SORPTION BEHAVIOR OF ZEOLITE P AND ITS MODIFIED FORMS IN THE
REMOVAL OF SOME HEAVY METALS AND OXYANIONS FROM
AQUEOUS MEDIA
TAN SEE HUA
UNIVERSITI TEKNOLOGI MALAYSIA
iii
To Jesus Christ, my Lord, Savior and Provider,
And
My Parents, Sis, and Nanny.
iv
ACKNOWLEDGEMENT
I would like to thank my supervisor, Prof. Dr. Alias Mohd. Yusof for giving
me the opportunity to do this research project and for his assistance throughout my
studies. His encouragement, patience and academic guidance were crucial in the
successful completion of this work. His diligence, dedication and vision are good
examples for me to follow.
It has been a pleasure for me to work with many enthusiastic people as part
of chemistry department. Many thanks to present and former members, especially to
Mohammad Adil, Nik Ahmad Nizam, Lee Kian Keat, Jei Ching Yih, Wong Hon
Loong and Chia Chai Har. Your great support and friendship during this period
helped me to survive the long hours we spent together in the laboratory.
I would to extend my thanks to Ibnu Sina Institute for Fundamental Science
Studies, UTM for allowing me to use the chemical instruments there. Special thanks
dedicated to Mr. Lim Kheng Wei, for his willing help in operating the instruments.
Besides that, I would like to grateful acknowledge the assistance of Prof. Dr.
Hamzah Mohamad, Geology Department UKM, Kajang for XRF elemental analysis.
This thesis would not have been accomplished without the unconditional love
and support of my family members as well as brothers and sisters in Christ. Their
understanding and prayer make the work of thesis writing a lot more enjoyable.
The financial assistance from IRPA grant for this project is grateful
acknowledged. A special thank to Universiti Teknologi Malaysia for providing the
Research Student Grant for me.
v
ABSTRACT
Due to their toxicity and persistence, hazardous metal ions such as lead
(Pb2+), cadmium (Cd2+) and zinc (Zn2+) as well as oxyanions like selenite, Se (IV)
and selenate, Se (VI) pose a worrying threat to the environment and human health
when released into water resources as constituents of waste. This study covers the
synthesis, characterizations and analytical works on the development of an
inexpensive and excellent inorganic sorbent, i.e. zeolite Na-P2 which was
synthesized using local rice husk ash as the raw material. The product was well
characterized with various sophisticated techniques and further modified into its
nearly-homoionic sodium and calcium form zeolite through ion exchange in order to
investigate the sorption behaviors of these cationic form zeolite samples towards the
selected hazardous metal ions. The sorption of selected metals such as Pb2+, Cd2+
and Zn2+ was proven to be ion-exchange process through batch adsorption studies.
The removal efficiencies of these zeolite species were investigated via several
variables such as time, concentration, pH and competition within the solutes. The
binary ion-exchange isotherms were constructed using thermodynamic equilibrium
model and the standard free energies of exchange were calculated as well. The
selectivity sequence of zeolite Na-P2 was as Pb2+>Cd2+>Na+>Zn2+ whereas for Caexchanged garronite which denoted as Homo-Ca, the selectivity sequence was
Pb2+>Ca2+>Cd2+>Zn2+. The multicomponent exchange of zeolite was also
investigated. On the other hand, the original zeolite Na-P2 was loaded with
aluminium ions using aluminium sulfate post desilication in order to investigate its
capability in the removal of selenite and selenate species in water. Different variables
of the selenium species adsorption onto aluminium-loaded zeolite Na-P2 such as
time, concentration and ionic strength were also studied. The results showed that the
aluminium-loaded zeolite Na-P2 (sample 10Al-P) performed well in the removal of
selenium oxyanions from water compared to other materials. As conclusion, zeolite
Na-P2 and its modified forms can be used as excellent metal-removing agents in the
water purification process.
vi
ABSTRAK
Disebabkan oleh ketoksikan dan kekekalan yang wujud, ion-ion logam
merbahaya seperti plumbum (Pb2+), Kadmium (Cd2+) and Zink (Zn2+) serta oksianion
seperti selenit, Se (IV) and selenat, Se (VI) memaparkan sebagai ancaman terhadap
alam sekitar dan kesihatan manusia apabila mereka dilepaskan ke dalam sumbersumber air sebagai bahan sisa. Penyelidikan ini merangkumi kerja-kerja sintesis,
pencirian dan analisis ke atas pembangunan suatu penjerap tak organik yang murah
dan cekap, iaitu zeolit Na-P2 di mana ia disintesis dengan menggunakan abu sekam
padi tempatan sebagai bahan mentah. Produk itu dicirikan dengan pelbagai jenis
teknik yang canggih dan seterusnya ia dimodifikasi kepada bentuk natrium dan
kalsium hampir-homoionik agar dapat mengkaji tabiat penjerapan bagi sampel zeolit
yang berbentuk kationik ini terhadap ion-ion logam merbahaya terpilih. Penjerapan
ion-ion logam terpilih seperti Pb2+, Cd2+ and Zn2+ telah dibuktikan sebagai proses
penukargantian ion melalui kajian penjerapan berkelompok. Kecekapan
penyingkiran bagi spesies-spesies zeolit ini telah dikaji melalui beberapa
pembolehubah seperti masa, kepekatan, pH and persaingan di antara bahan terjerap.
Isoterma penukargantian ion binari telah dibina dengan menggunakan model
keseimbangan termodinamik dan tenaga bebas piawai bagi penukargantian juga telah
dikira. Susunan kepilihan bagi zeolit Na-P2 adalah Pb2+>Cd2+>Na+>Zn2+ manakala
bagi garronit tertukarganti kalsium yang dilabel sebagai Homo-Ca, susunan
kepilihannya adalah Pb2+>Ca2+>Cd2+>Zn2+. Penukargantian komponen multi bagi
zeolit Na-P2 juga dikaji. Di samping itu, zeolit Na-P2 asal dimuatkan dengan
menggunakan aluminium sulfat selepas penyingkiran silika untuk mengkaji
kecekapannya dalam penyingkiran spesies selenit and selenat dalam air.
Pembolehubah bagi penjerapan spesies-spesies selenium ke atas zeolit Na-P2termuat-aluminium seperti masa, kepekatan dan kekuatan ionik juga telah dikaji.
Keputusan menunjukkan zeolite Na-P2-termuat-aluminium (sampel 10Al-P)
mempunyai prestasi yang baik berbanding dengan bahan-bahan lain dalam
penyingkiran oksianion selenium daripada air. Sebagai kesimpulannya, zeolit Na-P2
dan bentuk-bentuk terubahsuai dapat digunakan sebagai agen penyingkiran logam
yang cekap dalam proses penulenan air.
vii
TABLE OF CONTENTS
CHAPTER
TITLE
PAGE
THESIS STATUS DECLARATION
SUPERVISOR’S DECLARATION
1
2
TITLE PAGE
i
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
xii
LIST OF FIGURES
xiv
LIST OF SYMBOLS
xviii
LIST OF ABBREVIATIONS
xxi
LIST OF APPENDICIES
xxiv
INTRODUCTION
1
1.1 Background of Study
1
1.2 Research Description and Objectives
3
1.3 Organization of Thesis
6
LITERATURE REVIEW
7
2.1 Hazardous Elements and Their Impact on Health
7
2.1.1
Zinc (Zn)
11
viii
2.1.2
Cadmium (Cd)
12
2.1.3
Lead (Pb)
13
2.1.4
Selenium (Se)
14
2.2 Conventional and Advanced Methods for
15
Hazardous Elements Removal from the
Contaminated Water – A Brief Review
2.3 Features of Zeolites
2.3.1
General Aspects of Hydrothermal
19
22
Synthesis of Zeolites
2.3.2
Low Cost Synthetic Zeolites
2.4 Zeolites of the Gismondine Group (GIS)
2.4.1
Zeolites P with GIS Framework
2.5 Sorption Theory
3
23
24
26
27
2.5.1
Adsorption
27
2.5.2
Ion Exchange
30
2.5.3
Surface Complexation
34
EXPERIMENTAL
37
3.1 The Determination of Silica in Untreated Rice
37
Husk Ash
3.2 Syntheses of Zeolite P
3.2.1
Detailed Description of the Zeolite P
38
39
Synthesis Condition with Starting
Compositions of 4Na2O: Al2O3: 10 SiO2:
130H2O
3.3 Modification of Zeolites
40
3.3.1
Desilication
40
3.3.2
Ion exchange with Sodium or Calcium
41
Ions
3.3.3
Loading of Aluminium
3.4 Characterizations of Zeolite Samples
3.4.1
X-ray Diffraction (XRD)
41
42
42
ix
3.4.2
Fourier-Transform Infrared Spectroscopy
42
(FTIR)
3.4.3
Wavelength Dispersive X-ray
43
Fluorescence Spectroscopy (WDXRF)
3.4.4
Scanning Electron Microscopy (SEM)
43
3.4.5
Thermogravimetric-Differential Thermal
43
Analysis (TG-DTA)
3.4.6
Surface Analysis with Nitrogen
44
Adsorption
3.4.7
Solid-State Nuclear Magnetic Resonance
44
Spectroscopy (NMR)
3.5 Batch Sorption Experiments
3.5.1
44
Divalent Metals Removal
45
3.5.1.1
45
Kinetic of Divalent Metal Ions
Removal
3.5.1.2
Effect of pH towards Removal
46
of Divalent Metal Ions
3.5.1.3
Binary Ion Exchange of Divalent
46
Metal Ions with Indigenous Ions
in Zeolites
3.5.1.4
Multicomponent Ion Exchange
47
of Divalent Metal Ions with
Indigenous Ions In Zeolites
3.5.2
Selenium Oxyanions Removal
48
3.5.2.1
49
Kinetic of Selenium Oxyanions
Removal by Aluminium-loaded
Zeolite P
3.5.2.2
Construction of Adsorption
49
Isotherm
3.5.2.3
Effect of Ionic Strength towards
50
Removal of Selenium Oxyanions
by Aluminium-loaded Zeolite P
3.6 Flame Atomic Absorption Spectroscopy (FAAS)
50
x
4
RESULTS AND DISCUSSION: SORBENTS
53
DEVELOPMENT
4.1 Synthesis of Zeolite P
53
4.2 Modification of Zeolite Na-P2
60
4.2.1
Structural Change of Zeolite Na-P2 upon
61
Ion Exchange
4.2.2
Investigation of the Possibility of
69
Preparing Protonated Zeolite P through
Calcination
4.2.3
Loading of Aluminium onto Desilicated
72
zeolite Na-P2
5
RESULTS AND DISCUSSION: SORPTION
76
STUDIES ON THE SORBENTS
5.1 Cation Removal
5.1.1
76
Kinetic Studies of Ion Exchange on the
76
Zeolite
5.1.2
Characterization of the Ion Exchange
85
Products
5.1.3
Effect of Solution pH Value on the Metal
86
Uptake
5.1.4
Construction of Binary Ion Exchange
90
Isotherm
5.1.4.1
Exchanges with Pb2+ as the
90
Entering Cation
5.1.4.2
Exchanges with Zn2+ as the
91
Entering Cation
5.1.4.3
Exchanges with Cd2+ as the
92
Entering Cation
5.1.5
Kielland Plots
93
5.1.6
Multicomponent Ion Exchange
98
5.2 Anion Removal
101
xi
5.2.1
Selection of Optimum Aluminium-Loaded
101
Zeolite Na-P2 through Kinetic Studies
5.2.2
Modeling of Se (IV) and Se (VI)
106
Adsorption Isotherm
5.2.3
Effect of Ionic Strength of Solution on the
109
Selenium Uptake
6
5.2.3.1
Uptake of Selenite
109
5.2.3.2
Uptake of Selenate
111
CONCLUSION AND SUGGESTIONS
114
6.1 Conclusion
114
6.2 Contributions
116
6.3 Suggestions for Future Studies
116
REFERENCES
117
APPENDICES
134
xii
LIST OF TABLES
TABLE NO.
2.1
TITLE
Biological significance of classification of metals based on
PAGE
10
the last electron subshell in the atom to be occupied
3.1
Operating parameters of FAAS (Perkin-Elmer AAnalyst
52
400) in the measurement of the desired elements
4.1
Comparison of Si/Al ratio for original and desilicated
61
zeolite Na-P2
4.2
X-ray diffraction data of zeolite Na-P2 (Ori-P)
63
4.3
X-ray diffraction data of garronite (Homo-Ca)
64
4.4
Chemical compositions of zeolites determined by WDXRF
65
4.5
Unit cell compositions of zeolites (on the basis of 32
66
oxygen)
4.6
Assignment of 29Si NMR chemical shifts to the local Si
68
environment in the zeolites
4.7a
2θ values of desilicated zeolite Na-P2 and series of
74
aluminium-loaded zeolite Na-P2
4.7b
d-spacings of desilicated zeolite Na-P2 and series of
74
aluminium-loaded zeolite Na-P2
4.8
27
Al chemical shift for aluminium-loaded zeolite Na-P2 in
75
NMR spectra
5.1
Pseudo-second-order rate constant, calculated qe and
81
experimental qe values for the zeolites in the removal of
Pb2+, Zn2+ and Cd2+ ions
5.2
Intraparticle diffusion rate constant for the sorption of
2+
2+
2+
Pb , Zn and Cd onto zeolites
84
xiii
5.3
Maximum exchange capacity qmax, thermodynamic
98
equilibrium constants KA and standard free energy ∆G° of
investigated equilibria at 302 ± 2K
5.4
Pseudo second-order rate constant, calculated q e values
105
and initial sorption rate h for sample 10Al-P in the removal
of Se (IV) and Se (VI)
5.5
Intraparticle diffusion rate constant for the sorption of Se
105
(IV) and Se (VI) onto sample 10Al-P
5.6
The parameters for Langmuir and Freundlich isotherms for
108
Se (IV) and Se (VI) removal
5.7
Parameters for Langmuir and Freundlich isotherms for
111
selenite removal with the presence of different
concentration of electrolyte
5.8
Parameters for Langmuir and Freundlich isotherms for
selenate removal with the presence of different
concentration of electrolyte
112
xiv
LIST OF FIGURES
FIGURE NO.
2.1
TITLE
Classification of elements based on the last electron
PAGE
9
subshell in the atom to be occupied
2.2
Secondary Building Units (SBU) of Zeolites
21
2.3
Periodic building unit constructed from 4-fold connected
25
D8Rs
2.4
Connection mode and unit cell content in GIS seen along
a.
25
The bold part indicates a double crankshaft chain
which consists of 2-fold (1,2)-connected double 4-rings
2.5
Fused intersections viewed along a (left) and b (right)
26
2.6
Isotherms typically found for a binary ion exchange
32
2.7
The three mechanisms of cation adsorption on a siloxane
35
surface (e.g. montmorillonite)
4.1
X-ray diffractogram for field-burnt rice husk ash
53
4.2
X-ray diffractogram of final products when field-burnt
54
RHA was employed as silica source in synthesis
4.3
X-ray diffractogram of zeolite Na-P2
55
4.4
X-ray diffractogram of zeolite Na-P1
55
4.5
FTIR spectra of (a) zeolite Na-P1 and (b) zeolite Na-P2
56
4.6
SEM image of zeolite Na-P2
57
4.7
SEM image of zeolite Na-P1
57
4.8
X-ray diffractogram of three stable phases appeared in
58
product
4.9
X-ray diffractogram of products with different ratio of
reactant compositions
59
xv
4.10
X-ray diffractogram of zeolite Na-P2 after desilication at
60
60 °C
4.11
SEM image of zeolite Na-P2 after desilicated at 60 °C
61
4.12
X-ray diffractogram of desilicated- calcium ion
62
exchanged zeolite (garronite)
4.13a
29
Si NMR spectra of zeolite Na-P2 and garronite
67
4.13b
27
Al NMR spectra of zeolite Na-P2 and garronite
67
4.14
TG-DTA thermogram of sample Ori-P
69
4.15
TG-DTA thermogram of desilicated zeolite P2
70
4.16
TG-DTA thermogram of ammonium-exchanged
70
desilicated-zeolite P2
4.17
X-ray diffractogram for ammonium-exchanged
71
desilicated zeolite P2 and its H-form product at different
temperature
4.18
FTIR spectra for ammonium-exchanged desilicated
72
zeolite P2 and its H-form product at different
temperature
4.19
Comparison of the X-ray diffractogram between
73
desilicated zeolite Na-P2 and aluminium-loaded zeolite
Na-P2
4.20
27
Al NMR spectra of (a) desilicated zeolite Na-P2 and
75
(b) aluminium-loaded zeolite Na-P2
5.1
Plot of sorbed amount versus time for Pb2+ ions by the
77
zeolites
5.2
Plot of sorbed amount versus time for Zn2+ ions by the
77
zeolites
5.3
Plot of sorbed amount versus time for Cd2+ ions by the
78
zeolites
5.4
Pseudo-second-order sorption kinetics of Pb2+, Zn2+ and
80
Cd2+ ions onto zeolites
5.5
Morris-Weber kinetic plots for the uptake of Pb2+ions
onto zeolites
82
xvi
5.6
Morris-Weber kinetic plots for the uptake of Zn2+ions
83
onto zeolites
5.7
Morris-Weber kinetic plots for the uptake of Cd2+ions
84
onto zeolites
5.8
X-ray diffractogram of sample Ori-P after exchanged
85
with the targeted metal ions
5.9
Concentration of metal ions in the working solutions with
87
various pH value without the presence of zeolite
5.10
The effect of initial pH on Pb2+ ions removal by the
88
zeolites
5.11
The effect of initial pH on Zn2+ ions removal by the
89
zeolites
5.12
The effect of initial pH on Cd2+ ions removal by the
89
zeolites
5.13
Binary ion exchange in zeolites for Pb2+ ions at 302 K ±
91
2K
5.14
Binary ion exchange in zeolites for Zn2+ ions at 302 K ±
92
2K
5.15
Binary ion exchange in zeolites for Cd2+ ions at 302 K ±
93
2K
5.16
Kielland plots in zeolites for Pb2+ ions at 302 K ± 2K
95
5.17
Kielland plots in zeolites for Zn2+ ions at 302 K ± 2K
95
5.18
Kielland plots in zeolites for Cd2+ ions at 302 K ± 2K
96
5.19
Plot of sorbed amount of metal ions onto sample Ori-P
99
versus initial concentration in the multi-metal solution
5.20
Plot of sorbed amount of metal ions onto sample Homo-
100
Na versus initial concentration in the multi-metal solution
5.21
Plot of sorbed amount of metal ions onto sample Homo-
100
Ca versus initial concentration in the multi-metal solution
5.22
Plot of sorbed amount versus time for Se (IV) by the
103
series of aluminium-loaded zeolites
5.23
Plot of sorbed amount versus time for Se (VI) by the
series of aluminium-loaded zeolites
103
xvii
5.24
Pseudo-second order sorption kinetics of Se (IV) and Se
104
(VI) onto sample 10Al-P
5.25
Morris-Weber kinetic plots for the sorption of Se (IV)
105
and Se (VI) onto sample 10Al-P
5.26
Plot of sorbed amount of Se (IV) and Se (VI) onto sample
106
10 Al-P versus equilibrium concentration, Ce
5.27
Linearized Langmuir isotherms for Se (IV) and Se (VI)
107
removal by sample 10 Al-P
5.28
Linearized Freundlich isotherms for Se (IV) and Se (VI)
108
removal by sample 10 Al-P
5.29
Plot of sorbed amount of Se (IV) onto sample 10Al-P
109
versus equilibrium concentration, Ce with the presence of
different concentration of electrolyte
5.30
Linearized Langmuir isotherms for Se (IV) removal by
110
sample 10Al-P with the presence of different
concentration of electrolyte
5.31
Linearized Freundlich isotherms for Se (IV) removal by
110
sample 10Al-P with the presence of different
concentration of electrolyte
5.32
Plot of sorbed amount of Se (VI) onto sample 10Al-P
112
versus equilibrium concentration, Ce with the presence of
different concentration of electrolyte
5.33
Linearized Langmuir isotherms for Se (VI) removal by
113
sample 10Al-P with the presence of different
concentration of electrolyte
5.34
Linearized Freundlich isotherms for Se (VI) removal by
sample 10Al-P with the presence of different
concentration of electrolyte
113
xviii
LIST OF SYMBOLS
°C
-
Celsius degree
K
-
Kelvin degree
C0
-
Initial concentration
Ce
-
Equilibrium concentration
Ct
-
Concentration, after a prescribed duration
cm
-
Centimeter
g
-
Gram
kg
-
Kilogram
L
-
Liter
m
-
Meter
µm
-
Micrometer
nm
-
Nanometer
M
-
Molar
mA
-
Miliampere
λ
-
Wavelength
meq
-
Miliequivalent
mg
-
Miligram
µg
-
Microgram
h
-
Hour
min
-
Minute
s
-
Second
µs
-
Microsecond
mL
-
Mililiter
mm
-
Milimeter
mmol
-
Milimol
N
-
Normal
xix
qt
-
Sorbate uptake after a prescribed duration
qe
-
Sorbate uptake at equilibrium
qmax
-
Maximum uptake capacity
KA
-
Thermodynamic equilibrium constant
t
-
Time
V
-
Volume of solution
Å
-
Angstrom
2θ
-
2-Theta value in X-ray diffraction
%T
-
Percent transmission
KHz
-
Kilohertz
MHz
-
Megahertz
k1
-
Equilibrium rate constant of pseudo-first-order sorption
k2
-
Equilibrium rate constant of pseudo-second-order sorption
r2
-
Correlation coefficient
kid
-
Rate constant of intraparticle diffusion
∆Hhydr
-
Enthalpy of hydration
C
-
Concentration or activity of free metal in solution according to
Langmuir and Freundlich model
S
-
Quantity of the metal ions sorbed according to Langmuir and
Freundlich model
M
-
Maximum sorption capacity of the sorbent according to
Langmuir model
b
-
Coefficient related to bonding energy according to Langmuir
model
KF
-
Freundlich empirical constant which related to adsorption
capacity
n
-
Freundlich empirical constant which related to intensity of
adsorbent
zi
-
Valency of ion i
M
-
Molar concentration
W
-
Zeolite mass
γ
-
Solution-phase activity coefficient
I
-
Ionic strength of solution
xx
ai
-
Ion size parameter
A and
-
Constants in the Debye-Hückel term
ρo
-
Density of water
ε
-
Dielectric constant of water
T
-
Temperature
∆G˚
-
Gibbs standard free energy
∆H˚
-
Standard enthalpy
∆S˚
-
Standard entropy
B
xxi
LIST OF ABBREVIATIONS
FAO
-
Food and Agriculture Organization of the United
Nations
XRD
-
X-ray diffraction
FTIR
-
Fourier-transform infrared spectroscopy
MAS/NMR
-
Solid- state nuclear magnetic resonance
spectroscopy under magic angle spinning
WDXRF
-
Wavelength dispersive x-ray fluorescence
spectroscopy
FAAS
-
Flame atomic absorption spectroscopy
SEM
-
Scanning electron microscopy
TG-DTA
Thermogravimetric-differential thermal analysis
EDAX
Energy dispersive x-ray microanalysis
Pb
-
Lead
Cd
-
Cadmium
Zn
-
Zinc
Se
-
Selenium
GIS
-
Gismondine
IUPAC
-
International Union of Pure and Applied Chemistry
DNA
-
Deoxyribonucleic acid
RNA
-
Ribonucleic acid
FIAM
-
Free ion activity model
HDL
-
High density lipoprotein
LDL
-
Low density lipoprotein
HgbA1C
-
Glycated hemoglobin
SLI
-
Staring-lighting-ignition
xxii
CNS
-
Central nervous system
PKC
-
Protein kinase C
AC
-
Alternate current
DC
-
Direct current
ELM
-
Emulsion liquid membrane
EC
-
Electrocoagulation
ETS-10
-
Engelhard titanosilicate-10
SBU
-
Secondary building units
ANA
-
Analcime
TLM
-
Triple layer model
IIS
-
Ibnu Sina Institute for Fundamental Science Studies
LOI
-
Loss of ignition
H2SO4
-
Sulfuric acid
HF
-
Hydrofluoric acid
NaOH
-
Sodium hydroxide
NaAlO2
-
Sodium aluminate
DDW
-
Distilled-deionized water
NaNO3
-
Sodium nitrate
KCl
-
Potassium chloride
Ca(NO3)2
Calcium nitrate
NH4NO3
Ammonium nitrate
rpm
Revolution per time
KBr
Potassium bromide
CRM
Certified standard material
PP
Polypropylene
C2H2
Acetylene
HCL
Hollow cathode lamp
EDL
Electrodeless-discharged lamp
QCS
Quality control sample
RHA
Rice husk ash
PDF
Powder diffraction file
Ori-P
As-synthesized zeolite Na-P2
Homo-Na
Nearly-homoionic zeolite Na-P2
xxiii
Homo-Ca
Calcium exchanged zeolite Na-P2 (corresponded to
garronite)
CEC
Cation exchange capacity
H2SeO3
Selenious acid
10Al-P
Desilicated zeolite Na-P2 loaded with 10 mmol/L
aluminium sulfate
NaCl
Sodium chloride
n.v
Negative value
xxiv
LIST OF APPENDICES
APPENDIX
A
TITLE
National Drinking Water Quality
PAGE
134
Standards, 2000 of Malaysia for Some
Inorganic Species and Frequency of
Monitoring
B-1
EDAX Spectrum for Zeolite Na-P1
136
B-2
EDAX Spectrum for Zeolite Na-P2
137
B-3
EDAX Spectrum for Desilicated Zeolite
138
Na-P2
C
X-ray Diffractogram of Well-Mixed
139
Zeolite Na-P2
D-1
Surface Analysis of Zeolite Na-P2
140
Using Nitrogen Adsorption
D-2
E-1
Calculation of Si/Al Ratio through 29Si
NMR
Ion exchange Kinetics Data of Pb2+,
141
143
Zn2+ and Cd2+
E-2
The Effect of Initial pH on Metal Ions
148
Removal
E-3
Binary Ion Exchange Isotherm Data for
152
2+
Pb Uptake by Zeolites
E-4
Binary Ion Exchange Isotherm Data for
Zn2+ Uptake by Zeolites
154
xxv
E-5
Binary Ion Exchange Isotherm Data for
156
Cd2+ Uptake by Zeolites
E-6
Multicomponent Ion Exchange Isotherm
158
Data
F-1
Sorption Kinetics Data of Se (IV) and
160
Se (VI) by the Series of AluminiumLoaded Zeolites
F-2
Sorption Isotherm Data of Se (IV) and
164
Se (VI) by 10 Al-P
F-3
Sorption Isotherm Data of Se (IV) and
Se (VI) in NaCl Solution of Different
Ionic Strength
166
CHAPTER 1
INTRODUCTION
1.1
Background of Study
The presence of hazardous metals such as lead, zinc, cadmium as well as
some metalloids like selenium and arsenic in the environment particularly in water
have been drawing more and more public concern due to their toxicity and acute
impacts to the human health. Pollution of the environment and the human exposure
to these metallic or semi-metallic elements may occur naturally (e.g. erosion of
surface deposits of metal minerals and natural weathering of rock), or from
anthropogenic activities (mining, smelting, fossil fuel combustion and industrial
application of metals).
Concerned for sustaining healthy water resources, public are calling for more
and more environmental restriction. Consequently, industries and scientists are
searching for economic and efficient methods in protecting water resources from
pollution. Using the sorption process for the removal of harmful metals from
wastewater has a relatively shorter history if compared to other water purification
processes. In 1785, Lowitz observed that charcoal would decolorize many liquids.
This is the earliest documented use of carbon for the removal of impurities in
solutions [1]. Nowadays adsorption on activated carbon is a recognized method for
the removal of harmful metals from wastewater while the high cost of activated
carbon production and application limits its use in adsorption. A search for low cost
2
and easily available adsorbent has led to the investigation of materials of agricultural
and biological origin as potential metal sorbents [2].
Mineralogists have studied zeolites for two and half centuries beginning with
the first member, stilbite, which was discovered in 1756 [3]. However their
spectacular applications in industry have been developed only in the last 50 years.
The openness of the anionic frameworks ensures the easier mobility both of cations
in ion exchangers and of water molecules or other guest species. Additions and
removals of guest species can be fully reversible, and so zeolites may be excellent
sorbents for gases, vapors and liquids.
