Dissertation Final copy

Alkaline Extraction of Brucite from Olivine using methylated amines.

Charlotte Tutton

School of Earth and Ocean Science,

Cardiff University, Main Building Cardiff CF10 3AT

Declaration

This work has not been previously accepted in substance for any degree and is not being

concurrently submitted in candidature for any degree.

Signed:

Date:

Statement

This dissertation is being submitted in partial fulfilment of the requirements for the degree of

Master of Earth Sciences.

Signed:

Date:

Statement

The dissertation is a result of my own independent work, except where otherwise stated

Signed:

Date:

3

ABSTRACT

This paper investigates using methylated amines as the source of alkalinity for digestion. This

is in order to extract brucite from olivine. Which can then be used to sequester atmospheric

CO2, in turn helping to reduce impacts of climate change from CO2 emissions. Methylated

amines were selected as due to their low boiling points these materials could be recycled

through fractional distillation process reducing the overall cost of alkaline digestion process

as a CCS (Carbon capture storage) technology. Olivine was reacted with triethylamine and

with tripropylamine using different reaction temperatures (20°C, 50°C, and 80°C) and

different reaction durations (24 hours and 2 weeks). Analysis included measurement of pH

change, thermogravimetric analysis and X-Ray Diffraction (XRD) analysis. During the

reaction pH of the reactants decreased indicating changes in the chemistry of reaction solution

and therefore reactions taking place. XRD analysis showed that the reactions were removing

brucite from the olivine. Potentially transforming it in other minerals or dissolving it into the

solution. Not the desirable effect. Some brucite appeared in products of the reaction procedure

however formation of brucite cannot be conclusively confirmed from the XRD results.

Therefore it appears that methylated amines are not viable options for alkaline digestions

potentially due to safe range of reaction temperatures being considerably lower than those

used in other experiments. Future research should focus on finding an alkaline material that is

effective in extracting brucite and that has the ability to effectively be recycled in the process.

4

Contents

ABSTRACT..........................................................................................................................................4

1. INTRODUCTION........................................................................................................................8

1.1 The problem with Carbon Dioxide (CO2) Emissions...............................................................8

1.2 Definition of Carbon Capture and Sequestration (CCS).........................................................9

1.3 Carbon Capture Technologies...................................................................................................9

1.3.1 Post Combustion Technologies............................................................................................10

1.3.2 Oxyfuel combustion capture................................................................................................11

1.3.3 Pre Combustion Technologies.............................................................................................12

1.1.3.4 Chemical looping combustion (CLC)................................................................................13

1.4 Carbon Sequestration/ Storage Technologies.........................................................................15

1.4.1 Ocean Sequestration............................................................................................................15

1.4.2 Geological Sequestration.....................................................................................................18

1.4.3 Terrestrial Sequestration.....................................................................................................20

1.4.4 Mineral Carbonation...........................................................................................................22

1.4.5. Brucite Extraction...............................................................................................................25

1.5 Proposed investigation.............................................................................................................26

2. METHODOLOGY.........................................................................................................................28

2.1 Materials...................................................................................................................................28

2.1.1 Olivine.................................................................................................................................28

2.1.2 Methylated Amines..............................................................................................................29

2.2 Methods.....................................................................................................................................30

2.2.1 Experimental Procedure......................................................................................................30

2.2.2 Gravimetric Analysis...........................................................................................................33

2.2.3 XRD Analysis.......................................................................................................................34

3. RESULTS........................................................................................................................................36

3.1 pH change.................................................................................................................................36

3.2 Thermogravimetric analysis....................................................................................................40

3.3 Colour Changes........................................................................................................................45

3.4 XRD Analyses...........................................................................................................................47

4. DISCUSSION.................................................................................................................................57

5. CONCLUSIONS.............................................................................................................................61

REFERENCES...................................................................................................................................62

ACKNOWLEDGEMENTS...............................................................................................................66

5

APPENDICES....................................................................................................................................67

Table of Figures

Figure Page 1.1 Post Combustion CO2 capture 111.2 Oxyfuel CO2 capture process 111.3 Gasification process 131.4 Chemical looping combustion process 141.5 Summary of Direct and Indirect carbonation methods 231.6 Extraction of brucite from olivine using NaOH 261.7 Proposed reaction mechanism 272.1 Images of experimental procedure equipment 312.2 Images of pH meters used 322.3 Image of Vecstar LF3 muffler furnace used 333.1 Demonstration of Colour change at 1000°C 453.2 Demonstration of Colour change at 500°C 453.3 Summary of reactions observed from olivine specimen with 53% Fayalite 463.4 Diffractogram of control olivine sample , dried 473.5 Diffractogram of control olivine sample , heated to 500°C 483.6 Diffractogram of control olivine sample , heated to 1000°C 483.7 Diffractogram of olivine treated with triethylamine sample , dried 503.8 Diffractogram of olivine treated with triethylamine sample , heated to 500°C 503.9 Diffractogram of olivine treated with triethylamine sample , heated to 1000°C 513.10 Diffractogram of control olivine sample treated with tripropylamine , dried 523.11 Diffractogram of control olivine sample treated with tripropylamine , 500°C 533.12 Diffractogram of control olivine sample treated with tripropylamine , 1000°C

53

6

Abbreviations

CCS Carbon Capture Storage

XRD X-Ray Diffraction

GHG Greenhouse Gas

HNLC High Nutrient- Low Chlorophyll

MEA Monoethanolamine

XRF X-ray Fluorescence

GWP Global Warming Potential

PCO2 Partial pressure of CO2

BP Biological Pump

OIF Ocean Iron Fertilization

DSF Deep Saline Formation

EOR Enhanced Oil Recovery

ECBM Enhanced Coalbed Methane

recovery

IPCC Intergovernmental Panel on

Climate Change

Me Metal

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INTRODUCTION

1. INTRODUCTION

Introduction to the problem Definition of CCS technologies Capture Capture Technoligies Capture Sequestration methods Proposed Investigation

1.1 The problem with Carbon Dioxide (CO2) Emissions

“Irreversible does not mean unavoidable” H.D.Matthews and S. Solomon. (2013) stated that

the effects of anthropogenic emissions of CO2 are “irreversible on a timescale of at least the

next 1000 years” (Matthews and Solomon 2013). By now it is well known that anthropogenic

CO2 emissions have increased the total concentration of CO2 in the atmosphere since the

industrial revolution. This is an issue because CO2 affects the climate through its interactions

as a greenhouse gas (GHG) as well as affecting ocean chemistry. Therefore it is desirable to

cut these emissions from the atmosphere preferably down to zero. However even if we were

to cut all emissions to zero it will take hundreds of years for the levels to stabilise back to pre-

industrial levels, hence effects have been said to be irreversible for at least the next 1000

years. This is partially due to long residence times in certain parts of the carbon cycle such as

the oceans, vegetation and ice. CO2 can take a long time to get into stable parts of the carbon

cycle such as those with long residence times where it can be stored. The oceans-atmosphere

interface for carbon is at near equilibrium, therefore removing carbon dioxide from the

atmosphere may instigate a shift in equilibrium, causing CO2 to go from the oceans back into

the atmosphere until a new equilibrium is established. In order to return levels back to

preindustrial times, the anthropogenic CO2 that has been built up in the atmosphere and

oceans needs to be actively removed and permanently stored. This is where carbon capture

and sequestration (CCS) technologies come into play. CCS technologies are a portfolio of

different mechanisms which aim to remove CO2 from the atmosphere and sequester it

permanently and safely. These methods may prove essential given our previous failures in

reducing CO2 emissions, to stabilize or lower historically unprecedented global atmospheric

CO2 levels and associated effects on climate and ocean chemistry (Rau and Lackner 2013).

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INTRODUCTION

1.2 Definition of Carbon Capture and Sequestration (CCS).

Carbon Capture and Sequestration is a broad term that includes a portfolio of different

technologies. It could be thought to be separated into two parts the capture and sequestration.

It can be separated in this way as not all carbon that is captured is sequestered. Some of it is

recycled for beneficial reuse in industry such as in enhanced oil recovery. The term capture

can be used to describe the separation and concentration of CO2 from flue gases or the

ambient air. Research in this area primarily focuses on capture of CO2 from flue gases from

power stations or similar industries. This is because these are major sources of CO2 emissions.

There are also some technologies that are being developed to separate CO2 from the ambient

air but they are generally more costly. Carbon sequestration is defined by the oxford

dictionary as “a natural or artificial process by which carbon dioxide is removed from the

atmosphere and held in solid or liquid form.” There are many different reservoirs that have

been investigated as mediums to sequester carbon, including the ocean, geological formations,

vegetation, soils and minerals as well as artificial sequestration reservoirs. Some technologies

seek to increase the capacity and uptake by natural systems by methods such as ocean

fertilization, forestation and increasing photosynthesis. In addition, some methods try to

mimic natural processes such as mineral carbonation. Furthermore, others see the systems

merely as storage vessels, for example, underground injection into geological formations or

the oceans where carbon used to be stored.

1.3 Carbon Capture Technologies

The main source of CO2 into the atmosphere is fossil fuel power stations. These power

stations emit over 30% of anthropogenic CO2 into the atmosphere. They can be considered as

point sources of emissions to the atmosphere. The flue gases from the combustions processes

have CO2 concentrations much higher than the ambient air. Therefore it makes it is logical to

capture this CO2 before it reaches the atmosphere as it is easier to remove a substance present

in high concentrations than low concentrations due to the energy required. It makes it a lot

more cost effective to remove CO2 from the flue gases. There are two options for uses of the

captured CO2. The first is finding beneficial reuse for the CO2, this could be as a fuel or as a

part of a chemical reaction in an industry. The second option is to sequester the CO2 storing it

permanently and safely so it can no longer contribute to atmospheric CO2 emissions. The

sequestration is more favourable with regard to cutting CO2 emissions however if profit can

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INTRODUCTION

be made through beneficial reuse then it is more likely to be the preferred option. There are

several different methods for capturing CO2 from power stations. These are post combustion

technologies, pre combustion technologies, oxyfuel combustion and Chemical looping

combustion they are further explained in the sections 1.3.1-1.3.4 below.

1.3.1 Post Combustion Technologies

Post combustion technologies involve separation of CO2 from flue gases after combustion has

taken place. This is shown in Figure 1.1 which shows fuel and ambient air being combusted to

produce energy and flue gases. These flue gases are then transported to a CO2 separation step

where the CO2 is removed from the gas stream and stored. There are several options for the

CO2 separation step including adsorption, absorption, membrane and biotechnology options.

