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FT-IR and XRD analysis of natural Na-bentonite and Cu(II)-loaded Na-bentonite
Spectrochimica Acta Part A 79 (2011) 1013–1016
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
FT-IR and XRD analysis of natural Na-bentonite and Cu(II)-loaded Na-bentonite Liu Zhirong a,∗ , Md. Azhar Uddin b , Sun Zhanxue a a b
Department of Applied Chemistry, East China Institute of Technology, Fuzhou, Jiangxi 344000, PR China Department of Material and Energy Science, Graduate School of Environmental Science, Okayama University, Tsushima Naka, Okayama 700-8530, Japan
a r t i c l e
i n f o
Article history: Received 23 February 2011 Received in revised form 29 March 2011 Accepted 10 April 2011 Keywords: Na-bentonite Adsorption Cu(II) XRD FT-IR
a b s t r a c t Na-bentonite has been studied extensively because of its strong adsorption capacity and complexation ability. In this work, surface area, total pore volume, mean pore diameter, TG, DTA, FT-IR and XRD were carried out in order to reveal the characteristics of natural Na-bentonite. XRD and FT-IR of natural Nabentonite (China) and Cu-loaded Na-bentonite as a function of Na-bentonite dosage and temperature using batch technique were characterized in detail, respectively. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Bentonite is a kind of clay composed primarily of the montmorillonite. Compared with other clay types, montmorillonite has excellent adsorption properties and possesses adsorption sites available within its interlayer space as well as on the outer surface and edges. Montmorillonite has a 2:1 layer structure and it is composed of two tetrahedral sheets of silicon ions surrounding a sandwiched octahedral sheet of aluminum ions [1]. The binding force between the stacked layers of basic units is mainly the weak Van Der Waals type of force, which facilitates change in the interlayer space depending on the humidity conditions and/or the type of material encountered within the interlayer space of the clay [2,3]. In China, the bentonite is abundant mineral resource and its reserve amount ranks the first place in the world. Bentonite is considered as main candidate for the environmental remediation of wastewater contaminated by heavy metal ions [4–7]. Bentonite is usually classified into sodium (Na-bentonite) or calcium (Ca-bentonite) types due to dominant exchangeable cation. Na-bentonite in Gaomiaozi County (Inner Mongolia Autonomous Region, China) (herein Na-bentonite was named as Gaomiaozi Nabentonite) has been selected as the candidate of backfill material for nuclear waste repository. Detailed adsorption studies for Nabentonite were given in the literature for copper too. However, the characterization of the natural Gaomiaozi Na-bentonite and Cu(II)loaded Na-bentonite using XRD and FT-IR are still scarce and have
not been studied in detail [8,9]. The purpose of this work is to characterize the natural Na-bentonite and Cu(II)-loaded Na-bentonite using XRD and FT-IR in detail after adsorption of Cu(II) from aqueous solution onto Na-bentonite was investigated as a function of Na-bentonite dosage and temperature using batch technique. 2. Experimental 2.1. Chemicals The sample of Na-bentonite was obtained from Gaomiaozi County (Inner Mongolia Autonomous Region, China). The Gaomiaozi Na-bentonite was dried, and ground to 53 m. The N2 -BET surface area of the sample was 28.82 m2 /g. The total pore volume of 0.072 cm3 /g was composed of mesopore volume of 0.060 cm3 /g and micropore volume of 0.012 cm3 /g. The mesopore diameter for the sample was about 4.000 nm and micropore diameter was about 0.595 nm (Micromeritics Gemini, Shimadzu). The chemical analysis followed those methods reported by Wilson [10]. The copper stock solution was prepared by dissolving 3.8017 g Cu(NO3 )2 ·3H2 O (Wake Pure Chemical Industries, Ltd., Japan) in doubly distilled water and then diluted to 1000 mg/mL. All chemicals used in the experiments were purchased in analytical purity. Doubly distilled water was used in the experiments. 2.2. Characterization
∗ Corresponding author. Tel.: +86 794 8258987; fax: +86 794 8256673. E-mail address: [email protected] (L. Zhirong). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.04.013
The thermogravimetry (TG) and differential thermal analysis (DTA) were obtained simultaneously by using DTG-50H Thermal Analyzer (Shimadzu). The sample of the natural Na-bentonite and
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Table 1 Chemical composition of Na-bentonite.
