MgCl2 brines present a number of potential advantages for the processing of saprolite ores for nickel production. Concentrated MgCl2 solutions enhance the activity of acid used, allow atmospheric leaching at elevated temperature and inhibit magnesium dissolution, which reduces acid consumption and increases metal selectivity. However, with a chloride system it is economically requisite to recover hydrochloric acid, conventionally accomplished by pyrohydrolysis. This work was performed in conjunction with a novel flowsheet for the processing on saprolite ores, which recovers HCl by the precipitation and subsequent decomposition of magnesium hydroxychlorides, alleviating some of the issues with pyrohydrolysis. Leaching and iron control experiments have been conducted in concentrated MgCl2 brines, up to 4.5 m, to determine the most amenable process conditions. It was determined that > 95% extraction of metals was possible using both aqueous and gaseous HCl. In addition, the feasibility of iron control by precipitation with MgO addition was proven.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Heat transfer through the sidewall accounts for a significant proportion of the energy loss from an aluminium reduction cell. At the same time, the ledge formed on the sidewall has important consequences with regards to the cell service life and the dynamic heat balance during various disturbances associated with the smelting operation such as alumina feeding, anode changing, metal tapping and anode effect. Several studies have been carried out to investigate the ledge heat transfer. However, the reported heat transfer coefficients in the literature not only vary over a wide range of values but provide insufficient information on the ledge heat transfer. A heat transfer probe and measurement techniques were developed for studying the ledge heat transfer in a full-scale 3-D air-water model. Quantitative measurements were conducted to determine the bath/ledge heat transfer characteristics at various positions, and under different operating conditions such as anode-ledge distance, current density and bath depth. Variation of the heat transfer were also examined as a function of the anode bottom inclination, the anode slot width and the position on the side ledge relative to the anode slot. The results illustrate that the ledge profile in an operating cell will take on a different shape in compliance with the heat transfer variation. A similitude analysis was carried out to interpret the measured results in a meaningful manner for use in a reduction cell. As a result, the heat transfer coefficient in industrial cells under various operating parameters, and at different positions on the side ledge, can be estimated using the empirical correlations presented. Gas bubble behaviour and bubble impingement on the side ledge were observed in the water model. Observations made on the 2-D and 3-D water models indicate that anode gas evolution in the 3-D model cell will reflect more closely the flow pattern in actual cells and hence provide more reliable quantitative results. A simple 2-D thermal model for the prediction of ledge thickness and profile as a moving boundary was developed and solved simply and efficiently with a commercial spreadsheet software using the finite difference method. The ledge profile was predicted using the ledge heat transfer coefficients measured extensively from the full-scale 3-D physical model. The results show that the ledge shape is highly sensitive to the positional variation of the heat transfer coefficient. It is also shown that the ledge heat transfer coefficients obtained from industrial measurements assuming 1-D heat flow are much lower than the actual values in a Hall-Heroult cell. A transient thermal model derived by considering the Stefan problem$/sp[*]$ for the sidewall/ledge region was developed. A fixed-grid and deforming-grid spacing were respectively superimposed on the sidewall and the ledge region in order to track the moving front of the phase change zone. Various aspects of the process dynamics with respect to the variation of ledge thickness and sidewall shell temperature were presented. The model considered dynamic heat loss through the sidewall which results in a closer approximation to the real situation. ftn$/sp[*]$N.B.: In the strict sense the problem of the ledge is not a classical Stefan problem. The classical Stefan problem involves conduction on both sides of the interface. The ledge problem involves conduction on the side and convection on the other. / Subscription resource available via Digital Dissertations only.

Doctor of Philosophy / Department of Chemical Engineering / James H. Edgar / Semiconducting icosahedral boron arsenide, B[subscript]12As[subscript]2, is an excellent candidate for neutron detectors and radioisotope batteries, for which high quality single crystals are required. Thus, the present study was undertaken to grow B[subscript]12As[subscript]2 crystals by precipitation from metal solutions (nickel) saturated with elemental boron and arsenic in a sealed quartz ampoule. B[subscript]12As[subscript]2 crystals of 8-10 mm were produced when a homogeneous mixture of the three elements was held at 1150 °C for 48-72 hours and slowly cooled (3°C/hr). The crystals varied in color and transparency from black and opaque to clear and transparent. X-ray topography (XRT), Raman spectroscopy, and defect selective etching confirmed that the crystals had the expected rhombohedral structure and a low density of defects (5x10[superscript]7 cm[superscript]-2). The concentrations of residual impurities (nickel, carbon, etc) were found to be relatively high (10[superscript]19 cm[superscript]-3 for carbon) as measured by secondary ion mass spectrometry (SIMS) and elemental analysis by energy dispersive x-ray spectroscopy (EDS). The boron arsenide crystals were found to have favorable electrical properties (μ = 24.5 cm[superscript]2 / Vs), but no interaction between a prototype detector and an alpha particle bombardment was observed. Thus, the flux growth method is viable for growing large B[subscript]12As[subscript]2 crystals, but the impurity concentrations remain a problem.

