SURFACTANT MODIFIED ZEOLITE Y AS A SORBENT FOR SOME CHROMIUM AND ARSENIC SPECIES IN WATER NIK AHMAD NIZAM NIK MALEK

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1 SURFACTANT MODIFIED ZEOLITE Y AS A SORBENT FOR SOME CHROMIUM AND ARSENIC SPECIES IN WATER NIK AHMAD NIZAM NIK MALEK A thesis submitted in fulfillment of the requirements for the award of the degree of Master of Science (Chemistry) Faculty of Science Universiti Teknologi Malaysia JANUARY 2007

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6 To my beloved mother, father, brothers, sisters and my bestfriend iii

7 iv ACKNOWLEDGEMENT In the name of Allah the Almighty, thanks to Him for giving me the opportunity and will to finish this research and to complete this thesis. I would like to express my sincere appreciation and gratitude to my research supervisor, Prof Dr Alias Mohd Yusof for his knowledge, acquaintance, guidance, supervision, critics, evaluation, encouragement, and for supporting me throughout the undertaking of this research. I am also very thankful to my research team friends, especially, to Mr Mohamad Adil, Tan See Hua, Lee Kian Keat and Chia Chai Har for giving me the motivation, knowledge, assistance, critics, information, opinion and for their kind contribution for helping me to finish my research. A thousand thanks also to all of the staffs in chemistry department, faculty of science for helping me during this research, particularly, the lab assistants. Not forgetting my lovely bestfriend, Ms Nor Suriani Sani for the motivation, support, encouragement, friendship, advice and understanding. I greatly appreciate it. I want to extend my utmost gratitude and appreciation to my parents, family, fellow friends and those who provided assistance in this research either intentionally or unintentionally at various conditions and occasions during the progress of this research and the completion of this thesis. All of their supports towards the completion of this thesis will be reciprocated by Allah the Almighty. Without their supports and contributions, this thesis would not have been the same as presented here. Thank you very much.

8 v ABSTRACT The removal of some chromium and arsenic species from water by the surfactant-modified zeolite Y (SMZY) and unmodified zeolite Y was studied. Zeolite NaY was successfully synthesized from rice husk ash via seeding method involving the preparation of two separate gel formations. The synthesized and commercial zeolite NaY were characterized with XRD, FTIR, surface area and elemental analysis. The total cation exchange capacity (CEC) and external cation exchange capacity (ECEC) for the synthesis was higher than the commercial one due to the lower ratio of silica to alumina for the synthesized than the commercial zeolite Y. The zeolite NaY was subsequently modified with hexadecyltrimethyl ammonium (HDTMA) at the amount equal of 50%, 100% and 200% of ECEC of the zeolite. The study of Cr(III) removal showed the synthesized zeolite NaY effectively removed Cr(III) than the commercial one. The equilibrium sorption data fitted the Langmuir and Freundlich isotherm models and the kinetic study was followed the pseudo second order model. The slight decrease of the Cr(III) removal capacity for SMZY indicated that the sorbed cationic surfactant blocked sorption sites for Cr(III). While the unmodified zeolite had little affinity for the Cr(VI) and As(V) species, the SMZY showed significant removal of both species. The adsorption equilibrium data are best fitted to the Langmuir model. The removal of Cr(VI) was highest when the synthesized zeolite NaY was modified such that HDTMA achieved 100% of its ECEC. The SMZY-synthesis showed an adsorption of As(V) capacity higher than the SMZY-commercial. Because the As(III) exists form as neutral species in water, the removal of As(III) from water between unmodified and SMZY showed only a slight difference. The effects of different surfaces coverage of HDTMA-zeolite on the sorption of these species were insignificant. The SMZY was proven to be useful in removing cationic and anionic forms of arsenic and chromium in water simultaneously compared to the unmodified zeolite Y since it has the affinity for both cations and anions.

9 vi ABSTRAK Penyingkiran beberapa spesies kromium dan arsenik daripada air oleh zeolit Y yang diubahsuai dengan surfaktan (SMZY) dan zeolit Y yang tidak diubahsuai telah dikaji. Zeolit NaY telah berjaya disintesis daripada abu sekam padi melalui kaedah pembenihan yang melibatkan penyediaan dua pembentukan gel yang berasingan. Zeolit NaY yang disintesis dan zeolit komersil dicirikan dengan XRD, FTIR, luas permukaan dan analisis unsur. Kapasiti penukaran kation (CEC) dan kapasiti penukaran kation luaran (ECEC) bagi zeolit yang disintesis didapati lebih tinggi daripada zeolit komersil disebabkan oleh nisbah silika kepada alumina bagi zeolit yang disintesis lebih rendah berbanding zeolit Y komersil. Zeolit NaY kemudiannya diubahsuai dengan heksadesiltrimetil ammonium (HDTMA) pada amaun 50%, 100% dan 200% daripada ECEC zeolit tersebut. Kajian menunjukkan penyingkiran Cr(III) oleh zeolit NaY yang disintesis adalah lebih berkesan berbanding zeolit komersil. Data penjerapan keseimbangan berpadanan dengan model isoterma Langmuir dan Freundlich manakala kajian kinetik mengikuti model pseudo tertib kedua. Penurunan sedikit terhadap kapasiti penyingkiran Cr(III) bagi SMZY menunjukkan surfaktan kationik yang dijerap menghalang tapak penjerapan bagi Cr(III). Zeolit yang tidak diubahsuai mempunyai sedikit sahaja afiniti terhadap Cr(VI) dan As(V) manakala SMZY menunjukkan penyingkiran yang ketara bagi kedua-dua spesies. Data penjerapan keseimbangan berpadanan dengan model Langmuir. Penyingkiran Cr(VI) adalah paling tinggi apabila zeolit NaY yang disintesis diubahsuai dengan HDTMA yang memenuhi 100% daripada ECEC zeolit tersebut. SMZY-sintesis menunjukkan kapasiti penjerapan As(V) lebih tinggi berbanding SMZY-komersil. Oleh kerana As(III) terbentuk dalam air sebagai spesies yang neutral, penyingkiran As(III) daripada air antara zeolit tidak diubahsuai dan SMZY menunjukkan perbezaan yang sedikit sahaja. Kesan perbezaan litupan permukaan bagi HDTMA-zeolit terhadap penjerapan spesies-spesies ini tidak terlalu ketara. SMZY terbukti berguna dalam penyingkiran logam yang membentuk kationik dan anionik dalam air secara serentak berbanding zeolit Y yang tidak diubahsuai kerana ia mempunyai sifat afiniti terhadap kation dan anion.

10 vii TABLE OF CONTENTS CHAPTER TITLE PAGE THESIS STATUS DECLARATION SUPERVISOR S DECLARATION TITLE PAGE DECLARATION DEDICATION ACKNOWLEDGEMENT ABSTRACT ABSTRAK TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF SYMBOLS LIST OF ABBREVIATIONS LIST OF APPENDICES i ii iii iv v vi vii xii xiv xviii xix xxi 1 INTRODUCTION Introduction Rice Husk Ash Zeolite Zeolite NaY Synthesis of Zeolite NaY Seeding Technique 15

11 viii Ageing Characterization X-Ray Diffraction Technique Infrared Spectroscopy Elemental Analysis Ion Exchange Capacity Surfactant Modified Zeolite Toxic Metals in Water Chromium Arsenic Removal of Toxic Metals in Water Adsorption Theory Research Background and Objectives of the 45 Study 2 MATERIALS AND METHODS Preparation of Rice Husk Ash Characterization of Rice Husk Ash X-Ray Diffraction Technique Infrared Spectroscopy Elemental Analysis Synthesis of Zeolite NaY Characterization of Zeolite NaY Surface Area and Porosity Elemental Analysis Decomposition of Zeolite Samples Determination of Sodium Determination of Aluminum Determination of Loss on Ignition and Percentage of Silica Determination of Unit Cell 56

12 ix Determination of Cation Exchange Capacity Total Cation Exchange Capacity External Cation Exchange Capacity Preparation of Surfactant Modified Zeolite Y Characterization of Surfactant Modified Zeolite Y Elemental Analysis Dispersion Behavior Maximum Adsorption of HDTMA Adsorption Studies Adsorption of Cr(III) Kinetic Study Effect of Initial ph Isotherm Study Determination of Cr(III) by FAAS Adsorption of Cr(VI) Effect of Initial ph Isotherm Study SMZY-Chromate Structure Study Determination of Cr(VI) by UV- Vis Spectrophotometer Adsorption of As(V) and As(III): Preliminary Study Adsorption of As(V) Effect of Initial ph Isotherm Study Determination of Arsenic by FAAS 72

13 x 3 RESULTS AND DISCUSSION: SORBENTS DEVELOPMENT Rice Husk Ash as a Source of Silica Synthesis of Zeolite NaY X-ray Diffraction Technique Infrared Spectroscopy Elemental Analysis Physicochemical Properties Characterization of Surfactant Modified Zeolite Y X-ray Diffraction Technique Infrared Spectroscopy Elemental Analysis Surface Area and Porosity Dispersion Behavior Maximum Adsorption of HDTMA 98 4 RESULTS AND DISCUSSION: APPLICATION OF SORBENTS Removal of Cr(III) Kinetic Study Effect of Initial ph Isotherm Study Removal of Cr(VI) Effect of Initial ph Isotherm Study SMZY-Chromate Structure Study Removal of Arsenic Preliminary study: Adsorption of Arsenate and Arsenite Removal of Arsenate Effect of Initial ph 125

14 xi Isotherm Study CONCLUSIONS AND SUGGESTIONS Conclusions Suggestions 136 REFERENCES 137 Appendices A - I

15 xii LIST OF TABLES TABLE NO. TITLE PAGE 1.1 Element sources in the zeolites and their function Composition ratio of synthesis Zeolite NaY The assignments of the main infrared bands for zeolites The abbreviation of the surfactant modified zeolite Y Solutions for calibrating flame photometer Chemical composition of rice husk ash Zeolite NaY infrared assignments IR assignments for commercial, synthesized zeolite NaY and zeolite Y (SiO 2 /Al 2 O ) 3.4 Percentage amount of major elements contained in the zeolite samples from the first approach 3.5 Percentage amount of major elements contained in zeolite samples by XRF technique 3.6 The physicochemical properties of the synthesized (Zeo- NaY-S) and commercial zeolite NaY (Zeo-NaY-C) Peak lists of SMZY infrared spectrum The content of Na 2 O in the SMZY and their parent zeolite 3.9 Elemental data of the SMZY obtained from the CHNS analyzer 3.10 Surface area and porosity of the SMZY and unmodified zeolites

16 xiii 3.11 Fitted Langmuir parameters for sorption of HDTMA by synthesized zeolite Y 4.1 Values of the pseudo second order model parameters for the adsorption of Cr(III) by synthesized and commercial zeolite NaY 4.2 Fitted Langmuir and Freundlich parameters for Cr(III) sorption on SMZY and the unmodified synthesized and commercial zeolite NaY 4.3 Fitted Langmuir parameters for sorption of Cr(VI) by SMZY 4.4 Values of the adsorption of As(III) and As(V) by SMZY and respective parent zeolite Y 4.5 Values of the Langmuir parameters for sorption of As(V) by SMZY

17 xiv LIST OF FIGURES FIGURE NO. TITLE PAGE 1.1 The sodalite cages (truncated octahedral) connected on the hexagonal faces in zeolite Y. The three types of cation sites are shown Derivation of Bragg s law for X-ray diffraction The illustration of the X-ray powder diffraction method The structure of hexadecyltrimethyl ammonium bromide (HDTMA-Br) Schematic diagram of HDTMA micelle formation in solution and admicelle formation on the zeolite surface and the uptake substance onto surfactant modified zeolite 1.6 The structure of the anion form of arsenate (a, b, c and d) and the neutral form of arsenite (e) species The XRD diffractogram of RHA Infrared spectrum of rice husk ash The X-ray diffraction patterns of the product obtained from the synthesis without ageing and seeding technique (NA-NS-Zeo) and the product from the synthesized zeolite Y with ageing but without seeding technique (A-NS-Zeo) The X-ray diffraction pattern of mixed synthesized zeolite NaY (Zeo-NaY-S) via seeding and ageing techniques match up with the sodium aluminum silicate hydrate NaY (Na 2 Al 2 Si 4.5O 13.xH 2 O) pattern existed in PDF 77

18 xv 3.5 The compilation of X-ray diffractograms of the synthesized zeolite NaY The X-ray diffraction pattern of the commercial zeolite NaY The infrared spectrum of Zeo-NaY-S The infrared spectrum of Zeo-NaY-C The illustration of infrared spectrum of zeolite Y (Si/Al = 2.5) in the region from 1250 to 420 cm The comparison of the infrared spectrum of synthesized zeolite NaY (Zeo-NaY-S) and rice husk ash (RHA) The XRD patterns of the surfactant modified zeolite Y together with the parent zeolites The comparison of the Na 2 O amount (mg/g) present in the SMZY and respective unmodified zeolite The comparison of the specific surface area (m 2 /g), total pore volume (cc/g) and average pore size (Ǻ) for SMZY and unmodified zeolite Y Photographs show the distribution of SMZY and unmodified zeolite NaY solid particles when added to hexane-water mixture Photographs showing the distribution of SMZY and unmodified zeolite Y solid particles The sorption isotherm plotted of HDTMA onto the synthesized zeolite Y The plotted of 1/q e against 1/C e where q e is the HDTMA adsorbed at equilibrium (mmol/kg) and C e is concentration of HDTMA at equilibrium (mmol/l) Schematic diagram of the theoretical HDTMA formation on the zeolite Y structure Sorption kinetics graph for synthesized zeolite NaY from two different initial concentrations of Cr(III) Sorption kinetics graph for commercial zeolite NaY with two different initial concentrations 102

19 xvi 4.3 Percentage of the Cr(III) removal by synthesized (Zeo- NaY-S) and commercial zeolite NaY with [Cr(III)] initial = 250 mg/l. 4.4 Percentage of the Cr(III) removal by synthesized (Zeo- NaY-S) and commercial zeolite NaY with [Cr(III)] initial = 500 mg/l The effect of ph on the Cr(III) removal by synthesized and commercial zeolite NaY The adsorption isotherm of Cr(III) sorption on SMZY from the synthesized zeolite NaY together with the unmodified synthesized zeolite NaY The adsorption isotherm of Cr(III) sorption on SMZY from the commercial zeolite NaY together with the unmodified commercial zeolite NaY The adsorption isotherm of Cr(III) sorption on unmodified synthesized and commercial zeolite NaY The K f (Freundlich constant) values for the adsorption of Cr(III) by SMZY and unmodified zeolite Y Effect of ph solution on Cr(VI) removal by SMZY Sorption of Cr(VI) by SMZY and unmodified synthesized zeolite Y Sorption of Cr(VI) by SMZY and unmodified commercial zeolite Y The comparison of the maximum adsorption (Q o ) calculated from the Langmuir isotherm model for the sorption of Cr(VI) by SMZY XRD patterns of the unmodified synthesized zeolite NaY (Zeo-NaY-S), SMZY-100-S and after contacting with chromate solution (SMZY-100-S-Chromate) IR spectra of SMZY-100-S and SMZY-100-S- Chromate IR spectra of unmodified synthesized zeolite NaY (Zeo-NaY-S) and SMZY-100-S-Chromate Schematic diagram for the mechanism of Cr(VI) sorption by SMZY 121

20 xvii 4.18 Adsorption of As(III) by the SMZY and unmodified zeolite NaY The adsorption of As(V) species from aqueous solution by SMZY and unmodified zeolite NaY Effect of the initial ph solution in the removal of As(V) by SMZY As(V) sorption from aqueous solution by SMZY-50-S, SMZY-50-C and respective parent zeolite NaY As(V) sorption from aqueous solution by SMZY-100- S, SMZY-100-C and respective parent zeolite NaY As(V) sorption from aqueous solution by SMZY-200- S, SMZY-200-C and respective parent zeolite NaY Comparison of the maximum adsorption (Q o ) value calculated from the Langmuir isotherm model for the As(V) sorption by each of the SMZY 130

21 xviii LIST OF SYMBOLS C - Degree Celsius C o - Initial concentration C e - Equilibrium concentration cm - Centi meter dm - Deci meter g - Gram kg - Kilo gram kv - Kilo Volt L - Liter m - Meter M - Molar ma - Mili ampere meq - Mili equivalent mg - Mili gram min - Minute ml - Mili Liter mm - Mili meter mmol - Mili mol N - Normal nm - Nano meter ppm - Part per million ppb - Part per billion Å - Angstrom μg - Micro gram μl - Micro Liter

22 xix LIST OF ABBREVIATIONS AAS - Atomic Absorption Spectroscopy APHA - American Public Health Association ASTM - American Society for Testing and Materials ATP - Adenosine Tri-Phosphate BET - Brunauer, Emmet, and Teller BTEX - Benzene, Toluene, Ethylene and Xylene CCA - Chromated Copper Arsenate CEC - Cation Exchange Capacity CHNS - Carbon Hydrogen Nitrogen Sulphur CMC - Critical Micelle Concentration CQ - Chloroquin CRM - Certified Reference Materials DDTMA - Decadecyltrimethyl Ammonium DHA - Dehydroabietic Acid ECEC - External Cation Exchange Capacity EPA - Environmental Protection Agency FAAS - Flame Atomic Absorption Spectroscopy FAU - Faujasite FTIR - Fourier Transform Infrared HDTMA - Hexadecyltrimethyl Ammonium ICDD - International Centre for Diffraction Data ICPMS - Inductively Coupled Plasma Mass Spectrometry IEC - Ion Exchange Capacity IR - Infrared LEDs - Light Emitting Diodes

23 xx LOI - Loss on Ignition LTA - Linde Type A MCL - Maximum Contaminant Levels MTDC - Malaysian Technology Development Corporation NAA - Neutron Activation Analysis NIOSH - National Institute for Occupational Safety and Health NMR - Nuclear Magnetic Resonance ODTMA - Octadecyltrimethyl Ammonium OTS - Octadecyltrichlorosilane PCE - Perchloroethylene PDF - Powder Diffraction File PFC - Plug Flow Combustor PTFE - Polytetrafluoroethylene QC - Quality Control R&D - Research and Development RHA - Rice Husk Ash SIRIM - Standards and Industrial Research Institute of Malaysia SMC - Surfactant Modified Clinoptilolite SMZ - Surfactant Modified Zeolite SMZY - Surfactant Modified Zeolite Y TCE - Trichloro Ethylene TDTMA - Tetradecyltrimethyl Ammonium TEA - Tetraethyl Ammonium TOC - Total Organic Carbon UV-Vis - Ultra Violet-Visible WHO - World Health Organization XRD - X-Ray Diffraction XRF - X-Ray Flourescence

24 xxi LIST OF APPENDICES APPENDIX TITLE PAGE A Elemental analysis for the zeolite NaY 148 A-1 Analysis data for the determination of sodium in the zeolite NaY samples by AAS 148 A-2 Analysis data for the determination of Al by ICP-MS 149 A-3 Analysis data for the determination of loss on ignition (LOI) and the percentage of silica (%SiO 2 ) 150 A-4 X-Ray Fluorescence (XRF) accuracy 150 B Physicochemical Properties of the Zeolite NaY 151 B-1 Surface area and porosity 151 B-2 Determination of the unit cell 152 B-3 Determination of CEC and ECEC 153 C D E F Infrared spectra of SMZY matching with respective parent zeolite 155 Determination of sodium in SMZY and unmodified zeolite Y 158 Surface area and porosity of the surfactant modified zeolite Y 159 Maximum adsorption of HDTMA on the zeolite Y 160 G Removal of Cr(III) study 161

25 xxii G-1 Kinetic study of the Cr(III) uptake by the synthesized and commercial zeolite NaY 161 G-2 Effect of the initial ph for the Cr(III) removal 164 G-3 Isotherm adsorption study of the Cr(III) by modified and unmodified zeolite NaY 168 H Removal of Cr(VI) study 174 H-1 Effect of the initial ph solution on the removal of Cr(VI) by SMZY 174 H-2 Isotherm study of the removal of Cr(VI) by SMZY 180 I Removal of arsenic study 192 I-1 Preliminary study of the As(III) and As(V) adsorption by SMZY and unmodified zeolite Y 192 I-2 Effect of the initial ph solution on the removal of As(V) by SMZY 193 I-3 Isotherm study of the As(V) sorption by SMZY 195 J Presented papers and expected publications from this study 198

26 CHAPTER 1 INTRODUCTION 1.1 Introduction Water is not only ubiquitous in nature, but is a necessary ingredient for all forms of life. The human embryo is approximately 90 percent water, and adults are 65 to 70 percent water; the percentage of water then decreases in old age (McCaull and Crossland, 1974). Water is essential for life and no person can live more than a few days without it. There are many sources of water such as lakes, rivers, oceans, groundwater, rain and streams. In reality, water is not pure in nature because approximately half of the known chemical elements have been found dissolved in nature. A clean running stream, even in its unpolluted state, contains a complex mixture of organic and inorganic substances. Today, as the population expands and industry evolves, there are many different disease-causing microorganisms and complex human health hazards that can be related to the organic and inorganic substances i.e. toxic metals, dumped in the water in mammoth quantities by our fast-changing technological civilization. Because of this problem, the regulations and laws for standard limitation of contaminants in water have become the main priority for the environment institutional in every country and world organization to overcome the exceeding value of contaminants in water for the protection of human health. To ensure that wastewater treatment process in industrial facilities and the water purification process for drinking water comply with the

27 2 regulations, these processes require the best technology to reduce the amount of contaminants. The method of treatment required for the removal of contaminants or their reduction to acceptable limits, depends in part on the fineness of the material. Therefore, the development of cost effective alternative sorbents material for treatment of contaminants in water is needed. There are many sorbent materials exist in this world either occurring naturally or produced synthetically. Nowadays, alternative cost effective technologies or sorbents are greatly required to overcome the exceeding value of contaminants in water. The materials produced from natural materials that are available in large quantities or certain waste products from industrial or agricultural operations may have the potential to be used as inexpensive sorbents. One of the natural products that produced in abundance in Malaysia is the rice husk which can be used as a source of silica for the preparation of the zeolite; the material which has adsorption properties. 1.2 Rice Husk Ash as a Source of Silica Rice husk ash is the natural sheath that forms on rice grains during their growth and it has no commercial value. In Malaysia, rice husk is produced in abundance after every paddy harvesting season and contributes to major agricultural waste. The husks are eliminated by burning them in the field at high temperature leaving behind a white blackish powder which is the constituents of silica. The presence of the silica ash causes a number of problems to the environment that causes pollution and disposal problems because of its nonbiodegradable property. Therefore, useful applications of the rice husk are desirable to solve this problem. The major constituent of rice husk after complete burning at high temperature is silica (SiO 2 ) in amorphous structure which formed as white powder and some amount of metallic impurities (Yalcin and Serinc, 2001).

