UNIVERSITI PUTRA MALAYSIA

SYNTHESIS AND CHARACTERISATION OF CERIUM-EXCHANGED ZEOLITES AND ITS APPLICATION IN THE REMOVAL OF ARSENIC

FROM WASTEWATER SAMPLES

FARHA BINTI AB RAHIM

FS 2008 53

SYNTHESIS AND CHARACTERISATION OF CERIUM-EXCHANGED ZEOLITES AND ITS APPLICATION IN THE REMOVAL OF ARSENIC FROM

WASTEWATER SAMPLES

By

FARHA BINTI AB RAHIM

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in

Fulfilment of the Requirements for the Degree of Master of Science

November 2008

Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfillment of the requirements for the degree of Master of Science.

SYNTHESIS AND CHARACTERISATION OF CERIUM-EXCHANGED ZEOLITES AND ITS APPLICATION IN THE REMOVAL OF ARSENIC FROM

WASTEWATER SAMPLES

By

FARHA BINTI AB RAHIM

November 2008

Chairman : Professor Md Jelas Haron, PhD

Faculty : Science

Zolite P was synthesized from silica of rice husk ash (SRHA) via alkaline hydrothermal

technique with sodium aluminate and sodium hydroxide. The zeolite produced was

characterized by X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy

(FTIR) and, the morphology was analysed by Scanning Electron Microscopy (SEM),

and the elemental analysis was carried out by Energy Dispersive X-ray (EDX) and

inductively coupled plasma-atomic emission spectrometry (ICP-AES). The synthesized

zeolite P was exchanged with cerium (III) and cerium (IV) ions. The ability of Ce(III)

exchanged zeolite P (Ce3ZP) and Ce(IV) exchanged zeolite P (Ce4ZP) to sorb and

remove arsenic (V) from aqueous solution was investigated. Parameters investigated for

arsenic removal include pH, initial As(V) concentration, temperature and effect of

foreign ions on the sorption. The sorbent was tested for removal of arsenic from

industrial wastewater samples of wood treatment industry which utilized the largest

amount of arsenic compound.

2

The XRD pattern shows that the zeolite produced was zeolite P which has GIS frame

work topology of type NaP1. The XRD intensity of zeolite P increases for increased

ratio of SRHA:Al during preparation, indicating the progress in crystallization of the

product. SEM-EDX analysis shows that the zeolite P produced contains Si/Al ratio of

2:1 with the formula of Na6Al6Si12O36.8H2O. The formation of zeolite was also confirm

by FTIR absorption at 1040 cm-1 and 432 cm-1, the regions commonly observed in

aluminosilicate due to Si-O and Al-O stretching and bending modes. Exchange capacity

of Ce(III) and Ce(IV) in the zeolite increased with increased in temperature with highest

loading obtained 75.4 and 170.0 mg/g, respectively. The existence of cerium in the

zeolite was confirmed by EDX spectrum. The resulting cerium exchanged zeolites were

used for As(V) sorption experiments.

Sorption of As(V) by both modified zeolite occurred over a wide pH range, which was

pH 1 – 11 for Ce4ZP and pH 3-10 for Ce3ZP with maximum sorption at about pH 4.

The sorption capacities increased with increasing initial As(V) concentrations and

followed the Langmuir model with maximum sorption capacities of 22.0 mg g-1 at 25°C

and increased to 34.0 mg g-1 at 90°C. This is higher than the values for Ce3ZP which

was 8.72 mg g-1 at 25°C and increased to 23.42 mg g-1 at 90°C, indicating that the As(V)

sorption process is endothermic. The endothermic nature of sorption process was

confirmed by the positive value of sorption enthalpy change, ΔH°. The free energy

change, ΔG° for the sorption was negative showing that the sorption process is

spontaneous. The increase in ΔS0 upon As(V) sorption could be partly due to the release

3

of coordinated water molecules from Ce(IV) ion in the zeolite. Kinetic study showed

that the As(V) sorption by Ce4ZP follows a second order kinetic model.

The unmodified Zeolite P did not significantly remove As(V). This result infers that the

active sorption site for As in the Zeolite was the cerium metal ion. In the acidic to

natural pH range, sorption of arsenate ion was also followed by increase in pH of the

solution from its initial value. The mechanism of sorption process could be a ligand

exchange reaction with hydroxide ion on the surface of cerium ion and the formation of

surface complexes between oxygen on the arsenate with the cerium metal ion on the

zeolite.

