An extensive amount of natural gas trapped in the subsurface is found as methane hydrate. A fundamental understanding of natural hydrate-bearing sediments is required to engineer production strategies and to assess the risks hydrates pose to global climate change and large-scale seafloor destabilization. This thesis reports fundamental studies on hydrate nucleation, morphology and the evolution of unsaturation during dissociation, followed by additional studies on sampling and pressure core testing. Hydrate nucleation is favored on mineral surfaces and it is often triggered by mechanical vibration. Continued hydrate crystal growth within sediments is governed by capillary and skeletal forces; hence, the characteristic particle size d10 and the sediment burial depth determine hydrate morphologies in natural sediments. In aged hydrate-bearing sand, Ostwald ripening leads to patchy hydrate formation; the stiffness approaches to the lower bound at low hydrate saturation and the upper bound at high hydrate saturation. Hydrate saturation and pore habit alter the pore size variability and interconnectivity, and change the water retention curve in hydrate-bearing sediments. The physical properties of hydrate-bearing sediments are determined by the state of stress, porosity, and hydrate saturation. Furthermore, hydrate stability requires sampling, handling, and testing under in situ pressure, temperature, and stress conditions. Therefore, the laboratory characterization of natural hydrate-bearing sediments faces inherent sampling disturbances caused by changes in stress and strain as well as transient pressure and temperature changes that affect hydrate stability. While pressure core technology offers unprecedented opportunities for the study of hydrate-bearing sediments, careful data interpretation must recognize its inherent limitations.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-03-28T17:23:27Z No. of bitstreams: 1 Dissertação_Christiene_FINAL_.pdf: 2691556 bytes, checksum: 6c071c6fc087c647c3aae5c59f4526d4 (MD5) / Made available in DSpace on 2016-03-28T17:23:27Z (GMT). No. of bitstreams: 1 Dissertação_Christiene_FINAL_.pdf: 2691556 bytes, checksum: 6c071c6fc087c647c3aae5c59f4526d4 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências-Geoquímica. Niterói, RJ / A diagênese recente de metais-traço redox-sensitivos, nutrientes e produtos metabólicos (Mn, Fe, ΣNO3-, NH4+, PO43-, SO42-, ΣH2S, sílica dissolvida (SiD), e alcalinidade) nas águas intersticiais e os fluxos de ΣNO3-, NH4+, PO43- e SiD na interface água-sedimento (IAS) foram estudados em três ambientes que representam cenários diferentes de aportes antrópicos da zona costeira do estado do Rio de Janeiro, incluindo a Baía de Cabo Frio (CF), a Enseada de Jurujuba (JU) e a Baía de Sepetiba (SE). As razões C:N:P e as assinaturas isotópicas (13C e 15N) dos sedimentos indicaram que a MO é de origem marinha no testemunho CF e JU. Já em SE ocorre matéria orgânica (MO) de origem marinha e terrestre, havendo predominância de origem fitoplanctônica. As concentrações de COT demonstraram similaridades no acúmulo do material orgânico entre a BC e a SE, enquanto JU apresentou concentrações mais altas. Os padrões de distribuição das zonas redox dentro da coluna sedimentar, baseado nos perfis de água intersticial, nos ambientes estudados mostraram serem influenciados pela variabilidade do teor de COT e processos de bioturbação e/ou físicos. Na CF, sob condições subóxicas, as principais reações redox foram bem identificadas nos sedimentos superficiais e seguiu a sequência teórica do consumo oxidante: ΣNO3->MnO2>Fe(OH)3, a zona de redução de SO42- não foi evidenciada nesse perfil. Na JU, sob condições anóxicas, os perfis de água intersticial indicaram um zoneamento redox “comprimido”, favorecendo a contração das zonas óxica-subóxica e expansão da região sulfídrica. As altas concentrações de alcalinidade, amônio e sulfeto indicaram degradação intensiva de matéria orgânica no testemunho JU, dominado pela zona de redução de sulfato e uma influência menor pela das reduções de ΣNO3-, MnO2 e Fe(OH)3. Na SE, sob condições subóxicas e a presença de macrofauna observada no sedimento, duas sequências diagenéticas sobrepostas foram observadas. A primeira