Considering the operation cost and efficiency, natural mineral zeolites such as
chabazite, clinoptilolie, mordenite etc. with high exchange capacity and specific
selectivity towards certain metal cations, have been utilized widely in water
purification [4-9]. Nevertheless, an unavoidable problem of the utilization is the
coexistence of the considerable impurities with the zeolitic tuffs, which interferes the
exchange behavior of natural zeolites with the toxic elements. As an alternative,
synthetic zeolites which usually possess higher exchange capacity, controlled and
known physicochemical properties relative to that for natural zeolites [10], have been
emphasized. Since the cost effectiveness is still the main consideration, low cost and
locally available natural materials should be the first priority in the zeolite synthesis
attempts.
Among the available local natural materials, rice husk which contains high
percentage of silica has drawn attention of researchers worldwide. Rice husk is an
agricultural waste material generated as by-product of rice refining process.
According to the Food and Agriculture Organization of the United Nations (FAO),
the annual world rice production amounts to 614,654,895 metric tons in the year of
2005 [11], of which 10-23% is husk [12]. The big amounts of rice husk produced are
treated as waste, causing disposal and pollution problem.
Silica is one of the basic raw materials in zeolite synthesis. Many authors
[13-15] have characterized and concluded that rice husks are outstanding source of
high-grade amorphous silica, approximately 92%-97% in the ash from the
3
combustion of this material at moderate temperature. The utilization of rice husk ash
as silica source in the synthesis of zeolite were well investigated by H. Hamdan et al.
[16]. They showed that that amorphous silica extracted from the rice husk by the
physical combustion with controlled temperature contains only *Si(OSi)4 tetrahedral
units and is the most reactive silica source in the synthesis of zeolite Y.
P.K. Bajpai and his co-workers [17-18] were the first group in the past who
has successfully synthesized mordenite-type zeolite using rice husk ash as silica
source. Later, Ajay K. Dalai and his group [19] have synthesized sodium X zeolite
by using this silica source for the first time. The syntheses of other zeolite species
with silica source from rice husk ash were carried on by other researchers. For
instance, zeolite Pc (cubic P), HS (hydroxysodalite), Z-21 (unknown structure, like
Linde-N), analcime, ZSM-5, ZSM-48 etc. were attempted to be produced in last two
decades [20-22]. Obviously, rice husk ash is suitable for low cost zeolite synthesis,
and this advantage certainly decreases the cost needed in the water purification
process, especially for drinking water resources.
The superior selectivity properties of the zeolites and their modified forms
towards hazardous substances deserve wide and further exploration and
development. In general, it must be recognized that relatively less attention has been
given in the beginning to study the sorption behavior of synthetic zeolites toward dand p-block metals and metalloids if compared to aspects of synthesis, gas separation
and catalysis. The comparative neglect was clearly biased since the incorporation of
zeolite with metals is often an essential component in the preparation and/or
manufacturer of zeolites for use either as sorbents or catalysts. This has been
motivating worldwide researchers to investigate the sorption behavior of zeolites
including ion exchange and adsorption since the past two decades.
1.2
Research Description and Objectives
With the view of long-term bioaccumulation risk of trace level harmful
metals to the livings’ health, the aim of this research is to compare several types of
4
modified sorbents, originated from a known extremely good water softener called
low silica zeolite P in the removal of some selected toxic metals and inorganic
oxyanions from water. The whole experimental design was based on the comparison
basis in which sorption behavior of the sorbents were interpreted according to their
batch sorption kinetic and equilibrium data in various conditions.
The study was mainly divided to three major component including material
development and characterization, cation exchange studies of the materials with
some metallic cations as well as adsorption of one of its modified form with
selenium oxyanions. Considering the cost efficiency factor, the original low silica
zeolite P was synthesized directly from the extremely low cost material, namely rice
husk ash as the silica source. The synthesis conditions were investigated and
optimized in the system Na2O-Al2O3-SiO2-H2O. Factors affecting the formation of
products such as composition of starting materials, heating temperature and
crystallization period were also studied.
The as-synthesized zeolite P was converted to nearly homoionic sodium and
calcium forms through exhaustively exchange with high concentration sodium and
calcium salt solution. The original zeolite was also partially loaded with aluminium
sulfate post modification step called desilication. Controlled desilication is an
advanced technique where the framework silica of the zeolite is partially removed in
basic medium. This technique has been introduced as an effective approach to create
significant extraporosity in various zeolites [23-24] and increase cation exchange
capacity [25-26].
The zeolite samples were well characterized with appropriate techniques
including structural analysis with x-ray diffraction (XRD), Fourier transformed
infrared spectroscopy (FTIR), solid state NMR under magic angle spinning (MAS);
elemental analysis either by wavelength dispersive x-ray fluorescence spectroscopy
(WDXRF) or atomic absorption spectroscopy (AAS) post sample decomposition;
morphological study with scanning electron micrography (SEM) and surface study
with nitrogen adsorption analysis.
5
Comparisons of the metallic cation sorption behaviors were done among the
nearly homoionic sodium and calcium form of the zeolites with the as-synthesized
zeolite P. Meanwhile, the aluminium-loaded zeolites P were tested and compared
with the original one in the removal of inorganic metalloid species. Divalent lead
(Pb), cadmium (Cd), zinc (Zn) and inorganic species of selenium, i.e. Se (IV) and Se
(VI) as well were chosen as the target adsorbates due to their toxicity and persistency
in the aqueous environment.
Batch mode studies were conducted throughout the whole research instead of
column studies. This is the most commonly used technique because of its ease of
laboratory operation and ease of data handling. This technique involves placing the
known quantity of sorbent and solution containing the known concentration of the
metals into a vessel and mixing the samples for a prescribed time. The sorbent
and/or solution phases are then analyzed by an accurate elemental analyzer (e.g.
atomic absorption spectrophotometry or inductively coupled plasma emission
spectrometry), after separation of the mixture with centrifugation and/or filtration.
The goal of this research is to examine the interaction of rice husk ashsynthesized zeolite P and its modified forms with various ions in solutions under
ranging conditions to elucidate the mechanism of sorption and ion exchange. The
specific objectives of this research are to:
•
Optimize the synthesis of zeolite P with gismondine (GIS) framework by using
local available rice husk ash as the silica source.
•
Investigate the physical and chemical changes of zeolite P after modification with
different solid-state techniques.
•
To understand the sorption behavior of the as-synthesized and modified zeolites
including exchange rate, equilibrium, and selectivity towards selected metallic
elements and metalloids under different conditions.
•
To evaluate the performance of as-synthesized and modified zeolites in the
removal of selected toxic metals and metalloids from aqueous media.
6
1.3
Organization of Thesis
This thesis consists of six chapters. Chapter 1 presents the general research
background, research description, objectives and the thesis organization. Chapter 2
introduces the general nature of zeolites as well as metallic elements and metalloids
as contaminants. The following description emphasizes on the materials under study,
i.e. gismondine (GIS) group zeolites generally and zeolite P particularly. This
chapter also presents extensive review of research relevant to the present study.
Chapter 3 describes the synthesis method of material, characterization techniques and
the experimental conditions employed in this work. Discussions on the synthesis
condition and characterization are the main body in chapter 4 whereas the sorption
behaviors of the materials toward the hazardous metals and metalloid oxyanions are
focused in chapter 5. The last chapter contains the concluding remarks and also
some recommendations for future studies.
CHAPTER 2
LITERATURE REVIEW
2.1
Hazardous Elements and Their Impact on Health
The large-scale release of hazardous elements into natural waters requires
human intervention. Many supposedly natural metal-rich rivers in fact drain areas
with a history of mining activity, so that the rivers receive either contaminated
minewaters or runoff from ageing spoil heaps [27]. Industrial wastewaters are
another obvious source of hazardous element discharges. In addition there are the
more diffused source of urban runoff and leachate from solid waste disposal site,
both of which may be rich in these elements. Direct toxicity to human and aquatic
life and indirect toxicity through accumulations of metals and metalloids in the
aquatic food chain are the focus of this threatening concern.
The term hazardous elements stated here specifically refer to those transition
elements, which are located in group IIIB through IIB and p-block poor metals like
lead in periodic table as well as some metalloids lie along the diagonal line. Living
organisms needs some of them in trace amounts but excessive levels can be
detrimental to the organisms. Some of the metals like lead and mercury have no
known beneficial on organisms and their accumulation over time in bodies can cause
serious illness. The term heavy metals have been used in the publication and
legislation for many years. The public and the politicians are crying out for the
reduction of heavy metal usages in the daily life. Nevertheless, satirically but
obviously, most of them grasp only scanty knowledge about the meaning of these
8
“guilty” heavy metals. These so-called heavy metals are often referred as a group
name for metals and semimetals (metalloids) that have been associated with
contamination and potential toxicity or ecotoxicity. The term “heavy” in conventional
usage implies high density. Knowledge of density is insufficient for the prediction of
biological effects of metals, especially since the elemental metals or their alloys are, in
most cases, not the reactive species with which living organisms have to deal [28]. It
is alleged that metals that are toxic in nature are heavy metals, but the fact of the
matter is that there is no authentic evidence behind this statement.
There is a tendency, unsupported by the facts, to assume that all so-called
“heavy metals” have highly toxic or ecotoxic properties. This immediately prejudices
any discussion of the use of such metals, often without any real foundation. The term
heavy metal has been used inconsistently. There is no exact definition of heavy
metals in literature. The major definitions made in the literature for the term “heavy
metals” are briefly reviewed herein.
(a).
Metals with element densities above 7g/cm3 [29].
(b).
Metals with a specific gravity greater than 4 [30].
(c).
Metals with atomic weight greater than that of sodium, i.e. greater than 23,
thus starting with magnesium [31].
(d).
Metals of atomic weights greater than 40, thus starting with scandium [32].
(e).
Elements commonly used in industry and generically toxic to animals and to
aerobic and anaerobic processes, but not every one is dense nor entirely
metallic. Includes As, Cd, Cr, Cu, Pb, Hg, Ni, Se, Zn [33].
Besides the mentioned definitions, there are still dazzling explanations of this
tricky term sprouted in the literature according to the elements’ densities, atomic
weights, atomic numbers, other chemical properties and even without clear basis other
than toxicity. Considering the confusion appeared and controversial usage, the term
heavy metals is obsolete in the whole body of thesis. For clearer discussion of the
chosen elements in this study as the basis of toxicity assessment without referring to
any “heaviness”, the elements were classified based on the last electron subshell in the
atom to be occupied. This is one of the chemical classifications recommended by the
International Union of Pure and Applied Chemistry (IUPAC) [28].
9
Figure 2.1: Classification of elements based on the last electron subshell in the
atom to be occupied
The periodic table shown in Figure 2.1 enables one to classify the nonmetallic, metallic and semi-metallic (metalloid) elements into four broad categories,
i.e. s-block, d-block transition, p-block and f-block (lanthanide and actinide). Table
2.1 summarizes the biological significant properties of these four categories. The
limitation of this scheme in sufficiently emphasizing the broad differences within the
elements can be overcome by complementing with the concept of Lewis acid behavior
of the metal ions [34]. With this combination, rational consideration of the chemical
and biological of metallic elements and compounds can be provided.
To understand the toxicity of metals, the electronic configuration must be
borne in mind. Electrons are usually intended to be in pair as they whiz around the
outside of atoms and give stability to the form of the atom or molecule. When, for any
reason, these paired electrons become separated, the molecule is damaged. These
damaged molecules are called “free radicals” and are highly reactive, attacking other
cellular structures to grab electron in order to form pairs again. Normally there are
enough free electrons in the vicinity to satisfy the demands of the free radicals
10
Table 2.1: Biological significance of classification of metals based on the last
electron subshell in the atom to be occupied [28]
Grouping
Biologically significant chemical properties
The alkali metal ions are highly mobile, normally forming only weak
complexes. Biologically, they act chiefly as bulk electrolytes. The
alkaline earths form more stable complexes and have more specialized
s-block
functional roles as structure promoters and enzymes activators. Neither
group has any significant redox chemistry in vivo.
Some limited redox chemistry, e.g. Pb4+/Pb2+ complicates the action of
these metals. They generally form more stable complexes than the s-
p-block
block. The higher atomic number elements tend to bind strongly to
sulfur, this is a major cause of their toxicity.
Shows an extremely wide range of both redox behavior and complex
d-block
formation. These properties underlie their catalytic role in enzyme
action.
The lanthanide and actinide elements show a wide range of redox
f-block
behavior and complex formation. Usually biologically unimportant, but
some (the actinide group) may be significant pollutants.
beyond a certain level, the cellular protective electron-donating mechanisms, which
usually keep these molecules in check, is exceeded. This circumstance makes great
numbers of these radicals are released and compete for stable electron-pairs formation.
Cell membranes are made of unsaturated lipids. The unsaturated lipid
molecules of cell membranes are particularly susceptible to this damaging free
radicals process and readily contribute to the uncontrolled chain reaction. Oxidative
damage, another name for the chemical reaction that free radicals cause, can lead to a
breakdown or even hardening of lipids, which makeup all cell walls. If the cell wall is
hardened (lipid peroxidation) then it becomes impossible for the cell to properly
11
get its nutrients, get signals from other cells to perform an action (such as firing of a
neuron) and many other cellular activities can be affected. In addition to the cell
walls, other biological molecules are also susceptible to damage, including RNA,
DNA and protein enzymes. Hence, when toxic metals are in body tissues, there is
free radical destructive activity going on constantly which induces rapid ageing and
degeneration [35].
The ability of metals to disrupt the function of essential biological molecules,
such as protein, enzyme and DNA is the major cause of their toxicity. Displacement
of certain metals essential for cell by similar metal is another cause of toxicity. For
example, calcium and zinc, which play important roles in stabilizing protein
structures, can be displaced in certain proteins by lead and cadmium respectively
[36-38]. Lead can also replace calcium in bones and teeth [39]. These substitutions
may produce only a subtle change in the protein structure, but the effect on the
protein’s function can be profound.
The following review emphasizes on the production, application and the
poisoning of the targeted transition metals, post-transition metal and metalloid i.e.
zinc, cadmium, lead and selenium. The targeted elements were chosen based on
their acute impacts to the human health in case of exceeded and long-term exposure.
2.1.1
Zinc (Zn)
Sphalerite (zinc sulfide) is and has been the principal ore mineral in the world
[40]. In the year of 2005, about two-thirds of zinc in the United States is produced
from ores (primary zinc) and the remaining one-third from scrap and waste (primary
and secondary slab zinc) [41]. Zinc metal is widely used as a coating to protect iron
and steel from corrosion (galvanized metal), as alloying metal to make nickelled
silver, various soldering formulas and brass, as zinc-based die casting alloy in the
automobile industry, and as rolled zinc. Zinc compounds such as zinc oxide is used
as a white pigment in water colors or paints, and as an activator in the rubber
12
industry. Zinc chloride is applied in deodorant production and can be use as wood
preservative.
Even though zinc is an essential micronutrient for human health, too much
zinc is detrimental. Metallic zinc is not considered as toxic, but free zinc ions in
solution are highly toxic. The free ion activity model (FIAM) is widely cited in the
literature [42-43] and shows that micromolar of free ions mean death. FIAM
assumes the free ions form of metals - small, slightly charged forms of molecules - is
the most easily transported. Symptoms of zinc toxicity include nausea/vomiting,
fever, cough, diarrhea, fatigue, neuropathy and dehydration. Further signs include
growth retardation, altered iron function, anemia, copper deficiency, decreased
immune function, decreased HDL (high density lipoprotein), increased LDL (low
density lipoprotein), and increased HgbA1C (glycated hemoglobin) [44].
2.1.2
Cadmium (Cd)
From the environmental viewpoint the exploitation of cadmium is an
enigmatic business. It is being obtained wholly as a by-product in the production of
zinc and lead, and apparently would have been released to the environment if it were
not so recovered. Estimated world resources of cadmium based on the identified
zinc resources were about 6 million tons and the world refinery production of
cadmium in the year of 2005 was about 18000 metric tons [41].
The first major commercial application of cadmium was in paint pigment.
Other earliest uses of cadmium included low-melting alloys, electroplating, glass
making, photography, as salt in dentistry, dying and calico printing, and as chemical
reagent as well [45]. Nowadays, about three-fourth of cadmium is used in nickelcadmium (Ni-Cd) batteries. The remaining quarter is used mainly in pigment,
coatings and plating, and stabilizer for plastic. Cadmium compounds are also used in
some semiconductors such as cadmium sulfide, cadmium selenide, and cadmium
telluride, which can be used for light detection or solar cells. Incidentally HgCdTe is
sensitive to infrared.
13
The chronic effects of cadmium poisoning of human beings are drawing more
and more attention since this element and solutions of its compounds are extremely
toxic even in low concentrations. Urinary and blood cadmium concentrations are
generally much lower in non-occupationally exposed people, for whom the most
important sources of exposure are cigarette smoking and, especially in polluted areas,
contaminated air, food and water leads to a buildup of cadmium in the liver and
kidneys. Compounds containing cadmium are also known carcinogenic agents.
Cadmium poisoning is the cause of the itai-itai disease [46-47], which literally
means "pain pain" in Japanese. In addition to kidney damage, patients suffered from
osteoporosis and osteomalacia.
2.1.3
Lead (Pb)
As a malleable poor metal (post-transition metal), lead was located in the p-
block in the periodic table and known to possess highest atomic number of all stable
elements. Lead is extracted together with silver, zinc and copper from the ore by
drilling or blasting. The majority of naturally occurring lead is in the form of mineral
i.e. galena (lead sulfide, most common form), cerrussite (lead carbonate) and
anglesite (lead sulfate) [48]. Identified world lead resources are more than 1.5 billion
tons [41]. Anyway, more than half of lead used currently comes from the lead scrap
recycling.
The industrial revolution and introduction of leaded gasoline in 1923 [49]
have brought great change to world lead cycling. Following the withdrawal of
leaded gasoline from the market due to the environmental concern, the lead end-use
pattern has undergone a significant shift by the mid of 1980’s. The lead-acid
batteries industry appears as the principle user of lead. The batteries were mainly
used as staring-lighting-ignition (SLI) batteries for automobiles and trucks. In
addition, the application of lead in non-SLI batteries has also continued to grow [41].
Lead was also used as pigment in paint of white, yellow and red colors.
About one-tenth of lead was used in ammunition, casting material, sheets for
14
radiation shielding, pipes, traps and extruded products; cable covering, calking lead,
and building construction; solder; and oxides for glass, ceramics, pigments, and
chemicals.
Lead posed as a poisonous metal for many years. Acute lead poisoning
usually affects the haematological systems, the central nervous system (CNS) and the
renal system. The concern about mental retardation among children resulted by lead
poisoning has brought about widespread reduction of its uses. It has been reported
that during the peak years of gasoline-carried lead distribution (circa 1972), as much
as 35% of the U.S. population between 6 months and 6 years of age had their I.Q.
permanently reduced approximately 7 points by their blood lead levels [50]. Two
types of cells, i.e. brain and bone are already well known to be pathologically
affected by the environmental Pb level at least partially via Pb-PKC (protein kinase
C) interaction [38, 51].
2.1.4
Selenium (Se)
Selenium is a representative of oxyanion-forming elements. Such elements
are often found in high concentrations in leachates due to their enhanced mobility in
alkaline media. This element is found in sulfide ore and chemically related to sulfur
and tellurium. Selenium is a common byproduct during the electrolytic refining of
copper [52] or the production of sulfuric acid.
Selenium exhibits both photovoltaic, where light is directly converted into
electricity, and photoconductive properties, where the electrical resistance decreases
with increased illumination. These properties make selenium useful in the
production of photocells and exposure meters for photographic use as well as solar
cells. Selenium is also extensively used in rectifiers to convert alternate current (AC)
to direct current (DC). Below its melting point, selenium is a p-type semiconductor
and is finding any uses in electronic and solid-state applications.
15
Selenium is used in xerography for reproducing and copying documents,
letters, etc. It is used by the glass industry to decolorize glass and to make rubycolored glasses and enamels. It is also used as a photographic toner, and as an
additive to stainless steel. In the pharmaceutical industry, selenium mono- and
disulfide are used in the making of anti-dandruff products and its sulfides have also
been used to treat the fungal infection Tinea versicolor. Small amounts of [75Se]
selenomethionine have been used as in medical diagnostic and scanning for certain
organs, which are difficult to examine using conventional X-rays [52].
Under oxidizing conditions, the oxyanionic species selenite (SeO32-) and
selenate (SeO42-) are the predominant forms of Se. The Se species HSe- and H2Se
are only stable under strongly reducing conditions [53]. Elemental Se (Se0) and most
metallic selenides have relatively low toxicity due to their low bioavailability. By
contrast, selenite and selenate species are soluble in water, very toxic and possess
similar action mode as arsenic. On the other hand, H2Se is an extremely toxic and
corrosive gas.
Though human need trace level selenium as micronutrient that plays a role in
protecting tissues from oxidative damage as a component of glutathione peroxidase
[54], it is also toxic in excess amount. High blood selenium concentration
(>100mg/dL) can result in a condition called selenosis [55]. The symptoms of
selenosis included gastrointestinal upsets, hair loss, white blotchy nails, garlic breath
odor, fatigue, irritability, and mild neurological damage. Acute cases of selenosis
may cause cirrhosis of the liver, pulmonary edema and death.
2.2
Conventional and Advanced Methods for Hazardous Elements Removal
from the Contaminated Water – A Brief Review
Hazardous elements contamination can be separated from water using a
variety of technologies, including chemical, physical, and biological. In this section,
numerous conventional and advanced physico-chemical methods used for water
purification i.e. chemical precipitation, solvent extraction, coagulation,
16
electrodialysis, adsorption, ion exchange and more recently complexationultrafiltration process and membrane separation technology will be discussed briefly.
The detailed ion exchange properties of zeolites will be explained in section 2.5.2.
Due to the difference of scope, biological treatments such as aerobic/anaerobic
bioreactors, enzymatic reduction, biological volatilization etc. will not be included in
this section.
The method most employed for harmful metal removal is chemical
precipitation. This method is based on metal hydroxide precipitation by pH
adjustment with an alkaline reagent such as caustic soda, lime, soda ash etc. and
subsequent removal of the precipitate by sedimentation or filtration. However, this
method generates a large amount of sludge which is difficult to handle [56]. In
addition, the precipitation of selenite and selenate is ineffective due to the high
solubility of both ions at a wide range of pH.
Solvent extraction technology gains wide commercial application in the
selective removal of harmful metal ions from the wastewater streams. This process
is principally used for large-scale operations where the concentrations of
contaminants are high. Positively charged metal ions are extracted by acidic or
chelating extractants. For instance, Cu(II) or Au(I) can be eliminated by aromatic
oxime molecules such as LIX984N, LIX860 (Cognis) and Acorga P50 (Avecia) in
their commercial names [57-59]. However, for wastewater with low concentrations
of metal ions, such technology is limited by the need for high aqueous to organic
phase ratios. This presents a considerable cost to the process and the pollution of the
aqueous stream with organics can also cause hazards. Emulsion liquid membrane
(ELM) is a technique currently used, which is similar to solvent extraction where
selenium ions are transferred from the bulk wastewater phase to a liquid extractant
phase containing inside organic droplets [60]. The aqueous strip phase is present as
emulsion within the organic droplet. Once the selenium oxyanions is transferred into
the aqueous strip phase, the organic emulsion is subsequently recovered.
There are four main types of chemical coagulation in water treatment, i.e.
aluminum sulfate, iron salts (usually as ferrous sulfate or ferric chloride),
polyelectrolytes and polyaluminium chloride [61]. These polymeric forms of metal
17
coagulants have become increasingly used in the water treatment due to their wider
availability and reduction in cost. Recent technical improvements combined with the
growing needs for small-scale decentralized water treatment facilities have led to a
reevaluation of electrocoagulation, which had not be accepted as mainstream water
treatment in the past [62]. For instance, there are researchers evaluating the
utilization of electrocoagulation (EC) to remove arsenate and arsenite from water
[63]. Also, with the combination of electrocoagulation and electrofloatation, the
removal of chromium (VI) from wastewater without any filtration was performed
[64].
Electrodialysis is another process that proves its reliability and efficiency.
The main application of the electrodialysis is its utilization for the brackish water
desalination [65]. For the treatment of wastewater and effluents, electrodialysis
shows several advantages such as highly selective desalination, high water recovery,
partial chemicals addition and the possibility of a stop-and-go operation [66].
Anyway, it has a drawback of common membrane process, which requires clean
feed, careful operation and periodic maintenance to avoid damage to the stack. In
addition, power consumption of an electrodialysis is directly proportional to the ion
concentration of the feed stream. As the purity of the product water increases, its
electrolytic conductivity decreases. This higher resistance makes it increasingly less
efficient to remove the remaining salt.
At low solute feed solution, the techniques above lose their advantages. For
this instance, alternative technologies are needed. As it is easy to remove the
adsorbent from aqueous media after treatment, adsorption technique is generally
considered to be a promising method for the hazardous metal removal. Adsorption is
a mass transfer process where a substance is transferred from the liquid phase to the
surface of a solid and becomes bound by chemical or physical forces. Activated
carbon is the most widely used adsorbent for wastewater treatment applications
throughout the world. Its non-polar surface, and low cost has made it the adsorbent
of choice for of a range of organic pollutants [67-69]. However, activated carbon
requires complexing agents to improve its removal performance for inorganic
matters. Therefore, this situation makes it no longer competitive to be widely
applied in small-scale industries because of cost inefficiency [70].
18
So far, there are numerous low cost adsorbents available instead of activated
carbon in the removal of harmful metals. Most of the naturally occurring adsorbents
are biosorbents, silicate minerals and certain waste products from industrial
operations. For instance, the application of chitin and chitosan (mostly from crab
shells and other arthropods), bark, peat moss, algae or alginate, sawdust, rice husk,
green tea, wool, coffee bean, xanthates, fly ash, coal, clays and even chicken feathers
have been extensively evaluated for their performances in the heavy metals removal
[71-89].
Ion exchange technology has many features in common with adsorption. Ion
exchange from the liquid phase with benign ionic species in a solid phase is an
attractive option because of its relatively simple and safe application, as mild
operating conditions are applied [90]. So far, there are many commercialized ion
exchange resin which can be applied for hazardous metals and oxyanions removal.
For instance, Duolite GT-73, Dowex 50WX8, Dowex A1, Amberlite IR-120 and
Amberlite 200 were used to remove Hg2+ (with Duolite); Cu2+, Mn2+, Co2+ and Zn2+
(with Dowex); Cu2+, Cd2+, Ag+ and Zn2+ (with Amberlite) from the water [91-94].
Ion exchange for selenium removal is accomplished by using a strong base anion
exchange resin [60]. Selenate is extracted more effectively than selenite, but the
removal of selenate is adversely affected by the presence of sulfate. The nonselective properties of ion exchange resin towards selenium makes this technique
expensive in case of significant presence of other anions along with selenium [95].
Most resins can perform well in the water treatment but are limited by
breakdown at high temperatures and in the presence of ionizing radiation. For these
reasons, the inorganic ion exchangers have been widely investigated, since they are
particularly stable under these conditions. Examples of inorganic ion exchangers
besides aluminosilicates are heteropolyacid salts, hydrous oxide of polyvalent metals
and acid salts of polyvalent metals. In a recent study, a new heteropolyacid-based
ion exchanger called zirconium (IV) selenomolybdate has been synthesized and the
separation of Zn2+–Cd2+, Zn2+–Co2+, Ni2+–Cd2+and Ni2+–Co2+ using this exchanger
has been evaluated [96]. Besides that, another novel ion exchanger called
titanosilicate ETS-10 which possesses two negative charge sites for each tetravalent
Ti atom in the octahedron readily exchange with more heavy metal ions in the
19
solution. The unusual high performance of ETS-10 in the removal of Pb2+ has been
showed by George X.S. Zhao et al. [97].
Another promising method for toxic metal removal is complexationultrafiltration process, which based on the combinational function of precipitation
and ion exchange. As the small heavy metal ions are small enough to be retained by
filter, they are first complexed with the water-soluble macroligand and the
macromolecular complex formed will then be trapped by ultrafiltration [98]. Besides
that, the coupling of complexation-ultrafiltration with electrolysis offers an elegant
method of metal recovering in a pure metallic form [99].