100 90 Percentage present/%
SiO2 Al2 O3 Na2 O K2 O CaO Fe2 O3 FeO MgO MnO TiO2 Loss of ignition
69.17 14.43 1.95 0.83 1.29 3.12 0.02 3.31 0.04 0.13 5.40
Cu(II)-loaded Na-bentonite were characterized using Fourier transform infrared (Thermo Nicolet AVATAR 360 FTIR, America) in pressed KBr pellets (0.4 mg of sample and 200 mg of KBr). The spectral resolution was set to 4 cm−1 , and 64 scans were collected for each spectrum. The X-ray powder diffraction (XRD) pattern of the natural Na-bentonite crystal and Cu(II)-loaded Na-bentonite crystal was recorded on Lab X XRD-6100 X-ray diffractometer (Shimadzu). XRD analysis was performed with CuK␣ radiation ( = 0.1541 nm). X-ray diffractometer was used to measure the change in d-spacing of the layered silicate and the composite materials. The 2-scanning rate was 2 min−1 . 2.3. Adsorption procedures All experiments were carried out using batch technique. The dosage effects were studied under three different solid/liquid ratios. The various amounts of Na-bentonite and copper stock solution were mixed in the glass tubes (100 ml) at the desired solid/liquid (S/L) ratio (2.0000 g/(100 ml 1000 mg/ml) (S/L = 20/1), 1000 mg/l) (S/L = 2/1), 0.0200 g/(100 ml 0.2000 g/(100 ml 1000 mg/ml) (S/L = 0.2/1), respectively under the temperature of 10 ◦ C. The solutions at pH 3 were adjusted by adding negligible volumes of 0.10 or 0.01 M HCl or NaOH. The glass tubes were shaken for 2 h at different solid/liquid ratio. The solid and liquid phases were separated by centrifugation at 15,000 rpm for 5 min (Himac CF 15 R High-speed Micro Centrifuge, Shimadzu). The Cu-loaded Na-bentonite was dried in 110 ◦ C oven for 5 h. The concentration of Cu(II) in supernatant was measured by using flame atomic absorption spectrophotometer (TAS-990, Beijing Geological Instrument Factory). The flame type was air-acetylene and absorption wavelength was Cu(II) cations (324.8 nm). The adsorption percentage (%) of Cu(II) cations on Na-bentonite ((Co − Ce )/Ce × 100%) was derived from the difference of initial concentration (Co ) and equilibrium concentration (Ce ). The thermal effects were studied under three different temperatures. 0.2000 g Na-bentonite and 100 ml 1000 mg/ml copper solution were added and mixed (Mix Rotor VMRC-5) in the glass tubes (100 ml) at the desired temperatures (10 ◦ C, 30 ◦ C, 50 ◦ C), respectively. The solutions at pH 3 were adjusted by adding negligible volumes of 0.10 or 0.01 M HCl or NaOH. The glass tubes were shaken for 2 h at different temperature. The solid and liquid phases were separated by centrifugation at 15,000 rpm for 5 min (Himac CF 15 R High-speed Micro Centrifuge, Shimadzu). The Cu-loaded Na-bentonite was dried in 110 ◦ C oven for 5 h. 3. Results and discussion Chemical composition of natural Na-bentonite is summarized in Table 1. The study shows that the bentonite are mainly composed of SiO2 , Al2 O3 , CaO, Na2 O, K2 O, MgO, Fe2 O3 , FeO, MnO and TiO2 .
80
Transmittance(%)
Constituent
70 60 50 40 30 20
3629 cm-1 OH 3425,1654,3284 cm-1 H2O 1031,696,634 cm-1 Si-O 912 cm-1 Al-Al-OH 796 cm-1 Quartz 545,460 cm-1 Al-Si-O,Si-O-Si
10 0 4000
3600
3200
2800
2400
2000
1600
1200
800
400
Wavenumber(cm-1 ) Fig. 1. FT-IR of natural Na-bentonite.
The contents of CaO and Na2 O (K2 O) reflect interlayer cation in montmorillonite. Different contents of CaO and Na2 O can classify a kind of bentonite as either Ca-bentonite or Na-bentonite. In the perfect montmorillonite structure, the total theoretical content of SiO2 and Al2 O3 is 92%, and the content ratio of SiO2 to Al2 O3 is 2.6. In the Na-bentonite, the total content of SiO2 and Al2 O3 is 83.60%, and the corresponding ratio of SiO2 to Al2 O3 is 4.79. The SiO2 to Al2 O3 ratio is nearly twice as the theoretical value, indicating relatively high SiO2 content and relatively low Al2 O3 content. The (Na + K)/Ca is 2.2. It also shows that the high-silica montmorillonite are enriched with sodium and potassium. The CaO content is less than K2 O and Na2 O contents, so this kind of raw ore belongs to the Na-bentonite category. The TG/DTA of the natural Na-bentonite shows three main steps of weight loss. The first weight loss (80–215 ◦ C) corresponds to both adsorbed and interlayer water. The second weight loss (550–750 ◦ C) is attributed to crystal water. The third weight loss (850–1050 ◦ C) is related to destroyed lattice of Na-bentonite. The dosage of Na-bentonite and temperature are important variables for the adsorption percentage of Cu(II) cations. The adsorption percentage of Cu(II) cations increases when the solid/liquid ratio increases from 0.2/1 to 20/1. The increase in dosage may be explained by an increase in the surface area of Na-bentonite for adsorption. The adsorption percentage of Cu(II) cations increases with an increase in the temperature from 10 to 50 ◦ C. The increase in temperature may be attributed to either increase in the number of active surface sites available for adsorption or decrease in the mass transfer resistance. 3.1. FT-IR and XRD characterization of natural Na-bentonite Fig. 1 shows the FT-IR spectrum of natural Na-bentonite sample. The absorption band at 3629 cm−1 is due to stretching vibrations of structural OH groups of Na-bentonite. A sharp band at 796 cm−1 indicates quartz admixture in the sample, which has been confirmed by X-ray diffraction extensively. The band at 696 cm−1 is due to the deformation and bending modes of the Si–O bond. The bands at 545 and 460 cm−1 are due to Al–O–Si and Si–O–Si bending vibrations, respectively. The band corresponding to Al–Al–OH is observed at 912 cm−1 . The very strong absorption band at 1031 cm−1 is due to Si–O bending vibration [11]. The band at 3629 cm−1 is responsible for free uncomplexed hydroxyls, as well as the band 1654 cm−1 responsible for bending H–O–H vibration in water. The band 3425 cm−1 is responsible for hydroxyls bound via hydrogen bonds. The bands at 2957 cm−1 , 2874 cm−1 , 2925 cm−1 , 2853 cm−1 , 1457 cm−1 , 1385 cm−1 and 717 cm−1 are
