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Synthesis and characterization of zeolite X from lithium slag
Applied Clay Science 59–60 (2012) 148–151
Contents lists available at SciVerse ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Research paper
Synthesis and characterization of zeolite X from lithium slag Dan Chen a, b, Xin Hu a, Lu Shi a, Qun Cui a,⁎, Haiyan Wang a, Huqing Yao a a b
College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing, Jiangsu, China General Lithium (haimen) Corporation, Nantong, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 19 April 2011 Received in revised form 22 February 2012 Accepted 24 February 2012 Available online 5 April 2012 Keywords: Lithium sludge NaX zeolite Alkaline fusion Hydrothermal synthesis
a b s t r a c t Lithium slag was used as raw material to synthesize zeolite X by hydrothermal reaction with alkaline fusion. The synthesized zeolite (NaX-1) and commercial zeolite X (NaX) were characterized by XRD, SEM, IR, TG-DTA and N2 adsorption-desorption techniques. Also, water adsorption isotherms were determined by vacuum gravimetric method. Zeolite NaX-1 has similar performance to commercial zeolite X, its specific surface area and the dominant pore size are 847 m 2 g − 1 and 0.859 nm, respectively. The maximum adsorption capacity of NaX-1 for water vapor is 0.3208 kg/kg, i.e. it is comparable to NaX (0.3303 kg/kg). Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction Lithium slag is the solid by-product generated in the production of lithium carbonate, using the sulfuric acid method. Preparation of one ton of lithium carbonate produces about ten tons of lithium slag. However, only a small portion of lithium slag is utilized as a raw material for building manufacturing and construction (Glukhovskii et al., 1983), the remainder still being disposed by open-air storage or landfill, presumably causing environmental problems. The hydrothermal zeolite synthesis through transformation of natural silicates and industrial wastes has been used due to the search for cheap Al and Si sources. For example, the hydrothermal treatment of coal fly ash (Hui and Chao, 2006; Inada et al., 2005; Juan et al., 2009; Morayama et al., 2002; Querol et al., 1997, 2002; Shigemoto et al., 1990; Tanaka et al., 2003; Terzano et al., 2005), kaolin (Farzaneh et al., 1989; Lin et al., 2004; San Cristóbal et al., 2010), cupola slag (Anuwattana and Khummongkol, 2009; Anuwattana et al., 2008), diatomite (Sanhueza et al., 2004), oil shale ash (Machado and Miotto, 2005; Shawabkeh et al., 2004), perlite waste (Christidis et al., 1999) and smectite (Abdmeziem and Siffert, 1994) under alkaline conditions have been reported. Higher H2O/SiO2 ratios increase the rate of crystallization during synthesis of zeolite A from cupola slag and aluminum sludge (Anuwattana and Khummongkol, 2009). Zeolite synthesis from fly ash may include fusion of a mixture of fly ash and NaOH, whereby most of the fly ash particles convert to sodium silicate and aluminate salts, from which zeolite X forms by hydrothermal reaction without stirring (Shigemoto et al., 1990). So far, ⁎ Corresponding author at: College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing, Jiangsu, China. Tel.: + 86 025 83587188. E-mail address: [email protected] (Q. Cui).
