Advanced Powder Technology xxx (2013) xxx–xxx

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Advanced Powder Technology

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Original Research Paper

Synthesis and characterization of 13X zeolite from low-gradenatural kaolin

0921-8831/$ - see front matter � 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rightshttp://dx.doi.org/10.1016/j.apt.2013.08.002

⇑ Corresponding author. Tel./fax: +86 027 67885098.E-mail address: chjyan2005@126.com (C. Yan).

Please cite this article in press as: Y. Ma et al., Synthesis and characterization of 13X zeolite from low-grade natural kaolin, Advanced Powder Tech(2013), http://dx.doi.org/10.1016/j.apt.2013.08.002

Yunan Ma, Chunjie Yan ⇑, Aref Alshameri, Xiumei Qiu, Chunyu Zhou, Dan liEngineering Research Center of Nano-Geomaterials, Ministry of Education, China University of Geosciences, Lu Mo Road 388, Wuhan 430074, People’s Republic of China

a r t i c l e i n f o

Article history:Received 18 April 2013Received in revised form 13 July 2013Accepted 5 August 2013Available online xxxx

Keywords:Low-grade natural kaolinIllite13X zeoliteSynthesis

a b s t r a c t

In this study, 13X zeolite was successfully synthesized from low-grade natural kaolin via alkali fusionfollowed by hydrothermal treatment, without extra Si source or dealumination. Fusion with NaOH,followed by hydrothermal reaction, kaolinite, illite and trace of quartz in kaolin sample were convertedinto zeolite. The effects of various factors during the synthesis process such as NaOH addition amount,crystallization time and temperature on the crystalline products were studied. The optimum synthesisconditions to get purity 13X zeolite were found to be alkali fusion of kaolin with the weight ration ofNaOH/kaolin = 2.0 at 200 �C for 4 h, and crystallized at 90 �C for 8 h after homogenization by agitatedat 50 �C for 2 h. The product was characterized by X-ray diffraction (XRD), Scanning Electron Microscopy(SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and N2 adsorption–desorption. The BET surfacearea of the product was found to be 326 m2 g�1. It can be concluded that the study provides the basic dataand the process for extensive and efficient utilization of low-grade natural kaolin.� 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder

Technology Japan. All rights reserved.

1. Introduction

Zeolites are the most fascinating classes of nanoporous inor-ganic material, with wide ranging important applications in catal-ysis, separation and ion exchange [1–5]. Generally, zeolites aresynthesized from sodium aluminosilicate gel formed from varioussilica and alumina sources by hydrothermal treatment. However,the preparation of synthetic zeolites from chemical source of silicaand alumina is expensive. In order to reduce costs, numerous re-searches are seeking cheap raw materials for zeolite synthesis.Up to now, different geological materials and industrial wasteshave been used as a starting material for zeolite synthesis: wasteporcelain [6], coal fly ash [7], kaolinite [8], oil shale ash [9], bagassefly ash [10], paper sludge [11], high silicon fly ash [12], bentonite[13], waste sandstone cake [14,15], halloysite [16] and lithium slag[17].

Kaolinite [Al2Si2O5(OH)4] is a two-layered aluminosilicate claymineral, consisting of one alumina octahedron sheet and one silicatetrahedron sheet in a 1:1 stoichiometric ratio. It has been fre-quently used as the starting material for synthesis of zeolite A sinceits SiO2/Al2O3 molar ratio (around 2.0) is in close agreement withthat of zeolite A. But the synthesis of zeolite X requires an increaseof the Si/Al ratio to values above 2.5. That means further processingof the kaolinite either by eliminating Al [8,18,19] or adding Si

[20,21] in a suitable form. On the other hand, to lower thesynthesis costs, natural kaolin has begun to be used in synthesissystem to replace kaolinite [22]. However, it is really difficult toremove impurities (i.e. illite) from the raw materials. So, it is stillhighly required to explore new strategy for the synthesis ofzeolite X.