L. Zhirong et al. / Spectrochimica Acta Part A 79 (2011) 1013–1016
1015
600 Q
M-montmorillonite Q-quartz F-feldspars
Intensity(CPS)
500 400 300
M
F M
200
Q
M
Q M
100 0
0
10
20
30
Q
40
50
M
M
60
70
80
90
2θ(o) Fig. 2. XRD of natural Na-bentonite.
due to aliphatic hydrocarbons in the Na-bentonite [12]. The existence of aliphatic hydrocarbons possibly can explain the 5.40 percent loss of ignition in Na-bentonite. The XRD pattern of natural Na-bentonite is given in Fig. 2. The figure indicates that the clay is composed primarily of montmorillonite, with the characteristic features at d0 0 1 = 14.29 A˚ and ˚ The basal spacing, d0 0 1 = 14.29 A, ˚ indicates a predomd0 2 0 = 4.49 A. inance of sodium which allows to characterize the samples mainly as sodium bentonite (Na-bentonite). The other peaks are impurities corresponding to quartz and feldspar. 3.2. FT-IR and XRD characterization of Cu(II)-loaded Na-bentonite at different solid/liquid ratio Detailed analysis of FT-IR spectra in the whole spectral region (4000–400 cm−1 ) can be use for discern of the location of Cu(II) cations. The structural modifications of the tetrahedral and octahedral sheets due to the adsorbed Cu(II) cations influenced the fundamental vibrations of the Si–O and H2 O groups at different solid/liquid ratio 20/1, 2/1 and 0.2/1(Fig. 3). The FT-IR patterns of the Cu(II)-loaded Na-bentonite samples showed that a broad band of water near 3438, 3430 and 3430 cm−1 at different solid/liquid ratio of 20/1, 2/1 and 0.2/1 were shifted from 3425 cm−1 for the natural Na-bentonite. The changes in the Si environment after Cu(II) adsorption process were reflected in both the position and the shape of the Si–O stretching band near 1031 cm−1 . A slight shift of
Fig. 4. XRD of Cu(II)-loaded Na-bentonite at different solid/liquid ratio under the temperature of 10 ◦ C.
this band to higher frequencies indicated alteration of the structure [13]. The strong band near 1031 cm−1 , assigned to complex Si–O stretching vibration in the tetrahedral sheet, moved to 1041, 1037 and 1039 cm−1 at different solid/liquid ratio after Cu(II) adsorption process. The adsorption may be attributed to the replacement of alkaline metals with Cu(II) ions for natural Na-bentonite. Montmorillonite is known to be a kind of swelling clay that contains water of hydration. The extent of hydration of the clay is dependent on the type and nature of interlayer cations and temperature, in addition to its crystalline structure. Since the hydration state of montmorillonite is expected to be reflected by the size of its interlayer space, the effect of Cu(II) adsorption on the basal space (d0 0 1 and d0 2 0 ) of montmorillonite was studied using XRD (Fig. 4). The XRD patterns of the exchanged clay samples at various solid/liquid of 20/1 and 2/1 indicated a decreased shift in the position of the d0 0 1 peak from 14.29 to 12.48 and 12.23 A˚ and a slight decreased shift in the position of the d0 2 0 peak from 4.49 ˚ The reduction in the basal spacing of this feato 4.48 and 4.47 A. ture could be indicative of a decrease in the number of water layers in the interlayer space as a consequence of the Cu(II) adsorption. Other authors reported similar reductions in d0 0 1 of montmorillonite upon adsorption of Pb(II) and Zn(II) and concluded that bulky polynuclear complexes such as the hydrolysis products do not form in the interlamellar space of the clay upon the adsorption of these ions [14,15]. There are some possible reasons for this phenomenon. The Mg2+ and Fe3+ in Na-bentonite replaced the Si4+ in silicon–oxygen tetrahedron of the montmorillonite. The lattice replacement was produced to form a lot of negative charges in the interlayers. These negative charges adsorbed the hydrated cations in solution and formed the electric double layers. Because thickness of the electric double layers is inversely proportional to hydrated cation valence, the higher the hydrated cation valence, the larger the concentration is and the worse the expansibility is. Moreover, the expansibility of Na-bentonite was controlled by its chemical composition. The montmorillonite containing more Na(I) ion (higher ionic radius 0.097 nm) can expand constantly, while the montmorillonite with more Cu(II) ion (lower ionic radius 0.072 nm) can only reduce [16]. 3.3. FT-IR and XRD characterization of Cu(II)-loaded Na-bentonite at different temperature
Fig. 3. FT-IR of Cu(II)-loaded Na-bentonite under different solid/liquid ratio under the temperature of 10 ◦ C.
