The existence of railway lines is a very beneficial to the public in the country (Kampala- Wakiso, Uganda). They were constructed in a way that do connect different cities to the main city (small towns to big towns) of from one country to another. The Kampala- Wakiso railway line connects most of the small towns alongside the railway making transportation easy for the people to move The main objective was to investigate the effects of rail transport on the land use patterns in Kampala and Wakiso basing on the following specific objectives, to find out people`s opinions on land use alongside railway lines, to examine the property value trends along the railway lines, to assess the contribution of railway transport in boosting and encouraging urban economic development and to determine the challenges facing railway transport in urban Uganda. The research used mixed approach were both qualitative and quantitative research approach with a help of a number of methods. The sample size consisted of local residents of which 70 were selected using the simple sampling. Data was collected by questionnaire. The data was analyzed using excel tables and graphs were drawn using excel. Findings revealed that railway transport has an effect on the land use. The areas that are near the railway lines of the Kampala- Namanve railway are of many land uses which include commercial land use, residential land use, agriculture land use and industrial land use like Nakawa Industrial Park and among others. In addition, trading centers and markets have been set up along the railway lines because of the increased number of people, the railway its self being busy as it connects to different towns to the Kampala city as it is the major in Uganda. It was recommended that more attention should be devoted to predicting, planning, monitoring and assessing the effects of railway. It is recommended that peopled leaving along the railway lines should construct their properties far away from the railway lines and the railway reserve should be kept clear.

The Fischer-Tropsch synthesis (FTS) process, better known for its ability to produce synthetic fuel via the hydrogenation of CO, has shown potential to produce valuable chemicals when ammonia is added to the feed. In this work certain aspects of the pathway to the formation of N-containing compounds that form when NH3 is added during FTS, using mostly iron based catalysts is investigated. In addition, the effect this has on the FTS reaction itself is evaluated. To achieve this goal, both theoretical and experimental techniques are used in this study. The CO adsorption and dissociation reactions are assumed to be important elementary reactions for many proposed FTS pathways. In the theoretical part of this thesis, spin-polarized periodic density functional theory (DFT) calculations are employed to study aspects of the initial stage of the pathway on a model Fe(100) surface. Considering the formation of N-containing hydrocarbons, one would assume that NH3 initially adsorbs and dissociates on the catalyst surface, which could take place in the presence of CO. The surface chemistry of these adsorbates is well studied both experimentally and theoretically, but their co-existence has not yet been evaluated on model Fe surfaces. Initially a platform is generated by calculating the individual potential energy surfaces (PES) for the decomposition of CO and NH3 on Fe(100) at a coverage of θ = 0.25 ML. These calculations provided the basis for comparing the adsorption and dissociation profiles of CO and NH3 on the Fe(100) surface via the use of the same computational methodology, and importantly making use of the same exchange correlation functional (RPBE) for both adsorbates. Furthermore, it was desired to evaluate the kinetics and thermodynamics of the NH3 decomposition on the Fe(100) surface at relevant temperatures and pressures (by combining the DFT results with statistical thermodynamics) to better understand the role of NHx surface species involved in the pathway to the formation of the N-containing compounds on a model catalyst surface. The DFT results that are reported for the individual decomposition PES for CO and NH3 were generally found to be in close agreement with what has been reported in previous DFT studies and deduced experimentally for the relevant adsorption and decomposition pathways. The resulting Gibbs free energies for the PES suggests that NH2 may be kinetically trapped on the Fe(100) surface at a coverage of θ = 0.25 ML and the reaction conditions (T = 523 K and p∗ NH3 = 0.2 bar) where NH3 is co-fed with synthesis gas during FTS. The individual adsorptions of CO and NHx (with x = 3, 2, 1, 0) were compared to their coadsorbed states, by calculating the heat of mixing (
Emix) and the activation barriers (Ea) for CO dissociation in the presence and absence of the NHx surface species on the Fe(100) surface. Similar to the individual adsorption of NH3, the 0 K regime inherent to DFT calculations is bridged by calculating the Gibbs free energy of mixing for CO + NH3 on Fe(100) at higher temperatures. Both repulsive and attractive interaction energies were calculated for the various coadsorbed states (CO + NHx on Fe(100)) and similarly some configurations resulted in an energetically favored or unfavored heat of mixing. The activation barrier for CO dissociation was lowered when coadsorbed with NH3 and NH2, and raised when coadsorbed with NH and N. With all the coadsorbed structures the CO dissociation reaction became more endothermic. Previous experimental studies have shown a concomitant reduction in oxygenate selectivity with an increase in the selectivity for N-containing compounds, when NH3 is added during FTS. It is well-known that oxygenates undergo secondary reactions when using iron-based catalysts in FTS. In addition, the