there is not any background information on the synthesis of zeolites from lithium slag. In this paper, zeolite X was synthesized from lithium slag by hydrothermal reaction with alkaline fusion. The properties of the zeolite phase formed, such as crystal morphology, framework structure, pore structure and thermal stability were characterized by XRD, SEM, IR, N2-gas adsorption–desorption techniques and TG-DTA. Furthermore, the adsorption capacity for water vapor was investigated. The study provides the basic data for utilizing lithium slag extensively and efficiently. 2. Experimental 2.1. Material The lithium slag was obtained from General Lithium (haimen) Co. Ltd. It consists of quartz and leached spodumene (Fig. 1). The chemical composition was determined by X-ray fluorescence as follows (mass%): SiO2 71.73, Al2O3 25.16, SO3 1.58, CaO 0.21, Fe2O3 0.58, K2O 0.38, Na2O 0.06, TiO2 0.03. Commercial zeolite X sample (named as “NaX”) was purchased from Nanjing Inorganic Chemical Plant, and was used as standard sample. 2.2. Preparation of zeolite X Sodium hydroxide and lithium slag mixed of in a 1.5 weight ratio, were milled and fused in a platinum crucible at 600 °C for 4 h. The fused mixture was cooled at room temperature, ground further and added to water (5 g lithium slag /50 ml water). The slurry thus obtained was stirred mechanically for 30 minutes, aged in a teflon beaker at room temperature for 12 h, and was kept at 95 °C for 8 h
0169-1317/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2012.02.017
D. Chen et al. / Applied Clay Science 59–60 (2012) 148–151
149
(JPCDS card no. 38–0237), without additional phases (Meier et al., 1996). The degree of conversion of NaX-1 was estimated 94.31%. 3.2. SEM images The SEM images of NaX and NaX-1 are shown in Fig.3. NaX-1 has octahedral habit and uniform size 1–3 μm. On the other hand, NaX showed a wider range of crystal sizes. The SEM micrographs suggest that NaX-1 has a more uniform crystal size distribution compared with NaX. 3.3. IR spectra
Fig. 1. XRD patterns of lithium slag. (a) Leached spodumene, (b) quartz.
without stirring. The resultant precipitate was then repeatedly washed with distilled water to remove excess sodium hydroxide, filtered and dried. The synthesized zeolite was named as “NaX-1”. 2.3. Characterization
IR spectra of NaX and NaX-1 are shown in Fig. 4. The typical bands of NaX-1, attributed to asymmetric stretch (985 cm− 1), symmetric stretch (677 cm− 1), double six-member rings (D6R) (565 cm− 1) and T-O bend (462 cm− 1) are observed (where T = Al or Si). The band at about 1649 cm− 1 is attributed to H2O deformation mode due to incomplete dehydration of the zeolite samples. Moreover, the observed single strong band at 3464 cm− 1 ascribed to OH-stretching of water molecules present in the zeolite channels. All the characteristic IR bands of
The crystalline phases formed and the degree of conversion (%) of the starting materials to zeolite X were determined by X-ray diffraction (D8 ADVANCE with CuΚα radiation). The degree of conversion (%) was calculated by Eq. (1). The commercial zeolite X (NaX) was used as the standard. %Conversion ¼
∑intensity of XRD peaks of product 100 ∑intensity of XRD peaks of standard
ð1Þ
SEM images were taken with a QUANTA 200 scanning electron microscope. FT-IR spectra of the zeolites were obtained with a Nexus 670 Fourier transform infrared spectrometer. TG-DTA analyses were performed with a WCT-1 simultaneous thermal analyzer. Adsorption–desorption isotherms of N2 were recorded at 77 K using a Micromeritics model ASAP 2020 adsorption analyzer. The equilibrium isotherm data for water vapor were determined by the vacuum gravimetric method (Cui et al., 2005). 3. Results and discussion 3.1. XRD results The X-ray diffraction patterns of zeolites are given in Fig. 2. The diffraction maxima of NaX-1 are typical of FAU-type NaX zeolite
Fig. 2. XRD patterns of NaX and NaX-1.
Fig. 3. SEM images of NaX and NaX-1. (a) NaX and (b) NaX-1.
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D. Chen et al. / Applied Clay Science 59–60 (2012) 148–151 Table 1 Surface area and pore-structure parameters of NaX and NaX-1. Sample
Surface area (Langmuir) (m2 g− 1)
Micropore volume (t-plot) (cm3 g− 1)
Pore volume (cm3 g− 1)
Micropore size (HK) (nm)
NaX NaX-1
872 847
0.296 0.281
0.322 0.323
0.845 0.859
peak is due to the collapse of zeolite framework at 843 °C, and the second is attributed to crystal transformation at 995 °C (Xu et al., 2004). 3.6. Water adsorption capacity
Fig. 4. IR spectra of NaX and NaX-1.