The selectivity study showed that the sorption of As(V) was affected by the presence of

phosphate but not affected with bromide, chloride, nitrate, sulphate, carbonate and

chromium. The Ce exchanged zeolite was found effective for the removal of arsenic in

wastewater samples from wood treatment industries.

4

Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains.

SINTESIS DAN PENCIRIAN CERIUM TERTUKAR ZEOLITE DAN APLIKASI

DALAM PENYINGKIRAN ARSENIK DARI SAMPEL AIR SISA INDUSTRI

Oleh

FARHA BINTI AB RAHIM

November 2008

Pengerusi : Prof Md Jelas Haron, PhD

Fakulti : Sains

Zeolite P telah disintesis dari silika abu sekam padi SRHA melalui teknik hidroterma

dengan sodium aluminat dan sodium hidroksida. Zeolite yang terhasil telah dicirikan

dengan spektroskopi belauan sinar-x (XRD) dan spektroskopi infra merah transformasi

Fourier (FTIR), analisis morfologi menggunakan mikroskopi elektron pengimbasan

(SEM) dan, analisis unsur menggunakan kaedah penyerakan tenaga sinar-x (EDX) dan

spektrometri pemancaran atom plasma berganding aruh (ICP-AES). Zeolite P yang

disintesis diubahsuai melalui penukaran ion dengan cerium (III) dan cerium (IV).

Kebolehan zeolite P tertukar ion Ce(III) (Ce3ZP) dan zeolite P tertukar ion Ce(IV)

(Ce4ZP) untuk mengerap dan menyingkirkan arsenik (V) dari larutan akueus telah

dikaji. Parameter yang mempengaruhi erapan arsenik yang dikaji termasuklah pH,

kepekatan awal As(V), suhu dan kesan ion asing. Pengerap juga diuji keberkesanannya

bagi menyingkirkan arsenik dari sampel air buangan industri perawatan kayu yang mana

merupakan industri paling banyak menggunakan sebatian arsenik.

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Pola belauan sinar-x menunjukkan zeolite membentuk zeolite terhasil adalah zeolite P

yang mempunyai rangka topologi GIS jenis NaP1. Keamatan puncak sinar-x mengingkat

dengan peningkatan nisbah mol SRHA:Al semasa penyedian menunjukan peningkatan

pembentukan kristal dalam bahan yang terhasil. Analisis SEM-EDX menunjukkan

zeolite P yang terhasil mengandungi nisbah Si/Al 2:1 dengan formula

Na6Al6Si12O36.8H2O. Pembentukkan zeolite juga disahkan oleh serapan FTIR pada 1040

cm-1 dan 432 cm-1, merupakan kawasan serapan yang biasa diberikan oleh

aluminosilikat yang merupakan mod regangan dan mod bengkokan Si-O dan Al-O.

Muatan pertukaran ion Ce(III) dan Ce(IV) kedalam zeolite mengikat dengan

peningkatan suhu dan muatan pertukaran tertinggi diperolehi masing-masing adalah 75.4

dan 170.0 mg/g pada suhu 90˚C. Kehadiran cerium didalam zeolite disahkan oleh

spektrum EDX. Zeolite tertukar cerium yang terhasil digunakan dalam kajian erapan

As(V).

Erapan As(V) oleh kedua-dua zeolite terubahsuai berlaku pada julat pH yang besar, iaitu

pada pH 1-11 bagi Ce4ZP dan pH 3-10 bagi Ce3ZP dengna muatan erapan maksima

berlaku pada pH 4. Muatan erapan meningkat dengan kepekatan awal As(V) dan

mematuhi model isoterma Langmuir dengan muatan erapan maksima 22.0 mg g-1 pada

25°C dan meningkat kepada 34.0 mg g-1 pada 90°C untuk Ce4ZP. Nilai muatan ini

adalah lebih tinggi berbanding Ce3ZP iaitu 8.7 mg g-1 pada 25°C dan meningkat kepada

23.4 mg g-1 pada 90°C yang menunjukkan proses erapan adalah spontan. Peningkatan

perubahan entropi ΔS° selepas erapan As(V) pula mungkin disebabkan sebahagiannya

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oleh pelepasan molekul air terkoordinat daripada ion Ce(IV) pada zeolite. Kajian kinetic

pula menunjukkan erapan As(V) oleh Ce4ZP mematuhi model kinetik order kedua.

Zeolite P tidak terubahsuai didapati tidak dapat menyingkirkan As(V) secara berkesan.

