ABSTRACT
Three types of Nigerian bentonite based nanoclays – Potassium (sample A), Calcium (Sample B) and Sodium (Sample C) bentonites– were investigated for their potential as oil spill sorbents after modification with Cetyltrimethylammonium Bromide (CTAB). The nanoclay samples were purified and subjected to hydrothermal ion exchange reaction to synthesize organoclays under mild reaction conditions. Changes in the microstructural, morphological and physicochemical properties of the modified clays caused by the intercalation of CTA+ cations before and after the synthesis procedure were investigated. The changes in the chemical profile of the clays were studied by X-Ray Flouresence (XRF) and Neutron Activation Analysis (NAA). Crystallographic studies by X-Ray Diffraction (XRD), show higher intercalation time and surfactant loading, produce organoclays with higher basal spacing and more efficient oils sorption capacities. These observations were further explained by Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM) and Thermal Gravimetric Analysis (TGA). The presence of new (organic) groups in the characteristic bentonite structure of the nanoclays is prime evidence of successful synthesis. The organoclays were further tested in a simulated oil spill situation to assess their potential as oil sorbents and sorbed about 5 times their weight in water. To understand the manner and mechanism of the sorption procedure, batch kinetic and equilibrium studies were carried out using kinetic and equilibrium isotherm models. The kinetic data was best described by the Pseudo-second-order rate model (R2 = 0.999, 0.990 and 0.9975 for the organoclay Samples 2, 5 and 15 respectively) demonstrating that the sorption procedure and mechanism was by chemisorption and that more than one process may have occurred during the procedure. The Langmuir isotherm model best described the manner of crude oil sorption (R2 = 0.9968, 0.997 and 0.9936 for samples 2, 5 and 15 respectively) as predominantly monolayer. The results showed that these natural clays can be modified and used for the treatment of oil spillage. The organoclays present a cost effective and a suitably environmentally friendly alternative for the remediation of oil spill polluted lands in the Niger Delta region of Nigeria.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vii
Table of Contents viii
List of Tables xiv
List of Figures xv
List of Appendices xix
List of Abbreviations xxi
1.0 INTRODUCTION 1
1.1 Clay Minerals 4
1.2 Organoclays 5
1.3 Statement of the Problem 6
1.4 Justification for the Research 7
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1.5 Aim and Objectives 9
2.0 Literature Review 11
2.1 Oil Spillage 11
2.2 Oil spillage in the Nigerian Niger-Delta 11
2.3 Effect of Oil Spillage in the Environment 14
2.4 The Toxic Contents of Crude Oil 17
2.4.1 Toluene 18
2.4.2 Benzene 19
2.4.3 Cresols (a group of Phenolic compounds) 20
2.4.4 Polynuclear Aromatic Hydrocarbons (PAH) 21
2.5 Oil Spill Response Techniques 23
2.5.1 Mechanical recovery 24
2.5.2 Chemical methods 26
2.5.3 In-situ burning 28
2.5.4 Bioremediation 29
2.5.5 Natural removal 30
2.6 Sorbent for Oil Spillage Treatment 31
2.6.1 Types of Sorbents 32
2.7 Clays 34
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2.7.1 Smectite Clays 35
2.7.2 Bentonites 36
2.8 Organoclays 38
2.8.1 Application of organoclays 40
3.0 MATERIALS AND METHODS 42
3.1 Materials 42
3.2 Methods 44
3.2.1 Sample Preparation 44
3.2.2 Physicochemical characterization of clay samples 45
3.2.2.1 Bulk density determination 45
3.2.2.2 Moisture content (MC) determination 45
3.2.2.3 Volatile matter content (VMC) determination 46
3.2.3 X-Ray Florescence (XRF) Analysis 47
3.2.4 Scanning Electron Microscopy (SEM) 48
3.2.5 Thermal Gravimetric Analysis 48
3.2.6 Brauner-Emmet-Teller (BET) Analysis 49