Detailed analysis of FT-IR spectra in the whole spectral region (4000–400 cm−1 ) can be use for discern of the location of Cu(II)
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to 12.48, 12.17 and 12.16 A˚ and d0 2 0 from 4.49 to 4.48, 4.46 and ˚ at the temperature of 10 ◦ C, 30 ◦ C and 50 ◦ C, respectively. 4.45 A, XRD of Cu(II)-loaded Na-bentonite showed almost identical differences in terms of their XRD patterns upon Cu(II) adsorption. These differences indicated the effects of Cu(II) adsorption on the structure of clay minerals. 4. Conclusions
Fig. 5. FT-IR of Cu(II)-loaded Na-bentonite under different temperature under the solid/liquid ratio of 2:1.
The experimental results showed that Cu(II) cations can be adsorbed onto natural Na-bentonite by means of FT-IR and XRD study. The adsorption behavior of Na-bentonite for Cu(II) was depending on the solid/liquid ratio and temperature. XRD spectra indicated that the Cu(II) adsorption onto the Na-bentonite led to changes in unit cell dimensions and symmetry of the natural Na-bentonite. FT-IR studies showed that Cu(II) cations replaced the original metal ions in the interlayer or located into hexagonal cavities of Si–O sheet in the Cu(II)-loaded Na-bentonite samples. Construction modification of tetrahedral sheets due to the presence of Cu(II) cations either in hexagonal holes and/or in the previously vacant octahedral sites induced changes in the Si–O vibration modes. The shift of FT-IR and XRD were attributed to the Cu(II) adsorption mainly. The dosage of Na-bentonite and temperature has little influence on the shift of FT-IR and XRD extensively. Acknowledgments The authors appreciate the support of Jiangxi Association for Science and Technology’s Fund towards the overseas academic exchange. The authors are grateful to Prof. Kato Yoshiei from Okayama University for kindly allowing us to use Kato-Azhar laboratory during running the experimental program in this study. The authors would like to acknowledge the help provided by Ph.D. Andrei V. Veksha too.
Fig. 6. XRD of Cu(II)-loaded Na-bentonite under different temperature under the solid/liquid ratio of 2:1.
10 ◦ C,
30 ◦ C,
50 ◦ C
cations at different temperature of and (Fig. 5). The FT-IR patterns of the Cu(II)-loaded Na-bentonite samples showed that a broad band of water near 3438, 3436 and 3446 cm−1 at different temperature were shifted from 3425 cm−1 for the natural Na-bentonite. The strong band near 1031 cm−1 , assigned to complex Si–O stretching vibrations in the tetrahedral sheet, moved to 1041, 1035 and 1033 cm−1 at different temperature after Cu(II) adsorption process. The XRD patterns of the Cu(II)-loaded natural Na-bentonite are shown in Fig. 6. Several reflections were observed in the region 2◦ < 2 < 8◦ for the patterns of the Cu(II)-loaded Na-bentonite samples. One reflection situated at a higher 2 value corresponds to the basal spacing, while the other reflections situated at a lower 2 values are likely to appear because of the agglomeration of clay sheets. The adsorption of Cu(II) onto the natural Na-bentonite led to decrease in the basal spaces of the host materials, d0 0 1 from 14.29
References [1] J. Madejová, J. Bujdák, M. Janek, P. Komadel, Spectrochim. Acta A 54 (1998) 1397–1406. [2] O. Abollino, M. Aceto, M. Malandrino, C. Sarzanini, E. Mentasti, Water Res. 37 (2003) 1619–1627. [3] E. Álvarez-Ayuso, A. García-Sánchez, Clay Clay Miner. 51 (2003) 475–480. [4] Z.R. Liu, S.Q. Zhou, Process Saf. Environ. 88 (2010) 62–66. [5] C.M. Futalan, C.C. Kan, M.L. Dalida, K.J. Hsien, C. Pascua, M.W. Wan, Carbohyd. Polym. 83 (2011) 528–536. [6] O. Korkut, E. Sayan, O. Lacin, B. Bayrak, Desalination 259 (2010) 243–248. [7] T.K. Sen, D. Gomez, Desalination 267 (2011) 286–294. [8] M. Majdana, O. Maryuk, S. Pikus, E. Olszewskaa, R. Kwiatkowski, H. Skrzypek, J. Mol. Struct. 740 (2005) 203–211. [9] J.X. Li, J. Hu, G.D. Sheng, G.X. Zhao, Q. Huang, Colloids Surf. A 349 (2009) 195–201. [10] MAR Writers Group, Mineral Analyses of Rocks, first ed., Geology Press, Beijing, 1991 (in Chinese). [11] S.W. Wang, Y.H. Dong, M.L. He, L. Chen, X.J. Yu, Appl. Clay Sci. 43 (2009) 164–171. [12] A.A. Atia, Appl. Clay Sci. 41 (2008) 73–84. [13] J. Madejová, B. Arvaiová, P. Komadel, Spectrochim. Acta A 55 (1999) 2467–2476. [14] M. Auboiroux, P. Baillif, J.C. Touray, F. Bergaya, Appl. Clay Sci. 11 (1996) 117–126. [15] E. Eren, B. Afsin, J. Hazard. Mater. 151 (2008) 682–691. [16] W. Long, Z.T. Fan, X.T. Hu, China Foundry 6 (2009) 310–313.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