sequência envolveu a redução do NO3-, MnO2 e Fe(OH)3. A segunda sequência diagenética envolveu a redução do MnO2 e Fe(OH)3. A presença de duas sequências diagenéticas pode estar relacionada aos efeitos de bioturbação e/ou outras perturbações físicas, como eventos de dragagem em áreas adjacentes e atividades de embarcações que causam ressuspensão do sedimento. A ocorrência de variação da concentração de COT no topo do testemunho SE, ressalta a perturbação do sedimento. Foi evidenciado que os fluxos de NO3- e NH4+ em CF são influenciados pelos processos de desnitrificação, em JU pelo processo de desnitrificação e redução desassimilatória de nitrato para amônio, já em SE pelos processos de desnitrificação e nitrificação. O fluxo do PO43- foi afetado pela precipitação de mineral autigênico e bioturbação do sedimento. E o fluxo de SiD foi afetado pela gradual dissolução de sílica biogênica com o aumento da profundidade. Em JU foram observados os maiores fluxos de NO3-, NH4+ e SiD na IAS. No entanto, o fluxo de PO43- mais alto foi observado na IAS da Baía de Sepetiba, provavelmente devido às baixas concentrações de PO43- encontradas na água de fundo em relação às outras áreas de estudo / The early diagenesis of the redox-sensitive trace metals, nutrients, metabolic products (Mn, Fe, ΣNO3-, NH4+, PO43-, SiD, SO42-, H2S and alcalinity) in pore waters and the fluxes of the ΣNO3-, NH4+, PO43- and DSi at the sediment-water interface (SWI) were studied in three environments that represent different scenarios of anthropogenic inputs of the coastal zone of the state of Rio de Janeiro, including the Cabo Frio Bay (CF), Jurujuba Sound (JU) and Sepetiba Bay (SE). The C:N:P ratios and isotopic signatures (13C and 15N) of the sediments indicated that organic matter (OM) is of marine origin in CF and JU core. In SE occurs OM marine and terrestrial origin, with predominance of phytoplankton origin. The TOC concentrations have demonstrated similarities in the accumulation of organic material between BC and SE, while JU submitted higher concentrations. The distribution patterns of redox zones within the sedimentary column, based on pore water profiles, in the studied environments showed to be influenced by the variability of the TOC content and bioturbation and/or physical processes. In CF, under suboxic conditions, the main redox reactions have been identified in surface sediments and followed the theoretical result of oxidant consumption: ΣNO3-> MnO2> Fe (OH)3, the SO42- reduction zone was no evidence in this profile. In JU, under anoxic conditions, the pore water profiles indicated a redox zone ‘compressed’, favoring the contraction of the oxic-suboxic zones and expansion of sulfidic region. The high concentrations of alkalinity, ammonium and sulfide indicated intensive degradation of OM in JU core dominated by the sulfate reduction zone and a smaller influence by the ΣNO3-, MnO2 and Fe (OH)3 reductions. In SE, under suboxic conditions and with the observed presence of macrofauna in the sediment, two overlapped diagenetic sequences can be observed. The first sequence involved the reduction of ΣNO3-, MnO2 and Fe (OH)3. The second diagenetic sequence involved the reduction of MnO2 and Fe (OH)3. The presence of two diagenetic sequences may be related to effects bioturbation and/or other physical disturbances, such as dredging events in adjacent areas and craft activities that cause sediment resuspension. The occurrence of variation of TOC concentration at the top of the SE core, emphasizes the disturbance of sediment. It was evidenced that the fluxes of ΣNO3- and NH4+ in CF are influenced by denitrification processes, in the JU by process denitrification and nitrate dissimilatory reduction to ammonium, as in SE by nitrification and denitrification processes. The PO43- fluxes was affected by the precipitation of autigenic mineral and bioturbation of the sediment. And the SiD flux is affected by the gradual dissolution of biogenic silica with increasing depth. In JU were observed larger fluxes of ΣNO3-, NH4+ and DSi at the SWI were observed. However, the higher PO43- fluxes was observed at the SWI Sepetiba Bay, probably due to low concentrations of PO43- found in the overlying water in relation to other areas of study.