28 3 The utilization of rice husk ash as an alternative source of silica towards the synthesization of zeolites has been reported nearly 20 years ago by Bajpal and Rao (1981). They have synthesized mordenite type zeolite using silica from rice husk ash. Besides that, rice husk ash was also used as a source of silica in the preparation of zeolite NaX (Dalal and Rao, 1985). Apart from that, zeolite Y was also successfully synthesized and was readily patented in Malaysia by Halimaton Hamdan and Yeoh Ann Keat (1993). There are two forms of silica; amorphous and crystalline. The amorphous form of silica is active towards the synthesis of zeolite but the crystalline form is inactive. The combustion of rice husk under controlled atmosphere and temperature less than 800 o C will generate the amorphous silica in the form of white powder and this silica ash which is transformed from the husk by complete burning constitutes 15 to 20% of the total weight of the husk. Hence, it is appropriate to employ rice husk ash from combustion of rice husk at temperature lower than 800 o C as a source of silica in the synthesis of zeolite. It is important and essential to characterize rice husk ash before using it to synthesis zeolite because the successful synthesis of zeolite rely on the reactive source of raw materials especially silica. The main characterization methods of rice husk ash involves X-ray diffraction technique (XRD), Infrared spectroscopy (IR) and elemental analysis. The XRD diffractogram will indicate the phase of material, either crystalline or amorphous. Source of silica obtained from rice husk ash that will be used to synthesis zeolite must be in the complete amorphous form. This form of silica will be featureless in the XRD diffractogram and the appearance of diffused maximum at 2θ = 23º (Halimaton Hamdan et al., 1997). The IR spectroscopy is also an imperative tool to characterize rice husk because the spectrum of material can support the data from XRD. The IR spectrum of amorphous silica is illustrated by the intense peaks at 1100, 800 and 470 cm -1 which are contributed from the asymmetric, symmetric and bending vibration frequencies for Si-O-Si bonds respectively (Cross and Jones, 1969). The information about the quantity of silica contained in the rice husk ash is crucial prior to synthesizing of the zeolite because one of the factors affecting the production of zeolite is the amount

29 4 of raw material (Robson, 2001). Therefore, the percentage of silica enclosed in the rice husk ash must be determined. 1.3 Zeolite Zeolite is a crystalline material and its structure consists of hydrated aluminosilicates of metals from group I and group II, in particular, sodium, potassium, magnesium and calcium. Structurally the zeolites are framework aluminosilicates which are based on an infinitely extending three-dimensional network of AlO 4 and SiO 4 tetrahedra linked to each other by sharing all of the oxygen. The structural formula of a zeolite is represented by the crystalline unit cell as: M x/n [(AlO 2 ) x (SiO 2 ) y ].wh 2 O Where: M : cation n : valence cation w : the number of water molecule y/x : the ratio of the tetrahedral silica to alumina portion [ ] : framework composition The framework contains channels and interconnected voids which are occupied by the cation and water molecules. Zeolites consist of SiO 2, Al 2 O 3, alkali cation, water and other substances with varying functions from one another. Table 1.1 summarizes the function of each element in zeolites. The cations are quite mobile and may usually be exchanged to varying degrees by other cations. Intracrystalline zeolitic water in zeolites can be removed continuously and reversibly.

30 5 The appropriate definition of zeolites by Smith (Breck and Flanigen, 1964) is: A zeolite is an aluminosilicate with a framework structure enclosing cavities occupied by large ions and water molecules, both of which have considerable freedom of movement permitting ion exchange and reversible dehydration. Table 1.1: Element sources in the zeolites and their function. Source SiO 2 AlO 2 OH - Alkali cation Water Organic directing agent Function (s) Primary building units of the framework Origin of the framework charge Mineralizer, guest molecule Counter ion of framework charge Solvent, guest molecule Counter ion of framework charge, guest molecule, template Zeolites are often termed as molecular sieve because the zeolitic pores are microscopically small with approximately molecular size dimensions. The windows and channels of a zeolite allow it to discriminate among guest molecules and cations on the basis of size. Zeolites are divided into two main classes, namely, mineral such as clinoptilolite, mordenite and garronite and the synthetic zeolite such as zeolite A, X and Y. The zeolite molecular sieve has three major functions, which are as catalyst, ion exchanger and adsorbent material. In view of the fact that silicon typically exists in a 4+ oxidation state, the silicon-oxygen tetrahedral is electrically neutral. However, in the framework of zeolite, aluminum typically exists in the 3+ oxidation state so that aluminum-oxygen tetrahedral form a centre that is deficient of one electron. Thus, zeolite framework is typically anionic and charge-compensating cations populate the pores to maintain electrical neutrality. These cations can participate in ion exchange processes and will yield important properties for zeolites. When charge-compensating cation are soft cations such as sodium, zeolites are excellent water softeners because

31 6 they can pick up the hard magnesium and calcium cations as well as toxic metals cation in the water living behind the soft cation. The fundamental properties and applications of molecular sieve zeolites involve many scientific disciplines and cross many of the traditional boundaries. Fields involved are inorganic and physical chemistry with emphasis on surface and colloid chemistry and catalysis, biochemistry, the geological sciences of geochemistry, geology, mineralogy and physics, including crystallography, spectroscopy and solid state physics (Breck, 1971). One of the main applications of zeolites is ion-exchanger. The ionexchanger can be classified into organic and inorganic ion-exchanger. Resin is the organic form ion-exchanger while zeolites are classified as the synthetic inorganic ion exchanger. The major application of ion-exchanger is to remove toxic metals in the purification of water. The cation exchange behaviour depend on the nature of the cation species, the size of ion or complex cation, charge of ion or complex cation and type of zeolite structure (Breck, 1964). Thus, zeolites are capable for the removal of the toxic metals from water due to the ion exchange properties of zeolites. Adsorption and ion exchange are the most common and effective processes for removing ions discharged into the environment, with resins being the most important group of ion exchange materials followed by zeolites. However, resins are expensive and must be regenerated and activated carbon is generally less effective for most metals and also requires regeneration. Therefore, alternative effective and economic sorbents are needed. Many authors have studied the application of both synthetic and natural zeolites as sorbents for the removal of metals cation from water. Some authors have reported the applications of the synthetic zeolite in removing heavy metals, for instance, Shevade and Robert (2004) used zeolite Y for arsenate removal from pollutant water, Veronica Badillo-Almaraz et al. (2003) used zeolite X for the adsorption of Zn(II) species from aqueous solution and the utilization of Zeolite NaY as an ion-exchanger for Co(II) and Fe(II) by Kim and Keane (2000). Among the natural zeolite, clinoptilolite is the naturally occurring zeolite that mostly used as an ion-exchanger and adsorption in the purification of water as clinoptilolite is probably the most abundant zeolite found in

32 7 nature because of its wide geographic distribution and large size of deposits (Peric et al., 2004). There are many papers reporting on the application of clinoptilolite as an adsorbent for toxic metals including the removal of lead and cadmium (Maliou et al., 1992), arsenate and arsenite (Elizalde-Gonzalez et al., 2001b) and copper, zinc, cobalt, nickel and mercury (Blanchard et al., 1984). Therefore, zeolite is one of the promising inorganic materials in removing toxic metals in the purification of water Zeolite NaY Synthetic zeolite NaY is the synthesized zeolite Y of which sodium cation neutralize the framework structure of aluminosilicate and this material is in the same group with zeolite X. Both zeolites exhibit a structure similar to naturally occurring faujasite types. The differences between these zeolites are due to the composition and other physical properties brought about by the compositional differences. The Si, Al contents of zeolite Y are similar to that of faujasite whereas zeolite X is much more aluminous. Zeolite Y exhibits the FAU (faujasite) structure which has a 3-dimensional pore structure with pores running perpendicular to each other in the x, y and z planes similar to LTA, and is made of secondary building units 4, 6 and 6-6. The pore diameter is large at 7.4Ǻ since the aperture is defined by a 12 member oxygen ring, and leads into a larger cavity of diameter 12Ǻ. The cavity is surrounded by ten sodalite cages (truncated octahedral) connected on their hexagonal faces as shown in Figure 1.1. The unit cell is cubic (a = 24.7Ǻ) with Fd-3m symmetry. Zeolite Y has a void volume fraction of 0.48, with a Si/Al ratio of 2.43 (Bhatia, 1990).

33 8 Hexagonal faces Truncated octahedral (sodalite cage) Site I 12 member oxygen ring Site II Site III Figure 1.1 The truncated octahedral (sodalite cage) connected on the hexagonal faces in zeolite Y. The three types of cation sites are shown. The framework of both zeolite Y and X consists of a tetrahedral arrangement of the truncated octahedral, i.e. the octahedral are joined to the octahedral faces by hexagonal prisms (Figure 1.1). The truncated octahedral is referred to as the sodalite unit or sodalite cage. The cations in the structure occupy three types of positions. These are type I, type II and type III which are in the centres of the hexagonal prism, on the six membered rings and on the walls of the channels, respectively. In the sodium form of a typical zeolite Y there are 56 sodium ions per unit cell while in the zeolite X, 86 cations per unit cell. These are distributed in the 3 different sites where for the zeolite Y, 16 in site I, 32 in site II and 8 in site III while for the zeolite X, 16 in site I, 32 in site II and 38 in site III. A major difference between zeolite X and Y is the non-occupancy of the type III sites for zeolite Y (Breck, 1964). Zeolites can be grouped into six categories according to the number of O-atoms in their largest ring. The faujasite family including zeolite Y are categorized into the 12-membered oxygen ring systems (Chen et al., 1994). Zeolites in this group system are also known as large pore zeolites.

34 9 Zeolite Y was discovered by Breck in 1961 when his group of researchers found that it should be possible to synthesize the zeolite X structure with silica/alumina ratios as high as 4.7 but his trial resulted in the zeolite that have a significant change in properties at a ratio above 3.0. Since zeolite X had been defined in reported patent as having silica/alumina ratios between 2.0 and 3.0, the isostructural zeolite with ratios above 3.0 and up to 6.0 were named and patented as zeolite Y (Robson and Occeli, 1988). The chemical formula for zeolite Y expressed in terms of moles of oxides may be written as (Breck, 1964): 0.9 ± 0.2 Na 2 O : Al 2 O 3 : w SiO 2 ; x H 2 O Here w is a value greater than 3 up to about 6 and x may be a value up to about 9. Among the numerous synthetic zeolite, the widely used in many field is the zeolite Y. One of the important applications of zeolites is as a cracking catalyst. Zeolite Y being more stable at high temperature due to the higher Si/Al ratio than other synthetic zeolites is useful as a catalyst for the cracking of petroleum. That is why zeolite Y had taken the place of zeolite X in the 1960s as a catalyst (Smart and Moore, 1993). Besides that, zeolite Y has also been used as the ion exchanger in order to remove heavy metals from water because of its high surface area, cation exchange capacity and stability. Kim and Keane (2000) reported the study on the ion exchange of divalent cobalt and iron by zeolite NaY. They concluded that sodium-based zeolite Y is effective in removing divalent iron and cobalt from aqueous solutions over the concentration range mol dm -3. Oliveira et al. (2004) had studied the removal of the metallic contaminants using magnetic-zeolite Y which is a physical composite of iron and zeolite Y, as a way of applying magnetic property to separate metals from water.

35 Synthesis of Zeolite NaY The factors affecting the synthesis of zeolite Y is comparable to the synthesis of other synthetic zeolite. A few main parameters, conditions and materials related to the synthesis of zeolite must be recognized and moreover it is of utmost importance to know the source of the materials and technical grade materials to be assayed and analyzed for impurities before the synthesis of zeolite (Robson, 2001). The nature of the starting materials, overall chemical composition of the reactant mixtures, factors affecting nucleation, reaction time and pressure as well as temperature are also important in determining the zeolite species (Breck, 1974; Barrer, 1982). These variables and parameters do not necessarily determine the products obtained in hydrothermal reactions because the reactant mixtures may be heterogeneous and nucleation appears to be kinetically rather than thermodynamically determined and controlled (Barrer, 1982). Breck and Tonawanda (1964) in their reported patent explained more about the condition on how to synthesis zeolite Y. One of the conditions that should be followed is when an aqueous colloidal silica sol or reactive amorphous solid silica is employed as the major source of silica, zeolite Y may be prepared by preparing an aqueous sodium aluminosilicate mixture having a composition, expressed in terms of oxide-mole-ratio, which falls within one of the ranges shown in Table 1.2. Crystallization occurs readily between 80 and 125 ºC. The temperature affects the size of the crystals, with the larger crystals forming at lower temperatures. Table 1.2 : Composition ratio of synthesis Zeolite NaY Ratio Range 1 Range 2 Range 3 Na 2 O/SiO to to to 0.80 SiO 2 /Al 2 O 3 10 to to 30 7 to 30 H 2 O/Na 2 O 25 to to to 60

36 11 In the synthesis of zeolite, source and starting materials are very crucial to determine the production of zeolite. Three major source materials that should be emphasized are the source of water, aluminium and silica according to the term zeolites as an aluminosilicate. Zeolite NaY can be synthesized by many sources of silica. Silica can be obtained from sodium silicate, silica gels, silicic acid, aqueous colloidal silica sols and reactive amorphous solid silica. The source of silica in the synthesis of zeolite Y can also be obtained from the natural products, for instance, from the coal fly ash (Zhao et al., 1997) and rice husk ash (Halimaton Hamdan et al., 1997; Zainab Ramli et al., 1996). In this study, we have used rice husk ash as a source of silica to synthesize the zeolite NaY. There are researchers that have successfully synthesized zeolite NaY from rice husk ash whereby when the dried rice husk is burnt in controlled atmosphere and temperature below 800 ºC it will produce rice husk ash containing over 90% reactive amorphous silica (Halimaton Hamdan et al., 1997). According to the Breck and Tonawanda (1964), one of the conditions for successfully synthesized zeolite NaY is the reactive amorphous silica. In addition, the application for the production of zeolite NaY in this study is as a sorbent material less pure silica materials from rice husk ash can be employed in order to reduce the cost instead of using the costly commercial silica. There are some problems that occur during the synthesis of zeolite NaY since the source of material used in this synthesis is amorphous silica and also the formation of zeolite NaY is metastable. It is possible to produce two or more crystalline phases from the same unreacted gel components. In the case of the formation zeolite Y, during the crystallization sequence, the initial formation of the desired faujasite phase (NaY) occur and subsequently followed by the evolution of a transient phase closely, gmelinite and finally by the production of garronite (Zeolite NaP) (Chen et al., 1994). Beside that, other phases identified to crystallize when the Na 2 O/SiO 2 and H 2 O/Na 2 O were changed include herschelite, noselite and zeolites P and A (Szostak, 1992). In order to avoid such phenomena from occurring and to yield high purity of zeolite NaY, the seeding and ageing methods during the synthesizing of zeolite NaY from rice husk ash will be highlighted.

37 12 During the synthesis of the zeolite NaY, a number of parameters were emphasized in order to obtain the product with high purity of crystalline zeolite NaY and low impurities as well as the elimination of other undesirable phases. The synthesis of zeolite is also a typical inorganic reaction procedure, therefore, the parameters that have been highlighted and will affect the product are: 1) Type of starting materials. 2) Initial composition of the gel. 3) Alkalinity of the reaction. 4) Ageing period. 5) Crystallization temperature and time. These parameters will be discussed below as all of them play important roles for successful synthesis of zeolite NaY with a Faujasite structure. 1) Type of starting materials The starting materials used in the synthesis were rice husk ash as a source of amorphous silica (SiO 2 ), sodium aluminate as a source of aluminate and sodium hydroxide as a source for the alkaline condition. Hydrothermal synthesis of aluminosilicate zeolites involved a mixture of Si and Al species that were obtained from rice husk ash and sodium aluminate, respectively. The mixture was then converted via an alkaline supersaturated solution from sodium hydroxide (NaOH) solution into microporous crystalline aluminosilicates. Sodium hydroxide serves as a source of sodium ions and also assisted in controlling the ph. Zeolite Y is synthesized only from reactive amorphous silica while unreactive amorphous silica usually produces a mixture of zeolite Y and P (Zainab Ramli et al., 1996). Sodium aluminate was supplied by Riedel De Haen containing 50 to 56% of Al 2 O 3 and rice husk ash containing 91.65% of amorphous silica. Sodium aluminate was used to introduce aluminium in the anionic form since alkali salts have a strong electrolytic effect on gel formation after addition of alkali silicate solution (Robson, 2001). The high percentage of raw material will yield high purity of product because the structure and properties of the molecular sieve product are highly dependent on the physical and chemical nature of the reactants used

38 13 in preparing the reaction mixture, especially the composition of desired materials in the raw materials. In addition, according to the original patent for the synthesis of zeolite Y (Breck, 1964), amorphous silica from rice husk ash was indicated as one of the preferred sources of silica for obtaining Zeolite NaY. 2) Initial composition of gel The initial composition for the synthesis of zeolite NaY from RHA followed the Na 2 O-Al 2 O 3 -SiO 2 -H 2 O system. The overall composition of gel is 4.62 Na 2 O: Al 2 O 3 : 10 SiO 2 : 180H 2 O when expressed in terms of oxide-mole-ratios, results in Na 2 O/SiO 2 is 0.462, SiO 2 /Al 2 O 3 is 10 and H 2 O/Na 2 O is 45. This composition falls into range 2, referring to Table 1.2. Thus, the composition of initial gel was appropriate for the synthesis of zeolite Y from reactive amorphous silica as suggested by Breck et al. (1964). 3) Alkalinity of the reaction The ph of the mixture was controlled by sodium hydroxide solution to provide the alkaline ph of generally between 8 and 12. The alkaline condition is important in the synthesis of zeolite because [Al(OH) 4 ] - is most abundant in alkaline solution. The oligomeric silicate species react with this monomer [Al(OH) 4 ] - to produce aluminosilicate structure. Furthermore, the increased ph will accelerate crystal growth by shortening the induction period (period before formation of viable nuclei) (Wetkamp et al., 1994). The crystallization generally proceeds via the solution phase because the solubility of silicate, aluminate and aluminosilicate in the solution are important as crystallization mechanisms. Thus, the elevated ph is important since the solubility depends on the alkalinity. Besides that, the activity of SiO 2 in the aluminosilicate mixture also depends upon the alkalinity [OH - ]. The higher the [OH - ] the lower the activity; therefore the synthesis of zeolite with low SiO 2 /Al 2 O 3 requires high [OH - ]. Hence, the increase of Al 2 O 3 will provide more ion exchange sites necessary for ion exchange property.