The most commonly used is the absorption/stripping process using Monoethanolamine

(MEA). It has been used for 60 years in the natural gas industry and Produces a CO 2 recovery

rate of 98% using MEA (Yamasaki 2003). The adsorption is based on the same principle but

uses a porous solid such as activated carbon or zeolites. Chemical reactions may occur

between adsorbent and CO2 during the separation process and mainly uses pressure and

temperature swing processes. Membrane separation is expected to have an advantage over

other process due to increases in efficiency (Damle and Dorchak 2001; Xu et al. 2001) as

highly selective polymeric membranes can be developed to separate just CO2 from the

atmosphere. The main issue with these processes is the use of chemicals adsorbents or

absorbents can have high capital costs. Therefore in order to make this process cost efficient

ways for recycling or reusing these chemicals to keep costs low is essential. Moreover, the

concentrations of the CO2 in the flue gases are relatively low and other products need to be

separated such as NOx, SO4 and particulates.

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INTRODUCTION

1.3.2 Oxyfuel combustion capture

The process of oxyfuel combustion is demonstrated in figure 1.2. The first step of this process

is air separation. This step removes the nitrogen from the air causing the air to have a high

concentrations of Oxygen (O2) with minor constituents of other gases. This O2 rich air is used

as the oxygen and air source in combustion keeping the furnace temperature below the

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Figure (1.1) - Post combustion CO2 capture. Adapted from (Feron and Hendricks 2005)

CO2

Flue Gas

Fuel

Power

Air

CO2

Separation Energy

Conversion

INTRODUCTION

allowable point. Removing the nitrogen before combustion gets rid of the need for NOX

control equipment and makes the separation of CO2 easier. The resulting flue gas is mainly

comprised of CO2 and water (H2O) however there are still particulates and sulphur products

that require removal. These can be removed by a number of well-established technologies

such as baghouse filtration where the large particles are filtered out using a series of specially

designed filters. One issue with this technology is that there is increased erosion from high

Sulphur Dioxide (SO2) concentrations in flue gases. After the SO2 and particulates have been

removed, the exhaust gas stream is approximately 90% CO2 by volume on a dry basis (Yang

et al. 2008). Further separation of CO2 is not necessary and the CO2 can then be compressed

for storage or transportation. Although this removed need for NOX control technologies

Nitrogen (N2) still needs to be removed from the air; which could be costly. However the flue

gases that have been treated could potentially be recycled, cutting down the amount of

nitrogen that needs to be removed.

1.3.3 Pre Combustion Technologies

Precombustion technologies constitute of technologies that remove the CO2 before the

combustion occurs. This can essentially be described as removing CO2 from ambient air. The

idea behind this is that the energy conversion process does not involve combustion of carbon,

it uses fuel that does not contain carbon such as pure hydrogen gas. There are many different

process being developed, one of the most common is gasification described below.

An overview of the gasification is shown in figure 1.3. The first step of this reaction is fuel

conversion which is where the gasification process comes into play. In this step fuel such as

coal is partially oxidised. This produces a gaseous fuel that can be used for combustion and is

primarily comprised of CO2 and H2 and is commonly known as syngas. The CO2 in this

gaseous fuel is then removed by one of a number of separation techniques such as those

described for post-combustion processes as described in section 1.3.1 The remaining fuel

comprised of primarily H2 is then used as a fuel in a gas turbine or in fuel cell systems in

order to produce electricity.

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INTRODUCTION

1.1.3.4 Chemical looping combustion (CLC)

Chemical looping combustion is a process that prevents direct contact between combustion air

and fuel. Figure 1.4 illustrates how this process works. The air and fuel are separated into

separate reactors. The only thing passing between the reactors are metals in their normal and

oxidised forms. These metals act as an oxygen carrier in a fluidised bed system between the

two reactors. First of all metal oxides are produced in the air reactor. During this reaction the

metals are oxidised by air comprised of primarily N2 and O2. This is described by the reaction

below.

O2 + 2Me > 2MeO Where Me = Metal

This metal oxide is then injected into the fuel reactor fluidised bed system where it acts as the

oxygen source for combustion. In the process the metal oxide is turned back into a metal

which can then be recycled back into the air reactor and the process repeats again. The

reaction that occurs in the fuel reactor is shown below

CnHm + (2n + 1/2m) MeO > nCO2 +1/2m H2O + (2n + 1/2m) Me Where Me= Metal

The advantage of CLC over other reactions is that the flue gases produced from the fuel

reactor is primarily comprised of CO2 and H2O with the CO2 concentration being high. This

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Figure (1.3) - Gasification CO2 capture process. Adapted from (Feron and Hendricks 2005)

Fuel

Air

Flue CO2

H2

Air

Fuel Conversion

CO2

SeparationEnergy Conversion Power

INTRODUCTION

CO2 can then be separated from the flue gas using separation techniques such as those

described in the post combustion processes. In addition, if the CO2 concentration is high

enough it could even be separated by a condenser. Other advantages include no thermal

formation of NOx due to the low temperatures used and lack of a flame. (Yang et al. 2008).

All of these methods are important in preventing emissions to the atmosphere and they can be

considered as zero carbon technologies where the CO2 is no longer being emitted to the

atmosphere. What is important is the fate of the captured CO2. Ideally the captured CO2 will

be sequestered to prevent further emissions to the atmosphere. In order to reduce CO2 levels

back to preindustrial levels it is important that methods that remove carbon from ambient air

are developed to remove built up CO2 and not just zero emissions. Introduction of carbon

sequestration technologies including ones that remove CO2 from the ambient air are described

in the next section (Section 1.4).

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Figure (1.4) Chemical looping combustion process. Adapted from Ryden and Lyngfelt 2006. Me – Metal.

Products (CO2,

Fuel (CnHm)

MeO

Me

Air (N2,

Depleted air

Fuel ReactorAir Reactor

INTRODUCTION

1.4 Carbon Sequestration/ Storage Technologies

The Intergovernmental Panel on Climate Change (IPCC 2013) defines carbon sequestration as

the addition of carbon containing substances to a reservoir, e.g., the ocean, which has the

capacity to store, accumulate or release carbon. The aim of which is too permanently and

safely store CO2. This process is essential if we are to reduce atmospheric CO2 levels to pre-

industrial levels before damaging irreversible effects can occur. The main issue with this is

the costs involved as well as potential environmental impact with the various processes that

have been developed. Scientists are always trying to find new ways to improve the cost

effectiveness and efficiency of the processes. The ideal process would require low levels of

energy, chemicals, maintenance and sequester large amounts of CO2. Some technologies even

use the process to create new materials that are useful such as building materials or are

incorporated into processes that also get rid of other problems such as using waste materials

as a reservoir to store carbon into. This section discusses the major sequestration technologies

that have been developed including ocean, geological, terrestrial and mineral carbonation

techniques.

1.4.1 Ocean Sequestration

1.4.1.1 The ocean as a carbon reservoir

The ocean absorbs approximately 30% of anthropogenic CO2 (IPCC 2013). This offsets the

increase of CO2 in the atmosphere in a profound way. The oceans are the second largest

reservoir in the carbon cycle and contain about 38,000 Gt-carbon, with about 1.7±0.5 Gt taken

up annually from the atmosphere (Yamasaki 2003).The amount of carbon taken up by the

oceans depends on a number of factors; mainly partial pressure of CO2 in the atmosphere,

ocean chemistry and rates of primary production. It is well known that the ocean-atmosphere

interface is at near equilibrium. This means that as the CO2 concentration in the atmosphere

increases the ocean will uptake carbon from the atmosphere in order to try and reach

equilibrium as described by le Chatelier's principle (Le Chatelier 1898). This uptake of carbon

has an effect on the ocean chemistry, in particular the inorganic carbon system, which acts to

buffer the ocean. However, input of CO2 is thought to be lowering the pH of the ocean water

causing ocean acidification. This in turn can cause the destruction of pH sensitive organisms

such as those using Calcium Carbonate (CaCO3) shells whose shell formation acts as

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INTRODUCTION

biological form of carbon sequestration which could potentially lead to a reduction in uptake

of CO2 used for shell growth. The partial pressure of CO2 in the atmosphere cannot be directly

changed very easily and would require input of more CO2 into the atmosphere. The act of

doing so would counteract the purpose of carbon sequestration therefore the focus of carbon

sequestration technologies is to alter the ocean chemistry and/or the biological carbon

sequestration in the oceans.

1.4.1.2 Direct Injection

Direct injection into the ocean requires relatively pure CO2 streams. These are usually

produced by power or chemical plants and then transported to the injection point. There are

several methods for injection including methods that involve dissolution, dispersion and

isolation of the CO2 in the ocean. Pressures and temperatures need to be taken into

consideration when developing methods, as the state of the CO2 changes dependant on these

parameters. The state of the CO2 can control its buoyancy and determine at which depths it

should be injected. The major issue with this method is trying to account for the

environmental impacts of this input of CO2 on the ocean chemistry - particularly pH. Impacts

would occur principally to non-swimming marine organisms residing at depths of about

1000m or greater and their magnitude will depend on both the level of pH change and the

duration of exposure. This mechanism should promote efficient mixing and dispersal of the

CO2 where it is injected to avoid pockets of lethally high CO2 concentrations. For this to be a

viable technique most research must be done in the areas of ocean modelling, environmental

assessment and engineering analysis to ensure this method does not cause more harm than

good.

1.4.1.3 Shifting pH using Alkaline Material

One of the ideas for modifying and increasing the uptake of CO2 by the oceans is to input

large amounts of alkali material into the ocean to shift the pH to a more alkaline pH. This in

turn will absorb more CO2 to buffer the pH using the carbonate/hydrocarbonate system to

produce more H+. Materials that have been suggested include magnesium, sodium, calcium

oxide or hydroxide. These would let the atmosphere-ocean gas exchange pull carbon dioxide

directly from the air. (Lackner 2002). By adding alkalinity to the surface water a constant

Pco2 could be maintained effectively removing CO2 from the air. Alternatively long term you

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INTRODUCTION

could help maintain a constant pH or carbonate concentration to minimize impacts of

increasing CO2 on surface waters. (Lackner 2002) However more research needs to be done

into the environmental impacts, effectiveness and relative cost of implementing these projects

on the large scales they would need in order to have a significant effect on atmospheric CO2

levels.

1.4.1.4 Biological carbon sequestration in the oceans

One way that the ocean naturally uptakes carbon is through the biological pump (BP). The BP

describes a suite of process by which CO2 that is fixed by phytoplankton at the surface gets

transported into the deep ocean where it can be stored (Jiao 2014). Part of the carbon would

be released back into the atmosphere by respiration and the remaining would descend into the

deeper ocean in the form of particulate organic matter either by the death of phytoplankton or

after grazing (Yang et al. 2008). It has been suggested that by increasing the nutrient supply

for these organisms the amount of primary productivity will increase and more carbon will

become sequestered, (Yang et al. 2008). However, this needs to be carefully calculated as

large increases in amount of phytoplankton could cause algal blooms affecting light

penetration in the water column and the ecosystem.