Illite (K1–2Al[Si7–6.5Al1–1.5O20](OH)4) is a phyllosilicate or lay-ered alumino-silicate with high Si content. Structurally, illite isquite similar to muscovite. Recent studies have provided evidencethat illite will undergo a phase transformations under alkali fusionconditions [23–25]. Thus, when used alone as the starting material,illite could transform into zeolite X [26]. Expanding from theseempirical findings, we further deduce that it will be possible to di-rectly synthesize zeolite X from natural kaolin (mainly consists ofkaolinite and illite) via alkali fusion followed by hydrothermaltreatment since that illite might be acted as Si source. Neverthe-less, to the best of our knowledge, no previous effort has beentaken to use natural kaolin as starting material to directly synthe-size 13X zeolite, without the process of Si addition ordealumination.

In this work, we report the synthesis of 13X zeolite from low-grade natural kaolin via alkali fusion followed by hydrothermaltreatment. As expected, the kaolinite, illite and trace of quartz inthis kaolin could be activated completely by alkali fusion, and thenhydrothermally transformed into 13X zeolite. The effects of NaOHaddition amount, crystallization time and temperature on the crys-talline products were studied systematically. Furthermore, the

reserved.

nology

2 Y. Ma et al. / Advanced Powder Technology xxx (2013) xxx–xxx

properties of the synthesized products, such as crystal morphology,framework structure and pore structure were characterized byXRD, SEM, BET and FT-IR.

Table 1Chemical characterization of low-grade natural kaolin(wt%).

Component Content (%)

SiO2 56.30Al2O3 29.52TFe2O3 1.32MgO 0.35CaO 0.056Na2O 0.056K2O 2.99TiO2 0.28P2O5 0.32MnO 0.012H2O– 0.28LOI 9.18

2. Experimental

2.1. Physical properties of raw clay

The kaolin was purchased from Beihai Hepu Jinhai Kaolin Com-pany, China. The sample was prepared as a starting material forthe present experiments after crushing and air-drying. The particlesize distribution as follows: about 10% of particles were less than1.14 lm, 50% of particles were less than 6.22 lm, and about 40%of particles were less than 23.10 lm. The average diameter of par-ticle was 8.3 lm. Sodium hydroxide (NaOH) (analytical reagentgrade) was supplied from Sinopharm Chemical Reagent Co., Ltd.,China.

2.2. Synthesis process

13X zeolite sample was prepared using low-grade natural kao-lin as silica–alumina source via alkali fusion followed by hydro-thermal treatment. The optimal conditions were shown in Fig. 1:sodium hydroxide and kaolin with the weight ratio of 2:1 weremilled and fused in an MgO ceramic crucible at 200 �C for 4 h.The fused mixture was cooled at room temperature, ground furtherand added to water (10 g fused mixture/75 ml water). The slurryobtained was vigorous agitated for 2 h at 50 �C for homogenization(800 r/min), and then was crystallized at 90 �C for 8 h (300 r/min).Finally, the solid was separated by filtration and washed thor-oughly several times with deionized water until the pH reachedaround 8, then was dried at 105 �C and crushed.

2.3. Characterization

The samples were characterized by a variety of conventionaltechniques. Chemical composition of kaolin was determined byneutralization titration (GB/T 14506-2010 Methods for chemicalanalysis of silicate rocks, China), while mineralogical analysis ofthe raw sample was carried out by X-ray diffraction (Germany,Bruker D-8 FOCUS diffractometer). Data collection was carriedout in the 2h range 5–60� with a step size of 0.01�. Phaseidentification was performed by searching the ICDD powder dif-fraction file database, with the help of JCPDS (Joint Committee onPowder Diffraction Standards) files for inorganic compounds.

Fig. 1. The flow chart of synthesis zeolite.

Please cite this article in press as: Y. Ma et al., Synthesis and characterization o(2013), http://dx.doi.org/10.1016/j.apt.2013.08.002

Semi-quantitative weight percentages of samples were calculatedby using mineral intensity factors. Particle morphology was ob-served by a Japanese SU8010 scanning electron microscopeequipped with a cold-field emission gun, operating at 15 kV and10 lA.