Keputusan ini menunjukkan cerium merupakan tapak aktif untuk erapan As(V) pada

zeolite terubahsuai. Pada keadaan pH berasid hingga natural, erapan As(V) juga diikut

oleh peningkatan nilai pH berbanding pH larutan asal. Mekanisma erapan mungkin

merupakan proses pertukaran ligan dengan ion hidroksida pada ion cerium dan

pembentukan kompleks permukaan antara atom oksigen pada ion arsenat dengan ion

hidroksida pada logam cerium dalam zeolite.

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ACKNOWDLEGMENTS

I would like to take this opportunity to express my sincere gratitude to my supervisors,

Professor Dr Md Jelas bin Haron, Professor Dr Mohd Zobir bin Hussein and Associate

Professor Dr Halim bin Abdullah, for their assistance, suggestion, unfailing help and

constructive comments throughout the course of this project.

Sincere thanks are also extended to Madam Choo, Mr Kamal, Miss Yusliza, Mr

Kamarul, Mr Ridzuan Shah, Miss Sharifah, Miss Juliana, Miss Kharunisa, Miss Faezah,

Miss Diana, Mr Isal and Miss Zety Akhtar for their kindness in helping my work.

I would also like to express my deepest affection to my parents for all their love,

support, advice, understanding and encouragement during my study at UPM.

A special note of appreciation also extended to Pasca Siswazah Scheme Universiti Putra

Malaysia for the assistantship.

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I certify that a Thesis Examination Committee has met on 3 November 2008 to conduct the final examination of Farha binti Ab Rahim on her thesis entitled “Synthesis and Characterisation of Cerium-Exchanged Zeolite and its Application in the Removal of Arsenic from Wastewater Samples” in accordance with the Universities and University Collages Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The committee recommends that the student be awarded the (Master of Science). Members of the Thesis Examination Committee were as follows: Name of Chairperson, PhD Prof. Dr. Zulkarnain Zainal Faculty of Science Universiti Putra Malaysia (Chairman) Name of Examinar 1, PhD Prof. Dr. Anuar Kassim Faculty of Science Universiti Putra Malaysia (Internal Examiner) Name of Examinar 2, PhD Dr. Nor Azah Yusof Faculty of Science Universiti Putra Malaysia (Internal Examinar) Name of External Examiner, PhD Prof. Dr. Mohd. Marsin Sanagi Faculty of Science Universiti Teknologi Malaysia (External Examinar)

_______________________________ BUJANG KIM HUAT, PhD Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date: 19 February 2009

9

This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfillment of the requirement for the degree of Master of Science. The members of the Supervisory Committee were as follows: Name of Chairperson, Phd Professor Md Jelas Haron Faculty Of Science Univerisiti Putra Malaysia (Chairman) Name of Member 1, PhD Professor Zobir Hussein Faculty of Science Universiti Putra Malaysia (Member) Name of Member 2, PhD Professor Madya Halim Abdullah Faculty of Science Universiti Putra Malaysia (Member) _________________________________ HASANAH MOHD. GHAZAILI, PhD Profesor and Dean School of Graduate Studies Universiti Putra Malaysia

Date: 9 April 2009

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DECLARATION I declare that the thesis is based on my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at Universiti Putra Malaysia or at any other institutions. ____________________ FARHA AB RAHIM

