alkaline pressure oxidation of pyrite in the presence of ......anirudha dani masters of applied...
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Alkaline Pressure Oxidation of Pyrite in the Presence of Silica –
Characterization of the Passivating Film by
Anirudha Dani
A thesis submitted in conformity with the requirements for the degree of Master of Applied Science
Department of Chemical Engineering and Applied Chemistry University of Toronto
© Copyright by Anirudha Dani 2013
ii
Alkaline Pressure Oxidation of Pyrite in the Presence of Silica – Characterization of the Passivation Film
Anirudha Dani
Masters of Applied Science
Department of Chemical Engineering and Applied Chemistry
University of Toronto
2013
Abstract
Alkaline pressure oxidation, particularly in the presence of trona as additive, can be used to
oxidize high carbonate refractory gold ores as it prevents the formation of CO2 in the autoclave.
However, the presence of silica in the ore can lead to the encapsulation of pyrite due to the
formation of a passive layer. This phenomenon occurs due to the high solubility of silica in
alkaline solutions and its subsequent re-precipitation on the reacting pyrite surface. The present
study investigated the chemical composition and thickness of the passive layer on a rotating
pyrite surface in an aqueous slurry containing silica sand, sodium carbonate and calcium
carbonate at 230°C and under 7 bar of oxygen overpressure. Results obtained from XPS and
SEM show that a concentration of 2.5 g/L sodium carbonate gave the maximum thickness of
passivation on pyrite and that the passive layer consisted primarily of silicates and
aluminosilicates.
iii
Acknowledgments
I express my sincere gratitude to Professor Vladimiros Papangelakis for giving me an
opportunity to conduct research in a field I loved. His guidance and supervision have been
invaluable throughout my study.
Acknowledgements are due to Barrick Gold for funding the project, Dr Yeonuk Choi for
providing key background information on the industrial application of the project and Borregaard
for supplying proprietary dispersants.
I would like to thank all my colleagues in Aqueous Process Engineering and Chemistry group for
their enthusiasm, support and their generally acceptable taste in music. I am especially indebted
to Dr Ilya Perederiy for his invaluable assistance in setting up the experimental apparatus.
The assistance of George Kretschman in SEM imaging and Dr Rana Sodhi in XPS and SIMS
spectroscopy is gratefully acknowledged.
I dedicate this thesis to my grandparents, three of whom could not see me complete my
education. I would like to thank my parents for their patience and support throughout my time far
away from home. I have only gazed farther while standing on their shoulders. Finally, a great
thank you goes to my closest friends Aaron and Rhiad for being a second family and putting up
with most of my terrible humour.
iv
Table of Contents
Contents
Acknowledgments .......................................................................................................................... iii
Table of Contents ........................................................................................................................... iv
List of Tables ................................................................................................................................. vi
List of Figures ............................................................................................................................... vii
List of Appendices ......................................................................................................................... ix
Chapter 1 ......................................................................................................................................... 1
Introduction ................................................................................................................................ 1 1
1.1 Refractory Gold Ores .......................................................................................................... 1
1.2 Pressure Oxidation .............................................................................................................. 7
1.3 Role of Sulphuric Acid ....................................................................................................... 7
1.3.1 Alkaline Pressure Oxidation ................................................................................... 8
1.4 The Extended Singer-Stumm Model .................................................................................. 8
1.5 Role of the Carbonate Anion ............................................................................................ 10
1.6 Passivation of the Pyrite Surface during Oxidation .......................................................... 11
1.7 Project Objectives ............................................................................................................. 12
Chapter 2 ....................................................................................................................................... 13
Gold Operations Using Circumneutral/Alkaline POX ............................................................. 13 2
2.1 Mercur ............................................................................................................................... 13
v
2.2 Goldstrike .......................................................................................................................... 15
Chapter 3 ....................................................................................................................................... 16
Experimental Apparatus and Procedure ................................................................................... 16 3
3.1 Reagents and Preparation .................................................................................................. 16
3.2 Experimental Procedure .................................................................................................... 17
Chapter 4 ....................................................................................................................................... 19
Results and Discussion ............................................................................................................. 19 4
4.1 Effect of Sodium Carbonate Concentration ...................................................................... 19
4.2 Flashing ............................................................................................................................. 28
4.3 Effect of Organic Dispersants Addition ............................................................................ 32
4.4 Effect of Aluminum Sulphate Addition ............................................................................ 34
Chapter 5 ....................................................................................................................................... 35
Summary .................................................................................................................................. 35 5
5.1 Conclusions ....................................................................................................................... 35
5.2 Recommendations ............................................................................................................. 35
References ..................................................................................................................................... 37
Appendix A – SEM Images .......................................................................................................... 40
Appendix B – XPS Spectra ........................................................................................................... 47
Appendix C – Sample Calculation and Statistical Analysis ......................................................... 83
Sample Calculation of Average Thickness .............................................................................. 83
Statistical Treatment of Thickness Measurements ................................................................... 84
vi
List of Tables
Table 1: Brief description of existing oxidation technologies ........................................................ 4
Table 2: Total Al/Si atomic ratios at various Na2CO3 concentrations .......................................... 24
Table 3 - EDS elemental analysis of the product layer after flashing. ......................................... 31
Table 4: Decrease in product layer thickness with dispersant addition ........................................ 32
Table 5: Effect of dispersant addition on product layer composition ........................................... 33
vii
List of Figures
Figure 1: Gold grain encapsulated in pyrite .................................................................................... 2
Figure 2: A Breakdown of major pyrite oxidation technologies in use for refractory gold ores .... 3
Figure 3: A simplified process flowsheet for a typical acid POX circuit ....................................... 8
Figure 4: Mechanism for Fe3+
assisted oxidation of pyrite ............................................................. 9
Figure 5: Mechanism involving Fe(II) and Fe(III) carbonate complexes in pyrite oxidation ...... 11
Figure 6: Pyrite grains after oxidation in pure Na2CO3 (top) and Na2CO3+CaCO3+SiO2
(bottom).. ....................................................................................................................................... 12
Figure 7: A simplified flowsheet for the Mercur operation .......................................................... 14
Figure 8: Autoclave Apparatus Used for Pressure Oxidation ....................................................... 17
Figure 9: Post-experimental analysis ............................................................................................ 18
Figure 10 - Change in average product layer thickness with sodium carbonate concentrations. . 20
Figure 11 - A cross-sectional view of the product layer (dark phase) formed over bulk pyrite
(bright phase) in 10 g/L Na2CO3. .................................................................................................. 20
Figure 12: Schematic of silica dissolution and re-precipitation on the pyrite surface .................. 23
Figure 13: Aluminum and silicon solubilities as a function of sodium carbonate concentrations at
230 °C (generated using OLI simulation software) ...................................................................... 25
Figure 14 - Al 2p scans of product layers formed at various Na2CO3 levels.. .............................. 26
Figure 15 - S 2p scans show the absence of sulphates on the surface, due to the lack of peaks
beyond 166 eV .............................................................................................................................. 27
Figure 16 - Si 2s peaks close to 153 eV show the increase in silicate levels with increase in
Na2CO3 levels which can be attributed to the increasing solubility of SiO2. ............................... 27
viii
Figure 17: EDS Spectra of a product layer cross-section at 2.5 g/L Na2CO3.. ............................. 28
Figure 19 - Cross section of the product layer without flashing (top) and after flashing water
(bottom) at temperature. ................................................................................................................ 30
Figure 20: SEM cross-section of the oxide layer after flashing, with EDS analysis performed on
points across the layer. .................................................................................................................. 31
ix
List of Appendices
Appendix A – SEM Images .......................................................................................................... 40
Appendix B – XPS Spectra ........................................................................................................... 47
Appendix C – Sample Calculation and Statistical Analysis ......................................................... 83
1
Chapter 1
Introduction 1
1.1 Refractory Gold Ores
Metal sulphide ores are relevant to the extractive metallurgy of nickel, cobalt, gold, silver
and zinc, amongst others [1]. Iron sulphides, particularly pyrite (FeS2) are a major
impurity in any sulphide ore, especially since iron cannot be recovered as a by-product
commerically. Therefore any metal recovery process must take the chemistry of iron
sulphides and their oxidation into consideration.
Gold ores that do not yield acceptable recoveries upon direct cyanidation are termed
“refractory”, i.e. difficult to treat. Poor response to cyanidation could be a result of gold
being associated with cyanicides (e.g. pyrrhotite, aresenopyrite, copper compounds), or
associated with organic matter that adsorbs leached gold (carbonaceous materials), or
occurring as fine grains locked within gangue minerals [2]. A common example of the
last cause for refractoriness is gold encapsulated within pyrite, as seen in Figure 1. The
inert, non-porous nature of pyrite makes the gold impervious to lixiviant attack, keeping
it from being dissolved and subsequently recovered.
2
Figure 1: Gold grain encapsulated in pyrite [2]
In the context of gold extraction, many process routes for pyrite oxidation currently exist.
Common routes, summarized in Figure 2 and Table 1, all use gaseous oxygen as the
oxidant and generate iron oxides and sulphur oxides as products.