One of the proposed mechanisms for enhancing biological carbon sequestration is through

ocean fertilization. This involves inputting materials that contain limiting nutrients into the

ocean. The nutrients used are highly dependent on the ocean chemistry in that region. In

regions that receive a lot of nutrients from upwelling’s or terrestrial inputs it is often the

micronutrients that are the limiting nutrients. The main three nutrients that have been

researched are Nitrogen (N), Phosphorus (P) and Iron (Fe) which happen to be the three main

elements that inhibit phytoplankton growth (Woodward 2009). Numerous experiments have

been carried out adding iron to oceans (Ocean iron fertilization (OIF)) that have high nutrient

and low chlorophyll environments. There are many different proposals of the sources of this

iron with the main focus being on Iron Sulphate (FeSO4). One of the most interesting

suggested source of this iron is using mine water that is natural rich in iron and have some of

the highest iron concentrations on earth as well as being an environmental problem that needs

to be dealt with (Hedin & Hedin, 2015). The current Fe source for OIF projects is ferrous

sulphate heptahydrate (FeSO47H2O), which has a 20 % Fe content. Oxidative mine water

17

INTRODUCTION

treatment technologies can produce solids with 50–55 % Fe content, which could substitute

for FeSO47H2O in fertilization projects (Hedin & Hedin 2015). As irons involvement in

photosynthesis is enzymatic, a small addition of Fe can result is a very large increase in

primary production (Morel et al. 1991). In the laboratory studies of Fe-starved phytoplankton

cultures, additions of 1g of dissolved Fe were found to result in 30,000–100,000g of C

fixation (Buesseler and Boyd 2003). The results of all OIF experiments to date, indicate that

Fe fertilization of High Nutrient Low Chlorophyll (HNLC) ocean waters initiates a

phytoplankton bloom that increases primary production. If the bloom is dominated by

diatoms, a significant portion of the fixed C can settle to the ocean floor and are considered

sequestered. Blooms dominated by non-siliceous phytoplankton are heavily grazed and do not

provide sequestration benefits. Instead, the fixed C is incorporated into the food chain and

potentially increases the productivity of the location marine ecosystem.

Although these ocean methods seem technically feasible methods of sequestering large

amounts of CO2 they are limited by the potential environmental issues that could occur, most

of which involve disturbing chemical and biological processes in the ocean which could lead

to the death of many organisms within the food chain. In order to implement these techniques,

careful modelling and planning would need to be carried out in order to prevent

environmental impacts. For these reasons, other methods that have less environmental impacts

particularly focusing on water chemistry and living creatures are often favoured.

1.4.2 Geological Sequestration

Geology is the biggest reservoir in the carbon cycle. The main type of geological formations

of interest are sedimentary rocks. This is because they contain a larger amount of pore space

than other rock types and therefore have the capacity to store more CO2. The basic idea

behind geological sequestration is to trap CO2 in natural geological traps. The traps must

consist of a porous permeable rock reservoir overlain by an impermeable layer of cap rock.

These formations are often associated with locations you will find fossil fuels, so in a way

geological sequestration can be thought as returning the CO2 back to where it came from.

These formations must have the capacity to hold and store the carbon permanently and safely.

This means when determining whether a geological trap can be used for carbon storage a

number of factors need to be considered. These include the capacity, depth, porosity and leak

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INTRODUCTION

potentials of the trap. There are four main trapping mechanisms for CO2. These are structural,

residual, dissolution and mineral trapping. Structural trapping is where the CO2 rises through

the trap until it reaches the cap rock where it is prevented from migrating upwards. This leads

to a higher concentration of CO2 at the porous-cap rock interface, however travelling up to

this interface it may be trapped by other mechanisms. Residual trapping is where the CO2 gets

stuck in the pore spaces of the porous rock and becomes immobilized. Dissolution traps are

also known as solubility trapping, is where the CO2 dissolves in the water contained within

the formation this is more prominent in Deep saline formation (DSF) injection. This water

then becomes denser and sinks to the bottom of the formation. Finally, mineral trapping

occurs when dissolved CO2 forms carbonic acid in the water and reacts with the surrounding

rock to create carbonate minerals.

The main environments with which carbon is stored are Deep Saline Formations (DSF),

Depleted gas formations, depleted oil basins and deep unmineable coal seams. All of these

systems have the porous and cap rock systems in place. With regards to the depleted oil and

gas formations there may be equipment on site that was used to deplete these formations

which could be reused to inject CO2 into them. This will reduce the costs of injection as there

is likely to be a lot already known about the geology of the area. In some of the systems

primarily, depleted oil basins and deep unmineable coals seams, CO2 injection can be used to

recover more fossil fuel whilst storing the carbon which would help reduce the costs of the

operation as any fuels recovered can used or sold in the process. They are known as Enhanced

Oil Recovery (EOR) and Enhanced Coalbed Methane (ECBM) recovery respectively. The

idea behind this is that the injection of CO2 into existing oil fields will release oils and gases

from the formation. Then the released oils and gases will be moved towards and extracted by

extraction wells. Any CO2 that is extracted is separated and then reinjected into the formation.

Deep saline aquifers have very little economic use with regards to being a water source as

treatment for salinity is expensive, especially at such great depths. Therefore using them as

reservoir to inject CO2 into will not affect the potable water supplies if it is monitored and

managed correctly. All of these techniques need careful monitoring and planning in order for

environmental impacts to be controlled and for effective sequestration.

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INTRODUCTION

Geological sequestration receives a lot of attention from public media, not all positive. Many

people disagree with these methods as they would rather there be more focus on moving away

from the fossil fuel industry. Moreover, some of these methods are thought to be associated

with geologically disturbances such as contamination of water resources and triggering of

tremors in some cases. In addition, though these methods use technologies already developed

by the oil industry these processes are still expensive to run relative to other methods. This is

partially due to the large amount of maintenance required to prevent CO2 leaking or polluting

potable groundwater. Therefore sequestration methods that have less maintenance costs and

have less chance of producing contamination or other negative impacts are more popular. This

could potentially be solved by creating systems that mimic geological traps without the need

for injection underground though ex-situ geological sequestration which is likely be

expensive.

.

1.4.3 Terrestrial Sequestration

Terrestrial sequestration describes the action of storing carbon within the vegetation and soils

of the planet. There are two main methods currently being implemented. These are soil carbon

sequestration and afforestation.

1.4.3.1 Soil Carbon Sequestration

The soil is the third largest carbon pool on this planet (Woodward et al. 2009). It is estimated

to contain 2,500 petagrams (Pg.) C to one meter depth, and together with vegetation contains

some 2.7 times more C than the atmosphere. (Lal 2008). Most of this carbon is stored in the

form of organic matter and there is concern that warming temperatures will increase the rates

of microbial degradation of this organic matter leading to the emittance of CO2 as opposed to

the uptake (Woodward et al. 2009). It has been suggested that by better managing our

agriculture and degraded soils and returning them to a less disturbed state, more CO2 could be

sequestered. The amount of C contained in soil is determined by the balance between C input,

via primary productivity, and output, via decomposition processes, burning and soil erosion

(De Deyn et al. 2008). The use of soils for agriculture has vastly decreased the carbon content

of these soils and increased CO2 emissions.

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INTRODUCTION

A number of different mechanisms have been proposed to increase the amount of carbon in

agricultural soils. This includes adoption of no tillage agriculture which limits soil disturbance

(Cerri et al, 2004), the conversion of arable lands to perennial grassland which causes a build-

up of organic matter (McLauchlan et al. 2006) and the use of cover crops in rotations. (Lal

2004). Also the use of fertiliser to increase plant production and litter addition to soil can lead

to an increase in CO2 uptake. However this could also increase the microbial degradation of

organic matter by providing substrates for microbes. Many of the proposals above are

relatively straightforward and can improve the soil fertility in addition to increased CO2

uptake but could also lead to emissions of other substances such as N2O which has a much

higher Global warming potential (GWP) than CO2. In order for these methods to be

effectively implemented more needs to be known about interactions between plants, microbes

and the atmosphere. Precise modelling of this process is needed.

One method however does stand above the rest as an option. The introduction of biochar to

soils as a soil amendment. This combines soil sequestration with another approach to mitigate

climate change. In this case using the by-product of biofuel and bioenergy production by

pyrolysis. The idea being that because the biochar has a long residency time due to stability

and resistance to microbial decomposition therefore its addition to the soil will store CO2 in

the soil and act as long term carbon sink. It has also been thought that it can improve soil

fertility and crop production (Lehmann 2007). However there is still much uncertainty of the

effectiveness of this and more research still needs to be carried out (Woodward et al. 2008).

1.4.3.2 Afforestation

Deforestation since the industrial revolution is thought to have a significant effect on

atmospheric CO2 concentrations. The question is could restoring the global forests influence

the atmospheric CO2 concentration significantly? Simulations such as the Sheffield dynamic

global vegetation model aim to answer this question. A series of models that used the

emissions scenario “business as usual” where emissions continue at the same rate showed that

afforesting all the areas possible would reduce the temperature in 2050 by 0.74°C and reduce

CO2 concentrations by 76 ppm. This temperature decrease would have been higher at

approximately 2°C if it was not for the series of negative feedbacks afforestation would cause.

These included reduction of the carbon content in soils due to a reduction in leaf litter,

21

INTRODUCTION

reducing ocean carbon sequestration through lowering pCO2 and finally decreasing the albedo

effects by covering land with high albedo such as produced by snow cover in high latitude

forests. The different modelling approaches indicate that global scale afforestation would

have very limited impacts on global temperature change over the next 50 years, with a

business as-usual scenario of CO2 emissions. This is mainly due to the negative feedbacks

already mentioned. (Woodward et al. 2008)

The issues with terrestrial carbonation are primarily due to the large agricultural demand to

feed the population of this planet. In order to be effective, large amounts of agricultural land

would be put out of commission in order to return the CO2 lost to the soils. Land that is used

for agriculture needs to be left undisturbed for extended periods of time. Although agricultural

technologies are still being developed such as polyethene greenhouses, in areas like Almeria

where the plants grow without the need for conventional soils, the world's population is still

heavily reliant on more intensive agricultural methods. This pressure will only grow as

population increases. Therefore, these methods are not the sole solution to removing

atmospheric carbon from the atmosphere although they can contribute towards this goal when

combined with other technologies that can be implemented on a larger scale.

1.4.4 Mineral Carbonation

Mineral carbonation is the act of reacting CO2 with minerals in order to form environmentally

stable carbonates. This process occurs in nature due to the weathering of rocks by carbonic

acid in rainwater. The first suggestion of using minerals for carbon sequestration came from

Seifritz (1990). He suggested using silicates as a capture and storage technology for CO2. He

stated that carbon dioxide emissions to the atmosphere must be reduced and a possible way to

achieve this is to collect it and store it in empty natural gas fields or in the deep ocean. He also

suggested that “It would be advantageous if there were an abundant mineral to which the CO2

could be bound chemically to form a permanent substance” and suggested calcium silicates

may be a possible substance. Seifritz (1990) also stated the main problems are energy

requirements and producing fast enough reaction kinetics. Since this paper many different

mechanisms for carbon sequestration have been investigated. It has been stated that using

minerals to store carbon dioxide is the only form of permanent CO2 storage that seems to be

practically feasible (Azdarpour et al. 2015). Mineral carbonation can be described as in-situ or

22

INTRODUCTION

ex-situ. In situ carbonation is also known as geological sequestration and Ex-situ carbonation

involves the use of pre mined rocks and is the type of carbonation this paper will be focusing

on. The mechanisms for ex-situ carbonation can separated into two categories: direct

carbonation and indirect carbonation. The main issues mineral carbonation faces include

dissolution of materials, product layer diffusion and CO2 dissolution. A summary of the major

mechanism are described in the sections 1.4.1-1.4.4. One of the main advantages of mineral

carbonation over other carbonation techniques is that there are large amounts of natural

minerals and industrial wastes that can be utilised for carbonation. Furthermore, with the

reactions being carried out ex-situ there is little chance for environmental damage directly by

the sequestration method. When effectively sequestered there is also little change of CO2

leakage compared to the other methods. Figure 1.5 below summarises suitable feedstocks

available and an overview carbonation routes.

