Magister Scientiae - MSc / The current study investigated application of natural adsorbents in brine treatment. Brines are hypersaline waters generated in power stations and mining industries rich in Mg2+, K+, Ca2+, Na+, SO4 2- , Cl- and traces of heavy metals, thus there is a need for these brines to be treated to recover potable water and remove problematic elements. Natural adsorbents have been successfully used in waste water treatment because of their high surface area and high adsorptive properties when they are conditioned with acid or base. The investigation of pH showed that natural adsorbents did not perform well at low pH of 4 and 6. The adsorbents were able to work efficiently at the natural pH of 8.52 of the brine solution. These results show that natural adsorbents hold great potential to remove cationic major components and selected heavy metal species from industrial brine waste water. Heterogeneity of natural adsorbents samples, even when they have the same origin, could be a problem when wastewater treatment systems utilizing natural clinoptilolite and bentonite are planned to be developed. Therefore, it is very important to characterize the reserves fully in order to make them attractive in developing treatment technologies. / South Africa

The current study investigated application of natural adsorbents in brine treatment. Brines are hypersaline waters generated in power stations and mining industries rich in Mg2+, K+, Ca2+, Na+, SO4 2- , Cl- and traces of heavy metals, thus there is a need for these brines to be treated to recover potable water and remove problematic elements. Natural adsorbents have been successfully used in waste water treatment because of their high surface area and high adsorptive properties when they are conditioned with acid or base. The investigation of pH showed that natural adsorbents did not perform well at low pH of 4 and 6. The adsorbents were able to work efficiently at the natural pH of 8.52 of the brine solution. These results show that natural adsorbents hold great potential to remove cationic major components and selected heavy metal species from industrial brine wastewater. Heterogeneity of natural adsorbents samples, even when they have the same origin, could be a problem when wastewater treatment systems utilizing natural clinoptilolite and bentonite are planned to be developed. Therefore, it is very important to characterize the reserves fully in order to make them attractive in developing treatment technologies.

The current study investigated application of natural adsorbents in brine treatment. Brines are hypersaline waters generated in power stations and mining industries rich in Mg2+, K+, Ca2+, Na+, SO4 2- , Cl- and traces of heavy metals, thus there is a need for these brines to be treated to recover potable water and remove problematic elements. Natural adsorbents have been successfully used in waste water treatment because of their high surface area and high adsorptive properties when they are conditioned with acid or base. The investigation of pH showed that natural adsorbents did not perform well at low pH of 4 and 6. The adsorbents were able to work efficiently at the natural pH of 8.52 of the brine solution. These results show that natural adsorbents hold great potential to remove cationic major components and selected heavy metal species from industrial brine wastewater. Heterogeneity of natural adsorbents samples, even when they have the same origin, could be a problem when wastewater treatment systems utilizing natural clinoptilolite and bentonite are planned to be developed. Therefore, it is very important to characterize the reserves fully in order to make them attractive in developing treatment technologies.

