REACTIONS BETWEEN ALUMINUM AND
AMORPHOUS SiO
2
AND CRYSTALLINE QUARTZ:
A pH, CONCENTRATION, AND TIME DEPENDENT STUDY
Heidi Allison Van Atta
B.S., California State University, Sacramento, 2006
THESIS
Submitted in partial satisfaction of the requirements for the degree of
MASTER OF SCIENCE in
CHEMISTRY at
CALIFORNIA STATE UNIVERSITY, SACRAMENTO
FALL
2010

REACTIONS BETWEEN ALUMINUM AND
AMORPHOUS SiO
2
AND CRYSTALLINE QUARTZ:
A pH, CONCENTRATION, AND TIME DEPENDENT STUDY
A Thesis by
Heidi Allison Van Atta
Approved by :
__________________________________, Committee Chair
Jacqueline R. Houston, Ph.D.
__________________________________, Second Reader
Susan M. Crawford, Ph.D.
__________________________________, Third Reader
Roy W. Dixon, Ph.D.
____________________________
Date ii

Student: Heidi Allison Van Atta
I certify that this student has met the requirements for format contained in the University format manual, and that this thesis is suitable for shelving in the Library and credit is to be awarded for the thesis.
__________________________, Department Chair
Susan M. Crawford, Ph.D.
Department of Chemistry
___________________
Date iii

Abstract of
REACTIONS BETWEEN ALUMINUM AND
AMORPHOUS SiO
2
AND CRYSTALLINE QUARTZ:
A pH, CONCENTRATION, AND TIME DEPENDENT STUDY by
Heidi Allison Van Atta
Reactions between aqueous Al and amorphous SiO
2
and crystalline quartz were investigated in order to understand the speciation of dissolved Al in natural waters.
Although these solids have the same chemical makeup, their physical structures differ in that the amorphous mineral is disordered while quartz is highly crystalline. These minerals were examined over several weeks with [Al] ranging from 0.05 mM – 86 mM over a pH range of 2 – 8.2 to determine which reactions occur. Possible reactions include 1) precipitation of aluminosilicates; 2) precipitation of Al(OH)
3
; 3) ion exchange between dissolved Al and surface Si; 4) sorption of Al onto the Si mineral surface; and
5) desorption/dissolution of Al from the mineral surface. Graphite Furnace Atomic
Absorption (GFAA) was used to measure aqueous Al and Si concentrations before and after each reaction and
27
Al Magic Angle Spinning Nuclear Magnetic Resonance (
27
Al
MAS NMR at 11.7 T and 21.1 T) was used to analyze the coordination geometry of the solid Al species that formed.
Experiments involving amorphous SiO
2
(reaction time = 2 h) revealed that two reactions took place: Al sorption to the mineral surface occurred at pH > 3.7 while precipitation of an aluminosilicate occurred at pH > 5. Al geometry for both of these iv

sites was found to be tetrahedral. Aqueous Si and Al data from the time dependent experiments (7 days, pH = 4.3, 5.4, and 8.2) showed that Al was not released into solution, either via dissolution or desorption, even after 7 days of reacting. Dissolved Si increased after 7 days of continuous mixing, especially at pH 4.3, in which the amount of Si in solution nearly doubled. This additional Si in solution was due to dissolution of the solid phase over time. Experiments with higher [Al] (24 mM and 86 mM, pH = 4.7) forced aluminum hydroxide precipitation with both 5-coordinate and 6-coordinate Al geometry.
Investigation of the quartz mineral phase showed that dissolution did not occur over the pH range 4.3 – 8.2 at room temperature. With no dissolved Si available, an aluminosilicate precipitate did not form. At pH 6.4, there was some Al sorption to the surface but the majority of aqueous Al precipitated as aluminum hydroxide with 5coordinate and 6-coordinate Al geometry. These results were very similar to the aluminum hydroxide precipitate formed in the amorphous SiO
2
experiments at high Al concentrations. From these experiments, crystalline quartz appears to be stable at room temperature and does not react with aqueous Al. On the other hand, amorphous SiO
2 has a high surface area and many surface sites, which allows for Al sorption as well as dissolution which leads to formation of an aluminosilicate precipitate.
____________________________, Committee Chair
Jacqueline R. Houston, Ph.D.
____________________________
Date v

