La carbonatation minérale est une technique alternative de capture et stockage du CO2 anthropique. L'abondance des matériaux carbonatables sur terre en fait une solution à fort potentiel. En particulier, la carbonatation directe en voie aqueuse a été présentée dans la littérature comme la voie la plus intéressante d'un point de vue énergétique pour la carbonatation minérale ex-situ, à la condition que les cinétiques naturellement lentes de dissolution des silicates magnésiens en phase aqueuse puissent être accélérées de plusieurs ordres de grandeur. Cette thèse étudie en détail les verrous et mécanismes de cette réaction en présence d'additifs organiques tels que l'oxalate, connus pour leur capacité à accélérer la dissolution des silicates magnésiens. Dans un premier temps, la carbonatation en voie aqueuse sans additif d'une olivine modèle est étudiée de manière à mettre en évidence la nature des phénomènes limitants. Ensuite le travail se concentre sur l'étude du rôle de l'additif oxalate à travers des essais spécifiques et une analyse fine de la phase solide. Il est démontré que pour différentes concentrations de suspension et sous 20 bar de CO2, cet additif conduit à la formation de complexes aqueux stables du magnésium avec l'oxalate et à la précipitation de MgC2O4,2H2O (glushinskite), qui empêchent toute précipitation quantitative de magnésite. La simulation géochimique complète du système a été réalisée et a permis d'expliquer les résultats des essais par un mécanisme de dissolution à grain rétrécissant. L'extension de l'étude à un autre silicate (harzburgite) et à d'autres ligands organiques accélérateurs de la dissolution des silicates tels que le citrate et l'EDTA n'a pas non plus permis d'obtenir la formation quantitative de carbonate, à cause d'une forte complexation en phase aqueuse du Mg extrait du minerai. Ces travaux remettent en doute la perspective de développement d'un procédé industrialisable de minéralisation du CO2 en présence d'additifs organiques. / Mineral carbonation is an interesting option for mitigation of anthropogenic CO2 emissions. Direct aqueous mineral carbonation has been presented by many as a promising strategy for ex-situ mineral carbonation, on the basis that organic additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. This thesis discusses and extends the current understanding of this process through geochemical modelling and detailed solid characterization. First, mineral carbonation is investigated in water alone, without additives, in order to understand and quantify the actual limitations of the process with specific magnesium silicate ores. Dissolution kinetics being critical with this process, the role of disodium oxalate as a dissolution accelerating agent is thoroughly examined with olivine, through dedicated experiments and comprehensive analysis of both solid and liquid phases. Under 20 bar of CO2, and irrespective of the conditions used, it is found that the formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of precipitating significant amounts of magnesium carbonate. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model. Other promising ligands from a dissolution perspective, namely citrate and EDTA, were also investigated. Contrary to oxalate, these do not form any solid by-products with magnesium, and yet they do not produce better carbonation results. The results and findings from this work cast strong doubts about the possibility of developing a viable direct aqueous mineral carbonation process using organic salts.

Increasing global temperatures due to anthropogenic emissions of greenhouse gases is one of our times most dire and urgent challenges to overcome if we are to achieve a sustainable healthy planet. The primary way of accomplishing this is by reducing the amount of released greenhouse gases. However, a complementary measure that has been proposed by IPCC (UN, Intergovernmental Panel on Climate Change) to combat this challenge is the carbon dioxide removal technology bio-energy carbon capture and storage (BECCS). This study aims to investigate the suitability of areas located in the south-central part of Sweden for in-situ mineral carbonation, a relatively newly implemented method of permanently storing carbon dioxide in for instance Iceland. The project has been conducted in connection with the research project INSURANCE at Luleå University of Technology (LTU), which has as one of its main objectives to investigate the geological potential for land-based carbon dioxide storage in Sweden. Samples were taken from five different localities in the southern-central part of Sweden: Skutskär, Falun, Öje, Grums, and Åsensbruk. Fifteen representative field samples were then examined with optical microscopy, whole rock geochemistry analysis, scanning electron microscopy (SEM), and micro-XRF in order to characterize the area's bedrock with respect to their potential suitability for in-situ mineral carbonation. The investigations showed that the examined mafic rock units all contained various degrees of metamorphism and alteration, differing them from bedrock in which earlier in-situ mineral carbonation has been successfully tested (Carbfix, Iceland). However, the areas also generally contained considerable amounts of minerals with high Mg, Ca, and Fe ratios, indicating they have a potential for future in-situ mineral carbonation, however, further carbonation experiments are needed to better evaluate the potential.

