Philosophiae Doctor - PhD / Coal fly ash has been studied extensively to understand the environmental impacts associated with its disposal, management and reuse. Although several beneficiation processes have been proposed, there has been little or no emphasis on the environmental safety of such processes, products and wastes. Elemental analysis has revealed that toxic elements and radionuclides are present in coal fly ash. Rare earth elements (REE) such as La, Ce and Y are also present in significant amounts in coal fly ash. The aims of this study were to determine the total elemental composition of coal fly ash using different analytical techniques; to validate the application potentials of fly ash beneficiation processes in terms of their environmental safety; and to valorise coal fly ash with a view of recovering REE either by concentrating or leaching the REE in the coal fly ash, products or waste from the beneficiation processes. The beneficiation processes studied were treatment of acid mine drainage (AMD) with fly ash; and the synthesis of geopolymer from fly ash. The fresh fly ash sample used in this study was collected directly from the hoppers at Matla power station and the AMD sample was collected from Carletonville goldmine. A total of 54 major, trace and REE were accurately determined in the ash using different analytical techniques. It was shown that the elemental content of Matla fly ash was of the same order as the SRM NIST coal fly ash 1633b. The comparative study of the four analytical techniques established that ENAA can accurately determine the major, minor and trace elements; that XRF is best suited for the determination of the major and minor elements, whilst the LA ICP-MS is reliable for trace elements determination. The solid residue (AMD/FA) resulting from the AMD interaction with fly ash was characterized with fly ash and the results compared. The results revealed that the amounts of La (141.09 ± 3.85 mg/kg), Ce (27.45 ± 2.04 mg/kg), and Nd (63.73 ± 0.05 mg/kg) in AMD/FA residue was considerably higher than their average abundance in the earth crust that varies from 66 mg/kg in Ce and 40 mg/kg in Nd to 35 mg/kg in La. The results also showed that the AMD/FA residue contained As (11.39 ± 1.21 mg/kg), Cd (3.77 ± 0.02 mg/kg), Cr (72.43 ± 1.27 mg/kg), Hg (10.50 ± 0.85 mg/kg), Ni (124.15 ± 1.6 mg/kg) and Pb (22.46 ± 1.43 mg/kg) which are potentially harmful if leached in to the environment in excessive amounts.

Bibliography: pages 119-126. / Graphite Furnace Atomic Absorption Spectrometry (GFAAS) was used for the determination of cadmium and beryllium in coal and fly ash slurries. Sample preparation involved grinding the sample to a fine powder and slurrying it in a suitable solvent. Stable slurries were maintained by magnetic stirring during sampling. Pyrolytically coated graphite tubes were used for cadmium determinations, while beryllium was determined with platform atomisation. Ammonium dihydrogen orthophosphate and magnesium nitrate matrix modifiers were used for cadmium and beryllium determinations respectively. Calibration graphs constructed with aqueous standards containing the appropriate matrix modifier were rectilinear to at least 100 pg cadmium and 45 pg beryllium. Results were calculated with integrated peak area measurements. The detection limits were 2.9 pg for cadmium and 0.7pg for beryllium. Beryllium determinations were performed with semi-automatic sample introduction. The novel semi-automatic sampling unit utilised magnetic stirring for· the maintenance of stable slurries and operated with the standard Perkin-Elmer AS-40 autosampler. The principles of this unit were extended to the development of a fully automatic auto-sampling unit. The design and operation of both units are described. The accuracy of the methods was evaluated by analysing standard reference materials and in some cases, comparisons with acid digestion procedures. Data are presented for the analysis of South African coal and fly ash samples. The slurry methods had acceptable accuracy and precision. In comparison with the conventional acid digestion procedures using high pressure bombs, a time-saving advantage was realised.

Alkali silica reaction (ASR) is detrimental to concrete. It is a time-dependent phenomenon, which can lead to strength loss, cracking, volume expansion, and premature failure of concrete structures. In essence, it is a particular chemical reaction involving alkali hydroxides and reactive form of silica present within the concrete mix. Geopolymer is a type of alkaline activated binder synthesized through polycondensation reaction of geopolymeric precursor and alkali polysilicates. In this thesis, three types of reactive aggregates with different chemical compositions were used. Systematic laboratory experiments and microstructural analysis were carried out for the geopolymer concrete and the OPC concrete made with the same aggregates. The result suggests that the extent of ASR reaction due to the presence of three reactive aggregates in geopolymer concrete is substantially lower than that in OPC based concrete, which is explained by the pore solution change and verified through their microstructural variations and FTIR images.

No description available.

