Outline of the subsequent chapters

Besides this introductory chapter this thesis will also consist of the following chapters:

Chapter 2: Literature review

Chapter two will contain the reviews of different literature focusing on the source, physical and chemical properties, disposal, environmental impact and beneficiation of coal fly ash. The literature of REE, geopolymers and AMD was reviewed. The principles behind the analytical techniques used in this study were also reviewed.

Chapter 3: Sampling, experimental and analytical methods

The outline of sampling protocol, analytical procedures and experimental methods used in this study to address the research objectives will be presented in chapter 3. A detailed outline of the procedures used for the synthesis of foamed geopolymer from fly ash and the AMD treatment with fly ash will also be covered in this chapter. Furthermore the methods that were used in the characterisation, leaching

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and analysis of the fly ash samples, fly ash reuse products and waste will be presented in this chapter.

Chapter 4: Comparison of analytical techniques

Chapter 4 presents and discusses the results obtained in the elemental analysis of the Matla fly ash as. In this chapter the results are presented of ENAA, XRF, ICP- OES and LA ICP-MS analysis of the fly ash samples. The results will be discussed in order to understand the method that is best suited for determining the different categories of elements that are contained in coal fly ash.

Chapter 5: Application of fly ash for AMD treatment

In chapter 5 the use of coal fly ash in the treatment of AMD as specified in chapter 3 will be presented and discussed. The results obtained from the characterisation of the fly ash sample, the AMD before and after treatment with fly ash and the resulting AMD/FA residue will be presented. The results were used to determine the toxicity of the treated AMD and AMD/FA residue. The results were discussed and compared to that reported in literature and significant findings were highlighted.

Chapter 6: Application of fly ash in synthesis of geopolymer

In this chapter the use of fly as in the synthesis of geopolymer is presented and discussed. The results obtained from the characterisation of the fly ash and synthesised geopolymer samples are presented and compared in order to understand the changes in the elemental composition, morphology, mineralogical content of the feedstock and product. The results obtained from the DIN-S4 leaching test and the gamma ray spectroscopy was used to determine the leachability and radioactivity of the synthesised geopolymer with respect to environmental safety.

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Chapter 7: Possibility of REE recovery from fly ash

The results of the sequential leaching experiments will be presented and discussed in this chapter. The chapter will focus on determining where the REE are concentrating during the sequential extraction scheme. The results and findings were used to assess the overall efficiency of the process as well as the environmental implications of the process, products and wastes.

Chapter 8: Conclusion and recommendations

The conclusions reached from the investigation of the environmental safety of the fly ash beneficiations in terms of processes, products and waste are presented in this chapter. The knowledge and experience acquired from this study are used to make appropriate recommendations for future work.

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Chapter Two

2 Introduction

Chapter two contains the review of different literature focusing on the source, physical and chemical properties, disposal, environmental impact and beneficiation of coal fly ash in sections 2.1 to 2.10. The geopolymer literature will also be reviewed in section 2.11 in order to understand the synthesis methods, the physical, chemical properties and applications. The literature of AMD will also be reviewed with focus on its origin, characterisation and treatment methods in Section 2.12. Furthermore, the literature of the analytical techniques used in this study is also reviewed in sections 2.14 to 2.16. The chapter ends with a summary of the major findings from the review of the literature.

Coal fly ash is the major component of the waste material produced from the combustion of coal. It is produced as a waste product from the combustion of pulverised coal to generate electricity in power plants and steam generating plants. Fly ash is formed when pulverized coal and air are blown into the boiler's combustion chamber where it instantly ignites, the combustion generates heat and produces a molten mineral residue. Boiler tubes remove heat from the boiler resulting in the cooling of the flue gas and hardening of the molten mineral residue to form ash. Bottom ash or slag (which are coarse ash particles), fall to the bottom of the combustion chamber, while the lighter fine ash particles (fly ash), remain suspended in the flue gas. To prevent the release of fly ash into the atmosphere, the fly ash is removed by particulate emission control devices, such as electrostatic precipitators or filter fabric baghouses. About 80 % of the solid residue from the pulverised coal combustion is released as fly ash (www.fhwa.dot.gov).

The properties of fly ash depend on the physical and chemical properties of the coal source, the coal particle size, the combustion process, and the type of ash collector used. Fly ash usually consists of spheres composed of crystalline matter and some residual carbon. Although in bulk, fly ash is considered as

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homogeneous agglomerate consisting mainly of spherical particles ranging from a micron up to tens of microns in diameter. The individual particles vary in size, morphology, mineralogy and chemical composition. The variable physical and chemical properties of fly ashes are attributed to the influence of the coal source, particle size, type of combustion process and moisture content (Jankowski et al., 2006;Vassilev and Vasssileva, 2007; Sočo and Kalembkiewicz, 2009).

Fly ash is deemed to be highly contaminating because of the high surface area of the particles. This high surface area gives rise to the enrichment of potentially toxic elements which condense during cooling of combustion gases (Querol et al., 1996). Hence the disposal of fly ash is of major concern globally because of the enormous quantity that is generated and the environmental issues arising from the disposal methods that are currently employed. Worldwide huge amounts of coal fly ash are generated in order to meet energy demands and about 70 % of fly ash is disposed as waste (Haynes, 2009). In 2009, China generated over 375 million tons of coal ash (Greenpeace, 2010). In 2008, the coal-fuelled electric power industry generated approximately 72.4 million tons of coal fly ash, in the USA (www.epa.). India was predicted to generate about 170 million tonnes per annum (Sushil, and Batra, 2006). In South Africa, Eskom generated nearly 36.7 million tons of fly ash in 2009 from coal combustion, of which only 5.7% was utilised beneficially (www.eskom.co.za) while Sasol produced about 4 million tonnes annually (Mahlaba et al., 2011). Thus management of this combustion waste is of major concern. In the management of this combustion by-product the focus should not only be on the prevention of environmental pollution, but also on methods that can be used to produce or manufacture value-added products from stored fly ash