For the advanced membrane technology, reverse osmosis is a relatively
mature technique besides ultrafiltration in the water purification. Reverse osmosis is
a pressure driven process. The hydrostatic pressure gradient is the difference of
hydrostatic pressure in between two liquid phase separated by a semi-permeable
membrane. The smaller water molecules are literally pushed through the semipermeable membrane while the larger solute species retained. This is achieved by
applying a hydrostatic pressure greater than the osmotic pressure of the feed solution
[100]. The performance of reverse osmosis is dependent on membrane type,
operating pressure and the specific pollutants. Removal of multicharged cations and
anions is normally very high. Nanofiltration is a reverse osmosis-type technology for
treating low metal containing, selenium-bearing mine waters [60]. It has been
commercially applied in removing sulfate from seawaters and also agricultural water
containing high selenite, sulfate and total dissolved solids.
2.3
Features of Zeolites
Zeolites refer to crystalline microporous aluminosilicates with molecular
sieving properties. Many occur as natural minerals, but it is the synthetic varieties
which are among the most widely used sorbents, catalysts and ion-exchange
materials. The first discovery of a natural zeolite dates back to 1756 when a Swedish
mineralogist Axel F. Cronsedt discovered stilbite [101]. The word ‘zeolite’ which
20
signifies “boiling stones” was coined to describe the behavior of such materials,
where the water containing in their interior was evolved as gas bubbles upon heating.
Zeolites are the members of tectosilicate family of minerals and the chemical
composition can be represented as:
Mx/n [(Al2O3)x(SiO2)y]mH2O
where M is a cation of valency n and y/x has a value equal to or greater than 1, which
is in accordance with the Lowenstein’s rule. The fundamental building units of
zeolite frameworks are 4-fold-connected SiO4 and AlO4 to give three-dimensional
anionic network in which each oxygen of a given tetrahedron is shared between the
neighboring tetrahedra and the binding capability is as its maximum [102]. The
tetrahedra (primary building units) form rings of various sizes which are linked to
form more complex units (secondary building units, SBU). The SBU may be
assembled in numerous ways to give vast number of different zeolite framework.
The secondary building units of zeolites were shown in Figure 2.1.
Uncharged frameworks are obtained if all the tetrahedral in the framework
consist only of SiO4 units. For aluminosilicate zeolites, the isomorphous substitution
of Si4+ by trivalent Al3+ causes a negative excess charge of the framework. This
framework-unbalanced charge is compensated by loosely fixed electrochemically
equivalent of cations located in the channels. In contrast to other tectosilicates, the
tetrahedral linkage within zeolites leads to open network structures. This openness is
sufficient to accommodate water molecules and the cations: the water molecules can
move easily within the crystals and so do the cations in the aqueous solution. These
ions (with certain radii) therefore ready exchange with the interstitial cations of
zeolites.
21
Figure 2.2: Secondary Building Units (SBU) of Zeolites
Based on the pore size (the number of T-atoms in the ring opening), zeolites
are referred to as small (8 member-ring), medium (10 member-ring) and large (12
member-ring) pore zeolite. Based on the framework Si/Al composition, zeolites are
classified as low silica zeolites (Si/Al less than 2), medium silica zeolites (Si/Al = 25), high silica zeolites (Si/Al ~10-100) and pure silica molecular sieves. The Si/Al
ratio is one of the important properties of zeolites. Generally, by increasing the Si/Al
ratio, the thermal stability, acid strength and hydrophobicity are increasing, whereas
the ion exchange capacity decreases.
Unlike the two-dimensional aluminosilicate, the rigid three-dimensional
frameworks of zeolites do not undergo significant dimensional changes with ion
exchange. In addition, the high selectivity shown by particular zeolites for certain
cations can assist in the isolation and recovery of such ions. For instance,
clinoptilolite and mordenite showed their good selectivity towards cesium and
strontium, two of the troublesome by-products of nuclear fission [103-104].
22
2.3.1
General Aspects of Hydrothermal Synthesis of Zeolites
The synthesis of molecular sieve aluminosilicate zeolites is typically carried
out in the batch mode, in which a caustic alumina solution mixed together with a
caustic silicate solution in appropriate proportions and subjected to an elevated
temperature at autogenous pressure for some period of time. Such hydrothermal
synthesis of zeolite is a multiphase reaction-crystallization process and involving at
least one liquid phase and both amorphous and crystalline solid phases.
There are great deal of reviews and books regarding the synthesis and
development of molecular sieve zeolites over the years. While it is difficult to offer a
comprehensive account of the totality of the previous studies over so long a period,
the citations list in the extensive review of Cundy, C.S. and Cox, P.A. [105] can be
referred.
A favored reactant mixture has been a hydrous gel originated from freshly
prepared Al(OH)3, alkaline medium and silica sol; or from a soluble aluminate,
alkaline medium and silica sol. The dissolution of Al(OH)3 or soluble aluminate in
alkali give tetrahedral Al(OH)4- anions, which is a dominant species under alkaline
conditions. In soluble silicates as well, polymeric silicate anions was found as
mononuclear species such as Si(OH)4, Si(OH)3- and SiO2(OH2)22-in dilute solution
under alkaline condition. It is noteworthy that either Al or Si is in tetrahedral
coordination with respect to oxygen under alkaline medium consequently built up the
zeolite tectosilicate from hydrous gels and mixtures. The acid or neutral pH regime,
on the other hand facilitates the structural incorporation of those heteroatoms (e.g.
titanium) where the precursor species would be precipitated (e.g., as hydroxides) at
higher pH. The crystallization is mainly in the 6-coordination with respect to oxygen.
The advent of new families of zeotypes such as titanosilicates TS-1 [106-107]
through the inventions has considerably broadened the scope of zeolite synthesis.
Alkali cations were proposed as the templating or stabilizing agent for the
zeolite subunits formation in the early zeolite synthesis. It was normally carried out
at temperature near 100°C and yielded aluminous (low silica) zeolites. The addition
of organic compounds (particularly quaternary ammonium cations) to alkali
23
aluminosilicate gels was reported to produce high silica zeolites and “all-silica”
zeolites. The synthesis of siliceous zeolites are similar with aluminous zeolites but
with several differences, i.e. introduction of organic templates, longer preparation
time due to the slower crystal growth rate and higher synthesis temperature (~120200°C.
Temperature, alkalinity, composition of reaction mixtures, the nature of
reactants and pretreatment of the amorphous gel can all affect the crystallization
kinetic and the type of zeolite formed. Supersaturation of the synthesis solution
leading to the formation of the amorphous gel phase was greatly influenced by
nutrient concentration and temperature. The degree of supersaturation increases as
the nutrient concentration increase but decreases as the temperature of the system
become higher. However, the elevated temperature induce the greater kinetic of
reaction, thus the nucleation and crystal growth rate may be accelerated. The nature
of reactants may be critical in determining the nucleation process since chemical
impurities and physical impurities in the reactants can increase the nucleation
potential of a given system. In addition to the mentioned factors, other influences
such as the role of added salts, ripening period of the reaction mixtures, the order of
reactant are mixed and even whether the mixture is stirred or not during zeolite
formation may direct the course of reaction.
2.3.2
Low Cost Synthetic Zeolites
Zeolites were proven as potential ion exchangers and sorbents for
applications in aquatic pollution control especially in the removal of water hardness
and toxic metals. As alternative choices of the natural occurring zeolites, the
efficiencies of low cost synthesized zeolites in the water treatment have been
evaluated. The chemical composition of starting sources would be the first
consideration in the selection of raw materials. Generally, the sources should have
considerable amount of silica or alumina, or both. Moreover, these compositions
should be highly reactive taking part in the hydrothermal synthesis. Certainly, the
24
cost of these materials is preferably low to ensure the competitive price of final
products.
There are still many raw materials being studied in the synthesis of zeolite,
besides rice husk ash, which was discussed in Chapter I. Most of them are classified
as volcanic glass and rocks, natural clays and rocks, power plant by-product fly ash
and natural zeolites. These raw materials consist of silica and alumina in nature.
Many studies have showed that treating them with alkaline solution can produce
various types of zeolites. For example, Sir Lovat V.C. Rees and his co-worker have
synthesized zeolite P by the reaction of kaolinite in fluoride-containing medium at
elevated temperature [108]. Zeolite P was also being synthesized from other natural
clay and zeolite i.e. interstratified illite–smectite and clinoptilolite in sodium
hydroxide solution [109-110]. Bentonite was also shown as one alternative choice of
materials in the synthesis of zeolite Y [111], there are still some researchers worked
on the synthesis of zeolite X from volcanic zeolitized rocks [112]. Dyer, A. and coworkers [113-114] have done great deal of works in the synthesis of analcime (ANA)
using fused silica dish and also in the removal of heavy metals by analcime
synthesized from a volcanic glass named perlite. Considerable amount of studies
regarding the conversion of fly ash into zeolites are found, and some references are
enclosed herewith [115-116].
2.4
Zeolites of the Gismondine Group (GIS)
Natural zeolites of the gismondine (GIS) group include gismondine
(Ca4(Al8Si8O32) ·16H2O, P21/c, ao = 10.02 Å, bo = 10.62 Å, co = 9.84 Å, β = 92.42°),
amicite (Na4K4(Al8Si8O32) ·10H2O, I2, ao = 10.23 Å, bo = 10.42 Å, co = 9.88 Å, β =
88.32°), garronite (NaCa2.5(Al6Si10O32) ·13H2O, I41amd, ao = bo = 9.85 Å, co = 10.32
Å), and gobbinsite (Na5(Al5Si11O32) ·11H2O, Pmn21, ao = 9.80 Å, bo = 10.15 Å, co =
10.10 Å). They are Ca-, Na- or Ca-Na-bearing zeolites except amicite which is KNa-bearing. The naturally occurring gismondine-type zeolites are normally formed
under hydrothermal postmagmatic conditions; sedimentary formation conditions
seldom occur [117]. Gismondine-type zeolies are constructed with four double-
25
connected 4-ring building units consisting of (Si,Al)O4-tetrahedra. As the bold part
shown in Figure 2.2, the repeat unit of periodic building unit consists of a 4-fold
(1,2,3,4)-connected double 8-ring (D8R).
Figure 2.3: Periodic building unit constructed from 4-fold connected D8Rs
The framework of GIS contains one set of double crankshaft chains parallel
to [100] and another set parallel to [010]. The double crankshaft chains (bold in
Figure 2.3) are formed as the neighboring periodic building units connect through 4rings. The interconnecting channels formed from fused intersections are shown in
Figure 2.4.
c
b
a
Figure 2.4: Connection mode and unit cell content in GIS seen along a. The bold
part indicates a double crankshaft chain which consists of 2-fold (1,2)-connected
double 4-rings
The GIS framework is very flexible and has been described as the ‘most open
[tetrahedral] framework type generated so far’ [118]. The main reason of this
statement is the flexible distortion of the T-O-T bridges (T = Si or Al) due to
26
twinning, pseudo symmetry and extra framework disorder as well as easier
accommodation of different Si/Al ratios in the framework tetrahedral [119]. The Si,
Al atoms can be either disordered or ordered over the tetrahedral sites. The Si, Al
distributions accompany with different extraframework cations lead to the different
symmetry with the same framework.
c
c
b
a
a
b
Figure 2.5: Fused intersections viewed along a (left) and b (right)
Synthetic zeolites with GIS framework topology are coded as zeolite B or P
[120-122], MAPO-43 [123], MAPSO-43 [124], SAPO-43 [125] and ACP [126]. The
detail description of zeolite P is presented in the following section.
2.4.1
Zeolites P with GIS Framework
Zeolites Na-P (also termed zeolite B) is easily crystallized from sodium
aluminosilicate gels at around 100°C. At the early stage, several authors have done a
great deal of studies on the gel chemistry and structure of zeolite Na-P [121-122,127]
and designated it as Linde-B. From the start, establishment of the crystallographic
description of these types of zeolites was hindered by the lack of untwinned crystals
or well-crystallized powders, as well as pseudosymmetry and pronounced flexibility
of the framework. These zeolites at first were thought to belong to the harmotomephilipsite group due to some similarity of powder pattern of Na-P with philipsite and
its variants. At last, Baerlocher et al. [128] succeeded to relate the structure of P
zeolites with gismondine by assuming a composition Na6Al6SiO10O32. 12H2O of a
twinned Na-P crystal.
27
From the beginning, it was realized that several varieties of P zeolites could
be produced. Although all P zeolites are characterized by the same framework
topology, which is GIS framework, the formula, symmetry and structure of different
chemical composition, including the hydration level are difficult to establish [129].
Barrer et al. [121] claimed apparently three polymorphs of zeolite Na-P: cubic (NaP1), tetragonal (Na-P2) and more rarely orthorhombic (Na-P3) . Na-P1 has been
described as being body-centered tetragonal with a unit cell of pseudo-cubic
geometry [128] and more recently Staffan Hansen et al. [130] determined the
structure of Na-P2; orthorhombic, Pnma which originally thought to be tetragonal P
by Barrer. Hansen, S. et al. [131-132] also investigated the relationship between
crystal structure and the Si composition in GIS-based Na-P zeolites. The study
revealed the existence of three Na-P phases with increasing silicon content, i.e. low
silica P (8-10 Si/unit cell), orthorhombic medium silica P (10-12 Si/unit cell) and
tetragonal high silica P (12-13 Si/unit cell).
2.5
Sorption Theory
Mechanisms of metal retention by the solid surface, whether surface
adsorption, ion exchange, surface precipitation, co-precipitation and pure solid
formation are often difficult to distinguish through experiments. Retention involves
a progression of these processes. Sorption is a general term introduced in 1909 by
J.W. McBain [133] to describe selective transfer to a surface and/or the interior of a
solid (or a liquid). It was applied to encompass these phenomena, as the actual
mechanism of metal removal by the solid surface is not known [134]. It is necessary
to define the terms sorbate and sorbent in introducing sorption theory. The sorbate is
the contaminant that adheres to the sorbent or sorbing material.
2.5.1
Adsorption
Adsorption is defined as the accumulation of atoms, ions, molecules at the
28
interface between a solid phase and a solution or gas phase. Jakob Maarten van
Bemmelen was the founder of the theory of absorption (adsorption) from solution
with the publication Die Absorption in 1910 [135]. Adsorption differs from
precipitation in the case of metal as sorbate. Instead of forming a new threedimensional solid phase, the metal ions associate with the surfaces of existing
particles [134].
Adsorption can be classified as physisorption, chemisorption, or electrostatic
adsorption. Physisorption is driven by the weak molecular forces like Van der Waals
or hydrogen bonding force of attraction between the solid sorbent and the adsorbate
molecules (∆Hphysisorption ~ 20 kJ/mol), while chemisorption forms a surface complex
or compound through chemical reaction (∆Hchemisorption ~ 200 kJ/mol) [136].
Electrostatic adsorption involves the adsorption of ions through Coulombic force and
is normally referred to ion exchange, which will be discussed separately in section
2.5.2. In many cases, the uptake of adsorbate is confined only a single layer on the
surface of the solid, and even when many layers are involved, an average of ten
layers is rarely exceeded.
There are many models developed for gas phase adsorption in single and
multicomponent systems and some of them have been successfully applied to liquid
phase adsorption. A summary of these models can be found elsewhere [137-138].
Langmuir and Freundlich equations are most frequently used to describe the sorption
behavior of metals on solid surface. The Langmuir equation was first proposed by
Irving Langmuir in 1918 [139]. The derivation of this equation was based on the
assumption that adsorption is independent of surface coverage, that there is no
interaction between adsorbed ions, and that only a monolayer of adsorption take
place on the surface. The Langmuir isotherm is expressed as:
S=
M bC
1 + bC
(2.1)
where C is the concentration or activity of free metal in solution, S is the quantity of
the metal ions sorbed (mg metal sorbed/ g sorbent), M is the maximum sorption
capacity of the sorbent and b is the coefficient related to bonding energy.
29
By writing the Langmuir isotherm in its linear form, the equation become:
C C
1
=
+
S M bM
(2.2)
when C/S is plotted as a function of C, the slope is the reciprocal of the sorption
capacity, M and the intercept is 1/bM.
However, according to Donald Langmuir [140], such a linearized version is
incorrect since it produces an induced correlation with C. Alternatively, the author
has recommended the following linearization.
1
1
1
=
+
S bCM M
(2.3)
Based on the above equation, a plot of 1/S versus 1/C should produce a
straight line of slope 1/bM and intercept 1/M.
The Freundlich expression is an empirically derived equation to describe the
logarithmic decrease in adsorption energy with increase of surface coverage. In
contrast with Langmuir model, Freundlich adsorption model assumes an unlimited
supply of surface sites and the activity and concentration of surface site is assumed to
be equal. The Freundlicah model is defined as:
S = KFC
1
(2.4)
n
and the linearized form of Freundlich equation is:
log S = log K F +
1
log C
n
(2.5)
where S and C have the same definition as equation 2.1. KF and n are the Freundlich
empirical constant which related to adsorption capacity and intensity of adsorbent
respectively. The KF value gives a relative measure in adsorption capacity and
30
estimates bond strength [141]. The location of n value within 1 - 10 reveals
favorable adsorption whereas irreversible adsorption is noticed from n > 10 and
unfavorable adsorption from n < 1.
2.5.2 Ion Exchange
Ion exchange refers to the exchange of ionic components that occurs on
contacting an ionic solid with an electrolyte solution. The ion exchanger (sorbent)
may undergo exchange either with positive charged ions as cation exchange, or
negatively charged ions as anion exchange. The surface of solid carries either a net
negative or positive charge depending on the nature of the surface and the pH.
Solid like zeolites and clays possess permanent negative charge on the
surface due to the imbalance of charge resulting from the isomorphous substitution
of Al3+ for Si4+ on the tetrahedral positions and/or substitution of Mg2+, Fe3+, etc. for
Al3+ on the octahedral positions. The negative charges are independent from effect
of pH changes. On the other hand, pH dependent charged surfaces are associated
with the edges of clay minerals, with the surfaces of oxides, hydroxides and
carbonates, and with organic matter (acid functional groups) [142]. The charge
arises from the association and dissociation of protons from surface functional
groups.
Due to their predominant role in large-scale ion exchange application,
microporous aluminosilicate zeolites will be highlighted in this section. However,
the general term and theoretical bases can be applied by other ion exchangers and
exchange systems as well. The cation exchange behavior of zeolites depends on the
nature of the cation species, radii, hydration level and the valency. Besides that, the
exchange temperature, concentration of cation species in solution, the anion species
associated with the cation in solution, solvent type and structural characteristics of
zeolite also influence the ion exchange behavior [102].
31
In order to construct the isotherm for an ion exchange reaction in zeolite, a
basic assumption has to be made to ensure that cations in the liquid phase are
exchanged with one type of solid-state cations while the other cations of the
materials are inaccessible [143]. The common way of expressing a binary exchange
reaction that was introduced by Vanselow [144] is presented as:
+
z A B (ZZB) + z B A (ZSA)
+
+
z A B (ZSB) + z B A (ZZA)
+
(2.6)
where zA and zB are respectively the valencies of the exchanging cation A and B and
the subscript (z) and (s) refer to the zeolite and solution phase. The equivalent
fractions of the exchanging cation in the solution and the zeolite phase are
respectively defined as:
XA(s) =
XA(z) =
z A M A, f
(2.7)
z A M A ,i
z A(M A,i − M A,f )V
W.CEC
(2.8)
where MA, i and MA,f = initial and final molar concentration of in-going cation
respectively. V= solution volume, W = zeolite mass (0.1 g) and CEC = cation
exchange capacity which is directly related to the quantity of aluminium present in
the zeolite framework. The selectivity coefficient is defined as
X AZB( Z ) X BZA( S )  γ BZA( S )

Kc = ZA
X B ( Z ) X AZB( S )  γ AZB( S )




(2.9)
The plot of the equivalent fraction of the entering cation in the zeolite, XA(z)
against the equivalent fraction of the cations in the solution, XA(s) at a given
temperature gives the ion exchange isotherm. Figure 2.5 shows four typical ion
exchange isotherms that are frequently observed for binary ion exchange in zeolites
[102]. Isotherm (a) is usually found when the zeolite has a preference for the
entering cation over the entire range of zeolite composition while isotherm (b) is
32
observed when the zeolite prefers the leaving cation over the entering one. Isotherm
(c) reveals that the entering cation has a selectivity reversal with increasing
equivalent fraction in zeolite. Isotherm (d) would be observed as the effect of ionic
sieving effect where the size of cation might be too large to fit into zeolite pore and
leads to incomplete exchange.
Figure 2.6: Isotherms typically found for a binary ion exchange
The mean activity coefficients of individual strong electrolytes must be known
to obtain the selectivity equation. The solution-phase activity coefficient fraction
ZB
(γ ZA
B ( S ) /γ A ( S ) ) might not be merely considered as unity since the interaction of ionic
species in solutions was significant [140]. Debye-Hückel limiting law was applied to
estimate the value of γi(s) in the solution with ionic strength ≤ 0.02 mol/kg.
log γ i = − A z i2 I
(2.10)
For the solution with ionic strength more than 0.02 mol/kg and approached
0.1 mol/kg, Debye-Hückel limiting law was no longer accurate to estimate the value
of γi(s), hence extended form of Debye-Hückel equation was applied.
33
log γ i =
− A z i2 I
(2.11)
1 + B ai I
where zi = charge of ion i, I = ionic strength of solution with formula I = 1 2 ∑(mizi2),
ai = ion size parameter, A and B are the constants in the Debye-Hückel term, where
1
A = 1.824928 × 10 6 ρ o 2 ( ε T)
B = 50.3 (ε T )
−1
-3
2
(2.12)
(2.13)
2
with ρo the density of water, ε the dielectric constant of water and T in Kelvin. The ε
value at different temperature can be calculated using the following relationship:
ε = 2727.586 + 0.6224107 T − 466.9151 ln T − 52000.87 / T
(2.14)
The increase of ln γi values with ionic strength can be modeled by adding
positive terms to some form of the extended Debye-Hückel expression of log γi. For
solutions with ionic strength greater than 0.1 mol/kg, the empirical Davies expression
was applied.


− 0.3I 

1 + I

log γ i = − A z 2 
I
(2.15)
Normally, the ion exchange of zeolite is difficult to achieve to XA(z)=1 due to
the ion-sieving effect. Therefore, normalization procedure is needed to obtain the
Kielland plot (ln K 'c versus X’A(z)), in which the observed XA(z) values are multiplied
by a factor f (1/XA(z)max), where XA(z)max is the maximum observed XA(z) value [145].
Sherry and Walton [146] have proposed a method to evaluate the standard free
energies, standard enthalpies and standard entropies, which was originally developed
by Gaines and Thomas [147] for the ion exchange in clay minerals. By neglecting
salt imbibition and assuming water activity to be unity, the thermodynamic
34
equilibrium constant was calculated from isotherm data and Kielland plots with the
following equation.
1
ln KA = (zB – zA) +
∫ ln K
'
c
dX 'A(Z)
(2.16)
0
The obtained thermodynamic equilibrium constant was used to calculate the
Gibbs standard free energy, ∆G˚ of the binary exchange according to the formula
below.
∆G o = -
RT
ln K A
zA zB
(2.17)
The standard enthalpy, ∆H˚ and entropy, ∆S˚ can be calculated by the relationship:
∆H o = RT 2
∆S o =
2.5.3
d ln K A
dT
∆H o − ∆G o
T
(2.18)
(2.19)
Surface Complexation
Surface complexation models have been used to provide quantitative
description of ion interactions with oxide surfaces [eg. 148-149]. These models are a
mathematical representation of adsorption, each based on the hypothesis describing
the interaction between an adsorbate and an adsorbent resulting in a molecular
arrangement [150].
The triple layer model (TLM) is the commonly used complexation model in
describing adsorption behavior. This model defines three planes of adsorption i.e. (a)
the o-plane at the surface for the adsorption of H+ and OH- and strongly adsorbed
35
ions (specifically or chemically adsorbed or inner sphere complexes), (b) the near
surface plane (β-plane) for weakly adsorbed ions, which could also be referred as
outer sphere complexes, and (c) diffuse layer plane, representing the closest approach
of dissociated charge. These three mechanisms of adsorption are showed in Figure
2.6 [150].
Figure 2.7: The three mechanisms of cation adsorption on a siloxane surface
(e.g. montmorillonite)
Metal presents in the diffuse ion association or in an outer sphere complex are
surrounded by water molecules (hydrated) and are not directly bound to the solid
surface. These metals accumulate at the interface of charged surface in response to
the electrostatic forces. Hence, the interaction within metal and surface can also be
termed as exchange reactions due to the readily replacement of these loosely bound
metal by other adsorbate in sufficient concentration.
On the other hand, metal are bound directly to the solid surface in inner
sphere complexation without the involvement of water of hydration. Instead of weak
Van der Waals force, ionic and/ or covalent forces drive the interaction within the
metal and the surface. Therefore, a much higher bonding energy is involved than
outer sphere complexation and it was also termed as specific adsorption. The
specifically adsorbed cations are relatively immobile and hardly to be affected by the
high concentration of the major cations in the solution.
The relative affinity of the surface towards the free metal ions depends on the
tendency of the metal to form inner sphere complexes with the surface. The less
36
hydrated ions are preferred because they can fit closer with the surface. Specific
adsorption sites will be occupied initially at low concentration followed by the outer
sphere complexation as it becomes saturated. The metal ions adsorbed by the nonspecific sites are potentially mobile and exchangeable with other metal ions [151152].
CHAPTER 3
EXPERIMENTAL
3.1
The Determination of Silica in Untreated Rice Husk Ash
The field-burnt rice husk ash was obtained from the collection of Solid-State
Chemistry Laboratory, Ibnu Sina Institute for Fundamental Science Studies (IIS),
UTM from Bernas Milling (Beras Nasional). The oven dried rice husk ash was
accurately weighed in a platinum crucible (m1) and ignited in a muffle furnace at
1000°C for 30 minutes, followed by cooling in a desiccator to constant weight (m2).
The weight of empty platinum crucible is initially weighed as m0. Loss of ignition
(% LOI) can be calculated with the formula
Loss of ignition (% LOI) =
m1 − m2
× 100%
m1 − m0
(3.1)
About 1 mL of 50 % H2SO4 (Ashland Chemical) was then added slowly to
the weighed residue. The platinum crucible was heated gently until the white fuming
ceased, followed by the continuous heating in muffle furnace (Carbolite) at 900°C
for another 30 minutes. The treated residue was cooled in a desiccator and weighed
again as m3. Then, the residue was dissolved in 1:5 mixture of H2SO4: HF (HF
purchased from J.T.Baker, 49 %v/v). It was slowly heated on a hot plate until no
further white fumes evolved. The residue was ignited again in a muffle furnace at
900°C for another 30 minutes and the final weight m4 was obtained after cooling.
38
The whole procedure was conducted on duplicates in order to get the mean value of
silica percentage in the rice husk ash.
SiO2 percentage, %SiO2 =
3.2
m3 − m 4
× 100%
m 2 − m0
(3.2)
Syntheses of Zeolite P
Initially, attempts have been made to synthesize zeolite P from the field-burnt
rice husk ash with the starting reactant compositions 6.2Na2O: Al2O3: 8SiO2: 112
H2O based on previous study. NaOH solution, which was prepared from sodium
hydroxide pellets (Merck), was added to the weighed rice husk ash. The alumina
source of the synthesis was obtained from technical grade sodium aluminate (Riedel
de Haën) and the clear solution of NaAlO2 was then added to the rice husk ash in the
alkaline medium. The mixture was left to homogenize under continuous stirring for
2 hours before transferring to a Teflon bottle, which was tightly closed and heated in
an oven at 100°C for 3-5 days.
The crystalline product was filtered off by employing a vacuum force,
washed thoroughly with distilled water and then dried at 100°C overnight. The oven
dried zeolite cake was ground with mortar and pestle to a fine powder. Then it was
equilibrated under constant humidity for at least three days, supplied by a saturated
potassium chloride (AJAX Chemical) solution in a desiccator, to yield a fully
hydrated product prior the following analyses.
In the process of optimizing the synthesis condition, other efforts were also
attempted to synthesis zeolite P using untreated rice husk ash with starting
compositions of 5Na2O: Al2O3: 8SiO2: 112 H2O. The procedures on synthesis were
similar with the previous recipe but the rice husk ash was first well dissolved in
NaOH solution for about 1 hour prior to the addition of sodium aluminate. To
encounter the inconsistency of the product formation, several versions of
experimental conditions were tried in the synthesis. These included varying the
39
heating period, altering the heating temperature and also the starting composition
such as silica, alkalinity and water content. Finally, starting compositions of 4Na2O:
Al2O3: 10 SiO2: 130H2O, crystallized at 106°C for 8 days was utilized to synthesize
bulk amount of desired product.
