Amin Ur Rahman, Farid Ullah Khan, Waheed Ur Rehman, Sanum Saleem

825

SYNTHESIS AND CHARACTERIZATION OF ZEOLITE 4A USING SWAT KAOLIN

Amin Ur Rahman, Farid Ullah Khan, Waheed Ur Rehman, Sanum Saleem

ABSTRACT

Zeolites are microporous crystalline materials of a wide range of application. They are commonly used for wa-ter purification and for toxic heavy metals removal. Zeolite 4A was synthesized from local kaolin containing 45.39 % SiO2 and 32.57 % Al2O3. Kaolin was initially converted to metakolin at 800○C. Sodium was then incorporated in its structure by a hydrothermal process. The X-ray diffraction study carried out verified the successful formation of zeolite 4A. The zeolite metal exchange rate for calcium, cadmium, chromium, lead and nickel was determined.

Keywords: zeolite 4A, clay, kaolin, metakaolin, XRD, ion exchange.

Received 19 May 2017Accepted 15 Decembet 2017

Journal of Chemical Technology and Metallurgy, 53, 5, 2018, 825-829

Materials Science Center, PCSIR Labs.Complex Peshawar, PakistanE-mail: aminpcsir@gmail.com

INTRODUCTION

Zeolites are crystalline microporous hydrated alu-minosilicates of alkali and alkaline earth metals. They consist of tetrahedral units producing three dimensional frameworks of uniform pores and regular cavities of molecular dimensions [1]. The tetrahedral AlO4

-5 and SiO4

-4 units are linked with each other through shared oxygen. Zeolites are high internal surface area crystal-line materials and exhibit a very high surface activity inside its pores of molecular dimensions. They consist mainly of silicon and aluminum and are described by chemical formula Mx/n[(AlO2)x(SiO2)y]wH2O, where M is alkali or alkaline charge balancing non framework cation of a valence n, y/x ratio has a value ranging from 1 to 5, while w stands for the amount of molecular water in empty spaces. Silica (SiO2) is an uncharged solid, whose framework becomes negatively charged [2] when combined with Al. The framework requires an extra cation within its structure to stay neutral. These cations can be exchanged and as a result the zeolite is an ion-exchangeable material. The cations Na+, NH+, K+, H+, Zn2+, Mg2+ and Ca2+ are small enough to move through

the zeolites pores.There are three classes of zeolites - low silica or Al

rich zeolites, intermediate silica zeolites and high silica zeolites. Low silica zeolites have Si/Al ratio of 1 to 2. Zeolites A and X whose ion-exchange capability is ex-cellent belong to this group. Intermediate silica zeolites have Si/Al ratio varying from 1.5 to 3.8, while that of high silica zeolites ranges from 10 to 100.

The chemical formula of zeolite 4A is Na12[(AlO2) (SiO2)12].27H2O. Its structure contains two types of polyhedra. The octahedron (α-cages) connects 24-hedron (β- cages) creating thus a three dimensional structure of pores of 4.2 Å [3].

Zeolites have three main applications - as catalysts and adsorbents, as sensors and separation membranes, as participants in ion exchange and solar energy conversion processes. They have also health related application. Zeolite 4A is used for water softening and hazardous gases cleaning.

The aim of the investigation reported was to prepare zeolite 4A from indigenous available clays. Swat kaolin was selected as a raw material. The process variables were optimized to obtain the desired product.

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EXPERIMENTALSynthesis

Kaolin was analyzed by XRF (S4 Pioneer, Bruker, Germany). For the laboratory scale synthesis of zeolite 4A, pre-washed kaolin was calcined at 800○C in a muf-fle furnace for 1 h. The metakaolin obtained was mixed with sodium hydroxide in a ratio of 1: 1.4. Water was subsequently added (10 g clay/80 ml water). The resultant mixture was stirred for 3 h. The suspension thus obtained was stirred for 5 h at 90○C. The product formed was filtered and washed till pH dropped to 10 and then dried at 60○C [8, 9]. The flow diagram is shown in Fig. 3. Commercial sodium hydroxide was used as a sodium source for the zeolite synthesis.