>Magister Scientiae - MSc / Studies involving the use of natural clays such as bentonite, montmorillonite and natural zeolite clinoptilolite in water treatment have been reported. Researchers suggested cost effective processes, such as ion-exchange and adsorption for the removal of heavy metals from waste waters by using naturally occurring and synthetic materials. The current study investigated application of natural adsorbents in brine treatment. Brines are hypersaline waters generated in power stations and mining industries rich in Mg2+, K+, Ca2+,Na+, so,': cr and traces of heavy metals, thus there is a need for these brines to be treated to recover potable water and remove problematic elements. Natural adsorbents have been successfully used in waste water treatment because of their high surface area and high adsorptive properties when they are conditioned with acid or base. The natural adsorbents used in this study were obtained from Ecca Holdings company (Cape bentonite mine) Western Cape in South Africa, comprising bentonite clay and natural zeolite (clinoptilolite) and another clinoptilolite sample was obtained from Turkey. These adsorbents were investigated in their natural and pretreated form for removal of toxic elements in brine water. The pretreatment was aimed at removing Na+, K+, Ca2+, Mg2+ from the clinoptilolite as well as the bentonite and replacing these cations with the H+ cation to activate the materials. The cation exchange capacity (CEC) of natural zeolite from South Africa was found to be 2.14 meq/ g, Turkish Clinoptilolite was 2.98 meq/ g while South African bentonite was 1.73 meq/g. at 25°C using ammonium acetate (pH 8.2) method. Characterization of these natural adsorbents was done prior to pretreatment and after the treatment. ICP-AES analysis was used for determination of toxic elements in brines before and after sorption. The morphology of clays was characterized by X-ray diffraction (XRD), Brunauer Emmett Teller (N2-BET) and Scanning electron microscopy (SEM) for confirmatory purposes and X-ray Fluorescent spectroscopy (XRF) was used for the composition analysis of the natural adsorbent. The results from batch experiments prior to pretreatment of the natural adsorbents showed that these natural adsorbents contained Mg2+, K+, Ca2+, Na+ in their structures as charge balancing cations, thus needed pretreatment to remove the cations. The natural adsorbents were pre-treated with 0.02M HCI. After the pretreatment of natural adsorbents it was possible to enhance the percentage removal of the major cations from brine, and the Na+ and Mg2+ removal achieved (86 % and 85% respectively) from brine was more than C02+ (70% ) the SC was the adsorbent one that gave highest removal of cations in the brines. Trace elements removal was high with Cu2+and Zn2+ being the highest of toxic elements in brine. The optimum contact for the toxic element removal was found to be 30 min for the Turkish clinoptilolite and 1 hr for the South African clinoptilolite and South African bentonite clay. Leaching of Ae+ and Si4+ during adsorption was also investigated and it was found that less than 1 ppm of A13+ and Si4+ were leached into the solution during adsorption experiments indicating that these materials were stable. The investigation of pH showed that natural adsorbents did not perform well at low pH of 4 and 6. The adsorbents were able to work efficiently at the natural pH of 8.52 of the brine solution. These results show that natural adsorbents hold great potential to remove cationic major components and selected heavy metal species from industrial brine wastewater. Heterogeneity of natural adsorbents samples, even when they have the same origin, could be a problem when wastewater treatment systems utilizing natural clinoptilolite and bentonite are planned to be developed. Therefore, it is very important to characterize the reserves fully in order to make them attractive in developing treatment technologies.

O Estuário de Caravelas, localizado na costa nordeste brasileira (extremo sul da Bahia) é considerado uma zona relativamente não impactada, com importante papel econômico e ecológico, devido a presença de fragmentos de Mata Atlântica, manguezais e sua localização próxima ao Complexo recifal de Abrolhos, o maior e mais importante do Oceano Atlântico Sul. No entanto, especialmente no último século, este estuário tem sido sujeito a impactos naturais e antrópicos que podem ter contribuído com mudanças neste sistema. Portanto, este estudo, baseado em uma abordagem \"multiproxy\", como análise de metais traço, elementos maiores, mineralogia, parâmetros descritivos da composição da matéria orgânica como