In der Arbeit wird gezeigt, wie man die Bodensteifigkeit bei sehr kleinen Dehnungen sowie die Abnahme der Steifigkeit mit zunehmender Scherdehnung in Labor- und Feldversuchen ermitteln kann. Dazu werden typische Eigenschaften mineralischer und organischer Böden einschließlich Korrelationen zusammengestellt und wesentliche Unterschiede zum Bodenverhalten bei großen Dehnungen, insbesondere hinsichtlich der Steifigkeit und der Spannungsabhängigkeit aufgezeigt. Weiterhin wird dargelegt, wie man mit dem hypoplastischen Stoffgesetz mit intergranularen Dehnungen das Bodenverhalten bei kleinen Dehnungen wirklichkeitsnah erfassen kann und wie die Stoffparameter zu bestimmen sind. Für die realistische Erfassung des Bodenverhaltens infolge zyklischer Belastung einschließlich der Ausbildung von Hystereseschleifen wird eine Modifizierung des hypoplastischen Stoffgesetzes unter Einführung eines zusätzlichen Stoffparameters vorgenommen. Es wird gezeigt, wie dieser Parameter in zyklischen Laborversuchen bestimmt werden kann und wie damit die Akkumulation von Dehnungen bei drainierten Bedingungen bzw. von Porenwasserdrücken bei undrainierten Bedingungen zuverlässig prognostiziert werden kann. Anhand der dynamischen Beanspruchung eines Eisenbahndammes auf weichem, organischem Untergrund wird das modifizierte hypoplastische Stoffgesetz mit intergranularen Dehnungen für ein bodendynamisches Randwertproblem angewendet und gezeigt, dass damit das Bodenverhalten realistisch abgebildet werden kann. Die Berechnungsergebnisse zeigen eine gute Übereinstimmung mit Ergebnissen von Schwingungsmessungen und Langzeitverformungsmessungen. Es werden bodendynamische Berechnungen zur Wellenausbreitung sowohl eindimensional als auch im Halbraum mit unterschiedlichen Stoffgesetzen geführt und Vergleiche mit analytischen Lösungen vorgenommen. Dazu wird gezeigt, welche Anforderungen an numerische Berechnungen zur Wellenausbreitung, insbesondere hinsichtlich Wahl der Zeitschritte, Elementgröße bzw. Knotenabstände, Größe des FE-Netzes und Modellierung der FE-Ränder erforderlich sind.:1 Einführung 2 Bodensteifgkeit 2.1 Defnition der Scherdehnung und der Schubspannung 2.2 Versuchstechnische Ermittlung der Bodensteifgkeiten 2.3 Ermittlung der Bodensteifgkeiten im Feld 2.4 Ermittlung der Bodensteifgkeiten im Labor 2.5 Bodensteifgkeit bei sehr kleinen Dehnungen 2.6 Abnahme der Steifigkeit mit zunehmender Scherdehnung 2.7 Bodenverhalten und Scherdehnungsgrenzen 2.8 Weitere bodendynamische Eigenschaften 3 Hypoplastisches Stogesetz 3.1 Allgemeine Formulierung der Hypoplastizität 3.2 Intergranulare Dehnungen 3.3 Bereich mit sehr kleinen Dehnungen 3.4 Bereich mit kleinen bis mittleren Dehnungen 3.5 Vergleich der Ergebnisse mit dem HS-Small-Modell 3.6 Zusammenfassung und Wertung der Ergebnisse 4 Numerische Berechnungen zur Wellenausbreitung 4.1 Eindimensionale Wellenausbreitung 4.2 Wellenausbreitung im Halbraum 4.3 Wellenausbreitung im porösen Medium 5 Anwendungsbeispiel 5.1 Geometrische Situation, Baugrundschichtung 5.2 Bodenmechanische und bodendynamische Kennwerte 5.3 Schwingungsmessungen 5.4 Messung von bleibenden Verformungen 5.5 Belastung 5.6 Numerische Modellierung 5.7 Hypoplastische Berechnung 5.8 Vergleich Mess- und Berechnungsergebnisse 5.9 Linear elastische Berechnung 5.10 Vergleich der Ergebnisse mit hypoplastischer und elastischer Berechnung 6 Zusammenfassung und Ausblick Summary Literaturverzeichnis Symbolverzeichnis Anhang A Berechnungen zur Wellenausbreitung Anhang B Eingabedateien für Berechnungen mit TOCHNOG Anhang C Herleitungen der Biot-Theorie / In this thesis it is shown how to determine the soil stiffness at very small strains, as well as the decrease in