3
Figure 2: A Breakdown of major pyrite oxidation technologies in use for refractory gold ore processing
Pyrite Oxidation
Roasting Bio-
Oxidation
Pressure Oxidation
Acid POX Non-Acidic
POX
Circum-neutral pH
Alkaline
NaO
H/N
a2 C
O3
Bac
teri
a
H2SO
4
4
Table 1: Summary of major existing oxidation technologies [2]
Technology Commercialization
Date
Oxidation Reaction Process
Conditions
Advantages Disadvantages Operational
Application
Roasting Late 19th century 4FeS2 +11 O2 = 2Fe2O3 +
8SO2
450 - 700°C,
ambient
pressure
- Treats
carbonaceous
material
effectively
- Can generate
sulphuric acid as
by-product
- Emission of
SOx, As2O3, Hg
- Loss of gold
through
volatilization,
over-roasting
Giant Yellowknife
(1948 – 1999)
Bio-oxidation 1984 4FeS2 + 15O2 + 2H2O =
2Fe2(SO4)3 + 2H2SO4
35 – 80°C,
ambient
pressure
- Reaction occurs
under mild
conditions
- Retention time
is very high
- Does not work
with high solids
loading
Ashanti Refractory
Sulphide Plant
(1994 – present)
5
- Nutrient inputs
are an added
OPEX
Acid POX 1985 4FeS2 + 15O2 + 8H2O =
2Fe2O3 + 8H2SO4
4FeS2 + 3O2 = 2Fe2O3 +
8S
180 – 230°C
140 – 700 kPa
O2
overpressure,
- Very high
oxidation extents
and gold
recoveries
- Expensive,
corrosion
resistant
equipment
required
- High reagent
consumption
(acid, lime)
- Carbonaceous
material not
treated
Campbell Red
Lake (1991 –
present)
Circumneutral
POX
1988 4FeS2 + 15O2 + 4CaCO3 =
2Fe2O3 + 8CaSO4+4CO2
200 – 215°C,
380 kPa O2
- Elimination of
acid and lime
- Low oxidation
extents and gold
Mercur (1988 –
1998)
6
overpressure,
6.5<pH<7.5
requirements
- Reduction in
anhydrite scaling
- Formation of
stable hematite
residue
- Inexpensive
materials of
construction
recoveries
- Silicate scaling
- Separate As
precipitation
required
Alkaline POX 2009 [3] 4FeS2 + 15O2 + 4Na2CO3
= 2Fe2O3 + 8Na2SO4 +
4CO2
>200°C, upto
700 kPa O2
overpressure
- Improved gold
recovery
compared to
circumneutral
- Elimination of
anhydrite scaling
- Reduced
oxidation extent
due to silicate
passivation
Goldstrike -(2009
– present)
7
1.2 Pressure Oxidation
Acidic pressure oxidation was developed in the 1980s as an environmentally acceptable
alternative to roasting. Another advantage from the process point of view is that strict process
control is not essential in the operation of a pressure leach plant, as opposed to a roasting facility
[4]. While both technologies essentially use gaseous oxygen to oxidize pyrite, the difference is
that pressure oxidation generates aqueous sulphur oxidation products whereas roasting produces
gaseous oxidation products. Of the three, solid sulphates are far easier to dispose of, usually in
the form of gypsum or other insoluble sulphates. Aqueous oxidation of pyrite can be represented
by:
3242222 442
152 OFeSOHOHOFeS
1.3 Role of Sulphuric Acid
The acidic nature of the acid pressure oxidation (POX) keeps ferric iron in solution, which is
known to be more effective as an oxidant than dissolved oxygen [5].
The oxidation of pyrite, which proceeds according to the following reactions,
42322342
23422424
424222
33)(
)(2
12
22272
SOHOFeOHSOFe
OHSOFeOSOHFeSO
SOHFeSOOHOFeS
generates sulphuric acid, which serves to facilitate the oxidation reactions by keeping ferric ion
soluble. The autoclave discharge, however, has to be subsequently neutralized and adjusted to
pH ~ 9-10 prior to cyanidation by the addition of lime/limestone.
In case of ores with high levels of carbonates (in the form of calcite, dolomite, etc.), input acid
and pyrite-generated acid is consumed by the carbonates to generate CO2:
22444233
224423
222. COOHMgSOCaSOSOHMgCOCaCO
OHCOCaSOSOHCaCO
8
Evolution of CO2 inside the autoclave decreases the oxygen partial pressure and therefore the
oxidation potential. To avoid this, carbonates are removed as CO2 in a preacidulation step, using
recycle solution or fresh acid, as seen in Figure 3. Preacidulation may prove prohibitively
expensive in terms of acid consumption if the carbonate levels are higher than 10% [2]. To
process high carbonate ores cost effectively, circumneutral/alkaline pressure oxidation can be a
viable alternative.
Crushing,
Grinding,
Thickening
Ore Acidification Slurry PreheatingPressure
Oxidation
Flash
Depressurization
NeutralizationCILCarbon StrippingElectrowinningGold Dore
H2SO4 O2
CaONaCN
Cyanide Detox
Tailings
Figure 3: A simplified process flowsheet for a typical acid POX circuit [6]
1.3.1 Alkaline Pressure Oxidation
Na2CO3 is a source of alkalinity and has been shown [7] [8] [9] to effectively accelerate pyrite
oxidation under alkaline conditions. High pH is one cause for accelerated kinetics – the increased
availability of OH- allows the neutralization of H
+ produced by S2
2- oxidation and Fe
3+
hydrolysis. Moreover, the CO32-
ion plays an important role in accelerating oxidation [10].
1.4 The Extended Singer-Stumm Model
Research into acid mine drainage led to the following 3-step mechanism for pyrite oxidation:
9
316215814
22
1
1222
7
2
4
2
2
3
2
2
3
2
2
2
4
2
222
StepHSOFeOHFeFeS
StepOHFeHOFe
StepHSOFeOHOFeS
This mechanism, known as the Singer-Stumm model [11]was initially proposed for acidic
conditions. In the original model, the oxidation of Fe2+
in step 2 is considered rate limiting
because it is slower than the oxidation of pyrite by Fe3+
in step 3. Moses et al. [12] argue that
because pyrite is diamagnetic and molecular oxygen paramagnetic, direct reactions between
them would be spin-restricted. Ferric ions, while also paramagnetic, are amenable to
complexation by diamagnetic ligands such as H2O. In this way, Fe(III) complexes can eliminate
spin-restrictions and react with diamagnetic pyrite effectively.
At low pH, Fe3+
solubility is high enough for it to be the primary oxidant. Although Fe3+
solubility is very limited above pH~2, Moses and Herman [13] conclude that it continues to be
the primary oxidant near the surface and have proposed a model in which the oxidation of pyrite
occurs via surface adsorption of Fe(II) and Fe(III) complexes on the pyrite surface. As illustrated
in Figure 4, only Fe(III)(ads) can accept electrons from pyrite, while D.O. accepts electrons from
Fe(II)(ads). This model can be considered an extension of the Singer-Stumm model since it
maintains the oxidation of Fe(II) as the rate limiting step.
Figure 4: Mechanism for Fe3+
assisted oxidation of pyrite [13]
10
1.5 Role of the Carbonate Anion
It has been postulated that in neutral to alkaline solutions and elevated temperatures (80 °C),
CO32-
is able to form stable complexes with both Fe2+
and Fe3+
ions such as [Fe(CO3)(OH)]-,
[Fe(CO3)2]-, [Fe(CO3)2]
2- and FeCO3
+ [10]. Additionally, Fe(II)-CO3
2- complexes are high-spin
species and as such energetically easier to oxidize [14], compared to uncomplexed Fe2+
. Since
the oxidation of Fe2+
to Fe3+
is the rate determining step, its acceleration improves the overall
rate of pyrite oxidation. Fe(III)-CO32-
complexes also increase the solubility of Fe(III) and
therefore increase its availability as a pyrite oxidant.
A third effect of CO32-
is its ability to buffer the protons released by pyrite oxidation:
3
2
3 HCOHCO
By removing the products of pyrite oxidation, the buffer system shifts the oxidation reaction
equilibrium further towards the products. The overall pyrite oxidation mechanism, as shown in
Figure 5, is similar to the one described by Moses and Herman in that Fe(III) remains the direct
oxidant of pyrite. The mechanism involves hydroxylation of the pyrite surface, which is
enhanced by the presence of holes (h+) on the anodic portion [15]. Complete hydroxylation of the
surface, followed by oxidation, results in the formation of meta-stable thiosulphates (S2O32-
) that
are eventually oxidized to sulphates [16]:
HOHFeShOHFeS )(222
HOHSOHFehOHOHFeS 3)()(33)( 22222
OHHOSCOFexCOhOHSOHFe x
x 2
2
32
2
3
2
3222 22])([2)()(
11
Figure 5: Mechanism involving Fe(II) and Fe(III) carbonate complexes in pyrite oxidation
[10].
1.6 Passivation of the Pyrite Surface during Oxidation
In 2009, bench scale testing was initiated for alkaline POX for refractory ores with low sulphide
S and high carbonate levels – 1.67 wt% S and 11.35 wt% CO32-
[17]. Addition of sodium
carbonate clearly showed a positive effect on oxidation extent and soluble sulphur. The study
showed two competing effects of sodium carbonate in the presence of silica, namely enhancing
the oxidation of pyrite and enhancing the dissolution of silica, resulting in the formation of a
passivating coating, seen in Figure 6. The solubility of silica increased with pH, and a significant
amount dissolved into the bulk solution. The pyrite surface generates H+, Fe(II) and Fe(III) ions,
leading the dissolved silica to re-precipitate as an iron silicate coating on the surface.
12
Figure 6: Pyrite grains after oxidation in pure Na2CO3 (left) and Na2CO3+CaCO3+SiO2
(right). SiO2 is shown to produce a denser, more continuous passive coating. Unreacted
pyrite is also seen, an indication of incomplete oxidation [18].
1.7 Project Objectives
This study aimed to further the investigation into passivation by silica during alkaline POX. The
emphasis was shifted from the oxidation extent, studied previously [17], to the passivation layer
and the effect of sodium carbonate concentration on the thickness and composition of that layer.
The goal was to find the optimum sodium carbonate concentration that minimizes the passivation
thickness. The mechanism of silica precipitation was investigated to find whether precipitation
occurs at temperature during steady state oxidation, or as the slurry cools down by the end of the
reaction. The possibility of using dispersants to decrease passivation thicknesses was also tested.
13
Chapter 2
Gold Operations Using Circumneutral/Alkaline POX 2
Commercial application of circumneutral/alkaline POX has been limited, primarily due to its
specificity to high carbonate ores and lower recoveries compared to acidic POX. The first
operation to use circumneutral POX was the Barrick Gold Mercur in Nevada, USA(1988 – 1998)
[19]. Since 2011, Barrick Gold has operated an alkaline POX circuit at its Goldstrike, Nevada,
operation.