1.4.4.1 Direct Carbonation

Direct carbonation methods involve only one step and is thought to be the simplest approach

to carbonation. Two methods for direct carbonation included direct gas solid mineral

carbonation and direct aqueous mineral carbonation. Direct gas to solid mineral carbonation is

23

Figure 1.5 - Summary of Direct and indirect carbonation methods Adapted from Azdarpour et al 2015.

Gas-Solid

Waste Ashes

Chemically

pH swing

Stepwise

Aqueous

Indirect

Mining

Direct

Steelmaking

Cement

Olivine

Serpentine

Carbonation

Natural Industrial

Suitable

Wollastonite

Mineral

INTRODUCTION

simply the reaction of CO2 with minerals to produce carbonates such as shown in the reaction

below:

Ca/Mg- Silicate + CO2 > Ca (Ca/Mg) + SiO2

However the rate of this reaction is very slow and has all but been abandoned as it’s unlikely

to substantially reduce CO2 emissions (Olajire 2013). The experimentally obtained

carbonation conversions of direct dry Ca/Mg-silicate carbonation are still insignificant, even

at elevated pressure (Zevenhoven et al. 2002). Activation of the feedstock by heat treatment

can improve the carbonation rate, but this is still energy-consuming (Zevenhoven and

Kohlmann 2002).

Direct aqueous mineral carbonation is the reaction of CO2 with minerals in an aqueous

solution. It works due to three reactions. The first reaction being the dissolution of CO2 into

water:

CO2 + H2O > H2CO3 > H+ + HCO3-

This reaction then feeds into two other reactions. One leaching Ca/Mg from silicates:

Ca/Mg- Silicates + H+ > Ca/Mg2+ + SiO2, + H2O.

And finally production of Ca/Mg carbonates:

Ca/Mg2+ + HCO3- > Ca/MgCO3 + H+.

The limiting step to these reactions is thought to be the silicate dissolution. (Olajire 2013).

Therefore this is where the majority of research on this method focuses on improving the

kinetics of the silicate dissolution step of the reaction. Aqueous mineralisation often occurs at

faster rates than gas-solid mineralisation, however, these reactions are both often slower

compared to indirect carbonation methods with several steps. Also, the indirect methods tend

to produce higher purity products than direct methods (Azdarpour et al. 2015).

1.4.4.2 Indirect carbonation

Indirect carbonation involves process that take place over two or more steps. Methods for

mineral carbonation include indirect multistage gas-solid mineral carbonation, pH swing

process and chemically enhanced methods as illustrated in Figure 1.5.

Multistage gas-solid mineral carbonation involves dividing the gas-solid mineral carbonation

route up into several steps which is thought to improve the conversion rates. It works by first

24

INTRODUCTION

transforming Ca/Mg Silicates into Ca/Mg oxides or hydroxides. The reaction for this is

dependent on the silicate source used. Then the Ca/Mg oxides or hydroxides are reacted with

CO2 to produce carbonates. This reaction is faster that direct gas-solid carbonation however

that is at the expense of energy and chemical costs. There is not enough evidence for its

effective application to industry, this could be due to the large amounts of heat required which

increase the energy loss in the process. (Azdarpour et al. 2015)

The most popular method is the pH swing methods which consist of a twostep reaction that

uses changes in pH to control the reactions. The reactions start with a low pH to maximise the

extraction of magnesium or calcium ions used for carbonation. It is then shifted to a high pH

to facilitate the precipitation of carbonates. The ideal pH for precipitation is commonly

thought to be around 10. This produces high purity products with high carbonation rates. Most

of these methods involve the additions of strong bases to acids in order to shift the pH, though

some in-situ pH swing methods have been proposed. Investigations by Maroto-Valer et al.

(2005) showed the most effective acid to extract magnesium and calcium is Sulphuric acid

(H2SO4) for extraction from serpentine. Another method proposed by Wang and Maroto-Valer

(2011) later found the use of ammonium salts for pH swing processes and found Ammonium

bisulphate (NH4HSO4) was the most efficient for extracting Magnesium. The pH swing

method however is not without its downfalls, mainly the multiple steps involved and the

amount of chemicals consumed in the process making the method cost inefficient. However, it

has been proved to be more efficient than other mineral carbonation methods due to the low

operating temperatures and pressures required. Recovery and reuse of chemicals is therefore a

priority in future research into the method with particular focus on recyclable ammonium salts

and other chemicals that have the potential to be recycled.

1.4.5. Brucite Extraction

One technology that is of particular interest as a carbon capture storage is the extraction of

Brucite from other minerals. Brucite (Mg (OH) 2) naturally absorbs CO2 from the atmosphere

to form Magnesium carbonate. It can also absorb CO2 via dissolution in H2O and reacting

25

INTRODUCTION

purged CO2. Brucite slurries have also been successfully used to separate CO2 from gas

mixtures via liquid-gas scrubbing (Maddedu et al. 2015):

Mg (OH) 2 + CO2 -> MgCO3 + H2O

The main issue with Brucite is that the mineral is rare in nature. Therefore mechanisms for

producing brucite in an efficient and cost effective way are in demand. If an economical

method could be found, this could be a real potential method of absorbing CO2 from exhaust

flue gases.

The extraction of Brucite from magnesium silicates via chemical processing benefits from the

large availability of magnesium silicate materials. As well as having faster reaction kinetics

than carbonation of magnesium silicates. There are currently technologies available to extract

brucite from magnesium bearing minerals such as olivine and serpentine, most commonly

reactions involving acids such as solid state reactions with ammonium salts at 400-500° C or

dissolution with Hydrochloric acid (HCl) at 150°C (Madeddu et al. 2015). Both of these

methods are pH swing methods in which there are two steps the dissolution step in acidic

conditions and a precipitation step using alkaline conditions. Although these methods have

proven to be effective at extracting Mg (OH) 2 there are still high costs associated with

consumption of chemicals. In recent years procedures using alkaline digestions instead of the

pH swing method have been proposed as a more efficient single step reaction to extract

brucite.

1.5 Proposed investigation

This investigation combines the ideas from two recently published papers in order to come up

with a new reaction mechanism for alkaline digestion of olivine to produce brucite. The first

of which is by Madeddu et al. (2015) which looked into extraction of brucite from silicate

minerals using NaOH assisted with H2O where they were able to produce a yield of 64.8-

66%. The reaction mechanism of which is illustrated in figure 1.6

26

INTRODUCTION

The second paper is by Balucan et al. (2015), which describes the use of methylated amines as

the alkaline material to swing the pH in a pH swing method. The Madeddu et al (2015) paper

proved that it was possible to extract brucite using just an alkaline material without the need

for using a pH swing method which is much more costly. The issue with the Madeddu et al

(2015) paper is the cost of using and recycling the Sodium Hydroxide (NaOH) shown in

figure 1.6. The idea to use methylated amines came from the Balucan paper where they were

used as part of a pH swing process. Methylated amines are amines that have alkyl groups

attached to them. The reason methylated amines were used is that due to the low boiling

temperatures of methylated amines they would be easier and more cost effective to recycle as

they simply could be heated up to boiling point evaporated, collected and condensed and

reused in the process. If this works this could provide a better, more cost effective option for

producing brucite.

The magnesium silicate mineral selected in this experiment is Olivine which is abundant in

nature. Extracting brucite from olivine involves extracting magnesium ions then causing

Mg(OH)2 to precipitate. Once the brucite is formed very little needs to be done to it in order

to make it sequester carbon. Thus making it more cost efficient than carbonation of

magnesium silicate minerals directly. The proposed reaction is illustrated in Figure 1.7. Here

magnesium silicates in this case olivine is heated in methylated amine solution in the

expectation that the amine is strong enough to both extract the magnesium ions and

precipitate the brucite. It then shows the solution being sent through to a recycling process

27

CO2

Figure 1.6- Extraction of Brucite from Olivine using NaOH. Adapted from Maddedu et al 2015.

H2O

Heat +Energy

Na(OH)+CaCO3

NaHCO3

+ Ca(OH)

SiMg(OH)2

Brucite

OlivineNaHCO3

pH 12NaOH

INTRODUCTION

where the solution is heated to the boiling point of the methylated amines allowing them to

evaporate and be recycled back into the beginning of the reaction. There is also the potential

that silicate could precipitate in this step as the pH increases.

28

Figure 1.7 - Flow chart of reaction mechanism

90°CpH 9

50°CpH 12

Silicate/Methylamines

Recycled Methylated Amines

SilicateBrucite

Olivine/

METHDOLOGY

2. METHODOLOGY

Descriptions of materials used Explanation of experimental procedure Thermogravimetric analysis XRD analysis Explanation of statistical analysis used

2.1 Materials

2.1.1 Olivine

Olivine is an olive-green mineral that is found in most basic igneous rock. It is mainly

comprised of magnesium and iron silicates with trace amounts of other elements. Olivine has

been attractive for use in the carbon sequestration industry due to it being widely available,

reacting with CO2 from the atmosphere through chemical weathering and its ability to be

readily dissolved by acids. However the reaction rates for CO2 sequestration using Olivine are

slow and require energy in the form of chemical processes and physical processing to

sequester carbon sufficiently. One thing that is essential in using olivine is grinding it down to

create more surface area for reactions, in order to increase reaction rates. This makes it more

favourable to transform olivine into other minerals that can sequester carbon with less energy

and lower cost required such as brucite.

The Olivine used in this reaction is sourced from the Åheim plant in Møre og Romsdal

County (Western Norway, from Minelco Ltd.). It was ground using a tungsten carbide tema

mill (University of Birmingham). It was found to have a forsterite (Mg2SiO4) composition of

greater than 80% assuming the Mg content (from XRF analysis) is wholly derived from this

phase (Renforth et al, 2015) with the remaining mainly being comprised of Fayalite (Fe2SiO4)

and other minor trace elements. The particle was analysed by dry sieving using size ranges

from >500um to <45um. 78% of olivine had diameters greater than 125 um however particles

smaller than <5um were found attached to surface of other particles when using Scanning

electron microscope (JEOL JSM-840A Scanning electron microscope fitted with a secondary

electron detector; Oxford). (Renforth et al. 2015)

29

METHODOLOGY

2.1.2 Methylated Amines

Methylated amines were chosen as the alkaline material digestion due to a number of reasons.