NaX-1 are similar to NaX. A Si/Al ratio of 1.2 was calculated for NaX-1 from the shift of the IR vibrational band at 748–837 cm− 1 characteristic for O–T–Osym stretching vibrations (Loshe et al., 1995).
The adsorption isotherms of NaX and NaX-1 for water vapor at 25 °C are shown in Fig. 7. They are typical Langmuir isotherms. The maximum adsorption capacity of NaX-1 is 0.3208 kg/kg, approaching that of commercial NaX (0.3303 kg/kg).The results indicate that NaX-1 has a high adsorption capacity of water vapor. It seems that specific surface area, pore structure and surface hydrophilicity of NaX-1 zeolite enhance water adsorption capacity. 4. Conclusion
3.4. N2 adsorption surface area and pore size distribution Fig. 5 illustrates the N2 adsorption-desorption plots at 77 K for NaX and NaX-1, which correspond to typical Langmuir isotherms. There is a steep increase for nitrogen adsorption capacity when the relative pressure (p/po) is lower than 0.04. N2 adsorption for NaX and NaX-1 is completely reversible, without hysteresis. The results of surface area and pore-structure parameters are shown in Table 1. The specific surface area and micropore volume of NaX-1 are 847 m 2 g − 1 and 0.281 cm 3 g − 1 respectively. The high surface area of NaX-1 in comparison with NaX is a promising parameter for different applications related to adsorption. Further, the dominant pore size of NaX-1 is 0.859 nm, i.e. it is slightly larger than that of NaX.
Zeolite X (NaX-1) was synthesized from lithium slag by hydrothermal reaction with alkaline fusion. Crystallinity of NaX-1 as high as 94.31% was attained, SEM observation revealed that NaX-1 was a
3.5. TG-DTA analysis The weight losses and endothermic peaks (Fig. 6) of NaX and NaX-1 at temperatures lower than 500 °C are due to the loss of water adsorbed on the zeolite surface and that present in the zeolite channels. Similar to NaX, there are two exothermic peaks in the DTA curve of NaX-1 between 800 °C and 1000 °C. The first exothermic
Fig. 5. N2 adsorption-desorption isotherms of NaX and NaX-1.
Fig. 6. TG-DTA curves of NaX and NaX-1. (a) NaX and (b) NaX-1.
D. Chen et al. / Applied Clay Science 59–60 (2012) 148–151
Fig. 7. Sorption isotherm of water by NaX and NaX-1 at 25 °C.
octahedral crystal. TG-DTA results indicated that it had remarkable thermal stability. Zeolite X (NaX-1) was synthesized from lithium slag by hydrothermal reaction with alkaline fusion. A high degree of conversion of the starting material to NaX-1 (94.31%) was attained. SEM observation revealed that NaX-1 had octahedral habit. TG-DTA results indicated that it had remarkable thermal stability. The maximum adsorption capacity of NaX-1 for water vapor is 0.3208 kg/kg, approaching that of commercial (0.3303 kg/kg). Zeolite X synthesized from lithium slag has good potential for application as molecular sieve. References Abdmeziem, K., Siffert, B., 1994. Synthesis of large crystals of ZSM-5 zeolite from smectite clay mineral. Applied Clay Science 8, 437–447. Anuwattana, R., Khummongkol, P., 2009. Conventional hydrothermal synthesis of Na-A zeolite from cupola slag and aluminum sludge. Journal of Hazardous Materials 166, 227–232. Anuwattana Jr., R., Balkus, K.J., Asavapisit, S., Khummongkol, P., 2008. Conventional and microwave hydrothermal synthesis of zeolite ZSM-5 from the cupola slag. Microporous and Mesoporous Materials 111, 260–266. Christidis, G.E., Paspaliaris, I., Kontopoulos, A., 1999. Zeolitisation of perlite fines: mineralogical characteristics of the end products and mobilization of chemical elements. Applied Clay Science 15, 305–324.
