Fabrication and Characterization of Zeolites and its Application in Heavy Metal Capture

ABSTRACT

Zeolite crystals were synthesized by mixing sodium silicate and sodium aluminate to obtain aluminosilicate gel which was further treated hydrothermally to obtain the final product. The zeolite crystals were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD result identified the synthesized crystals as zeolite z; additional evidence was provided by the SEM images which showed that the zeolite crystals were disc-shaped and the particle sizes ranged between 13.4 – 53.6 µm. batch adsorption studies using the synthetic zeolite showed efficient removal of chromium (III) ion from aqueous solution. The atomic absorption spectroscopy (AAS) result which gave the final metal ion concentration indicated that the rate of adsorption increased with increase in the mass of adsorbent (zeolite) and decrease in particle size of the zeolite crystals. In the course of treatment, different quantities of zeolite ranging from 0.5 – 2.5 g were used; also different concentrations of Cr (III) ion (10, 15, 20, 25, 30 ppm) were used to determine the extent of adsorption. The percentage adsorption increased from 55.75 – 96.6 % and decreased from 98 -88.3 % respectively in each case. As the pH values were adjusted between 1 – 11, percentage adsorption increased from 55 – 97 % with a sharp increase at pH 7. While in the case of the zeolite samples with different particle sizes, the percentage adsorption reduced from 98.9 -70 % as particle sizes increased from 13.4 – 53.6 µm. The high percentage adsorption of the zeolite samples suggests that zeolites are good adsorbents for the removal of Cr from aqueous solutions. Also the batch experiment conducted showed that the adsorption pattern followed the Langmuir and Freundlich isotherm models with correlation factors (R2 ) values of 0.997 and 0.963 respectively.

TABLE OF CONTENT

Title page i

Approval page ii

Certification iii

Dedication iv

Acknowledgement v

Table of Content vi

List of Table ix

List of figures x

List of abbreviations xi

Abstract xii

CHAPTER ONE

1.0 Introduction 1

1.1 Background of Study 2

1.2 Statement of Problem 4

1.3 Objective of Study 4

1.4 Justification of Study 5

CHAPTER TWO

2.0 Literature Review 6

2.1 Zeotypes 6

2.2 Natural Zeolites 7

2.3 Synthetic Zeolites 9

2.4 Structure 11

2.4.1 Primary Building Units 13

2.4.2 Secondary Building Units (SBU) 15

2.5 Properties and Characteristics of Zeolites 16

2.5.1 Sorption and Ion Exchange 16

2.5.2 Molecular Sieving 17

2.5.3 Volume Exclusion 17

2.5.4 Swelling 17

2.5.5 Salt Imbibitions 17

2.5.6 Pore Size Modification 18

2.6 Applications of Zeolite 20

2.6.1 Catalysis 20

2.6.2 Ion exchange 20

2.6.3 Adsorption 21

2.6.3.1 Mechanism of adsorption 22

2.7 Synthesis of zeolites 25

2.7.1 Hydrothermal and microwave synthesis of nanoporous zeolites 27

2.8 Applications of zeolite for the removal of heavy metals from waste water 36

2.8.1 Heavy metals 36

CHAPTER THREE

3.0 Experimental 45

3.1 General 45

3.2 Methods of zeolite synthesis 46

3.2.1 Preparation of starting gel 47

3.2.2 Crystallization 47

3.2.3 Product Recovery 47

3.3 Product Characterization 48

3.4 Batch Adsorption Studies 48

3.4.1 Effect of metal ion concentration 49

3.4.2 Effect of Adsorbent Dosage 49

3.4.3 Effect of pH on adsorption rate 49

3.4.4 Effect of varying Particle sizes 50

CHAPTER FOUR

Results and Discussion 51

4.1Characterization of samples 51

4.2 Adsorption of heavy metal (chromium) ion 55

4.3 Adsorption Isotherm 62

CHAPTER FIVE

Conclusion 66

REFERENCES 67