Mineral carbonation contributes to CO2 reduction, and it may also reduce the cost of mineral processing by improving the mechanical properties of rock/ore. Here, we study and compare the mechanical properties of two minerals, forsterite (Mg2SiO4) and magnesite (MgCO3) using molecular dynamics (MD) simulation. The goal is to understand whether carbonation results in hardness reduction of rock and subsequently comminution energy during the crushing and processing of the ore. We investigated how these materials respond to different physical conditions, such as temperature and strain rate, to understand their behavior under stress. By examining the molecular structure of forsterite and magnesite at temperatures ranging from 300K to 700K and strain rates of 0.001, 0.01, and 0.05ps-1, we observed how they deform when subjected to both tensile and compressive forces. This study has shown that at higher temperatures, both forsterite and magnesite monocrystals undergo deformation more easily under pressure. Forsterite is found relatively hard and shows maximum strength before deformation compared to magnesite. The stiffness of magnesite decreases at elevated temperatures which reduces the energy requirement for the comminution process. We also looked at how pressure and temperature changes affected their elasticity. Ultimately, our findings suggest that magnesite may be more suitable for processes like comminution, which involves breaking down materials, compared to forsterite. This insight into the effects of mineral carbonation on geomaterials contributes to our understanding of how these minerals behave under different conditions and could have implications for various industries. / Master of Science / Mineral carbonation contributes to CO2 reduction, and it may also reduce the cost of mineral processing by improving the mechanical properties of rock/ore. Here, we study and compare the mechanical properties of two minerals, forsterite (Mg2SiO4) and magnesite (MgCO3) using molecular dynamics (MD) simulation. The goal is to understand whether carbonation results in hardness reduction of rock and subsequently comminution energy during the crushing and processing of the ore. We investigated how these materials respond to different physical conditions, such as temperature and strain rate, to understand their behavior under stress. By examining the molecular structure of forsterite and magnesite at temperatures ranging from 300K to 700K and strain rates of 0.001, 0.01, and 0.05ps-1, we observed how they deform when subjected to both tensile and compressive forces. This study has shown that at higher temperatures, both forsterite and magnesite monocrystals undergo deformation more easily under pressure. Forsterite is found relatively hard and shows maximum strength before deformation compared to magnesite. The stiffness of magnesite decreases at elevated temperatures which reduces the energy requirement for the comminution process. We also looked at how pressure and temperature changes affected their elasticity. Ultimately, our findings suggest that magnesite may be more suitable for processes like comminution, which involves breaking down materials, compared to forsterite. This insight into the effects of mineral carbonation on geomaterials contributes to our understanding of how these minerals behave under different conditions and could have implications for various industries.

This thesis investigates sustainability measures for quicklime and cement clinker production. It is the aim of this thesis to contribute to the effort of creating a more sustainable modus of industrial production. The methods used comprises process simulations through multicomponent chemical equilibrium calculations, fuel characterization and raw materials characterization through dynamic rate thermogravimetry. The investigated measures relate to alternative fuels, co-combustion, oxygen enrichment, oxyfuel combustion, mineral carbonation and optimizing raw material mixes based on thermal decomposition characteristics. The predictive multicomponent chemical equilibrium simulation tool developed has been used to investigate new process designs and combustion concepts. The results show that fuel selection and oxygen enrichment influence energy efficiency, and that oxyfuel combustion and mineral carbonation could allow for considerable emission reductions at low energy penalty, as compared to conventional post-combustion carbon dioxide capture technologies. Dynamic rate thermogravimetry, applied to kiln feed limestone, allows for improved feed analysis with a deeper understanding of how mixing of different feed materials will affect the production processes. The predictive simulation tool has proven to be of practical value when planning and executing production and full scale campaigns, reducing costs related to trial and error. The main conclusion of this work is that several measures are available to increase the sustainability of the industry.

M. Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / Several technologies are currently being developed to mitigate the greenhouse gas CO2. One of these promising processes is industrial mineral carbonation whereby alkaline industrial wastes are taken as raw material. The process is a multi-step process which involves the extraction of calcium from industrial alkaline wastes and the subsequent reaction of extracted calcium rich supernatant with CO2 at elevated pH to form stable carbonates. Steelmaking slags were selected from four different plants in SA and used for this investigation owing this to their high calcium content. The potentially-suitable four slags were selected on the basis of their Ca content and high chemical reactivity. The objective of this investigation was to develop a common leach process for all four steel slags to achieve a complete Ca extraction from slags. A Ca rich solution was carbonated to achieve a stable carbonate that can be used. Experiments were carried out using ammonium reagents and a hydroxide reagent to investigate their suitability for the rapid, selective extraction of calcium. Calcium was leached under different experimental conditions including varying leachant concentrations, temperatures and solid to liquid ratios. The slags exhibited contrasting reactive properties to different leachants, which can essentially be explained in terms of differences in mineralogical composition, hence mineral solubility characteristics. Leaching with 2M NH4NO3 aqueous solution at room temperature extraction efficiency increased with increasing concentration. The extent of extraction was different for the four slags. WMO5 showed a complete dissolution of Ca within 20 min of experiment. This difference is due to their different Ca-containing minerals. Same is observed with aqueous NH4CL but WMO5 did not reach a complete dissolution as with NH4NO3. Aqueous NaOH made it impossible for Ca extraction due to its high pH and upon slag addition it was more elevated. Increasing solid to liquid ratio had an influence in percentage slag loss. The pH of leach solution was elevated to 9 making it difficult to extract Ca. Under controlled conditions (pH kept under 1) optimal slag dissolution was achieved with traces of larnite and large amount of brownmillerite. The generated Ca-rich leachate was carbonated in a 600 ml reactor vessel with liquid CO2. A stable carbonate aggregate was produced. / Council for Geoscience Vaal University of Technology

O regolito é o manto do intemperismo existente sobre as rochas. Este manto pode ser constituído estruturalmente por três entidades distintas denominadas, solo, sedimento e saprolito. Ambas são produtos da intemperização das rochas. No entanto, o saprolito é definido como o único produto não transportado da intemperização isovolumétrica do litotipo originário. Diferente dos solos, dos sedimentos ou das rochas, não existe uma ciência específica para o estudo dos saprolitos. A saprolitologia não existe oficialmente, porém, pode ser implicitamente encontrada em trabalhos científicos de todo o mundo. No primeiro capítulo da tese, apresenta-se o estado da arte dos estudos dos saprolitos e sugere-se a consolidação da saprolitologia com o intuito de incentivar o incremento das pesquisas voltadas a esta entidade ainda pouco conhecida. De fato, os processos relacionados à intemperização isovolumétrica das rochas ainda não foram completamente compreendidos. Neste contexto, o Estado de Pernambuco, no nordeste do Brasil, apresenta condições geomorfológicas e climáticas propícias ao estudo da formação de saprolitos. No segundo capítulo da tese, demonstra-se que o intemperismo isovolumétrico de treze rochas cristalinas foi mais influenciado pelas condições microambientais, a exemplo da dinâmica da água através da microestrutura, do que pelas condições macroambientais. Posteriormente ao intemperismo isovolumétrico, diferenças morfológicas e geoquímicas ocorrem durante a evolução vertical do regolito. Entretanto, os domínios da saprolitogênese e da pedogênese são difíceis de diferenciar. No terceiro capítulo da tese, avaliou-se a evolução morfológica, estrutural e geoquímica de treze perfis formados por sistemas solo-saprolitos derivados do embasamento cristalino do Estado de Pernambuco. Anomalias nos índices de mensuração do intemperismo demonstram que o aumento gradual do grau de intemperização dos horizontes mais superficiais em relação aos horizontes inferiores não é a regra durante a evolução vertical do regolito. Em adição, a geoquímica e a morfologia dos perfis estudados indicam que alguns sistemas solo-saprolitos desenvolveram-se de forma interligada e outros apresentam evidências de que a formação do saprolito