Thesis -- Departmental honors in Chemistry. / Bibliography: ℓ. 40-42.

O presente trabalho visa se aprofundar em estudos para se obter uma melhor compreensão das maneiras que os processos de intemperismo químico na região tropical influem no rebaixamento do relevo. Este tema é de grande relevância e sua adequada compreensão é necessária para o avanço dos conhecimentos de geomorfologia da atualidade. Assim pretende-se a partir da compartimentação do relevo efetuar análises físicas e químicas de horizontes do solo e do manto de alteração, em perfis de contexto de litologia ígnea e metamórfica, efetuando comparações e demonstrando através dos resultados dos parâmetros selecionados de que forma o horizonte B se relaciona com o horizonte C do solo, bem como as semelhanças e diferenças ocasionadas pelos diferentes compartimentos litológicos. Para isso será efetuado um estudo de caso no Planalto do Paraitinga/Paraibuna-SP procurando correlacionar indicadores de maneira a demonstrar possíveis caminhos que forneçam informações quanto ao rebaixamento do relevo através de processos geoquímicos. / This study aims to deepen studies trying to understand ways of the chemical weathering processes influence the relief in the tropics. This matter have great relevance and need be better understanding to advance the geomorphology knowledge. Thus it is intended from the partitioning of relief make physical and chemical analysis of soil horizons and alteration mantle, in the context of igneous and metamorphic lithology profiles, making comparisons and demonstrated by the results of the selected parameters that form the B horizon is related to the soil horizon C as well as similarities and differences caused by different lithologic compartments. For it will be made a case study at the Plateau Paraitinga/Paraibuna-SP to correlate indicators in order to demonstrate possible ways to provide information regarding the lowering of relief through geochemical processes.

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One of the most essential resources for life on our planet is water. A concern for water resource sustainability has shifted towards the sustainable development of clean water body resource (SWDF, 2009). Data for the Vaal River water chemistry is in abundance. However, research on the historic natural conditions influencing the inorganic water quality, is not as extensive. Inorganic data was obtained from the Department of Water Affairs, for the period 1972 to 2011, for identified monitoring stations along the Vaal River. Water quality was evaluated using various geochemical techniques to analyse the data. The results of the study indicate that the water chemistry of the Vaal River is controlled by: 1. Chemical weathering of siliceous sediment, intrusive igneous rocks and metamorphic rocks (Na+, K+, Mg2+, Ca2+ and (HCO3)-). 2. Anthropogenic influences increasing the sulphate (SO4) concentration There is no major increase in ion concentrations for the stations. However the concentrations of bicarbonate (HCO3)- and SO4 change as it progresses downstream from the first upstream station to the last downstream station. Based on the chemical characterisation, three groups have been identified. (1) Group 1 stations appear to suggest a higher influence in chemical weathering than the group 2 stations. (2) Group 2 stations appear to suggest a greater influence from SO4. (3) Group 3 stations appear to suggest an influence from both the bicarbonate and the SO4 influences. Geographically the chemical weathering is an indication of the three different groups with strong anthropogenic influences in the middle group. The water chemistry for the Vaal River is controlled by two processes, namely chemical weathering and anthropogenic influences. The prominent indication of the difference in these two influences can be seen between group 1 and group 2. A secondary conclusion indicates that a total dissolved solid (TDS) alone is not an accurate representation of anthropogenic influence (or poor water quality) on inorganic water quality of the Vaal River. The natural weathering or geological influences appears to play a more dominant role in certain sections or catchments with lower contributions from anthropogenic influences. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

One of the most essential resources for life on our planet is water. A concern for water resource sustainability has shifted towards the sustainable development of clean water body resource (SWDF, 2009). Data for the Vaal River water chemistry is in abundance. However, research on the historic natural conditions influencing the inorganic water quality, is not as extensive. Inorganic data was obtained from the Department of Water Affairs, for the period 1972 to 2011, for identified monitoring stations along the Vaal River. Water quality was evaluated using various geochemical techniques to analyse the data. The results of the study indicate that the water chemistry of the Vaal River is controlled by: 1. Chemical weathering of siliceous sediment, intrusive igneous rocks and metamorphic rocks (Na+, K+, Mg2+, Ca2+ and (HCO3)-). 2. Anthropogenic influences increasing the sulphate (SO4) concentration There is no major increase in ion concentrations for the stations. However the concentrations of bicarbonate (HCO3)- and SO4 change as it progresses downstream from the first upstream station to the last downstream station. Based on the chemical characterisation, three groups have been identified. (1) Group 1 stations appear to suggest a higher influence in chemical weathering than the group 2 stations. (2) Group 2 stations appear to suggest a greater influence from SO4. (3) Group 3 stations appear to suggest an influence from both the bicarbonate and the SO4 influences. Geographically the chemical weathering is an indication of the three different groups with strong anthropogenic influences in the middle group. The water chemistry for the Vaal River is controlled by two processes, namely chemical weathering and anthropogenic influences. The prominent indication of the difference in these two influences can be seen between group 1 and group 2. A secondary conclusion indicates that a total dissolved solid (TDS) alone is not an accurate representation of anthropogenic influence (or poor water quality) on inorganic water quality of the Vaal River. The natural weathering or geological influences appears to play a more dominant role in certain sections or catchments with lower contributions from anthropogenic influences. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Chemical weathering reactions are important for the physical, chemical, and biological development of the critical zone. We present findings from aqueous phase chemical analyses of surface and soil pore waters during a 15 month study in a small semi-arid mountain catchment of the Santa Catalina Mountain Critical Zone Observatory. Stream water geochemical solutes are sourced to two distinct locations - fractured bedrock baseflow stores and soil quickflow stores. Solid phase observations of albite, anorthite, and K-feldspar transformation to Ca-montmorillonite and kaolinite are supported by stream water saturation states calculated via a PHREEQC geochemical model. While differences in mineral assemblages, soil depths, and horizonation suggest greater weathering in schist versus granite lithologies and in hillslope divergent versus convergent zones, soil pore water solute ratio analysis does not readily distinguish these differences. However, preliminary investigation of aqueous rare earth elements suggests detectable lithologic and landscape positional differences warranting focus for future research efforts.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science, School of Animal, Plant and Environmental Sciences, 2017. / Acidification of freshwater systems by Acid Mine Drainage (AMD) is a persistent risk to aquatic ecosystems in South Africa, particularly in Gauteng and Mpumalanga. From several studies that have been conducted, it is clear that AMD has profound effects on aquatic life and functionality of the ecosystem. One of the ecosystem processes affected by AMD is the decomposition process. It has been established that AMD-affected streams inhibit the decompositon process. [Abbreviated Abstract. Open document to view full version] / LG2018