Firstly, they already had proven effective as an alkaline material using a pH swing method

(Balucan et al. 2015) by which brucite was extracted from magnesium bearing solids using

amines and acids. Due to the characteristic low boiling point of these amines they have the

potential to be effectively recycled using very little energy. The amines have the potential to

simply be collected after the process evaporated, condensed and then reused in the system.

The two amines used were selected from the paper by Balucan et al.(2015) in which they were

used as the alkaline material for the precipitation part of the process .The two tertiary amines

that were proved to be the most effective were triethylamine and tripropylamine and these are

the ones used in this paper. Triethylamine (C6H15N) is a volatile clear fluid that has a boiling

point of 90 degrees and a strong fish like odour. It is commonly used for organic synthesis as

base. Tripropylamine (C9H21N) has a similar physical appearance and smell to triethylamine

and has a boiling point of 156°C.

The trimethylamine and tripropylamine purchased were 99% and 98% purity respectively.

These were then diluted down to concentrations of 300 mmol. The concentration was selected

as it is close to the 5% w/w concentration used in the Balucan et al. (2015) paper for

methylated amines. Reactions with these proportions of 5% were proved to just as effective as

using higher concentrations. Therefore we chose to use 300 mmol as this was equivalent near

5% w/w and would keep costs down. When diluted the pH measured were 13.02 and 11.93

for the Triethylamine and Tripropylamine 300 mmol solutions.

30

METHODOLOGY

2.2 Methods

2.2.1 Experimental Procedure

The first step of this reactions was to measure out 10g of Olivine into the reaction vessels

shown in Figure 2.1. 50 ml of the required methylated amine solutions was added to the 10g

of Olivine. These vessels were then put into the water bath see Figure 2.1 for a variety of

temperatures (20°C, 50°C,80°C) and times (24hours, 2 weeks). The different parameters for

each planned run are explained in Table 2.1. The temperature bath used was a fisher isotemp

water bath shown in Figure 2.1.

Table 2.1 - Parameters for planned runs of the experimental procedure.

Run Name Methylated Amine Temperature °C Duration

R1E Triethylamine 50 24 Hours

R1P Tripropylamine 50 24 Hours

R2E Triethylamine 50 2 Weeks

R2P Tripropylamine 50 2 Weeks

R3E Triethylamine 20 (Room Temp) 2 Weeks

R3P Tripropylamine 20 (Room Temp) 2 Weeks

R4E Triethylamine 80 24 Hours

R4P Tripropylamine 80 24 Hours

R5E Triethylamine 80 2 Weeks

R5P Tripropylamine 80 2 Weeks

31

METHODOLOGY

After this reaction the solids were separated from the fluids through vacuum filtration. The

solids are then retained for further analyses and the fluids disposed of following correct

disposal methods. If this method proved effective in producing significant amounts of brucite

the fluids would also be retained. These fluids would then be heated up to the specific boiling

temperature of the amine in question, the vapours collected, condensed and then reused in the

process.

Before and after the experimental procedure pH measurements were taken. These were taken

by two devices, the thermo scientific Orion meter and a metrohm titrando shown in Figure

2.2. Measuring the pH before and after would indicate if there had been a change in chemical

composition. The solid residue that was collected at the end of the reaction was put into

preweighed labelled crucible and then dried in an oven at 110 degrees overnight or until dry.

After drying the crucibles were weighed. The samples were then put in the furnace shown in

2.3 at a variation of temperatures to try and decomposed certain minerals. Samples were put

in at 400C to try and dehydrolyse any brucite that may have formed, 1000C to assess if there

were any carbonates present in the samples and 500°C to investigate colour changes that were

being observed. After each temperature in the furnace the samples were cooled and reweighed

in order to measure the mass change at that given temperature before going back in the

furnace at a higher temperature. Samples were removed between each different temperature

and at the end of the analysis and crucibles reweighed before the furnace. A select few of the

32

b)a)

Figure 2.1 - Images of Experiment procedure equipment. a) Reaction vessels, b) Fisher scientific isotherm water bath.

METHODOLOGY

samples collected were then sent off for XRD analysis with the aims of observing any

structural changes that occurred during the process.

33

b)a)

Figure 2.2 - pH meters used the thermoscientific orion meter (a) metrohm titrando (b)

METHODOLOGY

2.2.2 Gravimetric Analysis

Thermal Gravimetric analysis was carried out measuring the mass change of a sample

exposed at a certain temperature over time as the temperature changed. The mass change was

supposed to represent components of the material being decomposed and removed from the

sample. Identifying what components have been removed can help determine the rough

composition of a sample. This is done through using a variation of different temperatures that

cause different components to be volatilised from the sample. The idea behind this is the

temperatures inside the furnace will act as activation energy for decomposition of certain

components within the sample. For example brucite would undergo the following reaction

with the mass lost as water:

Mg (OH)2 > MgO + H2O

By assuming this is the only reaction taking place at that given temperature the mass lost can

be converted into mass of brucite in the sample by calculating the number of moles of H2O

lost and calculating the equivalent mass of brucite that would account for. In order to carry

this out the samples were weighed put in furnace at temperature, cooled, weighed again and

34

Figure 2.3- Image of Vecstar LF3

METHODOLOGY

then put in at the next highest temperature. The furnace used was the Vecstar LF3 Muffler

Oven and scale that measured to two decimal places.

2.2.3 XRD Analysis

An X-ray diffraction is a non-destructive analytical technique used to identify the atomic and

molecular structure of crystalline compounds within a sample. The results given are mineral

or compound names as opposed to a list of the individual elements. When this is combined

with analytical methods that list the individual elements, the structure of these elements can

be determined. Both solid and powdered samples could be analysed. Each pure mineral or

compound has a specific X-ray diffraction pattern that can be used to identify compounds

within the sample. The patterns generated from the analysis of the sample were compared to a

database of known patterns for given compounds in order to evaluate the unknown

compounds. One issue with this is the software that finds these matches can often become

confused by signals that are produced at similar values and can misinterpret these. This can

sometimes be rectified by excluding compounds from the analysis, therefore getting

excluding of compounds not relevant to the research.

The way it works is first by powdering a solid sample and putting it in packing it flat into an

aluminium holder which is then inserted into the sample holder in the goniometer and

bombarding with X-Rays radiation of known wavelength in this case generated from a copper

tube. The X-Rays are refracted by the sample and are then collected by a detector which

measures the angle of incidence which is then relayed to a computer. This computer then

measures the angle of incidence of the X-rays. Using this information and the Bragg’s

equation it is converts this information to d- values where d corresponds to the lattice spacing.

Using this information the program creates a Diffractogram which graphically illustrate the

diffraction pattern. Comparing this to the database of diffractograms the compounds can be

identified. The specifications of the instrument use is the Philips PW1710 Automated Powder

Diffractometer, with X-rays being generated using Copper (CuKα ) Radiation at 35 kV 40mA.

The computer software used is PW1877 APD version 3.6 and identification software is

PW1876 PC-Identify version 1.0b.

35

METHODOLOGY

2.2.4 Statistical analysis

In order to assess whether a parameter has caused a significant change compared to another a

student t test will be carried out. This student t test will be carried out in excel using the data

analysis function T-test two tailed assuming unequal variances. The null hypothesis for all

these T tests will be set to zero, meaning that the null hypothesis is that there is no significant

difference between the two data sets. The alpha value for this test is seat at 0.05 this is the

confidence level for this null hypothesis this means that there is 95% confidence in the result.

When analysing the results to student t test the p value needs to be compared to the alpha

value of 0.05. If p value >0.05 then the null hypothesis cannot be rejected , if p value < 0.05

null hypothesis can be rejected , meaning that there is significant difference between the two

data sets used.

To compare to different parameters within the same dataset the data needs to be split into the

two parameters that you want to compare .For example to access the effect of duration on a

reaction out, all results corresponding to two weeks reaction time will be grouped together

and all of those with 24 hour reaction times will be grouped together individual data sets.

These two data sets will then be compared to one another using the student t test with one set

being compared to the other. Using means, variance and standard deviated in order to

calculated an probability of the null hypothesis being true. Once these are know it can be

determined if there is a significant difference between the two. If there is a significant

difference in can indicate that that parameter influences has an effect on the reaction outcome.

36

RESULTS

3. RESULTS

Changes in pH during reaction Thermogravimetric analysis Colour change observed during thermogravimetric analysis XRD Results – Diffractogram and mineral comparison

3.1 pH change

The change in pH was measured before and after all ten reactions. Table 3.1 shows all the pH

values measured and the calculated change in pH. As can be seen the initial pH values are

very similar to each other with triethylamine reactions varying from 13.03-12.92 and

tripropylamine reactions varying from 11.78-11.62. This indicates that the stock solution pH

did not change through the course of the experiments.

Table 3.1 - pH changes through experimental procedure for all run throughs.

Run pH Before pH After pH Change

R1 E 12.92 12.84 0.08

R1 P 11.78 11.53 0.25

R2 E 12.94 12.60 0.34

R2 P 11.62 10.80 0.82

R3 E 13.03 12.95 0.08

R3 P 11.64 11.34 0.3

R4 E 12.98 11.61 1.37

R4 P 11.78 9.91 1.87

R5 E 13.01 8.22 4.79

R5 P 11.78 8.59 3.19

As can be seen from Table 3.1 the pH change varied from 0.08 to 4.79 with a mean value of

1.309 and a standard deviation of 1.575, as the standard deviation is larger than the mean it

can be said that the pH change values experience a large range.

37

RESULTS

In all the reactions the pH of the solution decreased. Indicating that chemical changes were

happening within the solution, increasing the amount of H+ ions in the solution. This could be

due to CO2 dissolving into the solution from the headspace inside the reaction vessel

production carbonic acid. This reaction however favours cool temperatures and the bigger pH

changes corresponded to those with high temperatures as seen in Table 3.2.Therefore CO2

contamination is not likely to be responsible for these pH changes although it is possible that

it may contribute a small fraction of the observed change.

Table 3.2 Table showing pH changes observed in numerical order from highest to lowest and

the associated conditions of reaction with that given pH change.

pH Change Amine Used Temperature (°C) Duration

4.79 Ethylamine 80 2 Weeks

3.19 Propylamine 80 2 Weeks

1.87 Propylamine 80 24 hours

1.37 Ethylamine 80 24 hours




0.25 Propylamine 50 24 hours

0.08 Ethylamine 50 24 hours


In order to identify the effect the parameters have on the pH change. The pH change values

were put in numerical order from highest to lowest with the corresponding temperature, amine

and duration reaction parameters next to them this can be found in Table 3.2

From Table 3.2 a series of patterns with reference to the reaction parameters can be noticed.