pode ter ocorrido após a formação do solo sobrejacente. Durante a evolução do regolito, o solo e o saprolito influenciam processos essenciais ao meio ambiente. No quarto capítulo da tese, descrevem-se as implicações agrícolas e ambientais dos treze perfis descritos no terceiro capítulo. Os resultados sugerem que os processos geoquímicos existentes nos sistemas solo-saprolitos, a exemplo da \"mineral carbonation\", influenciam o fluxo de elementos através do ecossistema circundante e demonstram que os saprolitos possuem importância agrícola e ambiental análoga à dos solos, influenciando processos de relevância agroambientais tais como a dinâmica da água, a retenção e transporte de nutrientes e/ou a retenção e transporte de contaminantes ou poluentes. / The regolith is the mantle of weathering above the rocks. This mantle may consist of three structurally distinct entities denominated sediment, soil and saprolite. All are products of rock weathering. Saprolite is defined as the product of in situ, isovolumetric weathering of the lithotype. Unlike the soils, sediments or rocks, there is no specific science dedicated to the study of saprolite. The saprolihtology does not exist formally. However, it can implicitly be found in scientific papers from around the world. The first chapter of the thesis presents the state of the art of saprolite studies and suggests the consolidation of saprolithology in order to encourage the development of research focused in this entity poorly known. In fact, the processes related to the isovolumetric weathering of rocks are not yet fully understood. In this context, the Pernambuco State in Northeastern Brazil have geomorphological and climatic conditions prone to the study of the saprolite formation and evolution. The second chapter of this thesis demonstrates that the isovolumetric weathering of the thirteen crystalline rocks was more influenced by microenvironmental conditions, such as the water dynamics through the microstructure, than the macro-environmental conditions. Subsequent to isovolumetric weathering, morphological and geochemical differenciation occur during the vertical evolution of regolith. However, it is difficult to differentiate the domains of saprolithogenesis and pedogenesis. The third chapter of the thesis reports the morphological, structural and geochemical evolution of the thirteen profiles formed by soil-saprolite systems derived from the crystalline basement of the Pernambuco State. Anomalies in the weathering measurement indexes showed that the gradual increase in the degree of weathering from the surface horizons towards the subsurface horizons is not the rule for the vertical development of regolito. In addition, the geochemistry and the morphology of the studied profiles indicate that some soil-saprolite systems evolved in an interconnected way and others provide evidence that the formation of saprolite may have occurred after the formation of the overlying soil. During the regolith evolution, soil and saprolite influence key environmental processes. The fourth chapter describes the agricultural and environmental implications of the processes acting in the thirteen profiles described in the third chapter. The results suggest that existing processes in geochemical soil-saprolite systems, such as the mineral carbonation, have influenced the elements flow through the surrounding ecosystem and demonstrate that saprolites have agricultural and environmental importance analogous to soil, influencing processes such as water fluxes, retention and transport of nutrients and/or of contaminants or pollutants.

O regolito é o manto do intemperismo existente sobre as rochas. Este manto pode ser constituído estruturalmente por três entidades distintas denominadas, solo, sedimento e saprolito. Ambas são produtos da intemperização das rochas. No entanto, o saprolito é definido como o único produto não transportado da intemperização isovolumétrica do litotipo originário. Diferente dos solos, dos sedimentos ou das rochas, não existe uma ciência específica para o estudo dos saprolitos. A saprolitologia não existe oficialmente, porém, pode ser implicitamente encontrada em trabalhos científicos de todo o mundo. No primeiro capítulo da tese, apresenta-se o estado da arte dos estudos dos saprolitos e sugere-se a consolidação da saprolitologia com o intuito de incentivar o incremento das pesquisas voltadas a esta entidade ainda pouco conhecida. De fato, os processos relacionados à intemperização isovolumétrica das rochas ainda não foram completamente compreendidos. Neste contexto, o Estado de Pernambuco, no nordeste do Brasil, apresenta condições geomorfológicas e climáticas propícias ao estudo da formação de saprolitos. No