2.1 Mercur
Mercur pioneered non-acidic POX on a commercial scale. Mercur ore contained an average of 1
- 2% sulphide sulphur, 16% carbonate and 0.4% organic carbon [20]. The operation separated
oxide and refractory ore after grinding. The refractory ore, containing around 2 g/t Au, was
thickened and fed to the autoclave without prior acidulation, according to the flowsheet in Figure
7. The autoclave was operated at 220°C and 3200 kPa. The discharge pH was around 7.5.
14
Crushing,
Grinding,
Thickening
Ore Slurry PreheatingPressure
Oxidation
Flash
Depressurization
CILCarbon StrippingElectrowinningGold Dore
O2
NaCN
Cyanide Detox
Tailings
Steam
Figure 7: A simplified flowsheet for the Mercur operation [2]
The only sources of alkalinity were calcium and magnesium carbonates present in the ore feed,
and as such the alkalinity was limited by their solubility. 70% of sulphide sulphur was oxidized
in the autoclave and the subsequent gold recovery was 82%. The presence of carbonaceous
material necessitated a Carbon-in-Leach (CIL) circuit with high carbon concentration was
necessary during cyanidation to prevent the adsorption of leached gold onto the carbonaceous
material.
The absence of highly corrosive acid allowed for the use of cheaper materials of construction
throughout. For example, agitators in the autoclave could now be made of SS-316L instead of
titanium and flash valves out of Hastelloy [19].
The low oxidation extent compared to typical extents found in acid POX (>90%) can be
attributed to slower oxidation kinetics, as well as the passivation of the pyrite surface, both due
to the circumneutral pH of the system [19].
)(2)(4)(32)(3)(2)(2 4442
15gsssgs COCaSOOFeCaCOOFeS
15
2.2 Goldstrike
Barrick’s Goldstrike operation processes a wide variety of gold ores, ranging from high grade,
high sulphide refractory ores, to low grade carbonaceous ores. To accommodate this diversity in
feed, Goldstrike operates a range of treatment circuits – acidic POX for refractory sulphides,
roasting for high carbonaceous content ores, heap leaching for low grade non-refractory ores and
direct CIL for oxide ores. Alkaline POX with trona has been pioneered at Goldstrike for treating
high carbonate refractory ores. Trona is a natural mineral with the formula
Na2CO3.NaHCO3.2H2O that occurs in large quantities in Wyoming, California and Colorado.
These deposits constitute 96% of the total world reserves and provide an economical alternative
to synthetic soda ash [21]. As it is inexpensive, plentiful and locally available, it can potentially
be used as a source of soluble carbonate for alkaline POX. Commercialization of alkaline POX
has been achieved by simply converting three of the six existing autoclaves from the
conventional acidic to alkaline configuration.
The autoclave feed contains around 80% silica, present as quartz as well as clays. As a result,
oxidation extents are very low, in the region of 60%.
Anhydrite (CaSO4) is a major issue in POX autoclaves due to the formation of insoluble
precipitates that scale up vessel internals, reducing throughput and heat transfer efficiency [22].
In alkaline POX conditions, the presence of soluble sodium alkali reduces anhydrite scaling due
to high solubilisation of sulphate:
)(3)(42)(4)(32 saqsaq CaCOSONaCaSOCONa [17]
Mercury emissions due to the presence of cinnabar (HgS) in the ore, were increased. A mercury
abatement system had to be installed as a result. Low sulphide content meant that autogenous
heating was not possible, and significant steam input was required [3].
16
Chapter 3
Experimental Apparatus and Procedure 3
3.1 Reagents and Preparation
Natural pyrite cubes (approx. 4 cm x 4 cm x 4 cm, sourced from La Rioja, Spain) were obtained
from the Geode Gallery (Roseville, IL, USA). These cubes were cut into smaller, uniform 1.5 cm
x 1.5 cm x 1.5 cm cubes using a Buehler Isomet 5000 linear precision diamond saw. The cube
surface to be oxidized (target surface) was polished progressively down to a 6 µm fineness using
Buehler MetaDi diamond suspensions, cleaned sequentially in hexane and 3M hydrochloric acid,
and then rinsed with DI water and acetone before being used in experiments. The autoclave setup
used in this study is shown in Figure 8. A 5 cm diameter Polytetrafluoroethylene (PTFE) disk
was machined with a 1.5 cm x 1.5 cm x 1.5 cm cubic openning in the centre that matched the
dimensions of the pyrite cubes. One pyrite cube was wrapped in PTFE tape, embedded in the
opening and held in place with four SS-316 screws, such that only one surface was exposed to
water, the rest of the surfaces being covered within PTFE. The disk was attached to the bottom
of the impeller shaft via a stainless steel base and rotated at 300 rpm during operation. All
experiments were carried out in a 2 L Parr titanium autoclave, at 230°C, under 100 psi of oxygen
overpressure in 1.2 L of DI water. Sodium carbonate (Fisher ACS certified) was used to provide
alkalinity. Calcium carbonate (Fisher ACS certified) and silica sand (Acros) were added in large
excess of their solubilities (24 g and 22.6 g respectively) to maintain saturation levels in the
solution.
17
Figure 8: Autoclave Apparatus Used for Pressure Oxidation
3.2 Experimental Procedure
The autoclave was loaded with grade sodium carbonate solution, calcium carbonate and silica
sand, and the pyrite sample mounted in its disk. After sealing the autoclave, it was evacuated to
remove air from the headspace to prevent premature oxidation during heatup. Using two 2 kW
band heaters, the vessel was heated to 230 °C in less than 15 minutes before 100 psi of oxygen
gas was injected. The system was maintained at temperature and pressure for 1 hour. Process
control was maintained using a LabView script. After 1 hour, the system was cooled down to
ambient temperature using tap water in copper cooling coils. Following the experiment, the
pyrite sample was rinsed in DI water to remove adsorbed ions from the oxidized surface and
stored under acetone. The oxidized surface was then analyzed for its chemical composition using
X-ray Photoelectron Spectroscopy (XPS) (Thermo Scientific) and for its thickness using
Scanning Electron Microscopy (SEM) (JEOL JSM6610-Lv) as shown in
Figure 9.
FeS
2
A Single
Exposed Surface
PTFE disk
Embed
18
Figure 9: Post-experimental analysis
XPS was carried out with a monochromatic Al K- source, with 400 µm spot size and flood gun
for charge neutralization. The surface was sputter-cleaned with Ar+ to remove adsorbed
impurities for 5 – 10 minutes prior to spectral acquisition. The analysis sequence consisted of
acquiring wide-spectrum surveys followed by high resolution scans of Si 2s, S 2p, Al 2p, Fe 2p,
Na 1s, O 1s and C 1s spectra (Si 2s spectra replaced Si 2p spectra for quantification due to
interference of Fe 3s with the latter). The C 1s spectra was used for calibration, with adventitious
carbon at 284.6 eV used as the reference peak. Quantification was done using Gaussian-
Lorentzian peak-fitting algorithms and Shirley backgrounds in Thermo Scientific’s Avantage
software.
In order to measure product layer thicknesses, one surface normal to the oxidized target surface
was ground and polished progressively down to 1 µm fineness, which gave a clear cross-section
of the oxide as well as the bulk pyrite visible under SEM. Imaging was performed under
backscatter electron compositional (BEC) mode with an accelerating voltage of 20 kV. Energy
Dispersive X-ray Spectroscopy (EDS) was used to identify the pyrite-oxide interface as well as
for elemental analysis of the product layer.
Following SEM, the cube was cleaned in an ultrasonic 3 M HCl bath at 60 °C for 2 hours in
order to dissolve the product layer and regenerate a fresh pyrite surface. HCl was used for its
ability to dissolve oxides while not reacting with pyrite. The surface was subsequently polished
in preparation for the next experiment. The cubes were re-used for multiple experiments in this
manner and only discarded if fracturing was observed on the target surface.
Scanning Electron Microscopy
Product layer
Unreacted
Pyrite Unreacted
Pyrite
Product Layer
X-ray Photoelectron Spectroscopy
19
Chapter 4
Results and Discussion 4
4.1 Effect of Sodium Carbonate Concentration
The effect of Na2CO3 concentrations on passive layer thickness was investigated at 230 °C, 1
hour reaction time and 100 psig O2 overpressure. Concentrations ranging from 0 to 12.5 g/L
Na2CO3 were tested and plotted against corresponding thicknesses produced. Average
thicknesses were calculated from SEM images (see Appendix A for SEM images) as the area of
the product layer divided by the length of the cube,
tot
avex
dxtt
.
The area of the product layer and the corresponding length of the cube were measured in the
freeware image editing software GIMP 2 (see Appendix C for details). Up to 13% of the length
of the cross-section was photographed for each experiment by capturing SEM snapshots at
random points along the length. This assured that the reported average was representative of the
entire product layer for every experiment. Edges of the cube were not included in the average to
discount edge effects and the inevitable damage inflicted upon the edges during polishing. The
product layer, as seen in Figure 11, was uniform on the outer surface and somewhat uneven at
the pyrite-oxide interface. Given that the pyrite surface was polished before oxidation, the
smooth outer oxide surface has to correspond to the initial surface, which means that the product
layer formed from outside and developed inwards as the pyrite surface receded. This indicates
that the oxidation takes place via a shrinking core mechanism. The shrinking core mechanism
has been observed for pyrite oxidation at lower temperatures [23] [24], as well as higher ones
[25] so this observation is consistent with earlier studies.
20
0 2 4 6 8 10 12 14
0
5
10
15
20
25
Pro
du
ct L
aye
r T
hic
kn
ess (
µm
)
Sodium Carbonate Concentration (g/L)
Figure 10 - Change in average product layer thickness with sodium carbonate
concentrations. Hollow circles indicate the maximum and minimum measured thicknesses
at the corresponding concentrations.
Figure 11 - A cross-sectional view of the product layer (dull phase) formed over bulk pyrite
(bright phase) in 10 g/L Na2CO3.