Particles size distribution of samples was determined with aChina JL-1155 laser light-scattering particle size analyzer withwater used as the medium. The FT-IR spectrum of 13X zeolitewas obtained by means of a China 370-DTGS-AVATAR FT-IR spec-trometer in the range 400–4000 cm�1 using the KBr pellet tech-nique. An America Automatic ASAP2020 volumetric absorptionanalyzer was employed to measure nitrogen adsorption anddesorption isotherms at 77 K and the surface area was measuredby BET method.

3. Results and discussion

3.1. Characterization of kaolin clay

From Table 1, it is observed that the main constituents of thelow-grade natural kaolin were silica (56.30%) and alumina(29.52%), whereas the loss of ignition (LOI) 9.18%. The X-ray pat-tern of the low-grade natural kaolin is shown in Fig. 2. It can beseen that the major crystalline phases are kaolinite (JCPDS cardNo. 06-0221), as identified by the sharp peak (7.14 ÅA

0

) and illite(JCPDS card No. 26-0911), as identified by the sharp peak (9.95ÅA0

). The low intensity peak at 3.34 ÅA0

belongs to quartz (JCPDS cardNo. 5-0490). The X-ray diffraction analysis indicated that the low-

Fig. 2. XRD pattern of the low grade natural kaolin.

f 13X zeolite from low-grade natural kaolin, Advanced Powder Technology

Fig. 3. SEM images of (a) natural clay, (b) fused material, and (c) synthesized zeoliteobtained by natural kaolin.

Fig. 4. XRD patterns of kaolin clays fused with sodium hydroxide in differentweight ratio (a) 1.0, (b) 1.5, and (c) 2.0.

Fig. 5. XRD patterns of the reaction as-synthesized products obtained at differentcrystallization times (a) 0 h, (b) 1 h, (c) 4 h, (d) 6 h, (e) 8 h, (f) 12 h, and (g) 24 h.

Fig. 6. XRD patterns of the synthesized products obtained at different temperature(a) 50 �C, (b) 70 �C, (c) 90 �C, and (d) 100 �C.

Y. Ma et al. / Advanced Powder Technology xxx (2013) xxx–xxx 3

grade natural kaolin was mainly composed of kaolinite (55%), illite(44%), and quartz (1%). The SEM microphotograph (Fig. 3a) revealsthat natural kaolin was the mixture of grain kaolinite and platy il-lite, and the particle size range from about 1 to 10 lm, which isagreement with the particles size distribution of the natural kaolin.

3.2. Alkaline fusion

The effect of NaOH addition amount in the process of alkalinefusion was study with the weight ratio of NaOH/kaolin at 1.0, 1.5and 2.0. In order to distinguish whether the clay activated com-pletely without the effect of sodium salt, the samples was washed

Please cite this article in press as: Y. Ma et al., Synthesis and characterization o(2013), http://dx.doi.org/10.1016/j.apt.2013.08.002

by water and dried. Fig. 4 represents the XRD patterns of kaolinclays fused with sodium hydroxide in different weight ratio. Com-

f 13X zeolite from low-grade natural kaolin, Advanced Powder Technology

4 Y. Ma et al. / Advanced Powder Technology xxx (2013) xxx–xxx

pared with unheated sample, the intensity of kaolin (kaolinite, il-lite, quartz) reflection peaks decreased with the increase of NaOHaddition. When the weight ratio of NaOH/kaolin reaches 1.5, thetypical reflection peaks of kaolinite and illite disappear, indicatingthe structures of kaolinite and illite are destroyed. When theweight ratio rises to 2.0, the reflection peaks of quartz also disap-pear, indicating that quartz is dissolved into sodium silicate dueto thermal- and alkali-activation. Also, it can be seen clearly thatthe fused material contains very tiny grains resulting in the layerstructure of clay being damaged after alkaline fusion (Fig. 3b).