An economical process for the elimination of nutrients to receiving waters.is a major problem now facing modern wastewater treatment. The purpose of this investigation was to determine the feasibility of soluble phosphate removal in a flyash contact system. The investigation consisted of experiments involving batch adsorption studies and continuous flow studies. Removal kinetics and relationships between contact time, “t” , and flyash concentration, “D_f”, were evaluated using batch adsorption techniques. Of the two flyash samples tested the high alumina content flyash exhibited the best rate of phosphate removal. The high alumina content flyash yielded an average removal capacity of 2.47 x l0⁻⁴ grams of phosphorus per gram of flyash, whereas the low alumina content flyash yielded an average capacity of only 1.61 x 10⁻⁴ grams of phosphorus per gram of flyash. Continuous flow operations were conducted using both types of flyash so as to observe the removal in an actual process situation. The phosphate removal was concluded to be both physical and chemical in nature, with two removal mechanisms predominating. The primary physical mechanism involved the phosphate adsorption on the alumina surface found in the flyash. The chemical removal mechanism was postulated to be the precipitation of phosphate as Mg₃(PO₄)₂ and Ca₃(PO₄)₂ at pH levels above 8.0. / Master of Science

Thesis (Master of Engineering in Chemical Engineering)--Cape Peninsula University of Technology, 2018. / Zeolites have found applications as heterogeneous or solid catalyst in the petrochemical and refining industries. Zeolite ZSM-5 in particular is a highly siliceous solid catalyst with a porous network that consists of medium pore structure (pore openings 5-5.5 A). The solid catalyst (ZSM-5) is well known for its high temperature stability and strong acidity, which makes it an established catalyst used for different petrochemical processes such as Methanol-To-Gasoline (MTG), isomerisation, disproportionation, and cracking. Unlike in the past, the synthesis of zeolite ZSM-5 from other sources that contains silica (Si) and alumina (Al) with the addition of a template (TPBr) as a structure-directing agent is eminent. Its synthesis can be achievable from coal fly ash that is a waste material and a cheap source of Si and Al. Coal fly ash is a waste material that is produced during the combustion of coal to generate electricity. The elemental composition of coal fly ash consists of mostly SiO2 and Al2O3 together with other significant and trace elements. Zeolite ZSM-5 catalyst synthesised from coal fly ash by previous authors required an excessive amount of additional source of silica even though the XRD spectra still show the presence of quartz and mullite phase in the final products. These phases prevented the use of fly ash (solid) as a precursor to synthesise zeolite ZSM-5 products. However, the synthesis of high purity zeolite ZSM-5 products by extracting silica and alumina from South African fly ash and then using it with small amounts of fumed silica was investigated This aim was achieved by fusing fly ash (FA) with sodium hydroxide (NaOH) under hydrothermal condition set at 550 oC for 1 hour 30 minutes. The quartz and mullite phase observed by previous authors was digested by the fusion process. Thereafter, the treatment of fused fly ash filtrate (FFAF) with concentrated H2SO4 (98-99%), precipitated silica and removed Al that therefore increased the Si/Al ratio from 1.97 in fly ash (FA) to 9.5 in the silica extract (named fused fly ash extract). This route was designed to improve the quality of the final products and reduced the amount of fumed silica added to the synthesis mixture prior to hydrothermal synthesis. In this line of investigation, the process of adding fumed silica to the hydrothermal gel was optimised. H-FF1 with a Si/Al ratio of 9.5 was synthesised using the silica extract without the addition of fumed silica. Its XRD, SEM and relative crystallinity results proved that H-FF1 was inactive and hence was not further characterised and utilised in the conversion of methanol to hydrocarbons (MTH). Purer phase zeolite ZSM-5 products (H-FF2 and H-FF3) that were synthesised from silica extract with the addition of small amounts of fumed silica were characterised and successfully used in the methanol to hydrocarbons (MTH) reaction. The synthesised ZSM-5 products had different Si/Al ratio, different morphology, crystal size, BET surface area, and relative crystallinity as well as different trends in the MTH reaction. It was also observed that H-FF2 and H-FF3 (pure phase) solid catalyst deactivated faster than the commercial H-ZSM-5 in the MTH reaction. However, the MTH conversion over H-FF2 competed with that of the commercial H-ZSM-5 within 3 hours of time on stream (TOS) but later deactivated at a faster rate. This was caused by the large crystal size and reduced BET surface area of H-FF2 when compared to the commercial H-ZSM-5. However, H-FF2 performed better than H-FF3 on stream (MTH reaction) due to its smaller crystal size and higher BET. This study has successfully utilised a route that synthesised high purity zeolite ZSM-5 products from the South African fused fly ash extract (FFAE) with the addition of small amounts of fumed silica. The properties of the synthesised zeolite ZSM-5 products (H-FF2 and H-FF3) were similar to that of the commercial H-ZSM-5 as well as active in the MTH reaction. This promoted the utilisation of a waste material (coal fly ash) to synthesise highly siliceous zeolite ZSM-5 products that avoided the presence of mineral phases from fly ash in the final products.