39 14 4) Ageing period. After the aluminosilicate gel was prepared, the hydrogel was kept for 24 hours at ambient temperature. This ageing process is crucial in obtaining a high purity product especially in the synthesis of zeolite Y. The important step during the ageing period is the dissolution or depolymeriztion of the silica sol that will increase the concentration of dissolved silica promoted by the alkaline. The ageing time of 24 hours was selected because Breck (1964) has proven that this period is optimum in producing a high yield of zeolite Y that is 92%. Bo and Hongzhu (1998) also reported that the rate of crystallization and composition of the crystalline products depend strongly on the ageing time and temperature in the synthesis of zeolite Y. This fact is also supported by another author, Zhao et al. (1997) which emphasized that ageing process was the important role in achieving the favorable hydrothermal aluminosilicate chemistry for zeolite formation. Along with this process and seeding method, they had successfully synthesized zeolite Y without marked presence of other impurities especially the absence of the formation of zeolite P. 5) Crystallization temperature and time. The crystallization temperature in hydrothermal condition is around 100 ± 3 o C since the crystallization is most satisfactorily effective at a temperature from 80 o C to 125 o C. At lower temperatures (below 200 o C), the crystals which are formed are smaller in size than those generated at higher temperature (Breck, 1964). Whereas the increasing temperature of crystallization favours the formation of the zeolite P followed ultimately by analcime (Breck, 1974). The crystallinity of the product normally increases in time. However, this is only partially true because zeolite synthesis is governed by the occurrence of successive phase transformation (Ostwald rule of successive phase transformation). As a result, the thermodynamically least favorable phase will crystallize first and will be successively replaced in time by more stable phases. In case of the Zeolite Y formation, the crystallization sequence is: amorphous Faujasite NaP

40 15 (Gismondine type) (Wetkamp et al., 1994). Therefore, with the aim to avoid such formation from occuring; crystallization time was fixed for 24 hours. In order to prevent contamination, Teflon and PTFE containers were used during the preparation of all solutions, for the reaction mixture and for the crystallization process. Glass vessels were not used and were avoided since glass participates in the reaction and silica, alumina and boron are known to be leached out of glass (Robson, 2001). These containers were washed with hydrofluoric acid (5%) before and after experiments to eliminate the silica and alumina as well as other contaminants contained inside the containers as the HF is known to able to dissolve these substances. After crystallization, it was necessary to filter the solid product immediately and washed with hot water because there was so much unreacted base left which can destroy the structure of the zeolite Y and reduce the degree of crystallinity. Washing with hot distilled water will eliminate these undesired substances (Bo and Hongzhu, 1998). During the synthesis, safety must be considered as the experiments involved hazardous materials. Measures taken include wearing gloves and face mask when handling the caustic materials. The reaction vessels were opened immediately after they were taken out from the oven (100 o C) in order to prevent damage to the vessel Seeding Technique Seeding and ageing are two important techniques in zeolite synthesis in order to obtain a pure crystalline phase with high percentage of desirable product as well as low impurities. Seeding is a technique in which the supersaturated system (seed gel) is inoculated with small particles of materials to be crystallized. The seeding method necessitates the preparation of two separate gels; seed gel is about 5 percent from overall and the remaining is feedstock gel. These two gels will be mixed together in the final part of the synthesis. Adding seed crystals to a crystallization system will result in increased crystallization rate. The enhanced rate might be due to the increasing existing

41 16 surface area but also might be the result of enhanced nucleation of new crystals (Robson, 2001). The secondary nucleation mechanism referred to as initial breeding results from microcrystalline dust being washed off of seed crystal surfaces in a new synthesis batch. These microcrystalline fragments grow to observable sizes and result in greatly enhanced crystallization rates due to the significantly increasing crystal surface area compared to the unseeded system. Consequently, it is to be expected that addition of seed to a synthesis system will introduce sub-micron sized crystallites into the system which will serve as nuclei. Finally, the same particulates which appear to catalyze zeolite nucleation in unseeded systems may remain in sufficient number to catalyze nucleation in seeded systems, since they are inherently present in the seed crystal sample and may be impossible to eliminate via typical filtration techniques. In the seeding technique, if the surface area provided by the seed crystals is larger than the one supplied by fresh nuclei, the seeding technique provides a favourable condition for measuring linear growth rates (Barrer, 1982) Ageing Ageing is a process in which the mixture of aluminosilicate is left for a period of time at room temperature or below the crystallization temperature. In case of the formation of zeolite Y, the appropriate period of time is 24 hours. Preliminary ageing of the reaction mixture at room temperature after gel formation followed by subsequent crystallization at a higher temperature of 100 o C improves the crystallization process because the ageing process will proceed more quickly than in the non aged case. During the gel aging, germ nuclei will be formed within the solution and they grow to observable sizes upon subsequent high-temperature synthesis (Cook and Thompson, 1988). After the initial gel formation, the aging step is necessary in order to equilibrate the heterogeneous gel mixture with the solution, resulted in the lower SiO 2 /Al 2 O 3 ratio in the gel necessary to form zeolite Y (Breck, 1974). Therefore, the ageing process will be emphasized during the synthesis progress as it can provide a major consequence in

42 17 successfully synthesizing zeolite NaY from rice husk ash with high percentage of zeolite Y in resultant product Characterization In general, the characterization of a zeolite has to provide information about structure and morphology, the chemical composition, the ability to sorb and retain molecules and the ability to chemically convert these molecules. Information on the structural, chemical and catalytic characteristics of zeolites is essential for deriving relations between their chemical and physicochemical properties on the one side and the sorptive and catalytic properties on the other. Such relations are of high importance, as they allow the rational development of sorbents, catalyst and advanced structural materials. In this study, the zeolite was synthesized from rice husk ash and the main uses are as cation exchangers and sorbent, thus only characterizations with respect to these applications are being dealt with in depth. There are many characterization techniques but the important ones in this study are X-ray diffractogram (XRD), infrared spectroscopy (IR), elemental analysis and ion exchange capacity (IEC). Each of the characterization techniques will be described below X-Ray Diffraction Technique For zeolites produced in the laboratory, X-ray powder diffraction data is the most commonly used to validate the synthesized zeolite and to identify a newly synthesized material as well as to monitor the effects of a post-synthesis modification. X-ray powder diffraction data is also the most commonly used technique as a fingerprint in the identification of a material because each crystalline solid has its own characteristic X- ray powder pattern (West, 1988). The measured pattern is compared to an existing one,

43 18 whether it is a pattern in the Collection of Simulated XRD Powder Patterns for Zeolites, the Powder Diffraction File (PDF) of the ICDD or an in-house data file (Robson, 2001). In recent days, the use of X-ray diffraction technique is of utmost importance in identifying the synthesized zeolite because of the general availability of powder X-ray diffraction facilities and the increasing application of computers to automate sample scanning and data analysis as well as to enable rapid collection of data on a large number of samples essentially in the absence of an operator (Jarman, 1985). Besides for identification material, XRD diffractogram provides much information such as the degree of crystallinity, the presence of other phases or impurities and the determination of crystal structure. The X-ray diffraction technique is based on the Bragg s Law. The Bragg approach to diffraction is to regard crystals as built up of layers or planes such that each acts as a semi-transparent mirror. Some of the X-rays are reflected of a plane with the angle of reflection equal to the angle of incidence, but the rest are transmitted to be subsequently reflected by succeeding planes. The derivation of Bragg s law is shown in Figure 1.3. The relation between lattice planes with a distance d, the angle of reflection, θ and measured at wavelength, λ can be described by Bragg s law in equation 1: n λ = 2d sinθ (1) The primary use of Bragg s law is in the determination of the spacing between the layers in the lattice for, once the angle θ corresponding to a reflection has been determined, d may readily be calculated. θ d Figure 1.2 Derivation of Bragg s law for X-ray diffraction

44 19 The mostly used XRD technique for zeolites is the powder diffraction technique because zeolite is mainly in the powder form. Powder diffraction techniques are used to identify a sample of a solid substance through the comparison of the positions of the diffraction lines and their intensities with a large data bank which can be acquired from the powder diffraction file, maintained by the International Centre for Diffraction Data (ICDD) and contains information of about crystalline phases. The principles of the powder diffraction technique are shown in Figure 1.4. A monochromatic beam of X- rays strikes a finely powdered sample that, ideally, has crystals randomly arranged in every possible orientation. In such a powder sample, the various lattice planes are also present in every possible orientation. For each set of planes, therefore, at least some crystals must be oriented at the Bragg angle, θ, to the incident beam and thus, diffraction occurs for these crystals and planes. The diffracted beams may be detected by surrounding the sample with a detector. Source filter sample Detector Figure 1.3 The illustration of the X-ray powder diffraction method The most important use of the powder method is in the qualitative identification of crystalline phases or compounds. While most chemical methods of analysis give information about the elements present in a sample, powder diffraction is very different and perhaps unique that it tells which crystalline compounds or phases are present with no direct information about their chemical constitution. The determination of the unit cell dimension of zeolites can also be obtained from the X-ray technique. Zeolites are in the form of crystal, thus its structure is built up of regular arrangements of atoms in three dimensions; these arrangements can be represented by a repeating unit or motif called the unit cell. The unit cell is defined as

45 20 the smallest repeating unit which shows the full symmetry of the crystal structure (West, 1988). The unit cell dimension of a freshly synthesized faujasite-type zeolite is a sensitive measure of composition which, among other uses, distinguishes between the two synthetic faujasite type zeolite, X and Y. The unit cell dimension, a of the zeolite can be calculated from the equation: a = {( d ) ( h k l )] (2) hkl + + where hkl = the miller indices (Ǻ) d = distance between reflecting planes having the Miller indices. The d-spacing can be derived from equation 1 as: 1 2 λ d hkl = (3) 2sinθ The wavelength of X-ray radiation ( λ ) for CuKα 1 is Ǻ ( nm). The value of unit cell dimension from this equation thus can be used to determine the Si/Al ratio of zeolite Y by Breck s equation (Breck, 1974): Si Al = 1 a (4) Hence, it is useful to characterize the raw material, synthesized zeolite and the modified zeolite by the X-ray diffraction technique as it can give many valuable information about the materials that had been studied Infrared Spectroscopy The fundamental basic theory of the infrared spectroscopy is that the infrared radiation will promote transitions in a molecule between rotational and vibrational

46 21 energy levels of the ground (lowest) electronic energy state (Cross and Jones, 1969). The vibrational modes, involving pairs or groups of bonded atoms can be excited at higher energy states by the absorption of radiation of appropriate frequency. In the infrared spectroscopy technique, the frequency of the incident radiation is varied and the quantity of radiation absorbed or transmitted by the sample is obtained. The infrared spectra of solids are usually complex with a large number of peaks corresponding to each particular vibrational transition. In order for a particular mode to be active towards infrared, the associated dipole moment must vary during the vibrational cycle consequently centrosymmetric vibrational modes are infrared inactive. Zeolites are crystalline aluminosilicates consisting of corner linked tetrahedral where the Al and Si atom lie at the centres of tetrahedral and oxygen atom lie at the corners. As a result, the vibrations of the framework of zeolites give rise to typical bands in the mid and far infrared. The usually used region of infrared for the characterization of zeolites is the mid-infrared region which is from 200 to 1300 cm -1 since it contains the fundamental vibrations of the Si, AlO 4 or TO 4 units in all zeolites framework (Rabo, 1976). In this region, there is a specific range for a typical band related to the zeolites structure that was studied by many earlier researchers in order to provide the information for the structural characteristics. Rabo (1976) reported that Flanigen, Khatami and Szymanski are the earlier researchers who studied the mid-ir spectroscopy in the characterizations of zeolite. The original assignments of the main IR bands were described in Table 1.3. (Robson, 2001). They classified the mid-ir vibrations for the zeolites structure into two types of vibrations which are related to the internal vibrations of the TO 4 tetrahedra and the vibrations primarily related to external linkages between tetrahedral. The internal vibrations mainly in the primary building unit in zeolite frameworks tend to be insensitive to variations in framework structure, while the external linkages are sensitive to the framework topology and to the presence of symmetrical clusters of tetrahedral in the form of larger polyhedra.

47 22 Table 1.3 : The assignments of the main infrared bands for zeolites i) Internal tetrahedral (Structure insensitive vibrations) a) cm -1 Asymmetrical stretch of Si-O-T b) cm -1 Symmetrical stretch of Si-O-T c) cm -1 T-O bend ii) External linkages (Structure sensitive vibrations) a) cm -1 Double ring vibrations b) cm -1 Pore opening vibrations c) cm -1 Asymmetrical stretch of Si-O-T d) cm -1 Symmetrical stretch of Si-O-T T = Si, Al The strongest band is in the region of 1250 to 920 cm -1 related to the T-O stretch and the next strongest band in the 420 to 500 cm -1 is from the T-O bending mode while stretching modes involving mainly the tetrahedral atoms are in the region of 650 to 820 cm -1. A band in the 500 to 650 cm -1 region related to the presence of the double rings in the framework structures which is observed in all of the zeolite structures that contain the double 4- and double 6-ring that can be found in zeolite Y (Breck, 1974). Although organic chemists are frequently concerned with the use of infrared spectroscopy data for the identification of compounds, it is also helpful for inorganic chemists to characterize the inorganic materials. However, the infrared spectroscopy data is barely used to support data from X-ray diffractogram which is the fingerprint for the identification of zeolites and its new derivatives. Besides that, the spectra is also used to compare between raw material (silica) and the synthesized zeolite. Flanigen (Rabo, 1976) from Union Carbide Corporation reported that the infrared spectroscopy can yield information not only on short range bond order and characteristics but also on long range order in crystalline solid caused by lattice coupling, electrostatic and other effects and can serve as very rapid and useful structural techniques. Additionally, infrared spectroscopy is also a valuable technique for exploring and studying the nature

48 23 of hydroxyl groups in zeolite, the interaction of cations with adsorbed molecules and the fundamental framework structure of zeolites (Gould, 1974). In the infrared spectrum of zeolites in the range of 300 to 1300 cm -1, for some of the structure sensitive and insensitive bands, a linear relation between the wavenumber and the number of lattice aluminum atoms (N Al ) is reported (Rabo, 1976). After calibration, it is possible to use this relation to derive the number of lattice aluminum atoms from the band positions. Since the structure insensitive asymmetric stretch (σ 1 ) ( cm -1 ) and the structure sensitive symmetric stretch band (σ 2 ) ( cm -1 ) frequencies increase with decreasing Al content in a linear manner, these frequencies can be used in the determination of the number of lattice aluminum atoms (N Al ) for zeolite Y. The number of Al in the framework of zeolite NaY sample can be calculated according to the following equation derived by Kubelkova et al. (1988) 3 N = σ ] [ N + N ] (5) Al [ 1 3 N = σ ] [ N + N ] (6) Al [ 2 Al Al Si Si where [N Al + N Si ] for zeolite Y is equal to 192. The value of the number of lattice aluminium atoms from equation 5 and 6 can be used for the calculation of Si/Al and SiO 2 /Al 2 O 3 ratio according to the equation 7 and 8, respectively: Si Al N Al = 192 (7) N Al SiO2 Al O N Al = (8) N Al 2

49 Elemental Analysis The structure of zeolite NaY consist of a three dimensional framework of SiO 4 and AlO 4 tetrahedra with the sodium cation to balance the framework charge while the water molecule is enclosed in the large cavities of the framework. Thus, the determination of the bulk elemental composition of zeolites is important in many aspects of zeolite synthesis, characterization and applications. This information is used to verify the synthesis formulation, the bulk of silica and alumina ratio (Si/Al ratio), the cations concentration, degree of ion exchange and the detection of contaminant elements such as impurities and poison (Robson, 2001). Corbin et al. (1987) had studied the comparison of analytical techniques for the determination of silicon and aluminium content in zeolites. The techniques include atomic absorption spectroscopy (AAS), neutron activation analysis (NAA), proton inelastic scattering, X-ray fluorescence (XRF), wet chemical, inductively coupled plasma-mass spectrometry (ICP-MS) and nuclear magnetic resonance (NMR). They concluded that the effectiveness of each of the technique differs from each other and requires the appropriate modification of the sample preparation prior to measurements. From their study it can be summarized that there are many techniques for the determination of elemental composition in zeolites. The elements and species that are important to be determined are sodium, aluminum, silica and water. The instrumental method to determine these elements involves inductively coupled plasma mass spectroscopy (ICPMS) for the determination of aluminium and flame atomic absorption spectroscopy (FAAS) for the determination of sodium cation. These instrumental techniques are the most common techniques employed for the determination of compositional metals because they offer the advantage of reducing interferences and matrix effects and have advanced accuracy, precision and speed well than classical wet chemistry. In general, the sensitivity of ICP-MS is better than the conventional flame AAS. However, flame AAS has rather better sensitivity for group IA elements, including sodium, hence the reason for the determination of sodium using AAS and aluminum with ICP-MS. Both ICP-MS and AAS necessitate that the sample be introduced as liquid, thus decomposition is necessary

50 25 prior to analysis and similar preparation schemes apply for both techniques. The approach for decomposition sample that are used in this research is the beaker digestion with hydrofluoric acid. The digestion requires the addition of hydrofluoric acid in order to solubilize the Si. Besides ICP-MS and AAS, the X-ray fluorescence (XRF) also can be used for the determination of composition in zeolites. As compared to ICP and AAS, the wavelength dispersive XRF had the benefit which include the ability to determine some non-metals, conceptually require simpler sample preparation and with improved precision. However, in many cases XRF cannot perform the complete characterization due to its poor sensitivity for light elements and sensitivity to changes in the matrix composition. While XRF has its greatest use in a controlled manufacturing environment, ICP and AAS is often the technique of choice in the research and development (R&D) environment. The determination of loss on ignition at a specified temperature and time will be used to determine the percentage of water. The results from the elemental analysis can provide information to calculate the ratio of silica to alumina which determines the thermal and chemical stability of the zeolite, the hydrophilic nature of the zeolite, the numbers and strength of the acid sites in the acid form and the capacity of the ion exchange. Breck and Tonawanda (1964) who was the first person to discover the zeolite Y had patented the zeolite Y having silica/alumina ratio above 3.0 and up to 6.0 since zeolite X had been defined as having silica/alumina ratios between 2.0 and 3.0. Changing the Si/Al ratio also changes its cation content and the stability. Fewer Al atoms means that the zeolites are more siliceous, thus fewer exchangeable cations will be present and the thermal stability improves Ion Exchange Capacity Because of zeolites are composed of crystalline aluminosilicates with the structure based on tetrahedral SiO 4 and AlO 4 units, connected by shared oxygen atoms,

51 26 they are one of the synthetics inorganic cation-exchangers. This kind of threedimensional structure has small pores where the exchangeable ions are located and where the ion exchange reactions take place. Silicon is tetravalent and aluminium is trivalent, which result in negatively charged framework structures. Thus each mole of aluminium produces one equivalent of cation exchange capacity for the zeolite framework. Ion exchange is a chemical reaction in which free mobile ions of a solid, the ion exchanger, are exchanged for different ions of similar charge in solution. The exchange reactions in typical zeolite can be written as follows: M + X - + N + N + X - + M + (9) Where: M + X - = Zeolite with M + is framework and X - is counterion. N + = Cation in the solution The ion exchange properties of zeolites are mainly based on the charge density and pore size of the materials (Breck, 1974). In zeolites where the internal void space consists of portions accessible only through smaller pores, the total ion exchange capacity may be available to the smallest ions but only part to larger ions. However, the majority of the total ion exchange capacity is available to the most common cations. Furthermore, the cation exchange behaviour also depends on the temperature, concentration of the cation species in solution, the anion species associated with the cation, the solvent, the structural characteristics of the particular zeolite and the nature of the cation species, size, both anhydrous and hydrated and cation charge (Breck, 1974). In addition, the chemical composition is also the factor governing the cation exchange of zeolite as a higher exchange capacity. This is observed with zeolites of low silica per alumina ratio since each AlO 4 tetrahedra in the zeolite framework provides a single cation exchange sites. Zeolite X exhibits higher cation exchange capacity than zeolite Y because it has lower silica to alumina ratio hence higher framework charge. Cation exchange capacity (CEC) can be defined as the sum of the exchangeable cations that a mineral can adsorb at a specific ph, i.e. a measurement of the negative

52 27 charges carried by the mineral (Wilson, 1994). The ion exchange capacity of zeolite ion exchanger is a function of their silicon oxide/aluminium oxide mole ratio, since AlO 4 tetrahedra in the zeolite framework provides a single cation exchange sites (Sherman, 1978) and its commonly measured in terms of moles of exchangeable cation per gram (or 100 grams) of zeolites, moles/g or in terms of equivalents of exchangeable cation per gram (or 100 grams) of zeolites, meq/g. Using CEC expressed in terms of miliequivalents per gram (meq/g) makes it easy to compare how much of any cation can be exchanged by a particular zeolite, without having to worry about the charge on the cation involved. The exchange process involves replacing one singly-charged exchangeable atom in the zeolite by one singly-charged atom from the solution, in this study; the singly-charged atom that is used to exchange sodium cations in zeolite NaY is ammonium cation, NH + 4 which possesses single charged ion. So, it is of utmost importance to know and verify the ion exchange capacity of the synthesized zeolite because the main function of the zeolite in this study is for ion exchange with heavy metals in the aqueous phase. The total cation exchange capacity is the sum of external cation exchange capacity (ECEC) and internal cation exchange capacity. Because of large molecule of hexadecyltrimethyl ammonium, HDTMA, this molecule cannot enter the angstrom size of pore zeolite and will exchange on the surface of zeolite. The measurement ECEC is to differentiate between internal and external cation exchange sites that would enable better investigation of changes in modified mineral properties as a function of surfactant loading and also to characterize the exchange capacity of the mineral surface for HDTMA (Li and Bowman, 1997). Therefore, it is essential to determine the external cation exchange capacity by using HDTMA cation as the exchanged cation before the modification of zeolite surface. From the measured external cation exchange capacity, the maximum uptake of the HDTMA will be known and will provide information for internal cation exchange capacity.