Firstly larger pH changes are observed for reactions that use tripropylamine over those that

used triethylamine. With changes for tripropylamine ranging from 3.19 - 0.25 with an average

1.286, standard deviation 1.248 and triethylamine ranging from 4.79-0.08 with an average of

38

RESULTS

1.332 and standard deviation 2.005. Although the mean from triethylamine is higher it has a

large standard deviation than mean indicating the wide range of results. This may indicate that

tripropylamine is having a more profound effect on the reaction. This is especially interesting

as the tripropylamine had a lower pH than triethylamine and perhaps this caused a greater

amount of magnesium ions to dissolve due to magnesium dissolution favouring lower pH

environments.

Secondly as temperature of reaction increases so does the change in pH with all the reactions

occurring at 80°C having the 4 largest pH changes and the lowest change in pH corresponding

with the lowest reaction temperature of 20°C. In order to get rid of the bias towards lower pH

readings caused by the higher temperatures as described by the Nernst equation. The samples

were allowed to cool to room temperature before the readings were taken. This indicates that

at higher temperatures there is a higher rate of reaction that causes larger changes in pH. This

is probably due to increased temperatures allowing for higher energy collisions to happen

with activation energy high enough to cause a chemical change, which in turn could produce

more H+ ions reducing the pH further than at lower temperatures.

The correlation between temperature and increase pH change is almost perfect with the

exception of R3P which was run at 20 degrees for 2 weeks and experiences a higher pH

change than R2P&R2E at 50C only ran for 24 hours. This indicates that time also had

influence on the pH change of this reaction. This makes sense as increasing the reaction time

allows for more reactions to take place and more products to be formed. The amount of pH

change will continue to increase with increasing duration until the reaction reaches

equilibrium and the pH becomes stable.

Finally the longer the duration of reaction the larger the change in pH observed. This is

expected as the longer the time of reaction the more change there is for successful reactions to

occur therefore more opportunity for the pH to change.

Student t tests for comparing pH change results of Triethylamine to Tripropylamine,

Temperature of 80°C to 50°C and duration of 24 hours to 2 weeks were carried out the results

are shown in Table 3.3.

39

RESULTS

Table 3.3 - T test results for reaction condition comparisons of pH change results.

Parameters Compared Alpha Value P(T<=t) two-tail

Triethylamine- Tripropylamine 0.05 0.966

80°C - 50°C 0.05 0.0527

24 hours - 2 weeks 0.05 0.710

For all of the results from the T test refer to figures A1, A2, A3 in the appendices.

From this it can be shown that the only parameter that is close to having a statistically

significant effect on the change in pH is the temperature of the reaction. With a P value of

0.0527 which is only marginally larger than the alpha value of 0.05. However as none of these

values are lower than the alpha value of 0.05 which assess the null hypothesis with a

confidence of 95% The null hypothesis , which is that there is no difference between the data

sets cannot be rejected. This however does not mean that there is not a relationship between

these parameters but that there is there is no statistically significant differences between the

data sets.

40

RESULTS

3.2 Thermogravimetric analysis

The results of thermogravimetric analysis on our samples is expressed in Table 3.4 as the

percentage mass change when heated at the given temperature. The reason mass changes were

not measured for all temperatures was due to time available for investigation and discoveries

made through the investigation. Initial samples were only run at 1000°C. This would measure

mass changes for anything and everything that is decomposed at this temperature or lower.

One result of this was the observation of a distinct colour change described in section 3.4.As

well as mass change being measured. In order to try and identify mass change corresponding

to brucite it was decided to set the furnace at a temperature 400°C in order to remove brucite

from the sample through the reaction of brucite to form magnesium oxide as described in

section 2.2.It was then decide due to the colour change observed to run the samples at

different temperatures in order to assess at what temperature the colour changed. This lead to

several samples being put in the furnace at 500°C where the beginnings of colour change

were observed which are described in section 3.4.

Table 3.4 - Overview of all the mass change (%) measured at 400, 500 and 1000C exposures

in the furnace.

Run Mass Change 400°C (%) Mass Change 500°C (%) Mass Change 1000°C (%)

R1E - - 1.997146933

R1E2 - - 1.117318436

R1P - - 2.170963365

R2E 1.162790698 - 2.352941176

R2P 0 - 2.475247525

R3E - 1.101928375 1.470588235

R3P - -1.246105919 1.764705882

R4E - 0.801603206 0.888888889

R4P - 1.669449082 0.609756098

R5E 0.664451827 - 1.672240803

R5P 0.863930886 - 1.525054466

41

RESULTS

As can be seen from Table 3.4 the mass changes measured were not large for any of the

reactions all with values under 3% change in mass. However the range of mass change did

vary from 0.609 to 2.475 with a mean of 1.640 and a standard deviation of 0.598 for samples

treated at 1000°C. Indicating that reaction parameters may have an influence on the mass

change observed. In order to assess whether the reactions had an effect on the mass change

control samples were carried out and the values measured are displayed by Table 3.5. For this

samples of untreated olivine were put through the same process as the treated samples initially

being dried and then heated in the furnace whilst measuring the mass change.

Table 3.5 - Mass change results using controls of unreacted olivine.

Run Mass Change at 500°C (%) Mass Change at 1000°C (%)

1 1.450589302 1.468624833

2 - 2.128851541

3 - 2.037037037

Comparing Tables 3.4 & 3.5 revealed that the mass changes for reacted samples seem a fair

bit lower than those measured by the treated samples. Only one control was run at 500°C in

order to get a comparison, the change measured in the control fits within the range of mass

changes measured at 500°C. Indicating that the reaction may not have had altered the original

olivine considerably.

Samples treated at 1000°C had a mean of 1.640 and control with a mean of 1.878.In order to

assess whether a parameter has an effect on the mass change measured a series of student t

tests were carried out to compare one parameter to another will the null hypothesis being that

there is no significant difference between the two data sets. The results of these are

summarised in Table 3.7. The results for comparing samples to controls gave a p value

reading of 0.419 this is much larger than 0.05 therefore the null hypothesis cannot be rejected,

meaning that the samples mass change is not significantly different to those of the control

samples, this could indicate the reactions carried out have not had a large impact in changing

the composition of olivine. Though XRD analysis results in section 3.4 should show any

chemical changes that have occurred through these reactions.

42

RESULTS

.

For the samples that were exposed to temperatures of 400°C the mass change measured was

very small with a maximum of 1.16% mass change being achieved for the 4 samples that

underwent this. The two runs that were exposed were R2E&P and R5E&P the only change in

parameters between these 4 runs was the reaction temperatures with R2 at 50°C and R5 at

80°C. The mass change appears to be higher for the experiments run at a lower temperature

however running a t test on this it is not statistically significant with p value of 0.808 for a

student t test therefore the null hypothesis of no change could not be rejected and there is no

significant difference between these two values

At 500°C the mass change was slightly higher than those observed at 400°C with a maximum

of 1.67% change observed. Although none of the samples ran at 400°C were also ran at 500°C

so this change is expected as it will include the mass change at 400°C. Two runs were ran at

500°C these were R3E&P and R4E&P. These two runs had contrasting temperature and run

time with R3 at 20°C and 2 Weeks run time and R4 at 80°C and 24 hours run time

respectively. We would therefore expect the mass losses to differ from each other due to the

differences in reaction parameters. However the results do not seem to reflect this. In fact for

some reason for one of the measurements there was a mass gain. T test comparison results

shown in Table 3.7 backs this up producing a p value of 0.486. This means the null hypothesis

cannot be rejected and therefore the differences observed cannot be considered significant.

All samples were run in the furnace at 1000°C. In order to observe patterns in how different

parameters affected the mass change , the mass change results were put into descending order

and the reaction conditions corresponding to that value are displayed next to them. This is

illustrated by Table 3.6 where the reaction parameters amine used, temperature and duration

are displayed. From this pattern of how parameters affect mass change can be evaluated.

43

RESULTS

Table 3.6 shows the percentage mass changes observed at 1000°C in descending order with

the experimental procedure conditions next to them.

Mass Change (%) Methylated Amine Temperature (°C) Duration

2.475248 Tripropylamine 50 2 Weeks

2.352941 Triethylamine 50 2 Weeks

2.170963 Tripropylamine 50 24 Hours

1.997147 Triethylamine 50 24 Hours






0.888889 Tripropylamine 80 24 Hours


The first observation that can be made from Table 3.6 is that the samples of the reactions

using tripropylamine observed a greater mass change % than the reactions using triethylamine

as the alkaline digestion medium, this could be due to the tripropylamine reacting differently

to triethylamine potentially having a faster reaction rate. T test results comparing all the mass

changes recorded using triethylamine and tripropylamine show that there is not a significant

difference between results from triethylamine and tripropylamine, as with a p value of 0.556

the null hypothesis cannot be rejected.

The second observation made is that samples of the reactants that occurred at 50C had higher

values than those that occurred at 80°C or 20°C. This may be due to the reaction temperature

being optimal for chemical reactions to take place. It is also possible that because these were

some of the first samples analysed and they went through rather no previous furnace

temperature or the lower temperature at 400°C that a large percentage of mass was lost due to

the lack of treatment in the furnace at previous temperatures. A student t test comparing the

44

RESULTS

results at 50°C to those at 80°C showed that the difference between these values is significant

the test produced a p value of 0.0455 which is less than the alpha value of 0.05. This means

the null hypothesis that there is no difference between the results can be rejected and there is

at least a 95% confidence that there is a significant difference between mass changes at these

different temperatures.

Finally the samples from experiments that have run for 2 weeks as have a higher observed %

mass change than the experiments that ran for 24 hours. A student t test comparing the mass

changes observed from these two durations showed that there was no significant difference in

results caused by change in duration, with a p value of 0.194 the null hypothesis of no

difference cannot be rejected. Although this does not mean that duration does not have an

effect on the reaction merely that the effect is not statistically significant.

Table 3.7- t test results from pair t test assuming equal variances. Comparison of mass

changes for different parameters.

Parameters compared Alpha value P value

Samples to Controls 0.05 0.419051

R2’s to R5’s (400°C) 0.05 0.808697

R3’s to R4’s (500°C) 0.05 0.486079

E to P (1000°C) 0.05 0.555807

80°C to 50°C (1000°C) 0.05 0.045473

24 hours to 2 weeks (1000°C) 0.05 0.193751

For all of the results from the T test refer to figures A4 to A9in the appendices.

45

RESULTS

3.3 Colour Changes

During the Thermogravimetric analysis the colour of the solid material changed considerably

from olive green to a rust red colour as illustrated by Figure 3.1 This colour change was

present after being heat treated in the furnace at 1000° C but not at 400°C. Due to this colour

change it was decided to put the samples in at different temperatures until the beginning of the

colour change was observed. Two sets of samples were run at 500°C and the colour was

observed to start becoming darker and browner in colour. As shown in figure 3.2 this was not

something that was anticipated. In order to determine whether the colour change was a

function of the treatment the olivine had undergone. A control sample of olivine was run

through the same drying and furnace temperature. The untreated olivine was found to change

colour in the furnace. This indicates that the colour change is unlikely to be due to the

reactions but merely a property of the olivine itself.