segundo capítulo da tese, demonstra-se que o intemperismo isovolumétrico de treze rochas cristalinas foi mais influenciado pelas condições microambientais, a exemplo da dinâmica da água através da microestrutura, do que pelas condições macroambientais. Posteriormente ao intemperismo isovolumétrico, diferenças morfológicas e geoquímicas ocorrem durante a evolução vertical do regolito. Entretanto, os domínios da saprolitogênese e da pedogênese são difíceis de diferenciar. No terceiro capítulo da tese, avaliou-se a evolução morfológica, estrutural e geoquímica de treze perfis formados por sistemas solo-saprolitos derivados do embasamento cristalino do Estado de Pernambuco. Anomalias nos índices de mensuração do intemperismo demonstram que o aumento gradual do grau de intemperização dos horizontes mais superficiais em relação aos horizontes inferiores não é a regra durante a evolução vertical do regolito. Em adição, a geoquímica e a morfologia dos perfis estudados indicam que alguns sistemas solo-saprolitos desenvolveram-se de forma interligada e outros apresentam evidências de que a formação do saprolito pode ter ocorrido após a formação do solo sobrejacente. Durante a evolução do regolito, o solo e o saprolito influenciam processos essenciais ao meio ambiente. No quarto capítulo da tese, descrevem-se as implicações agrícolas e ambientais dos treze perfis descritos no terceiro capítulo. Os resultados sugerem que os processos geoquímicos existentes nos sistemas solo-saprolitos, a exemplo da \"mineral carbonation\", influenciam o fluxo de elementos através do ecossistema circundante e demonstram que os saprolitos possuem importância agrícola e ambiental análoga à dos solos, influenciando processos de relevância agroambientais tais como a dinâmica da água, a retenção e transporte de nutrientes e/ou a retenção e transporte de contaminantes ou poluentes. / The regolith is the mantle of weathering above the rocks. This mantle may consist of three structurally distinct entities denominated sediment, soil and saprolite. All are products of rock weathering. Saprolite is defined as the product of in situ, isovolumetric weathering of the lithotype. Unlike the soils, sediments or rocks, there is no specific science dedicated to the study of saprolite. The saprolihtology does not exist formally. However, it can implicitly be found in scientific papers from around the world. The first chapter of the thesis presents the state of the art of saprolite studies and suggests the consolidation of saprolithology in order to encourage the development of research focused in this entity poorly known. In fact, the processes related to the isovolumetric weathering of rocks are not yet fully understood. In this context, the Pernambuco State in Northeastern Brazil have geomorphological and climatic conditions prone to the study of the saprolite formation and evolution. The second chapter of this thesis demonstrates that the isovolumetric weathering of the thirteen crystalline rocks was more influenced by microenvironmental conditions, such as the water dynamics through the microstructure, than the macro-environmental conditions. Subsequent to isovolumetric weathering, morphological and geochemical differenciation occur during the vertical evolution of regolith. However, it is difficult to differentiate the domains of saprolithogenesis and pedogenesis. The third chapter of the thesis reports the morphological, structural and geochemical evolution of the thirteen profiles formed by soil-saprolite systems derived from the crystalline basement of the Pernambuco State. Anomalies in the weathering measurement indexes showed that the gradual increase in the degree of weathering from the surface horizons towards the subsurface horizons is not the rule for the vertical development of regolito. In addition, the geochemistry and the morphology of the studied profiles indicate that some soil-saprolite systems evolved in an interconnected way and others provide evidence that the formation of saprolite may have occurred after the formation of the overlying soil. During the regolith evolution, soil and saprolite influence key environmental processes. The fourth chapter describes the agricultural and environmental implications of the processes acting in the thirteen profiles described in the third chapter. The results suggest that existing processes in geochemical soil-saprolite systems, such as the mineral carbonation, have influenced the elements flow through the surrounding ecosystem and demonstrate that saprolites have agricultural and environmental importance analogous to soil, influencing processes such as water fluxes, retention and transport of nutrients and/or of contaminants or pollutants.