CharacterizationX-Rays diffractometer (JDY 3532, JEOL, Japan) was

used to characterize metakaolin and the zeolite prepared.

Application testsThe zeolite powder was mixed with kaolin in a ratio

of 2:1 ratio aiming to prepare zeolite granules. A granu-lator was used. This step was followed by calcination for 1 h in a muffle furnace at 700○C. The metal uptake efficiency of the powder zeolite in respect to calcium, lead, chromium, cadmium and nickel were studied. 25 ml of the metal solution were taken from each stock solution (100 ppm) prepared in advance on the ground of 1000 ppm standard solutions (Merck, Germany). 1 g of the zeolite was added and the mixture was stirred for 10 min. The solution obtained was analyzed for metal concentration using an atomic absorption spectropho-tometer (Z-8000, Hitachi, Japan) and a flame photom-eter (Jenway, PFP7, UK). The zeolite regeneration was carried out by adding 25 ml of 0.1 M NaOH solution to 1 g of the zeolite. The mixture was stirred for 10 min. The regenerated zeolite was isolated from the solution. Then it was washed and dried. The metal exchange rate of the regenerated zeolite was tested as described above.

RESULTS AND DISCUSSIONThe clay containing kalonite as a major constituent

is known as china clay. It contains silica and alumina and is a convenient starting material for the synthesis of zeolites. Extensive work has been carried out to pre-pare zeolite 4A from kaolin. These studies reveal that

kaolin of Si/Al ratio of 1 is best suited for the synthesis of zeolite 4A [4]. Pakistan has rich deposits of kaolin in Nagarparker (Sindh) and Swat (Khyber Pakhtunkhwa). These clays are mainly used in ceramic industry and as fillers in plastics, rubbers and paper. Swat kaolin deposits are among the largest known deposits of Pakistan with an estimated reserve of 2.5 million tons [5]. Extensive studies have been carried out for its evaluation. The chemical composition of Swat kaolin is given in Table 1. It is evident that the clay is mainly composed of silica and alumina. It contains also iron oxide (1.91 %), which affects greatly the brightness of the product.

Synthesis of zeolite from kaolin is a two step pro-cess, i.e. metakaoliniziation and zeolitilization. The volatile matter of the clay evolves and dehydroxylation takes place in the course of calcination at 800○C:

2Al2Si2O5(OH)4 → 2Al2Si2O7 + 4H2O

The kalonite structure collapses during the heating and the clay becomes amorphous [6].

This amorphous form of the clay is known as me-takaolin. The XRD patterns of metakaolin are given in Fig. 1. They show that the characteristic peaks of kaolin-

Constituents mass %

SiO2 45.39

Al2O3 32.57

MgO 0.93

CaO 3.08

Na2O 1.18

K2O 0.30

Fe2O3 1.91

TiO2 0.13

Cr2O3 0.01

MnO 0.03

SrO 0.09

P2O5 0.09

SO3 0.03

LOI 14.57

Table 1. XRF analysis of Swat Kaolin.

Amin Ur Rahman, Farid Ullah Khan, Waheed Ur Rehman, Sanum Saleem

827

ite disappear during the calcination step. The small peaks observed in metakaolin spectrum refer to iron oxide. They match those of ICCD Pattern No. 39-1346 (Maghemite).

Metakaolin is more reactive than kaolin due to its disordered structure [7]. It accepts readily sodium ions during the zeolitization step. They reside in its structure:

Al2Si2O7 + 2NaOH → Na2O-Al2O3-2Si O2-4.5H2O

The appearance of peaks in the zeolite powder XRD diffractogram (Fig. 2) and their matching to those of zeo-lite 4A (ICCD Pattern No. 39-0222) verifies the success-ful zeolitilization of metakolin at 90C○. The additional peaks in the pattern indicate the presence of crystalline impurities. Table 2 illustrates the metal uptake rate of the zeolite powder. The metal ions concentration is drasti-cally decreased in this case. The zeolite metal uptake

Fig. 1. XRD patterns of metakaolin.