46

b)a)

Figure 3.1 - Demonstration of colour change of sample exposure in a furnace at 1000°C a) Dried Sample b) Sample after 1000°C.

Figure 3.2 - Colour changes observed

after sample exposure at 500°C

RESULTS

Upon further research it is likely that this colour change is due to the oxidation of the iron in

the sample. The iron in the olivine is mainly in the form of Fayalite (Fe2SiO4) this can be

oxidised to form Hematite (Fe2O3) and Amorphous silica (SiO2). A paper by Koltermann

(1962). Investigated atmospheric oxidation of powdered olivine’s that had a varying amount

of Fayalite present. Kolterman (1962). Proposed the different stages of the reactions taking

place and how they altered with different temperatures, a summary of these reactions is

described by the figure 3.2

Figure 3.3 shows that different end products are formed with when the temperature and

duration of the reaction varied. Our conditions are similar to the second equation with

temperatures of 1000°C and a short reaction time. This reaction forms hematite which could

be responsible for the red colouration of the sample. XRD analysis of the samples taken

before the furnace, after treatment at 500°C and after treatment at 1000°C will indicate the

structural changes of the sample throughout this process. The results of XRD analysis are in

section 3.5 following this section. Additionally a paper by Champness (1970) investigated the

nucleation and growth of iron oxides in olivine found that low temperature oxidation between

500-800°C produced hematite and magnetite like precipitates along with amorphous silica.

Hematite is a copper red colour and magnetite is dark in colour. It may be possible that the

formation of these in the furnace at temperatures of 500°C and 1000°C degrees could be

responsible for the colour changes observed

47

Figure 3.3 - Summary of reactions observed with olivine specimen with 53% Fayalite. Adapted from Champness (1970)

Fe3O4 Magnetite

MgSiO3 Enstatite

SiO2

CristobaliteMg2SiO4

Forsterite

With Prolonged Heat

Fe2O3 Hematite

MgSiO3 Enstatite

Mg2SiO4

ForsteriteSiO2

Cristobalite1080°c

1100°c

820°c

Fast Reaction

Fast Reaction Fe2O3 Hematite

SiO2

Amorphous Silica

Mg2SiO4

Forsterite(Mg,Fe)2SiO4

Olivine

RESULTS

3.4 XRD Analyses

Nine samples were sent off for XRD analysis. The samples selected were R4E, R4P and

Control samples. For each of these runs a dry sample, a sample after exposure to 500°C and a

sample after exposure to 1000°C were sent off to be analysed. These samples were selected in

order to compare the effect on the different amines on the change in composition of the

olivine as well as investigate the chemical changes that are responsible for the colour changes

observed during thermogravimetric analysis at different temperatures. These are described in

section 3.3. The resulting diffraction patterns are displayed in figures 3.3. To 3.11. Where

they are displayed as diffractograms with the mineral names and percentage present in the

sample displayed over the top. Table 3.12 shows the chemical formulas of the minerals

observed in order assist in observing the chemical changes that are occurring.

Figure 3.4- Diffractograms for control olivine sample (Dried)

48

RESULTS

Figure 3.5 - Diffractograms for control olivine sample (500°C)

Figure 3.6 - Diffractograms for control olivine sample (1000°C)

Figures 3.4-3.6 show the mineral changes that occur to olivine as it is heated at 500°C and

1000°C. Table 3.8 shows the presence of minerals present in each of the three samples.

49

RESULTS

Table 3.8 - Minerals present in Olivine samples dry, after 500°C and after 1000°C

Mineral % in dried % in 500°C % in 1000°C

Forsterite 42 48 69

Antigorite 27 19 -

Brucite 13 12 -

Clinochlore 6 6 -

Talc 4 5 -

Tremolite 4 - -

Goethite 4 - -

Quartz - 10 -

Hematite - - 18

Clinoenstatite - - 13

Forsterite (Mg2SiO4) is what makes up the largest percentage of olivine composition.

Throughout the heating process its concentration becomes greater as other smaller compounds

are transformed. As the samples are treated all of the other minerals present in the dried

olivine sample are transformed. With Tremolite and Goethite disappearing after treatment at

500°C and Antigorite , Brucite , Clinochlore and Talc disappearing after treatment at 1000°C.

The key mineral of interest is brucite it is interesting to note that the brucite is present in

samples of untreated olivine. As the aim of this investigation is to produce brucite from the

magnesium compounds present in the Olivine and that heating it at 1000°C removes the

brucite from the sample but not 500°C.Indicating that the temperature corresponding to

turning brucite into magnesium oxide is more than expected. With regard to the colour change

observed at 1000°C the appearance of Hematite in the sample is most likely responsible for

the colour and is likely formed due to oxidation of iron bearing minerals in the sample such as

Antigorite or Goethite.

50

RESULTS

Figure 3.7 - Diffractograms of dried sample from Olivine and Triethylamine reaction at 80°C

for 24 hours.

Figure 3.8- Diffractograms of sample treated at 500°C from Olivine and Triethylamine

reaction at 80°C for 24 hours.

51

RESULTS

Figure 3.9- Diffractograms of sample treated at 1000°C from Olivine and Triethylamine

reaction at 80°C for 24 hours.

Table 3.9- Mineral composition of product of Olivine treated with triethylamine dry, heated to

500°C and treated to 1000°C.

Mineral Dried % 500°C % 1000°C %

Forsterite 27 62 79

Dolomite 38 12 -

Antigorite 20 10 -

Brucite 7 6 -

Clinochlore 3 6 -

Talc 3 2 -

Tremolite 2 2 -

Hematite - - 11

Enstatite - - 10

52

RESULTS

Figures 3.7-3.9 show the mineral changes that occur to olivine that has been reacted with

triethylamine as it is heated at 500°C and 1000°C. Table 3.9 shows the presence of minerals

present in each of the three samples.

As with Table 3.8 forsterite is present in all of the samples and with heating most of the other

minerals disappear increasing the concentration of forsterite in the sample. However this

reaction using triethylamine to treat olivine has formed Dolomite which was not present in the

previous reactions therefore producing carbonate. The two possible source of carbon for the

formation of this Dolomite could be from the ethyl groups in the triethylamine during the

reaction or from the air itself when the sample was being dried. Only when the sample was

heated to 1000°C was the disappearance of minerals observed. At 500°C all of the minerals

present in the sample with the exception of forsterite went down in concentration indicating

that they were transforming, by the time it was treated at 1000°C all of these minerals had

disappeared and new minerals were now present. The two new minerals present are Hematite

yet again is likely to produce the colour change observed and enstatite which is another

magnesium silicate compound.

Figure 3.10 - Diffractogram of Olivine and Tripropylamine sample at 80°C for 24 hours dried.

53

RESULTS

Figure 3.11- Diffractogram of Olivine and Tripropylamine sample at 80°C for 24 hours after

heating to 500°C

Figure 3.12 – Diffractogram of Olivine and Tripropylamine sample at 80°C for 24 hours after

heating to 1000°C

54

RESULTS

Figures 3.10-3.12 show the mineral changes that occur to olivine that has been reacted with

tripropylamine as it is heated at 500°C and 1000°C. Table 3.10 shows the presence of

minerals present in each of the three samples.

Table 3.10- Mineral composition of products of Olivine treated with tripropylamine dry, after

heating to 500°C and after treating to 1000°C.

Mineral Dried % 500°C % 1000°C %

Forsterite 90 39 75

Dolomite - 40 -

Antigorite 2 5 -

Clinoenstatite - 5 -

Brucite - 4 -

Clinochlore 3 4 -

Talc - 2 -

Tremolite - 1 -

Enstatite 5 - 18

Hematite - - 7

Much the same as Tables 3.8&3.9 forsterite is present in all of the samples with its

concentration increasing as the sample is heated to 1000°C. However the concentration of

forsterite drops rapidly when it has been treated at 500°C. This appears to be likely due to the

high concentration of dolomite, brucite and other minerals that appear in the sample at 500°C

before disappearing again at 1000°C. It is possible that as R4E&P were heated in the furnace

at the same time that sample from the triethylamine reaction could have contaminated the

sample. Again at 1000°C Hematite is formed which backs up the idea that the colour change

is produced by the production of Hematite.

In order to assess how treatment with triethylamine and tripropylamine transforms olivine.

The XRD results for the dried product before they underwent thermogravimetric analysis

need to be compared to each other to determine their similarities and differences. Table 3.11

55

RESULTS

illustrates the minerals present in control sample, sample treated with triethylamine and

sample treated with tripropylamine.

Table 3.11 - Mineral composition of Olivine control, Olivine treated with triethylamine and

Olivine treated with tripropylamine.

Mineral Olivine % R4 E % R4 P %

Forsterite 42 27 90

Dolomite - 38 -

Antigorite 27 20 2

Brucite 13 7 -

Clinochlore 6 3 3

Talc 4 3 -

Tremolite 4 3 -

Enstatite - - 5

Goethite 4 - -

The minerals that are present in all three of the samples are Forsterite , Antigorite and

Clinochlore which are all magnesium and iron silicates this makes sense as these are the

primary constituents of an olivine. Brucite is the mineral of interest for this investigation with

the aim of producing Brucite from the reactions, however this does not seem to have worked

as the substance with the highest percentage Brucite present is in fact the untreated sample.

This means that is likely that brucite already present in the olivine has been transformed into

something else such as perhaps Dolomite which could be the product of a brucite carbonation

reaction or carbonation of other compounds. This dolomite is only found in the reactions

using triethylamine and tripropylamine and could indicate that the reaction or products

formed in the reaction are actively up taking carbon dioxide.

56

RESULTS

Table 3.12 - Mineral Names and formulas found in figures 3.3-3.11

Name Formula

Forsterite Mg2SiO4

Enstatite MgSiO3

Clinochlore Mg6Si4O10(OH)8

Antigorite (Mg,Fe(II))3Si2O5(OH)4

Dolomite CaMg(CO3)2

Hematite Fe2O3

Brucite Mg(OH)2

Talc Mg3Si4O10(OH)2

Tremolite Ca2Mg5Si8O22(OH)2

Clinoenstatite Mg2Si2O6

Quartz SiO2

Goethite FeO(OH)

The results from these XRD analysis show that the amount of brucite reduces as it is treated in

the and that our estimation of brucite removal occurring at 400°C was much too low with the

actually temperature falling somewhere between 500°C and 1000°C. Also that by reaction the

olivine with triethylamine and tripropylamine the concentration of brucite decreased. In

addition to this is can be determined that the colour change that occurred during the

thermogravimetric analysis process is down to the oxidation of iron within the sample as

explained by the series of equations by Koltermann (1962) in section 3.3 where hematite is

formed producing the red colour and to back it up even further the presence of enstatite

formation at the same time as the hematite appear at 1000°C indicating that iron oxidation

processes are occurring

57

DISCUSSION

4. DISCUSSION

Has the aim of the investigation been achieved How to make this investigation better Errors with measurements Further research direction

With regards to the aim of this investigation which is to produce Brucite from olivine the

desired result has not been achieved. XRD analysis shows that the concentration of Brucite in

the samples after treatment was much lower than in the untreated olivine. Though this could

be due to the brucite dissolving out into the solution that was discarded or it could have

reacted with amines to form dolomite. There is some potential Brucite formation in the

reaction of Triethylamine and Olivine sample in the furnace at 500°C. This could be due to

the heat causing a reaction to occur producing Brucite or it could be contamination from the

other sample in the furnace at the time, which was a sample of Tripropylamine and Olivine

products which had Brucite present in its dried state. Further investigation into whether there

is brucite production occurring during the heating could prove interesting if it were being

produced by heating and not a function of contamination.