3.2.7 X-ray Diffraction (XRD) Analysis 50
3.2.8 Fourier Transform Infra-Red (FTIR) Analysis 51
3.2.9 Neutron Activation Analysis 51
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3.2.10 Purification of Clays 53
3.2.11 Organoclay synthesis 54
3.2.12 Removal of hydrocarbon spill from water surface 56
4.0 RESULTS 57
4.1 Physicochemical properties of raw and organically modified bentonites 57
4.1.1 Effect of intercalation properties on weigh on Bulk Density 61
4.2 X-Ray Fluorescence Analysis 65
4.3 Neutron Activation Analysis 67
4.4 X-Ray Diffraction Analysis 72
4.5 Fourier Transform Infrared Spectral Analysis 81
4.6 Thermal Gravimetric Analysis 91
4.7 Scanning Electron Micrographs of Raw and Modified Bentonites 99
4.8 Sorption Studies of Crude Oil on Bentonites and Organoclays 106
4.8.1 The effect of sorbent dosage on oil sorption capacity 107
4.8.2 The effect of initial oil concentration on oil sorption capacity 108
4.8.3 The effect of contact time on the oil sorption capacity 109
4.8.4 Equilibrium sorption studies 110
4.8.5 Kinetic Isotherm studies 116
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5.0 DISCUSSION 122
5.1 Physicochemical Characterization of Raw and Modified Nanoclays 122
5.1.1 Proximate characteristics 122
5.1.2 Brauner-Emmet-Teller (BET) Analysis 123
5.1.3 pH in solution 124
5.1.4 Bulk Density 124
5.2 X-Ray Florescence (XRF) Analysis 127
5.3 Neutron Activation Analysis (NAA) 128
5.3.1 Interlayer/Exchangeable cations. 128
5.3.2 Octahedral Sheet Cations 129
5.3.3 Trace elements content 130
5.4 X-Ray Diffraction (XRD) Analysis 130
5.4.1 The effect of reaction time on the d(001) spacing 131
5.4.2 The effect of surfactant loading on d(001) spacing 132
5.4.3 The effect of temperature on intercalation 133
5.4.4 The effect of surfactant type on intercalation 134
5.5 Fourier Transform Infrared (FTIR) Analysis 135
5.6 Thermo-Analytical Studies 137
5.7 Scanning Electron Microscopy 140
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5.8 Sorption Studies 141
5.8.1 Sorption of crude oil on clay and organoclay samples 142
5.8.2 Equilibrium Sorption Studies 145
5.8.3 Kinetics Sorption Studies 150
6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS 156
6.1 Summary 156
6.2 Conclusion 157
6.3 Recommendations 158
REFERENCES 159
APPENDICES 183
CHAPTER ONE
1.0 INTRODUCTION
Oil is the life blood of our modern industrial society. It fuels the machineries and lubricates the wheels of the world’s production (Tahir and Mustaque, 2005; Adebiyi and Adeyemi, 2010). It is one of the most important energy and raw material resource for synthetic polymers and chemicals worldwide (Annunciado et al., 2005). However, when this vital resource is out of control, it can destroy lives and devastate the environment and economy of a particular region (Aynechi, 2004; Tahir and Mustaque, 2005).
An oil spill is the release of a liquid petroleum hydrocarbon into the environment due to human activity, and is a form of pollution (Rusu, 2010; Adelana et al., 2011). The term often refers to marine oil spills, where oil is released into the ocean or coastal waters. The oil may be a variety of materials, including crude oil, refined petroleum products (such as gasoline or diesel fuel) or by-products, oily refuse or oil mixed with waste. Spills take months or even years to clean up (Adelana et al., 2011). Due to its destructive properties, once an area has been contaminated with oil, the whole character of the place is damaged and when it encounters something to cling to, whether it be a beach, a rock, the feathers of a duck or a bathers hair, it does not readily let go (Aynechi, 2004). Hence, pollution by petroleum oils affects sea life, economy, tourism and leisure activities because of the coating properties of these materials (Hussein et al., 2008).