ACKNOWLEDGMENTS
I would first like to thank Dr. Jacqueline Houston for being an outstanding mentor throughout this entire process. From the time I started this research until I finished writing about it, she checked in with me on a weekly basis to ensure I was on track to graduate in a timely manner. Although she had limited time outside of teaching, she made time for me to ensure that I understood all aspects of my work. I sincerely appreciate all the time and thoughtfulness she has contributed in guiding me throughout this research.
I would also like to thank Dr. Crawford and Dr. Dixon for being on my thesis committee. I know that they also had busy semesters but they made the time to read through my thesis and make thoughtful comments, which I truly appreciate.
Thank you Sean, my husband, for being supportive and patient, especially over the last few months in which I started writing. Most of my time at home was spent in front of the computer and rather than complaining, he gave me the time I needed to complete this work. I love you and thank you.
To all of my family and friends who have asked along the way how I was doing with my research, and how was my writing going, and how my presentation was coming along, thank you. I am lucky to have such wonderful people in my life to keep me motivated. vi

DEDICATION
I would like to dedicate this thesis to my parents, Otto and Nancy Spaeth. Since I was young, I have always liked going to school and learning and they have always been so supportive of that. They have given me opportunities to get as far as I wanted in school and I am grateful for their support and encouragement. I love you both so much.
Thank you. vii

TABLE OF CONTENTS
Page
Acknowledgments ……………….………………………………………………..... vi
Dedication ………………………………………………………………………….. vii
List of Tables ……………………………………………………………….………. xi
List of Figures ………………………………………………………………………. xii
List of Schemes …………………………………………………………………….. xviii
Chapter
1. INTRODUCTION ………………………………………………………………. 1
Al in the Environment ……………………………………………………….. 1
Si in the Environment ………………………………………………………... 3
Reactions Between Al and Si ……………………………………………...… 5
Previous Studies on Reactions Between Al and Si ……………………...…... 9
Instrumental Techniques …………………………………………………….. 12
Graphite Furnace Atomic Absorption (GFAA) ……………………... 12
27 Al Magic Angle Spinning Nuclear Magnetic Resonance ………….. 15
Spectroscopy ( 27 Al MAS NMR)
Present Research ………………………………………………………..……. 25
2. EXPERIMENTAL ……………………………………………………….……… 28
Aqueous Chemistry Experiments ……………………………………………. 28 viii

Page
Graphite Furnace Atomic Absorption (GFAA) …………………………….... 30
Matrix Effect …………………………………………………………………. 30
Analysis for Uncertainty ……………………………………………………... 31
27
Al Magic Angle Spinning Nuclear Magnetic Resonance …………………... 32
Spectroscopy (
27
Al MAS NMR)
3. RESULTS ……………………………………………………………………….. 33
Amorphous SiO
2
: Analysis of Aqueous Chemistry Samples ………..……… 33
Amorphous SiO
2
:
27
Al MAS NMR Analysis of Solid Samples …….………. 37
Quartz: Analysis of Aqueous Chemistry Samples …………………...……… 42
Quartz: 27 Al MAS NMR Analysis of Solid Samples …………….………….. 47
Matrix Effect on Concentration Measurements ………………...….………… 47
4. DISCUSSION ……………………………………………………..…………….. 49
Amorphous SiO
2
: Analysis of Aqueous Chemistry Samples ………..……… 49
Amorphous SiO
2
:
27
Al MAS NMR Analysis of Solid Samples …....……….. 53
Amorphous SiO
2
: pH Dependence of Reactions ……………………..….….. 60
Amorphous SiO
2
: Time Dependence of Reactions ………………….…..…... 61
Quartz: Analysis of Aqueous Chemistry Samples …………………...……… 62
Quartz: 27 Al MAS NMR Analysis of Solid Samples ……………..……….… 64 ix