21
As shown in Figure 10, SEM results showed the average passivation thickness rising to a
maximum of 22.9 µm for 2.5 g/L Na2CO3 before declining down to nearly the same as that for a
system with zero sodium carbonate. This inflexion in thickness indicates a complex precipitation
mechanism involving the reactive pyrite surface and aqueous silica.
In the absence of reliable solubility data at 230 °C, a qualitative explanation of the shape of the
curve is made, and illustrated in Figure 12. Concentration of sodium carbonate has two effects on
the product layer thickness (i.e. the amount of Fe-silicate/aluminosilicate precipitated):
The rate of pyrite oxidation increases with carbonate concentration. This is evident from
the work of previous researchers, albeit at lower temperatures. As carbonate
concentration increases, the rate of oxidation increases, increasing the availability of Fe2+
and Fe3+
in the solution. This promotes increased precipitation of Fe-
silicates/aluminosilicates.
Solubility of Si increases with increase in Na2CO3 concentration (due to increasing pH).
Passivation of the pyrite surface can be seen as the consequence of the dissolution of silica and
its subsequent re-precipitation as silicates:
Step 1: Dissolution of silica from quartz [26]:
)(4)(2)(2 )(2 aqls OHSiOHSiO
x
xOHSixOHOHSi ])([)( 44
Silica solubility increases with alkalinity since the availability of OH- facilitates the formation of
hydroxyl complexes and polymerization through Si-O-Si bridges.
Step 2: Precipitation as silicates:
)(4
3/2
)()(4 ])([])([ szxyaq
x
aqx OHSiFeyFeOHSiz
The presence of Fe2+
/Fe3+
ions from the dissolution of pyrite prompts the precipitation of silica
as iron silicates, after a critical level of supersaturation in solution is attained. The saturation
22
ratio, S =[Si]dissolved
[Si]equilibriumdetermines the rate and amount of precipitation, when S exceeds 1 [27]. The
precipitation thickness therefore is a function of S, and it is postulated that S peaks at
intermediate Na2CO3 concentrations, as does thickness.
The active pyrite surface generates protons and Fe2+
/Fe3+
by oxidation, as described by the
Singer-Stumm model. Consequently, a boundary layer is formed near the surface that is rich in
Fe2+
, Fe3+
and H+. Supersaturation occurs within this boundary layer, as acidity and metal cations
reduce silica solubility with respect to more insoluble compounds.
As silica concentration within the boundary layer drops due to silica precipitation, a
concentration gradient develops and as more silica diffuses from solution towards the interface, it
becomes supersaturated as the solubility decreases. The saturation ratio therefore becomes
)(][
][
BLyerboundaryla
bulk
Si
SiS .
At low Na2CO3 concentration, bulk solution pH is not very high and [Si]bulk is correspondingly
low. The rate of pyrite oxidation is also low, and therefore the difference in bulk and boundary
layer pH is not high. Consequently, S and passivation thickness remain low.
As Na2CO3 concentration increases, pyrite oxidation is accelerated by the carbonate effect,
which serves to lower the boundary layer pH. At the same time, bulk pH increases and [Si]bulk
increases with it. Passivation thickness, therefore, increases with increasing Na2CO3.
However, as Na2CO3 concentrations increase beyond a certain level, the ability of the bulk
solution to neutralise the acidifying surface also increases, apparently taking over and resulting
in a net gradual increase of the interfacial pH which drops the supersaturation and reducing the
thickness of the passivating layer. The existence of a maximum thickness with Na2CO3 increase
provides evidence that there are two opposing phenomena in effect.
23
Figure 12: Schematic of silica dissolution and re-precipitation on the pyrite surface
The detection of significant amounts of aluminum in the product layer led us to analyse the feed
materials for aluminum impurities, since no aluminum compounds were added explicitly to the
system. X-Ray Fluorescence (XRF) showed that the silica sand contained 0.887 wt% aluminum
(as Al2O3), probably as a feldspar impurity, while pyrite contained 0.073 wt%. The presence of
aluminum affected the results markedly, since large quantities of aluminum seem to have leached
from sand and re-precipitated as aluminosilicates on the pyrite surface. The presence of a
feldspar impurity actually simulated the Goldstrike ore feed better, since the latter contained
significant amounts of orthoclase, kaolinite, illite and smectite, all aluminosilicate minerals [28].
XPS was also performed on the oxide surface to determine its chemical composition. The
presence of aluminum and iron ions is known to decrease the solubility of silica [29] due to the
formation of silicates and the decrease in the activity of water (which in turn is caused by the
hydration of iron and aluminum). This was confirmed by XPS spectra, which showed the
formation of silicate and aluminosilicate species in every case. In the absence of sodium
carbonate, aluminum was dominant in the product layer whereas silicon was negligible. The
introduction of sodium carbonate drastically increased the presence of silicon as silicates and
reduced the presence of aluminum, as seen in Table 2 (see also Appendix B). Aluminum
solubility at high temperatures decreases rapidly with increase in pH. In the absence of silica,
aluminum solubility would ordinarily increase with pH owing to the amphoteric nature of Al3+
24
and its ability to form [Al(OH)x]3-x
complexes. However, in the presence of silica, aluminium
solubility decreases as seen in Figure 13. The decrease is attributed to the formation of
aluminosilicates that are known to form under these conditions [26].
Table 2: Total Al/Si atomic ratios at various Na2CO3 concentrations
Na2CO3
(g/L)
Al/Si atomic ratio
0
1.25
2.5
10
87.54
0.265
0.676
0.197
25
Figure 13: Aluminum and silicon solubilities as a function of sodium carbonate
concentrations at 230 °C (generated using OLI simulation software)
It was also evident that passivation due to anhydrite formation did occur even in the absence of
sodium carbonate, as sulphates were not detected in significant amounts on the surface, with or
without sodium carbonate (Figure 15 and Appendix B). Anhydrite was likely formed away from
the acidic pyrite surface and in the bulk alkaline solution. Instead, the product layer was
dominated by silicates, aluminum oxides/aluminosilicates and iron oxides. Si 2p spectra could
not be interpreted due to interference from Fe 3s nearby [30]. However, Si 2s spectra, as shown
1.E-05
1.E-04
1.E-03
1.E-02
1.E-01
1.E+00
0 2.5 5 7.5 10 12.5
Tota
l Al (a
q) m
ol/
L
Na2CO3 (g/L)
Al (in presence of Si)
Al (without Si)
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 2.5 5 7.5 10 12.5
Tot
Si(a
q) m
ol/
L
Na2CO3 (g/L)
Si (in presence of Al)
Si (without Al)
26
in Figure 16, were used and showed that silicon was present as silicates rather than silica
confirming a dissolution-precipitation mechanism supported by the lower solubility of silicates
compared to silica [26]. Detailed characterization of precipitated silicate could not be performed
due to the amorphous and non-uniform nature of the precipitate. It was certain, however, that the
precipitate contained silicates rather than just silica because Si 2s peaks are seen between 153 –
154 eV, as opposed to 155 eV, which is indicative of silica. Peaks between 153 and 154 eV have
been identified as characteristic of various natural silicates [31]. Aqueous silica at alkaline pH
exists as various polysilicates, which are polymerized froms of the monomeric SiO32-
. Since
these polysilicate ions are not of uniform size, they cannot arrange themselves along with metal
ions into a regular crystal lattice. Iron spectra could not be used to determine iron chemistry
because of the effect of sputtering on iron oxides [32]. Ar+ sputtering has been shown to reduce
Fe(III) to Fe(II) oxides and has almost certainly altered the iron chemistry in the present study.
Fe2p 3/2 spectra were dominated by lower binding energy peaks that correspond to Fe(II)
species. The predominance of Fe(II) could be either due to the incomplete oxidation of pyrite or
its re-reduction by Ar+ sputtering. Based on the results by Peters et al., [18], reduction due to
sputtering seems the more plausible explanation.
Figure 14 - Al 2p scans of product layers formed at various Na2CO3 levels. Note the
prominence of Al in the absence of Na2CO3.
27
Figure 15 - S 2p scans show the absence of sulphates on the surface, due to the lack of
peaks beyond 166 eV. Peaks at 162 eV are sulphides from the pyrite surface.
Figure 16 - Si 2s peaks close to 153 eV show the increase in silicate levels with increase in
Na2CO3 levels which is attributed to the increasing solubility of SiO2.
28
Figure 17 shows EDS Linescans performed on product layer cross-sections, which show that the
product was fairly homogenous as far as the chemical composition is concerned, indicating a
constant kinetic regime and further proving the absence of adsorbed or deposited silica.
Figure 17: EDS Spectra of a product layer cross-section at 2.5 g/L Na2CO3. Elemental
concentrations are largely uniform throughout. Dark spots are aluminosilicate inclusions
present in the pyrite sample that contain no iron.
4.2 Flashing
It was suspected that the formation of the passivating silicate layer may have occurred as the
autoclave cooled down rather than at temperature, due to the decreasing solubility of silica with
decreasing temperature [33]. To test this hypothesis, tests were run in which water was flashed
from the system at temperature before the bomb was allowed to cool down, thus preventing any
precipitation from solution during cool-down. This was achieved by withdrawing water from the
1
1
2
2
3
3 4
4
5 5
29
bottom of the reactor via a dip tube. The results, when compared to a conventional cool-down
with solution inside the bomb, showed that there was no appreciable difference in chemical
composition, as shown in Figure 18 and Appendix B. The product layer thickness, however, was
slightly greater when compared to a conventional cool-down, as shown in Figure 19. EDS
analysis of the cross section revealed that the concentration of silicon was relatively constant
from the pyrite-oxide to the oxide-solution interfaces, which would not be the case if silicates
precipitated after the iron oxide formed and during the cool down period, as shown in Figure 20
and Table 3. It was therefore concluded that the product layer, including silicates, was formed at
process temperature and not during cool-down.
Figure 18 - Si peaks are near identical with or without flashing the solution.
30
Figure 19 - Cross section of the product layer without flashing (top) and after flashing the
solution (bottom) at temperature.
31
Figure 20: SEM cross-section of the oxide layer after flashing, with EDS analysis
performed on points across the layer.