Fly ash is a lightweight coal combustion by-product (CCB) separated from the exhaust gases of power generating plants using suspension-fired furnaces in which pulverized coal is used as the fuel. Its physical and chemical properties make it useful in construction and industrial materials, especially in cement manufacturing, concrete, liquid waste stabilization, and hydraulic mine backfill. The addition of fly ash into aluminum alloys has the potential to reduce the cost and density of aluminum castings while improving other physical and mechanical properties of the resulting metal matrix composites (MMCs). <p> This study investigated the effect of fly ash addition on the mechanical properties and microstructural behaviour of aluminum casting alloy A535. The unreinforced A535 alloy and its MMCs containing a mixture of 5 wt.% fly ash and 5 wt.% silicon carbide, 10 wt.% fly ash and 15 wt.% fly ash were investigated in the as-cast and solution heat treated conditions. Microhardness measurements, Charpy impact testing, tensile testing, optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), inductively coupled plasma/mass spectrometry (ICP/MS), X-ray diffractometry (XRD), and X-ray fluorescence spectroscopy (XRF) were used to evaluate these effects. <p> The results of this study show that increasing the fly ash content of the melt increased the porosity of the castings, which ultimately affected the density, tensile and impact properties of the MMCs. The density, microhardness, tensile strength and Charpy impact energy of the composites decreased with increasing fly ash content. The decline in density of the MMCs was due to extensive porosity developed with fly ash addition. Depletion of solid solution strengthening magnesium in the matrix was the reason observed for the decline in hardness. The loss in Charpy impact energy and tensile properties of the MMCs are also attributed partly to the depletion of solid solution strengthening magnesium atoms from the matrix and partly to porosity. <p> Microstructural studies revealed non-uniform distribution of reinforcement particles in the composites. The fly ash particles were found to congregate at the boundaries of a-aluminium dendrites in the castings. Mg content of A535 alloy decreased with increasing weight fraction of fly ash. Mg was found to be tied up in a complex network of Mg2Si thereby reducing its availability in the matrix for solid solution strengthening.

Fly ash is a lightweight coal combustion by-product (CCB) separated from the exhaust gases of power generating plants using suspension-fired furnaces in which pulverized coal is used as the fuel. Its physical and chemical properties make it useful in construction and industrial materials, especially in cement manufacturing, concrete, liquid waste stabilization, and hydraulic mine backfill. The addition of fly ash into aluminum alloys has the potential to reduce the cost and density of aluminum castings while improving other physical and mechanical properties of the resulting metal matrix composites (MMCs). <p> This study investigated the effect of fly ash addition on the mechanical properties and microstructural behaviour of aluminum casting alloy A535. The unreinforced A535 alloy and its MMCs containing a mixture of 5 wt.% fly ash and 5 wt.% silicon carbide, 10 wt.% fly ash and 15 wt.% fly ash were investigated in the as-cast and solution heat treated conditions. Microhardness measurements, Charpy impact testing, tensile testing, optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), inductively coupled plasma/mass spectrometry (ICP/MS), X-ray diffractometry (XRD), and X-ray fluorescence spectroscopy (XRF) were used to evaluate these effects. <p> The results of this study show that increasing the fly ash content of the melt increased the porosity of the castings, which ultimately affected the density, tensile and impact properties of the MMCs. The density, microhardness, tensile strength and Charpy impact energy of the composites decreased with increasing fly ash content. The decline in density of the MMCs was due to extensive porosity developed with fly ash addition. Depletion of solid solution strengthening magnesium in the matrix was the reason observed for the decline in hardness. The loss in Charpy impact energy and tensile properties of the MMCs are also attributed partly to the depletion of solid solution strengthening magnesium atoms from the matrix and partly to porosity. <p> Microstructural studies revealed non-uniform distribution of reinforcement particles in the composites. The fly ash particles were found to congregate at the boundaries of a-aluminium dendrites in the castings. Mg content of A535 alloy decreased with increasing weight fraction of fly ash. Mg was found to be tied up in a complex network of Mg2Si thereby reducing its availability in the matrix for solid solution strengthening.