stiffness with increasing shear strain amplitude in laboratory and field tests. Typical properties and empirical correlations of coarse-, fine-grained and organic soils are collected and significant differences in soil stiffness and stress-dependence at small strains compared to large strains are shown. Further it is shown how one can realistically reproduce the soil behaviour at small strains with the hypoplastic constitutive model with intergranular strains and how the material parameters are determined. For a realistic prediction of soil behaviour due to cyclic loading including hysteresis loops in the stress-strain relationship, a modification of the hypoplastic constitutive model is made by using an additional material parameter. It is shown how this additional parameter can be determined in cyclic laboratory tests and how the accumulation of strains in drained conditions and excess pore pressures built up in undrained conditions can be realistically reproduced. Based on the dynamic load on a railway embankment on soft marshy ground, the modified hypoplastic constitutive model with intergranular strains is applied for a boundary value problem. It is demonstrated, that the soil behaviour can be reproduced realistically. Numerical results show a good agreement with results of vibration measurements and measurements of permanent displacements. A dynamical numerical analysis is performed for both one-dimensional and half-space conditions. Different constitutive models have been applied and compared with analytical solutions. The results demonstrate requirements on numerical analysis of wave propagation, in particular with regards to time steps, element size, node spacing, size of the FE mesh and boundary conditions.:1 Einführung 2 Bodensteifgkeit 2.1 Defnition der Scherdehnung und der Schubspannung 2.2 Versuchstechnische Ermittlung der Bodensteifgkeiten 2.3 Ermittlung der Bodensteifgkeiten im Feld 2.4 Ermittlung der Bodensteifgkeiten im Labor 2.5 Bodensteifgkeit bei sehr kleinen Dehnungen 2.6 Abnahme der Steifigkeit mit zunehmender Scherdehnung 2.7 Bodenverhalten und Scherdehnungsgrenzen 2.8 Weitere bodendynamische Eigenschaften 3 Hypoplastisches Stogesetz 3.1 Allgemeine Formulierung der Hypoplastizität 3.2 Intergranulare Dehnungen 3.3 Bereich mit sehr kleinen Dehnungen 3.4 Bereich mit kleinen bis mittleren Dehnungen 3.5 Vergleich der Ergebnisse mit dem HS-Small-Modell 3.6 Zusammenfassung und Wertung der Ergebnisse 4 Numerische Berechnungen zur Wellenausbreitung 4.1 Eindimensionale Wellenausbreitung 4.2 Wellenausbreitung im Halbraum 4.3 Wellenausbreitung im porösen Medium 5 Anwendungsbeispiel 5.1 Geometrische Situation, Baugrundschichtung 5.2 Bodenmechanische und bodendynamische Kennwerte 5.3 Schwingungsmessungen 5.4 Messung von bleibenden Verformungen 5.5 Belastung 5.6 Numerische Modellierung 5.7 Hypoplastische Berechnung 5.8 Vergleich Mess- und Berechnungsergebnisse 5.9 Linear elastische Berechnung 5.10 Vergleich der Ergebnisse mit hypoplastischer und elastischer Berechnung 6 Zusammenfassung und Ausblick Summary Literaturverzeichnis Symbolverzeichnis Anhang A Berechnungen zur Wellenausbreitung Anhang B Eingabedateien für Berechnungen mit TOCHNOG Anhang C Herleitungen der Biot-Theorie

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, weathered, dry disposed ash in an ash dump site at Tutuka - a South African coal burning power station.

<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>

<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>

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, weathered, dry disposed ash in an ash dump site at Tutuka - a South African coal burning power station.