catalyst used in aforementioned studies (precipitated Fe/K) are active for the amination reactions of oxygenates. It is therefore hypothesized that some oxygenates produced via the primary FTS pathway are converted to N-containing compounds via a secondary reaction. The experimental part of this thesis is therefore aimed at testing this hypothesis. A base case study included a comparison between a Fe-catalyzed slurry phase FTS reaction and a FTS reaction with all parameters remaining unchanged, except for the addition of 1 vol % NH3 to the syngas (CO + H2) feed. The activity (CO and H2 conversion) data collected did not reveal any appreciable loss in the rate of the FTS reaction when 1 vol % NH3 was added and steady state was reached (, that is after 48 hours time on stream (TOS)). A slower carburization period was however observed when comparing the CO conversion during the first 24 hours TOS, and further supported by the slow increase in CO2 selectivity during the same period. The use of two-dimensional gas chromatography (GC × GC-TOF/FID) allowed for the discovery of a formation of a range of secondary and tertiary amines, not reported in previous studies. The expected loss in oxygenate selectivity was observed and further probed by co-feeding 1-octanol with the feed (CO + 2 H2 + 1 vol % NH3) via a saturator. These results clearly indicated a significant loss in oxygenate formation as a result of secondary conversion to N-containing compounds. Questions regarding the stability of aliphatic nitriles prompted the co-feeding of nonanitrile under similar conditions. The results obtained after co-feeding nonanitrile, suggests that nonanitrile is readily converted to secondary and tertiary amines and that the ratios of aliphatic alcohols and nitriles are close to equilibrium. The use of CO2 as carbon source, the investigation of the product spectrum at higher space velocities and the use of Rh-based catalysts, when NH3 is added during FTS were included in shorter studies. The combination of these results, adds to the knowledge pool for the case where NH3 is present in the FTS regime, as a poison or reactant. Additional information regarding the path to the formation of N-containing compounds was obtained via the detailed analysis of the product spectra with two-dimensional gas chromatography and the subsequent co-feeding reactions. The results obtained via co-feeding reactions, can be used to devise strategies to increase the selectivity of the desired N-containing compounds.

Ore breakage characterisation is a methodology that is used to determine the ore hardness, or resistance to breakage which can be compared across a database of different rock types. It thus develops a relationship between specific energy input and degree of breakage which can be applied to impact breakage in comminution devices. The present study is focussed on investigating the breakage properties of UG2 chromitite, pyroxenite, spotted anorthosite and mottled anorthosite grab samples from run-of-mine (RoM) ore stockpile (particle selection method) and cut drill core particles (cut core method). A mineralogical analysis of UG2 chromitite, pyroxenite, spotted anorthosite and mottled anorthosite was performed using Leica EZ4D optical microscope and QEMSCAN 650F to determine their mineral composition and texture. The presence of cracks in chromitite stockpile and cut drill core samples was also explored using a Nikon XTH 225 ST micro-focus X-ray system. RoM ore stockpile and cut drill core particles of each of these rock types were subjected to impact breakage in the JK Rotary Breakage Tester (RBT). The progeny particle size distributions and degrees of breakage of UG2 rock types obtained via the particle selection and cut core methods were compared. Standard breakage characterization models were fitted to the breakage data of different rock types and the relative hardness parameters compared. It was found that UG2 chromitite comprised mainly fine, isolated, round chromite grains in a plagioclase matrix. Pyroxenite samples were found to be made up of granular orthopyroxene, interstitial plagioclase and clinopyroxene. The mineralogical analysis also revealed that spotted anorthosite primarily contains plagioclase with orthopyroxene crystals forming isolated “spots” creating a poikilitic texture. Mottled anorthosite is made up of mainly plagioclase. Results from breakage tests showed that the progeny particle size distributions and the degrees of breakage for particles sourced from the RoM ore stockpile breaks into a finer product compared to cut drill core samples. This was attributed to the presence of cracks in the RoM ore particles as revealed by the tomographic scans. No visible cracks were found in the cut core particle. The ore hardness parameters were determined from fitting the breakage data to standard impact breakage characterisation models (t10 breakage and size dependent breakage model). Samples obtained via the particle selection method were consistently found to offer less resistance to impact breakage as shown by the higher Axb values compared to the cut drill core samples. Using the ore hardness classes presented by Napier-Munn et al (1999), UG2 chromitite, spotted anorthosite, mottled anorthosite and pyroxenite were thus classified as very soft, soft to very soft, soft to very soft and medium to soft respectively. The hardness indicator, 3600.M.fmat.x, for each size class determined using the parameters obtained from the size dependent breakage model decrease with an increase in the parent particle size. This shows that particles become more resistant to impact breakage as the initial particle size increases. However, for pyroxenite, spotted and mottled anorthosite, the indicator decreases between the particle sizes 14 to 28.6 mm but then increases for 41.1 mm.