Crystalline Quartz Reactions
Summary: Comparison of Amorphous SiO
2
Page
and ………………….………... 66
5. CONCLUSION ………………………………………………………….………. 67
6. FUTURE STUDIES ………………………………………….………………….. 68
References ……………...………………………………………….………………... 69 x

LIST OF TABLES
Page
Table 1. Aqueous [Al] (mM) during long-term experiments with quartz. …………. 44
Table 2. Amounts of dissolved Si (mM) during long-term experiments …………… 46
with quartz. xi

LIST OF FIGURES
Page
Figure 1. Solubility of gibbsite (Al(OH)
3
) over pH range of 2-12. ……………...….. 2
Species vary depending on Al concentration (M) and pH.
7
Figure 2. Examples of silanol structures with terminology. ……………………...… 4
Figure 3. Dissolution of a silicate mineral when exposed to water.
12
……………… 4
Figure 4. Solubility of amorphous SiO
2
(mmol/L) over the pH …………………..... 5
range of 0 to 14.
14
Figure 5. Plot of surface charge (C m
-2
) vs pH for a synthetic ………………...…… 7
amorphous SiO
2
solid (Aerosil 200) in a solution of
0.7 M NaCl.
16
Figure 6. Possible complexes formed after Al sorbs to the Si mineral ……….……. 8
surface. a) outersphere complex; b) monodentate innersphere
complex; c) bidentate innersphere complex.
Figure 7. Diagram of pH dependence of aqueous Al sorption or ……….…………. 12
precipitation with amorphous SiO
2
.
15
Figure 8. Example of a valence electron being excited by external …………..……. 13
energy (light in this case) and moving into a higher energy
level.
Figure 9. General diagram of the scheme of an atomic absorption …….……..…..... 14
spectrometer.
28
Figure 10. Energy diagram when I = ½. Two spin states result ……….……......…. 17
when an external magnetic field is applied. The bold
arrows show the direction of the spin. Explanation
of ΔE is given in equation 3.
33 xii

Page
Figure 11. Diagram of how a toy top spins on an axis as it precesses …………..….. 18
about another axis that is perpendicular to the surface of
which it spins (left). Shown on the right is a spinning
nucleus that precesses about an axis that is parallel with the
external magnetic field (B
0
). The frequency of precession
is called the Larmor Frequency (ω).
33
Figure 12. Diagram illustrating the spin flip phenomenon of a nucleus ………..….. 19
within an NMR instrument.
33
Figure 13. Diagram of two nearby nuclei within a magnetic field …………...…….. 21
used to describe dipole-dipole interactions.
34
Figure 14. Example of a quadrupolar nucleus. The surrounding ………..………… 22
electric charges are from electrons and other nearby
nuclei and these cause an electronic field gradient (efg).
Because the quadrupolar nucleus is nonspherical, it
undergoes unbalanced charge distribution within the efg.
35
Figure 15. The six spin states for a quadrupolar nucleus with I = 5/2. ………...…… 23
Due to quadrupolar effects, in a solid sample the ΔE between
each spin state is not equal (shown on left). When the
sample is static, the different ΔE values are observed on the
NMR spectrum as separate signals (a solid sample of AlCl
3
is shown on right).
36
Figure 16. An example of a
27
Al MAS NMR spectrum. This spectrum ………..…. 24
is of a silicaluminophosphate molecular sieve and was acquired
with a spin rate of 12.5 kHz.
38
Using MAS NMR for solid
samples reduces the signals from satellite transitions (*).
Figure 17.
27
Al MAS NMR spectrum showing all three Al coordination ……....….. 25
sites: octahedral near zero ppm, pentacoordinate near 35 ppm,
and tetrahedral between 55-80 ppm.
41
Figure 18. Structural composition of SiO
2
: quartz (on left) and …………....……… 26
amorphous (on right).
42 xiii