Date:4 May 2009

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TABLE OF CONTENTS

page

ABSTRACT ii

ABSTRAK v

ACKNOWLEDGEMENTS viii

APPROVAL SHEETS x

DECLARATION xi

TABLE OF CONTENTS xii

LIST OF TABLES xvi

LIST OF FIGURES xvii

LIST OF PLATES xx

LIST OF ABBREVIATIONS xxi

CHAPTER

1 INTRODUCTION 22

2 LITERATURE REVIEW 26

Arsenic 26

Zeolites 28

Synthesis of zeolite 29

Source of alumina for synthesis of zeolite 29

Source of silicon for synthesis of zeolite 30

Source of cations for synthesis of zeolite 30

The effect of concentration, temperature, pressure

and time on synthesis of zeolite 30

2.2.6 Zeolite crystallization 31

Zeolite P 32

Sorption of anion by modified zeolite 39

12

Removal of arsenic ion by cerium related

adsorbents 47

Scope of the present research 49

3 MATERIALS AND METHOD 51

Reagent 51

Cerium stock solution 51

Arsenate (V) stock solution 51

Zeolite P and Zeolite Y 51

Chloride solution 52

Phosphate solution 52

Sulphate solution 52

Nitrate solution 52

Carbonate solution 53

Bromide solution 53

Instrument 53

Inductively Couple Plasma Atomic

Emission Spectrometry (ICP-AES) 53

pH meter 53

Rotary shaker 54

X-ray Diffraction (XRD) 54

Fourier Transform Infrared

Spectroscopy (FT-IR) 54

Scanning electron microscopy and

energy dispersive x-ray analysis 54

Synthesis of zeolite P rice husk gismondine 55

Materials 55

Zeolite P (gismondine) 55

Preparation of cerium-exchanged zeolite

(Ce-Zeolites) 56

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3.5 Sorption of arsenic ion by Ce-Zeolite 56

3.5.1 Sorption kinetic of As(V) by Ce-Zeolite 57

3.5.2 Sorption isotherm of As(V) by Ce-Zeolite 57

3.5.3 Effect of foreignions of the As(V) sorption

capacity byCe-Zeolite 58

3.5.4 Desorption of As(V) 58

(a) Preparation of Ce-Zeolite containing

As(V) 58

(b) Desorption As(V) from arsenic-loaded

Ce-Zeolite 58

3.5.5 Removal of arsenic from wastewater

arsenic by Ce-Zeolite 59

4 RESULT AND DISCUSSION 60

Synthesis of zeolite P 60

Characterization of zeolite P 60

Effect of temperature on exchange capacity

of Ce-zeolite 64

Characterization of unmodified and

cerium-exchanged zeolites 65

XRD patterns of zeolites and cerium-echanged

zeolites 65

FTIR spectra of unmodified and modified

zeolites 68

SEM-EDX of zeolite exchanged with

cerium 70

Sorption of arsenate ion by zeolite and

cerium-exchanged zeolite 74

4.4.1 Effect of pH 74

4.4.2 Effect of initial As(V) concentration

and temperature on the sorption 76

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4.4.3 Thermodynamics of the sorption 85

4.4.4 Sorption kinetic 87

4.4.5 Intraparticle diffusion 93

4.5 Effect of foreign ions on As(V) removal 97

4.6 Desorption of sorbate from sorbent 98

4.7 Removal of arsenic ion from industrial wastewater

samples 100

5 CONCLUSIONS 102

BIBLIOGRAPHY 106

BIODATA OF STUDENT 115

LIST OF PUBLICATION 116

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LIST OF TABLES

Table page

4.1 The effect of different mol ratio of SRHA/Al of zeolite P by

EDX and ICP-AES technique or method 63

4.2 Freundlich, Langmuir and D-R isotherm constants for the

sorption of As(V) onto Ce3ZP and Ce4ZP at various temperature. 84

4.3 Sorption capacities of As(V) from recent literature by

inorganic sorbents. 95

4.4 Thermodynamic parameters for the sorption of As(V)

on Ce-zeolite 87

4.5 Kinetic parameters for the sorption of As(V) on Ce-zeolite. 93

4.6 Percentages removal of arsenic ion from sample of wastewater

from wood treatment industry 101

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LIST OF FIGURES

Figure page

4.1 The XRD patterns (a) SRHA and ZP synthesized by using

different ratios of SRHA/Alumina (b) 4/1, (c) 16/1 and

(d) 20/1; (♦) is zeolite NaP1 from JCPDS 39-0219 61

4.2 The FTIR patterns of (a) SRHA and (b) ZP synthesized by

using ratios of SRHA:Al, 20:1 62

4.3 Effect of temperature on cerium loading capacity onto zeolites 65

4.4 The XRD patterns of (a) unmodified ZP and Ce4ZP prepared

at (b) 25 oC, (c) 70 oC and (d) 90 oC 66

4.5 The XRD patterns of (a) unmodified ZP and Ce3ZP prepared

at (b) 25 oC , (c) 70 oC and (d) 90 oC 67

4.6 The XRD patterns of (a) unmodified ZY and Ce3ZY prepared

at (b) 25 oC , (c) 70 oC and (d) 90 oC 67

4.7 The FTIR patterns (a) unmodified ZP and Ce4ZP prepared at

(b) 25 oC , (c) 70 oC and (d) 90 oC 68

4.8 The FTIR patterns (a) unmodified ZP and Ce3ZP prepared at

(b) 25 oC , (c) 70 oC and (d) 90 oC 69

4.9 The FTIR patterns (a) unmodified ZY and Ce3ZY prepared at

(b) 25 oC , (c) 70 oC and (d) 90 oC 69

4.10 Spectra of zeolites obtained by EDX (a) ZP, (b) Ce4ZP and

(c) As-Ce4ZP 73

4.11 Spectra of zeolites obtained by EDX (a)ZP, (b) Ce3ZP and

(c) As-Ce3ZP 73

4.12 Spectra of zeolites obtained by EDX (a) ZY, (b) Ce3ZY and

(c) As-Ce3ZY 74

4.13 Effect of pH on the sorption of As(V) onto zeolites and

cerium-exchanged zeolites. As(V): 160 ppm (Ce4ZP), 20 ml;