3.2.1
Detailed Description of the Zeolite P Synthesis Condition with Starting
Compositions of 4Na2O: Al2O3: 10 SiO2: 130H2O
Initially, an alkaline medium was prepared by dissolving 6.6814 g of sodium
hydroxide pellets in 50 mL DDW. About 28.14 g of rice husk ash was then mixed
with the alkaline medium. It was homogenized with the assistance of magnetic
stirrer and spatula to become a smooth dark-brownish solution indicating that rice
husk ash was dissolved well in the alkaline medium.
Approximately 13.6163 g of sodium aluminate was mixed with 50 mL DDW
in a PTFE beaker and stirred under mild heating until a transparent solution formed.
(It may be observed as slightly greenish-grey solution). The sodium aluminate
solution was then poured into the alkaline medium containing the rice husk ash. A
viscous mixture was formed immediately. Without any delay, the viscous mixture
was stirred with spatula and continually homogenized with magnetic stirrer for 2
hours. The mixture became less viscous at the end of stirring and was transferred
into a Teflon bottle.
The Teflon bottle was closed tightly and heated in an oven at 106°C for 8 days
without disturbance. The formed product was filtered off by employing a vacuum
force, washed thoroughly with distilled water and then dried at 100°C for overnight.
The oven dried zeolite cake was ground with mortar and pestle to fine powder. Then
it was equilibrated under constant humidity for at least three days, supplied by a
saturated potassium chloride solution in desiccator, to yield fully hydrated product
prior the following analyses.
40
3.3
Modification of Zeolites
In order to study the difference of sorption behavior towards inorganic
contaminants in water, the as-synthesized zeolite P was further modified through
incorporation of sodium, calcium or aluminium ions by ion exchange and/or
desilication. The detailed procedures are shown as below.
3.3.1
Desilication
About 3 g of oven-dried zeolites was added to 0.2 M sodium carbonate
solution (Merck) after the solution was preheated in a water bath up to 60°C (1g/20
mL). After mild stirring for 2 hours, the zeolite suspension was immediately cooled
down in an ice bath. The treated zeolite was filtered and washed several times with
distilled water. Finally, the product was dried overnight at 100°C and stored over the
saturated KCl solution prior to the analysis. The as-synthesized zeolites was carefully
treated in mild alkaline medium with an expectation that ion exchange capacity could
be increased by the density enhancement of framework Al sites, after the preferential
extraction of Si from the framework. The cleavage of Si-O-Si bonds happen in the
presence of OH- ions [153-154] and the desilicated zeolite will experience some
healing with formation of some new surface siloxane bonds [155].
The possibility of converting the desilicated zeolite P to H-form was also
investigated. H-form zeolite is expected to perform well in the removal of hazardous
metal ions through the rapid ion exchange between the lighter H+ ions with heavier
metal ions. Three consecutive exchanges of the desilicated zeolite with 0.1 N
NH4NO3 (Fluka) at 333 K followed by air calcination at different temperature,
ranging from 523 K to 673 K for two hours were done. The deammoniation
behaviour and structural changes were monitored by TG/DTA, FTIR and XRD.
41
3.3.2
Ion exchange with Sodium or Calcium Ions
Na-exchanged form of zeolite P was prepared as nearly homoionic as
possible by 3 times of repeated treatment of the zeolite powder with 2 N NaNO3
solution (Riedel de Haën) in a round bottom flask placed in a constant temperature
oil bath maintained at 353 K for 48 hours. The ratio of the mass of zeolite the
solution volume was maintained at 1 g/20 mL. The product was filtered, washed and
dried in oven at 100°C. Then, it was placed over a saturated KCl solution prior to the
chemical analyses and ion exchange experiment.
Near-homoionic calcium form zeolite was also prepared through exhaustively
exchange of the desilicated zeolite P with concentrated Ca(NO3)2 solution (prepared
from calcium nitrate 4-hydrate, Riedel de Haën). The modification procedures were
similar with the sodium exchange but the time for three exhaustively calcium
exchange with 2 N of Ca(NO3)2 solution was prolonged to 60 hours to ensure the
maximum calcium uptake.
3.3.3
Loading of Aluminium
The deposition of hydrolyzed species of trivalent aluminium on the surface of
zeolite is expected to act as scavenger in the removal of oxyanions through noncovalent forces. The desilicated zeolite P was mixed with aluminium solution,
prepared from aluminium sulfate octadecahydrate (Merck) in a 250 mL Erlenmeyer
flask (4 g/250 mL). The concentrations of aluminium sulfate solutions were
prepared in a series of 10, 20, 30, 40 and 50 mmol/L. The mixtures were agitated at
150 rpm using a Hotech orbital shaker for 24 hours. After the shaking, the solid and
aqueous phase was separated by filtration and the solid samples were washed several
times with deionized water. The collected solid samples were dried overnight at
100°C and stored over the saturated KCl solution prior to the characterization.
42
3.4
Characterizations of Zeolite Samples
The collection of information on the structural and chemical characteristics of
zeolites ought to derive relations between their chemical and physicochemical
properties on the one side and the sorptive properties on the other. Here, several
characterization techniques were employed to further understand such relationships
for the original and modified zeolites.
3.4.1
X-ray Diffraction (XRD)
The zeolite sample was poured into the depression of a sample holder until
completely filled. The solid was packed down and leveled off with a glass slide to
get a flat and smooth surface. The powder X-ray diffraction patterns of the sample
was measured at room temperature in a D8 ADVANCE X-ray diffractometer (Bruker
AXS GmbH) with Cu Kα radiation (λ = 1.5418Å). Data were collected in the 2θ
range of 5 ° to 50 ° at a scan rate of 0.050°/s.
3.4.2
Fourier-Transform Infrared Spectroscopy (FTIR)
The solid sample was dispersed in a potassium bromide (KBr) medium and
ground well to ensure a homogeneous mixture of the sample with KBr. The weight
ratio of sample to KBr was about 2:100. Then, the mixture was pressed in an
evacuated die to give the transparent disc. The disc was irradiated with infrared and
the spectrum was recorded in percent transmission (%T) over the range 400-1300
cm-1 on a Shimadzu 8300 FTIR spectrophotometer.
43
3.4.3
Wavelength Dispersive X-ray Fluorescence Spectroscopy (WDXRF)
The chemical compositions of samples were determined by wavelength
dispersive X-ray fluorescent spectrophotometer. The fused glass beads were
prepared by mixing sample and 100 Spectroflux (Johnson and Mathey) in ratio 1:10
in Pt-Au crucibles, and burnt at 1000°C for 20 minutes in an automatic glass bead
preparation machine (Claisse Bis 10 Fluxer model). The homogeneous melts were
shaped into 3 mm thick, 32 mm diameter glass beads using Pt-Au moulds. Standards
were also prepared using the same procedures. The samples were analyzed with
afully automated Philips PW 1480 spectrometer. Certified Standard Material (CRM)
coded USGS GA was used as quality control sample of analyses. Ten major
elements determined by WDXRF include SiO2, TiO2, Fe2O3, Al2O3, MnO, CaO,
MgO, Na2O, K2O and P2O5
3.4.4
Scanning Electron Microscopy (SEM)
The zeolite samples were mounted on the aluminium stubs using a double-
sided tape. Gold sputter coating of the stub surface was achieved using a Bio-Rad
Polaron division SEM coating system. The scanning electron microscopy images of
samples were recorded at 20 KV in a Philips XL 40 SEM.
3.4.5
Thermogravimetric-Differential Thermal Analysis (TG-DTA)
A Perkin-Elmer Diamond TG/DTA unit was used with purging gas (in N2
atmosphere). The reference cell was remained empty during the analysis. TG/DTA
runs was done using the following conditions: initial temperature 50°C; rate
10.00°C/min, final temperature 700°C; nitrogen flow 20 mL/min and sample mass <
6 mg.
44
3.4.6
Surface Analysis with Nitrogen Adsorption
BET surface area and total pore volume of as-synthesized zeolite P was
determined by Quantachrome Autosorb-IC Automated Gas Sorption System. Prior
to the nitrogen adsorption, the sample was degassed for 3 hours at 150°C. Data was
collected through three-points analysis.
3.4.7
Solid-State Nuclear Magnetic Resonance Spectroscopy (NMR)
Solid-state NMR was performed on a Brucker 400 MHz NMR spectrometer.
The sample was packed into 4 mm zirconia rotor and spun in air. The 29Si NMR
spectra was obtained using magic angle spinning (MAS) at a spinning rate of 7 KHz,
pulse length of 4 µs, recycle delay time of 9 s and 5000 number of scan. Tetrakis
(trimethylsilyl)silane (TMS) was used as the external reference material for 29Si
chemical shift determination.
27
Al NMR spectra were measured on the sample
packed in a 4mm rotor spinning at 7 KHz using 0.10 µs pulse length, 1000 number of
scan and 1 s recycle delay time. Aqueous Al(H2O)63+ solution was used as reference
of chemical shifts.
3.5
Batch Sorption Experiments
The performance of the as-synthesized zeolite P and its modified forms in
removing hazardous metals and metalloids were investigated using batch mode
sorption tests. Batch mode sorption means sorption of the known concentration
sorbates by known quantity of sorbent (eg. zeolite in this work) in a vessel within a
prescribed time. The uptake of metals or metalloids (sorbate) by the zeolite samples
was obtained from the concentration difference before and after sorption. The
following equation (3.3) was used to calculate the sorbate uptake in mg by a
quantified mass of zeolite.
45
q=
(C 0 − C t )V
1000m
(3.3)
where q = sorbate uptake, mg/g of sorbent; C0 = initial concentration, mg/L; Ct =
concentration, after a prescribed duration (t), mg/L, V= volume of solution, mL; and
m = mass of sorbent used, g. The detailed procedures are described in the following
sections.
3.5.1
Divalent Metals Removal
The selected divalent metals included lead (Pb), cadmium (Cd) and zinc (Zn).
The stock solutions of the metals were prepared from analytical grade lead (II) nitrate
(Riedel de Haën), cadmium nitrate tetrahydrate (AJAX Chemical) and zinc nitrate
hexahydrate (Emory). All glassware and polypropylene tubes were washed by
immersing them in 10% HNO3 for 24 h followed by rinsing with distilled water.
3.5.1.1 Kinetic of Divalent Metal Ions Removal
The single metal solution with 2000 mg/L concentration was prepared by
dissolving analytical grade nitrate salt of the targeted metal in a 250 mL Erlenmeyer
flask by using distilled-deionized water (DDW). The alkalinity of the metal solution
was adjusted to pH~3 with 2.0 % nitric acid prior to the addition of zeolite. The pH
below 2.5 was inhibited to avoid zeolite structure destruction.
Accurately weighed 1.0 g of as-synthesized zeolite P, sodium-exchanged
form or calcium-exchanged form zeolite was mixed with the solution and stirred with
a magnetic stirrer at ambient temperature. Less than 1% of solution, i.e. 1.0 mL was
withdrawn with a micropipette at an appropriate time interval of 3 days and taken
into account in determining the volume removed in the solid/solution ratio. The
withdrawn solutions were rapidly diluted with 0.2 % nitric acid and analyzed for
46
Pb2+, Cd2+ and Zn2+ concentrations using an atomic absorption spectrometer (PerkinElmer AAnalyst 400).
3.5.1.2 Effect of pH towards Removal of Divalent Metal Ions
The removal of the selected metal ions by the zeolites was also investigated
within pH 3- 7. Solutions of a single element (5000 mg/L) were prepared by
dissolving nitrate metal salts in DDW. The initial pH of the solution was measured
with a CyberScan pH/Ion 510 pH meter (Eutech Instruments). The solutions were
adjusted to the desired pH with 2.0 % nitric acid or 0.5 M sodium hydroxide.
Approximately 0.1 g of as-synthesized zeolite P, sodium-exchanged form or
calcium exchanged form zeolite was mixed with 10 mL of the pH-adjusted solution
in the 50 mL polypropylene (PP) centrifuge tubes. The pH of mixture was measured
and adjusted again to the desired pH. The PP tubes were sealed and agitated at 150
rpm for 3 days at ambient temperature to reach equilibrium. The mixtures were
rapidly filtered with a Whatman filter paper No.2 and the concentrations of the metal
in the supernatants were analyzed with AAS after appropriate dilution with 0.2 %
nitric acid. The pH-adjusted solutions without the addition of zeolite were analyzed
as well to elucidate the decrease of metal concentration due to precipitation. The
experiments were cone in duplicates.
3.5.1.3 Binary Ion Exchange of Divalent Metal Ions with Indigenous Ions in
Zeolites
Binary ion exchange isotherms for the selected divalent metal ions were
constructed at room temperature (302 ± 2 K). Accurately measured 0.1 g of zeolite
sample (as-synthesized zeolite P, sodium-exchanged or ca-exchanged forms) was
equilibrated with 10 mL of lead (II), cadmium (II) or zinc (II) solution in a 50 mL
47
polypropylene centrifuge tube. The initial concentration of hazardous metals was not
maintained constant and it was increased in order to reach higher XA(Z) values.
The pH of initial metal solutions was adjusted to ~3 prior to the addition of
zeolite and the experiments were conducted without further buffering. pH values
lower than 2.5 were avoided to prevent dealumination of zeolite framework. The
centrifuge tubes were sealed and agitated with a Hotech orbital shaker at 150rpm for
5 days, which was proven through the previous study that the equilibrium of
exchange could be reached within the shaking time. Each experiment data was
repeated twice or thrice to ensure reproducibility. After the equilibrium has been
reached, the solutions were filtered rapidly using a Whatman filter paper No.2. The
supernatants were diluted with 0.2% nitric acid and the concentrations of the
acidified solutions were then analyzed again with the same atomic absorption
spectrometer.
Binary ion exchange data of Pb2+ by zeolites were obtained through varying
the initial concentration from 900.00mg/L to 9500.00 mg/L. On the other hand, the
isotherms of Cd2+ uptake were obtained from the solutions with initial Cd2+
concentration ranging from 300.00 mg/L to 4000.00 mg/L while the initial
concentration of Zn2+ series was varied from 400.00 mg/L to 5000.00 mg/L. The
tests were done in duplicates or triplicates to ensure reproducibility.
3.5.1.4 Multicomponent Ion Exchange of Divalent Metal Ions with Indigenous
Ions In Zeolites
The multicomponent ion exchange of divalent metal ions (ternary sorbates)
with indigenous ions in zeolites was performed to investigate the influence of
multicomponent solutions on the exchange equilibrium of individual hazardous
metals on the zeolites.
A series of metal solutions containing three types of metals, i.e. Pb2+, Cd2+
and Zn2+ was prepared by mixing the same concentration of the individual metal
48
stock solutions (in mg/L) in the volumetric flask followed by serial dilution using
DDW. The pH of multi metal solutions was kept constant at pH~3 by adding 2 %
nitric acid. The initial concentration of the individual metals in the multicomponent
solutions was varied from 100 mg/L to 2000 mg/L.
Accurately weighed 0.1 g of zeolite sample (as-synthesized zeolite P,
sodium-exchanged or ca-exchanged forms) was mixed with 10 mL of the
multicomponent solution in a 50 mL PP centrifuge tube and equilibrated with the
assistance of Hotech orbital shaker at 150 rpm for three days. The mixture was then
filtered with Whatman filter paper No.2 and the filtrate was analyzed with atomic
absorption spectrometer to determine the residue content. The results were obtained
from the mean value of duplicate experiments.
3.5.2
Selenium Oxyanions Removal
The series of aluminium-loaded zeolite P which was prepared by varying the
modifier (aluminium sulfate) concentration, was preliminarily screened through
adsorption kinetic test in order to select the most efficient sorbent towards selenium
oxyanions. The selected aluminium-loaded zeolite P will be evaluated through
adsorption isotherm and other tests. The concentration of selenium species is always
given as the concentration of elemental selenium.
In order to maintain the pH of solution during the adsorption, both adsorption
kinetic and isotherm were investigated in the buffered system. Acetate buffer with
pH 4.8 was selected in the experiments. The preparation of acetate buffer was done
according to Chandra Mohan [156]. About 200 mL of 0.1 M acetic acid (prepared
from analytical grade glacial acetic acid, Merck) was mixed with 300 mL of 0.1 M
sodium acetate solution (prepared from sodium acetate trihydrate salt, Merck) in a
1000 mL volumetric flask. The mixture of solution was adjusted to the mark with
DDW. The final pH of the solution was adjusted using a sensitive CyberScan pH/Ion
510 pH meter (Eutech Instruments).
49
For the adsorption kinetic and isotherm study, the Se (IV) stock solution was
prepared by dissolving 0.3267 g of selenious acid pure (Merck) in 50 mL acetate
buffer. Stock solution of Se (VI) was prepared by dissolving 0.4786 g of sodium
selenate (Fluka) in 50 mL acetate buffer. The stock solutions were stored in a
refrigerator prior to further dilution. All glassware and polypropylene tubes were
washed by soaking in 10 % HNO3 for 24 h followed by washing with distilled water.
3.5.2.1 Kinetic of Selenium Oxyanions Removal by Aluminium-loaded Zeolite P
Either 100 mg/L of Se (IV) or Se (VI) was prepared from serial dilution of
the stock solution using acetate buffer. Accurately weighed 1.0 g of aluminium–
loaded zeolite P was mixed with 250 mL of Se (IV) or Se (VI) solution in an
Erlenmeyer flask. The mixture was agitated at ambient temperature (~29 °C) with an
orbital shaker (Hotech). The shaking rate was 150 rpm and duration was between
250- 300 minutes. Less than 2% of solution, i.e. 2.0 mL was withdrawn with
micropipette at different intervals. The withdrawn solutions were rapidly diluted
with the prepared acetate buffer and analyzed for selenium concentration using an
atomic absorption spectrometer (Perkin-Elmer AAnalyst 400).
3.5.2.2 Construction of Adsorption Isotherm
The most efficient adsorbent selected from the kinetic test was further studied
through adsorption isotherm. A series of Se (IV) or Se (VI) was prepared through
serial dilution of the stock solutions using acetate buffer. The initial concentration of
Se (IV) series was varied from 1.5 mg/L to 50.0 mg/L while the concentration range
of Se (VI) series was varied from 1.5 mg/L to 60.0 mg/L. About 20 mL of the
solution was mixed with 0.1 g aluminium-loaded zeolite P in a polypropylene
centrifuge tube. The mixture was agitated at room temperature (~29°C) using a
Hotech orbital shaker (150 rpm) for 24 hours, which was proven through the kinetic
50
study that the sorption equilibrium could be reached before end of the shaking time.
The experiments were done in duplicates.
The aqueous phase was separated from the solid phase using a Whatman
filter paper No.2 after the sorption equilibrium was reached. The remaining
selenium concentration in the solution was determined with the same atomic
absorption spectrometry technique.
3.5.2.3 Effect of Ionic Strength towards Removal of Selenium Oxyanions by
Aluminium-loaded Zeolite P
The Se (IV) stock solution was prepared by dissolving 0.1307 g of pure
selenious acid (Merck) in 20 mL DDW. Stock solution of Se (VI) was prepared by
dissolving 0.1914 g of sodium selenate (Fluka) in 20 mL DDW. 0.01 M, 0.1 M or
1.0 M NaCl electrolyte solution were prepared from the sodium chloride salt (Merck)
and used as background diluent to prepare three series of Se (IV) or Se (VI) solutions
with different initial concentrations from the selenium stock solution. The batch
equilibrium sorption experiments were conducted at ambient temperature (~29°C) by
adding 0.1 g of the selected aluminium-loaded zeolite P to either 20 mL of 0.01 M,
0.1 M and 1.0 M NaCl containing Se (IV) or Se (VI) at different concentrations.
The suspensions in the sealed PP centrifuge tube were agitated using a orbital
shaker for 24 hours and subsequently filtered with a Whatman filter paper No. 2.
The filtrate was analyzed for the residue content using AAS.
3.6
Flame Atomic Absorption Spectroscopy (FAAS)
The concentration of the interested elements in the solutions before and after
the sorption was determined in air-acetylene (C2H2) flame using flame atomic
absorption spectrometer (model Perkin-Elmer AAnalyst 400). For the analysis, a
51
sample is converted into aerosol through a pneumatic nebulizer. The aerosol
(sample), oxidant (air) and fuel (acetylene) are then directed into a slotted burner,
which provides a flame that is usually 5 or 10 cm in length.
A light beam is directed through the flame into a monochromator and onto a
detector that measures the amount of light absorbed by the atomic vapor. The lamps
used to provide the light beam in this study included hollow cathode lamps (HCL)
and electrodeless-discharged lamp (EDL). These lamps, when subjected to a current,
emit the spectrum of the desired element together with that of the filler gas. Each
element has its own characteristic absorption wavelength, and therefore lamps
composed of each element were employed.
The amount of radiation absorbed in the flame is proportional to the
concentration of the element present in the flame and this is commonly shown by the
Lambert-Beer law:
I =I0 e-kbc
(3.4)
where I0 = intensity of the incident radiation of frequency v; I = intensity of the
incident radiation after absorption; k = absorption coefficient; l = pathlength of the
radiation through the vapor; c = concentration of the absorbing analyte.
For analytical purpose the absorbance A is used:
A = log
I0
= abc
I
(3.5)
The calibration curves of all analyses were obtained by employing serial
metal solutions diluted from 1000 mg/L standard stock solutions (purchased from
Merck and Riedel de Haën). Prior to the analyses, the instrument and the lamp were
optimized according to the manufacturer’s manual. Quality control sample (QCS)
was analyzed at a selected point midway through the group of samples to be
analyzed to monitor the performance of instrument. The operating parameters of
FAAS during the analyses were shown in Table 3.1.
52
Table 3.1: Operating parameters of FAAS (Perkin-Elmer AAnalyst 400) in the
measurement of the desired elements
Current
Wavelength
Slit width
(nm)
(nm)
75
589.00
1.8/0.6
10
55
422.67
2.7/0.6
coded HCL
10
72
283.31
2.7/1.05
Cd
coded HCL
4
50
228.80
2.7/1.35
Zn
coded HCL
15
45
213.86
2.7/1.8
Se
coded EDL
280
56
196.03
2.7/2.3
Element
Type of Lamp
Na
HCL
8
Ca
HCL
Pb
(mA)
Energy
CHAPTER 4
RESULTS AND DISCUSSION: SORBENTS DEVELOPMENT
4.1
Synthesis of Zeolite P
Prior to the synthesis, the broad peak obtained at 2θ around 22-23° for field-
burnt rice husk ash (RHA) which is shown in Figure 4.1 indicating the presence of
amorphous silica, was proven to be highly active for direct synthesis of zeolites
Intensity (a.u.)
[157].
2 Theta Scale (°)
Figure 4.1: X-ray diffractogram for field-burnt rice husk ash
The silica content in the rice husk ash was determined as 94 % w/w in spite
of 1.95 % loss of ignition through the conventional gravimetric analysis. The
54
first attempt of synthesis was done with the reactant composition of 6.2 Na2O: Al2O3:
8SiO2: 112 H2O. Zeolite Na-P1 appeared as the main phase of product when the
starting silica source was untreated RHA; sodalite is the minor impurity, which coexists with the zeolite P. There are no conversions of the product phases when the
heating was prolonged to four or five days as shown in Figure 4.2. One can observe
the crystallinity of zeolite Na-P1 phase increased when heating period was extended
Intensity (a.u.)
to five days.
2 Theta Scale (°)
a
3 days crystallization time
b
4 days crystallization time
zeolite Na-P1
c
5 days crystallization time
sodalite
Figure 4.2: X-ray diffractogram of final products when field-burnt RHA was
employed as silica source in synthesis
The content of Na2O in the initial starting composition was reduced by using
less NaOH in the synthesis, which led to a modified ratio of reactant composition of
5Na2O: Al2O3: 8SiO2: 112 H2O. The less alkaline medium was hoped to eliminate
the impurities of sodalite in the zeolite phase [109]. The preliminary dissolution of
rice husk ash in NaOH was also aimed to increase the reactive sodium silicates in the
hydrothermal reaction. In Figure 4.3, it was surprising that zeolite Na-P2 phase
appeared as a dominant phase in the product while only a slight portion of sodalite as
the minor part, which was negligible.
Intensity (a.u.)
55
2 Theta Scale (°)
zeolite Na-P2
sodalite
Figure 4.3: X-ray diffractogram of zeolite Na-P2
The orthorhombic zeolite Na-P2 phase and sodalite were found to transform
completely to zeolite Na-P1 phase when the heating period of the gel with same
composition was extended from 4 days to 6 days, as shown in Figure 4.4. This
finding is quite similar with the work of Andrea Katović et al [158]. They have found
that tetragonal form of zeolite P appears as the first crystalline phase and transforms
Intensity (a.u.)
completely into the cubic form at extended reaction times.
2 Theta Scale (°)
Figure 4.4: X-ray diffractogram of zeolite Na-P1
56
The structural properties of zeolites Na-P1 and Na-P2 were further
investigated by Fourier transform infrared spectroscopy. The IR spectra revealed
that the structure of zeolite Na-P1 and Na-P2 are almost similar. The broad peaks
around 1300-920 cm-1 was assigned to T-O asymmetrical stretch; 682.8 cm-1 as
symmetrical stretch; 436.8 cm-1 and 433.0 cm-1 as O-T-O bend; 606.6 cm-1 as
double-ring vibrations of external linkage. The main difference is the appearance of
a small shoulder at 852.5 cm-1 for zeolite Na-P1. In addition, one T-O symmetrical
strectching for external linkage of zeolite Na-P2 as indicated by 776.3 cm-1 was
found lower than 782.1 cm-1 from that of zeolite Na-P1. This result suggested that
the stretching mode vibration of external linkage would shift to lower frequency
when the tetrahedral aluminium atoms increase, i.e. the Si/Al ratio decrease [159].
743.5
682.8
852.5
782.1
776.3
682.8
743.5
606.6
606.6
436.8
433.0
1098.4
1116.7
1007.7
(a)
1002.0
(b)
Figure 4.5: FTIR spectra of (a) zeolite Na-P1 and (b) zeolite Na-P2
The shifting of the vibration mode to lower frequency for zeolite Na-P2 due
to the increase of tetrahedral aluminium atoms was proven by the elemental analysis
using energy dispersive x-ray microanalysis (EDAX), which was coupled to the
scanning electron microscope (refers to Appendix B). The Si/Al ratio of zeolite NaP1 obtained from the EDAX elemental analysis was 1.85 whereas the Si/Al ratio of
zeolite Na-P2 was 1.81, indicating the higher aluminium content in zeolite Na-P2.
57
The scanning electron micrograph of both zeolite Na-P2 and Na-P1 in Figure
4.6 and Figure 4.7 respectively showed spherulitic aggregates with no specific
shapes. One can observe the size of particles of zeolite Na-P2 which are generally
uniform and larger (approximately 7 µm in diameter) if compared with the
morphology of zeolite Na-P1. The distribution of particle size for the latter was
larger and the diameter of the smallest particle could be less than 5 µm.
Figure 4.6: SEM image of zeolite Na-P2
Figure 4.7: SEM image of zeolite Na-P1
58
Although the conversion of zeolite Na-P2 to zeolite Na-P1 could be done by
prolonging the heating period, the reproducibility was difficult to be achieved. The
same attempt was repeated again with 6 days heating but the product still remained
as zeolite Na-P2. While higher heating temperature was applied to the crystallization
process, i.e.110 °C, three dominant stable phases in Na2O-Al2O3-SiO2-H2O system
appeared as final products in the mixture. They are zeolite Na-P1, analcime and
Intensity (a.u.)
sodalite [102].
2 Theta Scale (°)
Zeolite Na-P1
Sodalite
analcime
Figure 4.8: X-ray diffractogram of three stable phases appeared in product.
The formation of zeolite Na-P2 was, somehow hardly obtained with the same
starting reactants composition in the following synthesis. This may be attributed to
the nature of untreated rice husk ash that exhibits different reactivity, depending on
which portion of bulk rice husk ash is used in the synthesis. Modification of the
reactant compositions was therefore carried out in the series with 4Na2O: Al2O3: 10
SiO2: 130H2O as basis. The heating period was extended to 8 days. The series of
obtained products with different starting compositions were exhibited in Figure 4.9.