There are countless opportunities for oil to go out of control (Al Malek and Mohamed, 2005). Many are due to mechanical failure of the equipment, to deliberate act or due to human carelessness or mistakes (Anderson and LaBelle, 2000; Aynechi, 2004; Al Malek and Mohamed, 2005; Adelana et al., 2011). According to the United Nations Development
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Program (UNDP, 2006), Niger Delta human development report, spills occur accidentally and also through the deliberate actions of the local people, who sabotage pipelines in protest against the action of the Federal Government and oil companies. There are also risks implicated in the materials involved and the means of transporting the oil. The risks involve terminals, loading docks, refineries, tankers, freighters and pipelines, tanks, trucks, filling stations, just to name a few (Aynechi, 2004, Wang et al., 2013). In addition, the changing pattern of refining location has significantly increased the proportion of crude products moved over greater distances (Jagger, 1970). The increasing movement and storage of products has also increased the risk of instant water contamination (Jagger, 1970; Yammama, 1997).
The environmental effects of oil pollution are well known. They include the degradation of forest and depletion of aquatic fauna. Long term impacts are also possible, as in cases where mangrove swamps and ground water resources are harmed. In aquatic habitat, oil can be toxic to the frogs, reptiles, fish, water fowl and the animals that live in or other wise use the water (United State Environmental Protection Agency -USEPA, 2004a). Oiling may affect not only wild life but also plants that are rooted in or float in water, harming both the plants and the animals that depend on them for food and shelter. The implications of these findings are frightening, given that human health is tied to the food web (UNDP, 2006).
Spilled oil has an undesirable taste and odour and causes several environmental damages on water fowl, material life and affects tourisms and economy (Kingston, 2002). They harm the beauty of polluted sites; the strong odour can be felt miles away and the excessive growth of green algae alters sea colour and the landscape (Annunciado et al., 2005). Cleaning up an oil contaminated area is time consuming, difficult and very costly. The term costly does not refer
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only to the amount of money needed for the clean-up, but also to the destruction of wild life and fish, damage to properties, contamination of public water supplies and many other losses. These losses may extend for months or years (Stanley, 1969).
The adverse impact to ecosystems and the long term effect of environmental pollution call for an urgent need to develop a wide range of materials for cleaning-up oil from oil impacted areas especially as the effectiveness of oil treatment varies with time, the type of oil and spill, the location and weather conditions (Adebajo et al., 2003). Thus, various processes are being developed to remove oil from contaminated areas by use of booms, dispersants and skimmers, oil water separators or by use of different kinds of sorbents (Nahla, 2008).
Sorbents are used in different arrangements to collect spilled oil and oil products (Sirotkina and Novoselova, 2005). Absorbents materials are attractive for some applications because of possibility of collection and complete removal of the oil from their oil spill site. The addition of absorbents to oil spill areas facilitate a change from liquid to semi-solid phase and once this change is achieved, the removal of the oil by the removal of the absorbent structure then becomes much easier. Furthermore these materials can in some cases be recycled (Adebajo et al., 2003).
Oil sorbents can be categorized into three major classes: Inorganic mineral products, organic synthetic products and organic vegetable products (Hussein et al., 2008). Sorbents with large surface areas and affinity to organic compound could be developed from cost effective and readily available natural materials and by-products (Diya’udeen et al., 2008; Tiwari et al., 2008; Site, 2001).
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1.1 Clay Minerals
Clays are naturally occurring minerals with variability in their constitution depending on their groups and sources (Batra et al., 2007). These minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays form flat hexagonal sheets, similar to the micas, containing water trapped in the structure, hence good plasticity (Singh and Arbad, 2014). They are very common in fine grained sedimentary rocks such as shale, mudstone, siltstone and in fine grained metamorphic slate and phyllite (Merriman et al., 2003).