COT, NT, razão Corg/Ntotal, &#948;13C, teve o objetivo de avaliar registro deposicional natural e antropogênico, do último século em 3 testemunhos datados por 210Pb e 137Cs. As taxas de sedimentação obtidas através do modelo CRS foram de 1,07 &#177; 0,13 cm ano-1 para o testemunho T2 (estuário médio), 0,65 &#177; 0,06 cm ano-1 para o testemunho T5 e 0,85 &#177; 0,09 cm ano-1 (desembocadura). O testemunho localizado no estuário médio (T2) apresentou uma maior influência terrígena com contribuição de plantas C3 para a matéria orgânica (- 26,50 < &#948;13C < -24,39; 21,38 < Corg/Ntotal < 37,67) e teores maiores do argilomineral caulinita, enquanto os testemunhos T5 e T8, localizados próximo a desembocadura do estuário, apresentaram uma maior influência marinha (- 26,48 < &#948;13C < -23,24; 4,18 < Corg/Ntotal < 21,34). Além disso, uma mudança significativa nos \"proxies\" orgânicos e inorgânicos, no início da década de 1960, mostrou a influência da abertura natural de um canal (Boca do Tomba) na hidrodinâmica e na distribuição dos sedimentos. A distribuição de elementos maiores e metais traço não apresentou um enriquecimento significativo e foi associada ao aporte litogênico, indicando o papel do Grupo Barreiras como uma importante fonte de material terrígeno para o estuário de Caravelas. / The Caravelas estuary, located on the Brazilian northeast coast (extreme South of Bahia) is considered a relatively unimpacted zone, with an important economic and ecological role, due to the presence of fragments of Atlantic Forest and mangroves, and its location next to the Abrolhos Bank, the largest and most important reefs of the south Atlantic Ocean. However, especially in the last century, this estuary has been subject to natural and anthropogenic impacts that may have contributed to changes in this system. Therefore, this study, based on a multiproxy approach, such as analysis of trace metals, major elements, mineralogy, parameters describing the composition of organic matter such as TOC, TN, Corg/Ntotal ratio, &#948;13C, had the main goal of evaluating the natural and anthropogenic depositional record, of the last century, in 3 sediment cores dated by 210Pb and 137Cs. The sedimentation rates obtained through CRS model were 1,07 &#177; 0,13 cm y-1 for sediment core T2 (middle estuary), 0,65 &#177; 0,06 cm y-1 for the T5 and 0,85 &#177; 0,09 cm y-1 for T8 (estuary mouth). The sediment core T2 showed a greater terrigenous influence with C3 plant contribution to the organic matter (- 26,50 < &#948;13C < -24,39; 21,38 < Corg/Ntotal < 37,67) and higher contents of kaolinite, meanwhile sediment cores T5 and T8, located at the mouth of the estuary, had a greater marine influence (- 26,48 < &#948;13C < -23,24; 4,18 < Corg/Ntotal < 21,34) and higher contents of calcite and aragonite. Furthermore, a significant change in the organic and inorganic proxies in the early 1960s showed the influence of the natural opening of an inlet (Boca do Tomba) on hydrodynamics and sediment deposition. Finally, the distribution of major and trace elements did not present a significant enrichment and was associated to lithogenic contribution, indicating the role of the Barreiras Group as an important source of terrigenous material to the Caravelas estuary.

O Estuário de Caravelas, localizado na costa nordeste brasileira (extremo sul da Bahia) é considerado uma zona relativamente não impactada, com importante papel econômico e ecológico, devido a presença de fragmentos de Mata Atlântica, manguezais e sua localização próxima ao Complexo recifal de Abrolhos, o maior e mais importante do Oceano Atlântico Sul. No entanto, especialmente no último século, este estuário tem sido sujeito a impactos naturais e antrópicos que podem ter contribuído com mudanças neste sistema. Portanto, este estudo, baseado em uma abordagem \"multiproxy\", como análise de metais traço, elementos maiores, mineralogia, parâmetros descritivos da composição da matéria orgânica como COT, NT, razão Corg/Ntotal, &#948;13C, teve o objetivo de avaliar registro deposicional natural e antropogênico, do último século em 3 testemunhos datados por 210Pb e 137Cs. As taxas de sedimentação obtidas através do modelo CRS foram de 1,07 &#177; 0,13 cm ano-1 para o testemunho T2 (estuário médio), 0,65 &#177; 0,06 cm ano-1 para o testemunho T5 e 0,85 &#177; 0,09 cm ano-1 (desembocadura). O testemunho localizado no estuário médio (T2) apresentou uma maior influência terrígena com contribuição de plantas C3 para a matéria orgânica (- 26,50 < &#948;13C < -24,39; 21,38 < Corg/Ntotal < 37,67) e teores maiores do argilomineral caulinita, enquanto os testemunhos T5 e T8, localizados próximo a desembocadura