FT-IR and XRD analysis of natural Na-bentonite and Cu(II)-loaded Na-bentonite Liu Zhirong a,∗ , Md. Azhar Uddin b , Sun Zhanxue a a b
Department of Applied Chemistry, East China Institute of Technology, Fuzhou, Jiangxi 344000, PR China Department of Material and Energy Science, Graduate School of Environmental Science, Okayama University, Tsushima Naka, Okayama 700-8530, Japan
a r t i c l e
i n f o
Article history: Received 23 February 2011 Received in revised form 29 March 2011 Accepted 10 April 2011 Keywords: Na-bentonite Adsorption Cu(II) XRD FT-IR
a b s t r a c t Na-bentonite has been studied extensively because of its strong adsorption capacity and complexation ability. In this work, surface area, total pore volume, mean pore diameter, TG, DTA, FT-IR and XRD were carried out in order to reveal the characteristics of natural Na-bentonite. XRD and FT-IR of natural Nabentonite (China) and Cu-loaded Na-bentonite as a function of Na-bentonite dosage and temperature using batch technique were characterized in detail, respectively. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Bentonite is a kind of clay composed primarily of the montmorillonite. Compared with other clay types, montmorillonite has excellent adsorption properties and possesses adsorption sites available within its interlayer space as well as on the outer surface and edges. Montmorillonite has a 2:1 layer structure and it is composed of two tetrahedral sheets of silicon ions surrounding a sandwiched octahedral sheet of aluminum ions [1]. The binding force between the stacked layers of basic units is mainly the weak Van Der Waals type of force, which facilitates change in the interlayer space depending on the humidity conditions and/or the type of material encountered within the interlayer space of the clay [2,3]. In China, the bentonite is abundant mineral resource and its reserve amount ranks the first place in the world. Bentonite is considered as main candidate for the environmental remediation of wastewater contaminated by heavy metal ions [4–7]. Bentonite is usually classified into sodium (Na-bentonite) or calcium (Ca-bentonite) types due to dominant exchangeable cation. Na-bentonite in Gaomiaozi County (Inner Mongolia Autonomous Region, China) (herein Na-bentonite was named as Gaomiaozi Nabentonite) has been selected as the candidate of backfill material for nuclear waste repository. Detailed adsorption studies for Nabentonite were given in the literature for copper too. However, the characterization of the natural Gaomiaozi Na-bentonite and Cu(II)loaded Na-bentonite using XRD and FT-IR are still scarce and have
not been studied in detail [8,9]. The purpose of this work is to characterize the natural Na-bentonite and Cu(II)-loaded Na-bentonite using XRD and FT-IR in detail after adsorption of Cu(II) from aqueous solution onto Na-bentonite was investigated as a function of Na-bentonite dosage and temperature using batch technique. 2. Experimental 2.1. Chemicals The sample of Na-bentonite was obtained from Gaomiaozi County (Inner Mongolia Autonomous Region, China). The Gaomiaozi Na-bentonite was dried, and ground to 53 m. The N2 -BET surface area of the sample was 28.82 m2 /g. The total pore volume of 0.072 cm3 /g was composed of mesopore volume of 0.060 cm3 /g and micropore volume of 0.012 cm3 /g. The mesopore diameter for the sample was about 4.000 nm and micropore diameter was about 0.595 nm (Micromeritics Gemini, Shimadzu). The chemical analysis followed those methods reported by Wilson [10]. The copper stock solution was prepared by dissolving 3.8017 g Cu(NO3 )2 ·3H2 O (Wake Pure Chemical Industries, Ltd., Japan) in doubly distilled water and then diluted to 1000 mg/mL. All chemicals used in the experiments were purchased in analytical purity. Doubly distilled water was used in the experiments. 2.2. Characterization
∗ Corresponding author. Tel.: +86 794 8258987; fax: +86 794 8256673. E-mail address: [email protected] (L. Zhirong). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.04.013
The thermogravimetry (TG) and differential thermal analysis (DTA) were obtained simultaneously by using DTG-50H Thermal Analyzer (Shimadzu). The sample of the natural Na-bentonite and
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L. Zhirong et al. / Spectrochimica Acta Part A 79 (2011) 1013–1016
Table 1 Chemical composition of Na-bentonite.