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Na carbonatação mineral pela rota indireta utiliza-se ácidos, bases ou sais de amônia para a extração do magnésio, principalmente, presente na rocha silicato a fim de a formar carbonatos estáveis. Destaca-se que a etapa de dissolução ácida é uma fase limitante para o processo de carbonatação mineral, principalmente por apresentar baixa taxa de reação. O objetivo deste trabalho é utilizar o ácido clorídrico (HCl) e dois serpentinitos oriundos do estado de Goiás e Minas Gerais para avaliar o processo de dissolução ácida. Os serpentinitos foram preparados, selecionados e caracterizados para determinar a composição elementar. Aplicou-se o planejamento experimental e arranjo L9 de Taguchi na avaliação dos fatores que influenciam o processo de dissolução, tais como, temperatura do processo, concentração do HCl, tamanho médio das partículas da matéria prima e excesso de ácido. Os 9 ensaios previstos na matriz de planejamento para cada serpentinito foram executados de forma aleatória e em duplicata. Os produtos finais, resíduo sólido retido no papel filtro e solução contendo os elementos de interesse, foram analisados obtendo-se a composição elementar das soluções. Considerando-se os testes previstos na matriz de planejamento, a condição de melhor ajuste para extração de Mg foi utilizando-se a granulometria média de 69 µm, temperatura de 70°C, HCl 2 M com quatro vezes a quantidade estequiométrica. Nas soluções foram obtidas as concentrações de 29 % e 76 % de Mg para as amostras de serpentinito de Minas Gerais e de Goiás, respectivamente. Foram também avaliadas as melhores condições para extração de Fe e Ca e menor extração de Si, uma vez que o Si diminui a conversão no processo. Na análise estatística verificou-se que para a amostra de Minas Gerais todos os fatores apresentaram significância. No caso da a amostra de Goiás a temperatura no nível alto (70°C) apresentou maior significância. / In this dissertation, acid dissolution reaction of Brazilian silicate rocks was investigated aiming the implementation in a Carbon Capture and Storage process named Mineral Carbonation. In the mineral carbonation by indirect route, acids, bases or salts of ammonia are used for magnesium extraction, mainly, present in the silicate rock in order to form stable carbonates. It is noteworthy that the acid dissolution step is a limiting step in the process of mineral carbonation, mainly because of its low reaction rate. The objective of this study was to use hydrochloric acid (HCl) and two serpentinites from Goiás and Minas Gerais states to evaluate the acid dissolution process. The serpentinites were prepared, selected, and characterized to determine the elemental composition. The L9 experimental design and Taguchi arrangement were applied to evaluate the factors that influence in the dissolution process, such as process temperature, HCl concentration, average particle size of material and acid excess. The nine tests prescribed in planning matrix for each serpentinite were performed at random and in duplicate. The end products, solid residue retained on the filter paper and the solution containing the elements of interest were analyzed obtaining the elemental composition of the solutions. Considering the prevised tests on planning matrix, the best adjust condition for Mg extraction was using the average particle size of 69 µm temperature of 70°C, 2 M HCl with four times the stoichiometric amount. In the solutions, the concentrations obtained were 29 % and 76 % Mg for samples of serpentinite from Minas Gerais and Goiás, respectively. The best conditions for the extraction of Fe and Ca and lower extraction of Si were evaluated, since Si decreases the conversion in the process. In the statistical analysis was found that in Minas Gerais sample all factors were significant. In the case of Goiás sample, the temperature at the high level (70°C) showed greater significance.

Philosophiae Doctor - PhD / Coal combustion accounts for 95% of electricity generation in South Africa while globally coal combustion for energy generation stands at 42%. It has been predicted that coal utilization for energy generation will continue due to its low cost and availability in huge quantities in different parts of the world. Additionally brine and gaseous emissions are produced in the power generation and coal combustion processes. In fact, it has been established that CO2 emissions from power plants are the main cause of the green-house effect leading to global warming. Mitigation of the effects of disposal of fly ash, brine and CO2 emissions is critical for sustainable energy generation from coal and environmental protection. The study investigated whether South African coal fly ash could be used for brine remediation and CO2 capture using fly ash based hydrotalcites and zeolites. Four main objectives were investigated. These were; firstly, to compare the natural CO2 capture potential of a power station ash dam with an accelerated ex-situ mineral carbonation process. Secondly, to probe the effect of accelerated ex-situ mineral carbonation on brine quality with regards to major, minor and trace elements concentration. Furthermore, the study investigated the feasibility of synthesizing hydrotalcites from fly ash by optimizing the synthesis parameters such as acid concentration, aging time, aging temperature, pH during aging, crystallization time and crystallization temperature. Finally the study compared the