In natural systems, the solution concentration and hence, potential bioavailability of trace metals is primarily controlled by adsorption-desorption reactions at the mineral-water interface. While many studies have been conducted to understand the adsorption of trace metals to soil minerals, less is known about long-term adsorption/desorption processes. In this study, we examined the influence of mixing and sorption period on the desorption of lead from goethite. Lead sorption was rapid and essentially complete in 1 h, with no change in the quantity of lead adsorbed over the 6 month sorption period. Desorption of lead was slower than the adsorption reaction and was best modeled by two first order equations. At all sorption densities, the desorption of lead followed the order Short-term (24 h) > Long-term non-stirred (6 months) > Long-term stirred (6 months). However, statistical analysis indicated that these differences were not statistically significant. Furthermore, the desorption rate coefficients were very similar for all the experiments indicating that there was no significant residence time effect in this study. However, a sample from a previous study that was allowed to age 5 years and then analyzed by the desorption procedure did have statistically significant differences between the long-term (5 years) and the short-term (5 months). These results suggest that longer adsorption periods, perhaps a number of years, may be necessary to determine if residence time effects are an artifact of the experimental conditions or truly the length of the adsorption period. / Master of Science

Not available / text

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Russell T. Johns. Vita. Includes bibliographical references.

Com a atual preocupação ambiental e a necessidade de se conhecer os processos que regem o movimento da água e de solutos no solo, são necessários estudos que possibilitem aumentar a eficiência do uso de insumos no setor agrícola, que de certa forma possam mitigar o impacto das atividades deste setor sobre contaminação de águas subterrâneas. Portanto, objetivou-se com a presente pesquisa verificar os parâmetros de transporte do íon nitrato, diante de uma análise da influência dos respectivos íons acompanhantes, a partir de fontes distintas de nitrato, em seu deslocamento, com a elaboração de curvas de distribuição de efluentes (Breakthrough Curves (BTC)), em condições de amostras de solo deformadas e indeformadas. O trabalho foi realizado em condições de solo saturado e regime permanente, via aplicação de uma solução de nitrato na concentração de 50 g m-3 de NO3 -, por três diferentes fontes (Ca(NO3)2, NH4NO3 e KNO3), para dois tipos distintos de solos tropicais: Latossolo Vermelho Amarelo e Nitossolo Vermelho. O experimento foi conduzido no Laboratório de Solos e Qualidade de Água, do Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura \"Luiz de Queiroz\", em Piracicaba - SP. Os parâmetros de transporte do íon nitrato na concentração de 50 g m-3 nos respectivos solos foram obtidos por um ajuste numérico utilizando-se o software STANMOD. Pelos resultados obtidos, pôde-se verificar que o deslocamento do nitrato está atrelado com as caraterísticas dos solos e que houve maiores efeitos de lixiviação para o Nitossolo Vermelho. Em termos da influência dos cátions acompanhantes do nitrato, em suas diferentes fontes distintas, pode-se dizer que não foram observados seus efeitos na mobilidade do nitrato no perfil do solo. / With the current environmental concerns and the need to understand the processes that govern the movement of water and solutes in soil, studies are needed to allow increasing the efficiency of input use in agriculture that somehow can mitigate the impact of activities of this sector on groundwater contamination. Therefore, the objective of this work was to verify the transport parameters of the nitrate, by analyzing the influence of the accompanying cation on nitrate displacement, through the development of distributions curves of effluents (Breakthrough Curves (BTC)), under conditions of disturbed and undisturbed samples in saturated soil and steady state conditions, via application of nitrate solution at a concentration of 50 g m-3 NO3 -, by three different sources (Ca(NO3)2, NH4NO3 and KNO3) and for two types of tropical soils: Yellow Oxisol and Anfisol. The experiment was conducted in the Laboratory of Soil and Water Quality, Department of Biosystems Engineering from Escola Superior de Agricultura \"Luiz de Queiroz\", Piracicaba - SP. The transport parameters of the nitrate at a concentration of 50 g m-3 in their respective soils were obtained by a numerical fit using the software STANMOD. From the results, it could be seen that the nitrate displacement is linked with the soil characteristics and the leaching was higher in Anfisol. In terms of the influence of accompanying cations of nitrate, in its various different sources, it can be said that their effects were not observed in nitrate mobility in the soil profile.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 214-220). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Vita. Includes bibliographical references (leaves 309-318). Available also in a digital version from Dissertation Abstracts.