The froth flotation process has found substantial usage in the mineral processing industry for over a century and as long as minerals continue to exist in the earth’s crust, the demand for upgrading and recovery of these natural yet valuable resources will continue to exist. It relies on the principle that a bubble-particle collision process should be accompanied by the formation of an attachment between the pair. Of particular importance to the flotation process is the stability of froths. This will affect the mass pull, which, in turn, will affect recovery and the grade that is attainable. Froth stability is affected by many factors, viz. machine properties, hydrodynamics within the flotation cell, reagent suites, as well as mineral particle properties. Of particular interest to reagent suites is the frother dosage and its influence on the prevention of coalescence which has been fairly well studied. Regarding froth stability, the frother influences the amount of water that reports to the concentrate as well as the bubble surface viscosity, limiting drainage and subsequent bubble coalescence. Most of the other factors influence the amount of particles that report to the froth, but it is the particle properties that have the overriding influence on the froth stability. It is in the interest of flotation modelling and optimisation to be able to find relationships for the impact of particle properties on froth stability. This project has focussed on the influence of two main particle properties, i.e. size and hydrophobicity, and their interactive effects on froth stability. In order to establish relationships between particle properties and froth stability, two devices were built in the laboratory, i.e. a non-overflowing stability column to measure froth stability and a bench-scale continuous flotation cell to provide metallurgical information, besides being able to measure froth stability using water recovery and froth surface bubble burst rate. In the first part of the investigation, particles of discrete sizes as well as mixtures of particles sizes were utilised at a constant hydrophobicity. Results obtained show a power law relationship between froth stability and particle size, with all particle combinations falling on the same relationship. Froth stability decreased with increasing particle size. A large increase in froth stability occurred for feed particles of average size below 50 μm. This was attributed to particles in the finer range reporting to the froth by both true flotation and entrainment. These fine particles would result in a higher interfilm viscosity resulting in reduced drainage. A useful linear relationship between froth stability and the reciprocal of feed particle size was obtained. The reciprocal of feed particle size was used to represent the specific surface area of the particles. It was found that as the specific surface area of the particles increased, their froth stabilising effect also increased in a linear fashion. In the second part of the investigation, the influence of particle hydrophobicity and the interactive effects of particle size and hydrophobicity on froth stability were explored. In common with other studies, it was found that froth stability increased with increasing particle hydrophobicity up to an optimum value between 66° and 69° and thereafter it decreased. The smallest size particles (28 μm) produced the highest variation in froth stability with increasing hydrophobicity. The response of the coarse particles to froth stability with increasing hydrophobicity was less pronounced. Particle size was found to have a greater influence on froth stability than particle hydrophobicity. Variations in froth stability were about 1.5 times greater for changes in particle size than changes in hydrophobicity over the relatively large ranges of size and hydrophobicity tested. The relationship between froth stability and feed particle specific surface area was investigated at different hydrophobicities and found to be linear for most practical particle sizes. However, a deviation from linearity occurred at very small particles sizes (28 μm) for particles of optimum hydrophobicities. The slopes of the froth stability versus feed specific surface area relationships in the linear region were found to increase with increasing hydrophobicity, up until an optimum contact angle of between 64° and 68°, whereafter they decreased. Thus, this family of curves would allow the prediction of froth stability of varying hydrophobicities on a size-by-size basis. This relationship was shown to hold for two real ores: a platinum-bearing UG2 ore and an Itabirite iron ore. Thus, a simple linear calibration of grind versus froth stability would allow a prediction of froth stability for a particular ore. A Langmuir-type model was developed to relate the froth stability to the concentrate particle surface area. It was found to be a good fit to the experimental data. This shows that it is possible to model froth stability in terms of the particle packing at the air-water interface in much the same way that surfactant molecular packing at the interface is modelled. The increasing particle surface area affects the surface tension of the films and reduces film drainage. In studying the interactive effects of particle size and hydrophobicity, it was found that all data points of all hydrophobicities fell on the same relationship when froth stability was plotted as a function of concentrate surface area. It was therefore, concluded that particle size and hydrophobicity define the amount of particles that will report to the froth phase, but once in the froth, it is the surface area of the particles that will define the froth stability.