151
Cui, Q., Tao, G., Chen, H.J., Guo, X.Y., Yao, H.Q., 2005. Environmentally benign working pairs for adsorption refrigeration. Energy 30, 261–271. Farzaneh, F., Oskooie, M.K., Nejad, M.M.A., 1989. The synthesis of zeolites A, X and HS from natural Iranian kaolinite and the study of the transformation of zeolites X to HS and zeolites Y to P by X-ray diffraction and scanning electron microscopy. Journal of Sciences-Islamic Republic of Iran 1, 23–28. Glukhovskii, V.D., Zaitsev, Y., Pakhomov, V., 1983. Slag-alkaline Cements and Concrete Structure, properties, technological and economical aspects of use. Silicates Industriels 481, 197–200. Hui, K.S., Chao, C.Y.H., 2006. Pure, single phase, high crystalline, chamfered-edge zeolite 4A synthesized from coal fly ash for use as a builder in detergents. Journal of Hazardous Materials B137, 401–409. Inada, M., Eguchi, Y., Enomoto, N., Hojo, J., 2005. Synthesis of zeolites from coal fly ashes with different silica-alumina composition. Fuel 84, 299–304. Juan, R., Hernandez, S., Andres, J.M., Ruiz, C., 2009. Ion exchange uptake of ammonium in wastewater from a sewage treatment plant by zeolitic materials from fly ash. Journal of Hazardous Materials 161, 781–786. Lin, D., Xu, X., Zuo, F., Long, Y., 2004. Crystallization of JBW, CAN, SOD and ABW type zeolite from transformation of meta-kaolin. Microporous and Mesoporous Materials 70, 63–70. Loshe, U., Pitsch, I., Schreier, E., Parlitz, B., Schnabel, K.-H., 1995. Cubic and hexagonal Jaujasites with varying Si/ Al ratios I. Synthesis and characterization. Applied Catalysis A: General 129, 189–202. Machado, N.R.C.F., Miotto, D.M.M., 2005. Synthesis of Na–A and –X zeolites from oil shale ash. Fuel 84, 2289–2294. Meier, W.M., Olson, D.H., Baerlocher, C., 1996. Atlas of Zeolite Structure Types. Elsevier, New York. Morayama, N., Yamamoto, H., Shibata, J., 2002. Mechanism of zeolite synthesis from coal fly ash by alkali hydrothermal reaction. International Journal of Mineral Processing 64, 1–17. Querol, X., Alastuey, A., Lopez-Soler, A., Plana, F., Juan, J.M., Ruiz, C.R., 1997. A fast method for recycling fly ash: microwave-assisted zeolite synthesis. Environmental Science and Technology 31, 2527–2533. Querol, X., Moreno, N., Umana, J.C., Alastuey, A., Hernandez, E., Lopez-Soler, A., 2002. Synthesis of zeolite from coal fly ash: an overview. International Journal of Coal Geology 50, 413–423. San Cristóbal, A.G., Castelló, R., Martín Luengo, M.A., Vizcayno, C., 2010. Zeolites prepared from calcined and mechanically modified kaolins: A comparative study. Applied Clay Science 49, 239–246. Sanhueza, V., Kelm, U., Cid, R., López-Escobar, L., 2004. Synthesis of ZSM-5 from diatomite: a case of zeolite synthesis from a natural material. Journal of Chemical Technology and Biotechnology 79, 686–690. Shawabkeh, R., Al-Harahsheh, A., Hami, M., Khlaifat, A., 2004. Conversion of oil shale ash into zeolite for cadmium and lead removal from wastewater. Fuel 83, 981–985. Shigemoto, N., Hayashi, H., Miyaura, K., 1990. Selective formation of Na-X zeolite from coal fly ash by fusion with sodium hydroxide prior to hydrothermal reaction. Journal of Materials Research 28, 4781–4786. Tanaka, H., Matsumura, S., Furusawa, S., Hino, R., 2003. Conversion of coal fly ash to NaX zeolites. Journal of Materials Science Letters 22, 323–325. Terzano, R., Spagnuoloa, M., Medici, L., Tateo, F., Ruggiero, P., 2005. Zeolite synthesis from pre-treated coal fly ash in presence of soil as a tool for soil remediation. Applied Clay Science 29, 99–110. Xu, R.R., Pang, W.Q., Yu, J.H., Huo, Q.S., Chen, J.S., 2004. Chemistry-Zeolites and Porous Materials, 1st ed. Science Press, Beijing.