Varieties of masonry units such as burnt clay bricks, stones and concrete products are used for masonry construction. Even though these materials are durable, they are considered as unsustainable options because of the issues concerning energy, environment and conservation of natural resources. The walling materials are consumed in bulk quantities and hence large quantities of natural resources are depleted. There is a need for energy efficient and environment friendly alternative materials for masonry. Fly ash is an industrial by-product from the coal based thermal power plants which can be exploited for manufacturing of masonry units such as fly ash blocks/bricks, which are an alternative for conventional masonry units. Fly ash-Lime-Gypsum (FaL-G) bricks can be manufactured by compaction of a mixture of fly ash-lime-gypsum and water. The behaviour of FaL-G brick masonry is inadequately explored area and hence the thesis is focused on understanding the flexural behaviour of FaL-G brick masonry and bond development phenomenon at FaL-G brick-mortar interface. A brief introduction to the fly ash-based masonry units and literature review with respect to utilizing fly ash in manufacturing masonry units are presented. Characteristics of raw materials used and the procedure followed in casting of masonry units/compacts, mortar and their assemblages including testing methods have been discussed. Characteristics of FaL-G brick, mortars, FaL-G brick masonry are presented. Apart from determining the stress-strain relationships for these materials shear strength parameters of FaL-G compact, mortar and brick-mortar joint were determined. Mohr-Coulomb failure envelopes for FaL-G compact and mortar are presented. The mechanism of bond development in masonry is discussed. FaL-G brick masonry shows considerably higher bond strength when compared with the bond strength of conventional brick masonry. Results of micro-structure analysis (SEM, XRD and TGA) of the FaL-G brick-mortar interfaces confirm the formation of chemical bond in addition to mechanical interlocking of cement hydration products into brick pores. Flexural behaviour of FaL-G brick masonry wallettes in the two orthogonal directions was studied. The flexural strength, displacement profiles and load-displacement curves were determined, and moment-curvature relationships were established. Linear elastic analysis performed closely predicted the cracking flexural stress in FaL-G brick masonry. A brief introduction to the computational modelling of masonry using different approaches has been presented. Literature review with respect to simplified micro-modelling approach has been discussed. The flexural behaviour of FaL-G brick masonry panels under lateral loads was predicted using a non-linear 3D finite element analysis. The finite element model reasonably predicted the flexural behaviour of FaL-G brick masonry panels. The thesis ends with summary of research work with a note on scope for further research.

>Magister Scientiae - MSc / Coal is the main source of electricity in South Africa, the combustion of which produces a large amount of waste (coal fly ash) annually. The large-scale generation of coal fly ash places major strain on landfills and the material is toxic in nature. The high silicon and aluminium content in fly ash makes it a suitable starting material for zeolite synthesis. Utilisation of fly ash as a starting material for zeolite synthesis alleviates an environmental burden by converting a waste product to an industrially applicable material. In this study, hierarchical zeolite X was synthesised from coal fly ash via the fusion method. The clear fused fly ash (FFA) extract (with molar composition 0.12 Al·14.6 Na·1.00 Si·163 H₂O) served as the synthesis solution for hydrothermal treatment. The influence of synthesis parameters (such as Si/Al ratio, aluminium source, hydrothermal temperature and stirring) on hierarchical zeolite X formation was studied to determine the cause behind the formation of this material. Synthesised zeolites and starting materials (Arnot coal fly ash and fused fly ash) were characterised by various analytical techniques such as XRD and SEM-EDS to determine the phase purity, morphology and elemental composition (framework Si/Al ratio) of these materials. The synthesis of hierarchical zeolite X under hydrothermal conditions was found to be highly sensitive to the aluminium content of the synthesis solution. The hierarchical morphology of zeolite X was formed preferentially in relatively aluminium-deficient (i.e. high Si/Al ratio) synthesis environments under stirred hydrothermal conditions of 90 °C for 16 hours. In the case of sodium aluminate addition, octahedral shaped zeolite X crystals were formed in relatively low Si/Al ratio synthesis environments, which was attributed to the presence of excess sodium cation content in the synthesis solution. Selected hierarchical zeolites (D2 and E2) were characterised further to gain more insight into the properties of this material. HR-TEM and FTIR revealed that hierarchical zeolite D2 and E2 exhibited the typical structural features of zeolite X. Zeolite D2 and E2 contained both micropores and mesopores and had a high BET surface area of 338-362 m²/g. These zeolites also exhibited appreciable solid acidity (0.81-1.12 mmol H/g zeolite). These properties make hierarchical zeolite X a favourable material for application in catalysis or adsorption. Overall, the formation of zeolite X with hierarchical morphology was proposed to be linked to the presence of zeolite P1 structural units in the framework of the zeolite. / National Research Foundation