40 ppm (Ce3ZP and Ce3ZY), 20 ml; sorbent dosage 0.15 g 75

4.14 Sorption of As(V) by Ce3ZP as function of initial concentration

17

and temperature 77

4.15 Sorption of As(V) by Ce4ZP as function of initial concentration

and temperature 77

4.16 Freundlich plot of As(V) onto Ce3ZP at various temperatures 79

4.17 Freundlich plot of As(V) onto Ce4ZP at various temperatures 79

4.18 Langmuir plot for sorption of As(V) onto Ce3ZP at various

temperatures 80

4.19 Langmuir plot for sorption of As(V) onto Ce4ZP at various

temperatures 81

4.20 D–R adsorption isotherm for As(VI) sorption on Ce3ZP at

various temperature 82

4.21 D–R adsorption isotherm for As(V) sorption on Ce4ZP at

various temperature 83

4.22 Van’t Hoff plot for the sorption of As(V) by cerum-loaded

zeolite As(V):20mL, 160 ppm (Ce4ZP); 40 ppm (Ce3ZP) 86

4.23 Variation of As(V) sorption capacity by Ce4ZP against

time at various temperatures. Sorbent dose, 0.15 g; initial

As(V) concentration, 160 mg/L, 20 ml; pH 4 89

4.24 The first order kinetic plots for the adsorption of As(V)

onto Ce4ZP at various temperatures 90

4.25 Pseudo-second order kinetic plots for the adsorption of

As(V) onto Ce4ZP at various temperatures 90

4.26 Arrhenius plot for for the adsorption of As(V) onto

Ce4ZP at various temperatures 91

4.27 Intra particle diffusion plot sorption of As(V) onto

Ce4ZP at various temperatures 96

4.28 Reichenberg model for the adsorption of As(V) onto

Ce4ZP at various temperatures 96

4.29 Variation percentages of As(V) sorption capacities in

the presence of foriegen anions at different concentration

ratios (ppm). As(V) initial concentration 160ppm,

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20mL;CeIVZP dosage 0.15g 97

4.30 Variation percentages of As(V) sorption capacities in the

presence of foriegen anions at different concentration

ratios (ppm). As(V) initial concentration 160ppm,

20mL;CeIIIZP dosage 0.15g 98

4.31 Percentage of desorption of As(V) from Ce4ZP by

phosphate, sulfate, hydroxide and chloride 99

4.32 Percentage desorption of As(V) from Ce3ZP in the

presence of phosphate, sulfate, hydroxide and chloride 100

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LIST OF PLATES

Plate page

4.1 SEM micrograph of zeolite P by using SRHA/Al (4/1) 63

4.2 SEM micrograph of zeolite P by using SRHA/Al (16/1) 64

4.3 SEM micrograph of zeolite P by using SRHA/Al (20/1) 64

4.4 SEM micrograph of Ce4ZP 71

4.5 SEM micrograph of Ce3ZP 71

4.6 SEM micrograph of ZY 72

4.7 SEM micrograph of Ce3ZY 72

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LIST OF ABBREVIATIONS

α : Limiting amount of metal ion that can be taken per

mass of adsorbent

ppm : part per million

RHA : Rice husk ash

XRD : X-ray diffraction

FTIR : Fourier transform infrared

SEM-EDX : Scanning Electron Microscopy and Energy Dispersive

X-ray Analyses

CeIVZP : Cerium (IV) loaded with Zeolite P

CeIIIZP : Cerium (III) loaded with Zeolite P

CeIIIZY : Cerium (III) loaded with Zeolite Y

n : Parameter of Freundlich equation

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CHAPTER 1

INTRODUCTION

Arsenic is harmful to man and living organisms and suspected carcinogenic [Cantor