59
Intensity (a.u.)
a
b
c
d
e
2 Theta Scale (°)
a
4Na2O : Al2O3 : 10 SiO2 : 130H2O
d
3.5Na2O : Al2O3 : 10 SiO2 : 130H2O
b
3Na2O : Al2O3 : 10 SiO2 : 130H2O
e
4Na2O : Al2O3 : 11 SiO2 : 130H2O
c
3Na2O : Al2O3 : 11 SiO2 : 130H2O
Figure 4.9: X-ray diffractogram of products with different ratio of reactant
compositions.
From the series of products, one can observe that too high a silica
composition in the gel (sample d and e) failed to form zeolite P. On the other hand,
relatively lower Na2O compared to the silica content (lower Na2O/SiO2) hardly
provide an effective alkaline medium for zeolite P synthesis. This was revealed by
the rather amorphous phase in samples b and c. The synthesis of zeolite Na-P2 was
successful with the starting reactant compositions of 4Na2O: Al2O3: 10 SiO2:
130H2O. The production of zeolite Na-P2 with this recipe was consistently achieved
and bulk amount of zeolite Na-P2 was continuously synthesized. It was confirmed
by powder diffraction file (PDF) 80-0700.
The zeolites Na-P2, which were synthesized from different batches with the
same recipe, were well mixed to provide a bulk amount of zeolite P for the following
sorption studies. The mixing of products did not affect the structure of zeolite NaP2. This was proven by the well-maintained structure of mixture of zeolite Na-P2
through XRD pattern (refers to Appendix C) and the BET surface area of the sample
60
was measured as 19.37 m²/g (Appendix D-1). The synthesized zeolite Na-P2 was
denoted as sample Ori-P.
4.2
Modification of Zeolite Na-P2
Further modification of rice husk ash-synthesized zeolite Na-P2 through ion
exchange alters the structural characteristics of the original sample. Incidentally,
desilication of sample Ori-P by alkaline medium, i.e. 0.2 M sodium carbonate under
mild heating (~60°C), was proven to preserve the structure of the zeolite. Referring
to the X-ray diffractogram and scanning electron micrograph of the desilicated
zeolite Na-P2, which was respectively shown in Figure 4.10 and Figure 4.11
explained this conclusion. The framework structure of zeolite Na-P2 was well
maintained in the provoking alkaline medium in spite of little sacrifice of
Intensity (a.u.)
crystallinity.
2 Theta Scale (°)
Figure 4.10: X-ray diffractogram of zeolite Na-P2 after desilication at 60 °C
From the previous study [26], the researchers have found that upon wellcontrolled desilication, the ion exchange capacity of zeolites was proven to increase
61
owing to the increase of the density of aluminium tetrahedral sites after the removal
of some silicon from the framework. However, the enhancement of ion exchange
capacity for zeolite Na-P2 through desilication was predicted to be insignificant.
This was supported by the slight changes of Si/Al ratio of original zeolite Na-P2 and
desilicated zeolite Na-P2 (Table 4.1), as obtained from the elemental analysis by
energy dispersive x-ray microanalysis.
Figure 4.11: SEM imageof zeolite Na-P2 after desilicated at 60 °C
Table 4.1: Comparison of Si/Al ratio for original and desilicated zeolite Na-P2
Sample
Original zeolite Na-P2
After desilicated in 0.2 M sodium carbonate at
60°C for 2 h
4.2.1
Si/Al ratio
1.81
1.75
Structural Change of Zeolite Na-P2 upon Ion Exchange
It was realized from the beginning that zeolite P belongs to the gismondine
(GIS) family, which was found as the one of the most flexible zeolite frameworks
62
both from geometrical point of view, because of the possible distortion of the T-O- T
bridges between perpendicular crankshaft chains; and from the chemical point of
view, because it can easily accommodate different Si/Al ratios (1-2.5) in the
framework tetrahedral [160]. Its conformation depends on the extra-framework ions,
the state of dehydration, and the chemical composition [161].
In this study, further exhaustively sodium exchange did not change the
structure of zeolite Na-P2. It was denoted as sample Homo-Na. Nevertheless, the
incorporation of calcium ions post desilication through exhaustively ion exchange
converted sample Ori-P into the structure identical to garronite. The conversion of
zeolite Na-P2 to synthetic garronite through desilication-ion exchange has not been
reported yet even though Ghobarkar and Schäf [162] and Chen et al. [163] have
synthesized garronite through CaO-Al2O3-SiO2-H2O and Na2O-CaO-Al2O3-SiO2H2O systems respectively using synthetic glasses. The X-ray diffractogram of the
Ca-form was exhibited in Figure 4.12 and confirmed with PDF 79-1336. The sample
was denoted as Homo-Ca. The X-ray diffraction data of original zeolite Na-P2 (OriP) and the calcium-exchanged zeolite (garronite, Homo-Ca) were shown in Table 4.2
Intensity (a.u.)
and 4.3 respectively, for clearer discussion.
2 Theta Scale (°)
Figure 4.12: X-ray diffractogram of desilicated-calcium ion exchanged zeolite
(garronite)
63
One can observe that a sharp peak appear at 2θ in the range of 12-13° for
sample Homo-Ca instead of a split peak for zeolite Na-P2 (Ori-P, referred to Figure
4.3). The peak around 15° disappeared after the conversion and only one peak was
observed at 2θ =17.894°. The peak which was located around 27° was absent as well
in XRD of sample Homo-Ca. The intensities of two peak around 27-29° for sample
Homo-Ca showed a reverse with the peaks of zeolite Na-P2 in the same range. The
split of peaks for sample Homo-Ca at 2θ around 33-34° was not clearly distinguished
if compared to zeolite Na-P2
Table 4.2: X-ray diffraction data of zeolite Na-P2 (Ori-P)
Zeolite Na-P2 (this study)
PDF 80-0700 [126]
d (Ǻ)
I / Io
d (Ǻ)
I / Io
7.15819
76.7
7.13589
100
7.04754
76.9
7.06207
86
5.77821
11.6
5.78531
5
5.06072
52.5
5.03813
52
4.91120
24.2
4.93494
27
4.43061
9.9
4.43290
6
4.11055
100.0
4.10421
92
4.04610
23.1
4.05946
17
3.53368
9.2
3.52799
1
3.33411
18.9
3.33008
12
3.19581
91.4
3.18755
100
3.11611
56.7
3.12672
74
2.97979
13.0
2.98760
4
2.69673
50.2
2.69120
50
2.68060
40.5
2.68063
32
2.65811
23.3
2.65801
29
2.52682
9.2
2.52528
7
64
Table 4.3: X-ray diffraction data of garronite (Homo-Ca)
Garronite (this study)
PDF 79-1336 [154]
d (Ǻ)
I / Io
d (Ǻ)
I / Io
7.12852
100
7.14834
100
4.95302
64.7
4.96485
47
4.15703
70.1
4.15416
48
4.07844
26.2
4.07562
13
3.51008
6.7
3.50985
1
3.24495
24.9
3.24564
31
3.14832
94.6
3.15077
70
2.96655
8.0
2.84232
7.7
2.71618
4
2.67884
55.5
2.68063
44
2.65974
6
2.57610
6
2.60127
8.4
2.58008
12.5
The elemental analysis of sample Ori-P, Homo-Na as well as Homo-Ca was
conducted by wavelength-dispersive X-ray fluorescence spectrometer (WDXRF).
WDXRF analysis was chosen instead of other techniques due to its simpler sample
preparation, ability to determine some non-metals and improved precision [164].
From the result of analyses as shown in Table 4.4, one can observe that the
synthesized zeolite Na-P2 (Ori-P) continued to incorporate sodium ions during the
exhaustive sodium exchange and the sodium concentration in the unit cell
composition was increased from 5.33 to 5.59 (sample Homo-Na), as exhibited in
Table 4.5.
On the other hand, the sodium content of sample Ori-P was greatly replaced
by calcium during the calcium exchange and a small portion of it, which was located
at the inaccessible sites of the framework, was found to be intact. The original trace
level potassium content in the sample Ori-P was driven off by the incoming cations
during the exhaustive ion exchange. It was indicated by the value of K/(Ca+Na+K)
of sample Homo-Na and Homo-Ca, which were found to be negligible. There was
no great change of SiO2/ Al2O3 ratio of the zeolites showing that the desilication step
65
only selectively removed a slight amount of tetrahedral silicon from the framework.
The presence of other elements in the zeolite samples was originated from the raw
material and was positioned as considerably stable values throughout the ion
exchange.
All zeolites contain natural molecular water as an intracrystalline fluid, which
can be removed by elevated temperature and evacuation. The water can normally be
re-adsorbed by exposing the crystal to water vapor [3]. In this study, the water
content of sample Homo-Na which corresponded to the loss of ignition was found
higher than the original zeolite Na-P2 (sample Ori-P). The water molecules
penetrated into the intrazeolitic channel and cavity system after equilibration over
saturated potassium chloride solution. In this case, extra amount of sodium content
which was introduced into the zeolite by exhaustively exchange enhanced the water
re-adsorption. However, the water content of sample Homo-Ca was observed lower
than the unmodified zeolite after the replacement of Na+ by Ca2+. The replacement
of Na+ by Ca2+ or Cs+ in analcime led to the formation of an anhydrous structure as
well [3]. The observation concluded that the water content partially attributed to the
cation types and their amount present in the zeolite.
Table 4.4: Chemical compositions of zeolites determined by WDXRF
Composition
Sample Ori-P
Sample Homo-Na
Sample Homo-Ca
(%wt.)
(%wt.)
(%wt.)
SiO2
46.81
42.03
48.4
TiO2
0.02
0.05
0.04
Fe2O3
0.13
0.14
0.13
Al2O3
21.91
20.12
23.04
MnO
0.05
0.05
0.04
CaO
0.55
0.41
12.30
MgO
<0.01
0.12
0.21
Na2O
12.59
11.95
0.84
K2O
0.74
0.11
0.08
P2O5
0.28
0.33
0.31
Loss of ignition
16.92
24.69
14.97
66
Table 4.5: Unit cell compositions of zeolites (on the basis of 32 oxygen)
Composition
Sample Ori-P
Sample Homo-Na
Sample Homo-Ca
Si
10.23
10.14
10.02
Al
5.65
5.71
5.80
Na
5.33
5.59
0.36
Ca
0.13
0.10
2.81
K
0.21
0.03
0.02
SiO2/ Al2O3
3.62
3.55
3.52
Ca/(Ca+Na+K)
0.02
0.02
0.88
Na/(Ca+Na+K)
0.94
0.98
0.11
K/(Ca+Na+K)
0.04
0
0
Figure 4.13a and 4.13b respectively exhibited the 29Si and 27Al NMR spectra
of sample Ori-P (Na-P2) and Homo-Ca (garronite). The framework Si/Al ratio was
calculated using the following equation [165] according to the relative intensity of
each peak in the 29Si NMR spectra.
4
Si/Al =
∑I
Si ( n Al )
n =0
(4.1)
4
∑ 0.25n I
Si ( n Al )
n =0
where I is relative NMR signal intensities the and n is the number of Al atoms
sharing oxygens with the SiO4 tetrahedron under consideration.
In Figure 4.13a, the 29Si NMR spectra of both zeolites were characterized by
five well-resolved Q4 coordination (Q4 stands for SiO4 tetrahedron connected to 4
other tetrahedral via oxygen bridging). The line assignments were shown in Table
4.6. The five observed resonances correspond to silicon atom with aluminium atom
in the next coordination sphere ranging from Si(0Al) to Si(4Al).
The 29Si peaks of zeolite Na-P2 were found to be shifted to the downfield
after exchange with calcium, accompanied by the decrease of relative intensities of
peaks Si(4Al) through Si(1Al). On the other hand, the relative intensity of
67
Si(0Al,4Si) resonance was slightly increased. Si/Al ratio obtained from NMR
spectra yield 1.74 and 1.78 for zeolite Na-P2 and garronite respectively (The
calculation of Si/Al ratio was enclosed in Appendix D-2). Both of them agreed well
with the WDXRF results.
3
2
4
1
5
garronite
5
zeolite Na-P2
3
2
4
1
1
Si (4Al)
2
Si (3Al)
3
Si (2Al)
4
Si (1Al)
5
Si (0Al)
Figure 4.13a: 29Si NMR spectra of zeolite Na-P2 and garronite
52.824ppm
garronite
54.421ppm
zeolite Na-P2
Figure 4.13b: 27Al NMR spectra of zeolite Na-P2 and garronite
68
However, 29Si NMR was speculated to overestimate the Si/Al ratio of
garronite (Homo-Ca) in this study. A Q3 coordination, i.e. Si(3Si,OH) may overlap
with Si(1Al, 3Si) resonance in garronite after exhaustively desilication and calcium
ion-exchange. The slight change in Si/Al ratio of the products agreed with the
finding of Groen et al. [166] that the presence of high aluminium in the zeolite
framework (low Si/Al ratio) prevents Si from being extracted. The fact that
aluminium is more difficult to extract can be explained by the negative charge
associated with Al tetrahedra in the zeolite framework, hindering its extraction of
aluminium through hydrolysis of Si-O-Al bonds by negatively charged hydroxyl
groups [167].
Table 4.6: Assignment of 29Si NMR chemical shifts to the local Si environment in
the zeolites
Chemical Shift (ppm vs. TMS)
Local Si environment in the zeolites
Zeolite Na-P2
Garronite
(this study)
(this study)
Si(4Al,0Si)
-88.74
-89.89
Si(3Al,1Si)
-92.89
-94.34
Si(2Al,2Si)
-98.61
-99.82
Si(1Al,3Si)
-103.86
-105.88
Si(0Al,4Si)
-109.17
-110.67
Si/Al NMR
1.74
1.78
Si/Al WDXRF Analysis
1.81
1.73
The 27Al NMR spectra in Figure 4.13b indicated that all the aluminium was
tetrahedrally coordinated in both samples. No octahedral coordination of aluminium
was detected. Due to the flexibility of GIS framework, after the incorporation of
calcium into zeolite Na-P2 via ion exchange, the 27Al line shifted from 54.421 ppm
to 52.824 ppm. The phenomenon was accompanied by the line broadening and
asymmetry of Al peak, indicating the distortion of zeolite framework post ion
exchange.
69
4.2.2
Investigation of the Possibility of Preparing Protonated Zeolite P
through Calcination
Calcination of NH4- exchanged zeolite at high temperature is one of the most
convenient methods to generate the H-form zeolite through deammoniation. The
possibility to generate protonated form of zeolite P with this technique was
investigated. The original (sample Ori-P), desilicated and ammonium-exchanged
desilicated-zeolite P2 was analyzed with the thermogravimetry/differential thermal
analyzer in order to study the behavior of these materials under controlled heat
treatment.
The thermograms of the sample Ori-P (Figure 4.14) and desilicated zeolite P2
(Figure 4.15) were similar to each other, where the percentage of weight loss
between 50 °C to 700 °C was attributed to the elimination of volatile substance like
water, which was around 14-15%. Two significant endothermic peaks due to the loss
of water were observed for both samples at temperatures below 150 °C. One can
observe that the dissociation of water from the desilicated zeolite P2 appeared at
higher temperatures if compared to sample Ori-P. This might be due to the alteration
of pore characteristics of zeolite P after desilication has taken place.
100°C
Figure 4.14: TG-DTA thermogram of sample Ori-P
70
Figure 4.15: TG-DTA thermogram of desilicated zeolite P2
For the ammonium-exchanged desilicated-zeolite P2, the weight loss observed
via TG curve in Figure 4.16 was higher than the former two samples, i.e. ~19% when
it was being heated between 50 °C to 700 °C. This weight loss corresponded to the
loss of water plus ammonia from the sample. The ammonium exchanged desilicated
zeolite P2 only showed one small endothermic peak around 104 °C which was
attributed to water loss, but one new endothermic peak appeared around 260 °C to
360 °C indicating the release of ammonia plus water from the zeolite framework.
Figure 4.16: TG-DTA thermogram of ammonium-exchanged
desilicated-zeolite P2
71
Though the deammoniation of zeolite P is possible in the preparation of Hform zeolite, the poor thermal stability of low silica zeolite P resulted in the collapse
of the structure at high temperature. Hence, the temperature for deammoniation is
critical for zeolite P in order to preserve its crystalline structure. It was proven by
investigation of the heat resistance of the ammonium-exchanged desilicated-P2 in a
muffle furnace for one hour by altering the temperature of heating.
The structures of the products were investigated with X-ray diffraction and
infrared spectroscopy. The X-ray diffractogram in Figure 4.17 revealed that the
generation of protonated zeolite P at 250 °C has resulted in an amorphous phase
forming in the zeolite structure and continuous heating at higher temperature, i.e. 300
°C to 350 °C brought damage to the zeolite P structure. The finding was supported
by infrared spectrum as indicated in Figure 4.18 where the finger-print area for
zeolite P structure around 900-500 cm-1 disappeared at higher heating temperature.
The study concluded that this technique was not suitable for H-form zeolite P
Intensity (a.u.)
formation.
2 Theta Scale (°)
a
ammonium-exchanged zeolite P
d
heated at 350 °C
b
heated at 250 °C
c
heated at 300 °C
Figure 4.17: X-ray diffractogram for ammonium-exchanged desilicated zeolite P2
and its H-form product at different temperature
72
a
Transmittance (%)
b
c
d
Wavenumber (cm-1)
a
d
ammonium-exchanged zeolite P
heated at 350 °C
b
heated at 250 °C
c
heated at 300 °C
Figure 4.18: FTIR spectra for ammonium-exchanged desilicated zeolite P2 and its Hform product at different temperature
4.2.3
Loading of Aluminium onto Desilicated zeolite Na-P2
The pH of the aluminium sulfate solution series with the concentration
ranging from 10 mmol/L to 50 mmol/L was found to be in between 3 and 4. As the
hydrolysis products of trivalent aluminium, both Al3+ and polynuclear species of Al
(III) such as AlOH2+ and Al(OH)22+ may exist in the acidic pH range [168]. The
deposition of aluminium on the surface and/or in the cavity of desilicated zeolite NaP2 was thus proposed to be governed by either cation exchange of Al3+ for Na+ in
desilicated zeolite Na-P2 and/or deposition of the polynuclear species onto the
surface of zeolite.
Figure 4.19 exhibited the X-ray diffractogram of the original desilicated
zeolite Na-P2 and a series of selected modified products. One can notice that
73
structural characteristics of the modified samples almost duplicated those of the
desilicated zeolite Na-P2, suggesting that loading of aluminium species into the
zeolite cavities and surface did not damage the zeolite framework.
Intensity (a.u.)
50Al-P
30Al-P
10Al-P
Desilicated Zeolite Na-P2
2 Theta Scale (°)
Figure 4.19: Comparison of the X-ray diffractogram between desilicated
zeolite Na-P2 and aluminium-loaded zeolite Na-P2.
X-ray diffractogram of sample 10Al-P, 30Al-P and 50Al-P were displayed
herewith as the representatives of the whole modified series with the view that the
effect of the modifier dose (aluminium sulfate) on the structural characteristics could
be elucidated. The only significant change in the X-ray diffractogram was the slight
shifting of most of the peaks when the concentration of aluminium sulfate was
varied. Refering to the X-ray diffraction data in Tables 4.7a and 4.7b, there were
dramatic changes of 2θ values and d-spacings as the different loading of aluminium
was applied. The phenomenon indicated that zeolite framework suffered different
level of distortion upon the aluminium loading.
74
Table 4.7a: 2θ values of desilicated zeolite Na-P2 and series of aluminium-loaded
zeolite Na-P2
2θ value (º)
Desilicated zeolite Na-P2
10 Al-P
30 Al-P
50 Al-P
12.332
12.456
12.550
12.490
17.492
17.540
17.493
17.575
17.997
18.019
18.005
18.067
21.572
21.624
21.605
21.659
27.837
27.887
27.866
27.960
28.607
28.620
28.601
28.622
33.121
33.208
33.188
33.282
33.400
33.712
33.665
33.793
Table 4.7b: d-spacings of desilicated zeolite Na-P2 and series of aluminium-loaded
zeolite Na-P2
d-spacing (Å)
Desilicated zeolite Na-P2
10 Al-P
30 Al-P
50 Al-P
12.332
12.456
12.550
12.490
17.492
17.540
17.493
17.575
17.997
18.019
18.005
18.067
21.572
21.624
21.605
21.659
27.837
27.887
27.866
27.960
28.607
28.620
28.601
28.622
33.121
33.208
33.188
33.282
33.400
33.712
33.665
33.793
The 27Al line of the aluminium-loaded zeolite Na-P2 that was shown in the
NMR spectra (Figure 4.20) revealed that almost all aluminium species in the zeolite
were tetrahedrally coordinated with the absence of a significant peak for octahedral
aluminium. One can observe the presence of trace level octahedral aluminium for
75
sample 10 Al-P and 30 Al-P at chemical shift around 0 ppm. This indicated that
incorporation of extraframework aluminium onto zeolite P can be done by applying
optimum amount of aluminium sulfate. However, for zeolite sample 50 Al-P, there
is no any significant peak around 0 ppm. Data in Table 4.8 showed that the 27Al line
was generally shifted to the downfield when the aluminium species were loaded.
However, the shifting was not consistent.
Table 4.8: 27Al chemical shift for aluminium-loaded zeolite Na-P2 in NMR
spectra
Sample
Chemical shift (ppm)
Desilicated zeolite Na-P2
54.211
10 Al-P
52.263
30 Al-P
52.967
50 Al-P
52.844
0 ppm
50 Al-P
30 Al-P
10 Al-P
(a)
(b)
Figure 4.20: 27Al NMR spectra of (a) desilicated zeolite Na-P2 and (b)
aluminium-loaded zeolite Na-P2
CHAPTER 5
RESULTS AND DISCUSSION: SORPTION STUDIES ON THE SORBENTS
5.1
Cation Removal
Basically, the negative framework charges of zeolite generated by the
presence of tetrahedral aluminium are compensated by cation species that are not
framework atoms. It provides a platform to allow exchange reaction between the
loosely fixed cations and dissolved cations in the solution. The cation exchange
capacity of such aluminosilicates depends on the number of aluminium atoms in the
framework. Hence, as the zeolites are utilized as ion scavengers for cation species in
the aqueous solution, ion exchange shall be emphasized as the dominant mechanism
that drives the removal process.
5.1.1
Kinetic Studies of Ion Exchange on the Zeolite
Before the ion exchange equilibrium studies of hazardous metals could
commence, it was necessary to determine the equilibrium contact time required for
the metals (the time required to reach the equilibrium state after contact with the
zeolite). Figures 5.1 to 5.3 clearly showed that the initial uptake of Pb2+, Zn2+ and
Cd2+ occurred rapidly for all zeolite samples and most of the tests reached 90% of the
equilibrium in a time of less than 15 hours. The variations of the hazardous metal
concentrations in the solution were negligible after 20 hours of contact time. The
77
possible explanation for the variation is that the resorption of the exchangeable
cations to the zeolite surface may have been occurred as a result of stirring.
4
3.5
q (meq/g)
3
Ori-P
2.5
Homo-Na
2
Homo-Ca
1.5
1
0.5
0
0
20
40
60
80
time, t (hour)
Figure 5.1: Plot of sorbed amount versus time for Pb2+ ions by the zeolites
Generally, all zeolite samples showed higher preference to Pb2+ instead of
Cd2+ and Zn2+ ions. Samples Homo-Na exhibited slightly greater affinity towards
Pb2+ ions (Figure 5.1) but weaker retention towards Zn2+ and Cd2+ if compared to
sample Ori-P (Figure 5.2 and 5.3). This result agreed well with the previous
chemical analysis, which indicated lower theoretical cation exchange capacity (CEC)
of Homo-Na because of less aluminium atoms in the framework (Table 4.4).
3.5
q (meq/g)
3
2.5
Ori-P
2
Homo-Na
1.5
Homo-Ca
1
0.5
0
0
20
40
60
80
100
time, t (hour)
Figure 5.2: Plot of sorbed amount versus time for Zn2+ ions by the zeolites
In spite of the comparable performance of sample Homo-Ca in the removal of
Pb2+, its capability to draw Cd2+ from the solution was found poorer than the other
78
two samples. However, Homo-Ca has similar affinity with Homo-Na in the removal
of Zn2+.
3
q (meq/g)
2.5
2
Ori-P
Homo-Na
1.5
Homo-Ca
1
0.5
0
0
20
40
60
80
time, t (hour)
Figure 5.3: Plot of sorbed amount versus time for Cd2+ ions by the zeolites
It is well recognized that the characteristic of sorbent surface is a critical
factor that determines the uptake rate parameter and the diffusion resistance as an
important role in the overall transport of solutes. Several kinetic models were tested
to describe the changes in the sorption of studied ions with time. First-order rate
equation of Lagergren is one of the most widely used sorption rate equations for the
sorption of a solute from a liquid solution. It was the first rate equation for the
sorption of liquid/solid system based on solid capacity [169]. To distinguish kinetics
equation based on sorption capacity of solid from concentration of solution,
Lagergren’s first-order rate equation has been called pseudo-first-order [170-171].
The pseudo-first-order rate expression is written as:
dqt
= k1 ( q e − q t )
dt
(5.1)
Integrating Equation 5.1 for the boundary conditions t = 0 to t = t and qt = 0
to qt = qt, gives:
 qe
log
 q e − qt
  k1 
 = 
t
  2.303 
(5.2)
79
which is the integrated rate law for a pseudo-first-order reaction, where qe is the
amount of metal sorbed at equilibrium (meq/g); qt is amount of metal sorbed at time t
(meq/g); k1 is the equilibrium rate constant of pseudo-first-order sorption (1/h).
Equation 5.2 can be rearranged to fit a linear form:
 k 
log (q e − qt ) = log q e −  1  t
 2.303 
(5.3)
The slope and intercept of the straight-line plots of log (qe - qt) versus t are
used to determine the first-order rate constant k1. Nevertheless, in most cases in the
literature, the first-order rate expression of Lagergren does not fit well with the
whole range of contact time and is generally applicable over the initial stage of the
sorption process [172]. One has to treat qe as an adjustable parameter to be
determined by trial and error.
Pseudo-second-order rate equation was applied in this study instead of
Lagergren’s first-order rate model. The model was developed by Ho [173] for solidliquid sorption systems. According to the author, the pseudo-second-order equation
does not have the problem of assigning an effective sorption capacity. Besides that,
the sorption capacity, rate constant of pseudo-second-order and the initial sorption
rate all can be determined from the equation without knowing any parameter
beforehand.
The differential equation of pseudo-second-order is as follows:
dq t
= k 2 (qe − qt ) 2
dt
(5.4)
Integration of Equation 5.4 and applying the boundary condition will give:
1
1
=
+ k2t
q e − qt qe
(5.5)
80
Equation 5.5 can be rearranged into a linear form through the following
relationship:
1
1
t
=
+
t
2
qt k 2 qe q e
(5.6)
The definition of qe, qt and t are same with the Lagergren’s first-order kinetic
model. k2 value (g /meq h) is the rate constant of second-order kinetic model. The
pseudo-second-order rate equation shows how the sorption capacity of sorbate
depends on time. If the equilibrium sorption capacity of sorbate and the rate constant
k2 are known, then the sorption capacity of sorbate at any time can be calculated.
The plots of t/q versus t in Figure 5.4 provided useful information through the slope
and intercept for calculating the second-order rate constant k2 and qe. Table 5.1 listed
the calculated results obtained from the pseudo-second-order equation.
80
70
Pb (II) uptake by Ori-P
Pb (II) uptake by Homo-Na
t/qt (h g/meq)
60
Pb (II) uptake by Homo-Ca
Zn (II) uptake by Ori-P
50
Zn (II) uptake by Homo-Na
Zn (II) uptake by Homo-Ca
40
Cd (II) uptake by Ori-P
Cd (II) uptake by Homo-Na
30
Cd (II) uptake by Homo-Ca
20
10
0
time, t (hour)
Figure 5.4: Pseudo-second-order sorption kinetics of Pb2+, Zn2+ and Cd2+ ions onto
zeolites
81
Table 5.1: Pseudo-second-order rate constant, calculated qe and experimental qe
values for the zeolites in the removal of Pb2+, Zn2+ and Cd2+ ions
Sample
Ori-P
HomoNa
HomoCa
Reaction
k2
(g/meq h)
qe
(meq/g),
experimental
qe
(meq/g),
calculated
r2
Na+↔1/2Pb2+
18.922
3.130
3.100
1
Na+↔1/2Cd2+
0.844
2.711
2.500
0.996
Na+↔1/2Zn2+
0.425
2.640
2.705
0.996
Na+↔1/2Pb2+
3.649
3.408
3.386
1
Na+↔1/2Cd2+
0.369
2.288
2.191
0.916
Na+↔1/2Zn2+
1.068
1.765
1.795
0.999
Ca2+↔Pb2+
0.172
3.363
3.573
0.991
Ca2+↔Cd2+
0.997
1.121
0.713
0.934
Ca2+↔Zn2+
0.066
2.884
3.158
0.908
The correlation coefficients (r2), also shown in Table 5.1, were indicative of
the strength of the linear relationship, and were greater than 0.9. The theoretical qe
values agreed well with the experimental qe values, suggesting that the sorption data
tended to follow second-order kinetic model for the sorption of Pb2+, Zn2+ and Cd2+
into as-synthesized zeolites Na-P2 (sample Ori-P), nearly homoionic zeolite Na-P2
(sample Homo-Na) and its modified form, i.e. sample Homo-Ca (garronite).