However something interesting did show up on the XRD analysis that was not expected. This

was the presence of dolomite in both the treated products using triethylamine and

tripropylamine. Dolomite is CaMg (CO3)2 and its existence only in the treated samples

indicates that it exists as a function of the chemical reactions taking place through the

experimental procedure. The real question with this is what is the source of carbon used to

form the carbonate group of the dolomite is. It is most likely sourced from the ethyl and

propyl groups in the methylated amines used. However for the samples using tripropylamine

the dolomite only appeared after the sample had been reacted in the furnace at 500°C this

could be for a number of reasons first of all this could be an error in the reading at the

dolomite existed in the dried sample but this was not detected , secondly this dolomite present

could be contamination from the triethylamine sample that was also in the furnace at that time

or this could be the result of a chemical reaction taking place with the source of carbon

potentially being carbon dioxide from the ambient air. This could be an interesting thing to

58

DISSCUSSION

investigate further, seeing if the formation of dolomite from olivine or other minerals could be

a potential CCS technology.

Re-evaluating the reaction procedure looking at the temperatures used in the Madeddu (2015)

paper, the temperature for the reaction may have been too low. Madeddu (2015) used

temperatures of 180°C in order to extract the brucite from powdered dunite comprised mainly

of olivine using sodium hydroxide (NaOH), perhaps if higher reaction temperatures were used

it would decrease the pH and increase the energy enough so that the magnesium would

dissolve, form brucite and precipitate when the sample cooled. However this is not practically

feasible using the methylated amines used in this paper. This is because their low boiling

points at 90°C and 156°C for Triethylamine and Tripropylamine respectively. It would be

unsafe to heat these solutions up to 180°C due to their high flammability and risks of

combustion.

In addition to this I also think that the concentrations of methylated amines used in the

experiment were much too low to have the desired effect and it may work better with higher

concentrations. We used relatively low concentrations based upon the 5%w/w that was used

in the Balucan paper (2015) where they also used concentrations of 10% and 15%w/w for

their reactions, also in the Maddedu (2015) paper they used the sodium hydroxide (NaOH)

prepared at different molar ratios ranging from 1 to 2 moles of NaOH. Therefore I think the

concentrations used should have been higher for example 15%w/w. If the higher

concentrations proved effective then further studies could be carried out to find the most

effective concentration with regards to reaction rates and costs.

If I were to carry out this investigation again I would be more careful with how the

thermogravimetric tests were carried out. Ideally would have had one or more sample for each

of the runs. One that could be continuously measured as temperature changed without

removal of samples for XRD analysis and one sample from which samples would be taken. In

addition to these I would have carried out the thermogravimetric analysis at a larger variety of

temperatures such as every 100°C from 400°C up to 1000°C, in order to get a broader

understanding of the chemical reactions occurring. Ideally in order to prevent contamination

between samples only the samples corresponding to the same reaction procedure would be

59

DISSCUSSION

carried out at the same time however this would be both time consuming and use more

energy. Finally if my budget had allowed I would have liked to carry out XRD analysis for

more samples to assess the effect temperature and duration of the reactions had effected their

chemical changes within the furnace.

There are many errors associated with measurements in this experiment. pH measurements

have an error associated with the influence of temperature on the pH probe. Higher

temperatures increase a bias towards lower pH values. In order to combat this the pH probes

were frequently calibrated when in use and the solutions were allowed to cool before the

measurements were taken. To improve this a temperature probe should have been used in

order to determine the temperature the measurements were taken and try to replicate it will all

samples to exclude bias due to the temperature of the solution.

Another source error came with the weighing of the samples, when weighing out the olivine

for the samples for the initial experiments a scale that measured to 0.1g was used meaning

that there is a maximum error of +/- 0.05g. When measuring samples throughout

thermogravimetric analysis a more accurate weighing scale was used with smallest

measurable value being 0.01g producing a maximum error of +/-0.005g. One issue was

remembering to weigh the crucibles before the samples were put in them , this lead to some of

the crucibles being weighed after they had been washed preceding the reaction taking place

and this may have had an impact on the values of the small mass changes that were observed.

In order to avoid this in future better organisation would be key with all the crucibles labelled

and pre weighed in order to eliminate this error.

There are also errors associated with the XRD analysis that took place it is possible that there

are error associated with sample preparation. Systematic errors associated with sample

preparation include the specimen not being completely flat, the sample may not be ground

down fine enough, properties of the sample cause the X-rays to diffract in an unpredictable

manner and non-random orientation of crystallites could produce large variations in intensity

and limits the peaks that are seen. This is why the XRD was carried out by persons that are

experiences in carrying out these analyses and know how to prevent these errors occurring

where possible. In addition to this the information measured by the X-ray diffraction

60

DISSCUSSION

mechanism are put into pieces of software which creates the peaks and figures out what

minerals the can correspond to. With this errors can be found where substances with similar

patterns occur in the same sample causing greater intensity of peaks or for peaks to be hard to

associate with a given mineral. This can be partially resolved by writing an exclusion file in

order to tell the programme to only search for minerals with the elements you are interested

in. This mean the measurements of XRD may not be completely accurate but they provide the

best available overview we have of the mineral structure of the samples.

Further research in alkaline digestion of Olivine to produce Brucite should focus on finding

an alkaline material that has boiling point high enough (Over 180°C) that the reaction can be

carried out without risks of combustion. But also a boiling point low enough for the material

to be recycled through some sort of inexpensive fractional distillation method to evaporate

and separate the water used for dilution and the alkaline material. In order for it to be recycled

back into the process in turn saving on costs. Also it would be beneficial if this amine

compound did not contain carbon as this could be utilised to form carbonates within the

solution which could be mistaken as carbonation from CO2 from the ambient air.

61

CONCLUSION

5. CONCLUSIONS

The reaction olivine with triethylamine or tripropylamine did not conclusively produce any

observable brucite. In fact the reactions appeared to do the opposite and remove the brucite

that already existed in the olivine. This could be due to the brucite reacting with the carbon

atoms in the methylated amines producing dolomite, the brucite could also have been

dissolved into the solution of the reaction which was then disposed of at the end of the

reactions procedure.

The ineffectiveness of this reaction procedure to extract brucite from olivine could be for a

few possible reasons. If someone were to redo this reaction and change the parameters.

Higher concentration methylated amines should be used as this could be a likely effect how

the reaction occurs. Also the reaction temperature should have been increased to > 100°C as

the 80°C temperature may not have been high enough to overcome reaction energies that were

required of the desired reactions. However with this increasing temperature comes a problem

with the safety of the experiment due to the low boiling points of the methylated amines there

would be a greater risk of combustion and release of harmful gases into the environment.

For further investigation into extracting brucite from olivine or other magnesium bearing

silicates. It would be advisable to find an alkaline material that has a higher boiling than that

of methylated amines but a low enough boiling point to allow the material to be effectively be

recycled. A boiling point somewhere between 180°C and 200°C would be ideal. In addition to

this this material should be inorganic to prevent formation of carbonates which could be

misinterpreted as carbonation using CO2 from the ambient air.

62

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66

ACKNOWLEDGEMENTS

First of all I would like to thank my project supervisor Dr Phil Renforth of the School of Earth

and Ocean Sciences at Cardiff University. For the response to so many emailed questions

even whilst in Hawaii and for generally steering my project in the right direction.

I would also like to thank Anthony Oldroyd of the School of Earth and Ocean science at

Cardiff University for carrying out the XRD analysis for my samples, even though you were

busy. And for explaining how the process works to me as well as provide the procedural

specifications.

Finally I would like to thank Jen Pinnion of the School of Earth and Oceans sciences at

Cardiff University for unlocking the labs for me numerous times whilst Phil was away.

67

APPENDICES

APPENDICES

A1 – T test comparing pH values using triethylamine and tripropylamine.

Variable 1 Variable 2

Mean 1.332 1.286

Variance 4.01957 1.55723

Observations 5 5

Hypothesized Mean

Difference 0

Df 7

t Stat 0.043556232

P(T<=t) one-tail 0.48323728

t Critical one-tail 1.894578605

P(T<=t) two-tail 0.966474561

t Critical two-tail 2.364624252

A2 – T test comparing pH values using 80°C and 50°C.


Mean 0.3725 2.805

Variance 0.100625 2.340633333

Observations 4 4

Hypothesized Mean

Difference 0

df 3

t Stat -3.113694

P(T<=t) one-tail 0.0263648


P(T<=t) two-tail 0.0527296


A3 – T test comparing pH values using 24 hours and 2 weeks.

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APPENDICES


Mean 1.1 1.4483

Variance 0.4406 4.1399

Observations 4 6

Hypothesized Mean

Difference

0

df 6

t Stat -0.3894

P(T<=t) one-tail 0.3552


P(T<=t) two-tail 0.7104


A4 – T test comparing mass change values using samples and controls.


Mean 1.640441 1.878171

Variance 0.357267 0.127904

Observations 11 3

Hypothesized Mean

Difference 0

df 6

t Stat -0.86741





A5 – T test comparing mass change values using R2 and R5.


Mean 0.581395 0.764191

Variance 0.676041 0.019896

Observations 2 2

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APPENDICES

Hypothesized Mean

Difference 0

df 1

t Stat -0.30988





A6 – T test comparing mass change values using R3 and R4.


Mean -0.07209 1.235526

Variance 2.756633 0.376578

Observations 2 2

Hypothesized Mean

Difference 0

df 1

t Stat -1.04472





A7 – T test comparing mass change values using triethylamine and tripropylamine at 1000°C


Mean 1.536665 1.764972

Variance 0.387222 0.373601

Observations 6 5

Hypothesized Mean

Difference 0

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APPENDICES

Df 9

t Stat -0.6118





A8 – T test comparing mass change values, 80°C and 50°C at 1000°C.


Mean 2.022723 1.173985

Variance 0.289052 0.257048

Observations 5 4

Hypothesized Mean

Difference 0

df 7

t Stat 2.429211





A9 – T test comparing mass change values, 24 hours and 2 weeks at 1000


Mean 1.876796 1.356815

Variance 0.185598 0.476818

Observations 6 5

Hypothesized Mean

Difference 0

df 6

t Stat 1.46316



71

APPENDICES



72

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