3.3. Effect of crystalline time

To investigate the influence of crystallization time on structureof the products, zeolites were synthesized at 0, 1, 4, 6, 8, 12 and24 h. All samples were crystallized at 90 �C after homogenized2 h at 50 �C. Fig. 5 shows the XRD pattern of samples crystallizedfrom 0 to 24 h. Not any crystal diffraction peaks can be found afterhomogenized 2 h, indicating the sample is still amorphous. A fastcrystallization rate occurred after 2 h treatment. 13X zeolite (JCPDScard No. 12-0228) and zeolite A (JCPDS card No. 11-0590) crystal-lized under these experimental conditions. The maximum crystal-linity of the 13X zeolite occurred at 6 h. However, furtherprolonging the crystallization time up to 8 h and 24 h, the intensi-ties of 13X zeolite reflections decreased and the peaks of zeolitehydroxysodalite (JCPDS card No. 11-0401) appeared, indicatingthat 13X zeolite crystallization was almost complete within 6 hand may be transformed into more stable zeolite hydroxysodalite.On the other hand, the peaks of zeolite A disappeared and a pure-crystallized 13X zeolite was obtained after crystallization for 8 h.The XRD pattern obtained at this crystallization time is a goodagreement with reported values of commercial 13X zeolite [16].

3.4. Effect of crystallization temperature

The effect of varying crystallization temperatures was investi-gated at 50, 70, 90 and 100 �C after 8 h crystallization. Fig. 6 pre-sents the XRD patterns of the samples obtained at differenttemperatures and shows the presence of a broad band locatedaround 25� in 2h at 50 �C, due to the formation of amorphousphases without any peak. XRD patterns clearly revealed that thecrystallinity of the 13X zeolite sample increased while crystalliza-tion temperature was raised from 70 to 90 �C and then decreased

Fig. 7. FT-IR spectrum of 13X zeolite obtained at the optimum synthesis conditionsfrom low-grade natural kaolin.

Please cite this article in press as: Y. Ma et al., Synthesis and characterization o(2013), http://dx.doi.org/10.1016/j.apt.2013.08.002

when the crystallization temperature up to 100 �C. Therefore90 �C was chosen to form the pure phase of 13X zeolite.

3.5. Characterization of 13X zeolite

To study the physical properties of 13X zeolite obtained at theoptimum synthesis conditions, further characterizations were car-ry out by SEM, BET and FT-IR. Fig. 3c shows the morphology of thecrystals. Octahedral crystalline shape 13X zeolite particles can beidentified in the SEM image. The particle size of the product couldbe estimated to be ca. 1–3 lm. Specific surface area of synthesis13X was measured to be 326 m2 g�1. This result is a good agree-ment with that reported by Mezni [26] and Novembre [27], whosefound the specific surface area values of synthesis 13X zeilite was293 m2 g�1 and 339 m2 g�1, respectively. IR spectra of the 13X zeo-lite are shown in Fig. 7. The typical bands of as-synthesized prod-ucts, attributed to T–O bend (458 cm�1), double six-member rings(D6R) (561 cm�1), symmetric stretch (668 cm�1) and asymmetricstretch (978 cm�1) are identified (where T = Si or Al). The band at1640 cm�1 is attributed to H2O deformation mode due to incom-plete dehydration of the samples. Moreover, the observed singlestrong band at 3526 cm�1 corresponded to OH-stretching of watermolecules present in the zeolite channel. The data obtained fromFT-IR spectra are consent with reported values of commercial13X zeolite [17].

4. Conclusion

The results obtained in this study allow us to draw the follow-ing conclusions:

� The low-grade natural kaolin, which contained kaolinite, illiteand traces of quartz, was activated completely after fusion withNaOH (sodium hydroxide and kaolin mixed of in a 2.0 weightratio, 200 �C/4 h for the mixture calcinations).� The 13X zeolite was synthesized from low-grade natural kaolin

via alkali fusion followed by hydrothermal treatment (50 �C/2 hfor homogenization, 90 �C /8 h for crystallization). The XRD pat-terns shows comparable values to reported ones for commercialzeolites and SEM images revealed that the 13X zeolite was pureand exhibited octahedral crystalline shape.� Furthermore, FT-IR spectrum confirmed obtaining synthesized

13X zeolite and the specific surface area was 326 m2 g�1.� Based on these results, the 13X zeolite synthesized from low-

grade natural kaolin is in good agreement with that reportedvalues of 13X zeolite.

Acknowledgement

The financial supports form Chinese land resource ministry pro-ject are greatly acknowledge.

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