Table 3: EDS elemental analysis of the product layer after flashing shows an even
distribution of Si across the layer, indicating that the silicates grew along with the oxides
during the oxidation process.
Position Elemental wt%
C O Na Si S Fe
1 14.46 45.74 39.80
2 15.98 45.51 38.51
3 4.91 8.50 1.22 33.91 51.46
4 6.95 35.31 0.71 4.12 52.92
5 5.20 26.11 3.27 0.44 64.98
6 6.25 28.00 1.21 3.73 0.37 60.45
32
4.3 Effect of Organic Dispersants Addition
Organic dispersants are often used to prevent the agglomeration of molten sulphur in autoclaves
that operate in acidic conditions below 180 ºC [34] [35] and during flotation to enhance or
depress the flotability of certain sulphides [36]. Biopolymers are large organic polymers
produced from wood pulp by the sulphonation of lignin in the sulphite pulping process, with the
general formula R-SO3-M, where R is the long organic chain and M is an alkali or alkaline earth
metal cation. The organic component is derivative of lignin produced by the substitution of a
benzyl ether or alcohol group with SO3-
[37]. Sulphonation renders the lignin highly water
soluble since it can now be ionized and solvated as a salt:
)()(3)(32
aqaq
OH
s MRSOMRSO
Four dispersants, supplied by Borregaard, were evaluated for their ability to prevent silicate
precipitation on the pyrite surface. 21 mg/L of dispersant was added to the autoclave charge and
the resultant thicknesses were compared with peak baseline results. Out of the four dispersants
used, three reported significant reductions in product layer thicknesses (Table 4).
Table 4: Decrease in product layer thickness with dispersant addition
Dispersant Dispersant Type Average Thickness
(µm)
% Decrease
Compared to Baseline
Baseline
(2.5 g/L
Na2CO3)
- 22.89 -
D-618 Moderately
modified
14.54 36.5
D-619 Moderately
modified
24.26 -6
D-709 Mildly modified 11.07 51.6
D-748 Highly modified 10.67 53.4
33
The exact chemical formulation of the given dispersants was proprietary. However, it was known
that D-619, D-709 and D-748 were sodium salts while D-618 was a calcium salt. The mechanism
of thickness reduction can only be speculated here. There are two possible routes by which
anionic dispersants can affect the system: firstly by bonding on to the pyrite surface and secondly
by reacting with anions in solution. Bonding on to the pyrite surface or the hematite precipitate
can occur only through cation bridging, since the surface is expected to be negatively charged
(the point of zero charge pH values for pyrite and hematite range between 6 – 7 and 5 – 6.5
respectively [2]). The dispersants are not expected to react with silicate anions in the solution
either. Biopolymer anions may be reacting with positively charged aluminum and iron species,
namely Al3+
, [Al(OH)]2+
, [Al(OH)2]+, Fe
3+ [Fe(OH)]
2+and [Fe(OH)2]
+ only. Aluminum and ferric
ions have been shown to effect charge reversal on lyophobic colloids [38] [39]. If supersaturated
silica forms a sol under the process conditions, such a charge reversal may play a role in making
this sol reactive towards anions. However, given the very low concentration of dispersant, anions
in the solution are in a large excess. Therefore, any significant reduction in precipitation
thickness can only occur through the bonding of biopolymer anions on to the pyrite surface,
possibly facilitated by the relatively low pH in the boundary layer near the surface. Indeed, Table
5 shows that there was not much change in Si and Al concentrations in the product layer as
measured by XPS, when compared to baseline results shown in Table 2, which meant that Si
precipitation had not reduced in proportion to Fe and Al.
Table 5: Effect of dispersant addition on product layer Si/Al deposition
Dispersant Total Si
(at%)
Al/Si ratio
(at%/at%)
Baseline (2.5 g/L Na2CO3)
32.3 0.75
D-618 40.1 0.365
D-619 40.23 0.61
D-709 30.52 0.96
D-748 45.1 0.2
34
4.4 Effect of Aluminum Sulphate Addition
The precipitation of large amounts of aluminum in the product layer led to the testing of
Al2(SO4)3 addition as a means of forcing Al-silicate precipitation away from the pyrite surface
and in the bulk. Since the dosage was unknown, 4.16 g/L of Al2(SO4)3.18H2O was added as an
initial guess to the baseline 2.5 g/L Na2CO3 reaction mixture. The initial guess was based upon
an OLI estimate for the largest amount of aluminum that kept the pH above 7.0. The resultant
average thickness was 8.35 µm, a 63.5% decrease from the baseline. However, the chemical
composition of the product layer was seen to contain large amounts of aluminum, with very little
silicon – Al concentration was 93 at%, with Al/Si ratio of 930:1. Addition of aluminum
decreased the solution pH significantly due to hydrolysis and this option was not explored
further.
35
Chapter 5
Summary 5
5.1 Conclusions
The objective of this investigation was to understand better how passivation of the pyrite surface
occurs in a sodium carbonate solution, by growing passivation layers and characterizing them.
Experimental data has clearly shown two competing effects within a range of sodium carbonate
concentration levels, giving a maximum passive product thickness at intermediate sodium
carbonate levels. On one hand, sodium carbonate accelerated pyrite oxidation kinetics but on the
other, it promoted the solubilisation of silica and alumina, which re-precipitated as silicates and
aluminosilicates on the pyrite surface, thereby passivating it. The passive layer was chemically
characterized to be an iron silicate. Having established that the passive product thickness
declines at higher concentrations, and having known that higher concentrations also enhance
oxidation kinetics, we can recommend that Na2CO3 concentrations be maintained higher than 10
g/L to give the highest oxidation extents.
The passive product layer was shown to have formed at process temperature, i.e. 230 ºC due to
the low solubility of iron silicates. The occurrence of aluminum impurities in the pyrite itself as
well as the quartz sand introduced aluminosilicates to the passive layer. The precipitation of
aluminum in the product layer was seen to be very dependent on the pH, and was dominant at
low pH. Anionic dispersants or aluminum salts can be used to mitigate product layer thicknesses.
However, the mechanism by which anionic dispersants act upon the pyrite needs further
investigation.
5.2 Recommendations
It was originally planned to cast pyrite in an epoxy mold, which would have provided a perfect
single exposed surface. Since epoxies do not have service temperatures beyond 150 ºC,
polytetrafluoroethylene (PTFE) disks were used instead. Because PTFE cannot be molded to
encapsulate the pyrite sample, screws were used to hold the pyrite sample in place. Five of the
six pyrite surfaces were wrapped in PTFE tape to provide some protection against oxidation.
36
This was a relatively crude arrangement that allowed for partial oxidation of all six faces. The
constraint of a material with a service temperature around 230 ºC needs to be addressed in order
to design better experiments. A single, uniformly accessible surface could then be used as a
rotating disk, and generate more uniform product layers. The elimination of edge effects and
oxidation of non-targeted surfaces would allow for kinetic studies of pyrite oxidation under the
current conditions, which are industrially relevant. Nevertheless, this was the first study with
“rotation disc” configuration to operate at 230 ºC.
An investigation of product layer porosity and morphology, along with better chemical
characterization could be combined with the present results to better correlate the process
conditions with passivation of the pyrite surface. Solubility data in relevant conditions, namely
200 – 250 °C, pH 7 – 12, is absent, notably for Si and Al. Consequentially, only a qualitative
understanding of the supersaturation and precipitation phenomenon can be provided from the
data gathered in the current study. Filling these solubility data gaps would go a long way in
understanding alkaline pressure oxidation at the same way as acidic POX currently is.
Finally, a more fundamental investigation of the effect of dispersants on pyrite oxidation is
required to better interpret results gathered in the current study. If the mechanism involves the
adsorption of dispersants onto the pyrite surface, their addition may decrease oxidation extents in
the process of reducing silicate precipitation.