Page
Figure 19. Aluminum uptake curve for amorphous SiO
2
over pH …………………. 33
range 2.1 to 8.2. The %Al uptake was calculated using
equation 6. [Al] i
=0.48 mM. (The line is not of best fit
but is intended to guide the eye. Vertical error bars
represent an error in %Al uptake of ± 2.6% and horizontal
error bars represent an error in pH of ± 0.08.)
Figure 20. Plot of Al in solution (mM) over time. Data was acquired …….……… 34
from long-term experiments at pH 4.3 (blue), pH 6.4 (red),
and pH 8.2 (yellow). [Al] i
=0.41 mM. (Vertical error bars
at pH 4.3 represent an uncertainty in [Al] of ± 0.02 mM.)
Figure 21. Initial Si concentration (mM), before reacting with Al, over …….…….. 35
a pH range of 2.1 to 8.2. (The line is not of best fit but is
intended to guide the eye. Vertical error bars represent an
uncertainty in Si of ± 0.06 mM and horizontal error bars
represent an uncertainty in pH of ± 0.08.)
Figure 22. The change [Si] (mM) after a 2 h reaction time with Al ………….……. 36
([Al] i
= 0.48 mM) over a pH range of 2.1 to 8.2. This change
was calculated by subtracting the initial Si concentration (before
reacting with Al) from the final Si concentration (after 2 h
reaction with Al). (The line is not of best fit but is intended to
[Al] i
= 0.41 mM. (Error bars for pH 4.3 and 6.4 were too small to
show on plot. The uncertainty in Si concentration was ± 0.02 mM
at pH 4.3, ± 0.03 at pH 6.4, and ± 0.07 at pH 8.2.)
Figure 24.
27
Al MAS NMR spectra of solid samples after 2 h reaction ……………. 38
with Al ([Al] i
= 0.48 mM) at pH 3.7, 4.3, 4.7, 5.4, 6.4, and 8.2.
Spectra were collected at 11.7 T field strength and each
spectrum is normalized to the individual sample weight.
guide the eye. Vertical error bars represent an uncertainty in [Si]
of ± 0.02 mM and horizontal error bars represent an uncertainty in
pH of ± 0.08.)
Figure 23. Plot of [Si] (mM) over time. Data was acquired from long-term …….... 37
experiments at pH 4.3 (blue), pH 6.4 (red), and pH 8.2 (yellow). xiv

Page
Figure 25. 27 Al MAS NMR spectra of solid samples after 2 h ……………………… 39
reaction with Al ([Al] i
= 0.48 mM) at pH 4.3, 5.4,
and 8.2. Spectra were collected at 21.1 T field strength.
Figure 26.
27
Al MAS NMR spectra of solid samples after 2 h ……………………... 40
reaction with Al at pH 4.7. [Al] i
= 0.48 mM, 23.6 mM,
and 85.6 mM. Spectra were collected at 11.7 T field strength.
Figure 27.
27
Al MAS NMR spectra of solid samples after 2 h …………….……….. 41
reaction with dissolved Al at pH 4.7. The top spectrum
(red) is from the experiment in which the mineral surface
was present during the reaction (t = 2 h). The middle
spectrum (yellow) is from the experiment in which the
mineral surface was equilibrated for 22 h and was then
filtered out of the aqueous medium before adding Al (t = 2 h).
The bottom spectrum (blue) is from the experiment in which
no mineral surface was ever present in the aqueous medium.
[Al] i
~ 24 mM. Spectra were collected at 11.7 T field strength.
Figure 28. %Al uptake curve for quartz mineral surface over pH range 3.5 ……..… 42
to 8.2 (red) and uptake curve for amorphous SiO
2
as shown in
Figure 19. %Al uptake was calculated using equation 6.
[Al] i
= 0.48 mM. (The lines are not of best fit but are intended
to guide the eye. Vertical error bars were too small to show on
graph. There was an uncertainty in %Al uptake of ± 1.6% and
horizontal error bars represent an error in pH of ± 0.2.)
Figure 29. Plot of [Al] (mM) over time. Data was acquired from long-term …...…. 43
experiments at pH 5.4 (blue), pH 6.4 (green), and pH 8.2 (red).
[Al] i
= 0.41 mM. (Error bars were too small to show on plot.
Uncertainty at pH 5.4 was ± 0.0001 mM, at pH 6.4 ± 0.0002 mM
and pH 8.2 ± 0.0008 mM.)
Figure 30. Initial [Si] (mM), before adding Al, for reactions with ………………… 44
quartz, pH 4.3 - 8.2 (red). For comparison, the initial Si
concentration for amorphous SiO
2
reactions is also shown
(grey). (Vertical error bars were too small to show on plot
but uncertainty was ± 0.02 mM. Horizontal error bars
represent an uncertainty in pH of ± 0.2.) xv