53 Surfactant Modified Zeolite Some of the toxic metals may exist as cations, anions, non-ionized species and complex macromolecules in the aqueous phase (Sengupta, 2002), for instance, arsenic which is prominently carcinogen, can form anion as arsenate (As(V)) and non-ionized species as arsenite (As(III)). Another known toxic metal in water is chromium (Cr) which can also form Cr 3+ cation (Cr(III)) and the anionic form as chromate, CrO 2-4 for Cr(VI). Therefore, the materials that can remove this kind of toxic metals simultaneously in the water body are of great importance with regards to the water purification or wastewater treatment. To achieve this result, the composite ion exchanger has to be developed, for which it shall contain the properties of cation and anion exchanger at the same time. In order to sorb anion and cation, the modified surface must possess positively and negatively charged exchange sites. However, a typical zeolite cannot remove or sorb the anion species as its surface is in the anionic charges. By treating the zeolite with a cationic surfactant, an organic covering is created on the external zeolite surfaces and the charge is reversed to positive charge. Therefore, the modification surface of zeolite by cationic surfactant (i.e. HDTMA) can be made according to the successful clinoptilolite modified with HDTMA by Li and Bowman (1997) and they called it surfactant-modified zeolite (SMZ). Laboratory batch and column tests demonstrate that SMZ can simultaneously remove multiple types of contaminants from water, including inorganic anions such as chromate and hydrophobic organics such as chlorinated solvents and fuel components (Li et al., 1998b). Zeolite NaY resembles natural zeolite minerals that have permanent negative charges on their surface and large cation exchange capacity (CEC) which enables them to be modified by cationic surfactant to enhance their sorption of organic and anionic contaminants in water. The surfactant that is commonly employed to be attached on the zeolite surface in the previous studies is HDTMA, the quaternary amine hexadecyltrimethylammonium cation which is a long chain cationic surfactant that possesses a permanent positive charge. The HDTMA is in the group of cationic surfactant where they have positively

54 29 charged hydrophilic head group generally amine, attached to a hydrophobic tail of hydrocarbon moiety. The structure of the HDTMA is shown in Figure 1.5. The HDTMA structure consists of permanently charged trimethyl ammonium head group attached to a 16-carbon chain. It can be obtained as common salts such as HDTMA-bromide and HDTMA-chloride. Since the uses of this surfactant are mainly as hair conditioner, mouthwash and fabric softeners, it is assumed that low levels of HDTMA will not be harmful to the environment. The critical micelle concentration (CMC) is the minimum concentration of the surfactant needed to form a micelle and for HDTMA-Br is 0.9 mmol/l. The individual surfactant molecules will self associate into micellular clusters above the CMC. Hydrophobic tail 16 chain hydrocarbon Hexadecyl + N Br - Hydrophilic head Trimethyl ammonium Positive charge Bromide anion Negative charge Balance the ammonium charge Figure 1.4 The structure of hexadecyltrimethyl ammonium bromide (HDTMA-Br) Depending on the chemical structure of the cationic surfactant, it is possible to make a hydrophilic solid behaves as if it was hydrophobic or (less usual) to make a hydrophobic solid behave as if it were hydrophilic (Porter, 1994). When the adsorption of a surfactant onto a solid surface is considered, there are several quantitative points that are of interest. They include: i) The amount of surfactant adsorbed per unit mass of solid. ii) The solution surfactant concentration required to produce a given surface coverage or degree of adsorption. iii) The surfactant concentration at which surface saturation occurs. iv) The orientation of the adsorbed molecules relative to the surface saturation occurs.

55 30 v) The effect of adsorption on the properties of the solid relative to the rest of system In all of the above, it is assumed that such factors as temperature and pressure are held constant. The maximum surfactant loading on zeolite surface is a function of surfactant type, chain length and counter ion type (Li and Bowman, 2001a).Thus, the surface properties of zeolite can be modified by using cationic surfactants HDTMA because the surface of zeolite is the net negative charged resulting from isomorphic substitution of cations in the crystal lattice. Theoretically, when the zeolite contacting with HDTMA above the CMC in the aqueous phase, the HDTMA cation will selectively exchange with the inorganic cations on the external surface of zeolite framework. In the case of zeolite NaY, sodium cation (Na + ) will be exchanged and forms a surfactant bilayer with anion exchange properties. The equation of the exchange can be described below: 2M - Na + + HDTMA + M - Na + HDTMA + + Na + (10) where M is the framework of zeolite having negatively charge. The HDTMA molecule will be exchanged with the zeolite s cation in the external framework and limited exclusively to external surface of zeolite particles because the HDTMA molecule is too large to penetrate the internal pore spaces of the zeolite or to access the internal cation exchange positions since it has a long chain quaternary ammonium cations. The sorption of cationic surfactant onto a negatively charged surface of zeolite involves both cation exchange and hydrophobic bonding (Li and Bowman, 1997). It was suggested that at low loading levels of HDTMA exposed to a negatively charged zeolite surface, it will be retained by ion exchange and eventually form a monolayer at the solid-aqueous interface. At this stage, the surfactant molecules exist as monomers in aqueous solution at concentrations below the CMC which is typically below 1 mmol/l. When the surfactant concentration is greater than CMC, the surfactant molecules

56 31 associate to form solution micelles in addition to monomers. As the amount of HDTMA increases and the initial surfactant concentration is greater than CMC, the interaction among the hydrocarbon tails causes the formation of a bilayer or patchy bilayer with the first layer retained by cation exchange and the second layer by hydrophobic bonding and stabilized by counter ions. The sorbed surfactant creates an organic-rich layer on the zeolite surface and the charge on the surface is reversed from negative to positive. The positively charged head groups are then balanced by counter ions. A model for the interaction of HDTMA on the external surface of zeolite is shown in Figure 1.6. This theoretical phenomenon shows that the anion that counterbalanced the positive charge from HDTMA will be exchanged by more strongly held counter ions while the organic partitioning will absorb organic substances and the outer cations will be replaced with cation that neutralizes zeolite from the internal pore. H 3 AsO 3 CrO 3- Br - CrO 3- CrO 3- Cr 3+ Na + Br - + Br - Br - Br - Br - Br - Br H 3 AsO Anion exchange Organic partitioning Cation exchange Na Zeolite surface Figure 1.5 Schematic diagram of HDTMA micelle formation in solution and admicelle formation on the zeolite surface and the uptake substance onto surfactant modified zeolite. Along with its unique properties, the resultant surfactant modified zeolite (SMZ) is capable of simultaneous sorption of anions, cation and non-polar organic molecules from water.

57 32 The advantages of surfactant modified material are that it can be used to eliminate multiple types of undesired contaminants elements in water which are inorganic cation (e.g.; Pb 2+, Cd 2+, Cr 3+ ) and inorganic anion (e.g.; chromate, selenate, arsenate) as well as organic substances (e.g.; perchloroethylene (PCE), trichloro ethylene (TCE), benzene, toluene, ethylene and xylene (BTEX)) all together. The surfactant modified zeolite proved to be chemically and biologically stable at a long term period. Li et al. (1998b) studied the long term chemical and biological stability of surfactant modified natural zeolite, and they concluded that the SMZ was stable in high ionic strength, high and low ph environments, under both aerobic and anaerobic conditions and moreover resistant to microbial degradation. Recently, clinoptilolite is the natural zeolite that is mostly used in order to create the SMZ for the adsorption and removal of many types of contaminants in water and it has been working successfully. The studies on the use of SMZ from clinoptilolite for environmental remediation were limited to the removal of organic contaminants from water until Haggerty and Bowman (1994) showed that SMZ significantly increased the sorption of chromate. The sorption of chromate was attributed to anion exchange on the outermost surface created by the sorbed surfactant bilayer (Li et al., 1998a). Besides sorption of chromate, SMZ has also been proven to sorb other oxyanions such as sulphate (SO 2-4 ) and selenate (SeO 2-4 ) (Haggerty and Bowman, 1994), nitrate (NO 2-3 ) (Li, 2003) and also dihydrogenphosphate (H 2 PO - 4 ) (Vujakovic et al., 2000). Li et al. (2002) also reported that cation exchange by SMZ is reduced compared to the unmodified zeolite. They observed that the reduction in metal cation uptake by the SMZ is controlled by the surfactant loading on the zeolite surface and by the type of metal cations. There are many papers which reported on the sorption of organic contaminants in water by SMZ. Bouffard and Duff (2000) applied SMZ as adsorbents for the removal of dehydroabietic acid (DHA) from a model process white-water, Li and Bowman (2001a) studied the regeneration of SMZ after saturation with perchloroethylene, Hayakawa et al. (2000) used zeolite P and X that had been attached with hexadecyl-, tetradecyl- and dodecyltrimethylammonium bromides as a drug carrier and the release of chloroquin (CQ), besides that, SMZ as the new efficient adsorbents for mycotoxins was

58 33 studied by Tomasevic-Canovic et al. (2003). These literature reviews show that SMZ has many uses in the purification of water as the contaminants exist in many forms, cationic, anionic, neutral and organic form. 1.5 Toxic Metals in Water Heavy metals are metallic elements that have a high atomic number and are toxic to living organisms. Because they are toxic, heavy metals are sometimes referred to as toxic metals (Young, 2000). There are approximately 30 different toxic metals that have impacts upon human health and each of them will produce different behavioral, physiological and cognitive changes in an exposed individual. Examples of toxic metals are chromium (Cr), arsenic (As), selenium (Se), cadmium (Cd), nickel (Ni), lead (Pb), mercury (Hg), manganese (Mn), cobalt (Co), zinc (Zn) and copper (Cu). Although arsenic (As) and selenium (Se) are the elements on the border between metals and nonmetals and are known as metalloids, they are also considered as toxic metals because of their toxicity and well-known carcinogence since they exhibits some metallic properties. Heavy metals in natural waters may be suspended (particles >100 nm in size), colloidal (particles in the intermediate range between suspended and soluble) or soluble (particles <1 nm) (Rubin, 1974). The suspended and colloidal particles may consist of individual or mixed metals in the form of their hydroxides, oxides, silicates, sulfides or as other compounds, or they may consist of clay, silica or organic matter to which metals are bound by adsorption, ion exchange and complexation. The soluble metals may be ions, simple or complex or un-ionized organometallic chelates or complexes. Heavy metals enter the water systems; surface water, groundwater, supplied tap water and rain water from a variety of sources and can be divided into three major sources which are nature, human activities and agriculture. The largest natural source exposed to surface water is directly from rocks and soils. Dead and decomposing

59 34 vegetation and animal matters, also contribute small amounts of metals to adjacent waters. Large quantities of metals in water are also contributed from wet and dry fallout of atmospheric particulate matters derived from natural sources, for instance, the dust from the weathering of rock, from volcanic eruption and the smoke from forest fires and micrometeorites dust (Young, 2000). The second major source of heavy metals in the water system is from human activities that pollute and contaminate the water bodies through direct discharge of various treated or untreated municipal, residential or industrial effluents. Many of the toxic metals discharged in surface and groundwater are from the industrial wastes such as from the industries of metal mining operations, metallurgical, electroplating industries and tanneries (Rubin, 1974) mostly from wastewater treatment process especially located in big town areas. The concentration of various metals in industrial discharges depends upon the type of industries, specific processes operations and the wastewater treatment system. Besides that, the contamination of heavy metals in water is also contributed from illegal disposal of industrial effluents. The source of heavy metals in the natural water by human activities also include land clearing which is primarily related to the lumbering industry and the construction industry as well as for agricultural purposes. The clearing of land can be subjected to extreme erosion particularly during the construction period; hence increasing the potential for the carrying of heavy metals to the aquatic environment. In the domestic sewage, the amounts of metals may vary according to water usage, quantity and types of food eaten, time of year, economic status and the sewage system (Rubin, 1974). In supplied tap water, heavy metals come from the corrosion of the metal pipes used to carry water to consumers (Bailey et al., 1999). Agricultural activities also affect the source of metals in water particularly in the rural region. The used of fertilizers by humans applied to the soil and the death and subsequent decomposition of plants can affect the distribution of metals in groundwater. In addition to these sources, the lowering of ph in rain and surface water and the increased and widely used surfactants in consumer and industrial product have greatly enhanced the mobility of heavy metals in the environment (Sengupta, 2002).

60 35 Toxic metals can be distinguished from other toxic pollutants, since they are nonbiodegradable and can accumulate in living tissues, thus becoming concentrated throughout the food chain (Korngold et al., 1996). It is well known that toxic elements and their discharge into receiving waters cause detrimental effects on human health and will constitute a great risk for the aquatic and environment system. The health hazards presented by heavy metals depend on the level of exposure which are generally divided into two classes: acute exposure and chronic exposure. Acute exposure refers to contact with a large amount of the heavy metals in a short period of time whereas chronic exposure refers to contact with low levels of the heavy metals over a long period of time (Young, 2000). The toxicity of heavy metals is attributed to harmful and even lethal effects on the human body, particularly on the central nervous system, causing mental disorders such as fatigue, insomnia, decreased concentration, aggressive behaviour, memory loss, learning deficits, depression, irritability, gastric symptom, sensory symptom and motor symptom, and to the physical manifestations such as liver and kidney dysfunction, infertility, gout, hypertension, headache and Candida (yeast) infections (An et al., 2001). One of the papers reported from India, which is one of the countries having problems of increasing toxic metals in water system affecting many people; Singh et al. (2004) had studied the impact of the toxicants discharged from sewage treatment plants on the health, agricultural and environmental quality in the wastewater disposal area. The impact of the wastewater toxicants (metals and pesticide) on human health in the areas receiving wastewater was assessed through a standard questionnaire containing a total of 35 items, which cover eight neurobehavioral functions established to be affected by the chemicals exposures. The studied population was divided into exposed and unexposed groups. They found that there was a significant difference in the overall analysis between the exposed and unexposed population group. The levels of the metals in the human blood and urine samples of the exposed and unexposed groups were also studied to confirm the analysis of the questionnaire and they found that the levels of metals in the samples were higher in exposed population than those unexposed population groups. Thus, they concluded that there has been a considerable impact of these toxicants on human health in the exposed area.

61 36 The problems of toxic metals distribution and its toxicity in aquatic system are global problems which give pressure to the federal and state governments to overcome this issue. Growing levels of toxic metals pollution in the natural water system related to the evolution of the industrial and agricultural activities demand effective approach to overcome this problem Chromium Chromium is a transition metal, one of the elements found between group II and III in rows 4 through 6 of the periodic table. Its atomic number is 24, its atomic mass is and its chemical symbol is Cr. Chromium is one of the toxic metals that has been studied because it can be formed in both cationic and anionic in water. Chromium exists in oxidation states +2, +3, +4, +5 and +6, but the most common, stable and abundant forms are chromium (III) and chromium (VI) (Katz and Salem, 1994). Chromium (III) exists in the form of cation, Cr 3+ and it occurs naturally in the environment while chromium (VI) exists in the anionic form (chromate) produced by industrial process for laboratory reagents and manufacturing intermediates. Each of both forms has a unique chemistry and behaviour; for example, the chemical form of chromium is largely determined by their potential toxicity as Cr(VI) is believed to be carcinogenic in humans while Cr(III) is actually an essential micronutrient (Katz and Salem, 1993). In the aqueous solutions, Cr(VI) is very soluble and exists in the form of chromic acid (H 2 CrO 4 ) and in the form of dichromate (Cr 2 O 2-7 ) while in neutral solutions, Cr(VI) is present in the form of HCrO - 4 and CrO 2-4 (Korngold et al., 2003). Chromium is an ubiquitous element, not only because of its occurrence in nature, but also due to the many anthropogenic sources resulting from its widespread industrial application (Martinez-Bravo et al., 2001). Chromium and its compounds are used in refractories, drilling mud, electroplating cleaning agents in the metal finishing industry, mordants in the textile industry, catalytic manufacture, fungicides and wood

62 37 preservatives, in the production of chromic acid and specialty chemicals. They are also used as a constituent of inorganic pigments, as a sensitizer in the photographic industry, as dyes and pigments and in medicinal astringents and antiseptics. Other uses for chromium and its compounds include organic chemical synthesis, leather treatment, photomechanical processing and industrial treatment, including treatment of cooling tower water (Katz and Salem, 1994). As chromium is very widely used, there are many sources of leaching the chromium into the natural water system and it should be removed practically. Cr(VI) is toxic and a carcinogenic. It is quite soluble in the aqueous phase almost in the entire ph range and mobile in the natural environment. The carcinogence and toxicity of Cr(VI) is based on its state where the chromate anion resembles the form of sulfates and phosphate (Costa, 2003). In addition, the toxic nature of the Cr(VI) ions is attributed to their high oxidation potential and their relatively small size, which enables them to penetrate through biological cell membranes (Balarama-Krishna et al., 2005). At physiological ph, Cr(VI) exists as an oxyanion, with an overall charge of minus 2 having borrowed electrons from oxygen. In this form, Cr(VI) resembles oxyanions, such as sulfates and phosphates, which are used extensively in humans for many diverse biochemical processes. The individual cells of the body need to take up sulfate and phosphate and have active systems that transport these nutrients. However, chromate fools the cell s anion uptake system into thinking that Cr(VI) is sulfate or phosphate and the cells transport chromate from the outside of the cell into its interior. Thus, if chromate is delivered to any cell in the body regardless of the route of exposure it will be taken up into the cell. In contrast, Cr(III) does not resemble any biological nutrient and has no similar way to enter the cell. However, it is possible that Cr(III) may be oxidized into Cr(VI) in the appropriate condition, hence the toxicity of Cr(VI) take place. Usually, Cr(III) is readily oxidized to the hexavalent state at high ph (Katz and Salem, 1993). Presently, Cr(VI) has been recognized as a probable agent of lung cancer and it also produces gastrointestinal disorders, dermatitis and ulceration of skin in man (Balasubramanian and Pugalenthi, 1999).

63 38 The regulation for the limitation of the chromium concentration in water should be highlighted and emphasized in every country due to the toxicity, reactivity and probable carcinogens of chromium. Acceptable limits for the chromium in water differ in almost every country. As a guideline, the World Health Organization (WHO) recommends a maximum level of 50 μg/l (ppb) for Cr(VI) in drinking water (Zu, 1993) and the National Institute for Occupational Safety and Health (NIOSH) recommends that the levels of chromium should be reduced to 10-3 mg/m 3 (Rengaraj et al., 2003). The Environmental Protection Agency (EPA) has set the MCL (Maximum Contaminant Levels) at 0.1 ppm in drinking water because EPA believes, given the present technology and resources, this is the lowest level where the removal of this contaminant can be achieved in drinking water Arsenic Arsenic is the third member of the nitrogen family, which consists of elements in group 15 of the periodic table. Its atomic number is 33, its atomic mass is and its chemical symbol is As. Arsenic is characterized more by its ubiquity than by its abundance. Arsenic is a naturally occurring metalloid element, the 20 th most abundant element in the earth s crust and is the 12 th most abundant element in the human body (King, 1994). As a metalloid, arsenic has both metallic and nonmetallic properties. Arsenic displays various oxidation states that are -3, 0, +3 and +5. The commonly encountered oxidation states of arsenic in water are +3 (As(III) or arsenite) and +5 (As(V) or arsenate) of which the former mostly exist in the neutral form while the latter exist in the anionic form. The major chemical form in which arsenic appears to be thermodynamically stable is arsenate ion. At moderate or high redox potentials arsenic can be stabilized as a series of pentavalent (arsenate) oxyanions, H 3 AsO 4, H 2 AsO - 4, 2- HAsO 4 and AsO 3-4. However, under most reducing (acid and mildly alkaline) conditions and lower redox potential, the trivalent arsenite species (H 3 AsO 3 )

64 39 predominate (Mandal and Suzuki, 2002). The structures for arsenates and arsenite species are shown in Figure 1.6. O O As As HO OH OH HO O OH - (a) H 3 AsO 4 (b) H 2 AsO 4 - O As 2- O As HO O O O O O 2- (c) HAsO 4 3- (d) AsO 4 As HO OH OH (e) H 3 AsO 3 3- Figure 1.6 form of arsenite (e) species. The structure of the anion form of arsenate (a, b, c and d) and the neutral Arsenic is very widely distributed in nature with its abundance on earth is thought to be about 5 parts per million (Young, 2000). In waters, it occurs in rivers, lakes, streams, groundwater and in the seas and oceans. The arsenic concentration of most potable waters seldom exceeds 10 ppb, although values as high as 100 ppb have been reported (Cleseri et al., 1989). Exposure to arsenic may come from natural sources, from industrial sources or from food or beverages. Arsenic is increasingly being found in water in many parts of the world such as Bangladesh, Taiwan, Chile, West Bengal- India, Mexico, Argentina, Canada, Hungary and some parts of USA; Utah, Western Oregon and California (Mandal and Suzuki, 2002). The arsenic polluted areas of the world can be geologically subdivided into areas made of sediments derived from water or volcanic rocks characterized by the presence of geysers, gold and uranium mining areas (Kundu, 2004). These elevated arsenic concentrations are mostly of natural origin.