Doctor of Philosophy / Department of Chemical Engineering / Stefan H. Bossmann / Both chemotherapy for cancer treatment and antibiotic therapy for bacterial infections require systemic applications of the drug and a systemic application is always linked to a number of disadvantages. To circumvent these a targeted drug delivery system was developed. It utilizes the ability of phagocytes from the hosts own immune system to recognize and internalize antigens. Deactivated M. luteus, a non-pathogenic gram positive bacteria was loaded with high concentrations (exceeding the IC50 at least 60 fold in local intracellular concentration) the chemotherapeutics doxorubicin or DP44mt or with the bactericidal chlorhexidine. The modified bacteria is fed to phagocytes (Monocytes/Macrophages or neutrophils) and serves as protective shell for the transporting and targeting phagocyte. The phagocyte is recruited to the tumor site or site of infection and releases the drug along with the processed M. luteus via the exosome pathway upon arrival. The chlorhexidine drug delivery system was successfully tested both in vitro and in vivo, reducing the pathogen count and preventing systemic spread of a F. necrophorum infection in a mouse model. The doxorubicin drug delivery system reduced the viability of 4T1 cancer cells to 20% over the course of four days in vitro.

Thermodiffusion is one of the mechanisms in transport phenomena in which molecules are transported in a multicomponent mixture driven by temperature gradients. Thermodiffusion in associating mixtures presents a larger degree of complexity than non-associating mixtures, since the direction of flow in associating mixtures may change with variations in composition and temperature. In this study a new activation energy model is proposed for predicting the ratio of evaporation energy to activation energy. The new model has been implemented for prediction of thermodiffusion for acetone-water, ethanol-water and isopropanol-water mixtures. In particular, a sign change in the thermodiffusion factor for associating mixtures has been predicted, which is a major step forward in modeling of thermodiffusion for associating mixtures. In addition, a new model for the prediction of thermodiffusion coefficients for linear chain hydrocarbon binary mixtures is proposed using the theory of irreversible thermodynamics and a kinetics approach. The model predicts the net amount of heat transported based on an available volume for each molecule. This model has been found to be the most reliable and represents a significant improvement over the earlier models. Also a new approach to predicting the Soret coefficient in binary mixtures of linear chain and aromatic hydrocarbons using the thermodynamics of irreversible processes is presented. This approach is based on a free volume theory which explains the diffusivity in diffusion-limited systems. The proposed model combined with the Shukla and Firoozabadi model has been applied to predict the Soret coefficient for binary mixtures of toluene and n-hexane, and benzene and n-heptane. Comparisons of theoretical results with experimental data show a good agreement. The proposed model has also been applied to estimate thermodiffusion coefficients of binary mixtures of n-butane & carbon dioxide and n-dodecane & carbon dioxide at different temperature. The results have also been incorporated into CFD software FLUENT for 3-dimensional simulations of thermodiffusion and convection in porous media. The predictions show the thermodiffuison phenomenon is dominant at low permeabilities (0.0001 to 0.01), but as the permeability increases convection plays an important role in establishing a concentration distribution. Finally, the activation energy in Eyring’s viscosity theory is examined for associating mixtures. Several methods are used to estimate the activation energy of pure components and then extended to mixtures of linear hydrocarbon chains. The activation energy model based on alternative forms of Eyring’s viscosity theory is implemented to estimate the thermodiffusion coefficient for hydrocarbon binary mixtures. Comparisons of theoretical results with the available thermodiffusion coefficient data have shown a good performance of the activation energy model.

This thesis explores a rigorous approach to model the behaviour of an electrochemical cell. A simple planar electrochemical cell consisting of stainless steel electrodes separated by a sulfuric acid electrolyte layer is modeled from first principles. The model is a dynamic model and is valid under constant temperature conditions. The dynamic model is based on the Poisson-Nernst-Planck electrodiffusion theory and physical attributes such as the impact of nonlinear polarization, the stoichiometric reactions of the electrolyte and changes to the transport coefficients are investigated in stages. The system of partial differential equations has been solved using a finite element software package. The simulation results are compared with experimental results and discrepancies are discussed. The results suggest that the existing theory is not adequate in explaining the physics in the immediate vicinity of the electrode/electrolyte interface even though the general experimental and simulation results are in qualitative agreement with each other.