Philosophiae Doctor - PhD / 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, 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 (Al2O3·2SiO2). 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 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. / South Africa

<p>Cilj ove doktorske disertacija&nbsp; bio je razvoj&nbsp; novih, osetljivih, selektivnih i ekonomski<br />isplativih&nbsp; voltametrijskih&nbsp; radnih&nbsp; elektroda&nbsp; za&nbsp; praćenje&nbsp; odabranih&nbsp; analita&nbsp; kako&nbsp; u<br />laboratorijskim tako i pri terenskim uslovima.&nbsp; Ispitivana je&nbsp; mogućnost primene&nbsp; ovih&nbsp; radnih&nbsp; elektroda&nbsp; primenom&nbsp; voltametrijskih&nbsp; metoda&nbsp; kako&nbsp; u&nbsp; model&nbsp; rastvorima&nbsp; tako&nbsp; i&nbsp; u&nbsp; pojedinim realnim sistemima. SW-ASV&nbsp; zasnovana&nbsp; na&nbsp; elektrodama&nbsp; od&nbsp; staklastog&nbsp; ugljenika&nbsp; povr&scaron;inski modifikovanim&nbsp; Bi-MWCNT&nbsp; i&nbsp; BiOCl-MWCNT&nbsp; je&nbsp; primenjena&nbsp; za&nbsp; određivanje&nbsp; jona&nbsp; Pb(II)&nbsp; i Cd(II)&nbsp; pri&nbsp; optimizovanim&nbsp; uslovima&nbsp; merenja.&nbsp; Određivanje&nbsp; ciljnih&nbsp; jona&nbsp; vr&scaron;eno&nbsp; je&nbsp; pri&nbsp; radnom potencijalu&nbsp; od&nbsp; -1,2&nbsp; V&nbsp; (izmeren&nbsp; u&nbsp; odnosu&nbsp; na&nbsp; zasićenu&nbsp; kalomelovu&nbsp; elektrodu)&nbsp; i&nbsp; vremenu<br />elektrodepozicije jona&nbsp; od 120 s. Sva merenja su izvr&scaron;ena u rastvoru acetatnog pufera čija je pH-vrednost iznosila&nbsp; 4,0. Primenjeni koncentracioni opseg ciljnih analita iznosio je&nbsp; od 5 do 50&nbsp; &mu;g&nbsp; dm ^-3 .&nbsp; Primenom&nbsp; ovog&nbsp; tipa&nbsp; elektrode&nbsp; dobijene&nbsp; su&nbsp; vrednosti&nbsp; granice&nbsp; detekcije&nbsp; za&nbsp; jone Pb(II) i Cd(II) 0,57&nbsp; &mu;g dm ^-3i 1,2 &mu;g dm^-3 , redom. Dobijena RSD iznosila je manje od 10% za oba&nbsp; jona.&nbsp; Ova&nbsp; metoda&nbsp; je&nbsp; primenjena&nbsp; i&nbsp; za&nbsp; određivanje&nbsp; ciljnih&nbsp; jona&nbsp; u&nbsp; realnom&nbsp; uzorku&nbsp; porne vode&nbsp; sedimenta&nbsp; a&nbsp; rezultati&nbsp; dobijeni&nbsp; optimizovanom&nbsp; voltametrijskom&nbsp; metodom&nbsp; su&nbsp; u&nbsp; dobroj saglasnosti sa rezultatima koji su dobijeni primenom komparativne GFAAS metode. Bizmut oksihlorid-vi&scaron;ezidne ugljenične nanocevi kompozitni materijal je primenjen za povr&scaron;insko&nbsp; modifikovanje&nbsp; elektrode&nbsp; od&nbsp; staklastog&nbsp; ugljenika&nbsp; za&nbsp; brzo&nbsp; i&nbsp; jednostavno voltametrijsko&nbsp; određivanje&nbsp; tragova&nbsp; Zn(II)-jona&nbsp; primenom&nbsp; SW-ASV&nbsp; metode.&nbsp; BiOClMWCNT/GCE je pokazala linearan analitički odgovor u&nbsp; osegu koncentracija od&nbsp; 2,50 do&nbsp; 80,0 &mu;g&nbsp; dm ^-3sa dobijenom vredno&scaron;ću GD 0,75 &mu;g&nbsp; dm^-3pri akumulacionom vremenu od&nbsp; 120 s&nbsp; i potencijalu&nbsp; elektrodepozicije&nbsp; -1,40&nbsp; V&nbsp; u&nbsp; odnosu&nbsp; na&nbsp; ZKE.&nbsp; Merenja&nbsp; su&nbsp; vr&scaron;ena&nbsp; u&nbsp; acetatnom puferu pH 4,5. Dobijena RSD iznosila je 4,8 %. Upoređene su performanse novodizajnirane BiOCl-MWCNT/GCE elektrode&nbsp; i&nbsp; tradicionalne elektrode na bazi bizmut filma (BiF/GCE), MWCNT/GCE,&nbsp; BiF-MWCNT/GCE&nbsp; i&nbsp; nemodifikovane&nbsp; GC&nbsp; elektrode.&nbsp; Novodizajnirana elektroda je primenjena za&nbsp; detekciju&nbsp; i određivanje&nbsp; Zn(II)-jona&nbsp; u realnim&nbsp; uzorcima kao &scaron;to su<br />dijetetski&nbsp; suplement&nbsp; i&nbsp; pekarski&nbsp; kvasac.&nbsp; Dobijeni&nbsp; rezultati&nbsp; su&nbsp; uporedivi&nbsp; sa&nbsp; deklarisanom vredno&scaron;ću&nbsp; u&nbsp; slučaju&nbsp; dijetetskog&nbsp; suplementa&nbsp; a&nbsp; u&nbsp; slučaju&nbsp; pekarskog&nbsp; kvasca&nbsp; sa&nbsp; rezultatima dobijenih komparativnom FAAS .