65 40 Most arsenic is used in the form of compounds of which As 2 O 3 is the sole basic material. The largest consumers of arsenic trioxide are the USA, Malaysia and the UK (Merian, 2004). The uses of arsenic are to make alloys mostly with lead, transistor and light-emitting diodes (LEDs) and also in wood preservatives as CCA (Chromated Copper Arsenate) (Young, 2000). Arsenic and its compounds are toxic, poison and carcinogenic to animals and human with Arsenite (As(III)) is generally considered more acutely toxic than arsenate (As(V)). Arsenate and arsenite are thought to elicit acute toxicity via different mechanisms where arsenate mimicks phosphate and interfering with ATP production in the mitochondria while arsenite binds to and inactivates sulfhydryl-containing enzymes (Lantz et al., 1994). In low doses, arsenic produces nausea, vomiting and diarrhoea while in larger doses, it causes abnormal heart beat, damage to blood vessels and a feeling of pins and needles in hand and feet. Long term exposure to arsenic and its compounds can cause cancer where the inhalation can result in lung cancer and if swallowed, cancer is likely to develop in the bladder, kidneys, liver and lungs (Newton, 1999). Large doses of inorganic arsenic can cause death. The specific disease called arsenocosis that be related only if the doses of inorganic arsenic compounds are higher in the human body. Since arsenic is well known as toxic and carcinogenic that affects many people around the world, the Safe Drinking Water Act requires Environmental Protection Agency (EPA) to revise the existing 50 ppb standard for arsenic in drinking water. On January 22, 2001 EPA adopted a new standard and public water must comply with the 10 ppb standard beginning January 23, 2006 (EPA, 2001). In addition, arsenic is the one substance that is considered to be potential occupational carcinogens by National Institute for Occupational Safety and Health (NIOSH). In addition, the provisional guideline value recommended by the World Health Organization is 10 ppb (WHO, 1993).

66 Removal of Toxic Metals in Water As discussed in the previous sections chromium and arsenic are very toxic, carcinogenic and very harmful to human beings, in addition, the requirement to comply with the regulation made by the governments, the importance of removing both toxic metals in various sources before discharging them into surface water streams or for drinking water are very crucial. With the purpose to reduce or eliminate the concentration and quantity of both metals, the treatment of the affected water can be done by using many types of techniques and methods such as filtration, chemical precipitation, coagulation, ion exchange, adsorption, electrodeposition, reverse osmosis, cementation, solvent extraction and biological processing. All these approaches have their inherent advantages and limitation. The oldest and most frequently used method for removal those toxic metals from wastewater are precipitation. Although this process is effective to remove a large amount of toxic metals, it has some disadvantages. It produces a large amount of sludge which has a long settling time and harmful to the soil. For this reason, adsorption processes has been and actually are the most frequently applied method in the industries instead of precipitaion and consequently the most extensively studied. Recently, a wide range of sorbent is available for the removal of chromium from water especially the hexavalent chromium (chromate) since the toxicity and solubility of chromate anion is well-known to be extremely higher than trivalent chromium. The surfactant modified zeolite from the natural zeolite, i.e. clinoptilolite, is widely used to remove chromate from water (Ghiaci et al., 2004; Li, 2004; Haggerty and Bowman, 1994; Vujakovic et al., 2000). The other sorbent used for the removal of chromate includes biosorbent, for instance, chitosan (Schumi et al., 2001; Bodu et al., 2003), hazelnut shell (Cimino et al., 2000), sargassum sp. biomass (Cossich et al., 2002), Aeromonas cavidae (Loukidou et al., 2004) and bacillus sp. (Nourbakhsh et al., 2002), the ion exchanger resins in the anionic form (Korngold et al., 2003), the activated carbon (Selvi et al., 2001; Babel and Kurniawan, 2004) and coals (Lakatos et al., 2002). Since the toxicity of trivalent chromium is greatly less than hexavalent chromium, only a little

67 42 has been reported in the removal of trivalent chromium from water. The sorbent for the trivalent chromium includes biosorbent such as brown seaweed biomass (Yun et al., 2001) and Saccharomycess cerevisiae (Ferraz et al., 2004). Besides that, the ion exchanger resin in the cation form (Rengaraj et al., 2001; Rengaraj et al., 2003), zeolite (Barros et al., 2004; Bosco et al., 2005), bentonite (Chakir et al., 2002) and activated carbon (Cordero et al., 2002) have been used to remove trivalent chromium from water. Numerous sorbents have been developed to remove arsenic from water. The sorbent used for the removal of arsenate and arsenite from water are natural zeolitesclinoptilolite (Elizalde-Gonzalez et al., 2001b), cement (Kundu et al., 2004), granular ferric hydroxide (Thirunavukkarasu et al., 2003), zero-valent iron (Bang et al., 2005), iron hydroxide-coated alumina (Hlavay and Polyák, 2005), iron oxide-loaded slag (Zhang and Itoh, 2005), ferruginous manganese ore (Chakravarty et al., 2002), red mud (Altundogan et al., 2000), iron(iii) phosphate (Lenoble et al., 2005), Zr-loaded lysine diacetic acid chelating resin (Balaji et al., 2005), nanocrystalline titanium dioxide (Pena et al., 2005) and mesoporous alumina (Kim et al., 2004). Since the arsenate and arsenite exist in different forms in water, some sorbents cannot remove both species simultaneously. The commonly used sorbent for arsenate removal from water recently are synthetic zeolite (Shevade and Robert, 2004), natural zeolites (Xu et al., 2002), natural iron ores (Zhang et al., 2004), synthetic akaganeite (Deliyanni et al., 2003), strong-base anion-exchange resins (Korngold et al., 2001), metal-loaded clay (Lazaridis et al., 2002), Ce(IV)-doped iron oxide (Zhang et al., 2003) and biosorbents such as P. chrysogenum biomass (Loukidou et al., 2003). Papers reported on the removal of arsenite from water is limited since arsenite (As(III)) is difficult to be removed from water using normal available treatment process. It is usually necessary to change the trivalent arsenic to the pentavalent form by adding an oxidant, generally chlorine (Kartinen and Martin, 1995). There is no paper found reporting the removal of arsenic from water by surfactant-modified zeolite, however, Sullivan et al. (2003) had reported the sorption of arsenic from water soil-washing leachate since the pentavalent arsenic resembles chromate that can undergo anion exchange by surfactant modified zeolite.

68 Adsorption Theory The removal of toxic metals from sorbent is based on the adsorption at solidliquid interfaces. Adsorption from dilute aqueous solution onto the particulate matter present in suspension may involve specific chemical interaction between adsorbate and adsorbent. The most common interactions of this type include an ion exchange process in which the counter ions of the substrate are replaced by ions of similar charge. The experimental determination of the extent of adsorption usually involves shaking a known mass of adsorbent with a solution of known concentration at a fixed temperature and fixed period of time. The concentration of the supernatant solution is then determined by chemical means, which equilibrium conditions have been established. An adsorption isotherm is a graphical representation showing the relationship between the amounts adsorbed by a unit weight of adsorbent and the amount of adsorbate remaining in test media at equilibrium and at a fixed of temperature. The major factors determining the shape of an isotherm are the number of compounds in the solution, their relative adsorb abilities, the initial concentration in the solution, the degree of competition among solute for adsorption sites and the characteristic of the adsorbent. Equilibrium studies on adsorption provide information about the capacity of the adsorbent or the amount required to remove a unit mass of pollutant. The most widely used isotherm equation for modelling the adsorption are the Langmuir and Freundlich models. The simplest theoretical model that can be used to describe monolayer adsorption is the Langmuir equation. The Langmuir equation is based on a kinetic approach and assumes a uniform surface, a single layer adsorbed material at constant temperature. The Langmuir equation is: where: x m C e x m bq C o e = (11) 1 + bce : mass of adsorbate adsorbed (mg or mmol) : mass of adsorbent (g or kg) : equilibrium concentration (mg/l or mmol/l)

69 44 b Q o : langmuir constant related to the affinity of the binding site. : maximum adsorption at monolayer coverage (mg/g or mmol/kg) The equation (11) can be simplified, if: x = q = amount adsorbed at equilibrium (mg/g or mmol/kg) (12) e m Therefore: q e bq C o e = (13) 1 + bc e The nonlinear form (equation 13) can be evaluated by transforming to the linear equation: m = = + (14) x q Q bq C e o o e m When or against, a straight line graph is obtained with slope is x qe Ce bqo and 1 intercept-y is. Q o The Freundlich is an empirical equation based on the distribution of solute between solid phase and aqueous phase at equilibrium. The basic Freundlich equation is: x m e f 1 n e = q = K C (15) The abbreviation in equation 15 is similar to the Langmuir equation except for K f and n is the empirical Freundlich constant. Equation 15 can be rearranged into a linear form: x 1 log = log qe = log K f + logce (16) m n

70 45 When x log or log q e against logce, a straight line graph is obtained where the slope is m 1 and the intercept-y is log K f. n 1.7 Research Background and Objectives of the Study. In order to remove the toxic metals, i.e. chromium and arsenic that can exists in the form of cation (Cr(III)), anions (Cr(VI) and As(V)) and neutral (As(III)) species as H 3 AsO 3 in water depending on the oxidation states and the condition of water especially the ph of solution, the materials which have the properties of anion and cation exchanger simultaneously are essential and have to be developed. Therefore, the most important aim of this study is to develop such materials by attaching the zeolite with the cationic surfactant. Prior to modify the zeolite surface by cationic surfactant, the highly pure zeolite NaY must be produced and characterized by various characterizations techniques. The synthesis of the zeolite NaY requires a source of silica as a main raw material, hence, the rice husk ash which is known to have high content of silica can be used. In addition, the rice husk is produced in abundance in Malaysia as agro-waste and which needs to reprocess to value added product and thus to solve the environmental problem. The zeolite is well-known having permanent negative net charges allowed to cation exchanger and by attaching it to cationic surfactant, the external surface of zeolite may have positive charges resulting from the double layers provided by the hydrophobic bonding of surfactant at the external surface of zeolite enabling anion exchange. Thus, it can be used to sorb cation and anion species in aqueous solution. The objectives of the study are as follows: 1) To prepare and characterize the rice husk ash as a raw material. 2) To synthesize zeolite NaY from rice husk ash as a source of silica. 3) To characterize the synthesized zeolite NaY by various methods.

71 46 4) To prepare the surfactant-modified zeolite Y by modifying the surface of zeolite NaY with cationic surfactant (HDTMA). 5) To characterize the surfactant-modified zeolite Y by a variety of methods. 6) To study the effectiveness of the modified and unmodified zeolite for the removal of Cr(III), Cr(VI), As(III) and As(V) from water.

72 CHAPTER 2 MATERIALS AND METHODS 2.1 Preparation of Rice Husk Ash The raw material, rice husk was obtained from Bernas (Beras Nasional) milling, Selangor. Rice husk ash that was used as a source of silica in the synthesis of zeolite was prepared through physical combustion in a Plug Flow Combustor (PFC), located at the Solid State Laboratory, MTDC Building at Universiti Teknologi Malaysia (UTM). Prior to burning, the rice husk was washed by immersing them in distilled water to eliminate undesirable materials such as rice, sand and other agricultural wastes. The rice husk was then dried under sunlight for a period of time until the entire rice husk was completely dried. Then, the dried rice husk was burnt in the PFC at a constant temperature of 600 o C and constant pressure for an hour to ensure that the product is in an amorphous silica phase. The product obtained was white with slightly blackish powder form. The rice husk ash was ground using a mortar to homogenize and to get a powdered form of the material. The rice husk ash obtained from this process was labeled as RHA and it can be readily characterized and used as a source of silica in the synthesis of zeolite NaY.

73 Characterization of Rice Husk Ash. The preparation of the rice husk ash is to provide a source of silica for the synthesis of zeolite, thus a few characterization techniques related to the structure and the amount of silica produced were carried out. The characterization of the rice husk ash was done involving X-ray diffraction technique (XRD), infrared spectroscopy (IR) and X-ray fluorescence technique (XRF) for the elemental analysis X-Ray Diffraction Technique The phase identification of silica in the rice husk ash was determined using X-ray Diffraction (XRD) method on a Bruker AXS GmbH (German) machine. X-Ray diffraction patterns were recorded with a CuKα radiation at λ = Å at 40 kv and 20 ma in the range of 2θ = 5 o to 50 o with a scanning speed of 0.05 o per second Infrared Spectroscopy Rice husk ash sample was characterized with a Fourier Transform Infrared (FTIR) Spectrophotometer (model FTIR-8300, Shimadzu, Japan) using the KBr method. Approximately g of the rice husk ash was taken as a representative from the overall sample and transferred to the mortar crucible. A little KBr was then added in the ratio of sample to KBr of 1:100 and mixed thoroughly. These two substances were ground together using a mortar. The mixture was then pressed at a pressure of 7 tonnes for a minute to obtain the KBr sample disk. Finally, the disk was placed at the sample holder for the FTIR scanning from 400 cm -1 to 4000 cm -1.

74 Elemental Analysis The X-ray fluorescence (XRF) technique was used to determine the elements present in the rice husk ash quantitatively. The samples were further ground to microns grain size prior to the XRF analysis and for the determination of loss on ignition (%LOI). In the preparation of the specimen, firstly a mixture of 0.5 g sample and 5 g of spectroflux (Johnson & Mathey, London), giving a dilution ratio of 1:10 was prepared. The homogenous mixtures, placed in Pt-Au crucibles, were burnt for 20 min at 1000 ºC in an automatic glass bead preparation machine (Claisse Bis 10 Fluxer model). The homogenous melts were shaped into 3 mm thick, 32 mm diameter glass beads using Pt- Au moulds. Standards were also prepared by using the same procedure. For the XRF analysis, a set of standard parameter for 10 major elements was set on a fully automated Phillips PW 1480 Spectrometer. A standard calibration method was used, using 10 concentration-intensity curves, one for each element, constructed from 22 certified reference materials (CRM) of rocks, minerals, ores, soils, sediments, bricks, etc. It is believed that the matrix of the unknown is reasonably similar to those of CRM s, giving reasonably accurate results. The X-ray intensity of an element in a sample is compared to the appropriate standard curve, giving its concentration. The concentrations of major elements are reported as the weight percentages of the oxides, recalculated to 100%. Ten major elemental components determined by XRF are SiO 2, TiO 2, Fe 2 O 3, Al 2 O 3, MnO, CaO, MgO, Na 2 O, K 2 O and P 2 O 5. L.O.I. (loss on ignition) is the percentage of volatile components, mainly crystalbound water and organic carbon (as CO 2 ), driven off from a sample when heated at 1000 ºC. An accurate weight of g sample was placed in the muffle furnace, subsequently heated at 1000 ºC for an hour. The loss of weight of the sample after the combustion was compared to the weight of sample before the combustion to get the value of the percentage of loss on ignition.

75 Synthesis of Zeolite NaY The starting materials employed in the synthesis of zeolite NaY were sodium aluminate supplied by Riedel De Haen, sodium hydroxide (NaOH) pellets from Merck and silica from RHA. In order to prevent contamination, Teflon bottles and PTFE beakers were used for the preparation of all solutions and for the reaction mixture. For crystallization, Teflon bottles were employed. Glass vessels have been avoided as glass participates in the reaction because silica and alumina can leach out of glass. Teflon bottles and PTFE beakers were cleaned by immersing them in hydrofluoric acid 5% and left overnight prior to the synthesis of the zeolite NaY. The procedure for the synthesis of zeolite NaY was done according to Ginter, D. M. (Robson, 2001) but with different compositions and types of raw materials. They had successfully synthesized zeolite NaY by means of the seeding method. The preparation involved three major steps namely the preparation of seed gel, followed by feedstock gel and finally, the overall gel. Batch composition for seed gel is Na 2 O :Al 2 O 3 : 10SiO 2 :180 H 2 O and it contributed 5% from the overall gel composition. Firstly, NaOH pellets were weighed ( g) and transferred to the PTFE beaker; added with H 2 O (7.5 ml) and continuously stirred with a magnetic stirrer until a clear solution is obtained after dissolving the pellets. To prepare the aluminate solution, the prepared NaOH solution (2.0 ml) was added to the sodium aluminate, NaAlO 2 ( g) followed by stirring and heating it gently until the mixture became an apparent solution. For the preparation of silicate solution, RHA ( g) was mixed with the prepared NaOH solution in the PTFE beaker and subsequently stirred and heated in the water bath at boiling water temperature. The aluminate and silicate were then mixed in the PTFE beaker and stirred for half an hour to achieve homogenization. Then, the mixture was transferred to the Teflon bottle and capped for the ageing process to take place by leaving it at room temperature for 24 hours. After 24 hours of ageing, the loose brown gel would appear and it will be applied as seed gel for the seeding of the feedstock gel.

76 51 The second step is the preparation of feedstock gel which comprises 95% of the whole gel. The methodology is similar to the preparation of seed gel but different in the quantity of starting materials and required a larger PTFE beaker. Batch composition used in the preparation of the feedstock gel is 4.30 Na 2 O :Al 2 O 3 :10 SiO 2 :180 H 2 O. Initially, NaOH solutions were prepared by dissolving NaOH pellets ( g) with distilled water (142.5 ml) in the PTFE beaker, stirred with magnetic stirrer until a clear solution appeared. For the preparation of aluminate solution, sodium aluminate ( g) was dissolved in NaOH solution (42.5 ml) by stirring and heated gently on a hot plate until a clear solution appeared. In the preparation of silicate solution, NaOH solution (100 ml) was added to the RHA ( g) in the PTFE beaker. The mixture was then stirred and heated in a hot water bath. Then the aluminate and silicate solution were mixed in the PTFE beaker, subsequently stirred for 2 hours with the purpose of making it completely homogenized. This combination of solution was used as the feedstock gel. Lastly, the overall gel comprising the batch composition of 4.62 Na 2 O :Al 2 O 3 :10 SiO 2 :180 H 2 O was prepared by mixing the feedstock gel and seed gel. The feedstock gel was stirred magnetically and at the same time, the seed gel was added slowly and the mixture was continuously stirred for 2 hours. The mixture was then transferred into a Teflon bottle and left for ageing for 24 hours at room temperature. After ageing the mixture for 24 hours, the mixture in the Teflon bottle was heated in an oven at 100 o C for 22 hours. Teflon bottle was taken out, the cap was quickly opened and left to cool to room temperature. Subsequently, the solid product was separated by suction filtration and followed by washing with hot distilled deionized water and then dried overnight in the oven at 100 o C. Finally, the dried zeolite NaY was weighed and placed in the plastic bottle. The synthesis was repeated for 10 batches and labeled according to Zeo-NaY-S1 to S10. All of the synthesized zeolite NaY samples were mixed together in the plastic bottle and was closed tightly. The mixture was then homogenized for 12 hours to ensure good homogenization of the samples. The homogenized sample was sieved (250 mesh) to obtain desired size of zeolite samples and ready to be used for the characterizations and modifications steps and labeled as Zeo-NaY-S.

77 Characterization of Zeolite NaY The synthesized zeolite NaY, together with the commercial zeolite NaY was characterized by various characterization techniques including the X-ray diffraction (XRD) technique, infrared spectroscopy (IR), surface area and porosity, elemental analysis, the determination of unit cell and the ion exchange capacity (CEC and ECEC). The commercial zeolite NaY was supplied by Zeolyst International (CBV 100) having the SiO 2 /Al 2 O 3 ratio of 5.1. The procedure for XRD technique is similar to the one in Section but after the diffractogram pattern was obtained, it was compared to an existing pattern of zeolite Y from the powder diffraction files (PDF). For the infrared spectroscopy, since the samples are in powder form, the KBr technique was used as describe in Section Surface Area and Porosity The specific surface area and porosity of synthesized and commercial zeolite NaY were determined by using the QuantaChrome Autosorb-IC machine. Firstly, all of the samples were ground in a mortar to generate the smaller sized solid sample. Approximately 0.04 g sample was taken as the representative of the overall sample and was then transferred to the sample holder. Prior to the adsorption of N 2 gases, the sample was degassed at 350 o C for three hours. The analyses of samples were done according to the multipoint measurements provided by the BET surface area technique, total pore volume and average pore size.

78 Elemental Analysis As described in the Chapter 1, the sample must be in the liquid form prior to the analysis of sodium and aluminum by AAS and ICP-MS, respectively. Thus, the decomposition of sample through the digestion of solid sample with hydrofluoric acid was carried out. The procedure for the elemental analysis using XRF was performing according to the procedure stated in Section Decomposition of Zeolite Samples Prior to the elemental analysis by atomic absorption spectroscopy (AAS) and inductively coupled plasma mass spectrometry (ICP-MS), the solid samples must be decomposed to produce the liquid form. In this research, the decomposition procedure of the zeolite sample was adopted from the procedure used for clay as both have similar elemental composition in their structure (Wilson, 1994). During the decomposition process, the use of glassware was avoided because the hydrofluoric acid can react with the silica from the glassware. For the decomposition, 50 (± 0.01) mg of the prepared, representative sample was placed in a PTFE bottle with 0.5 ml aqua regia. The aqua regia solution is the solution in which 3 volumes of concentrated HCl was mixed with 1 volume of concentrated HNO 3 and this solution was used immediately after the preparation. The concentrated hydrofluoric acid (48%) (3 ml) was then added and the vessel was sealed tight instantaneously and was placed in an oven at 100 ± 5 o C for one hour. After cooling, the solution was transferred to a 50 ml plastic beaker containing boric acid (H 3 BO 3 ) (2.8 g) followed by the addition of distilled water (10 ml) and subsequently the mixture was stirred magnetically to dissolve any insoluble fluorides. The solution was diluted to 100 ml in the plastic volumetric flask and stored in a polyethylene bottle. This solution was ready for major elemental analysis.

