such as activation of sphalerite. Figure 16
shows the atomic percent of elements at the mineral surface before and after treating with
KAX.
As it can be seen, there is increasing the carbon atomic percent and decreasing the
oxygen content of mineral surface after conditioning which show increasing the existence
of alkyl chain at the surface and conclusively increasing the adsorption of KAX on the
surface of mineral. On the other hand, it can be observed the increasing the copper and
sulphur percent of the surface with increasing the concentration of KAX in solution. This
shows that the ion exchange of Zn
2+
and Cu
2+
and existence of CuS layer on the surface
of mineral. The maximum adsorption occurs for the KAX concentration of 2.96×10
-3
M
at pH 10.5. The XPS analysis of samples treated with KAX shows that KAX is present
with the formation of KAX layer on the smithsonite surface.
0
20
40
60
80
100
Pure mineral0.1 g/l0.3 g/l0.6 g/l
%Zinc
%Sulphur
%Copper
i
%Carbon
%Oxygen
Pure mineral
4.94×10
-4
M1.48×10
-3
M2.96×10
-3
M
Fig. 16- Atomic percent elements on smithsonite surface after adsorption of KAX
Vol.5, No.1 XPS & FTIR Study of Adsorption Characteristics 43
CONCLUSIONS
1. According to the results, the presence of RNH
2
on the surface of smithsonite was
confirmed. Hence, this is showed the adsorption of DDA onto smithsonite surface. XPS
results confirmed the presence of ZnS layer on the surface after sulphidising in amine
adsorption. The appearance of the N (1s) signal of the amine groups and
S (2p) signal of
ZnS which increased in the intensity of the signal of C (1s) peak by adsorption of DDA
on smithsonite with a simultaneous decrease in the peak intensities of oxygen.
2. The FTIR spectra revealed the presence of COO
-
on the surface of smithsonite and
this is confirmed the adsorption of OA onto surface. It is obvious that the most adsorption
occurs at around pH 10 and this is because of the existence of RCOO
-
is predominant in
solution and has interaction with mineral surface.
3. Experimental findings showed the presence of CS
2
on the surface of smithsonite and
the adsorption of KAX onto surface. XPS results show the presence of ZnS layer on the
surface after sulphidising and also the transferring the surface to CuS in KAX adsorption.
It is suggested that copper cations exchange with those of zinc during copper activation
of smithsonite such as activation of sphalerite.
Acknowledgements
We wish to thank Calcimine Co. for providing the samples, which were used in this
investigation. The authors thank Dr. A. V. Shchukarev, Department of Inorganic
Chemistry, Umeå University and also Mr. urban Jelvestam, Material Science Department,
Chalmers university of Technology, Sweden, for the XPS measurements.
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