37
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40
Appendix A – SEM Images
Na2CO3 (g/L) Average Thickness (μm) Comments
0 2.22 -
Na2CO3 (g/L) Average Thickness (μm) Comments
1.25 15.98 -
41
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 22 -
Na2CO3 (g/L) Average Thickness (μm) Comments
5 5.38 -
42
Na2CO3 (g/L) Average Thickness (μm) Comments
7.5 8.32 -
Na2CO3 (g/L) Average Thickness (μm) Comments
10 5.46 -
43
Na2CO3 (g/L) Average Thickness (μm) Comments
12.5 3.24 -
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 8.35 4 g/L Al2(SO4)3
44
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 14.54 0.021 g/L D-618
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 11.07 0.021 g/L D-709
45
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 26.9 0.021 g/L D-619
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 22.53 3 hr test
46
Na2CO3 (g/L) Average Thickness (μm) Comments
5 8.87 -
Na2CO3 (g/L) Average Thickness (μm) Comments
5 11 Flashed
47
Appendix B – XPS Spectra
Na2CO3 (g/L) Average Thickness (μm) Comments
0 2.22 -
48
49
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Si2s 152.76 2.68 4950.16 1.45 0.955
Si Total 1.45
Al2p 72.97 1.24 38531.84 19.40 0.537
Al2p A 73.69 1.06 54171.10 27.28 0.537
Al2p B 74.49 1.27 66822.66 33.66 0.537
Al2p C 75.64 1.45 15781.01 7.95 0.537
Al Total 88.29
O1s 529.97 1.28 14579.64 1.70 2.930
O1s A 532.42 1.28 5380.37 0.63 2.930
O1s B 530.70 1.12 16888.81 1.97 2.930
O1s C 531.50 1.14 12397.58 1.45 2.930
O Total 5.75
Fe2p3 709.96 3.05 1544.89 0.06 10.820
Fe2p3 A 712.43 2.68 560.76 0.02 10.820
Fe2p3 B 714.86 2.31 350.74 0.01 10.820
Fe Total 0.09
C1s 284.33 1.99 25140.18 0.00 1.000
C1s A 285.80 2.29 8537.11 2.55 1.000
C1s B 288.72 2.88 4683.02 1.40 1.000
C Total 3.95
50
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Ag3d5 367.11 1.18 5965.00 0.17 10.660
Ag3d5 A 367.89 0.80 4483.13 0.13 10.660
Ag3d5 B 368.44 0.67 1779.27 0.05 10.660
Ag3d5 C 369.09 1.44 3865.41 0.11 10.660
Ag Total 0.46
Na2CO3 (g/L) Average Thickness (μm) Comments
1.25 15.98 -
51
52
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Si2s 151.73 1.54 7936.79 14.61 0.955
Si2s A 154.12 1.76 3895.50 7.18 0.955
Si2s B 152.85 1.57 9394.31 17.30 0.955
Si Total 39.09
C1s 284.27 1.82 15903.87 0.00 1.000
C1s A 285.61 1.90 6114.10 11.45 1.000
C1s B 288.10 2.47 2269.28 4.25 1.000
C Total 15.7
Ca2p3 345.76 0.85 2443.22 1.41 3.350
Ca2p3 A 346.53 0.85 3769.58 2.17 3.350
Ca2p3 B 347.28 0.88 1937.64 1.12 3.350
Ca Total 4.7
Al2p 74.65 0.68 81.50 0.26 0.537
Al2p A 73.48 1.83 2069.37 6.55 0.537
Al2p B 75.75 1.59 1117.50 3.54 0.537
Al Total 10.35
Na1s 1071.92 1.23 398.13 0.17 8.520
Na Total 0.17
53
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
O1s 529.35 1.15 14077.24 10.31 2.930
O1s Scan A 530.26 1.54 12793.87 9.37 2.930
O1s Scan B 531.55 1.30 2500.02 1.83 2.930
O Total 21.51
Fe2p3 707.99 1.53 5335.13 1.20 10.820
Fe2p3 A 709.25 2.19 15779.29 3.55 10.820
Fe2p3 B 710.44 1.35 3251.31 0.73 10.820
Fe2p3 C 712.91 1.52 3233.00 0.73 10.820
Fe2p3 D 714.04 3.45 5112.76 1.15 10.820
Fe2p3 E 711.63 1.78 5061.22 1.14 10.820
Fe Total 8.5
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 22 -
54
55
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Si2s 153.13 2.96 8092.13 19.74 0.955
Si Total 19.74
S2p3 161.41 1.14 2106.26 4.44 1.110
S2p1 162.59 1.15 1056.47 0.00 0.567
S2p3 A 162.41 1.32 991.90 2.09 1.110
S2p1 A 163.59 1.32 497.06 0.00 0.567
S2p3 B 164.19 1.27 155.90 0.33 1.110
S2p1 B 165.37 1.27 78.01 0.00 0.567
S Total 6.53
Al2p 73.62 1.55 2171.08 9.10 0.537
Al2p A 74.90 1.19 1474.14 6.18 0.537
Al2p B 76.03 0.51 251.56 1.06 0.537
Al Total 16.34
O1s 530.27 1.24 4040.41 3.92 2.930
O1s A 531.29 1.20 3326.50 3.23 2.930
O1s B 532.14 0.93 1588.34 1.54 2.930
O1s C 533.04 1.33 1111.15 1.08 2.930
O Total 9.77
Fe2p3 707.10 1.11 2147.25 0.64 10.820
Fe2p3 A 708.48 1.97 6543.35 1.95 10.820
56
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Fe2p3 B 710.18 2.00 5588.51 1.66 10.820
Fe2p3 C 712.05 2.17 2775.43 0.83 10.820
Fe2p3 D 714.84 3.25 1913.39 0.00 10.820
Fe Total 5.08
Na1s 1071.06 1.11 1644.93 0.91 8.520
Na1s A 1072.13 1.78 8465.93 4.67 8.520
Na1s B 1073.01 0.72 541.53 0.30 8.520
Na Total 5.88
C1s 284.48 2.15 24884.10 0.00 1.000
C1s A 285.96 2.33 9030.59 22.41 1.000
C1s B 288.59 2.52 3633.96 9.03 1.000
C Total 31.44
Ca2p3 346.37 1.97 4866.77 3.72 3.350
Ca2p3 A 347.41 1.36 1564.69 1.20 3.350
Ca Total 4.92
Na2CO3 (g/L) Average Thickness (μm) Comments
7.5 22 -
57
58
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Fe2p3 706.91 0.98 2173.27 0.22 10.820
Fe2p3 A 710.01 3.53 28308.80 2.88 10.820
Fe2p3 B 715.14 3.32 3972.30 0.00 10.820
Fe2p3 C 712.54 2.08 2067.87 0.21 10.820
Fe Total 3.31
C1s 284.60 2.61 22053.07 0.00 1.000
59
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
C1s A 286.40 1.64 2023.03 1.72 1.000
C1s B 288.78 2.45 2731.64 2.32 1.000
C Total 4.04
Ca2p3 347.01 1.80 14711.94 3.84 3.350
Ca2p3 A 347.99 1.12 3450.47 0.90 3.350
Ca Total 4.74
Si2s 153.16 1.01 5428.32 4.53 0.955
Si2s A 153.75 2.42 44824.40 37.39 0.955
Si2s B 152.30 1.34 12546.56 10.46 0.955
Si Total 52.38
O1s 530.22 1.14 10072.13 3.34 2.930
O1s A 531.95 1.90 21655.51 7.19 2.930
O1s B 531.03 0.99 7724.89 2.56 2.930
O Total 13.09
Na1s 1071.32 0.52 831.56 0.16 8.520
Na1s A 1072.24 1.10 5984.37 1.13 8.520
Na1s B 1073.04 0.52 1356.32 0.26 8.520
Na1s C 1073.44 0.52 764.85 0.14 8.520
Na Total 1.69
Al2p 71.59 1.05 984.70 1.41 0.537
60
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Al2p A 74.13 2.19 13499.42 19.34 0.537
Al Total 20.75
Na2CO3 (g/L) Average Thickness (μm) Comments
10 5.46 -
61
62
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Si2s 153.18 2.42 68784.71 33.69 0.955
Si2s A 154.43 2.33 31184.54 15.28 0.955
Si2s B 154.78 1.99 26700.82 13.09 0.955
Si Total 62.06
O1s 532.07 2.05 32876.72 6.41 2.930
O1s Scan A 530.94 0.89 2717.16 0.53 2.930
O1s Scan B 530.13 1.34 5363.84 1.05 2.930
O Total 7.99
Al2p 73.28 1.17 4753.27 4.00 0.537
Al2p A 73.94 0.81 3879.43 3.26 0.537
Al2p B 74.57 0.82 4634.12 3.90 0.537
Al2p C 75.29 1.12 4560.54 3.84 0.537
Al Total 15.00
Fe2p3 706.85 1.10 905.29 0.05 10.820
Fe2p3 A 709.90 3.36 8294.32 0.50 10.820
Fe2p3 B 712.29 2.78 1311.92 0.08 10.820
Fe2p3 C 715.27 2.74 894.54 0.00 10.820
Fe Total 0.63
Na1s 1071.94 1.70 6305.46 0.70 8.520
Na1s A 1072.98 1.09 1745.81 0.19 8.520
63
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Na Total 0.89
Ag3d5 367.50 1.41 14000.92 0.68 10.660
Ag3d5 A 368.54 1.36 4302.03 0.21 10.660
Ag Total 0.89
Ca2p3 346.25 0.86 1850.53 0.28 3.350
Ca2p3 A 346.98 0.72 1834.73 0.28 3.350
Ca2p3 B 347.59 0.56 1671.10 0.26 3.350
Ca2p3 C 348.12 0.56 1350.91 0.21 3.350
Ca Total 1.03
S2p3 160.75 0.49 79.90 0.03 1.110
S2p1 161.93 0.48 39.95 0.00 0.567
S2p3 A 161.31 0.49 91.04 0.04 1.110
S2p1 A 162.49 0.49 45.52 0.00 0.567
S2p3 B 162.07 1.40 137.72 0.06 1.110
S2p1 B 163.25 1.40 68.86 0.00 0.567
S Total 0.13
C1s 284.34 2.01 43940.25 0.00 1.000
C1s A 285.80 2.12 16703.35 8.32 1.000
C1s B 288.14 2.75 6141.42 3.06 1.000
C Total 11.38
64
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 8.35 4 g/L Al2(SO4)3
65
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
O1s 529.73 1.25 7991.65 0.85 2.930
O1s A 530.55 1.44 28629.70 3.04 2.930
O1s B 531.51 1.47 16537.83 1.75 2.930
O1s C 532.77 1.24 2706.38 0.29 2.930
O Total 5.93
Fe2p3 708.12 3.52 394.08 0.01 10.820
66
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Fe2p3 A 711.08 2.60 381.70 0.01 10.820
Fe2p3 B 715.05 3.52 374.70 0.01 10.820
Fe Total 0.03
Al2p 73.02 1.46 62096.82 28.41 0.537
Al2p A 73.94 1.38 97500.01 44.62 0.537
