Alkaline Pressure Oxidation of Pyrite in the Presence of ......Anirudha Dani Masters of Applied...

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 -


1.25 15.98 -

41


2.5 22 -


5 5.38 -

42


7.5 8.32 -


10 5.46 -

43


12.5 3.24 -


2.5 8.35 4 g/L Al2(SO4)3

44


2.5 14.54 0.021 g/L D-618


2.5 11.07 0.021 g/L D-709

45


2.5 26.9 0.021 g/L D-619


2.5 22.53 3 hr test

46


5 8.87 -


5 11 Flashed

47

Appendix B – XPS Spectra


0 2.22 -

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


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


1.25 15.98 -

52



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


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


2.5 22 -

55



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


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


7.5 22 -

58



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


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


Al2p A 74.13 2.19 13499.42 19.34 0.537

Al Total 20.75


10 5.46 -

62



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


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


2.5 8.35 4 g/L Al2(SO4)3

65



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


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


2.5 14.54 0.02 g/L D-618

68



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


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


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


2.5 11.07 0.02 g/L D-709

72



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


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


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


2.5 26.9 0.02 g/L D-619

76



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


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


5 5.38 -

78



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


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


5 60 Flashed

81



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


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.


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


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.


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


Std. Error

Mean


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



Mean

Dif f erence

Std. Error


95% Conf idence

Interv al of the

Dif f erence


89

Avg thickness 54 8 21.964436 1.85499819 .65584090

40 3 14.545026 .54276366 .31336474


H0: µ1=µ2

H1: µ1≠µ2


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


H0: µ1=µ2

H1: µ1≠µ2








5.398 .039 -3.804 12 .003 -5.01108825

1.31718140 -7.8809799

-2.1411965


-3.538 7.692 .008 -5.01108825

1.41654725 -8.3005888

-1.7215876


Group Statistics

8 21.96444 1.85499819 .65584090

6 26.97553 3.07552807 1.255579

Exp

54

44

Av g thickness


Std. Error

Mean

91

Experiment 54 and 42:

Group Statistics


Avg thickness 54 8 21.964436 1.85499819 .65584090

42 3 11.054539 .81220533 .46892696


H0: µ1=µ2

H1: µ1≠µ2








2.917 .122 9.591 9 .000 10.9098970 1.13747469 8.3367505 13.483043


13.532 8.349 .000 10.9098970 .80623804 9.0641600 12.755634


92

Experiment 54 and 58:

Group Statistics


Avg thickness 54 8

21.9644368

1.85499819 .65584090

58 16 8.5368718 1.20762980 .30190745


H0: µ1=µ2

H1: µ1≠µ2








2.931 .101 21.454 22 .000 13.4275649 .62588125 12.129566 14.725563


18.598 10.070 .000 13.4275649 .72199404 11.820377 15.034752


93



H0: µ1=µ2

H1: µ1≠µ2


Group Statistics

3 8.2419487 .95039505 .54871084

8 21.96444 1.85499819 .65584090

Exp

37

54

Av g thickness


Std. Error

Mean


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



Mean

Dif f erence

Std. Error


95% Conf idence

Interv al of the

Dif f erence


Alkaline Pressure Oxidation of Pyrite in the Presence of ......Anirudha Dani Masters of Applied...

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