Another simplified model was also tested because the above equations are
unable to provide definite mechanism. It is also known that intensive stirring of the
reaction system; the intraparticle diffusion of the sorbate to travel from the solution
into the pore and/or channel of the sorbent could be a limiting step. In this study,
intraparticle diffusion model given by Weber and Morris [174] was applied. The rate
constant for Morris-Weber is expressed as:
qt = k id t 1 / 2
(5.7)
82
where qt is the sorbed amount of metal (meq/g) at time (h) and kid is the rate constant
of intraparticle transport (meq/g h1/2). According to this model, if a straight line
passing through the origin is obtained through the plotting of qt versus t1/2, one can
assume that the involved mechanism is the diffusion of the metal species.
In this case the slope of the linear plot is the rate constant of intraparticle
transport. The r2 values led to the conclusion that the intraparticle diffusion process
is the rate-limiting step. Higher values of kid illustrate an enhancement in the rate of
adsorption and also a better adsorption mechanism, which is related to an improved
bonding between in-going metal ions and the zeolite. The Morris-Weber kinetic
plots for the uptake of the targeted hazardous metals by the zeolites were exhibited in
Figures 5.5 to 5.7.
As can be seen in Figure 5.5, intraparticle diffusion is not the principal
mechanism for the Pb2+ ions transportation for sample Ori-P and Homo-Na. It was
supported by the poor r2 values, which were shown in Table 5.2. The mismatch of
the diffusion model could be understood since the open framework of zeolite P made
cations in the zeolite instantaneously available for exchange with the cations in
solution. The description of the exchange process using diffusion equation became
uncertain. Nevertheless, for times up to 10 hours, the Morris-Weber relationship
held good for sample Homo-Ca in the removal of Pb2+ (Figure 5.5).
4
3.5
qt (meq/g)
3
Pb (II) uptake by Ori-P
2.5
Pb (II) uptake by Homo-Na
2
1.5
Pb (II) uptake by Homo-Ca
1
0.5
0
0
2
4
t
1/2
6
8
10
1/2
(hour )
Figure 5.5: Morris-Weber kinetic plots for the uptake of Pb2+ions onto zeolites
83
One possible reason was that calcium atoms with larger ionic radius than
sodium distorted the structure of zeolite Na-P2 and reduced the content of water in
the crystal. The decrease of water content in zeolite Homo-Ca was supported by
lower percentage of ignition loss in Table 4.4. It may ease the imigration of large
hydrated Pb2+ through intraparticle diffusion.
The gradual slopes observed in the kinetic plots for Zn2+ removal by sample
Ori-P and Homo-Na (Figure 5.6) once again confirmed that diffusion is not the ratelimiting step of the sorption. Though the r2 value for sample Homo-Na is high, the
correlation with the low kid value cannot be established. The Morris-Weber
relationship held good for sample Homo-Ca in the removal of Zn2+ up to 28 hours.
However, the kid value was found far lower than the removal of Pb2+.
3.5
3
qt (meq/g)
2.5
Zn (II) uptake by Ori-P
2
Zn (II) uptake by Homo-Na
1.5
Zn (II) uptake by Homo-Ca
1
0.5
0
0
2
4
6
8
10
12
t 1/2 (hour1/2)
Figure 5.6: Morris-Weber kinetic plots for the uptake of Zn2+ions onto zeolites
For the removal of Cd2+ ions, as can be observed in Figure 5.7, all three
slopes for the trendlines were not steep. The trendlines have only possessed
moderate r2 values as shown in Table 5.2. It was noteworthy that generally most of
the k2 values for pseudo-second-order model were adversely posed if compared to kid
values in Morris-Weber model. For most cases, high k2 values mean low kid value.
If the tendency of uptake kinetic to follow pseudo-second-order model is higher, the
diffusion will contribute less to the sorption mechanism. For example, the k2 value
for sample Homo-Ca to adsorb Cd2+ was highest among three zeolite samples, but its
kid value was the lowest one among the samples.
84
qt (meq/g)
Cd (II) uptake by Ori-P
Cd (II) uptake by HomoNa
Cd (II) uptake by HomoCa
0
2
4
t
6
1/2
8
10
1/2
(hour )
Figure 5.7: Morris-Weber kinetic plots for the uptake of Cd2+ions onto zeolites
Table 5.2: Intraparticle diffusion rate constant for the sorption of Pb2+, Zn2+ and Cd2+
onto zeolites
Sample
Ori-P
Homo-Na
Homo-Ca
Reaction
k id (meq/g h1/2)
r2
Na+↔1/2Pb2+
0.006
0.002
Na+↔1/2Cd2+
0.127
0.732
Na+↔1/2Zn2+
0.120
0.282
Na+↔1/2Pb2+
0.003
0.066
Na+↔1/2Cd2+
0.406
0.751
Na+↔1/2Zn2+
0.157
0.903
Ca2+↔Pb2+
0.849
0.978
Ca2+↔Cd2+
0.079
0.647
Ca2+↔Zn2+
0.430
0.923
85
5.1.2
Characterization of the Ion Exchange Products
The filtered solid residues after the kinetic studies were collected and dried.
Considering the studied zeolite samples were originated from the same framework
i.e. GIS, only sample Ori-P was focused in the discussion on post ion exchange
kinetic test. The X-ray diffractogram in Figure 5.8 indicated that ion exchange of
GIS-type zeolites with different type of metals (heavier and hazardous) has brought
different level of irreversible structural destruction and/or structural transition to the
zeolites.
For Pb2+-exchanged zeolite P2, only partial structure of zeolite P2 remained.
The original peaks, which are located at 2θ around 12-13° and 17-18° were found to
be insignificant. However, the other three major peaks around 21-22°, 27-28° and
33-34° remained but had their positions slightly shifted. The finding was not in line
with Moirou et al. [175], who have observed almost complete collapse of zeolite Pc
(pseudo-cubic form zeolite P). The result suggested that the position of cation sites
in orthorhombic form zeolite P (zeolite Na-P2 in this study) was different with
pseudo-cubic form, which led to different site preference of in-going cations to the
zeolite phase.
Intensity/ a.u.
Zn2+-exchanged zeolite P2
Cd2+-exchanged zeolite P2
Pb2+-exchanged zeolite P2
2 Theta-Scale (º)
Figure 5.8: X-ray diffractogram of sample Ori-P after exchanged with the targeted
metal ions.
86
The structure of Cd2+-exchanged zeolite P2 was found not much difference if
compared to sample Ori-P, except the decrease in diffraction intensity which could
be observed for all exchanged zeolite P samples as well as shifting of the peak
positions due to the structure distortion because of replacement of indigenous ions in
zeolites by Cd2+ ions.
On the other hand, phase transition from orthorhombic to tetragonal zeolite P
(Pt) was noted for Zn2+-exchanged zeolite P2. The structural transition was
confirmed with PDF 71-0962 [128]. Similar finding on zeolite Pc has been observed
by Barrer and Munday [176]. They noticed that the symmetry of zeolite changed
from cubic (Na-Pc) to tetragonal (Na-Pt) during the successive incorporation of Li+,
K+ Rb+ and Cs+. According to the authors, the transition is due to the loss of water
during the exchange and to the site occupation of the entering cations. The
explanation is thus applicable for the orthorhombic phase zeolite P since the phase
transition within zeolites P species is reversible. Besides the phase transition, a few
new peaks appeared at 2θ = 19-20° and 29.5° in the XRD traces. It was very likely
that they came from the formation of a zinc oxide phase (unidentified by JCPDS
search).
5.1.3
Effect of Solution pH Value on the Metal Uptake
The pH value of solution had a pronounced effect on the removal efficiency
of the targeted metal ions. The main reason is that the speciation of metal is solely
influenced by the pH value. Ion exchange reaction in zeolite is mainly attributed to
the exchange of exchangeable light metal ions with the cationic species of the
entering metals. For many elements, the hydroxo complexes with little affinity for
zeolite surfaces can be formed as the pH of solution become alkaline and thus reduce
the cation exchange efficiency.
In this study, the series of working metal solution used were originated from
the same source, i.e. prepared from the same stock solution with serial dilution.
Therefore, the concentration of the metal ions was supposedly to be varying not very
87
much as the dilution factors were kept constant. However, as can be seen in Figure
5.9, the concentrations of the dissolved metal ions in the working solution without
the addition of zeolite were considerably different if compared with one another.
The results showed that pH adjustments to higher region has induced the formation
of insoluble hydroxo complexes (especially for Pb2+) which were filtered off
afterwards and undetectable with atomic absorption spectrometer.
Concentration of metal ions in
-1
solution (mg.L
)
(mg/L)
6000
5000
Pb (II) ions
4000
Zn (II) ions
Cd (II) ions
3000
2000
1000
0
3
4
5
6
7
pH
Figure 5.9: Concentration of metal ions in the working solutions with various pH
value without the presence of zeolite.
Numerous researchers in their literature concluded that the removal efficiency
of such metal ions increased with the pH adjustment to higher value. They did not
attribute the decrease of metal concentration in the final filtrate to either hydroxo
complexes precipitation or merely ion exchange. On the other hand, they considered
the overall decrease of the metal concentration in solutions was due to the high
performance of zeolite itself in high pH region. The examples of such discussion
could be found elsewhere [177-178].
The effect of initial solution pH on the removal of Pb2+, Zn2+ and Cd2+ ions
were depicted in Figures 5.10 to 5.12 respectively. The exchange capacities of
88
zeolite samples were presented in such a way that the decrease of metal ions caused
by precipitation was excluded. The Pb2+ removal was irregular and did not exhibited
a clear pattern between pH 3-5. Nevertheless, the removal of Pb2+ decreased rapidly
when the pH was increased above 5 due to the formation of a lead hydroxo complex
at a higher pH value, which have little affinity for cationic exchange sites.
The results indicated that the sample Ori-P possessed higher removal
efficiency towards Pb2+ followed by sample Homo-Na and Homo-Ca. For sample
Homo-Ca, the uptake of Pb2+ by ion exchange was unable to be measured because
the precipitation of lead hydroxyl species caused the uptake of Pb2+ by sample
Homo-Ca through ion exchange to be quite supressed.
450
350
Ori-P
300
Homo-Ca
250
Homo-Na
2+
mg of Pb /g zeolite
400
200
150
100
50
0
3
4
5
6
7
pH
Figure 5.10: The effect of initial pH on Pb2+ ions removal by the zeolites
Figure 5.11 illustrated the effect of pH towards the uptake of Zn2+ ions by
zeolite samples through ion exchange. It can be seen that the sorption of Zn2+
increased with pH and reached a maximum at pH 5. The lowest sorption amounts
for three zeolite samples were obtained at pH 3 and it may have been due to the
increase in competition for adsorption sites by H+. The uptake capacity dropped as
well as in the case of Pb2+. Generally, the removal efficiency of zeolite Ori-P and
Homo-Na were comparable and sample Homo-Ca was weaker than the former two
samples in retaining Zn2+.
89
140
mg of Zn2+/ g zeolite
120
100
Homo-Na
80
Homo-Ca
60
Ori-P
40
20
0
3
4
5
6
7
pH
Figure 5.11: The effect of initial pH on Zn2+ ions removal by the zeolites
All three zeolite samples did not show considerable change of exchange
capacity towards Cd2+ when the pH was within 3-5. As illustrated in Figure 5.9, the
formation of hydroxo complexes was not significant in this pH range and hence
maintained the removal of Cd2+ through ion exchange in a stable state within this pH
range. The hydroxyl precipitation which could block some of the ion exchange sites
was formed above pH 5 and eventually offset the overall Cd2+ removal efficiency.
350
mg of Cd2+/ g zeolite
300
250
Homo-Na
200
Homo-Ca
150
Ori-P
100
50
0
3
4
5
6
7
pH
Figure 5.12: The effect of initial pH on Cd2+ ions removal by the zeolites
90
5.1.4
Construction of Binary Ion Exchange Isotherm
For the effective application of a zeolite as an ion exchanger it is essential to
have chemical models that help to describe accurately hazardous metals exchange
equilibria. The ion exchange reaction in zeolite is a stoichiometric process, where
one equivalent of an ion in the solid phase is replaced by an equivalent ion from the
solution. Scientists use a variety of ion exchange models (e.g. the Gaines-Thomas,
Gapon, Vanselow and Rothmund-Kornfeld models) in which different conventions
are used to write the concentration of dissolved and adsorbed species [179].
In this study, thermodynamic equilibrium model developed from the Gaines
and Thomas’s approach was applied. This model involves the assumption that the
presence of different counterions does not affect the equilibrium exchange between
two particular ions. The non-ideal behavior of the liquid and solid phase is resulted
from the interaction among counterions. The selectivity coefficient is constant, while
in real systems it changes with the composition of the adsorbed matter [180]. The
detailed description and the equations of the model were given in section 2.5.2.
Ion exchange equilibrium isotherm were plotted in terms of the equivalent
fraction of in-coming cations in the solution (XA(s)) against that in the solid phase
(XA(z)). Since the synthetic zeolite P samples was prepared in pure Na-from and the
modified sample with Ca-form at elevated temperature (353 K) while the equilibrium
studies were conducted at ambient temperature, it seems reasonable to assume that
the potassium and magnesium content in the zeolite phase which had been assessed
through elemental analysis, are all inaccessible ion exchange sites and do not
participate in the ion exchange process with the hazardous metal ions at ambient
temperature.
5.1.4.1 Exchanges with Pb2+ as the Entering Cation
The ion exchange isotherm generated during the exchange of indigenous ions
in zeolite samples with Pb2+ in solution is shown in Figure 5.13. Note that all three
91
zeolite samples exhibited high selectivity towards Pb2+ in which convexly upward
curvatures can bee seen. The exchange of indigenous ions by Pb2+ ions approached
XA(z) = 0.9 and Pb2+ occupied most of the theoretical exchange sites in the Homo-Na
sample in this study which is approaching 100%. Inspection of the isotherm shapes
suggested that Pb2+ ions have slightly different selectivity for all zeolite samples to
some extent (i.e. XA(s) ≥0.4), with an increase of preference for sites of higher loading
of the in-coming Pb2+ ions but decreased from the highest point afterwards.
1.2
1
XA(Z)
0.8
Ori-P
Homo-Na
Homo-Ca
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
X A(S)
Figure 5.13: Binary ion exchange in zeolites for Pb2+ ions at 302 K ± 2K
5.1.4.2 Exchanges with Zn2+ as the Entering Cation
For the removal of Zn2+which was exhibited in Figure 5.14, on the other
hand, a plateau was observed within XA(s) = 0.14 to XA(s) = 0.7 for sample Homo-Ca
after a non-selective uptake of zinc occurred at XA(s) < 0.14. This phenomenon
indicated unfavorable exchange of Homo-Ca with Zn2+ ions in solution. The gradual
but slow increase of XA(z) is a typical reaction of unfavorable uptake where it
responded positively to the increase of metal concentration and retarded at XA(s) =0.3.
The uptake of Zn2+ by samples Ori-P and Homo-Na can be concluded as less
92
favorable exchange at XA(s) below 0.2 followed by gradually increase of XA(z) to its
maximum.
1
0.8
Ori-P
Homo-Na
Homo-Ca
XA(Z)
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
1
X A(S)
Figure 5.14: Binary ion exchange in zeolites for Zn2+ ions at 302 K ± 2K
5.1.4.3 Exchanges with Cd2+ as the Entering Cation
Figure 5.15 presented the ion exchange isotherms of Cd2+ with indigenous
ions of zeolites. In contrast with Pb2+ removal, only samples Ori-P and Homo-Na
showed high selectivity towards Cd2+ whereas sample Homo-Ca exhibited rather
poor capability in the retention of cadmium ions. This phenomenon can be easily
explained by the different types of indigenous ions presented in the extraframework
of zeolite. Sample Ori-P and Homo-Na which was initially occupied by sodium ions
showed a tendency to attract higher valency ions, such as Cd2+ rather than univalent
sodium, leading to the release of sodium from the zeolite replaced by cadmium ions.
Sample Homo-Ca, which holds divalent calcium, showed weaker affinity to adsorb
cadmium because of the charge similarity of Cd2+ and Ca2+.
Nevertheless, the exchange of Na+↔1/2Cd2+ and Ca2+↔Cd2+ for three zeolite
samples were not complete; only 53% and 50% of the theoretical exchange sites
93
available for samples Ori-P and Homo-Na respectively were attained as maximum
level (Figure 5.15). For sample Homo-Ca on the other hand, selectivity towards
cadmium was not significant at XA(s) below 0.3. The maximum exchange level
attained was 30% after a flat part of curve among XA(s) = 0.3 to XA(s) = 0.6.
0.6
0.5
XA(Z)
0.4
Ori-P
Homo-Na
0.3
Homo-Ca
0.2
0.1
0
0
0.2
0.4
0.6
0.8
1
X A(S)
Figure 5.15: Binary ion exchange in zeolites for Cd2+ ions at 302 K ± 2K
5.1.5
Kielland Plots
The curve for ln K c' versus X’A(z) known as Kielland plots for those ion-
exchange pairs of three zeolite samples were presented from Figures 5.15 to 5.17.
The thermodynamic equilibrium constants, KA calculated from the area under the
curve of normalized Kielland plots through polynomial equations, standard free
energy ∆G° and maximum exchange capacity were given in Table 5.3.
The detailed description of the Kielland plots and the formulae can be found
in section 2.5.2 as well. In order to get the selectivity coefficient Kc, it is essential to
know the mean activity coefficients of individual strong electrolytes. Historically,
soil scientists and geochemists have often ignored the aqueous and solid mole
fraction activity coefficients and expressed the exchange reaction in terms of easily
94
measurable aqueous concentrations and solid component mole fractions [140].
However, the prediction of ion exchange of ion exchange equilibria by assuming that
activity coefficients of all components are equal to unity both in solution and in
zeolite phase is not generally confirmed by experimental results especially when the
solutions with high concentration of ions are applied.
Several methods of calculating liquid phase activity coefficients can be found
in the literature and most of them are discussed in the section 2.5.2. All these models
express the mean activity coefficient in terms of molality concentration units. Since
the solution densities, measured as the function of equivalent fractions of the entering
cations showed no significant change, the conversion between molality and molarity
scales was ignored in this study.
Pitzer’s model is one the most utilized models in calculating the mean
activity coefficient [181-183]. Pitzer’s model can accurately account the effect of
interaction between anion and cation pairs, interaction between pairs of ions of the
same charge and also between three ions where two of them have the same charge.
These phenomena are further led by the high concentration of the solution [140].
Nevertheless, it is less accurate for dilute solutions. Hence, different equations in
section 2.5.2 were applied in this study to provide a more precise estimate of the
mean activity coefficients.
As can be seen in Figure 5.16, the ln K c' value in the Na+↔1/2Pb2+ exchange
for zeolite sample Ori-P and Homo-Na was considerably stable for X’A(z) value of ≤
0.7 and decreased afterwards when the exchange sites were progressively filled with
Pb2+ ions. On the other hand, the ln K c' value of Ca2+↔Pb2+ exchange for the sample
Homo-Ca continually decreased when the exchange reaction proceeded. However,
ln K c' of this exchange reaction was found higher than the former two samples for
X’A(z) value of ≤ 0.9 indicating that the sample Homo-Ca actually performed better
than the sample Ori-P and Homo-Na in the removal of Pb2+ before the exchange sites
approached saturation.
95
16
14
12
Ori-P
ln K'c
10
Homo-Na
Homo-Ca
8
6
4
2
0
0
0.2
0.4
0.6
0.8
1
X' A(Z)
Figure 5.16: Kielland plots in zeolites for Pb2+ ions at 302 K ± 2K
3
2
1
0
ln K'c
-1
Ori-P
Homo-Na
Homo-Ca
-2
-3
-4
-5
-6
-7
0
0.2
0.4
0.6
0.8
1
X' A(Z)
Figure 5.17: Kielland plots in zeolites for Zn2+ ions at 302 K ± 2K
The ln K c' values for the binary ion exchange of indigenous ions in all three
zeolite samples with Zn2+ in solution were much lower than lead and cadmium
removal as illustrated in Figure 5.17. Continuous decline of ln K c' for sample Ori-P
96
and Homo-Na with the increase of Zn2+ concentration in the solution indicated that
the exchange reaction is concentration dependent. It was observed that most of the
ln K c' values of three zeolite samples especially Homo-Ca lied in the negative region.
It reflected unfavorable uptake of Zn2+ by the zeolites in the unicomponent solution.
6
ln K'c
4
Ori-P
2
Homo-Na
Homo-Ca
0
-2
-4
0
0.5
1
X' A(Z)
Figure 5.18: Kielland plots in zeolites for Cd2+ ions at 302 K ± 2K
The Kielland plots of Cd2+exchange in Figure 5.18 indicated lower
ln K c' value than Pb2+ exchange for all three zeolite samples. Continuous decrease of
ln K c' for sample Ori-P and Homo-Na revealed that the selectivity towards the Cd2+
ions is dependent on the initial concentration of Cd2+ in the solution. For Ca2+↔Cd2+
exchange of sample Homo-Ca, the Kielland plot showed unfavorable exchange
where the curve was superposed.
The observations above were confirmed by the values of the thermodynamic
equilibrium constants KA and standard free energy ∆G° computed by processing the
Kielland plots. In Table 5.3, the values of ∆G° gave a clearer view for the selectivity
of the in-going ions. The negative free energy values indicate the feasibility of the
process and its spontaneous nature. The more negative the ∆G° values, the more
selective to the entering ions. One may observe that Ca2+↔Cd2+ of zeolite Homo-Ca
as well as Na+/Ca2+ ↔1/2 Zn2+/Zn2+ for all zeolite samples giving positive values of
97
the Gibbs free energy, indicating the exchange process was unfavorable. The finding
supported the observation in the exchange isotherm and Killend plots as shown in
Figures 5.17 and 5.18.
The general gismondine-type structure of zeolite P presents two connected
main channels penetrating the framework from the (100) direction (3.1 Å x 4.4 Å)
and from the (010) direction (2.8 Å x 4.9 Å) that are confined by eight membered
rings of tetrahedral (8MR) [184]. The hydrated ionic radius of Pb2+, Zn2+ and Cd2+
are 4.01 Å, 4.30 Å and 4.26 Å respectively [185]. Thus, the hydrated metal ions all
have a diameter larger than the windows of the cavities of gismondine-type zeolites
and the accommodation of all three metals in hydrated form in the channels of the
zeolite is impossible. This made the ion-sieving effects alone cannot explain the
different selectivity of the zeolite for the selected hazardous metal ions.
Partial dehydration of the hydrated metal ions must occur in order to be
adsorbed on the surface of zeolite. Generally, zeolites with GIS framework either
zeolite Na-P2 or Ca-exchanged garronite showed higher affinity to Pb2+ in unicomponent solution if compared to Zn2+ and Cd2+. This can be explained by
different enthalpy of hydration of these three metal ions. Cd2+ and Zn2+ possess
higher enthalpy of hydration (∆Hhydr cadmium = -1807 KJ/mol and ∆Hhydr zinc =
-2046 KJ/mol) compared to lead (∆Hhydr = -1481 KJ/mol) [186]. More hydrated
cations tended to remain in the solution whereas less hydrated cations tended to
concentrate into the zeolite phase. This phenomenon encouraged Pb2+ ions to enter
the zeolite phase more than Cd2+ and Zn2+.
The combination of ion exchange isotherm and standard free energy enable
the selectivity sequence to be obtained. The preference of metals in the binary ion
exchange for zeolite Na-P2 (sample Ori-P and Homo-Na) was as Pb2+>Cd2+>Na+>
Zn2+ whereas for Ca-exchanged garronite which denoted as Homo-Ca, the selectivity
sequence was as Pb2+>Ca2+>Cd2+>Zn2+.
98
Table 5.3: . Maximum exchange capacity qmax, thermodynamic equilibrium constants
KA and standard free energy ∆G° of investigated equilibria at 302 ± 2K
Sample
Ori-P
Homo-Na
Homo-Ca
5.1.6
Reaction
qmax,
meq/g
KA
∆G°, (KJ/eq)
Na+↔1/2Pb2+
4.14
891.797
-4.892
Na+↔1/2Cd2+
2.45
31.582
-2.167
Na+↔1/2Zn2+
3.20
0.161
1.145
Na+↔1/2Pb2+
3.93
13.383
-2.256
Na+↔1/2Cd2+
2.15
2.626
-0.606
Na+↔1/2Zn2+
3.68
0.759
0.174
Ca2+↔Pb2+
3.99
26279.12
-3.508
Ca2+↔Cd2+
1.37
0.024
0.851
Ca2+↔Zn2+
1.46
0.019
1.237
Multicomponent Ion Exchange
As a continuation effort on developing zeolite P2 ion exchanger for
hazardous metal removal from the water, the competitive sorption properties of
hazardous metals namely Pb2+, Zn2+ and Cd2+ on the synthesized and modified
zeolites P were examined. The simultaneous removal of the mentioned hazardous
metal ions by three zeolite samples were shown in Figure 5.19 to Figure 5.21.
The selectivity sequences of the zeolites with GIS framework towards the
metals in the multicomponent systems were found not in line with the binary ion
exchange. As depicted in Figures 5.19 to 5.21, Pb2+ outcompeted the co-existence of
high concentration zinc and cadmium in the solution especially for sample Homo-Ca.
However, the selectivity of three zeolites towards Pb2+ ions was fairly sustained at
higher concentration region in comparison with the low concentration region.
99
Cd2+ ions were found as the dominant species in the multicomponent system
where its removal was the leading mechanism concurrent with the increase of metal
concentration. As can be seen from the same illustrations, the removal of Zn2+ fully
reversed the affinity of zeolite samples for the selected metal ions where the
selectivity of zeolites towards Zn2+ was higher than Pb2+ at low concentration region.
The further uptake of Zn2+ ions was retarded relative to the high competition with
other heavier metal ions and the nature of zeolite as well in which the Zn2+ ions are
less favored. The selectivity towards Zn2+ was either declined steeply for sample
Ori-P or maintained unchanged for sample Homo-Na and Homo-Ca after reaching
the maximum points of removal.
The results concluded that the selectivity is concentration dependent. The
present of other competing metal ions in the solutions had discernable effect on the
selected metal removal. Hence, the difference on the hydration energy could not
stand anymore to explain the selectivity sequence of metal ions in multicomponent
solutions. Whether the alteration of the selectivity was due to the changes of the
metal coordination with water molecules in the restricted space of the zeolite or other
reasons was not fully determined.
1.4
1.2
q (meq/g)
1
Pb (II)
Zn (II)
Cd (II)
0.8
0.6
0.4
0.2
0
0
500
1000
1500
2000
2500
Initial concentration of metal in solution (mg/L)
Figure 5.19: Plot of sorbed amount of metal ions onto sample Ori-P versus initial
concentration in the multi-metal solution
100
1.6
1.4
q (meq/g)
1.2
Pb (II)
Zn (II)
Cd (II)
1
0.8
0.6
0.4
0.2
0
0
500
1000
1500
2000
2500
Initial concentration of metal in solution (mg/L)
Figure 5.20: Plot of sorbed amount of metal ions onto sample Homo-Na versus
initial concentration in the multi-metal solution
1.2
-1
q (meq.g
(meq/g) )
1
0.8
Pb (II)
Zn (II)
0.6
Cd (II)
0.4
0.2
0
0
500
1000
1500
2000
2500
-1
(mg/L))
Initial Concentration of metal in solution (mg.L
Figure 5.21: Plot of sorbed amount of metal ions onto sample Homo-Ca versus
initial concentration in the multi-metal solution
101
5.2 Anion Removal
Of the many toxic hazardous elements that may present as contaminants in
natural water resources and also wastewater streams, a few specifically arsenic,
chromium (VI) and selenium occur as oxyanions. The removal of selenite and
selenate are, in particular, an issue of increasing concern due to its potential toxicity
to all living organisms.