Al2p B 74.93 1.45 42654.86 19.53 0.537
Al Total 92.56
Si2s 152.99 2.87 389.80 0.10 0.955
Si Total 0.10
Na1s 1071.81 1.89 2291.49 0.14 8.520
Na Total 0.14
C1s 284.39 2.33 9504.60 0.00 1.000
C1s A 286.14 2.19 2340.70 0.63 1.000
C1s B 289.04 3.04 2244.26 0.61 1.000
C Total 1.24
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 14.54 0.02 g/L D-618
67
68
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Al2p 73.55 1.52 2109.31 8.30 0.537
Al2p A 75.35 1.83 1611.13 6.34 0.537
Al Total 14.64
O1s 529.71 1.00 7864.32 7.16 2.930
O1s A 530.82 1.37 10270.86 9.36 2.930
O1s B 530.24 0.76 2821.71 2.57 2.930
69
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
O1s C 531.99 1.24 2039.47 1.86 2.930
O Total 20.95
Ca2p3 345.43 0.90 1238.66 0.89 3.350
Ca2p3 A 346.09 0.77 2290.25 1.64 3.350
Ca2p3 C 346.91 1.14 4602.18 3.30 3.350
Ca Total 5.83
C1s 281.11 0.83 220.11 0.51 1.000
C1s A 284.54 2.86 7904.11 0.00 1.000
C1s B 285.39 3.39 2016.62 4.70 1.000
C1s C 288.24 2.48 1567.01 3.65 1.000
C Total 8.86
Fe2p3 708.45 1.63 4008.01 1.12 10.820
Fe2p3 A 709.41 1.59 3921.91 1.10 10.820
Fe2p3 B 710.51 3.46 18773.04 5.25 10.820
Fe2p3 sat 714.51 3.34 3460.04 0.00 10.820
Fe Total 7.47
Na1s 1071.37 0.79 1286.79 0.67 8.520
Na1s A 1072.19 0.89 1311.41 0.68 8.520
Na Total 1.35
O1s A 530.82 1.37 10270.86 9.36 2.930
70
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
O1s B 530.24 0.76 2821.71 2.57 2.930
O1s C 531.99 1.24 2039.47 1.86 2.930
O Total 13.79
Si2s 151.11 0.52 867.57 1.99 0.955
Si2s A 151.53 0.80 1881.32 4.31 0.955
Si2s B 152.95 1.89 10548.59 24.16 0.955
Si2s C 152.13 0.97 4210.93 9.64 0.955
Si Total 40.1
S2p1 161.81 2.24 121.66 0.00 0.567
S2p3 A 163.02 1.19 168.62 0.33 1.110
S2p1 A 164.15 1.19 84.44 0.00 0.567
S2p3 160.68 2.22 241.28 0.48 1.110
S Total 0.81
71
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 11.07 0.02 g/L D-709
72
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Al2p 73.38 2.05 5119.81 18.89 0.537
Al2p A 75.02 1.09 1725.05 6.37 0.537
Al2p B 76.29 0.88 1071.46 3.96 0.537
Al Total 29.22
Fe2p3 708.51 1.76 7195.95 1.89 10.820
Fe2p3 A 710.05 2.50 15624.10 4.10 10.820
73
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Fe2p3 sat 714.73 3.20 3932.82 0.00 10.820
Fe2p3 C 712.10 2.24 4643.97 1.22 10.820
Fe Total 7.21
O1s 529.77 0.65 4067.13 3.48 2.930
O1s A 530.24 0.91 6230.83 5.33 2.930
O1s B 531.00 1.79 9616.66 8.22 2.930
O1s C 529.32 0.74 2964.70 2.53 2.930
O Total 19.56
Na1s 1071.22 1.49 1294.23 0.63 8.520
Na1s A 1072.46 0.63 797.98 0.39 8.520
Na1s B 1071.67 0.52 258.36 0.13 8.520
Na Total 1.15
Si2s 151.88 1.57 7544.73 16.20 0.955
Si2s A 152.98 1.43 5089.08 10.93 0.955
Si2s B 154.10 1.20 1577.54 3.39 0.955
Si Total 30.52
C1s 283.57 1.39 1970.05 4.30 1.000
C1s A 286.29 1.75 1216.52 2.66 1.000
C1s B 284.73 1.79 6341.43 0.00 1.000
C1s C 288.35 2.29 1147.39 2.51 1.000
74
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
C Total 9.47
Ca2p3 345.21 0.66 633.73 0.43 3.350
Ca2p3 A 346.46 1.24 2607.66 1.75 3.350
Ca2p3 B 345.70 0.52 434.73 0.29 3.350
Ca2p3 C 347.44 0.86 606.95 0.41 3.350
Ca Total 2.88
Na2CO3 (g/L) Average Thickness (μm) Comments
2.5 26.9 0.02 g/L D-619
75
76
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Si2s 151.70 0.79 2809.46 3.65 0.955
Si2s A 153.18 2.29 23289.01 30.28 0.955
Si2s B 152.45 1.06 4844.57 6.30 0.955
Si Total 40.23
C1s 284.48 2.13 48879.92 0.00 1.000
C1s A 287.64 3.34 9182.28 12.15 1.000
C Total 12.15
Ca2p3 345.80 0.82 1106.66 0.45 3.350
Ca2p3 A 346.59 1.02 3215.38 1.31 3.350
Ca2p3 B 347.49 0.74 1300.98 0.53 3.350
Ca Total 2.29
Fe2p3 709.32 2.64 17280.74 2.74 10.820
Fe2p3 A 711.35 2.82 8399.47 1.33 10.820
Fe2p3 sat 714.71 3.11 3398.37 0.54 10.820
Fe Total 4.61
Al2p 73.39 1.57 6083.72 13.59 0.537
Al2p A 74.59 1.58 3634.94 8.12 0.537
Al2p B 76.04 1.69 1217.24 2.72 0.537
Al Total 24.43
O1s 529.71 1.09 8103.52 4.19 2.930
77
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
O1s A 531.70 1.69 10459.24 5.42 2.930
O1s B 530.77 1.06 8396.79 4.35 2.930
O1s C 530.11 0.75 3242.51 1.68 2.930
O Total 15.64
S2p3 161.46 3.23 579.34 0.65 1.110
S2p1 162.59 3.35 292.15 0.00 0.567
S Total 0.65
Na2CO3 (g/L) Average Thickness (μm) Comments
5 5.38 -
78
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Si2s 152.95 2.88 20169.53 38.09 0.955
Si Total 38.09
C1s A 288.14 0.49 253.83 0.49 1.000
C1s B 289.23 2.16 849.65 1.63 1.000
C1s C 281.42 2.11 374.94 0.72 1.000
C Total 2.84
Ca2p3 345.93 1.30 2367.85 1.40 3.350
79
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Ca2p3 A 346.96 1.08 2666.59 1.58 3.350
Ca2p3 B 348.04 1.39 2372.79 1.40 3.350
Ca Total 4.38
O1s 530.05 1.37 28616.13 21.50 2.930
O1s Scan A 531.23 1.72 10505.48 7.90 2.930
O1s Scan B 531.90 3.10 3948.78 2.97 2.930
O1s Scan C 528.22 2.54 1145.47 0.86 2.930
O Total 33.23
Fe2p3 708.93 2.45 26945.93 6.21 10.820
Fe2p3 A 710.47 2.21 12995.02 3.00 10.820
Fe2p3 B 711.98 3.12 17053.96 3.94 10.820
Fe2p3 C 715.22 3.37 7919.62 1.83 10.820
Fe Total 14.98
Na1s 1070.95 1.25 7501.05 3.20 8.520
Na1s A 1072.76 0.72 3158.10 1.35 8.520
Na1s B 1071.87 0.86 4561.45 1.95 8.520
Na Total 6.5
80
Na2CO3 (g/L) Average Thickness (μm) Comments
5 60 Flashed
81
Elemental ID and Quantification
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Fe2p3 708.38 1.96 19217.18 3.93 10.820
Fe2p3 A 709.71 1.63 11667.27 2.39 10.820
Fe2p3 B 710.88 1.81 8636.20 1.77 10.820
Fe2p3 C 712.25 2.56 8296.03 1.70 10.820
Fe Total 9.79
Si2s 152.36 2.06 16693.69 28.02 0.955
Si2s A 153.87 1.81 4924.88 8.27 0.955
C1s A 288.75 1.32 1043.21 1.78 1.000
Si Total 38.07
Ca2p3 346.01 0.90 1333.81 0.70 3.350
Ca2p3 A 346.91 1.55 3072.42 1.62 3.350
Ca Total 2.32
Na1s 1070.86 0.50 878.37 0.33 8.520
Na1s A 1071.59 0.82 3252.63 1.23 8.520
Na1s B 1072.39 0.60 1598.20 0.61 8.520
Na Total 2.17
O1s 529.58 1.35 22425.30 14.98 2.930
O1s A 530.55 1.80 13911.24 9.30 2.930
O1s B 531.56 1.97 3107.48 2.08 2.930
O Total 26.36
82
Name Peak BE FWHM eV Area (P) CPS.eV At. % SF
Al2p 72.77 1.23 1590.96 4.59 0.537
Al2p A 74.02 0.84 1789.42 5.16 0.537
Al2p B 75.12 1.19 2326.44 6.71 0.537
Al2p C 76.68 1.67 1667.37 4.82 0.537
Al Total 21.28
83
Appendix C – Sample Calculation and Statistical Analysis
Sample Calculation of Average Thickness
Since SEM was used to measure product layer thickness at high magnifications (750x – 5000x),
it was not practically feasible to measure the entire side of the cube under investigation. Instead,
portions of length were photographed at random and the corresponding thicknesses were
averaged arithmetically.
Step 1: A snapshot of the cross-section was taken under back-scatter electron mode
Step 2: The oxide layer was selected in GIMP using the free-hand select tool. The number of
pixels under the area, A was measured by the software. The length of the cross-section L was
also measured in pixels.
84
Step 3: Pixels were converted to micrometers using the scale provided on the image:
)(
)(
)(
)()(
pixelsScale
mScalex
pixelsLength
pixelsAreamThicknessAvg
In this particular image,
mmThicknessAvg
pixelsmScale
pixelsLength
pixelsArea
93.7)(
30020
2560
304515
Step 4: Thicknesses measured in this way for each image were averaged arithmetically for the
experiment
Statistical Treatment of Thickness Measurements
All statistical analyses were performed using SPSS 15 software. Analysis of variance (ANOVA)
tests were performed to prove that the thicknesses produced at various concentrations were
statistically dependent upon Na2CO3 concentrations. The Games-Howell ANOVA tests were
performed on sets of replicates, assuming normal distributions and non-equal variances between
replicates.