Contents lists available at SciVerse ScienceDirect
Applied Clay Science journal homepage: www.elsevier.com/locate/clay
Research paper
Synthesis and characterization of zeolite X from lithium slag Dan Chen a, b, Xin Hu a, Lu Shi a, Qun Cui a,⁎, Haiyan Wang a, Huqing Yao a a b
College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing, Jiangsu, China General Lithium (haimen) Corporation, Nantong, Jiangsu, China
a r t i c l e
i n f o
Article history: Received 19 April 2011 Received in revised form 22 February 2012 Accepted 24 February 2012 Available online 5 April 2012 Keywords: Lithium sludge NaX zeolite Alkaline fusion Hydrothermal synthesis
a b s t r a c t Lithium slag was used as raw material to synthesize zeolite X by hydrothermal reaction with alkaline fusion. The synthesized zeolite (NaX-1) and commercial zeolite X (NaX) were characterized by XRD, SEM, IR, TG-DTA and N2 adsorption-desorption techniques. Also, water adsorption isotherms were determined by vacuum gravimetric method. Zeolite NaX-1 has similar performance to commercial zeolite X, its specific surface area and the dominant pore size are 847 m 2 g − 1 and 0.859 nm, respectively. The maximum adsorption capacity of NaX-1 for water vapor is 0.3208 kg/kg, i.e. it is comparable to NaX (0.3303 kg/kg). Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction Lithium slag is the solid by-product generated in the production of lithium carbonate, using the sulfuric acid method. Preparation of one ton of lithium carbonate produces about ten tons of lithium slag. However, only a small portion of lithium slag is utilized as a raw material for building manufacturing and construction (Glukhovskii et al., 1983), the remainder still being disposed by open-air storage or landfill, presumably causing environmental problems. The hydrothermal zeolite synthesis through transformation of natural silicates and industrial wastes has been used due to the search for cheap Al and Si sources. For example, the hydrothermal treatment of coal fly ash (Hui and Chao, 2006; Inada et al., 2005; Juan et al., 2009; Morayama et al., 2002; Querol et al., 1997, 2002; Shigemoto et al., 1990; Tanaka et al., 2003; Terzano et al., 2005), kaolin (Farzaneh et al., 1989; Lin et al., 2004; San Cristóbal et al., 2010), cupola slag (Anuwattana and Khummongkol, 2009; Anuwattana et al., 2008), diatomite (Sanhueza et al., 2004), oil shale ash (Machado and Miotto, 2005; Shawabkeh et al., 2004), perlite waste (Christidis et al., 1999) and smectite (Abdmeziem and Siffert, 1994) under alkaline conditions have been reported. Higher H2O/SiO2 ratios increase the rate of crystallization during synthesis of zeolite A from cupola slag and aluminum sludge (Anuwattana and Khummongkol, 2009). Zeolite synthesis from fly ash may include fusion of a mixture of fly ash and NaOH, whereby most of the fly ash particles convert to sodium silicate and aluminate salts, from which zeolite X forms by hydrothermal reaction without stirring (Shigemoto et al., 1990). So far, ⁎ Corresponding author at: College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing, Jiangsu, China. Tel.: + 86 025 83587188. E-mail address: [email protected] (Q. Cui).