do estuário, apresentaram uma maior influência marinha (- 26,48 < &#948;13C < -23,24; 4,18 < Corg/Ntotal < 21,34). Além disso, uma mudança significativa nos \"proxies\" orgânicos e inorgânicos, no início da década de 1960, mostrou a influência da abertura natural de um canal (Boca do Tomba) na hidrodinâmica e na distribuição dos sedimentos. A distribuição de elementos maiores e metais traço não apresentou um enriquecimento significativo e foi associada ao aporte litogênico, indicando o papel do Grupo Barreiras como uma importante fonte de material terrígeno para o estuário de Caravelas. / The Caravelas estuary, located on the Brazilian northeast coast (extreme South of Bahia) is considered a relatively unimpacted zone, with an important economic and ecological role, due to the presence of fragments of Atlantic Forest and mangroves, and its location next to the Abrolhos Bank, the largest and most important reefs of the south Atlantic Ocean. However, especially in the last century, this estuary has been subject to natural and anthropogenic impacts that may have contributed to changes in this system. Therefore, this study, based on a multiproxy approach, such as analysis of trace metals, major elements, mineralogy, parameters describing the composition of organic matter such as TOC, TN, Corg/Ntotal ratio, &#948;13C, had the main goal of evaluating the natural and anthropogenic depositional record, of the last century, in 3 sediment cores dated by 210Pb and 137Cs. The sedimentation rates obtained through CRS model were 1,07 &#177; 0,13 cm y-1 for sediment core T2 (middle estuary), 0,65 &#177; 0,06 cm y-1 for the T5 and 0,85 &#177; 0,09 cm y-1 for T8 (estuary mouth). The sediment core T2 showed a greater terrigenous influence with C3 plant contribution to the organic matter (- 26,50 < &#948;13C < -24,39; 21,38 < Corg/Ntotal < 37,67) and higher contents of kaolinite, meanwhile sediment cores T5 and T8, located at the mouth of the estuary, had a greater marine influence (- 26,48 < &#948;13C < -23,24; 4,18 < Corg/Ntotal < 21,34) and higher contents of calcite and aragonite. Furthermore, a significant change in the organic and inorganic proxies in the early 1960s showed the influence of the natural opening of an inlet (Boca do Tomba) on hydrodynamics and sediment deposition. Finally, the distribution of major and trace elements did not present a significant enrichment and was associated to lithogenic contribution, indicating the role of the Barreiras Group as an important source of terrigenous material to the Caravelas estuary.

The origin of compositional gaps in volcanic deposits remains controversial. In Akaroa Volcano (9.6 to 8.6 Ma), New Zealand, a dramatic compositional gap exists between basaltic and trachytic magmas. Previously, the formation of more evolved magmas has been ascribed to crustal melting. However, the interpretation of new major and trace element analysis from minerals and bulk-rocks coupled with the mechanics of crystal-liquid separation offers an alternative explanation that alleviates the thermal restrictions required for crustal melting models. In a two-stage model, major and trace element trends can be reproduced by polybaric crystal fractionation from dry melts (less than 0.5 wt.% H2O) at the QFM buffer. In the first stage, picritic basalts are separated from an olivine-pyroxene dominant mush near the crust-mantle boundary (9 to 10 kbar). Ascending magmas stagnated at mid-crustal levels (5 to 6 kbar) and fractionated an olivine-plagioclase assemblage to produce the alkali basalt-hawaiite trend. In the second stage, trachyte melt is extracted from a crystal mush of hawaiite to mugearite composition at mid-to-upper crustal levels (3 to 5 kbar) after the melt has crystallised 50 vol.%. The fractionated assemblage of plagioclase, olivine, clinopyroxene, magnetite, and apatite is left in a cumulate residue which corresponds to the mineral assemblage of sampled ultramafic enclaves. The results of trace element modelling of Rayleigh fractionation using this extraction window is in close agreement with the concentrations measured in trachyte (= liquid) and enclaves (= cumulate residue). The compositional gap observed in the bulk-rock data of eruptive products is not recorded in the feldspar data, which show a complete solid solution from basalt and co-magmatic enclaves to trachyte. Complexly zoned plagioclases further suggest episodical magma recharge events of hotter, more mafic magmas, which lead to vigorous convection and magma mixing. In summary, these models indicate that the Daly Gap of Akaroa Volcano formed by punctuated melt extraction from a crystal mush at the brittle-ductile transition.