<br />Elektroda od ugljenične paste je povr&scaron;inski modifikovana pripremljenim kompozitom<br />koji je&nbsp; izgrađen od vi&scaron;ezidnih ugljeničnih nanocevi i čestica&nbsp; Sb₂O_3.&nbsp; Kompozitni&nbsp; materijal&nbsp; je okarakterisan&nbsp; primenom&nbsp; TEM,&nbsp; EDS&nbsp; i&nbsp; XRD&nbsp; mernih&nbsp; tehnika.&nbsp; Sb₂O₃-MWCNT/CPE&nbsp; je okarakterisana primenom ciklične voltametrije a merenja su vr&scaron;ena u rastvoru hlorovodonične kiseline&nbsp; (pH&nbsp; 2,0).&nbsp; Primenom&nbsp; SW-ASV&nbsp; metode&nbsp; ova&nbsp; radna&nbsp; elektroda&nbsp; je&nbsp; upotrebljena&nbsp; za određivanje&nbsp; jona Pb(II) i Cd(II)&nbsp; u&nbsp; koncentracionom opsegu 2,0-40,0&nbsp; &mu;g&nbsp; dm&nbsp; ^-3za&nbsp; Pb(II)-jon&nbsp; i 2,0-40,0&nbsp; &mu;g&nbsp; dm ^-3 za&nbsp; Cd(II)-jon&nbsp; pri&nbsp; čemu&nbsp; su&nbsp; dobijene&nbsp; dobre&nbsp; linearne&nbsp; zavisnosti&nbsp; za&nbsp; oba&nbsp; ciljna jona.&nbsp; Optimalna&nbsp; procedura&nbsp; uključuje&nbsp; primenu&nbsp; Sb2O3-MWCNT/CPE&nbsp; u&nbsp; 0,01&nbsp; mol dm ^-3<br />hlorovodoničnoj kiselini uz vreme elektrodepozicije jona iz rastvora od 120&nbsp; s&nbsp; na&nbsp; potencijaluod&nbsp; -1,2&nbsp; V,&nbsp; pri&nbsp; čemu&nbsp; su&nbsp; dobijene&nbsp; vrednosti&nbsp; za&nbsp; GD&nbsp; 1,1&nbsp; &mu;g&nbsp; dm ^-3 Cd(II)&nbsp; i&nbsp; 1,6&nbsp; &mu;g&nbsp; dm ^-3 Pb(II). Optimizovana&nbsp; metoda&nbsp; zasnovana&nbsp; na&nbsp; ovom&nbsp; tipu&nbsp; voltametrijskog&nbsp; senzora&nbsp; je&nbsp; uspe&scaron;no primenjena&nbsp; za&nbsp; određivanje&nbsp; jona&nbsp; Cd(II)&nbsp; u&nbsp; obogaćenom&nbsp; uzorku&nbsp; česmenske&nbsp; vode,&nbsp; gde&nbsp; su&nbsp; se dobijene vrednosti u&nbsp; saglasnosti sa očekivanom. Elektroda od ugljenične paste povr&scaron;inski je&nbsp; modifikovana primenom&nbsp; Sb₂O₃-MWCNT nanokompozitnog&nbsp; materijala&nbsp; i&nbsp; primenjena&nbsp; za&nbsp; direktno&nbsp; voltametrijsko&nbsp; određivanje imidakloprida&nbsp; u&nbsp; model&nbsp; rastvorima.&nbsp; U&nbsp; cilju&nbsp; postizanja&nbsp; &scaron;to&nbsp; boljih&nbsp; analitičkih&nbsp; performansi optimizovani su eksperimentalni uslovi merenja kao &scaron;to su pH-vrednost rastvora pomoćnog elektrolita&nbsp; i&nbsp; kondicioniranje&nbsp; povr&scaron;ine&nbsp; voltametrijskog&nbsp; senzora.&nbsp; Kao&nbsp; optimalna&nbsp; pH-vrednost pomoćnog elektolita (Britton-Robinsonovog pufera) odabrana je pH 7,0, a ponavljanje ciklusa cikliranja najmanje 4 puta povoljno utiče na stabilnost&nbsp; voltametrijskih signala. Optimizovana metoda primenjena je za SW direktno katodno određivanje imidakloprida u koncentracionom intervalu od 1,41 do 32,77 &mu;g cm ^-3 uz dobijeni korelacioni faktor od 0,9995. Na osnovu dobijenih rezultata može se zaključiti da su razvijene analitičke metode pre svega&nbsp; osetljive,&nbsp; selektivne,&nbsp; reproduktivne&nbsp; i&nbsp;&nbsp; jednostavne&nbsp; &scaron;to&nbsp; omogućava&nbsp; njihovu&nbsp; primenu&nbsp; za veliki broj uzoraka.&nbsp; Merenjima u model i realnim rastvorima dokazana je mogućnost njihove primene&nbsp; u&nbsp;&nbsp; komplikovanim&nbsp; matriksima,&nbsp; pri&nbsp; različitim&nbsp; pH&nbsp; vredostima&nbsp; pri&nbsp; čemu&nbsp; su&nbsp; dobijeni<br />rezultati koji su u saglasnosti sa rezultatima primenjenih komparativnih metoda. Naravno, za dobijanje&nbsp; reprezentativnih&nbsp; rezultata&nbsp; neohodno&nbsp; je&nbsp; izvr&scaron;iti&nbsp; optimizaciju&nbsp; uslova&nbsp; merenja&nbsp; &scaron;to podrazumeva sam odabir supstrat-elektrode, odabir povr&scaron;inskog modifikatora i optimizaciju eksperimentalnih uslova merenja.