Fig. 2. XRD patterns of zeolite 4A.

H2O

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rate in respect to Ca2+ , Pb2+, Cr3+, Cd2+ and Ni2+ is more or less same. Table 3 shows the calcium exchange rate of virgin and regenerated zeolite. Ca2+ exchange rate of the regenerated zeolite is less than that of the virgin one. Besides, it does not change with successive regeneration.

CONCLUSIONSSwat kaolin is suitable for the preparation of zeolite

4A. The iron content in the clay is high and so the product formed is yellowish in color. The calcium uptake rate of the prepared zeolite is sufficient to be used for water softening. It is also evident from its heavy metal uptake rate that it could be used for removal of heavy metals from waste water.

REFERENCES1. A.A. Ismail, R.M. Mohammed, O.A. Fouad, I.A.

Ibrahim, Synthesis of nanosized ZSM-5 using different alumina sources, Crystal Research and Technonology, 41, 145, 2006, 145-149.

2. K. Hussaro, T. Wessapan, N. Cheamsawat, GMSARN International Conference on Sustainable Development: Issues and Prospectus for the GMS, 12-14 November, 2008, 1.

3. I. D. Wilson, E.R. Adlard, M. Cooke, C.F. Poole, Encyclopedia of Separation Science, 6, Academic, University of Michigan, 2000, 256.

4. S. Chandrasekhar, P. Raghavan, G. Sebastian, A. D. Damodaran, Influence of metakaolinization tem-

Metal Ion

Metal exchange rate (ppm/g) in 10 minutes

Ca2+ 96.00

Pb2+ 98.22

Cr3+ 99.53

Cd2+ 99.98

Ni2+ 97.43

Table 2. Metal exchange rate of zeolite 4A powder.

Fig. 3. Flow diagram for the preparation of zeolite 4A from kaolin.

Material

Metal

exchange

rate for Ca

(ppm/g) in

10 minutes

Virgin zeolite 96

Regenerated zeolite (1st time) 92

Regenerated zeolite (2nd time ) 92

Regenerated zeolite (3rd time ) 92

Table 3. Metal exchange rate of regenerated zeolite 4A granules for calcium.

Amin Ur Rahman, Farid Ullah Khan, Waheed Ur Rehman, Sanum Saleem

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perature on the formation of zeolite 4A from kaolin, Applied Clay Science, 12, 221, 1997, 253-261.

5. M.A. Siddiqui, Z. Ahmad, A.A. Saleemi, Evaluation of Swat kaolin deposits of Pakistan for industrial uses, Applied Clay Science, 29, 55, 2005, 55-72.

6. I. Yamane, T. Nakazawa, Development of zeolite for non-phosphated detergents in Japan, Pure & Applied Chemistry, 58, 1397, 1986, 1397-1407.

7. J.R. Ugal, K.H. Hassan, H. Karim, H. Inam, Preparation of 4A type zeolite from Iraqi Kaolin: Characterization

and properties measurements, Journal of the Arab Universities for Basic and Applied Sciences, 9, 1, 2010, 2-5.

8. A.R. Chaudhuri, G.K. Dey, T.K. Pal, Synthesis and characterization of detergent-grade zeolite from Indian clay, Chemical Engineering and Technology, 25, 91, 2002, 91-95.

9. E. Costa, A. de. Lucas, M.A. Uguina, J.C. Ruizl, Synthesis of4A zeolite from calcined kaolins for use in detergents, Industrial and Engineering Chemistry Research, 27, 1291, 988, 1291-1296.