Page
Figure 31. The change in [Si] (mM) after a 2 h reaction time with ……………….... 45
Al ([Al] i
= 0.48 mM) over a pH range of 4.3 to 8.2 for the quartz
system (red). For comparison, the change in Si for the amorphous
SiO
2
system is also shown (grey). (Vertical error bars were too
small to show on plot but uncertainty was ± 0.01 mM. Horizontal
error bars represent an uncertainty in pH of ± 0.2.)
Figure 32. Plot of [Si] (mM) over time. Data was acquired from …………………. 46
long-term experiments at pH 5.4 (blue), pH 6.4 (green),
and pH 8.2 (red). [Al] i
= 0.41 mM. (Error bars were too
small to show on plot. Uncertainty at pH 5.4 was ± 0.0003 mM,
at pH 6.4 ± 0.0003 mM and pH 8.2 ± 0.0002 mM.)
Figure 33. 27 Al MAS NMR spectra of solid samples after 2 h reaction ……….…… 47
with Al at pH 6.4. [Al] i
= 0.48 mM, 22.8 mM, and 84.3 mM.
Spectra were collected at 11.7 T field strength.
Figure 34. Al adsorption curve presented by Dixit and Van Cappellen. …….…….. 50
Three different SiO
2
phases were investigated: Aerosil 200,
Chaetoceros mulleri, and biosiliceous ooze.
16
Figure 35. Comparison of the %Al uptake curves when the amorphous ……...……. 52
SiO
2
mineral surface was present (blue) and when the surface
was removed from the system (red). The curve that represents the
presence of solid and aqueous Si (blue) was calculated from the
results presented herein and the curve representing only aqueous
Si (red) is from results published by Houston et al.
15
Figure 36.
27
Al MAS NMR spectra from work by Houston et al.
15
…………..……. 54
The spectra were collected from aqueous Si experiments
performed at pH 5.4, 6.4, and 8.2. All spectra were
normalized to the total area.
Figure 37. Integration of
[4]
Al sorb
and
[4]
Al ppt
sites from
27
Al MAS NMR …...….….. 56
spectra collected at 21.1 T. The reaction at pH 5.4 is on the right
and pH 8.2 is on the left. The line fitting analysis was performed
using NUTSPro and the lineshapes are combinations of
Lorentzian and Gaussian.
Figure 38. Solubility of kaolinite with pH.
44
…………………………………….…. 57 xvi

Page
Figure 39. Al(OH)
3
solubility with pH. Red lines identify each ………………….... 60
[Al] that was investigated.
7 xvii

LIST OF SCHEMES
Page
Scheme 1. Three possible reactions that can occur between the SiO
2
………………. 6
mineral and aqueous Al (pH > 6): I) example of
precipitation of an aluminosilicate, II) precipitate of
Al(OH)
3
on the mineral surface, and III) ion exchange
between Si and Al. xviii