>Magister Scientiae - MSc / Millions of tonnes of fly ash are generated worldwide every year to satisfy the large demand for energy. Management of this fly ash has been a concern and various approaches for its beneficial use have been investigated. Over the last two decades, there has been intensive research internationally that has focused on the use of different sources of fly ash for zeolite synthesis.However, most of the studies have concentrated on class C fly ash and very few have reported the use of South African class F fly ash as feedstock for zeolite synthesis.Class F fly ash from South Africa has been confirmed to be a good substrate for zeolite synthesis due to its compositional dominance of aluminosilicate and silicate phases. However, because differences in quartz-mullite/glass proportions of fly ash from different sources produces impure phases or different zeolite mineral phases under the same activation conditions, the present study focused on optimization of synthesis conditions to obtain pure phase zeolite Na-P1 from class F South African coal fly ash. Synthesis variables evaluated in this study were; hydrothermal treatment time (12 - 48 hours), temperature (100 – 160 oC) and addition of varying molar quantities of water during the hydrothermal treatment step (H2O:SiO2 molar ratio ranged between 0 - 0.49).Once the most suitable conditions for the synthesis of pure phase zeolite Na-P1 from fly ash were identified, a statistical approach was adopted to refine the experiments, that was designed to evaluate the interactive effects of some of the most important synthesis variables. In this case, the four synthesis variables; NaOH concentration (NaOH: SiO2 molar ratio ranged between 0.35– 0.71), ageing temperature (35 oC – 55 oC), hydrothermal treatment time (36 - 60 hours) and temperature (130 oC – 150 oC) were studied. The response was determined by evaluating the improvement in the cation exchange capacity of the product zeolite.The starting materials (fly ashes from Arnot, Hendrina and Duvha power stations) and the synthesized zeolite product were characterized chemically, mineralogically and morphologically by X-Ray fluorescence spectrometry, X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. Other characterization technique used in the study were Fourier transform infrared spectroscopy to provide structural information and also monitor evolution of crystallinity during synthesis, as well as cation exchange capacity to determine the amount of exchangeable positively charged ions. Nitrogen adsorption was used to determine the surface area and porosity, and inductively coupled mass spectrometry for multi-elemental analysis of the post-synthesis supernatants.The results from the X-ray diffraction spectroscopy showed that the most pure zeolite Na-P1 phase was achieved when the molar regime was 1 SiO2 : 0.36 Al2O3 : 0.59 NaOH : 0.49 H2O and at synthesis conditions such that ageing was done at 47 oC for 48 hours while the hydrothermal treatment time and temperature was held at 48 hours and 140 oC, respectively. Results from statistically designed experiments show that there was a distinct variation of phase purity with synthesis conditions. From the analysis of linear and non linear interactions, it was found that the main effects were ageing temperature and hydrothermal treatment time and temperature, which also showed some interactions. This experimental approach enabled a clearer understanding of the relationship between the synthesis conditions and the purity of the zeolite Na-P1 obtained.The quality of zeolites is a major determinant in the efficiency of toxic element removal from waste water. Preliminary experiments conducted using optimised zeolite Na-P1 obtained in this study with a cation exchange capacity of 4.11 meq/g showed a high percentage removal of Pb,Cd, Ni, Mn, V, As, B, Fe, Se, Mo Sr, Ba and Zn from process brine obtained from Emalahleni water reclamation plant.In summary, a pure phase of zeolite Na-P1 was obtained from South African class F fly ash feedstock at relatively mild temperature. The systematic approach, incorporating statistical design of experiments, developed in this study resulted in a better understanding regarding the relationships of synthesis parameters in the formation of zeolites from fly ash. The zeolite Na-P1 synthesized with a high cation exchange capacity was effective for removal of toxic elements from brine.