79 Determination of Sodium The amount of sodium present in the synthesized samples and commercial zeolite NaY were determined with a flame atomic absorption spectroscopy (FAAS) (GBC, model Avanta, Australia) after the decomposition of the samples with hydrofluoric acid (HF). The glassware and plastic sample holder used in this procedure were washed with nitric acid 10%, (HNO 3 ) by immersing them overnight in order to dissolve and eliminate the contamination inside the apparatus, in particular the heavy metals as these elements will cause interferences during measurement with AAS. All of the decomposed samples were diluted 100 times with distilled water since the range of series standard solution is in low concentration, 0.4 to 2.0 ppm. The standard solution was prepared by diluting 1000 mg/l of stock sodium solution to the required series of standard solution using distilled water in a 100 ml volumetric flask. The standard and decomposed samples solutions were aspirated into the flame and the absorbance was recorded at nm, the specific absorbance for sodium. Water was aspirated between each sample. The standard calibration curve was prepared automatically by plotting the absorbance versus concentration for each standard and the concentration of sodium in samples was calculated automatically by the instrument, in mg/l. Quality control and spike recovery solution were measured after every five samples solution in order to evaluate and verify the data during the measurement of sodium in samples Determination of Aluminum Aluminum content in zeolite was determined by using inductively coupled plasma-mass spectrometry (ICP-MS) (Perkin Elmer, model Elan 6000) instrumental technique. Due to the high sensitivity of ICP-MS, double distilled deionized water and high purity reagents and acid were used in the preparation of samples and standard solution. All of the apparatus were washed with 10% nitric acid (HNO 3 ) by immersing them in this acid overnight with the aim to eliminate and dissolve the metals

80 55 contaminant. A series of standard solution ranging from 50 to 250 µg/l were prepared by diluting the stock multi-element ICPMS calibration standard solution, 1000 µg/l (Perkin Elmer) with addition of 2 ml of Ultra-pure nitric acid concentrated from subboiling distillation that was supplied from Fischer (optima grade). Nitric acid is preferred for ICP-MS in order to minimize polyatomic ion interferences. Each of the sample was prepared in three replicates and was diluted 1000 times prior to the determination by ICP-MS. Spike recovery studies and quality control were set up to verify the accuracy and precision of the instrument while measurements of samples were taken Determination of Loss on Ignition and Percentage of Silica The loss on ignition (LOI) method was carried out following Malaysian Standard procedure, MS ISO 3262: Certain weights of dried samples (about 0.2 g) were placed in small ceramic crucibles and placed in the oven at 100 o C overnight. The dried samples were then weight (about 0.1 g), m 0, placed in a platinum crucible and ignited in a muffle furnace (Carbolite muffle furnace, model: ELF 11/6B, Barloworld Scientific, England) at 1000 o C for 30 minutes, followed by cooling in a desiccator. After the temperature of the sample was in equilibrium with the room temperature, the sample was weighed (m 1 ). The LOI, as a percentage by mass, is given by the formula below: m0 m1 %LOI = 100% (17) m 0 Silica content was determined using the standard SIRIM method (ISO ). The residue from the determination of LOI was used to determine the percentage of SiO 2 content. The residue in the platinum crucible was added gradually with 1 ml of 50% sulfuric acid (H 2 SO 4 ). The crucible was heated gently until fuming has ceased in the fume cupboard. The crucible was then placed in a muffle furnace set at 900 o C for 30 minutes to continue heating. The residue was then removed from the furnace, cooled in

81 56 the desiccator and weighed (m 2 ). Later, the residue in the platinum crucible was added slowly with a mixture of H 2 SO 4 : HF (1:5) and heated on a hot plate until the white fumes no longer evolved. The heating was continued in the muffle furnace at 900 o C. The crucible was removed after 30 minutes from the muffle furnace, cooled in the dessicator and weighed (m 3 ). The calculation on the percentage silica present is based on this equation: m2 m3 % SiO 2 = 100% (18) m Determination of Unit Cell The determination of the unit cell of zeolites was carried out according to the standard test method for the determination of the unit cell dimension of a Faujasite-type zeolite (D ) provided by the international standard test method (ASTM International, 2003). As a summary of the method, a sample of the zeolite Y was mixed with powdered silicon and the zeolite unit cell dimension was calculated from the X-ray diffraction pattern of the mixture, using the silicon reflections as a reference. Firstly, about 1.5 g of powdered zeolite samples was placed in the drying oven at 110 ºC for 1 hour. The dried zeolite was then blended with about 0.05 g of silicon in a mortar and was ground until intimately mixed. The sample was put in the sample holder for the measurement of X-ray diffraction. The determination of the X-ray diffraction pattern was done as referred to the procedure in section The angle of the zeolite reflections at about 53.4º and 57.8º 2θ and that of the 56.1º silicon reflection to at least two decimal places were measured. The measured reflection angles for the zeolite were corrected by adding to each of the quantity (calculated minus measured angle of the silicon reflection). The unit cell dimension was then calculated in accordance with equations 2 and 3 in Section

82 Determination of Cation Exchange Capacity In order to determine the total cation exchange capacity (CEC) in the zeolites, the sodium cations which neutralize the framework of aluminosilicates are exchanged with other cation having a similar size of sodium. In contrast, the external cation exchange capacity (ECEC) of zeolite was done by exchanging the sodium cation with the larger cation of surfactant, i.e. HDTMA that could hardly penetrate into the pore of zeolite Total Cation Exchange Capacity The procedure for the determination of CEC was based on Chapman, 1965 (Wilson, 1994). This method was applicable to most soil and zeolite samples. The zeolite sample was mixed with an excess of sodium acetate solution, resulting in an exchange of the added sodium cations for the matrix cations. Subsequently, the sample was washed with isopropyl alcohol. An ammonium acetate solution was then added which replaced the adsorbed sodium with ammonium. The concentration of displaced sodium was then determined by AAS. The reagents used for this procedure were sodium acetate (NaOAc), 1.0 N, ammonium acetate (NH 4 OAc), 1.0 N and isopropyl alcohol supplied by Merck. Sodium acetate (NaOAc), 1.0 N was prepared by dissolving NaOAc (136 g) in water and diluted to 1000 ml in a volumetric flask. The ph of this solution was adjusted by adding a few drops of acetic acid or NaOH to the solution to ph 8.2. The 1.0 N of ammonium acetate (NH 4 OAc) was prepared by diluting glacial acetic acid (99.5%) (114 ml) with distilled water to a volume approximately one liter in a 2 L volumetric flask. The concentrated ammonium hydroxide (NH 4 OH) (138 ml) was then added and mixed with water to obtain an amount of about 1980 ml. The ph was adjusted with NH 4 OH to obtain a ph of 7 and this solution was diluted to the 2 L mark with distilled water.

83 58 For the preliminary step, about 0.2 g of the sample was weighed accurately and transferred to a 50 ml centrifuge tube. The sodium acetate, 1.0 N (6.6 ml) was added to the sample and the tube was closed tightly. This tube was shaken with an orbital shaker (150 rpm) for 10 minutes. The tube was then centrifuged to separate the solid and the solution into two phases until the supernatant liquid was clear. The liquid was decanted and this procedure was repeated three more times. Subsequently, about 6.6 ml of 99% isopropyl alcohol was added to the sample, the tube closed tightly, shaken for 10 minutes, centrifuged and finally, the liquid was decanted. This procedure was repeated two more times. The final step was the addition of ammonium acetate, 1.0 N (6.6 ml) into the solid sample in the centrifuge tube, stoppered tightly, and shaken with a mechanical shaker for 10 minutes and centrifuged for 10 minutes. The supernatant was kept in a 100 ml volumetric flask. This procedure was repeated three times. The combined solution was diluted to the 100 ml mark with ammonium acetate solution. The determination of the sodium concentration was analyzed by AAS (GBC, model Avanta, Australia) External Cation Exchange Capacity The procedure for the determination of ECEC was adopted from Bouffard (1998). The procedure for ECEC is similar to the determination of CEC but differs in the last step in which the sodium cation was replaced by HDTMA cation. The procedure for ECEC determination involved: (1) saturation of the sample with sodium cations, (2) exchanging the sodium cation by HDTMA and (3) analyzing the concentration of sodium using AAS. Chemicals used in this procedure were sodium acetate (NaOAc), isopropyl alcohol 99% and hexadecyltrimethyl ammonium bromide (HDTMA-Br) which were supplied by Merck. First, each sample was weighed accurately (0.2 g) and transferred to a 50 ml centrifuge tube. The saturation sample with sodium cations and wash with

84 59 isopropyl alcohol steps were followed the procedure for the determination of total cation exchange capacity (CEC) described in Section The last step involved the exchange of sodium cations with hexadecyltrimethyl ammonium cations. The HDTMA solution, 0.5 mmol L -1 (6.6 ml) was added to each sample taken from the previous step. The centrifuge tube was then closed tightly, shaken for 10 minutes and centrifuged. Liquid was then decanted into a volumetric flask (100 ml). This last procedure was repeated three times. The combined solution taken from the last step was diluted to the mark of volumetric flask with HDTMA solution. The concentration of displaced sodium was then determined by atomic absorption spectroscopy (GBC, model Avanta, Australia). 2.5 Preparation of Surfactant Modified Zeolite Y Three series of surfactant modified zeolite Y (SMZY) were prepared by reacting zeolite with aqueous solutions containing a single type of HDTMA. Hexadecyltrimethyl ammonium (HDTMA) bromide was supplied by Merck-Schuchardt. HDTMA was added in an amount equal to 50%, 100% or 200% of external cation exchange capacity (ECEC) of zeolite. This experiment was to study the effect of different surface coverage of HDTMA onto zeolite in the sorption of anions in water. The SMZY was identified by a prefix that stated the percentage of zeolite s ECEC which was supposedly to be occupied, followed by the abbreviation for the type of zeolite; i.e. S and C, for the synthesized zeolite NaY and commercial zeolite NaY, respectively. The abbreviation of each modified zeolites are listed in the Table 2.1.

85 60 Table 2.1: The abbreviation of the surfactant modified zeolite Y Precursor Percent surface coverage Abbreviation Synthesized Zeolite NaY 50% SMZY-50-S 100% SMZY-100-S 200% SMZY-200-S Commercial Zeolite NaY 50% SMZY-50-C 100% SMZY-100-C 200% SMZY-200-C For example, the preparation of SMZY-50-S needed g of HDTMAbromide to saturate 50% of the ECEC synthesized zeolite NaY (8 g). The calculation of the amount of HDTMA needed was shown below: ECEC of synthesized zeolite NaY = meq/100g Molecular weight of HDTMA bromide = g/mol For 1 meq/100g = adsorption sites. = 1 mmol/100g = 0.01 mmol/g = mol/g Hence, 1 g of synthesized zeolite with ECEC = meq/100 g can be satisfied by mol of cations to achieve 100% satisfaction Amount of HDTMA bromide needed = g g/mol = g HDTMA-bromide After the aqueous solutions were mixed with zeolite, the mixture was stirred using a magnetic stirrer for 5 days at room temperature. The mixture was then filtered by

86 61 vacuum filtration and the solid sample was dried at 60 ºC for overnight. The resultants SMZY were readily characterized and used for the adsorption study. 2.6 Characterization of Surfactant Modified Zeolite Y The surfactant modified zeolite Y was characterized by various techniques in order to study their structure, the elemental compositions and the other properties related to the modifications. The characterizations included X-ray diffraction technique, infrared spectroscopy, elemental analysis, surface area and porosity, dispersion behavior and the maximum adsorption of HDTMA onto the zeolite. The XRD technique and IR spectroscopy methods were done as described in Sections and 2.2.2, respectively. The elemental analyses involved the determination of sodium cation by flame photometer after the decomposition of samples and the analysis of carbon, hydrogen and nitrogen by Carbon-Hydrogen-Nitrogen-Sulfur analyzer (CHNS). The procedure for determining the surface area and porosity has been discussed in Section Elemental Analysis The determinations of sodium cation contained in the SMZY were carried out after the samples were decomposed using hydrofluoric acid. The procedure for the decomposition samples is described in the section The sodium content in the surfactant modified zeolite Y was determined by flame photometer (model PFP7, Burkard Scientific, UK). The determination procedure was done according to the method described for the chemical tests for cement proposed by the British Standards Institution (1970). The sodium stock solution (100 mg/l Na 2 O) was prepared by dissolving g of dried analytical reagent grade NaCl in distilled water and diluted

87 62 to 1000 ml. The calibration solutions were prepared using the quantities given in Table 2.2. Table 2.2: Solutions for calibrating flame photometer Calibration solution Sodium stock solution (ml) HNO 3 (ml) Water to make (ml) Equivalent concentrations, Na 2 O (mg/l) Scale-zero Scale Standard Standard Standard Standard The sodium light filter was set in the flame photometer to read 0 with scale-zero solution and 100 with scale-100 solution. The readings obtained for each of the intermediate calibration solutions was recorded and the calibration graph of instrument reading against mg per liter of Na 2 O was constructed. The decomposed samples solutions were then aspirated into the flame and the reading was recorded. The value of the concentration Na 2 O in the samples was calculated from the standard calibration curve. For the determination of the percentage of the amount of carbon, hydrogen and nitrogen in the zeolite and surfactant modified zeolite samples, CHNS analyzer model FlashEA 1112 series (Thermo Finnigan, Italy) was used. Helium was used as carrier gas whereas oxygen was the gas for sample oxidation. The furnace temperature was maintained at 900 ºC. About mg of the sample was weighed and introduced into the universal tin container with a spatula. The container was then closed using two spring tweezers. The tin container containing the sample was stored in the autosampler and dropped into the combustion reactor after a few seconds. Atropina (C 17 H 23 NO 3 ) was

88 63 used as the standard in the analyses. The amount of carbon, hydrogen, nitrogen and sulfur present in the samples were measured as a percentage (%) amount Dispersion Behavior In order to study the relative position in an oil-water mixture of unmodified and modified zeolites, an approximately 0.06 g of sample was added in the mixture of distilled water (2 ml) and n-hexane (2 ml) in a 10 ml glass bottle with stopper. The images of each glass bottle were taken immediately after the addition of sample. The relative positions of the particles in the mixture were compared. The dispersion behaviour study was to acquire information in relation to the spreading behaviour of the surfactant modified zeolite Y and the unmodified zeolite in aqueous solutions; either they disperse well in water or in the organic phase. The samples from the relative position study were shaken for 2 hours at room temperature. The images of each sample were taken instantaneously after the shaking. The emulsions formed were then left at ambient conditions for the coalescence of droplets to occur. The images were captured at an appropriate time. The dispersion behavior of each samples were compared Maximum Adsorption of HDTMA Prior to the isotherm study of uptaking HDTMA onto synthesized zeolite NaY, the synthesized zeolite were ground and sieved to the desired aggregate size (250 mesh). The synthesized zeolite NaY (0.5 g) was weighed accurately and added with the HDTMA solutions to yield cation dosages in the range from 25 to 250% of zeolite external cation exchange capacity (ECEC) in the 50 ml centrifuge tube. The suspensions of zeolites and HDTMA cation were shaken in an orbital shaker for 24 hours using an orbital shaker (Protech, model no. 722) at a constant agitation rate at the

89 64 ambient temperature. For the well separation of solid and liquid, the tube was then centrifuged (5000 rpm, 15 minutes) and subsequently the supernatant was decanted by the filtration technique using a Whatman filter paper (125 mm). The liquid supernatant was then analyzed for the determination of the concentration of the remaining HDTMA in the solution using the total organic carbon analyzer (TOC-Ve, Shimadzu, Japan). About 20 μl of the supernatant was taken with a syringe and injected into the injection port of TOC instrument. The concentration of the total organic carbon was determined automatically by the instrument. Assuming complete conversion of organic cations to CO 2 during TOC analysis, the TOC content of samples were converted to the equilibrium concentration of HDTMA (mmol/l). 2.7 Adsorption Studies The series of the surfactant modified zeolite Y (SMZY) were evaluated systematically using the isotherm equilibrium study for acquiring the value of the maximum adsorption of the toxic metals. In addition, the initial ph of the solution can also affect the adsorption process, thus the adsorption studies also include the effect of the initial ph of each species. Because the SMZY is possible to adsorb cation and anion, the adsorption studies for the Cr 3+ (Cr(III)), chromate anion (Cr(VI)), arsenate (As(V)) and arsenite (As(III)) were chosen Adsorption of Cr(III) The Cr(III) species exists in the form of cation, Cr 3+, thus the zeolite NaY can effectively remove this species from water because of its cation exchange property. Therefore, this study was highlighted in the adsorption studies of Cr 3+ by the unmodified synthesized and the unmodified commercial zeolite NaY. Studies done included the

90 65 kinetic study based on the different agitation time, the effect of the initial solution ph and the isotherm study. The isotherm study was done using the unmodified zeolite Y and SMZY. The determination of the concentration of chromium in the initial and final solution was carried out using the AAS technique and will be explained in Section Kinetic Study There are several parameters affecting the adsorption rate including stirring time. The kinetic study which was based on the effect of stirring time for the Cr(III) removal was carried out for the unmodified synthesized and the commercial zeolite NaY via the batch method and with different contact times. The stock solution of 250 and 500 mg/l of Cr(III) was prepared by dissolving an appropriate amount of Cr(NO 3 ) 3.9H 2 O (Merck) in 250 ml distilled deionized water. A constant amount of zeolite samples ( g) was mixed with 25 ml Cr(III) solution in 50 ml centrifuge tube. The suspension was shaken for varying periods of time starting from 10 minutes to 48 hours using an orbital shaker (Hotech) with constant agitation rate (120 rpm) and at room temperature. The solid phase was then separated by filtration through a Whatman filter paper (125 mm). The concentrations of chromium in the supernatant solution after adsorption were determined with the AAS technique Effect of Initial ph The ph of the solution also determines the ionic species present in the solution and the structure of zeolite. The effects of initial ph studies on the removal of Cr(III) was performed by the initial concentration of Cr(III) of 300 mg/l and g of both unmodified zeolite Y. The initial ph of the solution (2, 3, 4, 5) was adjusted using HNO 3

91 66 solution or diluted NaOH solution measured with a ph meter model CyberScan ph/ion 510 (Eutech Instruments). The solution was shaken for an appropriate time in the orbital shaker with constant agitation rate (120 rpm). The mixture was then withdrawn and filtered through a Whatman filter paper and the ph of the liquid checked. The filtrate was analyzed by flame atomic absorption spectroscopy (FAAS) after an appropriate dilution of the filtrate solution for the determination of Cr(III) Isotherm Study The adsorption equilibrium experiments on chromium were conducted to determine the adsorption capacity of Cr(III) under a given set of conditions. The sorption isotherm study was carried out via the batch method for the unmodified and modified zeolite Y. Essentially, 25 ml of a solution containing the trivalent chromium with an initial concentration ranging from 100 to 600 mg/l (ph 3.5) was mixed with precisely g of samples in a 50 ml centrifuge tube. The tubes were sealed and shaken for an appropriate time (according to the kinetic studies) with an orbital shaker (120 rpm) at room temperature. Finally, the solution was filtered through a Whatman filter paper (125 mm). The ph of the solution was measured before and after shaking. The concentration of the remaining Cr(III) in the solutions after contact with the samples was determined by FAAS. The Freundlich and Langmuir adsorption isotherms were then used to analyze the results as these isotherms have been shown as being useful in describing adsorption behaviour of metals on zeolites Determination of Cr(III) by FAAS The concentration of Cr(III) in the initial and final solutions were determined by the flame atomic absorption spectroscopy (FAAS) (Perkin Elmer, model AAnalyst 400).