100 90 Percentage present/%
SiO2 Al2 O3 Na2 O K2 O CaO Fe2 O3 FeO MgO MnO TiO2 Loss of ignition
69.17 14.43 1.95 0.83 1.29 3.12 0.02 3.31 0.04 0.13 5.40
Cu(II)-loaded Na-bentonite were characterized using Fourier transform infrared (Thermo Nicolet AVATAR 360 FTIR, America) in pressed KBr pellets (0.4 mg of sample and 200 mg of KBr). The spectral resolution was set to 4 cm−1 , and 64 scans were collected for each spectrum. The X-ray powder diffraction (XRD) pattern of the natural Na-bentonite crystal and Cu(II)-loaded Na-bentonite crystal was recorded on Lab X XRD-6100 X-ray diffractometer (Shimadzu). XRD analysis was performed with CuK␣ radiation ( = 0.1541 nm). X-ray diffractometer was used to measure the change in d-spacing of the layered silicate and the composite materials. The 2-scanning rate was 2 min−1 . 2.3. Adsorption procedures All experiments were carried out using batch technique. The dosage effects were studied under three different solid/liquid ratios. The various amounts of Na-bentonite and copper stock solution were mixed in the glass tubes (100 ml) at the desired solid/liquid (S/L) ratio (2.0000 g/(100 ml 1000 mg/ml) (S/L = 20/1), 1000 mg/l) (S/L = 2/1), 0.0200 g/(100 ml 0.2000 g/(100 ml 1000 mg/ml) (S/L = 0.2/1), respectively under the temperature of 10 ◦ C. The solutions at pH 3 were adjusted by adding negligible volumes of 0.10 or 0.01 M HCl or NaOH. The glass tubes were shaken for 2 h at different solid/liquid ratio. The solid and liquid phases were separated by centrifugation at 15,000 rpm for 5 min (Himac CF 15 R High-speed Micro Centrifuge, Shimadzu). The Cu-loaded Na-bentonite was dried in 110 ◦ C oven for 5 h. The concentration of Cu(II) in supernatant was measured by using flame atomic absorption spectrophotometer (TAS-990, Beijing Geological Instrument Factory). The flame type was air-acetylene and absorption wavelength was Cu(II) cations (324.8 nm). The adsorption percentage (%) of Cu(II) cations on Na-bentonite ((Co − Ce )/Ce × 100%) was derived from the difference of initial concentration (Co ) and equilibrium concentration (Ce ). The thermal effects were studied under three different temperatures. 0.2000 g Na-bentonite and 100 ml 1000 mg/ml copper solution were added and mixed (Mix Rotor VMRC-5) in the glass tubes (100 ml) at the desired temperatures (10 ◦ C, 30 ◦ C, 50 ◦ C), respectively. The solutions at pH 3 were adjusted by adding negligible volumes of 0.10 or 0.01 M HCl or NaOH. The glass tubes were shaken for 2 h at different temperature. The solid and liquid phases were separated by centrifugation at 15,000 rpm for 5 min (Himac CF 15 R High-speed Micro Centrifuge, Shimadzu). The Cu-loaded Na-bentonite was dried in 110 ◦ C oven for 5 h. 3. Results and discussion Chemical composition of natural Na-bentonite is summarized in Table 1. The study shows that the bentonite are mainly composed of SiO2 , Al2 O3 , CaO, Na2 O, K2 O, MgO, Fe2 O3 , FeO, MnO and TiO2 .
80
Transmittance(%)
Constituent
70 60 50 40 30 20
3629 cm-1 OH 3425,1654,3284 cm-1 H2O 1031,696,634 cm-1 Si-O 912 cm-1 Al-Al-OH 796 cm-1 Quartz 545,460 cm-1 Al-Si-O,Si-O-Si
10 0 4000
3600
3200
2800
2400
2000
1600
1200
800
400
Wavenumber(cm-1 ) Fig. 1. FT-IR of natural Na-bentonite.