<p>The management and disposal of huge volumes of coal combustion by products such as fly ash has constituted a major challenge to the environment. In most cases due to the inadequate alternative use of coal fly ash, the discarded waste is stored in holding ponds, slag heaps, or stock piled in ash dumps. This practice has raised concerns on the prospect of inorganic metals release to the surface and groundwater in the vicinity of the ash dump. Acceptable scientific studies are lacking to determine the best ash disposal practices. Moreover, knowledge about the mobility patterns of inorganic species as a function of mineralogical association or pH susceptibility of the dry disposed ash dump under natural weathering conditions are scarce in the literature. Fundamental understanding of chemical interactions of dry disposed ash with ingressed CO2 from atmosphere, percolating rain water and brine irrigation within ash disposal sites were seen as key areas requiring investigation. The mineralogical association of inorganic species in the dry disposed ash cores can be identified and quantified. This would provide a basis for understanding of chemical weathering, mineralogical transformations or mobility patterns of these inorganic species in the dry ash disposal scenario. The current study therefore aims to provide a comprehensive characterisation of weathered dry disposed ash cores, to reveal mobility patterns of chemical species as a function of depth and age of ash, with a view to assessing the potential environmental impacts. Fifty-nine samples were taken from 3 drilled cores obtained respectively from the 1 year, 8 year and 20-year-old sections of sequentially dumped,&nbsp / weathered, dry disposed ash in an ash dump site at Tutuka - a South African coal burning power station. The core samples were characterized using standard analytical procedures viz: X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transforms infrared (FTIR) techniques, Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and Acid neutralisation capacity (ANC) test. A modified sequential extraction (SE) method was used in this study. The chemical partitioning, mobility and weathering patterns in 1 year, 8 year and 20-year-old sections of the ash dump were respectively investigated using this modified sequential extraction scheme. The sequence of the extractions was as follows: (1) water soluble, (2) exchangeable, (3) carbonate, (4) iron and manganese and (5) residual. The results obtained from the 5 steps sequential extraction scheme were validated with the total metal content of the original sample using mass balance method. The distribution of major and trace elements in the different liquid fractions obtained after each step of sequential extraction of the 59 drilled core samples was determined by inductively coupled plasma mass spectrometry (ICPMS). The data generated for various ash core samples were explored for the systematic analysis of mineralogical transformation and change in ash chemistry with ageing of the ash. Furthermore, the data was analyzed to reveal the impact of ingressed CO2 from atmosphere, infiltrating rain water and brine irrigation on the chemistry of ash core samples. Major mineral phases in original ash core samples prior to extraction are quartz (SiO2) and mullite (3Al2O3&middot / 2SiO2). Other minor mineral phases identified were hematite (Fe2O3), calcite (CaCO3), lime (CaO), anorthite (CaAl2Si2O8), mica (Ca (Mg, Al)3 (Al3Si) O10 (OH)2), and enstatite (Mg2Si2O6). X-ray diffraction results show significant loss of crystallinity in the older ash cores. The presence of minor phases of calcite and mica in dry disposed ash cores are attributed to reduction in the pore water pH due to hydration, carbonation and pozzolanic reactions. The X-ray diffraction technique was unable to detect Fe-oxyhydroxide phase and morealuminosilicate phases in ash core samples due to their low abundance and amorphous character. X-ray fluorescence results of the original ash core samples showed the presence of major oxides, such as SiO2, Al2O3, Fe2O3, while CaO, K2O, TiO2, Na2O, MnO, MgO, P2O5, and SO3 occur in minor concentrations. The ratio of SiO2/Al2O3 classified the original core samples prior to extraction as a silico-aluminate class F fly ash. The ternary plot of major elements in 1-year-old ash core samples was both sialic and ferrocalsialic but 8 year and 20-year-old ash core samples were sialic in chemical composition. It is noteworthy that the mass % of SiO2 varies through the depth of the core with an increase of nearly 3 %, to 58 mass % of SiO2 at a depth of 6 m in the 1-year-old core whereas in the case of the 8-year-old core a 2 % increase of SiO2 to a level of 57.5 mass % can be observed at levels between 4-8 m, showing dissolution of major components in the matrix of older ash cores.. The Na2O content of the Tutuka ash cores was low and varied between 0.6-1.1 mass % for 1-year-old ash cores to around 0.6-0.8 mass % for 8-year-old ash cores. Sodium levels were higher in 1-year-old ash cores compared to 8 year and 20-year-old ashcores. Observed trends indicate that quick weathering