</p> / <p>The&nbsp; aim of this&nbsp; Ph.D. thesis&nbsp; was the development of new, sensitive, selective and economically&nbsp; viable&nbsp; voltametric&nbsp; working&nbsp; electrode&nbsp; for&nbsp; continuous&nbsp; monitoring&nbsp; of&nbsp; different target&nbsp; analytes.&nbsp; The&nbsp; use&nbsp; of&nbsp; these&nbsp; advantaged&nbsp; working&nbsp; electrodes&nbsp; was&nbsp; investigated&nbsp; using voltametric methods both in model solutions and in certain real systems.SW-ASV&nbsp; based on glassy carbon&nbsp; electrode surface modified with&nbsp; Bi- MWCNT and BiOCl-MWCNT&nbsp; were&nbsp; applied&nbsp; for&nbsp; determination&nbsp; of&nbsp; Pb(II)&nbsp; and&nbsp; Cd(II)&nbsp; ions.&nbsp; Voltametric determination&nbsp; of&nbsp; Pb(II)&nbsp; and&nbsp; Cd(II)&nbsp; ions&nbsp; was&nbsp; performed&nbsp; at&nbsp; working&nbsp; potential&nbsp; of&nbsp; -1.2&nbsp; V (measured against the saturated calomel electrode) and time of electrodeposition of 120 s. All measurements were performed in acetate buffer solution pH 4.0. Concentration range of targetanalites were&nbsp; 5-50 &mu;g&nbsp; dm -3 . Using this type of electrode,&nbsp; obtained&nbsp; detection limits for&nbsp; Pb(II) and Cd(II) ions&nbsp; were&nbsp; 0.57&nbsp; &mu;g&nbsp; dm -3 and 1.2&nbsp; &mu;g&nbsp; dm -3 , respectively, with RSD lower than 10%.This&nbsp; method&nbsp; was&nbsp; applied&nbsp; for&nbsp; target&nbsp; ions&nbsp; determination&nbsp; in&nbsp; sediment&nbsp; pore&nbsp; water&nbsp; sample,&nbsp; and obtained results are comparable with those who are obtained using GFAAS method. Bismuth oxychloride-multiwalled carbon nanotubes composite material was applied for&nbsp; surface&nbsp; modification&nbsp; of&nbsp; the&nbsp; glass-carbon&nbsp; electrode&nbsp; for&nbsp; quick&nbsp; and&nbsp; simple&nbsp; voltametric determination&nbsp; of&nbsp; Zn(II)&nbsp; ions&nbsp; using&nbsp; the&nbsp; SW-ASV&nbsp; method.&nbsp; BiOCl-MWCNT/GCE&nbsp; showed&nbsp; a linear&nbsp; analytical&nbsp; response&nbsp; in&nbsp; a&nbsp;&nbsp; concentration&nbsp; from&nbsp; 2.50&nbsp; to&nbsp; 80.0&nbsp; &mu;g&nbsp; dm -3 with&nbsp; a&nbsp; value&nbsp; of detection limit 0.75 &mu;g dm -3 at a acumulation time of 120 s and an electrodeposition potential of&nbsp; -1.40 V vs. saturated&nbsp; calomel electrode.&nbsp; Measurements were carried out in acetate buffer pH 4.5. The obtained&nbsp; value of the RSD&nbsp; was&nbsp; 4.8%. The performance of the newly designed BiOCl-MWCNT/GCE&nbsp; electrode,&nbsp; traditional&nbsp; bismuth-based&nbsp; electrode&nbsp; (BiF/GCE), MWCNT/GCE,&nbsp; BiF-MWCNT/GCE&nbsp; and&nbsp; unmodified&nbsp; GC&nbsp; electrodes&nbsp; were&nbsp; compared.&nbsp; The applied electrode shows very good electroanalytic properties when determining this target ion. Obtained results are in good agreement with declared value in case of dietetic suplement, and in the brewer&rsquo;s yeast sample results were comparable with FAAS results. Carbon&nbsp; paste&nbsp; electrode&nbsp; surface&nbsp; modified&nbsp; with&nbsp; new&nbsp; composite&nbsp; material&nbsp; based&nbsp; on multiwalled carbon nanotubes and&nbsp; Sb2O3&nbsp; particles. The composite is characterized by TEM, EDS and&nbsp; XRD measurment. Sb2O3- MWCNT/CPE was characterized by cyclic voltammetry and measurements were carried out in a&nbsp; hydrochloric acid&nbsp; solution&nbsp; (pH 2.0). Using the SWASV&nbsp; method,&nbsp; this&nbsp; working&nbsp; electrode&nbsp; was&nbsp; used&nbsp; to&nbsp; determine&nbsp; Pb(II),&nbsp; Cd(II)&nbsp; ions&nbsp; in&nbsp; the concentration range&nbsp; from&nbsp; 2.0&nbsp; to 40.0&nbsp; &mu;g dm -3 for Pb(II) and 2.0-40.0&nbsp; &mu;g dm -3 for Cd(II) ions. Newly&nbsp; designed&nbsp; sensor&nbsp; showed&nbsp; good&nbsp; linear&nbsp; dependences&nbsp; for&nbsp; both&nbsp; target&nbsp; ions.