The contents of CaO and Na2 O (K2 O) reflect interlayer cation in montmorillonite. Different contents of CaO and Na2 O can classify a kind of bentonite as either Ca-bentonite or Na-bentonite. In the perfect montmorillonite structure, the total theoretical content of SiO2 and Al2 O3 is 92%, and the content ratio of SiO2 to Al2 O3 is 2.6. In the Na-bentonite, the total content of SiO2 and Al2 O3 is 83.60%, and the corresponding ratio of SiO2 to Al2 O3 is 4.79. The SiO2 to Al2 O3 ratio is nearly twice as the theoretical value, indicating relatively high SiO2 content and relatively low Al2 O3 content. The (Na + K)/Ca is 2.2. It also shows that the high-silica montmorillonite are enriched with sodium and potassium. The CaO content is less than K2 O and Na2 O contents, so this kind of raw ore belongs to the Na-bentonite category. The TG/DTA of the natural Na-bentonite shows three main steps of weight loss. The first weight loss (80–215 ◦ C) corresponds to both adsorbed and interlayer water. The second weight loss (550–750 ◦ C) is attributed to crystal water. The third weight loss (850–1050 ◦ C) is related to destroyed lattice of Na-bentonite. The dosage of Na-bentonite and temperature are important variables for the adsorption percentage of Cu(II) cations. The adsorption percentage of Cu(II) cations increases when the solid/liquid ratio increases from 0.2/1 to 20/1. The increase in dosage may be explained by an increase in the surface area of Na-bentonite for adsorption. The adsorption percentage of Cu(II) cations increases with an increase in the temperature from 10 to 50 ◦ C. The increase in temperature may be attributed to either increase in the number of active surface sites available for adsorption or decrease in the mass transfer resistance. 3.1. FT-IR and XRD characterization of natural Na-bentonite Fig. 1 shows the FT-IR spectrum of natural Na-bentonite sample. The absorption band at 3629 cm−1 is due to stretching vibrations of structural OH groups of Na-bentonite. A sharp band at 796 cm−1 indicates quartz admixture in the sample, which has been confirmed by X-ray diffraction extensively. The band at 696 cm−1 is due to the deformation and bending modes of the Si–O bond. The bands at 545 and 460 cm−1 are due to Al–O–Si and Si–O–Si bending vibrations, respectively. The band corresponding to Al–Al–OH is observed at 912 cm−1 . The very strong absorption band at 1031 cm−1 is due to Si–O bending vibration [11]. The band at 3629 cm−1 is responsible for free uncomplexed hydroxyls, as well as the band 1654 cm−1 responsible for bending H–O–H vibration in water. The band 3425 cm−1 is responsible for hydroxyls bound via hydrogen bonds. The bands at 2957 cm−1 , 2874 cm−1 , 2925 cm−1 , 2853 cm−1 , 1457 cm−1 , 1385 cm−1 and 717 cm−1 are
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1015
600 Q
M-montmorillonite Q-quartz F-feldspars
Intensity(CPS)
500 400 300
M
F M
200
Q
M
Q M
100 0
0
10
20
30
Q
40
50
M
M
60
70
80
90
2θ(o) Fig. 2. XRD of natural Na-bentonite.
due to aliphatic hydrocarbons in the Na-bentonite [12]. The existence of aliphatic hydrocarbons possibly can explain the 5.40 percent loss of ignition in Na-bentonite. The XRD pattern of natural Na-bentonite is given in Fig. 2. The figure indicates that the clay is composed primarily of montmorillonite, with the characteristic features at d0 0 1 = 14.29 A˚ and ˚ The basal spacing, d0 0 1 = 14.29 A, ˚ indicates a predomd0 2 0 = 4.49 A. inance of sodium which allows to characterize the samples mainly as sodium bentonite (Na-bentonite). The other peaks are impurities corresponding to quartz and feldspar. 3.2. FT-IR and XRD characterization of Cu(II)-loaded Na-bentonite at different solid/liquid ratio Detailed analysis of FT-IR spectra in the whole spectral region (4000–400 cm−1 ) can be use for discern of the location of Cu(II) cations. The structural modifications of the tetrahedral and octahedral sheets due to the adsorbed Cu(II) cations influenced the fundamental vibrations of the Si–O and H2 O groups at different solid/liquid ratio 20/1, 2/1 and 0.2/1(Fig. 3). The FT-IR patterns of the Cu(II)-loaded Na-bentonite samples showed that a broad band of water near 3438, 3430 and 3430 cm−1 at different solid/liquid ratio of 20/1, 2/1 and 0.2/1 were shifted from 3425 cm−1 for the natural Na-bentonite. The changes in the Si environment after Cu(II) adsorption process were reflected in both the position and the shape of the Si–O stretching band near 1031 cm−1 . A slight shift of
Fig. 4. XRD of Cu(II)-loaded Na-bentonite at different solid/liquid ratio under the temperature of 10 ◦ C.