of the ash (within a year) leached out Na+ from the ash dump. No evidence of Na+ encapsulation even though the ash dump was brine irrigated. Thus the dry disposal ash placement method does not result in a sustainable salt sink for Na-containing species over time. The total content of each of the elements in 1 year and 20-year-old ash cores was normalised with their total content in fresh ash from same power station to show enrichment and depletion factor. Major elements such as K+, Mn showed enrichment in 1-year-old ash cores whereas Al, Si, Na+, Ti, Ca, Mg, S and Fe showed depletion due to over time erosion. Trace elements such as Cr, Sr, P, Ba, Pb, V and Zn showed enrichment but Ni, Y, Zr showed depletion attributed to over time erosion. In 20-year-old ash cores, major elements such as Al, Na+ and Mn showed enrichment while Si, K+, Fe, Mg and Ca showed depletion highlighting their mobility. Trends indicated intensive flushing of major soluble components such as buffering constituents (CaO) by percolating rain water. The 1-year-old and 20-year-old coal ash cores showed a lower pH and greater loss/depletion of the soluble buffering constituents than the 2-week-old placed ash, indicating significant chemical weathering within a year. Based&nbsp / on ANC results the leaching behaviours of Ca, Mg, Na+, K+, Se, Cr, and Sr were found to be controlled by the pH of the leachant indicating high mobility of major soluble species in the ash cores when in contact with slightly acid rain water. Other investigated toxic metals such as As, Mo and Pb showed amphoteric behaviour with respect to the pH of the leachant. Chemical alterations and formation of transient minor secondary mineral phases was found to have a significant effect on the acid susceptibility and depletion pattern of chemical species in the core ash samples when compared to fresh ash. These ANC results correlated well with the data generated from the sequential extraction scheme. Based on sequential extraction results elements, showed noticeable mobility in the water soluble, exchangeable and carbonate fractions due to adsorption and desorption caused by variations in the pore water pH. In contrast, slight mobility of elements in the Fe and Mn, and residual fractions of dry disposed fly ashes are attributed to the co-precipitation and dissolution of minor amount of less soluble secondary phase overtime. The 1-year-old dry disposed ash cores were the least weathered among the 3 drilled ash cores. Therefore low concentration of toxic metals in older ash cores were ascribed to extensive weathering with slower release from residual mineral phases over time. Elements were found to associate with different mineral phases depending on the age or depth of the core samples showing greater heterogeneity in dispersion. For instance the average amount of total calcium in different mineral associations of 1-year-old ash cores is as follows / water soluble (10.2 %), exchangeable (37.04 %), carbonate (37.9 %), Fe and Mn (7.1 %) and residual (2.97 %). The amount of total Na+ in different mineral phases of 1-year-old ash cores followed this trend: water soluble (21 %), exchangeable (11.26 %), carbonate (2.6 %), Fe and Mn (4.7 %) and residual (53.9 %). The non-leachable portion of the total Na+ content (namely that contained in the residual fraction) in the 1-year-old ash core samples under conditions found in nature ranged between 5-91 %. This non-leachable portion of the Na+ showed the metastability of the mineral phases with which residual Na+ associates. Results showed older ash cores are enriched in toxic elements. Toxic elements such as As, B, Cr, Mo and Pb are enriched in the residual fraction of older ash cores. For instance As concentration in the residual fraction varied between 0.0003- 0.00043 mg kg-1 for 1-year-old ash cores to around 0.0003-0.0015 mg kg-1 for 20-year-old ash cores. This suggests that the older ash is enriched in toxic elements hence dust from the ash dump would be toxic to human health. The knowledge of mobility and ecotoxicological significance of coal fly ash is needed when considering its disposal or reuse in the environment. The mobility and ecotoxicology of inorganic metals in coal fly ash are determined by (i) mineralogical associations of inorganic species (ii) in-homogeneity in the ash dumps (iii) long and short term exposure to ingress CO2 and percolating rain water. Management issues such as inconsistent placement of ash in the dumps, poor choice of ash dump site, in-homogeneity in brine irrigation, no record of salt load put on the ash dumps and lack of proper monitoring requires improvement. The thesis provides justification for the use of the modified sequential extraction scheme as a predictive tool and could be employed in a similar research work. This thesis also proved that the dry ash disposal method was not environmental friendly in terms of overall leaching potential after significant chemical weathering. Moreover the study proved that the practice of brine co-disposal or irrigation on ash dumps is not sustainable as the ash dump did not act as a salt sink.</p>

No description available.