92 67 The standard calibration solution was prepared from the appropriate dilution of the stock solution chromium nitrate, Cr(NO 3 ) 3.9H 2 O (Merck) 1000 mg/l. The concentrations of the standard solutions were prepared in the range from 0.1 to 5.0 mg/l. In order to get the precise value of the amount Cr(III) in the solution, the correlation coefficient of the standard calibration curve should be above The standard samples solutions were aspirated into the flame and the absorbance acquired at nm, the exact absorbance for chromium. An amount of distilled water was aspirated between each sample. The automatic plotting of the standard calibration curve was done by the instrument by plotting the absorbance against concentration for every standard measured. The series of the samples solution were diluted with an appropriate dilution before the samples were aspirated in the flame. The solutions containing known amounts of Cr(III) were introduced to the flame for every 5 to 10 samples for the quality control to avoid inaccurate value of the Cr(III) concentration. The concentrations of chromium in the solution were then automatically calculated by the instrument, in mg/l Adsorption of Cr(VI) The property of anion exchanger in the SMZY enabled them to adsorb the species of hexavalent chromium, Cr(VI) as it can exist in the form of chromate anions. Hence, the evaluation on the removal capacity of the chromate anion by SMZY was studied involving the effect of the initial ph of the Cr(VI) solution and the isotherm study. The Cr(VI) solution was prepared by dissolving a suitable amount of potassium dichromate, K 2 Cr 2 O 7 (Merck, Darmstadt, Germany) in distilled water. In order to prove that the structure of the framework zeolite did not collapse after the adsorption and to construct the adsorption model, the SMZY-chromate was prepared by contacting the SMZY in elevated concentration of chromate and subsequently their structure was studied. The determination of Cr(VI) in the solution will be described in Section

93 Effect of Initial ph The ph of the Cr(VI) solution (10 mg/l) was adjusted with the addition of NaOH or HNO 3 solution to obtain the ph 3, 5, 7, 8 and 10. The ph of the solution was measured by ph meter CyberScan ph/ion 510 ph meter (Eutech Instruments). An accurate amount of SMZY ( g) samples were mixed with the previously prepared Cr(VI) solution (20 ml) in a 50 ml centrifuge tube. The samples were then shaken for 48 hours. The supernatant was filtered through a Whatman filter paper (125 mm); the ph was checked and diluted prior to the determination of Cr(VI). The diluted supernatant was then analyzed for Cr(VI) left in the solution by UV-Vis spectrophotometer Isotherm study Isotherm study of Cr(VI) adsorption was conducted in aqueous solution and by batch studies. An accurate amount of the unmodified and modified zeolite (0.5 g) was placed in a centrifuge tube 50 ml and added with Cr(VI) solution having concentrations in the range of 10 to 70 mg Cr(VI)/L. The ph of the Cr(VI) solutions were kept between 3 and 4. The mixtures were shaken at room temperature at the agitation rate of 150 rpm using an orbital shaker (Hotech) for 48 hours (a period shown to be sufficient to reach adsorption equilibrium). The mixture was then filtered and the extracted solution was analyzed to determine the Cr(VI) concentration by UV-Vis spectrophotometer. The Langmuir isotherm was used to determine the maximum adsorption capacity of Cr(VI) onto the SMZY.

94 SMZY-Chromate Structure Study Approximately 5 g of the SMZY was weighed and placed in the PTFE beaker (250 ml). The samples were then mixed with 50 ml Cr(VI) solution (1000 mg/l). The suspension was stirred with a magnetic stirrer for 5 hours at room temperature. The suspension was then filtered and the solid residue was heated in the oven at 60 ºC for 24 hours in order to dry it. Subsequently, the solid sample was ground prior to the study of its structure. The identification of its structure was determined by X-ray diffraction (XRD) technique and infrared (IR) spectroscopy, summarized in the Sections and 2.2.2, respectively. The diffractogram of XRD and the spectrum of IR were compared before and after the adsorption of Cr(VI) Determination of Cr(VI) by UV-Vis Spectrophotometer The procedure for the determination of the hexavalent chromium, Cr(VI) in the solution was based on the standard method set up by American Public Health Association (APHA) (Cleseri et al., 1989). This procedure measured only hexavalent chromium (Cr(VI)) in which the hexavalent chromium was determined colorimetrically by reaction with diphenylcarbazide in acid solution. A stock chromium solution (50 mg/l) was prepared by dissolving potassium dichromate, K 2 Cr 2 O 7 (141.4 g) in water and diluted to 1000 ml. The diphenylcarbazide solution was prepared by dissolving 1,5- diphenycarbazide (250 mg) in acetone (50 ml). In the preparation of standard calibration curve, Cr(VI) standard solution was treated by the same procedure as the sample to compensate the slight losses of Cr(VI) during digestion or other analytical operations. The volume of standard chromium solution (5 mg/l) ranging from 2.00 to 20.0 ml was pipetted to give standards of 10 to 100 mg Cr, into 250 ml conical flasks. After the development of color, a suitable portion of each solution was transferred to a 1-cm absorption cell, the absorbance was measured at 540 nm. Distilled water was used as a reference. In order to get the accurate value of the concentration of Cr(VI) in the

95 70 solution, the correlation coefficient of standard calibration curve should be above For the development of color, an appropriate volume of sample solution (initial and final solution) was diluted by 1 M H 2 SO 4 in 25 ml volumetric flasks. It was then added with 0.5 ml 0.25% diphenylcarbazide solution, shaken and kept for full color development in 5 min. After the development of color, the solution was transferred to a 1-cm absorption cell and the absorbance was measured at 540 nm using an ultra violet-visible (UV-Vis) spectrophotometer (Perkin Elmer, model Lambda 25) and distilled water was used as a reference. Cr(VI) adsorption was determined from the difference between the initial and final concentrations using the unit mmol Cr(VI)/kg zeolite Adsorption of As(V) and As(III): Preliminary Study Prior to further adsorption study of arsenic by SMZY, the adsorptions of the single component of arsenate (As(V)) and arsenite (As(III)) solution were determined. The unmodified and modified zeolites samples were used in this preliminary study. The stock solution of As(III) (1000 mg/l) was prepared by dissolving As 2 O 3 (1.32 g) in a solution containing 4 g of NaOH pellet in 100 ml and after the dissolution was completed, the mixture was then added with 20 ml concentrated HNO 3 and finally diluted to the 1000 ml mark. The stock solution of As(V) was prepared by dissolving Na 2 HAsO 4 ( g) in a solution containing 0.2 g of NaOH in 10 ml and finally diluted to the 50 ml by distilled water. The stock solutions of both species were diluted to the desired concentrations with distilled water for the adsorption study. For the preliminary adsorption study, 0.1 g of samples were weighed accurately and placed in the 50 ml centrifuge tube containing the single component of As(III) (20 ml, 20 mg/l) or As(V) (ph 8, 20 ml, 20 mg/l) species. The centrifuge tube was then shaken for 24 hours by orbital shaker at a constant agitation rate (120 rpm). The solid sample and solution was filtered with a Whatman filter paper (125 mm). The filtrate was analyzed for the concentrations of the remaining As(V) or As(III) in the solution. FAAS

96 71 was used to determine the concentration of As(V) and As(III) and this procedure will be described in Section The adsorption capacities of both species were stated as the percentage of the adsorption Adsorption of As(V) The additional adsorption study was done for the adsorption of As(V) by modified and unmodified zeolite Y. The study also included the investigation on the effect of the initial ph and the isotherm patterns. The preparation of stock solution of the As(V) was described in Section and the determination of As(V) concentration followed the procedure in Section Effect of Initial ph The samples for this study comprised the SMZY from both type of zeolites. About 0.2 g of the sample was weighed precisely and placed in the 50 ml centrifuge tube. The solution containing 20 mg/l of As(V) (20 ml) having a different initial ph was added to the sample. The adjustment of the ph solution was carried out by the addition of NaOH or HNO 3 solution to obtain the ph 2, 4, 6, 7, 8, 10 and 12. The ph was measured using a CyberScan ph/ion 510 ph meter (Eutech Instruments). The mixture in the tube was shaken for 5 hours at a constant agitation rate (120 rpm) and at ambient temperature. The mixture was then separated by filtration and the ph of the filtrate was determined. Finally, the filtrate was analyzed for the concentration of As(V) using FAAS.

97 Isotherm Study For the purpose of acquiring the value of the maximum adsorption capacity of As(V) by surfactant modified zeolite Y and unmodified zeolite Y, the isotherm study was carried out with adsorption at different initial concentrations of As(V) solution. The As(V) solution was prepared with the appropriate dilution of the stock solution to get the required concentrations of As(V) of 10, 20, 30, 40 and 50 mg/l. About 0.2 g of sample was weighed precisely and added with 20 ml As(V) solution (ph 6) in the centrifuge tube 50 ml. The tubes were then shaken for 5 hours and the supernatant subsequently filtered. The filtrate was analyzed for the concentration of As(V) using FAAS technique (Section ) Determination of Arsenic by FAAS Because of the high concentration of both arsenic species used to construct the isotherm study and to study the effect of initial ph, the flame atomic absorption technique spectroscopy (Perkin Elmer, model AAnalyst 400) was utilized. The electrodeless lamp with the exact wavelength of nm for arsenic was used. Standard solutions of arsenic were prepared in the range of 15 to 60 mg/l by diluting the stock solution of arsenic (1000 mg/l) (BDH, Poole, England). The sample solution was aspirated in the flame followed by the solution having a known concentration of arsenic for the evaluation of quality control (QC). The concentration of the arsenic was calculated automatically by the instrument.

98 CHAPTER 3 RESULTS AND DISCUSSION: SORBENTS DEVELOPMENT 3.1 Rice Husk Ash as a Source of Silica Rice husk ash (RHA) was obtained from the combustion of rice husk at 600 C using the rice husk burner. The X-ray diffractogram pattern of RHA is shown in Figure 3.1. This diffractogram reveals that the silica present in RHA was completely amorphous to XRD as indicated by the featureless pattern and the absence of significant peak and the appearance of diffuse maximum at 2θ = 23 typical for amorphous silica (Halimaton Hamdan et al., 1997) Theta-Scale Figure 3.1 The XRD diffractogram of RHA

99 74 The infrared spectrum for RHA is shown in Figure 3.2. This spectrum demonstrates a very strong, intense and broad peak at 1100 cm -1 which corresponds to the Si-O-Si asymmetric vibration and due to the greater ionic character of the Si-O group, this band is much more intense than the corresponding C-O band for ether (Socrates, 1994). This spectrum also exhibits bands at 804 cm -1 and 470 cm -1 which correspond to the symmetric stretching of SiO 4 tetrahedra and Si-O bending band vibrations, respectively. This data indicates that the silica phase found in RHA was completely amorphous due to the absence of bands near 622 cm -1 which is identical to tridymite (crystalline phase) that shows the presence of the cristobalite phase (Willis et al., 1987). This observation also supports the results obtained from XRD that the RHA contains the amorphous form of silica %T RHA-P /cm Figure 3.2 Infrared spectrum of rice husk ash The composition of major elements present in the RHA as analyzed by X-ray fluorescence (XRF) technique can be seen in Table 3.1. The silica content in RHA is somewhat higher because most of the impurities were eliminated during combustion at that temperature. Table 3.1 : Chemical composition of rice husk ash Oxide SiO 2 TiO 2 Fe 2 O 3 Al 2 O 3 MnO CaO MgO Na 2 O K 2 O P 2 O 5 LOI %

100 Synthesis of Zeolite NaY The synthesized zeolite NaY (Zeo-NaY-S) together with the commercial zeolite NaY (Zeo-NaY-C) acting as comparison was characterized using XRD and FTIR for the identification of the structure; the XRF, ICPMS, AAS and classical wet methods for elemental analysis; and the physicochemical properties which are unit cell, ratio of silica/alumina, surface area and porosity, cation exchange capacity (CEC) and external cation exchange capacity (ECEC) X-Ray Diffraction Technique In order to prevent the formation of other zeolites or phases during the synthesis of zeolite Y and to get highly pure zeolite NaY from RHA, the seeding and ageing techniques were highlighted. As a comparison, the procedure for the synthesis of zeolite NaY from RHA either without ageing or seeding techniques was carried out and the products were characterized by XRD technique. This was done to study the effect of ageing and seeding techniques in the synthesis of zeolite NaY. The preliminary preparation of zeolite NaY from RHA without ageing and seeding techniques revealed that the mixture consisted of the zeolite Y and A. Besides that, we also prepared the zeolite NaY from RHA with ageing but without the seeding technique. It is clear that the main impurity in the synthesis of zeolite Y without the seeding technique was attributed to the formation of zeolite P. The XRD patterns of both products were assembled in Figure 3.3 while Figure 3.4 shows the XRD pattern of the zeolite NaY that was synthesized via the seeding and ageing techniques. The diffractogram of the zeolite NaY from the seeding and ageing techniques exhibit many significant peaks from 2θ = 5 to 50º indicating that the samples are in the crystalline form. Furthermore, when this pattern was matched up with the peaks corresponding to the zeolite NaY structure as shown in Figure 3.4, it shows that the product formed from

101 76 the synthesized zeolite NaY by seeding and ageing techniques was highly pure zeolite NaY because all of the peaks were well matched with the peaks of zeolite NaY structure. In addition, the diffractogram also demonstrates that no other significant peaks correspond to zeolite A and P emerged, which confirmed the elimination of the formation of zeolite A and P. There were also no impurities and other phases formed in the synthesized zeolite NaY. Y I n t e n s i t y A Y A Y Y A Y Y A A Y Y A Y A Y Y Y Y Y NA-NS-Zeo (a.u.) P P P Y Y Y P Y Y Y Y Y Y P Y Y Y A-NS-Zeo 5 2-Theta - Scale 5 Figure 3.3 The X-ray diffraction patterns of the product obtained from the synthesis without ageingand seeding technique (NA-NS-Zeo) and the product from the synthesized zeolite Y with ageing but without seeding technique (A-NS-Zeo). The diffractograms were marked with zeolite A (A), zeolite P (P) and zeolite Y (Y) patterns which existed in the powder diffraction file (PDF).

102 77 I n t e n s i t y (a.u.) 2-Theta-Scale Figure 3.4 The X-ray diffraction pattern of mixed synthesized zeolite NaY (Zeo- NaY-S) via seeding and ageing techniques match up with the sodium aluminum silicate hydrate NaY (Na 2 Al 2 Si 4.5O 13.xH 2 O) pattern existed in PDF. It was proven that zeolite NaY with high purity was successfully synthesized from RHA by seeding and ageing techniques without marked presence of impurities, i.e. zeolite P and A. This result revealed that the seeding and ageing techniques will induce the zeolite Y formation. In previous reports, Zhao et al. (1997) used these seeding and ageing techniques to generate zeolite Y with a maximum crystalinity of 72% from coal fly ash through hydrothermal treatment. In the absence of seed, zeolite P was found to be a competitive phase and the main impurity present in the resulting products. In the synthesis of zeolite Y, when a source of silica is from rice husk ash which is less pure than the commercial silica, this requires the addition of seeds or initial solution to provide nuclei, which can selectively induce the formation of zeolite Y and eliminate the processes of induction and nucleation. Without ageing, the period of crystallization became shorter resulting in the formation of zeolite A. The silica-rich zeolite A appears to crystallize well in a period of one hour which is followed by rapid conversion in many instances to hydroxysodalite (Breck, 1974). Breck and Flanigen (1964), in their early experiment showed that the synthesized product with 92% of zeolite Y was produced after ageing for 24 hours at

103 78 room temperature compared to the product produced without ageing was only 63% of zeolite Y. In addition, Ginter et al. (1992) who studied the effects of gel ageing on the synthesis of zeolite NaY from colloidal silica also reported that prolonged ageing led to incorporation of additional Si into the aluminosilicate solid and this gave rise to a larger number of smaller nuclei and resulted in a higher final yield of Zeolite NaY. They also found that in the absence of ageing, zeolite phases other than NaY were formed. Zeo-NaY-S10 Zeo-NaY-S9 I n t e n s i t y (a.u.) Zeo-NaY-S8 Zeo-NaY-S7 Zeo-NaY-S6 Zeo-NaY-S5 Zeo-NaY-S4 Zeo-NaY-S3 Zeo-NaY-S2 2-Theta-Scale Zeo-NaY-S1 Figure 3.5 The compilation of X-ray diffractograms of the synthesized zeolite NaY

104 79 Because of the successful production of highly pure zeolite NaY and the elimination of other phases and impurities via seeding and ageing techniques, the procedure was repeated ten more times and was labeled as Zeo-NaY-S1 to S10. Each of the synthesized samples was characterized by XRD to obtain the X-ray diffractogram as this is the crucial and important characterization technique in the identification of the synthesized crystalline zeolite NaY and for the observation if any impurities or other phases in the product. Figure 3.5 shows the X-ray diffraction patterns of 10 batches of the synthesized zeolite NaY through the seeding and ageing techniques. This figure reveals that the seeding and ageing techniques for the synthesis of zeolite NaY from RHA has successfully produced a pure zeolite NaY with high reproducibility. These products were mixed together and homogenized to get Zeo-NaY-S that were used for further characterizations and modification. Matching the diffractogram from the commercial zeolite NaY, it was found that the patterns are nearly the same as those of the synthesized zeolite but the crystallinity is higher and observable sharpness of the peaks is better for the commercial zeolite. The reason is that the commercial zeolite Y is typically prepared from highly pure starting materials, equipped with more expensive apparatus and utilization of high technology devices, while the synthesized zeolite NaY was produced from less pure silica contained in RHA and inexpensive lab scale devices and apparatus were employed. The XRD pattern of commercial zeolite NaY is shown in Figure 3.6. I n t e n s i t y (a.u.) Theta - Scale Figure 3.6 The X-ray diffraction pattern of the commercial zeolite NaY

105 Infrared Spectroscopy To support the XRD analysis, the mid infrared (IR) region of the spectrum was used (1300 to 400 cm -1 ) since this region contained the fundamental vibrations of the framework (Si,Al)O 4 tetrahedra and should expose the framework structure (Gould, 1974). The infrared spectrum for the synthesized zeolite NaY (Zeo-NaY-S) and commercial zeolite NaY (Zeo-NaY-C) are illustrated in the Figures 3.7 and 3.8, respectively %T 40.0 Zeo-NaY-S /cm Figure 3.7 The infrared spectrum of Zeo-NaY-S 60.0 %T 50.0 Zeo-NaY-C /cm Figure 3.8 The infrared spectrum of Zeo-NaY-C

106 81 The infrared spectra for the synthesized and commercial zeolite NaY show six significant peaks from 1250 to 400 cm -1 comparable to the spectrum zeolite NaY which was assigned by Flanigen and Khatami (Gould, 1974: Rabo, 1976). They explained that the IR spectrum for zeolite NaY in the region of 1300 to 400 cm -1, six significant peaks emerged which were related to zeolite NaY structure. A summary of the infrared assignments is contained in Table 3.2 and illustrated in Figure 3.9. Table 3.2 : Zeolite NaY infrared assignments Vibration mode Wavelength (cm -1 ) 1) Internal tetrahedra Asymmetric stretch Symmetric stretch T-O bend ) External linkages Double ring Symmetric stretch Asymmetric stretch Asymm. stretch Symm. stretch Dbl. ring T-O bend = Internal tetrahedra structure insensitive 2 = external linkages structure sensitive Figure 3.9 region from 1250 to 420 cm -1 The illustration of infrared spectrum of zeolite Y (Si/Al = 2.5) in the

107 82 Wright (Rabo, 1976) also studied the infrared spectra in the region of cm -1 for a series of type X and Y zeolites with varying Si/Al ratios. They assigned bands near 1140 cm -1 to a symmetric Si-O-Si stretching mode, 1075 cm -1 to a symmetric Si-O- Al stretching mode, the strongest band near 1000 cm -1 to both Si-O-Si and Si-O-Al asymmetric stretching modes. The shoulder near 500 cm -1 was found in NaY zeolite but absent in NaX, as assigned to an Si-O-Al out-of-plane bending mode. All of the peaks in the IR spectrum of the synthesized and commercial zeolite NaY are in the region discussed above and the presence of the shoulder peak near 500 cm -1 indicates that the zeolite NaY has been successfully synthesized. The IR spectra also shows strong, intense bands at 3500 cm -1 regions exhibited by discrete water absorption because of the hydrated property of zeolite. A summary of the synthesized and commercial infrared assignments is contained in Table 3.3. Table 3.3 : IR assignments for commercial, synthesized zeolite NaY and zeolite Y (SiO 2 /Al 2 O ) Vibration mode a Zeolite Y Zeo-NaY-C Zeo-NaY-S Asymmetric Stretch 1130 (msh) 1005 (s) (msh) (s) (msh) (s) Symmetric stretch 784 (m) 714 (m) (m) (m) (m) (m) Double rings 572 (m) (m) (m) Out-of-plane bending 500 (msh) (msh) (msh) T-O bend 455 (ms) (ms) (ms) Notes: a: SiO 2 /Al 2 O (Gould, 1971: Rabo, 1976), s: strong, ms: medium strong, m: medium, sh: shoulder From Table 3.3, it can be seen that each of peaks for Zeo-NaY-S is identical with the peaks from the zeolite Y which had been studied by Flanigen and Khatami (Gould, 1974: Rabo, 1976). Beside that, the spectra also explains the changes that occurred in the

108 83 structure of raw material, silica from RHA to a zeolite structure. This phenomenon is shown by the shifting of peak near 1000 cm -1 contributed from the transformation of Si- O-Si to Si-O-Al bonding as shown in Figure The intensity of the peak of the synthesized zeolite NaY is somewhat higher than silica since the zeolite structure is more rigid. From these infrared spectra and the assignments of peak, it can be concluded that infrared spectroscopy can assist the data from XRD diffractogram in the identification of zeolite and proved that the zeolite NaY was successfully synthesized %T 40.0 RHA Zeo-NaY-S /cm Figure 3.10 The comparison of the infrared spectrum of synthesized zeolite NaY (Zeo-NaY-S) and rice husk ash (RHA) Elemental Analysis The quantitative determinations of major elements contained in the zeolite samples were carried out using two different approaches. The first approach was the combination of the analysis after complete dissolution of the samples and the classical gravimetric method while the second approach was physical analysis method using the wavelength dispersive X-ray fluorescence (XRF) technique. These comparisons were done because there is no best technique for the elemental analysis of zeolite although there are a wide variety of techniques reported in the previous literature (Corbin et al., 1987). Table 3.4 gives the data of the Na 2 O, Al 2 O 3, SiO 2 and H 2 O amounts from the first