There are various adsorbents available for oxyanions removal (refers to
section 2.2) but for most of them, pose a problem in terms of either efficiency or in
cost. Zeolite Na-P2 has been proven as an efficient and economic cation exchanger
in the previous discussion. However, it has little affinity to the negative charge ions
due to the negative excess charge of the framework. By functionalizing the surface
of zeolite with suitable reagents, zeolite Na-P2 could be utilized to capture oxyanions
as well.
5.2.1
Selection of Optimum Aluminium-Loaded Zeolite Na-P2 through Kinetic
Studies
In order to select the optimized dose of aluminium loading onto desilicated
zeolite Na-P2, the adsorption kinetic tests were commenced by investigating the
removal rate of Se (IV) and Se (VI) ions by the aluminium-loaded zeolite Na-P2
series in response to time function. The effect of contact time on the amount sorbed
of Se (IV) and Se (VI) from the buffered solution onto the zeolite was illustrated in
Figure 5.22 and 5.23 respectively.
The zeolite sample which was loaded initially with 10 mmol/L aluminium
sulfate solution was found to be the best adsorbent in the removal of Se (IV) and Se
(VI) compared to desilicated zeolite Na-P2 without aluminium loading and also to
other samples which were loaded with higher amount of aluminium sulfate. The
significant decrease of the amount sorbed for other aluminium-loaded zeolite Na-P2
was probably due to the clogging of the micropores by the excessive deposition of
102
bound aluminium species [187]. Overall, aluminium-loaded zeolite Na-P2 can
remove higher amount of Se (IV) than Se (VI) anions.
Se (IV) prepared from selenious acid (H2SeO3) occurred as HSeO3- and
SeO32- in the aqueous solutions whereas Se (VI) prepared from sodium selenate
appeared as SeO42- in the solutions. The predominant bound aluminium species
present on the surface of the zeolite Na-P2 in the acidic medium were AlOH2+,
Al(OH)2+ and also polynuclear species such as Al13O4(OH)247+ [166]. Hence, the
sorption mechanism of Se (IV) from the buffered solution with pH 4.8 was assumed
to be the ligand exchange reaction between selenium oxyanions and hydroxide ions
[188] whereas sorption of Se (VI) occurred via the outer-sphere complexation
mechanism [189] as shown in the following equations.
(a). Proposed mechanisms of Se (IV) adsorption:
[AlOH2+]-zeolite + HSeO3- → [Al(HSeO3)2+]-zeolite + OH-
(5.8)
[2AlOH2+]-zeolite + SeO32- → [Al2(SeO3)2+]-zeolite + 2OH-
(5.9)
[Al(OH)2+]-zeolite + 2HSeO3- → [Al(HSeO3)2+]-zeolite + 2OH-
(5.10)
[Al(OH)2+]-zeolite + SeO32- → [Al(SeO3)+]-zeolite + 2OH-
(5.11)
[Al13O4(OH)247+]-zeolite + xHSeO3- → [Al13O4(OH)24-x (HSeO3)x7+]-zeolite + 2OH(5.12)
[Al13O4(OH)247+]-zeolite + xSeO32- → [Al13O4(OH)24-2x (SeO3)x7+]-zeolite + 2xOH(5.13)
(b). Proposed mechanisms of Se (VI) adsorption:
[AlOH2+]-zeolite + SeO42- → [Al(OH)2+ - SeO42-]-zeolite
(5.14)
[2Al(OH)2+]-zeolite + SeO42- → [2Al(OH)2+ - (SeO4)2-]-zeolite
(5.15)
103
[Al13O4(OH)247+]-zeolite + xSeO42- → [Al13O4(OH)247+ - (SeO4) x
7+
x
]-zeolite
mg of Se(IV) / g zeolite
6
10 Al-P
5
20 Al-P
4
30 Al-P
3
40 Al-P
2
50 Al-P
1
Desilicated zeolite
Na-P2
0
0
100
200
300
time (minutes)
Figure 5.22: Plot of sorbed amount versus time for Se (IV) by the series of
aluminium-loaded zeolites
3.5
mg of Se(VI) / g zeolite
3
10 Al-P
2.5
20 Al-P
2
30 Al-P
1.5
40 Al-P
1
50 Al-P
Desilicated zeolite
Na-P2
0.5
0
0
100
200
300
time (minutes)
Figure 5.23: Plot of sorbed amount versus time for Se (VI) by the series of
aluminium-loaded zeolites
(5.16)
104
The kinetic study revealed that the desilicated zeolite Na-P2 which was
loaded with 10 mmol/L aluminium sulfate (10Al-P) was the best adsorbent among
the zeolite series to remove selenium oxyanions. The adsorption kinetics of Se (IV)
and Se (VI) by sample 10Al-P were then further modeled with pseudo-second-order
equation as depicted in Figure 5.24. The calculated kinetic parameters were
presented in Table 5.4. It was found that the relationships among t/q and t for the
adsorption of both species (selenite and selenate) is linear and the high values of
correlation coefficient (r2), suggested a strong relationship between the parameters
and also explained that the process of sorption for each species followed pseudosecond-order kinetics.
120
t /q (min g/mg)
100
80
Se (IV)
60
Se (VI)
40
20
0
0
100
200
300
time, t (minutes)
Figure 5.24: Pseudo-second order sorption kinetics of Se (IV) and Se (VI) onto
sample 10Al-P
From Table 5.4, one can observe that the initial sorption rate, h of Se (IV)
removal was higher than the uptake of Se (VI). The calculated maximum adsorbed
amount qe of Se (IV) was also greater if compared to the adsorbed amount of Se (VI).
The good fitting of the experimental data with the model for both cases suggested
that the pseudo-second-order sorption kinetic was the predominant and that the
overall rate constant of each ion appeared to be controlled by the chemisorption
process [172].
105
Table 5.4: Pseudo second-order rate constant, calculated q e values and initial
sorption rate h for sample 10Al-P in the removal of Se (IV) and Se (VI)
Species
k2 (g/mg min)
qe (mg/g)
h (mg/g min)
r2
Se (IV)
0.0097
5.787
0.325
0.983
Se (VI)
0.0153
2.904
0.129
0.973
The kinetic data was also plotted using Weber-Morrison model as shown in
Figure 5.25 in order to investigate the relationship of the selenium oxyanions uptake
with intraparticle diffusion. From the poor r2 values of both adsorption cases as
exhibited in Table 5.5, it can concluded that the adsorption of selenite and selenate
by 10Al-P was not governed by intraparticle diffusion.
7
6
q (mg/g)
5
Se (IV)
Se (VI)
4
3
2
1
0
0
5
10
t
1/2
15
20
1/2
(min )
Figure 5.25: Morris-Weber kinetic plots for the sorption of Se (IV) and Se (VI)
onto sample 10Al-P.
Table 5.5: Intraparticle diffusion rate constant for the sorption of Se (IV) and Se
(VI) onto sample 10Al-P
Species
Kid (mg/g min1/2)
r2
Se (IV)
0.207
0.671
Se (VI)
0.083
0.844
106
5.2.2
Modeling of Se (IV) and Se (VI) Adsorption Isotherm
The adsorption isotherms for the removal of selenite and selenate from the
buffered aqueous solutions on to sample 10Al-P were exhibited in Figure 5.26. The
adsorption isotherm of selenate, Se (VI) removal was regular, positive and concave
to the concentration axis. As the monolayer was formed, it became increasingly
difficult for the sorbate, i.e. Se (VI) oxyanions to find available vacant active sites of
adsorption as more sites in the adsorbent are filled. However, the efficiency of
sample 10Al-P in removing Se (VI) at lower concentration region was not satisfying.
The adsorption isotherm of Se (VI) by sample 10Al-P comported with a type L2 in
the Giles classification system [190].
In contrary, zeolite 10Al-P exhibited high capability to remove Se (IV) in
which convexly upward curvatures can be seen. The initial steep increase of
adsorption density especially at lower concentration gave way to slow approach to
equilibrium at higher solute concentration. It was worth noting that the adsorption of
Se (IV) by sample 10Al-P continued to increase afterwards giving L3-type
adsorption isotherm according to the classification of Giles et al. [190].
5
4.5
4
q (mg/g )
3.5
3
Se (VI)
2.5
Se (IV)
2
1.5
1
0.5
0
0
20
40
60
C e (m g/L)
Figure 5.26: Plot of sorbed amount of Se (IV) and Se (VI) onto sample
10 Al-P versus equilibrium concentration, Ce
107
The isotherm parameters were evaluated using Langmuir and Freundlich
models as given in section 2.5.1. Through the plots in Figure 5.27 and Figure 5.28,
the constants of the two equations, which are, together with the correlation
coefficient summarized in Table 5.6.
The straight lines obtained in Figure 5.27 and Figure 5.28 accompanying the
high values of correlation coefficients (Table 5.6) indicated that the adsorption of Se
(IV) and Se (IV) by aluminium-loaded zeolite Na-P2 fitted with the two investigated
isotherm models. Note that most of the r2 values >0.98 except the fitting of Se (VI)
adsorption with the Langmuir model (r2 = 0.966). The finding agreed with the L3
type adsorption of Se (VI) shown in Figure 5.26 which indicated that multiplayer
adsorption may occurred at higher concentrations of Se (VI) in solution.
Either Langmuir or Freundlich model showed that aluminium-loaded zeolite
Na-P2 (sample10Al-P) has higher affinity towards Se (IV) oxyanions in the solution
rather than Se (VI). Although the Langmuir and Freundlich constants M and KF have
different meaning, in which M is the maximum monolayer adsorption capacity of the
zeolite and KF gives a relative measure in adsorption capacity, they led to the same
conclusion about the correlation of the experimental data with the sorption model.
The Freundlich adsorption isotherm is an indication of surface heterogeneity of the
adsorbent while Langmuir adsorption isotherm hints towards surface homogeneity of
the adsorbent.
8
7
1/S (g/mg)
6
5
4
Se (VI)
3
Se (IV)
2
1
0
0
0.2
0.4
0.6
0.8
1/C (L/mg)
Figure 5.27: Linearized Langmuir isotherms for Se (IV) and Se (VI)
removal by sample 10 Al-P
log S
108
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-1
Se (VI)
Se (IV)
0
0.5
1
1.5
2
log C
Figure 5.28: Linearized Freundlich isotherms for Se (IV) and Se (VI)
removal by sample 10 Al-P
From the M value of Langmuir equation, it was found that sample 10Al-P
possessed excellent capability in the removal of Se (IV) and Se (VI), which were
3.758 mg Se/g zeolite and 2.067 mg Se/g zeolite respectively if compared to
aluminium oxide-coated sand [191], which can remove 1.08 mg Se/g of selenite at
pH 4.80 and 0.92 mg Se/g of selenate at pH 4.90. The greater affinity of Se (IV)
than Se (VI) onto the solid phase was expected. Balistrieri and Chao [192] and
Merrill et al. [193] also found that at the same pH, selenate adsorption on goethite
and iron oxyhydroxide was much lower than selenite adsorption. The adsorption of
selenate on γ-alumina was also observed by Yuan [194] to be lower than that of
selenite. Selenite is considered to be a less mobile species and forms inner-sphere
complexes with surface functional groups under neutral to acidic conditions.
Selenate is more stable in aqueous solution and tends to form outer-sphere complex
through electrostatic attraction accompanied by protonation [195].
Table 5.6: The parameters for Langmuir and Freundlich isotherms for Se (IV) and
Se (VI) removal
Langmuir parameters
Freundlich parameters
Species
M
(mg/g)
b
(L/mg)
r2
KF
n
r2
Se (IV)
3.758
0.212
0.966
0.752
1.958
0.984
Se (VI)
2.067
0.056
0.985
0.110
1.208
0.995
109
5.2.3
Effect of Ionic Strength of Solution on the Selenium Uptake
Because of the presence of electrolytes in many contaminated waste streams,
the uptake behaviors of selenium oxyanions in the presence of electrolyte NaCl of
concentrations 0.01M, 0.1M and 1.0M were examined, and their adsorption
isotherms are explained in the following discussion.
5.2.3.1 Uptake of Selenite
The uptake of selenite by sample 10Al-P in solutions of different ionic
strength was presented in Figure 5.29. One may observe that when the concentration
of NaCl was increased to 1.0 N, the adsorption equilibrium properties of selenite
were significantly altered. The adsorbent failed to remove selenite ions at lower
concentrations in the presence of 0.1 N NaCl. The removal of selenite was only
found to be significant when the initial concentration of Se (IV) increased. It seems
that the uptake process of selenite can only bear a relatively low concentration of
background electrolyte, i.e 0.01 N and 0.1 N NaCl, where the L-type form according
to Giles classification was preserved.
4.5
4
3.5
0.01N NaCl
q (mg/g)
3
0.1N NaCl
2.5
1N NaCl
2
1.5
1
0.5
0
0
10
20
30
40
C e (mg/L)
Figure 5.29: Plot of sorbed amount of Se (IV) onto sample 10Al-P versus
equilibrium concentration, Ce with the presence of different concentration
of electrolyte
110
The adsorption of Se (IV) in different ionic strength solution was modeled
with Langmuir and Freundlich equation. The linear plots of these two models were
exhibited in Figures 5.30 and 5.31 respectively. Even though the adsorption of Se
(IV) seems to fit well with the model, the Langmuir’s parameters were indicated by
negative value for most studied cases. It could be concluded that the presence of
high concentration of sodium chloride has caused salt imbibition where the
undissociated salt layer tended to form on the surface of zeolite and covered the
monolayer adsorption sites of zeolite instead of selenite uptake.
5
4.5
1/S (g/mg)
4
3.5
0.01 N NaCl
3
2.5
0.1 N NaCl
2
1.0 N NaCl
1.5
1
0.5
0
0
2
4
6
8
1/C (L/mg)
Figure 5.30: Linearized Langmuir isotherms for Se (IV) removal by sample
10Al-P with the presence of different concentration of electrolyte
0.8
0.6
log S
0.4
0.2
0.01 N NaCl
0
0.1 N NaCl
-0.2
1.0 N NaCl
-0.4
-0.6
-0.8
-1
-0.5
0
0.5
1
1.5
2
log C
Figure 5.31: Linearized Freundlich isotherms for Se (IV) removal by sample
10Al-P with the presence of different concentration of electrolyte
111
The adsorption of selenite was well modeled after the Freundlich formula
rather than Langmuir’s. The results indicated that the adsorption capacity of Se (IV)
was irregular as the ionic strength of the solution increased. The adsorption of Se
(IV) was enhanced by the presence of 0.1 N NaCl with the highest KF and n value
but suppressed by the high concentration of electrolyte.
Table 5.7: Parameters for Langmuir and Freundlich isotherms for selenite
removal with the presence of different concentration of electrolyte
Ionic
Strength
Langmuir parameter
Freundlich parameter
M
(mg/g)
b
(L/mg)
r2
KF
n
r2
0.01 N
n.v*
n.v*
-
0.550
1.509
0.84
0.1 N
3.448
0.417
0.99
0.798
1.904
0.93
1.0 N
n.v*
n.v*
-
0.130
0.940
0.92
* negative value
Hayes and Leckie [196] indicated that it is possible to distinguish between
inner-sphere and outer-sphere complexes by examining whether or not the adsorption
edge of an ion shifts with the changing ionic strength. They concluded that innersphere complexes do not respond to ionic strength differences while the adsorption
of outer-sphere complexes at a given pH varies with the changing ionic strength.
Nevertheless, the assignment of the adsorption of Se (IV) by aluminium-loaded
zeolite Na-P2 to outer-sphere complexation was difficult to establish without further
investigation.
5.2.3.2 Uptake of Selenate
In contrast with the adsorption of selenite, the adsorption of selenate by
sample 10Al-P in the presence of different concentration of electrolyte was adversely
proportional to the increase of ionic strength especially when the initial concentration
of selenate increased. As can be seen in Figure 5.32, the curves followed typical
112
Langmuir adsorption pattern but it was worth to note that the adsorption of selenate
at low concentration region was suppressed by strong electrolyte solution.
2.5
2
0.01N NaCl
q (mg/g)
1.5
0.1N NaCl
1N NaCl
1
0.5
0
0
10
20
30
40
C e (mg/L)
Figure 5.32: Plot of sorbed amount of Se (VI) onto sample 10Al-P versus
equilibrium concentration, Ce with the presence of different concentration of
electrolyte
Table 5.8: Parameters for Langmuir and Freundlich isotherms for selenate removal
with the presence of different concentration of electrolyte
Ionic
Strength
Langmuir parameter
Freundlich parameter
M
(mg/g)
b
(L/mg)
r2
KF
n
r2
0.01 N
n.v*
n.v*
-
0.109
1.030
0.92
0.1 N
1.180
0.624
0.96
0.302
1.962
0.99
1.0 N
1.145
0.200
0.78
0.179
1.622
0.87
* negative value
The Langmuir and Freundlich linearized plots in Figure 5.33 and Figure 5.34
respectively showed good fitting with the adsorption data. From the parameters,
which were generated from the plots, one may observe in fact, that adsorption of
selenate in 0.01 N NaCl did not follow the Langmuir model and gave negative
113
values. However, higher r2 values obtained in Table 5.8 revealed that the adsorption
of selenate was more likely to follow Freundlich model. Once again the trend of
adsorption capacity of Se (VI) was not in line with the increase of ionic strength.
Among three types of electrolytes used, the aluminium-loaded zeolite Na-P2 showed
highest KF and n in the presence of 0.1 N NaCl.
12
1/S (g/mg)
10
0.01 N NaCl
0.1 N NaCl
1.0 N NaCl
8
6
4
2
0
0
2
4
6
1/C (L/mg)
Figure 5.33: Linearized Langmuir isotherms for Se (VI) removal by sample
10Al-P with the presence of different concentration of electrolyte
0.6
0.4
0.2
0
0.01 N NaCl
0.1 N NaCl
1.0 N NaCl
log S
-0.2
-0.4
-0.6
-0.8
-1
-1.2
-1
0
1
2
log C
Figure 5.34: Linearized Freundlich isotherms for Se (VI) removal by sample
10Al-P with the presence of different concentration of electrolyte
CHAPTER 6
CONCLUSION AND SUGGESTIONS
6.1
Conclusion
From the results and analyses, it can be concluded that the objectives of this
study have been achieved. The bulk production of an orthorhombic phase of zeolite NaP2 that belongs to the gismondine (GIS) family of zeolite was successful by employing
starting reactant compositions of 4Na2O: Al2O3: 10SiO2: 130H2O through hydrothermal
synthesis. Local field-burnt rice husk ash was used as the silica source in the synthesis
and it was found that zeolite Na-P2 at high purity can be obtained after optimizing the
synthesis condition.
The characterizations of the as-synthesized and modified zeolite Na-P2 with
various solid-state techniques revealed that the framework of the zeolites was flexible to
accommodate different guest species such as extra sodium, calcium, and aluminium
ions. Through the characterizations as well, the framework of zeolite P2 was found to
experience distortion and even phase transition. The structure of zeolite Na-P2 was
converted to a structure which corresponded to garronite post optimized desilication and
exhaustive ion exchange with calcium ions.
115
The as-synthesized zeolite Na-P2 and its modified forms (namely Homo-Na and
Homo-Ca in this study) possessed high capacity to remove Pb2+, Zn2+ and Cd2+ ions
from the aqueous solutions. The sorption kinetic tests revealed that the initial uptake of
the selected hazardous metal ions for all zeolite samples occurred rapidly and most of
them reached 90% of the equilibrium in a time of less than 15 hours. The binary ion
exchange isotherms enable the determination of the maximum sorption capacity and also
selectivity sequences of the zeolites towards the selected metal ions through the
calculation of standard free energies of exchanges.
The preference of metals in the binary ion exchange for zeolite Na-P2 (assynthesized zeolite P2 and sample Homo-Na) was given as Pb2+>Cd2+>Na+>Zn2+
whereas for the Ca-exchanged garronite (sample Homo-Ca), the selectivity sequence
was recorded as Pb2+>Ca2+>Cd2+>Zn2+. In the multicomponent solutions, the preference
of metals was found not in line with the ones in the binary exchange systems. It can be
concluded that the presence of other competing metal ions with high concentrations had
discernable effect on the individual metal removal.
Zeolite Na-P2 which was loaded with 10 mmol/L aluminium sulfate was proven
to possess the greatest capability among the studied series in the removal of the selenium
oxyanions in water. The affinity of selenite onto the aluminium-loaded zeolite na-P2
was greater than selenate. From the Langmuir isotherm, it was found that aluminiumloaded zeolite Na-P2 was able to remove 3.758 mg Se (IV)/g zeolite and 2.067 mg
Se(VI)/g zeolite. The study also revealed that changes of ionic strength of the solution
affected the performance of zeolite in the removal of selenite and selenate. The
capability of zeolite to capture selenium oxyanions was suppressed by the increase of its
ionic strength.
116
6.2
Contributions
•
A rarely found orthorhombic phase of zeolite Na-P2 was successfully
synthesized through a simple hydrothermal technique by using rice husk ash as
silica source.
•
The conversion of zeolite P2 structure to garronite post desilication-calcium
exchange provides a possible alternative route for the synthesis of natural
occurring calcium-bearing garronite.
•
The application of thermodynamic equilibrium model in the construction of ion
exchange isotherm provides comparable data sets for Pb2+, Zn2+ and Cd2+
removal by the gismondine-type zeolites.
•
The application of aluminium-loaded zeolite Na-P2 acts as an economic and
efficient agent in the removal of selenite and selenate at medium to high
concentrations.
6.3
Suggestions for Future Studies
In order to construct an efficient filter unit for drinking water, the breakthrough
point of the sorbent in the removal of hazardous metals should be investigated in column
experiment. The effects of other co-existing species in the water like light elements,
heavy elements, anions, organic compounds etc. should be considered in the adsorption
studies as well.
Instruments with higher sensitivity and better limits of detection should be used
in case the study focuses on the trace level of contaminants in the water. The
recommended instruments and techniques are inductively cold plasma-mass
spectrometry (ICP-MS), hydride generation atomic absorption spectrophotometer
(HGAAS) and neutron activation analysis (NAA).
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134
APPENDIX A
National Drinking Water Quality Standards, 2000 of Malaysia for
some inorganic species and frequency of monitoring
Parameters
Total
dissolved
solids (TDS)
Chloride
Ammonia
(as N)
Nitrate
(as N)
Fluoride
Hardness
Cyanide
Sodium
Sulfate
Iron
Aluminium
Manganese
Mercury
Cadmium
Arsenic
Lead
Chromium
Copper
Zinc
Selenium
Nickel
Silver
Magnesium
Antimony
Barium
Boron
Molybdenum
Uranium
Hydrogen
sulfide
Mineral oil
Bromate
Chrorite
Column I
Max.
acceptable
value
(mg/L)
Column II
Frequency to be monitored
Treatment Service
Distribution
reservoir
plant
system
outlet
outlet
Column III
Well/
spring
Source of
reference
1000
M
M
Y/2
2Y
WHO2
250
M
M
Y/2
2Y
WHO2
1.5
M
M
Y/2
2Y
WHO2
10
M
M
Y/2
2Y
WHO3
0.5-0.7
500
0.07
200
250
0.3
0.2
0.1
0.001
0.003
0.01
0.01
0.05
1.0
3
0.01
0.02
0.05
150
0.005
0.7
0.5
0.07
0.002
M
M
Y/4
Y/4
Y/4
M
M
M
Y/4
Y/4
Y/4
Y/4
Y/4
Y/4
Y/4
Y/4
WN
Y/4
Y/4
WN
WN
WN
WN
WN
M
M
Y/2
Y/2
Y/2
M
M
M
Y/2
Y/2
Y/2
Y/2
Y/2
Y/2
Y/2
WN
WN
WN
WN
WN
WN
WN
WN
WN
Y/2
Y/2
Y
Y
Y
Y/2
Y/2
Y/2
Y
Y
Y
Y
Y
Y
Y
WN
WN
WN
WN
WN
WN
WN
WN
WN
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
2Y
WN
WN
WN
WN
WN
WN
WN
WN
WN
MAL
WHO3
WHO2
WHO2
WHO2
WHO2
WHO2
WHO2
WHO2
WHO2
WHO2
WHO2
WHO2
WHO3
WHO2
WHO2
WHO2
MAL1990
MAL1990
WHO2
WHO2
WHO1
WHO2
WHO1
0.05
WN
WN
WN
WN
WHO2
0.3
0.025
0.2
WN
WN
WN
WN
WN
WN
WN
WN
WN
WN
WN
WN
MAL1990
WHO2
WHO2
135
M
Y/2
Y
2Y
WN
WHO1
WHO2
WHO3
MAL
indicates parameters to be monitored at least once a month
indicates parameters to be monitored at least once in 6 months
indicates parameters to be monitored at least once a year
indicates parameters to be monitored at least once in 2 years
indicates parameters to be monitored when necessary
indicates WHO guidelines for drinking water quality (appendum to
Vol. 1) 1998
indicates WHO guidelines for drinking water quality 1993/1996
indicates WHO guidelines for drinking water quality 1984
indicates values adapted for Malaysian conditions
136
APPENDIX B-1: EDAX Spectrum for Zeolite Na-P1
137
APPENDIX B-2: EDAX Spectrum for Zeolite Na-P2
138
APPENDIX B-3: EDAX Spectrum for Desilicated zeolite
Na-P2
139
APPENDIX C: X-ray Diffractogram of Well-Mixed Zeolite Na-P2
SH-zeo-mix
400
300
)
st
n
u
o
C
(
ni
L200
100
0
5
10
20
30
40
2-Theta - Scale
SH-zeo-mix - File: SH-zeo-mix.RAW - Type: 2Th/Th locked - Start: 5.000 ° - End: 50.000 ° - Step: 0.050 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 5.000 ° - Theta: 2.
Operations: Import
80-0700 (C) - Sodium Aluminum Silicate Hydrate Zeolite P2, syn - Na4(Al4Si12O32)(H2O)14 - Y: 50.00 % - d x by: 1. - WL: 1.5406 - Orthorhombic - I/Ic PDF 0.7 -
50
140
APPENDIX D-1: Surface Analysis of Zeolite Na-P2 by
Using Nitrogen Adsorption
Date:
Report
03/31/2005
Quantachrome Corporation
Quantachrome Autosorb Automated Gas Sorption System
Autosorb for Windows®
Sample ID
Description
Comments
Sample Weight
Adsorbate
choo
Cross-Sec Area
44.2
min
NonIdeality
03/17/2005 13:16
Molecular Wt
SHZEOPU6.RAW
Station #
Version 1.20
SH-ZEO-P-U-6
zeolite
0.0350 g
NITROGEN
16.2
Outgas Temp
150 °C
Ų/molec Outgas Time
3.0
Operator
hrs Analysis Time
6.580E-05
P/Po Toler
0
End of Run
28.0134 g/mol
Equil Time
3
File Name
1
Bath Temp.