85
Multiple Comparisons
Dependent Variable: Av g thickness
Games-Howell
-9.9106528* .86361412 .000 -12.6091743 -7.2121314
-19.369769* .82847405 .000 -22.0294755 -16.7100617
-4.7671831* .50063096 .000 -6.3142425 -3.2201236
-4.0465371* .48669115 .000 -5.5749493 -2.5181248
-1.7425965* .42888071 .005 -3.0874642 -.3977288
-1.8843462* .43063038 .002 -3.2438468 -.5248455
9.91065282* .86361412 .000 7.2121314 12.6091743
-9.4591158* 1.090917 .000 -12.8365409 -6.0816906
5.14346977* .86854018 .000 2.4340815 7.8528580
5.86411574* .86058060 .000 3.1709689 8.5572626
8.16805631* .82925832 .000 5.5560832 10.7800295
8.02630666* .83016458 .000 5.4107672 10.6418461
19.369769* .82847405 .000 16.7100617 22.0294755
9.45911576* 1.090917 .000 6.0816906 12.8365409
14.602586* .83360779 .000 11.9331057 17.2720654
15.323232* .82531138 .000 12.6679839 17.9784791
17.627172* .79259653 .000 15.0471985 20.2071457
17.485422* .79354466 .000 14.9018464 20.0689984
4.76718306* .50063096 .000 3.2201236 6.3142425
-5.1434698* .86854018 .000 -7.8528580 -2.4340815
-14.602586* .83360779 .000 -17.2720654 -11.9331057
.72064597 .49537963 .769 -.8230941 2.2643860
3.02458654* .43871558 .000 1.6637511 4.3854220
2.88283689* .44042618 .000 1.5080761 4.2575977
4.04653708* .48669115 .000 2.5181248 5.5749493
-5.8641157* .86058060 .000 -8.5572626 -3.1709689
-15.323232* .82531138 .000 -17.9784791 -12.6679839
-.72064597 .49537963 .769 -2.2643860 .8230941
2.30394057* .42273903 .000 .9573580 3.6505231
2.16219092* .42451401 .001 .8005551 3.5238267
1.74259651* .42888071 .005 .3977288 3.0874642
-8.1680563* .82925832 .000 -10.7800295 -5.5560832
-17.627172* .79259653 .000 -20.2071457 -15.0471985
-3.0245865* .43871558 .000 -4.3854220 -1.6637511
-2.3039406* .42273903 .000 -3.6505231 -.9573580
-.14174965 .35676678 1.000 -1.2800190 .9965197
1.88434617* .43063038 .002 .5248455 3.2438468
-8.0263067* .83016458 .000 -10.6418461 -5.4107672
-17.485422* .79354466 .000 -20.0689984 -14.9018464
-2.8828369* .44042618 .000 -4.2575977 -1.5080761
-2.1621909* .42451401 .001 -3.5238267 -.8005551
.14174965 .35676678 1.000 -.9965197 1.2800190
(J) concentrat ion
1.25
2.50
5.00
7.50
10.00
12.50
.00
2.50
5.00
7.50
10.00
12.50
.00
1.25
5.00
7.50
10.00
12.50
.00
1.25
2.50
7.50
10.00
12.50
.00
1.25
2.50
5.00
10.00
12.50
.00
1.25
2.50
5.00
7.50
12.50
.00
1.25
2.50
5.00
7.50
10.00
(I) concentration
.00
1.25
2.50
5.00
7.50
10.00
12.50
Mean
Dif f erence
(I-J) Std. Error Sig. Lower Bound Upper Bound
95% Conf idence Interv al
The mean dif f erence is signif icant at the .05 lev el.*.
86
T-tests with a significance of α =0.05 were performed to prove that the thicknesses produced in
the presence of dispersants were indeed different from those produced in pure Na2CO3. Each
dispersant experiment was compared to the baseline exp 54, which was performed with no
dispersants. The reproducibility of baseline thicknesses was also proven statistically.
Exp No Reagents
30 2.5 g/L Na2CO3
37 2.5 g/L Na2CO3 + 4.16 g/L Al2(SO4)3
54 2.5 g/L Na2CO3
56 2.5 g/L Na2CO3
40 2.5 g/L Na2CO3 + 0.021 g/L D-618
44 2.5 g/L Na2CO3 + 0.021 g/L D-619
42 2.5 g/L Na2CO3 + 0.021 g/L D-709
58 2.5 g/L Na2CO3 + 0.021 g/L D-748
87
Experiment number 54 and 30:
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Conclusion: Significance (p-value) is greater than α, reject H0 at 0.05 level. The two means are equal.
Experiment number 54 and 56:
Group Statistics
3 25.23118 2.68232513 1.548641
8 21.96444 1.85499819 .65584090
Exp
30
54
Av g thickness
N Mean Std. Dev iation
Std. Error
Mean
Independent Samples Test
.589 .463 2.334 9 .044 3.2667413 1.3998107 .10014950 6.433333
1.942 2.756 .155 3.2667413 1.6817897 -2.36328 8.896760
Equal variances
assumed
Equal variances
not assumed
Av g thickness
F Sig.
Levene's Test f or
Equality of Variances
t df Sig. (2-tailed)
Mean
Dif f erence
Std. Error
Dif f erence Lower Upper
95% Conf idence
Interv al of the
Dif f erence
t-test for Equality of Means
88
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Conclusion: Significance (p-value) is greater than α, reject H0 at 0.05 level. The two means are equal.
Experiment number 54 and 40:
Group Statistics
Exp N Mean Std. Deviation Std. Error Mean
Group Statistics
7 20.20416 3.67784806 1.390096
8 21.96444 1.85499819 .65584090
Exp
56
54
Av g thickness
N Mean Std. Dev iation
Std. Error
Mean
Independent Samples Test
1.501 .242 -1.195 13 .253 -1.760281 1.4725967 -4.94163 1.421071
-1.145 8.603 .283 -1.760281 1.5370406 -5.26192 1.741359
Equal variances
assumed
Equal variances
not assumed
Av g thickness
F Sig.
Levene's Test f or
Equality of Variances
t df Sig. (2-tailed)
Mean
Dif f erence
Std. Error
Dif f erence Lower Upper
95% Conf idence
Interv al of the
Dif f erence
t-test for Equality of Means
89
Avg thickness 54 8 21.964436 1.85499819 .65584090
40 3 14.545026 .54276366 .31336474
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Independent Samples Test
Levene's Test for Equality of Variances t-test for Equality of Means
F Sig. t df Sig. (2-tailed) Mean Difference
Std. Error Difference
95% Confidence Interval of the Difference
Lower Upper Lower Upper Lower Upper Lower Upper Lower
Avg thickness Equal variances assumed
4.482 .063 6.619 9 .000 7.41941042 1.12101029 4.8835089 9.9553118
Equal variances not assumed
10.207 8.932 .000 7.41941042 .72685951 5.7732211 9.0655996
Conclusion: Significance (p-value) is less than α, reject H0 at 0.05 level. The two means are significantly different.
Experiment number 54 and 44.
90
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Independent Samples Test
Levene's Test for Equality of Variances t-test for Equality of Means
F Sig. t df Sig. (2-tailed) Mean Difference
Std. Error Difference
95% Confidence Interval of the Difference
Lower Upper Lower Upper Lower Upper Lower Upper Lower
Avg thickness Equal variances assumed
5.398 .039 -3.804 12 .003 -5.01108825
1.31718140 -7.8809799
-2.1411965
Equal variances not assumed
-3.538 7.692 .008 -5.01108825
1.41654725 -8.3005888
-1.7215876
Conclusion: Significance (p-value) is less than α, reject H0 at 0.05 level. The two means are significantly different.
Group Statistics
8 21.96444 1.85499819 .65584090
6 26.97553 3.07552807 1.255579
Exp
54
44
Av g thickness
N Mean Std. Dev iation
Std. Error
Mean
91
Experiment 54 and 42:
Group Statistics
Exp N Mean Std. Deviation Std. Error Mean
Avg thickness 54 8 21.964436 1.85499819 .65584090
42 3 11.054539 .81220533 .46892696
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Independent Samples Test
Levene's Test for Equality of Variances t-test for Equality of Means
F Sig. t df Sig. (2-tailed) Mean Difference
Std. Error Difference
95% Confidence Interval of the Difference
Lower Upper Lower Upper Lower Upper Lower Upper Lower
Avg thickness Equal variances assumed
2.917 .122 9.591 9 .000 10.9098970 1.13747469 8.3367505 13.483043
Equal variances not assumed
13.532 8.349 .000 10.9098970 .80623804 9.0641600 12.755634
Conclusion: Significance (p-value) is less than α, reject H0 at 0.05 level. The two means are significantly different.
92
Experiment 54 and 58:
Group Statistics
Exp N Mean Std. Deviation Std. Error Mean
Avg thickness 54 8
21.9644368
1.85499819 .65584090
58 16 8.5368718 1.20762980 .30190745
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Independent Samples Test
Levene's Test for Equality of Variances t-test for Equality of Means
F Sig. t df Sig. (2-tailed) Mean Difference
Std. Error Difference
95% Confidence Interval of the Difference
Lower Upper Lower Upper Lower Upper Lower Upper Lower
Avg thickness Equal variances assumed
2.931 .101 21.454 22 .000 13.4275649 .62588125 12.129566 14.725563
Equal variances not assumed
18.598 10.070 .000 13.4275649 .72199404 11.820377 15.034752
Conclusion: Significance (p-value) is less than α, reject H0 at 0.05 level. The two means are significantly different.
93
Experiment number 37 and 54:
Level of significance α=0.05
H0: µ1=µ2
H1: µ1≠µ2
Conclusion: Significance (p-value) is less than α, reject H0 at 0.05 level. The two means are significantly different.
Group Statistics
3 8.2419487 .95039505 .54871084
8 21.96444 1.85499819 .65584090
Exp
37
54
Av g thickness
N Mean Std. Dev iation
Std. Error
Mean
Independent Samples Test
2.252 .168 -11.950 9 .000 -13.72249 1.1483279 -16.3202 -11.1248
-16.048 7.451 .000 -13.72249 .85510869 -15.7199 -11.7250
Equal variances
assumed
Equal variances
not assumed
Av g thickness
F Sig.
Levene's Test f or
Equality of Variances
t df Sig. (2-tailed)
Mean
Dif f erence
Std. Error
Dif f erence Lower Upper
95% Conf idence
Interv al of the
Dif f erence
t-test for Equality of Means
94