Clay minerals can be classified as 1:1 or 2:1, this originate from the fact that they are fundamentally built of tetrahedral silicate sheets and octahedral hydroxide sheets. A 1:1 clay would consist of one tetrahedral sheet and one octahedral sheet, and examples would be kaolinite and serpentine. A 2:1 clay consists of an octahedral sheet sandwiched between two tetrahedral sheets, and examples are talc, vermiculite and montmorillonite (Uddin, 2008). Clays are widely used in industrial products and processes. The use of clay suspensions is important in ceramic industry as well as in the production of paper, detergent and paints, foundry, civil engineering and in drilling operations (Yurudu et al., 2005).
The hydration of inorganic cations present in clay and the nature on Si-O groups impart a hydrophilic nature to the mineral surface and this property make them to absorb water but very difficult to disperse in polymer matrices, that is, organic compound cannot bond with adsorption site on the clay surfaces (Celis et al., 2000). As a result, natural clays are ineffective sorbents for poorly water soluble organic contaminants (Jaynes and Boyd, 1991). The surface of the clay may be modified greatly to make it strongly organophilic, however,
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by neutralizing the anionic framework of layer silicates by using positively charged organic species such as primary aliphatic amine salts and alkyl ammonium ion (Yurudu et al., 2006). In the modified form the clay surface may show organophilic nature and can bond strongly with organic compounds (Manocha, 2008).
Figure 1.1: Typical crystalline structure of layered silicates nanoclays
1.2 Organoclays
The clay materials have layered structure and layer thickness is around 1 nm, as shown in Figure 1.1. The lateral dimension may vary to a few micron or more depending upon the particular layered silicates. Stacking of the layered silicates lead to irregular layered van der
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Waal’s gap between the layers called interlayer or gallery (Patel et al., 2006). The clays used for the preparation of organoclays belong to the smectite group clays which are also known as 2:1 phyllosilicates, the most common which are montmorillonite and hectonite. The generic term layered silicate refers to natural clay as well as synthetic clays such as montmorillonite, laponite and hectonite (Bokopza, 2004). Organoclays can be obtained simply by the ion exchange reaction of hydrophilic clay with an organic cation such as an alkyl ammonium or phosphonium ion. The organic cation may enter into ion-exchange with exchangeable cations between the layers (Alemdar et al., 2005; Yurudu et al., 2006). In the modified form, the clay surface may show organophilic nature and can bond strongly with organic compounds.
1.3 Statement of the Problem
Residents of wetlands, like the Nigeria’s Niger-Delta, are concerned about the environmental impact of reoccurring and residual oil spill into receiving surface waters and land (Nwankwere, 2010). Hundreds of oil spills occur in Nigeria every year, causing significant harm to the environment, destroying local livelihoods and placing human health at serious risk (Amnesty International, 2013). The adverse impact of oil spillage to the ecosystem and the long term effect of environmental pollution call for an urgent need to develop a wide range of materials for cleaning up oil from oil impacted areas (Adebajo et al., 2003). Treating oil spillage could be costly and time consuming. Research into less costly and less time consuming technology calls for the need to investigate available natural resources that can remediate the environment. The most limiting problem with most natural materials is that they are generally highly hydrophilic in nature. Bentonite nanoclays can find application in oil spill treatment because of their nanostructured layer arrangement.
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1.4 Justification for the Research
The possibilities of cleaning oil pollution however, have not yet been sufficiently investigated (Nenkova et al., 2004) and there is still no suitable means of completely removing runoff in the water (Sirotkina and Nevoselova, 2005), pointing to a need for low-cost natural materials that are easy to dispose or biodegrade at the end of their service life. Absorbent materials are attractive for some applications because of the possibility of collection and complete removal of the oil from the oil spill site.