109 84 approach. As a comparison, the percent amount of these elements and other oxide elements from XRF technique is given in Table 3.5. Table 3.4 : Percentage amount of major elements contained in the zeolite samples from the first approach Elements Zeo-NaY-S Zeo-NaY-C Na 2 O (%) Al 2 O 3 (%) SiO 2 (%) H 2 O (%) Table 3.5 : Percentage amount of major elements contained in zeolite samples by XRF technique Elements Zeo-NaY-S Zeo-NaY-C SiO TiO Fe 2 O <0.01 Al 2 O MnO 0.04 <0.01 CaO MgO < Na 2 O K 2 O P 2 O L.O.I It is necessary to convert the quantity of sodium and aluminum to the oxide form in the samples because the preparation of zeolite was derived from the oxide moles of sodium and aluminum. Data from AAS and ICP-MS was accurate and reliable due to the

110 85 values from the quality control (QC) and spike recovery study. Furthermore, the correlation coefficient (r 2 ) for the standard calibration curve was nearly one indicating that the value of the amounts of sodium and aluminum were trustworthy and consistent. The data from AAS and ICP-MS together with the respective QC and spike recovery can be seen in Appendix A-1 and A-2 while the data for the determination of %LOI and %SiO 2 is in Appendix A-3. For the XRF technique, the measurement of accuracy is the relative error, i.e. the difference between the recommended value (given by the CRM s producer) and the observed value (given by UKM s XRF machine) of a certified reference material, stated as percentage. The CRM has been analyzed along with the samples. It is assumed that the relative errors of the CRM are equivalent to those of the 17 unknowns as indicated in Appendix A-4. The variation value of the major elements amount in zeolites for both approaches is due to the different way in which the treatment of the samples was done and the instrumental techniques used. For the first approach, the dissolution samples might not completely solubilize the solid samples and the slight losses of silicon from the digestion step by HF acid might be possibly due to the volatility of the resulting fluorides. As compared to AAS and ICPMS, the benefits of XRF include the ability to determine some non-metals, conceptually simpler sample preparation and improved precision. The disadvantages include poor sensitivity of light elements and sensitivity to changes in the matrix composition. Corbin et al. (1987) in their paper found that the atomic absorption spectroscopy data was to be the most reliable but the data obtained from XRF, wet chemical and ICP spectrometric analysis showed that alteration in the methodology of these techniques was needed to improve their precision. In addition, the utilization of AAS, ICP and XRF were found better than the classical wet chemistry methods because these methods offer the benefit of reduced interferences and matrix effects, and have improved accuracy, precision and speed. Besides that, a particular problem with zeolites is that the ambient humidity may affect the amount of sample moisture which can lead to uncertainties in the sample weights. As a conclusion, since these two approaches have their benefits and

111 86 disadvantage as well as the problem with zeolites itself, both data for the amount of major elemental analysis can be used Physicochemical Properties The information regarding the physicochemical properties of the synthesized and commercial zeolite NaY is very important and essential since the zeolites were used for surface modification and utilized as sorbents for toxic metals. The properties that had been studied are surface area, porosity, unit cell, silica per alumina ratio, total cation exchange capacity and the external cation exchange capacity. Table 3.6 gives a list of the physicochemical properties and respective values for the synthesized and commercial zeolite NaY. The analysis data for each properties study are in Appendix B. Table 3.6 : The physicochemical properties of the synthesized (Zeo-NaY-S) and commercial zeolite NaY (Zeo-NaY-C). Physicochemical properties Zeo-NaY-S Zeo-NaY-C Unit cell, a o (Ǻ) a SiO 2 /Al 2 O b SiO 2 /Al 2 O c SiO 2 /Al 2 O d SiO 2 /Al 2 O e SiO 2 /Al 2 O c Si/Al d Si/Al e Si/Al Notes: a: from elemental analysis, b: from XRF, c: from unit cell, d; from infrared spectrum (equation 5), e: from infrared spectrum (equation 6)

112 87 Table 3.6 (continue): The physicochemical properties of the synthesized (Zeo- NaY-S) and commercial zeolite NaY (Zeo-NaY-C). Physicochemical properties Zeo-NaY-S Zeo-NaY-C Surface area (m 2 /g) Total pore volume (cc/g) Average pore diameter (Ǻ) Cation exchange capacity, CEC (meq/g) External cation exchange capacity, ECEC (meq/g) Since the ratio of Si/Al was calculated from unit cell, it was defined as the ratio of the framework which corresponds to all tetrahedrally coordinated Si or Al atoms within the crystal lattice. In contrast, the bulk or elemental SiO 2 /Al 2 O 3 ratio comprises nonframework Al and Si atoms in addition to the entire framework Si and Al atoms. The value of SiO 2 /Al 2 O 3 in Table 3.6 shows that zeolite Y was successfully synthesized from RHA because zeolite Y was recognized in reported patent as having silica/alumina ratios between 3.0 and 6.0 as said by the Breck s patent (Breck, 1964). In general, thermal, hydrothermal and acid stability of zeolites improve as they become more siliceous or having the increasing value of silica to alumina ratio (Siantar et al., 1995). According to Flanigen s notation, low silica zeolites are defined as having 2<SiO 2 /Al 2 O 3 <4; intermediate SiO 2 /Al 2 O 3 zeolites as having 4<SiO 2 /Al 2 O 3 <10 and high silica materials as generally having SiO 2 /Al 2 O 3 ratios more than 10 (Chen et al., 1994). Thus, synthesized and commercial zeolite NaY are the low silica zeolites with the commercial zeolite NaY as is more siliceous than synthesized zeolite NaY. The synthesized zeolite NaY has higher CEC and ECEC than the commercial zeolite NaY due to the higher amount of Na 2 O contained in the synthesized as well as the lower ratio of SiO 2 /Al 2 O 3 since each AlO 4 tetrahedra in the zeolite framework provides a single cation exchange sites (Sherman, 1978).

113 Characterization of Surfactant Modified Zeolite Y The surfaces of the synthesized and commercial zeolite Y were modified by the cationic surfactant, HDTMA by way of exchanging the sodium cation that neutralized the external framework of aluminosilicate of the zeolite. The HDTMA molecule is too large to enter the angstrom size of zeolite Y s pore that will consequently exchange with sodium cation in the exterior framework. For that reason, the structure of the zeolite did not have an alteration after the modification process. In order to prove this hypothesis, each of the SMZY was characterized by XRD and IR techniques to obtain the structure information. Due to the exchange of the cation that neutralized the framework zeolite, the elemental analysis was done including the determination of sodium cation using flame photometer after the decomposition of samples and the elements that created the HDTMA molecule, i.e. carbon, hydrogen and nitrogen using CHNS analyzer. Other characterizations include the surface area and porosity, the dispersion behavior and the maximum adsorption of HDTMA onto zeolite that were related to the utilization of the SMZY as a sorbent for toxic metals in water. The dispersion behavior study was to observe the relative position and the behavior of the SMZY in the mixture of oil and water since the surface of the SMZY turns into partially hydrophobic. Lastly, it was essential to get the value of the maximum adsorption of HDTMA onto zeolite which can be used to study the orientation of the adsorbed HDTMA relative to the surface and solution in order to construct the schematic diagram of the theoretical adsorption study of HDTMA onto zeolite Y. The Langmuir isotherm was used to obtain the maximum adsorption value of HDTMA onto the zeolite X-Ray Diffraction Technique Because the XRD technique is found to be crucial and suitable for the determination of the zeolites structure, this technique was applied for the determination

114 89 of the SMZY structure in order to prove that the structure of zeolite Y has not changed after the modification. Figure 3.11 shows the compilation of XRD diffractograms for each of the SMZY together with the respective unmodified zeolite Y. This figure revealed that the structure of the zeolite was not changed after the modification process, thus proving the theoretical explained in previous section. The XRD patterns of each SMZY were nearly identical with the pattern of the parent zeolite. Furthermore, it can be seen that no other peaks emerged which confirmed that there are no impurities and other phases inside the structure after the modification process. SMZY-200-C I n t e n s i t y (a.u.) SMZY-100-C SMZY-50-C Zeo-NaY-C SMZY-200-S SMZY-100-S SMZY-50-S Zeo-NaY-S 2-Theta - Scale Figure 3.11 The XRD patterns of the surfactant modified zeolite Y together with the parent zeolites

115 Infrared Spectroscopy The infrared spectra for all SMZY together with the respective original zeolite Y can be seen in Appendix C. Every infrared spectrum of the SMZY was almost identical with their unmodified zeolites which only corresponded to the structure of the zeolite Y as described previously thus the structure was not changed after the modification process. Additionally, no other peaks emerged, hence there were no impurities or other formations and phases occured during the modification. The peak assignments of SMZY infrared spectrum are listed in Table 3.7. The infrared spectrum of each SMZY shows 6 peaks emerged which corresponds to the structure of zeolite Y as stated previously in Section The values of each peak wavenumber for SMZY are slightly different with the parent zeolite due to the sample preparation and the instruments factor. Table 3.7 : Peak lists of SMZY infrared spectrum Sample Asymmetric Stretch Symmetric stretch Double Rings Out of plane bending mode T-O bend SMZY-50-S msh 771.5m 569m 496.6msh 461.9ms s 692.4m SMZY-100-S msh 771.5m 569m 499.5msh 461.9ms s 696.3m SMZY-200-S msh 771.5m 569m 499.5msh 461.9ms s 696.3m SMZY-50-C msh 792.7m 578.6m 503.4msh 461.9ms s 720.4m SMZY-100-C msh 792.7m 578.6m 49.5msh 461.9ms s 720.4m SMZY-200-C msh s 792.7m 723.3m 575.7m 503.4msh 461.9ms Notes: s: strong, ms: medium strong, m: medium, sh: shoulder

116 Elemental Analysis The preparation of the series of SMZY was based on partially exchanging the HDTMA cation with sodium cation in the external framework of zeolite Y as described in the equation below: [Al-O-Si] - Na + + HDTMA + Br - [Al-O-Si] - Na + HDTMA + + Br - (17) Where the portion of [Al-O-Si] - represents the aluminosilicate framework of zeolite Y having a negative charge where the framework is neutralized by Na +. For this reason, the elemental analysis of sodium and HDTMA cation present in the SMZY and the unmodified zeolite Y was crucial in determining the decreasing amount of sodium and the increasing amount of HDTMA in the SMZY after the modification. The values of the Na 2 O content in the SMZY and the unmodified zeolite are listed in Table 3.8 while the graph bar showing the variations of these amounts were illustrated in Figure The analysis data are attached in Appendix D. Table 3.8 : The content of Na 2 O in the SMZY and their parent zeolite Samples [Na 2 O] (mg/g) [Na 2 O] (mmol/g) Zeo-NaY-S SMZY-50-S SMZY-100-S SMZY-200-S Zeo-NaY-C SMZY-50-C SMZY-100-C SMZY-200-C

117 [Na2O], mg/g Zeo- NaY-S SMZY- 50-S SMZY- 100-S SMZY- 200-S Zeo- NaY-C SMZY- 50-C SMZY- 100-C SMZY- 200-C Figure 3.12 respective unmodified zeolite The comparison of the Na 2 O amount (mg/g) present in the SMZY and Table 3.8 and Figure 3.12 reveal that the amounts of sodium in the SMZY were lower than the unmodified zeolite NaY, demonstrating that the sodium in the parent zeolite was partially removed and exchanged with the HDTMA cation after the modification process. The carbon-hydrogen-nitrogen-sulfur (CHNS) analyzer was used to determine the three elements (carbon, hydrogen and nitrogen) contained in the SMZY and also raw zeolite. The existence of carbon and hydrogen was due to the organic moieties in the samples whereas nitrogen was due to the existence of ammonium cations. Therefore, it was essential to determine the percentage of this element due to the surfactant that was used to modify zeolite possessing long chains of hydrocarbon tail and the ammonium as the charge head.

118 93 Table 3.9 : Elemental data of the SMZY obtained from the CHNS analyzer Samples Carbon (%) Hydrogen (%) Nitrogen (%) Sulfur (%) Zeo-NaY-S 0.46 ± ± 0.02 n.d 0.03 ± 0.01 SMZY-50-S 1.12 ± ± 0.10 n.d 0.04 ± 0.01 SMZY-100-S 3.88 ± ± 0.05 n.d 0.05 ± 0.01 SMZY-200-S 3.46 ± ± 0.11 n.d 0.04 ± 0.01 Zeo-NaY-C 0.07 ± ± 0.06 n.d 0.12 ± 0.06 SMZY-50-C 1.77 ± ± 0.04 n.d 0.04 ± 0.01 SMZY-100-C 2.06 ± ± 0.06 n.d 0.04 ± 0.01 SMZY-200-C 1.89 ± ± 0.08 n.d 0.04 ± 0.02 Note: n.d = not detected The carbon and hydrogen were supposedly not to be present in both of the unmodified zeolite Y. However, since some organic impurities and moisture were present in the zeolites, the variation of the results was acceptable. The percentage of carbon was somewhat higher in the synthesized zeolite Y than the commercial one because the source of silica in the synthesized zeolite was from the natural products, rice husk ash, which contained organic impurities that were not fully removed. The instrument could not detect the presence of the nitrogen in the samples because the concentration of this element was relatively too low as there is only one nitrogen for every surfactant. The insignificant values of the percentage of hydrogen in those samples were due to the possibility of the zeolites allowing the adsorption of water (H 2 O) from the environment. This data showed that the amount of carbon and hydrogen in the SMZY was higher than the respective unmodified zeolite Y validated that the HDTMA cation was exchanged with sodium in the zeolite Y after the modification process. The quantity of sodium and HDTMA was found to vary among the SMZY due to the different amounts of starting HDTMA used in the modification.

119 Surface Area and Porosity In general, the adsorption of metals onto the sorbents depends on its surface area and porosity. Bigger pore size creates wider surface area of the materials hence giving more exchange sites and resulted in higher adsorption capacity. Therefore, it is important to get the information about the surface area and porosity of the sorbents. Table 3.10 gives the value of the surface area and porosity for each SMZY together with their parent zeolite Y and the variation of these values was illustrated in Figure The analysis data are attached in Appendix E. Although the preparation of SMZY was based on the surface modifications of the zeolite, the HDTMA cation did not alter the area of the external surface of the zeolite since the HDTMA molecules did not have a long chain hydrocarbon tail compared of other cationic surfactant, for instance OTS (octadecyltrichlorosilane). Hadi Nur et al. (2005) had used OTS for covering the surface of zeolite NaY, and they found that the specific surface area of the modified zeolite NaY was lower than the unmodified because the OTS have the long chain hydrocarbon tail that tend to accumulate at the exterior framework of the zeolite. In contrast, the surface area of the SMZY became higher than the unmodified zeolite that tends to give more adsorption capacity for toxic metals in water. Table 3.10 : Surface area and porosity of the SMZY and unmodified zeolites. Samples Surface area (m 2 /g) Total pore volume (cc/g) Average pore size (Ǻ) Zeo-NaY-S SMZY-50-S SMZY-100-S SMZY-200-S Zeo-NaY-C SMZY-50-C SMZY-100-C SMZY-200-C

120 Zeo- NaY-S SMZY- 50-S SMZY- 100-S SMZY- 200-S Zeo- NaY-C SMZY- 50-C SMZY- 100-C SMZY- 200-C Surface area x 10 (m2/g) Total pore volume x 10E-2 (cc/g) average pore size (Angstrom) Figure 3.13 The comparison of the specific surface area (m 2 /g), total pore volume (cc/g) and average pore size (Ǻ) for SMZY and unmodified zeolite Y Dispersion Behavior The relative positions of SMZY and unmodified zeolite Y solid particles in an oil-water mixture when added to hexane-water mixture are shown in Figure The different distribution of modified and unmodified zeolite Y in the hexane water mixture can be seen in this figure where the SMZY forms a colloidal dispersion in the organic phase (dispersed in hexane) while the unmodified zeolite Y was dispersed well in aqueous phase (dispersed in water). It proves that the distinctive behavior of the SMZY from unmodified zeolite Y was due to the modification of zeolite surface by HDTMA that created a partially hydrophobic zeolite Y.

121 96 Synthesized zeolite Y Commercial zeolite Y (1) (2) (3) (4) (5) (6) (7) (8) Figure 3.14 Photographs show the distribution of SMZY and unmodified zeolite NaY solid particles when added to hexane-water mixture. The hexane solution is located at upper phase and the water was situated at lower phase. Legend: (1) Zeo-NaY-S, (2) SMZY-50-S, (3) SMZY-100-S, (4) SMZY-200-S, (5) Zeo-NaY-C, (6) SMZY-50-C, (7) SMZY-100-C, (8) SMZY-200-C In order to study the dispersion behavior of SMZY and unmodified zeolite NaY, the samples from the relative position in an oil-water mixture were stirred and subsequently the solid particles distribution was observed instantaneously after the stirring and after the static condition. Figure 3.15 shows the image of SMZY and unmodified zeolite NaY in hexane-water before stirring, after stirring for 2 hours and after static condition for 30 minutes and for 24 hours.

122 97 (1) (2) (3) (4) (5) (6) (7) (8) (a) Stirring for 2 hours (b) Static for 30 minutes (c) Static for 24 hours (d) Figure 3.15 Photographs showing the distribution of SMZY and unmodified zeolite Y solid particles; (a) when added to hexane-water mixture, (b) after stirring for 2h, (c) after keeping under static conditions for 30 minutes and (d) 24 hours. The legends are same with Figure 3.14.

123 98 The observation from Figure 3.15 confirms that the samples of SMZY were dispersed in aqueous solution (water) and in organic phase as well (hexane) after stirring for 2 hours due to the contact of the water molecule in the zeolite Y structure since the water molecules were able to enter the pore size of the zeolite structure. After 24 hours, the solid particles of both unmodified zeolite NaY settled out, whereas the samples SMZY remained well dispersed in aqueous water. This observation revealed that the dispersion behavior of zeolite Y was changed after the modifications of its surface by HDTMA. The modified zeolite Y with HDTMA became partially hydrophobic and hydrophilic. From these photographs as well, the dispersion behavior of the SMZY was not different among them because of the insignificant amounts of HDTMA in the series of the SMZY according to the elemental analysis Maximum Adsorption of HDTMA Sorption of cationic surfactants from solution onto solid surfaces can be described by the Langmuir isotherm. The sorption isotherm for HDTMA on the synthesized zeolite Y is presented in Figure 3.16 and the analysis data for this study can be seen in Appendix F. [HDTMA] sorbed, (mmol/kg [HDTMA]e, (mmol/l) Figure 3.16 The sorption isotherm plotted of HDTMA onto the synthesized zeolite Y

124 99 When fitting the data (Figure 3.16) into equation 14 in Section 1.6.1, it was found that the high coefficient of determination (r 2 ) as shown in Figure 3.17 indicating good agreement with Langmuir model. The maximum of the HDTMA adsorbed onto zeolite (Q o ) can be calculated from the equation given in the graph (Figure 3.17) and was tabulated in Table Li and Bowman (1997) also found the same result where the adsorption isotherms of HDTMA-Br, HDTMA-Cl and HDTMA-HSO 4 on the clinoptilolite surface were followed Langmuir isotherm /qe y = x R 2 = /Ce Figure 3.17 The plotted of 1/q e against 1/C e where q e is the HDTMA adsorbed at equilibrium (mmol/kg) and C e is concentration of HDTMA at equilibrium (mmol/l). Table 3.11 : Fitted Langmuir parameters for sorption of HDTMA by synthesized zeolite Y Slope (1/bQ o ) intercept (1/Q o ) Q o (mmol/kg) b (1/kg) r ,9754 The HDTMA molecule is sorbed ( mmol/kg) essentially quantitatively up to nearly twice the ECEC value of the synthesized zeolite Y (671.4 mmol/kg). Sullivan et al. (1998) also found the same results when they used clinoptilolite, the naturally occurring zeolite tailoring with HDTMA. It thus proved that the HDTMA molecule with

125 100 concentration above CMC creates an organic-rich layer on the zeolite surface and the charge on the surface is reversed from negative to positive. The positive charge on the outward-pointing HDTMA head groups is balanced by anions from the solution, forming an electrical double layer. The schematic diagram for this theory can be seen in Figure The anion properties in the surface of SMZY allow them to exchange the counter ions by other anions. Pore Cation (Na + ) balance the charge inside Internal area Br - Br - Br - Br - Br - Zeolite NaY Br - Br Br - Br - Br - Br - Br - Br - Br - HDTMA Bromide Surfactant modified zeolite Y (SMZY) Figure 3.18 structure Schematic diagram of the theoretical HDTMA formation on the zeolite Y

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