1997]. However, due to its unique properties arsenic compounds are still widely used in

many applications. They are used for the productions of wood preservative, lead shot,

storage batteries, semiconductors, pesticides and fertilizers [Brooks 2007]. In addition

to natural weathering of arsenic rocks and minerals, arsenic also enters the environment

through other anthropogenic activities such as petroleum refineries, fossil fuel power

plants and smelting of non-ferrous ores such as copper, lead, zinc, gold and uranium

[Korte and Fernando, 1991]. Most international drinking water standards for arsenic

were lowered to 0.01 mgl-1 as regulated by Word Health Organization [Johannesson

2002] where else many international standards for industrial waste effluent were set to

0.05 mgl-1 [Huang et al., 2007, Direct Art Company 2007]. Due to this scenario,

development of new methods and sorbents for arsenic removal from water has been the

subject of intense research lately.

Conventional precipitation methods for arsenic removals using iron and aluminum salts

have not been successful to meet drinking and effluent standards for As due to limitation

of solubility of the resultant products. Another problem is the production of a large

volume of a bulky toxic waste sludge which is difficult to dry and usually face disposal

problem. One of possible methods to improve this problem is using an adsorbent

including ion exchange materials [Leist et al., 2000, Vagliasindi and Benjamin, 1998].

22

The arsenic sorbed can be eluted and recovered in a smaller volume and the sorbent can

be reused. Among others, the removal of As(V) by adsorption methods have been

studied using spodic [Lindberg 1997], aquifer material [Carrillo and Drever, 1998],

oxides of antimony and manganese [Galer et al., 1997], iron hydroxide [Raven et al.,

1998] and iron coated catalyst [Huang 1997].

Zeolites are crystalline, hydrated aluminosilicate minerals containing exchangeable

alkaline and alkaline earth metal cations normally of group I and group II elements, in

particular, sodium, potassium, magnesium, calcium, strontium, and barium, as well as

water molecules in their structural frameworks. Structurally, they are complex, porous,

crystalline inorganic polymers, enclosing interconnected cavities in which the metal ions

and water molecules are contained. They are based on an infinitely extending three

dimensional network of AlO4 and SiO4 tetrahedra linked to each other by sharing all the

oxygen ions [Bhatia 1990]. Zeolites may be represented by an empirical formula of

M2/nAl2O3xSiO2.yH2O. In this oxide formula, M is metal cation, x is generally equal to

2 or greater, y represents the water contained in the voids of the zeolite and n is the

valence of metal cation which neutralize the permanent negative charge on the

aluminosilicate framework, which was created by the replacement of Si 4+ with Al3+

[Breck 1974]. The charge balancing counter ions, M can be easily exchanged with other

metal cation, which produce the cationic exchange properties of zeolite [Bordiga et al.,

1995].

Since zeolites have a permanent negative charge on their surface, they have no

affinity for anions. However recent studies have shown that modification of zeolites

23

with certain surfactants or metal cations yield sorbents with a strong affinity for many

anions [Li et al., 1998]. In order to sorb anions such as arsenate, the modified surface

must either possess positively charged exchange sites, or there should be replacement of

weakly held counter ions of the surfactant by more strongly held counter ions. Cationic-

surfactant-modified zeolites were shown to remove arsenate from aqueous solutions.

Since As(V) presence in water as arsenate anion in wide pH range, the removal of As(V)

by zeolites could be enhanced after loading it with various metal cations such as Al [Xu

et al., 2000], Fe [González, 2001], Pb [Gonzalez et al., 2001, Miranda and Olguin, 2007]

and La [Miranda and Olguin, 2007, Haron et al., 2007].

It is known that a stable and insoluble cerium arsenate can be produced by reacting

solution of cerium salt with arsenic acid [Alberti et al., 1969, Janardanan et al., 1998].

Cerium hydroxide has been known to adsorbed arsenic As(V) quantitatively from

aqueous solution [Plotnikov and Usatova, 1964]. Recently hydrous cerium oxide was

also shown to poses an anion exchange with high capacity for As(V) [Zhang et al., 2005]

and other anions [Misak and Mikhail, 1981, Tokunaga et al., 1995]. Further more

cerium doped iron oxide was reported to adsorb As(V) at higher capacity compared to

alumina [Zhang et al, 2003]. Our previous study also showed that Ce(III) loaded-

chelating exchanger could sorb As(V) effectively from aqueous solution [Haron et al.,

1997].

In this research, we prepared cerium exchanged-zeolite P (CeZP) and investigated its

ability to sorb As(V) from aqueous solution. The sorbent was tested for removal of

24