One important consequence of the charged nature of clays is that they are generally highly hydrophilic species and therefore naturally incompatible with wide range of non-polar systems (Patel et al., 2006). The conversion of natural clays to organically modified clays has two consequences, first the gaps between the single sheet is widened, enabling organic cations chain to move in between them and second, the surface properties of each single sheet are charged from being hydrophilic to organophillic (Patel et al., 2006). Organically modified layered silicate or nanoclays have become an attractive class of organic-inorganic hybrid materials because of their potential use in a wide range of applications such as polymer nanocomposites, rheological modifiers in paints, adsorbents for toxic gases, effluent treatment and drug delivery carrier (Patel et al., 2006).
It is also known that commercially available synthetic sorbents are very costly and not readily available, mostly due to the fact that a lot has been spent and to increase the sorption capacity of the synthetic product and they, unlike the natural sorbents, can hardly be reused nor are they biodegradable. A lot of research is therefore being carried out to develop natural potential sorbent materials for oil spill clean-up. Improved techniques for control and
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removal of oil slicks is one area of research under active development (Lee et al., 1999). Within the last decade, several methods were developed and used for modification of natural materials because natural materials on their own are not sufficient to treat oil spills. Modified natural resources have shown very high capacity to sorb oil from spill sites. In more recent times, researchers have focused on the use of nanohybrid materials, whose fundamental starting materials are nanoclays to remove oil residues from aqueous environments.
Nanoclays are abundant in Nigeria, especially in the North-Eastern zones. They exist in their impure form and are also very inexpensive. Research into the investigation of the potentials of these clay minerals for environmental remediation is limited. Very little work has been done on the modification of Nigerian nanoclays for the purpose of sorption of organic matter from aqueous solutions. Also, the chemical role of clay materials in sorption of crude oil hydrocarbons has not been fully understood. The potential input to the environment from this research includes:
i. Treatment of water resources from oil spillage, thereby conserving the natural mangroves, wildlife and water supply.
ii. Reduced incidence and severity of forest wildfires through reduced accumulated crude oil residue in mangroves.
iii. Protection of water resources from accumulation of excessive amounts of poisonous crude oil runoff, such as benzene, toluene, cresols and polynuclear aromatic hydrocarbons.
iv. Utilization of undervalued natural clay minerals to valuable sorption media which has the potential of providing economic incentives.
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v. Conversion of materials to biodegradable materials for oil spill clean-up to provide sustainable operations and development.
vi. A better understanding of sorption procedures (using natural materials) which will cause optimal use of sorption materials/processes.
vii. Application of the chemistry of the modification procedure in the development and improvement of other natural resources for similar applications.
1.5 Aim and Objectives
The aim of this research is to modify selected Nigerian bentonite clays, using Cetyl trimethylammonium cations under mild reaction conditions for subsequent application as sorbents for oil spill clean-up. The aim centres not only to provide an environmentally acceptable method of cleaning up oil spill but also to get an easily deployable and applicable technique which allows recovery for contingency. This aim is to be achieved via the following objectives:
i. Collection of three different bentonite based Nigerian clays
ii. Seperation and purification of the bentonite nanoclays
iii. Synthesis of organoclays by hydrothermal intercalation under several mild conditions using tertiary alkyl ammonium salts and investigation of the effect of those conditions, observing the optimum conditions that would produce the most efficient sorbents.
iv. Investigation of the influence of intercalation on the oil sorption capacity of the raw and modified samples.
v. Physico-chemical characterization of the raw and modified clay samples
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vi. Structural and morphological characterization of the raw and organically modified nanoclays by statistical, gravimetric, microscopic, crystallographic, thermal and spectrophotometric methods.
vii. Estimation the amount of spilled oil that can be treated by the nanoclays in a typical spill situation by applying sorption models.
viii. Development and recommendation of environmentally acceptable methods of cleaning up and recovery of spilled oil.
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