77.40
MULTIPOINT BET
P/Po
1.0013e-01
2.0152e-01
3.0264e-01
Volume
[cc/g] STP
1/(W((Po/P)-1))
2.9594
4.1774
5.4537
Area =
3.008E+01
4.834E+01
6.367E+01
1.937E+01 m²/g
Slope =
1.658E+02
Y - Intercept =
1.396E+01
Correlation Coefficient =
C =
0.998777
1.288E+01
TOTAL PORE VOLUME
Total pore volume = 8.436E-03 cc/g for
pores smaller than 26.0 Å (Diameter),
at P/Po = 0.30264
AVERAGE PORE SIZE
Average Pore Diameter = 1.742E+01 Å
141
APPENDIX D-2: Calculation of Si/Al Ratio through 29Si
NMR
3
2
4
1
5
Sample Ori-P
ppm
Peak
1
2
3
4
5
Chemical Shift (ppm)
-88.74
-92.89
-98.61
-103.86
-109.17
Relative Intensity (%)
32.77
76.92
100.00
46.15
7.69
4
Si/Al =
∑I
Si ( n Al )
n =0
4
∑ 0.25n I
Si ( n Al )
n =0
=
7.69 + 46.15 + 100 + 76.92 + 30.77
(0.25 × 0 × 7.69) + (0.25 × 1 × 46.15) + (0.25 × 2 × 100) + (0.25 × 3 × 76.92) + (0.25 × 4 × 30.77)
=
261.53
= 1.74
149.9975
142
3
2
4
1
5
Sample Homo-Ca
ppm
Peak
1
2
3
4
5
Chemical Shift (ppm)
-89.89
-94.34
-99.82
-105.88
-110.67
Relative Intensity (%)
32.00
80.00
100.00
48.00
14.40
4
Si/Al =
∑I
Si ( n Al )
n =0
4
∑ 0.25n I
Si ( n Al )
n =0
=
14.40 + 48.00 + 100.00 + 80.00 + 32.00
(0.25 × 0 × 14.40) + (0.25 × 1 × 48.00) + (0.25 × 2 × 100) + (0.25 × 3 × 80.00) + (0.25 × 4 × 32.00)
=
274.40
= 1.78
154.00
143
APPENDIX E-1: Ion exchange Kinetics Data of Pb2+, Zn2+ and Cd2+
Table E-1-1: Initial Concentrations of Metal Solutions
Zeolite Sample
Sorbate
Mean C0 (mg/L)
RSD (%)
Ori-P
Pb2+
Zn2+
Cd2+
1716.4
2110.5
1914.7
0.474
0.410
0.302
Pb2+
Zn
Cd2+
1889.4
1993.5
1839.0
0.192
0.412
0.619
Pb2+
1861.4
0.200
2+
2160.0
1898.3
0.563
1.055
Homo-Na
Homo-Ca
2+
Zn
Cd2+
Table E-1-2: Uptake Amount of Pb2+ Ions at the Prescribed Duration
Zeolite Sample
Ori-P
Duration, t
Mean Ct
SD
qt
(h)
(mg/L)
(mg/L)
(meq/g)
0.25
0.5
1
2
4
6
10
25
48
70
508.5
452.2
418.0
400.9
379.3
402.4
353.9
355.9
360.2
508.5
3.1
2.3
1.1
0.8
0.9
2.0
1.1
1.9
2.3
3.1
2.915
3.027
3.084
3.099
3.124
3.045
3.131
3.100
3.064
3.064
144
Zeolite Sample
Homo-Na
Duration, t
(h)
0.25
0.5
1
2
4
6
10
24
48
69
Mean Ct
(mg/L)
770.0
560.3
482.8
459.1
486.5
418.4
463.8
401.5
502.0
496.0
SD
(mg/L)
3.3
3.4
1.1
2.4
6.8
3.1
1.9
2.0
2.0
1.7
qt
(meq/g)
2.701
3.182
3.340
3.369
3.277
3.408
3.275
3.390
3.134
3.120
0.5
1453.5
5.2
0.976
1
2
4
6
10
25
48
70
1283.9
1100.8
904.3
814.9
413.5
385.2
435.1
383.7
6.0
4.6
3.6
4.0
3.4
1.8
2.1
1.9
1.371
1.792
2.236
2.424
3.328
3.363
3.222
3.309
Homo-Ca
Table E-1-3: Quality Control Sample Measurement for the Kinetics Data of Pb2+
Uptake
Sample
QCS
Concentrations (mg/L)
Recovery %
RSD (%)
6.10
101.67
0.933
4.24
105.93
0.346
Spiked
Observed
6.00
4.00
145
Table E-1-4: Uptake Amount of Zn2+ Ions at the Prescribed Duration
Zeolite Sample
Ori-P
Homo-Na
Homo-Ca
Duration, t
Mean Ct
SD
qt
(h)
(mg/L)
(mg/L)
(meq/g)
0.4
1
2
3.3
4
5
6.5
28
54
1992
1827
1852
1826
1844
1776
1834
1759
1804
7
8
5
10
11
8
8
7
9
0.906
2.164
1.969
2.163
2.022
2.533
2.085
2.640
2.297
0.4
1840
13
1.174
1
2
3.3
5
6
11
28
96
1842
1814
1810
1786
1751
1770
1759
1635
9
7
9
7
5
9
8
3
1.156
1.367
1.395
1.571
1.833
1.679
1.765
2.682
0.4
2048
5
0.857
1
2
4
5
6.5
11
28
54
2040
1978
2028
1977
1958
1912
1776
1929
8
9
7
6
8
6
4
7
0.917
1.387
1.007
1.386
1.523
1.867
2.884
1.732
146
Table E-1-5: Quality Control Sample Measurement for the Kinetics Data of Zn2+
Uptake
Sample
QCS
Concentrations (mg/L)
Spiked
Observed
1.00
0.995
Recovery %
RSD (%)
99.5
2.15
Table E-1-6: Uptake Amount of Cd2+ Ions at the Prescribed Duration
Zeolite Sample
Ori-P
Homo-Na
Duration, t
Mean Ct
SD
qt
(h)
(mg/L)
(mg/L)
(meq/g)
0.25
0.5
1
2
4
5
10
29
51
73
1538.00
1632.00
1480.00
1432.33
1467.00
1457.33
1273.00
1321.50
1290.00
1246.33
8.89
6.42
6.56
6.24
14.81
6.61
14.89
1.79
9.53
4.62
1.621
1.593
1.887
2.077
1.912
1.937
2.671
2.448
2.556
2.711
0.7
1611.33
8.51
1.013
1
2
3.7
4.5
5
6
7
10
23
44
72
1556.67
1515.00
1410.00
1472.00
1465.50
1457.50
1456.00
1289.50
1352.50
1378.33
1384.00
2.41
4.54
5.84
2.67
11.47
5.89
4.96
13.77
22.53
3.55
7.33
1.246
1.418
1.862
1.580
1.595
1.615
1.608
2.288
2.008
1.885
1.846
147
Zeolite Sample
Homo-Ca
Duration, t
Mean Ct
SD
qt
(h)
(mg/L)
(mg/L)
(meq/g)
0.25
1826.33
7.72
0.397
0.5
1
2
3
4
5
10
29
51
73
1763.33
1779.00
1761.67
1713.00
1820.50
1825.33
1725.00
1731.00
1640.33
1622.00
5.05
4.51
9.42
5.53
7.22
7.90
5.25
10.84
21.10
7.06
0.596
0.522
0.593
0.798
0.333
0.310
0.722
0.691
1.056
1.121
Table E-1-7: Quality Control Sample Measurement for the Kinetics Data of Cd2+
Uptake
Sample
QCS
Concentrations (mg/L)
Recovery %
RSD (%)
0.011
110
0.476
0.984
98.4
0.082
Spiked
Observed
0.01
1.00
148
APPENDIX E-2: The Effect of Initial pH on Metal Ions Removal
Table E-2-1: Initial Concentrations of Metal Ions in Solutions after pH Adjustment
Sorbate
Pb
2+
Zn
2+
Cd
2+
pH
Mean C0 (mg/L)
RSD (%)
3
5407
1.61
4
4536
0.91
5
5051
1.02
6
2.29
7
3496
2216
3
4216
0.45
4
4748
0.25
5
4994
0.32
6
4866
0.52
7
3772
0.30
3
4773
0.35
4
4791
0.49
5
4716
0.33
6
4407
0.45
7
3930
0.25
3.08
149
Table E-2-2: Removal of Metal Ions by Sample Ori-P at Different pH
Sorbate
Pb
2+
Zn
2+
Cd
2+
pH
Mean qe (mg/g)
RSD (%)
3
328.0
1.39
4
240.9
0.54
5
305.3
1.38
6
166.8
1.78
7
97.4
1.20
3
32.4
0.40
4
74.6
0.19
5
113.1
0.43
6
110.9
0.27
7
69.5
0.43
3
289.8
1.01
4
292.2
0.77
5
294.0
0.39
6
272.2
0.71
7
270.6
0.68
150
Table E-2-3: Removal of Metal Ions by Sample Homo-Na at Different pH
Sorbate
Pb
2+
Zn
2+
Cd
2+
pH
Mean qe (mg/g)
RSD (%)
3
406.8
2.48
4
311.2
1.53
5
370.2
1.72
6
236.2
1.39
7
109.5
2.64
3
27.6
0.31
4
98.6
0.38
5
115.1
0.55
6
94.8
0.33
7
40.7
0.45
3
291.9
0.64
4
297.2
0.59
5
285.2
0.67
6
254.0
1.00
7
241.3
0.93
151
Table E-2-4: Removal of Metal Ions by Sample Homo-Ca at Different pH
Sorbate
Pb
2+
Zn
2+
Cd
2+
pH
Mean qe (mg/g)
RSD (%)
3
271.1
1.05
4
178.7
0.69
5
228.5
0.78
6
28.9
0.98
7
-
-
3
7.4
0.24
4
45.3
0.44
5
63.7
0.33
6
61.4
0.37
7
53.7
0.35
3
268.2
0.73
4
254.8
0.62
5
252.4
0.69
6
235.9
0.59
7
247.7
0.63
152
APPENDIX E-3: Binary Ion Exchange Isotherm Data for Pb2+
Uptake by Zeolites
Table E-3-1: Removal of Pb2+ Ions by Sample Ori-P
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
18.063
0.007
2.899
1.806
13.444
8.861
22.713
28.276
32.620
35.637
0.016
0.014
0.040
0.081
0.280
1.207
2.783
1.923
1.029
0.533
0.608
0.469
1.343
0.885
2.267
2.820
3.234
3.443
44.047
57.187
63.057
73.341
7.304
17.650
27.229
31.932
0.819
0.470
0.447
0.762
3.674
3.954
3.583
4.141
Table E-3-2: Removal of Pb2+ Ions by Sample Homo-Na
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
13.444
8.861
18.063
22.714
28.276
35.637
44.047
57.187
63.057
73.341
81.022
0.003
0.004
0.017
0.034
0.057
1.091
8.264
19.639
25.794
34.087
44.637
6.518
5.317
1.596
0.818
0.690
7.668
0.291
0.556
0.849
0.501
0.376
1.344
0.886
1.805
2.268
2.822
3.455
3.578
3.755
3.726
3.925
3.638
153
Table E-3-3: Removal of Pb2+ Ions by Sample Homo-Ca
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
8.861
0.003
6.911
0.886
13.444
18.063
22.713
28.276
32.620
35.637
44.047
57.187
63.057
0.007
0.026
0.065
0.165
0.487
1.009
8.998
19.311
27.013
3.569
0.844
0.420
0.340
0.552
0.559
0.426
1.052
0.343
1.344
1.804
2.265
2.811
3.213
3.463
3.505
3.788
3.604
73.341
33.410
0.310
3.993
Table E-3-4: Quality Control Sample Measurement for the Pb2+ Removal
Sample
QCS
Concentrations (mg/L)
Recovery %
RSD (%)
1.061
106.00
1.19
2.791
93.03
1.08
Spiked
Observed
1.00
3.00
154
APPENDIX E-4: Binary Ion Exchange Isotherm Data for Zn2+
Uptake by Zeolites
Table E-4-1: Removal of Zn2+ Ions by Sample Ori-P
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
12.018
2.382
1.262
0.955
15.034
24.525
30.240
45.342
62.184
79.777
2.902
8.748
12.545
21.325
37.513
55.754
1.180
0.555
0.600
0.910
0.380
0.655
1.213
1.578
1.769
2.402
2.467
2.402
90.485
106.104
153.128
62.965
80.598
121.157
0.522
0.297
0.401
2.752
2.551
3.197
Table E-4-2: Removal of Zn2+ Ions by Sample Homo-Na
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
12.018
15.034
24.525
45.342
62.184
79.777
90.485
153.128
1.354
2.569
7.914
24.292
39.235
58.335
64.464
116.363
0.943
0.609
0.541
0.401
0.411
0.353
0.279
0.629
1.066
1.247
1.661
2.105
2.295
2.144
2.602
3.677
155
Table E-4-3: Removal of Zn2+ Ions by Sample Homo-Ca
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
0.307
0.009
7.711
0.029
0.791
1.483
3.110
4.635
12.018
15.034
24.525
30.240
45.342
0.033
0.214
0.705
1.695
8.305
10.928
18.421
23.998
37.433
7.303
1.438
1.366
0.453
0.239
0.260
0.561
0.484
0.252
0.042
0.144
0.227
0.366
0.691
0.727
0.751
0.794
0.826
62.184
79.777
106.104
153.128
51.841
69.356
94.304
138.545
0.366
0.417
0.250
0.406
0.834
0.869
0.889
0.905
Table E-4-4: Quality Control Sample Measurement for the Zn2+ Removal
Sample
QCS
Concentrations (mg/L)
Recovery %
RSD (%)
0.770
102.667
0.236
1.00
0.999
99.990
0.620
1.30
1.278
98.308
0.169
Spiked
Observed
0.75
156
APPENDIX E-5: Binary Ion Exchange Isotherm Data for Cd2+
Uptake by Zeolites
Table E-5-1: Removal of Cd2+ Ions by Sample Ori-P
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
5.708
0.027
2.314
0.568
6.813
15.714
17.674
23.678
35.623
37.283
0.075
1.308
2.206
6.035
16.544
17.993
2.786
1.116
0.947
0.937
1.286
1.371
0.674
1.441
1.547
1.764
1.908
1.929
47.088
38.155
75.260
24.371
20.779
52.558
2.151
0.559
0.606
2.272
1.738
2.270
Table E-5-2: Removal of Cd2+ Ions by Sample Homo-Na
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
8.000
9.426
6.813
11.262
13.599
21.226
28.212
37.283
38.155
75.260
0.025
0.080
0.078
0.238
1.756
6.528
13.472
18.806
21.222
57.860
1.922
5.580
3.828
5.718
0.368
0.605
0.747
0.863
0.745
0.551
0.568
0.935
0.673
1.085
1.185
1.471
1.475
1.848
1.693
1.740
157
Table E-5-3: Removal of Cd2+ Ions by Sample Homo-Ca
Ci
Mean Cf
RSD of Cf
q
(meq/L)
(meq/L)
%
(meq/g)
0.977
0.146
0.697
0.083
1.898
3.884
4.679
5.708
6.813
13.599
21.226
28.212
38.155
0.400
1.042
1.451
2.306
3.243
8.403
15.040
20.361
29.882
0.800
0.488
0.598
0.273
0.415
0.839
0.865
1.334
0.718
0.150
0.284
0.323
0.340
0.357
0.520
0.619
0.785
0.827
75.260
62.343
3.306
1.292
Table E-5-4: Quality Control Sample Measurement for the Cd2+ Removal
Sample
QCS
Concentrations (mg/L)
Recovery %
RSD (%)
0.984
98.40
0.082
100.00
94.15
94.15
0.585
250.00
226.60
90.64
0.170
Spiked
Observed
1.00
158
APPENDIX E-6: Multicomponent Ion Exchange Isotherm Data
Table E-6-1: Removal of Three Co-Existing Metals by Sample Ori-P
Pb2+
Cd2+
Zn2+
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
103.20
67.13
2.94
0.035
116.90
0.90
17.81 0.206
100.50
0.53
28.66
0.306
129.15
67.80
7.26
0.059
178.05
1.58
13.61 0.314
154.95
7.73
1.59
0.450
201.40
111.25
3.54
0.087
240.60
4.50
8.97
0.420
200.60
31.75
1.11
0.517
247.25
118.50
2.33
0.124
311.25
9.75
3.97
0.536
255.50
73.50
0.25
0.557
368.40
182.40
7.68
0.180
480.00 48.00
0.90
0.769
396.40
220.00
0.40
0.540
516.17
312.68
3.02
0.196
613.21 102.03
1.06
0.909
503.67
348.98
0.15
0.473
988.50
134.15
1.31
0.825
978.75 374.00
0.78
1.076
807.00
713.50
0.44
0.286
1211.0
312.68
0.97
0.867
1203.0 606.00
0.58
1.062
997.00
960.00
0.42
0.113
1881.0
1380.2
0.41
0.486
1965.0 1268.0
0.65
1.240
1618.5
1512.0
0.64
0.326
Table E-6-2: Removal of Three Co-Existing Metals by Sample Homo-Na
Pb2+
Cd2+
Zn2+
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
103.20
68.63
6.31
0.033
116.90
1.80
11.56
0.205
100.50
1.35
15.74
0.303
129.15
66.15
3.64
0.061
178.05
1.50
19.56
0.314
154.95
10.50
2.48
0.442
201.40
113.88
8.39
0.084
240.60
4.50
8.74
0.420
200.60
35.13
0.23
0.506
247.25
123.75
4.13
0.119
311.25
10.25
2.81
0.536
255.50
88.88
0.57
0.557
368.40
243.40
7.09
0.121
480.00
48.40
1.34
0.768
396.40 256.80
0.64
0.427
516.17
361.63
3.14
0.149
613.21
94.60
0.48
0.923
503.67 366.85
0.21
0.419
988.50
123.65
0.94
0.825
978.75 331.50
0.73
1.152
807.00 665.00
0.47
0.434
1211.0
330.38
2.84
0.867
1203.0 565.50
0.43
0.340
997.00 857.25
0.35
0.428
1881.0
1299.9
0.35
0.486
1965.0 1162.0
0.69
0.429
1618.5 1333.0
0.22
0.874
159
Table E-6-3: Removal of Three Co-Existing Metals by Sample Homo-Na
Pb2+
Cd2+
Zn2+
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
Ci,
mg/L
Cf,
mg/L
RSD
of Cf
q,
mg/g
103.20
81.08
5.05
0.021
116.90
35.63
0.84
0.145
100.50
61.73
0.72
0.119
129.15
77.48
9.06
0.050
178.05
61.65
0.64
0.207
154.95
99.68
0.46
0.169
201.40
131.00
2.42
0.068
240.60
99.63
1.07
0.251
200.60 155.13
0.63
0.139
247.25
142.13
5.06
0.101
311.25 137.25
0.34
0.310
255.50 200.00
0.51
0.170
368.40
367.80
2.92
0.001
480.00 253.80
0.32
0.402
396.40 335.00
0.25
0.188
516.17
477.68
1.83
0.037
613.21 340.73
0.32
0.485
503.67 446.60
0.57
0.175
988.50
155.25
0.78
0.804
978.75 601.00
0.30
0.672
807.00 719.00
0.65
0.269
1211.0
379.05
0.28
0.804
1203.0 815.25
0.39
0.690
997.00 935.25
0.39
0.189
1881.0
1059.5
0.28
0.796
1965.0 1329.0
0.42
1.132
1618.5 1414.0
0.59
0.626
Table E-6-4: Quality Control Sample Measurement fot the Multicomponent Metal
Removal
Sample
Concentrations (mg/L)
Recovery %
RSD (%)
0.943
94.30
1.681
0.50
0.515
103.00
0.339
0.10
0.09
90.00
0.666
Spiked
Observed
QCS Pb2+ 1 ppm
1.00
QCS Cd2+ 0.50 ppm
QCS Zn2+ 0.10 ppm
160
APPENDIX F-1: Sorption Kinetics Data of Se (IV) and Se (VI)
Table F-1-1: Initial Concentrations of Selenium Oxyanion
Zeolite Sample
Sorbate
Mean C0 (mg/L)
RSD (%)
Desilicated
zeolite Na-P2
Se (IV)
110.55
0.993
Se (VI)
106.30
0.829
Se (IV)
113.18
1.294
Se (VI)
83.58
0.762
Se (IV)
111.88
0.603
Se (VI)
83.58
0.588
Se (IV)
111.95
0.583
Se (VI)
86.72
0.629
Se (IV)
107.70
0.602
Se (VI)
85.45
0.526
Se (IV)
111.00
0.591
Se (VI)
89.45
0.455
10 Al-P
20 Al-P
30 Al-P
40 Al-P
50 Al-P
Table F-1-2: Uptake Amount of Se (IV) at the Prescribed Duration
Zeolite Sample
Desilicated
zeolite Na-P2
Duration,
Mean Ct
SD
qt
t (min)
(mg/L)
(mg/L)
(mg/g)
30
103.28
1.18
1.82
45
102.15
0.44
2.08
60
100.98
1.20
2.36
90
99.38
0.81
2.73
120
101.83
0.66
2.11
150
99.10
1.19
2.75
180
97.85
0.87
3.02
210
100.40
1.20
2.40
240
98.93
0.84
2.72
270
97.65
0.95
2.99
300
100.68
0.90
2.27
161
Zeolite Sample
10 Al-P
20 Al-P
30 Al-P
Duration,
Mean Ct
SD
qt
t (min)
(mg/L)
(mg/L)
(mg/g)
15
102.65
0.66
2.63
30
98.23
0.41
3.71
45
99.98
0.92
3.25
60
92.85
0.72
4.96
90
92.13
0.77
5.09
120
89.80
0.87
5.61
200
92.80
0.40
4.85
220
89.98
1.35
5.48
250
89.73
0.92
5.49
15
99.13
0.70
3.19
30
97.13
0.55
3.66
45
98.30
0.44
3.34
60
95.88
0.86
3.90
90
92.85
0.88
4.60
120
88.63
1.29
5.58
200
97.08
1.04
3.52
220
92.20
0.90
4.64
250
96.83
0.38
3.52
15
103.58
0.85
2.09
30
100.48
0.45
2.85
45
98.40
0.92
3.33
60
99.90
1.10
2.94
90
95.08
1.48
4.08
120
98.25
0.60
3.29
200
102.43
1.17
2.27
220
99.55
0.60
2.93
250
100.35
1.09
2.71
162
Zeolite Sample
40 Al-P
50 Al-P
Duration,
Mean Ct
SD
qt
t (min)
(mg/L)
(mg/L)
(mg/g)
15
103.88
0.69
0.96
30
104.13
0.72
0.89
45
101.95
1.09
1.41
60
103.63
1.26
0.99
90
96.03
0.85
1.34
120
102.10
1.11
0.96
200
103.68
0.62
0.96
15
110.95
1.33
0.01
30
107.70
0.91
0.82
45
107.08
0.83
0.97
60
106.45
1.31
1.11
90
107.78
0.82
0.78
120
105.33
0.88
1.36
200
106.23
0.67
1.14
220
109.35
0.48
0.39
250
103.91
0.90
1.66
Table F-1-3: Uptake Amount of Se (VI) at the Prescribed Duration
Zeolite Sample
Desilicated
zeolite Na-P2
Duration,
Mean Ct
SD
qt
t (min)
(mg/L)
(mg/L)
(mg/g)
30
100.93
0.85
1.34
45
99.65
1.08
1.65
60
99.95
1.20
1.56
90
99.40
0.64
1.68
120
100.78
0.79
1.34
150
99.40
0.66
1.66
210
99.85
1.72
1.52
240
98.88
1.33
1.74
270
98.05
0.72
1.91
163
Zeolite Sample
10 Al-P
20 Al-P
30 Al-P
40 Al-P
Duration,
Mean Ct
SD
qt
t (min)
(mg/L)
(mg/L)
(mg/g)
20
76.33
0.39
1.81
55
75.48
0.41
1.99
110
74.61
1.34
2.17
140
72.82
0.56
2.58
170
72.69
0.67
2.59
230
73.27
0.60
2.43
260
71.25
1.04
2.89
20
77.68
0.49
1.48
40
77.68
0.57
1.47
75
77.53
0.50
1.48
110
77.33
0.78
1.51
140
76.48
0.85
1.71
170
75.58
1.06
1.91
230
75.43
0.46
1.93
260
72.69
0.66
2.55
20
82.70
0.39
1.00
40
80.95
0.64
1.43
55
80.08
0.73
1.63
75
80.73
1.17
1.46
140
80.28
0.68
1.56
170
78.55
0.74
1.94
230
78.45
0.65
1.95
260
77.30
1.01
2.2
20
84.15
0.51
0.33
40
81.70
0.50
0.92
55
80.20
0.69
1.29
75
81.63
0.59
0.93
170
80.83
0.97
1.10
200
80.74
0.45
1.11
230
80.30
0.64
1.21
164
Zeolite Sample
50 Al-P
Duration,
Mean Ct
SD
qt
t (min)
(mg/L)
(mg/L)
(mg/g)
20
87.35
0.85
0.53
40
85.23
1.01
1.05
55
82.80
0.95
1.64
75
81.55
0.74
1.93
110
84.38
0.44
1.23
170
84.38
0.57
1.21
200
82.45
0.59
1.65
APPENDIX F-2: Sorption Isotherm Data of Se (IV) and Se (VI)
Table F-2-1: Removal of Se (IV) by 10 Al-P
Ci
Mean Cf
RSD of Cf
q
(mg/L)
(mg/L)
%
(mg/g)
1.53
0.76
19.44
0.15
2.05
6.16
11.69
16.46
21.30
25.94
30.27
34.24
51.52
0.84
1.49
3.97
6.47
9.50
12.60
15.69
18.78
28.17
16.66
11.85
6.72
2.48
1.43
1.05
1.17
0.77
0.49
0.24
0.93
1.54
2.00
2.36
2.67
2.92
3.09
4.67
165
Table F-2-2: Removal of Se (VI) by 10 Al-P
Ci
Mean Cf
RSD of Cf
q
(mg/L)
(mg/L)
%
(mg/g)
1.43
2.13
6.01
10.86
15.90
20.12
24.73
29.26
61.84
1.01
1.37
4.34
7.90
11.52
14.89
18.51
22.11
50.10
10.262
7.376
2.523
3.134
1.608
0.595
0.669
1.302
1.028
0.08
0.15
0.33
0.59
0.88
1.05
1.24
1.43
2.35
Table F-2-3: Quality Control Sample Measurement for the Se Removal
Sample
QCS
Concentrations (mg/L)
Recovery %
RSD (%)
20.44
102.20
0.777
10.00
11.42
114.20
0.704
20.00
20.41
102.05
0.596
Spiked
Observed
20.00
166
APPENDIX F-3: Sorption Isotherm Data of Se (IV) and Se (VI) in
NaCl Solution of Different Ionic Strength
Table F-3-1: Removal of Se (IV) by 10 Al-P in NaCl Solution of Different Ionic
Strength
Concentration
of NaCl
0.01 N
0.1 N
1.0 N
Ci
mg/L
1.901
Mean Cf
mg/L
0.775
RSD of Cf
9.280
q
mg/g
0.225
6.389
1.375
6.631
1.003
12.015
3.278
2.781
1.747
17.060
5.485
2.776
2.315
22.765
8.925
0.862
2.768
27.720
12.770
0.906
2.990
32.015
15.865
0.978
3.230
40.340
22.690
1.299
3.530
48.000
28.360
1.344
3.928
1.237
0.160
5.127
0.215
5.731
0.894
10.948
0.967
11.260
2.676
3.953
1.717
16.140
5.172
2.949
2.194
21.330
8.077
3.127
2.651
26.520
11.915
1.266
2.921
29.860
14.660
0.790
3.040
46.365
29.370
0.671
3.399
2.867
2.821
6.791
0.009
5.849
3.931
4.592
0.384
11.370
6.056
2.699
1.063
16.470
8.776
2.982
1.539
21.700
11.070
2.065
2.126
26.470
14.620
2.315
2.370
31.260
17.360
1.190
2.780
40.510
23.670
1.652
3.368
49.300
29.505
0.908
3.959
%
167
Table F-3-2: Removal of Se (VI) by 10 Al-P in NaCl Solution of Different Ionic
Strength
Concentration
of NaCl
0.01 N
0.1 N
1.0 N
Ci
mg/L
1.804
Mean Cf
mg/L
1.361
RSD of Cf
8.312
q
mg/g
0.089
5.748
3.358
2.479
0.478
10.550
6.095
2.077
0.891
15.455
9.551
1.381
1.181
20.195
12.755
1.096
1.488
24.290
15.830
0.957
1.692
28.345
19.150
0.673
1.839
37.070
26.235
0.677
2.167
41.575
30.620
0.397
2.191
1.052
0.249
23.707
0.161
5.243
2.950
4.205
0.459
10.350
6.691
0.638
0.732
14.660
9.758
1.908
0.980
19.525
13.915
1.715
1.122
24.845
17.985
0.698
1.372
28.215
20.335
1.332
1.576
36.950
29.040
0.563
1.582
43.000
33.500
0.321
1.900
2.632
1.339
15.360
0.259
6.067
4.137
5.174
0.386
11.700
9.662
3.139
0.408
16.970
12.030
0.543
0.988
22.270
16.185
0.633
1.217
26.750
20.530
0.879
1.244
30.420
24.030
0.920
1.278
45.120
36.385
1.981
1.747
%