there is not any background information on the synthesis of zeolites from lithium slag. In this paper, zeolite X was synthesized from lithium slag by hydrothermal reaction with alkaline fusion. The properties of the zeolite phase formed, such as crystal morphology, framework structure, pore structure and thermal stability were characterized by XRD, SEM, IR, N2-gas adsorption–desorption techniques and TG-DTA. Furthermore, the adsorption capacity for water vapor was investigated. The study provides the basic data for utilizing lithium slag extensively and efficiently. 2. Experimental 2.1. Material The lithium slag was obtained from General Lithium (haimen) Co. Ltd. It consists of quartz and leached spodumene (Fig. 1). The chemical composition was determined by X-ray fluorescence as follows (mass%): SiO2 71.73, Al2O3 25.16, SO3 1.58, CaO 0.21, Fe2O3 0.58, K2O 0.38, Na2O 0.06, TiO2 0.03. Commercial zeolite X sample (named as “NaX”) was purchased from Nanjing Inorganic Chemical Plant, and was used as standard sample. 2.2. Preparation of zeolite X Sodium hydroxide and lithium slag mixed of in a 1.5 weight ratio, were milled and fused in a platinum crucible at 600 °C for 4 h. The fused mixture was cooled at room temperature, ground further and added to water (5 g lithium slag /50 ml water). The slurry thus obtained was stirred mechanically for 30 minutes, aged in a teflon beaker at room temperature for 12 h, and was kept at 95 °C for 8 h
0169-1317/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2012.02.017
D. Chen et al. / Applied Clay Science 59–60 (2012) 148–151
149
(JPCDS card no. 38–0237), without additional phases (Meier et al., 1996). The degree of conversion of NaX-1 was estimated 94.31%. 3.2. SEM images The SEM images of NaX and NaX-1 are shown in Fig.3. NaX-1 has octahedral habit and uniform size 1–3 μm. On the other hand, NaX showed a wider range of crystal sizes. The SEM micrographs suggest that NaX-1 has a more uniform crystal size distribution compared with NaX. 3.3. IR spectra
Fig. 1. XRD patterns of lithium slag. (a) Leached spodumene, (b) quartz.
without stirring. The resultant precipitate was then repeatedly washed with distilled water to remove excess sodium hydroxide, filtered and dried. The synthesized zeolite was named as “NaX-1”. 2.3. Characterization
IR spectra of NaX and NaX-1 are shown in Fig. 4. The typical bands of NaX-1, attributed to asymmetric stretch (985 cm− 1), symmetric stretch (677 cm− 1), double six-member rings (D6R) (565 cm− 1) and T-O bend (462 cm− 1) are observed (where T = Al or Si). The band at about 1649 cm− 1 is attributed to H2O deformation mode due to incomplete dehydration of the zeolite samples. Moreover, the observed single strong band at 3464 cm− 1 ascribed to OH-stretching of water molecules present in the zeolite channels. All the characteristic IR bands of
The crystalline phases formed and the degree of conversion (%) of the starting materials to zeolite X were determined by X-ray diffraction (D8 ADVANCE with CuΚα radiation). The degree of conversion (%) was calculated by Eq. (1). The commercial zeolite X (NaX) was used as the standard. %Conversion ¼
∑intensity of XRD peaks of product 100 ∑intensity of XRD peaks of standard
ð1Þ
SEM images were taken with a QUANTA 200 scanning electron microscope. FT-IR spectra of the zeolites were obtained with a Nexus 670 Fourier transform infrared spectrometer. TG-DTA analyses were performed with a WCT-1 simultaneous thermal analyzer. Adsorption–desorption isotherms of N2 were recorded at 77 K using a Micromeritics model ASAP 2020 adsorption analyzer. The equilibrium isotherm data for water vapor were determined by the vacuum gravimetric method (Cui et al., 2005). 3. Results and discussion 3.1. XRD results The X-ray diffraction patterns of zeolites are given in Fig. 2. The diffraction maxima of NaX-1 are typical of FAU-type NaX zeolite
Fig. 2. XRD patterns of NaX and NaX-1.
Fig. 3. SEM images of NaX and NaX-1. (a) NaX and (b) NaX-1.
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D. Chen et al. / Applied Clay Science 59–60 (2012) 148–151 Table 1 Surface area and pore-structure parameters of NaX and NaX-1. Sample
Surface area (Langmuir) (m2 g− 1)
Micropore volume (t-plot) (cm3 g− 1)
Pore volume (cm3 g− 1)
Micropore size (HK) (nm)
NaX NaX-1
872 847
0.296 0.281
0.322 0.323
0.845 0.859
peak is due to the collapse of zeolite framework at 843 °C, and the second is attributed to crystal transformation at 995 °C (Xu et al., 2004). 3.6. Water adsorption capacity
Fig. 4. IR spectra of NaX and NaX-1.