Com a atual preocupação ambiental e a necessidade de se conhecer os processos que regem o movimento da água e de solutos no solo, são necessários estudos que possibilitem aumentar a eficiência do uso de insumos no setor agrícola, que de certa forma possam mitigar o impacto das atividades deste setor sobre contaminação de águas subterrâneas. Portanto, objetivou-se com a presente pesquisa verificar os parâmetros de transporte do íon nitrato, diante de uma análise da influência dos respectivos íons acompanhantes, a partir de fontes distintas de nitrato, em seu deslocamento, com a elaboração de curvas de distribuição de efluentes (Breakthrough Curves (BTC)), em condições de amostras de solo deformadas e indeformadas. O trabalho foi realizado em condições de solo saturado e regime permanente, via aplicação de uma solução de nitrato na concentração de 50 g m-3 de NO3 -, por três diferentes fontes (Ca(NO3)2, NH4NO3 e KNO3), para dois tipos distintos de solos tropicais: Latossolo Vermelho Amarelo e Nitossolo Vermelho. O experimento foi conduzido no Laboratório de Solos e Qualidade de Água, do Departamento de Engenharia de Biossistemas da Escola Superior de Agricultura \"Luiz de Queiroz\", em Piracicaba - SP. Os parâmetros de transporte do íon nitrato na concentração de 50 g m-3 nos respectivos solos foram obtidos por um ajuste numérico utilizando-se o software STANMOD. Pelos resultados obtidos, pôde-se verificar que o deslocamento do nitrato está atrelado com as caraterísticas dos solos e que houve maiores efeitos de lixiviação para o Nitossolo Vermelho. Em termos da influência dos cátions acompanhantes do nitrato, em suas diferentes fontes distintas, pode-se dizer que não foram observados seus efeitos na mobilidade do nitrato no perfil do solo. / With the current environmental concerns and the need to understand the processes that govern the movement of water and solutes in soil, studies are needed to allow increasing the efficiency of input use in agriculture that somehow can mitigate the impact of activities of this sector on groundwater contamination. Therefore, the objective of this work was to verify the transport parameters of the nitrate, by analyzing the influence of the accompanying cation on nitrate displacement, through the development of distributions curves of effluents (Breakthrough Curves (BTC)), under conditions of disturbed and undisturbed samples in saturated soil and steady state conditions, via application of nitrate solution at a concentration of 50 g m-3 NO3 -, by three different sources (Ca(NO3)2, NH4NO3 and KNO3) and for two types of tropical soils: Yellow Oxisol and Anfisol. The experiment was conducted in the Laboratory of Soil and Water Quality, Department of Biosystems Engineering from Escola Superior de Agricultura \"Luiz de Queiroz\", Piracicaba - SP. The transport parameters of the nitrate at a concentration of 50 g m-3 in their respective soils were obtained by a numerical fit using the software STANMOD. From the results, it could be seen that the nitrate displacement is linked with the soil characteristics and the leaching was higher in Anfisol. In terms of the influence of accompanying cations of nitrate, in its various different sources, it can be said that their effects were not observed in nitrate mobility in the soil profile.

The miscible displacement equations provide the mathematical model for simulating the displacement of a mixture of oil and miscible fluid in underground reservoirs during the Enhance Oil Recovery(EOR) process. In this thesis, I propose a stable numerical scheme combining a mixed finite element method and space-time discontinuous Galerkin method for solving miscible displacement equations under low regularity assumption. Convergence of the discrete solution is investigated using a compactness theorem for functions that are discontinuous in space and time. Numerical experiments illustrate that the rate of convergence is improved by using a high order time stepping method. For petroleum engineers, it is essential to compute finely detailed fluid profiles in order to design efficient recovery procedure thereby increase production in the EOR process. The method I propose takes advantage of both high order time approximation and discontinuous Galerkin method in space and is capable of providing accurate numerical solutions to assist in increasing the production rate of the miscible displacement oil recovery process.

Dispersion has been shown to degrade miscibility in miscible displacements by lowering the concentration of the injected solute at the displacement fronts. Dispersion can also improve oil recovery by increasing sweep efficiency. Either way, dispersion is an important factor in understanding miscible displacement performance. Conventionally, dispersion is measured in the laboratory by fitting the solution of one-dimensional convection-dispersion equation (CDE) to the effluent concentration from a core flood. However dispersion is anisotropic and mixing occurs in both longitudinal and transverse directions. This dissertation uses the analytical solution of the two-dimensional CDE to simultaneously determine longitudinal and transverse dispersion. The two-dimensional analytical solution for an instantaneous finite volume source is used to investigate anisotropic mixing in miscible displacements. We conclude that transverse mixing becomes significant with large a concentration gradient in the transverse direction and significant local variation in flow directions owing to heterogeneity. We also utilized simulation models similar to Blackwell's (1962) experiments to determine transverse dispersion. This model coupled with the analytical solution for two-dimensional CDE for continuous injection source is used to determine longitudinal and transverse dispersivity for the flow medium. The validated model is used to investigate the effect of heterogeneity and other first contact miscible (FCM) scaling groups on dispersion. We derive the dimensionless scaling groups that affect FCM displacements and determine their impact on dispersion. Experimental design is used to determine the impact and interactions of significant scaling groups and generate a response surface function for dispersion based on the scaling groups. The level of heterogeneity is found to most significantly impact longitudinal dispersion, while transverse dispersion is most significantly impacted by the dispersion number. Finally, a mathematical procedure is developed to use the estimated dispersivities to determine a-priori the maximum grid-block size to maintain an equivalent level of dispersion between fine-scale and upscaled coarse models. Non-uniform coarsening schemes is recommended and validated for reservoir models with sets of different permeability distributions. Comparable sweep and recovery are observed when the procedure was extended to multi-contact miscible (MCM) displacements. / text

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