this band to higher frequencies indicated alteration of the structure [13]. The strong band near 1031 cm−1 , assigned to complex Si–O stretching vibration in the tetrahedral sheet, moved to 1041, 1037 and 1039 cm−1 at different solid/liquid ratio after Cu(II) adsorption process. The adsorption may be attributed to the replacement of alkaline metals with Cu(II) ions for natural Na-bentonite. Montmorillonite is known to be a kind of swelling clay that contains water of hydration. The extent of hydration of the clay is dependent on the type and nature of interlayer cations and temperature, in addition to its crystalline structure. Since the hydration state of montmorillonite is expected to be reflected by the size of its interlayer space, the effect of Cu(II) adsorption on the basal space (d0 0 1 and d0 2 0 ) of montmorillonite was studied using XRD (Fig. 4). The XRD patterns of the exchanged clay samples at various solid/liquid of 20/1 and 2/1 indicated a decreased shift in the position of the d0 0 1 peak from 14.29 to 12.48 and 12.23 A˚ and a slight decreased shift in the position of the d0 2 0 peak from 4.49 ˚ The reduction in the basal spacing of this feato 4.48 and 4.47 A. ture could be indicative of a decrease in the number of water layers in the interlayer space as a consequence of the Cu(II) adsorption. Other authors reported similar reductions in d0 0 1 of montmorillonite upon adsorption of Pb(II) and Zn(II) and concluded that bulky polynuclear complexes such as the hydrolysis products do not form in the interlamellar space of the clay upon the adsorption of these ions [14,15]. There are some possible reasons for this phenomenon. The Mg2+ and Fe3+ in Na-bentonite replaced the Si4+ in silicon–oxygen tetrahedron of the montmorillonite. The lattice replacement was produced to form a lot of negative charges in the interlayers. These negative charges adsorbed the hydrated cations in solution and formed the electric double layers. Because thickness of the electric double layers is inversely proportional to hydrated cation valence, the higher the hydrated cation valence, the larger the concentration is and the worse the expansibility is. Moreover, the expansibility of Na-bentonite was controlled by its chemical composition. The montmorillonite containing more Na(I) ion (higher ionic radius 0.097 nm) can expand constantly, while the montmorillonite with more Cu(II) ion (lower ionic radius 0.072 nm) can only reduce [16]. 3.3. FT-IR and XRD characterization of Cu(II)-loaded Na-bentonite at different temperature
Fig. 3. FT-IR of Cu(II)-loaded Na-bentonite under different solid/liquid ratio under the temperature of 10 ◦ C.
Detailed analysis of FT-IR spectra in the whole spectral region (4000–400 cm−1 ) can be use for discern of the location of Cu(II)
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to 12.48, 12.17 and 12.16 A˚ and d0 2 0 from 4.49 to 4.48, 4.46 and ˚ at the temperature of 10 ◦ C, 30 ◦ C and 50 ◦ C, respectively. 4.45 A, XRD of Cu(II)-loaded Na-bentonite showed almost identical differences in terms of their XRD patterns upon Cu(II) adsorption. These differences indicated the effects of Cu(II) adsorption on the structure of clay minerals. 4. Conclusions
Fig. 5. FT-IR of Cu(II)-loaded Na-bentonite under different temperature under the solid/liquid ratio of 2:1.
The experimental results showed that Cu(II) cations can be adsorbed onto natural Na-bentonite by means of FT-IR and XRD study. The adsorption behavior of Na-bentonite for Cu(II) was depending on the solid/liquid ratio and temperature. XRD spectra indicated that the Cu(II) adsorption onto the Na-bentonite led to changes in unit cell dimensions and symmetry of the natural Na-bentonite. FT-IR studies showed that Cu(II) cations replaced the original metal ions in the interlayer or located into hexagonal cavities of Si–O sheet in the Cu(II)-loaded Na-bentonite samples. Construction modification of tetrahedral sheets due to the presence of Cu(II) cations either in hexagonal holes and/or in the previously vacant octahedral sites induced changes in the Si–O vibration modes. The shift of FT-IR and XRD were attributed to the Cu(II) adsorption mainly. The dosage of Na-bentonite and temperature has little influence on the shift of FT-IR and XRD extensively. Acknowledgments The authors appreciate the support of Jiangxi Association for Science and Technology’s Fund towards the overseas academic exchange. The authors are grateful to Prof. Kato Yoshiei from Okayama University for kindly allowing us to use Kato-Azhar laboratory during running the experimental program in this study. The authors would like to acknowledge the help provided by Ph.D. Andrei V. Veksha too.
Fig. 6. XRD of Cu(II)-loaded Na-bentonite under different temperature under the solid/liquid ratio of 2:1.
10 ◦ C,
30 ◦ C,
50 ◦ C
cations at different temperature of and (Fig. 5). The FT-IR patterns of the Cu(II)-loaded Na-bentonite samples showed that a broad band of water near 3438, 3436 and 3446 cm−1 at different temperature were shifted from 3425 cm−1 for the natural Na-bentonite. The strong band near 1031 cm−1 , assigned to complex Si–O stretching vibrations in the tetrahedral sheet, moved to 1041, 1035 and 1033 cm−1 at different temperature after Cu(II) adsorption process. The XRD patterns of the Cu(II)-loaded natural Na-bentonite are shown in Fig. 6. Several reflections were observed in the region 2◦ < 2 < 8◦ for the patterns of the Cu(II)-loaded Na-bentonite samples. One reflection situated at a higher 2 value corresponds to the basal spacing, while the other reflections situated at a lower 2 values are likely to appear because of the agglomeration of clay sheets. The adsorption of Cu(II) onto the natural Na-bentonite led to decrease in the basal spaces of the host materials, d0 0 1 from 14.29
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