NaX-1 are similar to NaX. A Si/Al ratio of 1.2 was calculated for NaX-1 from the shift of the IR vibrational band at 748–837 cm− 1 characteristic for O–T–Osym stretching vibrations (Loshe et al., 1995).
The adsorption isotherms of NaX and NaX-1 for water vapor at 25 °C are shown in Fig. 7. They are typical Langmuir isotherms. The maximum adsorption capacity of NaX-1 is 0.3208 kg/kg, approaching that of commercial NaX (0.3303 kg/kg).The results indicate that NaX-1 has a high adsorption capacity of water vapor. It seems that specific surface area, pore structure and surface hydrophilicity of NaX-1 zeolite enhance water adsorption capacity. 4. Conclusion
3.4. N2 adsorption surface area and pore size distribution Fig. 5 illustrates the N2 adsorption-desorption plots at 77 K for NaX and NaX-1, which correspond to typical Langmuir isotherms. There is a steep increase for nitrogen adsorption capacity when the relative pressure (p/po) is lower than 0.04. N2 adsorption for NaX and NaX-1 is completely reversible, without hysteresis. The results of surface area and pore-structure parameters are shown in Table 1. The specific surface area and micropore volume of NaX-1 are 847 m 2 g − 1 and 0.281 cm 3 g − 1 respectively. The high surface area of NaX-1 in comparison with NaX is a promising parameter for different applications related to adsorption. Further, the dominant pore size of NaX-1 is 0.859 nm, i.e. it is slightly larger than that of NaX.
Zeolite X (NaX-1) was synthesized from lithium slag by hydrothermal reaction with alkaline fusion. Crystallinity of NaX-1 as high as 94.31% was attained, SEM observation revealed that NaX-1 was a
3.5. TG-DTA analysis The weight losses and endothermic peaks (Fig. 6) of NaX and NaX-1 at temperatures lower than 500 °C are due to the loss of water adsorbed on the zeolite surface and that present in the zeolite channels. Similar to NaX, there are two exothermic peaks in the DTA curve of NaX-1 between 800 °C and 1000 °C. The first exothermic
Fig. 5. N2 adsorption-desorption isotherms of NaX and NaX-1.
Fig. 6. TG-DTA curves of NaX and NaX-1. (a) NaX and (b) NaX-1.
D. Chen et al. / Applied Clay Science 59–60 (2012) 148–151
Fig. 7. Sorption isotherm of water by NaX and NaX-1 at 25 °C.
octahedral crystal. TG-DTA results indicated that it had remarkable thermal stability. Zeolite X (NaX-1) was synthesized from lithium slag by hydrothermal reaction with alkaline fusion. A high degree of conversion of the starting material to NaX-1 (94.31%) was attained. SEM observation revealed that NaX-1 had octahedral habit. TG-DTA results indicated that it had remarkable thermal stability. The maximum adsorption capacity of NaX-1 for water vapor is 0.3208 kg/kg, approaching that of commercial (0.3303 kg/kg). Zeolite X synthesized from lithium slag has good potential for application as molecular sieve. References Abdmeziem, K., Siffert, B., 1994. Synthesis of large crystals of ZSM-5 zeolite from smectite clay mineral. Applied Clay Science 8, 437–447. Anuwattana, R., Khummongkol, P., 2009. Conventional hydrothermal synthesis of Na-A zeolite from cupola slag and aluminum sludge. Journal of Hazardous Materials 166, 227–232. Anuwattana Jr., R., Balkus, K.J., Asavapisit, S., Khummongkol, P., 2008. Conventional and microwave hydrothermal synthesis of zeolite ZSM-5 from the cupola slag. Microporous and Mesoporous Materials 111, 260–266. Christidis, G.E., Paspaliaris, I., Kontopoulos, A., 1999. Zeolitisation of perlite fines: mineralogical characteristics of the end products and mobilization of chemical elements. Applied Clay Science 15, 305–324.
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