&nbsp; The&nbsp; most optimal&nbsp; procedure&nbsp; involving&nbsp; application&nbsp; of&nbsp; Sb2O3-MWCNT/CPE&nbsp; in&nbsp;&nbsp; .01&nbsp; mol&nbsp; dm -3 hydrochloric&nbsp; acid,&nbsp; with&nbsp; electroposition&nbsp; time&nbsp; of&nbsp; target&nbsp; ions&nbsp; 120&nbsp; s&nbsp; at&nbsp; a&nbsp; electrodeposition potential&nbsp; of&nbsp; -1.2&nbsp; V.&nbsp; Obtained&nbsp;&nbsp; values&nbsp; of&nbsp;&nbsp;&nbsp; LOD&nbsp; 1,1&nbsp; &mu;g&nbsp; dm -3 for&nbsp; Cd(II)&nbsp; and&nbsp; for&nbsp; 1,6&nbsp; &mu;g&nbsp; dm -3 Pb(II)&nbsp; ions.&nbsp; An&nbsp; optimized&nbsp; method&nbsp; based&nbsp; on&nbsp; this&nbsp; type&nbsp; of&nbsp; voltametric&nbsp; sensor&nbsp; has&nbsp; been successfully&nbsp; applied&nbsp; for&nbsp; determination&nbsp; of&nbsp; Cd(II)&nbsp; ion&nbsp; in&nbsp; a&nbsp; spiked&nbsp; tap&nbsp; water&nbsp; sample.&nbsp; Results obtained during this measurment were in tune with expected results. CPE&nbsp; was&nbsp; surface&nbsp; modified&nbsp; using&nbsp; Sb2O3-MWCNT&nbsp; nanocomposite&nbsp; material&nbsp; and tested&nbsp; for&nbsp; direct&nbsp; voltametric&nbsp; determination&nbsp; of&nbsp; imidacloprid&nbsp; in&nbsp; model&nbsp; solutions.&nbsp; In&nbsp; order&nbsp; to achieve the best analytical performance, experimental conditions of measurement such as the pH value of the supporting electrolyte and conditioning of the voltametric sensor surface havebeen&nbsp; optimized.&nbsp; As&nbsp; an&nbsp; optimum&nbsp; pH&nbsp; value&nbsp; of&nbsp; the&nbsp; supporting&nbsp; electrolyte&nbsp; (Britton-Robinson buffer), a pH 7.0 was selected, and the repeating cycles of the cycling process at least 4 times favorably&nbsp; influenced&nbsp; the&nbsp; stability&nbsp; of&nbsp; the&nbsp; voltametric&nbsp; signals.&nbsp; The&nbsp; optimized&nbsp; method&nbsp; was applied for the SW direct cathodic determination&nbsp; of&nbsp; imidacloprid in the concentration range from 1.41 to 32.77 &mu;g cm -3&nbsp; with obtained correlation factor of 0.9995. Based on results it can be concluded that developed analytical methods are sensitive, selective, reproducibile and simple, which can enable their application for various number of samples. Measurements in the model and real solutions have demonstrated the possibility of their&nbsp; application&nbsp; in&nbsp; complicated&nbsp; matrices,&nbsp; at&nbsp; different&nbsp; pH,&nbsp; whereby&nbsp; obtained&nbsp; results&nbsp; are&nbsp; in accordance&nbsp; with&nbsp; the&nbsp; results&nbsp; of&nbsp; the&nbsp; applied&nbsp; comparative&nbsp; methods.&nbsp; For&nbsp; obtainig&nbsp; of representative&nbsp; results&nbsp; it&nbsp; is&nbsp; necessary&nbsp; to&nbsp; optimize&nbsp; conditions&nbsp; of&nbsp; measurment&nbsp; which&nbsp; include: selection of substrat electrode, surface modifier and optimization of experimental condition.</p>

This dissertation is concerned with the foundations in volume unstable soils and objects disorders which are related to this. The thesis was focused on the study of clay and loess soils which are abundant in the geological profile of the Czech Republic. First, the formation of the two groups of soils is introduced, then their properties are examined and finally the influence of vegetation on the former type and the influence of collapsibility in the latter type are investigated. The conclusion is, in fact, a recommendation on the design of structures so that the system of clay / structure is not damaged and that structures are not subject to renovations. Several instance of problems with structures are discussed which were subject to structural repairs employing both a civil and geotechnical engineers.