CO2 adsorption capacities of the fly ash based hydrotalcites with fly ash based zeolites NaA, and NaX. The natural carbonation potential of the wet disposed ash dam at Secunda was investigated by coring a 20 year old dam. Three cores (SI, S2 and S3) were obtained by air flush coring the dam along a geophysical line and establishing the geophysical profile of the three cores. The surface of the three cores was of medium resistivity with values between 9.3 and 12.2 nm while the midsections were of low resistivity with values ranging between 4 and 7 nm. The base section of core SI had a resistivity of 28.3 nm, that of S2 was between 16.2 and 21.4 nm and that of S3 between 12.2 and 16.2 nm; implying that SI had the lowest salt load while S3 had the highest salt content. Moisture content was observed to be high deeper down the profiles of S2 and S3 with samples appearing water logged while SI had the highest moisture content at the surface showing the inhomogeneity of the ash dam. The morphology of fresh fly ash taken from the ash collection hoppers at Secunda was observed to be spherical. Weathered ash from the ash dam showed irregularly agglomerated particles while accelerated ex-situ mineral carbonation resulted in the formation of acicular particles of calcite. Fresh ash, weathered ash and the accelerated carbonated ash were all class F with a sum total of silica, alumina and iron oxide totaling more than 70%. A reduction in silica and alumina content with instability of fly ash. Dumping of spent iron catalyst (resulting from the petrochemical operations as Sasol) on the ash dam led to an increase in Fe203 content of the weathered ash. Enrichment of Nb, Sr, Y, Th, Na, Cl, S04, K and S with natural carbonation as well as during accelerated ex-situ mineral carbonation was observed and was due to the contact of ash with brine during these two processes. Reduction of Zr, Rb, Pb, Ni, Co and V content of ash was observed with weathering. Mineralogically, all the ash samples had main phases of mullite, quartz, magnetite and hematite, with weathered and accelerated carbonated ash having additional phases of calcite. The aluminosilicious nature of the three ashes was identified by structural evaluation using Fourier transform infrared analysis which revealed that, bands associated with C-O in-plane and out of plane bending of carbonates was only visible in weathered and carbonated ash.

The cement and concrete industry stand for approximately 8% of the global CO2 emissions. The demand of concrete and cement is expected to increase rapidly with the growing world population and increased urbanization. This makes it of the utmost importance for the industry to try to mitigate its emissions. One way to reduce the industry’s environmental impact is by mineral carbonation curing through which CO2 can be sequestered in the concrete. This investigation studied the CO2 uptake of wollastonite (CaSiO3) which can be used for mineral carbonation. The CO2 uptake of different brands of wollastonite powders for different temperatures, pressures and water to solid ratios were tested through carbonation, and the samples were then analyzed through XRD, SEM and particle size analysis. The results showed large differences in CO2 uptake between the brands of wollastonite powders. They also indicate that lower temperatures lead to higher CO2 uptake but also possibly slow down the reaction rate and that higher CO2 pressures seem to increase CO2 uptake though the effect is small. There was significant variation of the effects of the water to solid ratios on CO2 uptake between the tested brands. The morphology of the powders also seemed to be of little relevance as an amorphous and crystalline powder were the two best performing powders, similarly particle size is not indicated by the result to have a large effect on CO2 uptake, though further studies are required to fully determine the effect of the morphology and particle size. / Cement- och betongindustrin står för cirka 8% av de globala koldioxidutsläppen. Efterfrågan på betong och cement förväntas öka snabbt med den växande världsbefolkningen och ökad urbanisering. Detta tyder på hur viktigt det är för industrin att minska sina utsläpp. Ett sätt att minska industrins miljöpåverkan är genom härdning av betongen via mineral karbonatisering, en process som binder in koldioxid i betong. I detta arbete studerades koldioxidupptagningen av mineralen wollastonit (CaSiO3) som kan användas för mineral karbonatisering. Olika märken av wollastonitpulvers koldioxidupptag vid olika temperaturer, koldioxidtryck och vattenhalter testades genom karbonatisering och proverna analyserades därefter genom XRD-analys, SEM-analys och partikelstorleksanalys. Resultaten visade stora skillnader i koldioxidupptagning mellan varumärkena av wollastonitpulver. De visar även att lägre temperaturer leder till högre upptag av koldioxid, men att reaktionshastigheten potentiellt saktar ner vid låga temperaturer. Högre koldioxidtryck verkar öka koldioxidupptagningen men effekten är liten. Det fanns signifikant variation av effekterna av vattenhalterna på koldioxidupptagning mellan de testade varumärkena. Pulvrens morfologi verkade inte ha en stor effekt då ett av de två bäst presterande pulvren var amorft och det andra kristallint. På samma sett verkade partikelstorleken inte ha en stor påverkan på koldioxidupptaget men ytterligare studier krävs för att fullständigt kunna bestämma effekten av morfologin och partikelstorleken.