With the atmospheric concentration of carbon dioxide steadily increasing and little sign of a reduction in fossil fuel demand worldwide, there is a well-established need for an alternative strategy for dealing with carbon emissions from energy production. One possible solution is the accelerated weathering of ultramafic rocks. Accelerated weathering is an environmentally benign route to a thermodynamically and kinetically stable form of carbon. The chemistry is based on naturally occurring reactions and the raw materials are abundant across the earth's surface. However, the reactions are relatively slow, and achieving reaction rates sufficient to match the carbon dioxide production rate at an energy conversion facility is challenging. This work addresses a number of the challenges facing the integration of accelerated weathering with energy conversion, and presents one view of how the integration could be achieved. This work begins by developing a suite of tools necessary for investigating the dissolution and precipitation of minerals. Chapter 2 starts with a description of the minerals that will be evaluated, and then goes on to develop the techniques that will be used. The first is a differential bed reactor, which is used for measuring the dissolution rates of minerals under tightly controlled conditions. Next a bubble column reactor is developed for the investigating the adsorption of carbon dioxide and the precipitation of mineral carbonates in a single vessel. These techniques, together with a batch reactor for studying direct carbonation reactions, constitute a comprehensive set of tools for the investigation of accelerated mineral weathering. With the necessary techniques developed and proven, Chapter 3 addresses the first challenge faced by accelerated mineral weathering; the dissolution rate of magnesium from a silicate mineral. While the dissolution of this mineral is thermodynamically favorable, the kinetics are prohibitively slow. It is thought that this is because silica from the mineral tends to accumulate on the particle surface creating a passivation layer, which limits the reaction rate of the mineral. In this work, the effects of a combination of chemical chelating agents, catechol and oxalate, are evaluated for their ability to circumvent this passivation layer. The results indicate that catechol and oxalate modify the passivation layer as it forms, both accelerating the dissolution rate of the mineral and maintaining pore volume, leading to greater dissolution rates. This pore modification process is proposed as the primary mechanism by which catechol affects the passivation layer. The combination of catechol and oxalate under acidic conditions is also shown be effective when the ambient solution approaches the saturation point of silica. Finally, the chelating does not impede the precipitation of carbonate products, a critical hurdle for a carbon storage process. The chelating agent work is extended in Chapter 4, with a sensitivity study that evaluates the response of the dissolution rate to changes in both pH and the concentration of the chelating agents. Oxalate and pH are found to exhibit a strong influence on the mineral dissolution rate, while the effect of catechol is more apparent after significant dissolution has taken place. These observations are in agreement with the model of passivation layer modification proposed. In addition, some alternatives to the chelating agent catechol are evaluated. It is found that when used in combination with oxalate, these alternatives appeared equivalent to catechol, but alone they had only a minor effect. Catechol was also noted to have a significant effect on the dissolution rate of iron from the silicate mineral, and a mechanism for this effect was proposed. The direct adsorption of carbon dioxide and precipitation of solid carbonates in a single reaction step presents another challenge for accelerated mineral carbonation. In general, the magnesium carbonates formed at ambient pressure and moderate temperatures tend to be hydrated, and at times contain unused hydroxides, leading to inefficiencies in both transport and storage. It is shown in Chapter 5 that by seeding reaction vessels with the anhydrous form of magnesium carbonate, it is possible to grow this desired phase with minimal formation of the metastable hydrated phases. The formation of this phase is primarily limited by the precipitation rate, but in some situations, carbon dioxide hydration kinetics and magnesium hydroxide precipitation kinetics also play a role. In Chapter 6, these developments in both magnesium silicate dissolution and carbonate precipitation are combined into a proposed technology for the direct capture and storage of carbon dioxide. This application of accelerated mineral weathering is shown to significantly reduce the carbon emissions of an energy conversion technology through life cycle assessment. This novel approach to the mitigation of carbon emissions presents a compelling argument for the continued development of accelerated mineral weathering as a combined carbon capture and storage technology.

Mémoire (M.Sc.A.)--Université du Québec à Chicoutimi, 1986. / 4 cartes géographiques sur feuillets pliés, en pochette. CaQCU Bibliogr.: p. 58-61. Document électronique également accessible en format PDF. CaQCU