Background Cities in developing countries are upgrading their public transport at unprecedented rates in efforts to create transportation systems that are more sustainable and equitable. South Africa and India are seeing massive investments in features that are improving operational characteristics of public transport systems. However, more effort will need to be expended in improving public transport access/egress conditions, in order to ensure that public transport is a competitive alternative to door to door motorised transport trips. Particular attention will need to be paid to non-motorised transport, as it is the most common means of access/egress for people in the Global South, despite conditions for pedestrians being uncomfortable and a threat to their safety and security. Traditional methods of evaluating the accessibility of public transport stations have been found to be overly mechanistic. Through improved operationalisation of built environment factors and crowd sourcing user perceptions, a better understanding of how supportive the built environment is for walking can be achieved. Study details This study presents the following: 1. The development and testing of an Android mobile phone application, along with its associated online dashboard. The mobile phone application allows for the collection of data on the pedestrian experience and is a shift away from the mechanistic approach to understanding pedestrian challenges. Using the application, users rate their walking environment along dimensions of safety, security, infrastructure and comfort, while geo-tagging walking routes. The dashboard is used to store and visualise the users’ perception data and multimedia captured using the mobile phones. 2. A proposed spatial analysis method, using Spatial Clustering Algorithms for analysing data captured using the mobile phone application. As crowd sourced datasets are very large, filtering approaches may not be capable of distinguishing between outliers and clusters of high/low ratings. Thus, more robust analysis methods are required in order to extract meaningful insights. 3. The piloting of the application and proposed spatial analysis method in Cape Town and New Delhi Results of pilot studies Six public transport locations across Cape Town and New Delhi were chosen for the pilot studies. Survey facilitators, with the application preloaded on mobile phones, intercepted public transport users travelling along their egress trips. Respondents were asked to make use of the application to report on their perception of the walking environment as they were escorted to their destination. Data from 538 egress trips were mapped and analysed. The application was able to capture nuances associated with the pedestrian experience, which may not be possible using traditional approaches. The challenges identified by respondents ranged from pedestrian infrastructure not being accessible due to road traffic violations by motorised transport, to pedestrians having to deal with filthy walking environments that made walking uncomfortable. Future work would need to consider the incorporation of video into the mobile application. Video would allow for the capturing of dynamic challenges faced by pedestrians, such as aggressive behaviour by motorists, which cannot be captured using pictures and voice notes. An addition consideration for future work would be to make the application available to the general public so that data can be truly crowd sourced. This would require investment in marketing the application and the study. Alternatively, future studies may look to make use of systematic random sampling of egress trips and larger sample sizes, in order for results to be representative.

On an industrial scale the need for improved flotation performance is of high importance in the current economic climate. Studies have shown that the pulp phase chemistry has a strong effect on the froth phase and therefore it is necessary to investigate how the manipulation of pulp chemistry factors can improve flotation performance. Research into the manipulation of this chemistry is well underway and factors including the pulp potential (Eh), pH, dissolved oxygen (DO) and ionic strength (IS) govern the pulp chemistry. This study aims to investigate how the manipulation of these factors affects the froth stability, bubble size and entrainment of the froth phase through Platinum Group Metal (PGM) flotation. In this study the Eh, pH, DO and IS were successfully manipulated to investigate their effects on froth stability and water recovery in 2-phase, as well as their effect on water and solids recovery, entrainment and the grades and recoveries of valuable minerals (copper, nickel, platinum and palladium) in 3-phase in the absence and presence of depressant at high dosages; 500 g/t Carboxymethyl Cellulose (CMC). Stability column tests were used to determine froth stability as a function of the dynamic stability factor (Barbian et al., 2005) and batch flotation tests were used to obtain the total water and solids recovered, the grades and recoveries of the valuable minerals as well as to determine entrainment. Further tests were performed to investigate the effect of changing the pH on the Eh in a 3-phase system in which all the other pulp factors were kept constant. The effect of changing the pulp factors on the froth bubble size was investigated by capturing side view images of the froth obtained in a batch flotation cell as each pulp factor was changed. This study has shown that careful control of the pulp chemistry, namely increasing IS, increasing pH, decreasing DO and decreasing Eh, resulted in improved froth stability. The Eh was found to be inversely proportional to the pH. This study has further shown that increased water recoveries and reduced bubble size in the froth were observed at 5 IS as compared to 1 IS due to the froth stabilising nature of the pulp at 5 IS. Operating at high Eh (500-730 mV) was observed to be detrimental to valuable mineral grades and recoveries and promotes entrainment. This kind of knowledge contribution may be key in improving flotation performance and increasing the grades and recoveries of valuable minerals obtained in South Africa’s PGM mining industry.

Screening in mineral processing is the practice of separating granulated ore materials into multiple particle size fractions, and is employed in most mineral processing plants. Models of screening performance have been developed previously with the aim of improving process efficiency. Different methods have been used, such as physical modelling, empirical modelling, and mathematical modelling including the discrete element method (DEM). These methods have major limitations in practice, and experimental data to validate the models have been difficult to obtain. Currently, the design and scale-up of screens still relies on rules of thumb and empirical factor methods rather than a fundamentally based understanding of the behaviour of the granular system. To go beyond the current state-of-the-art in screen modelling requires a clear understanding of the particle motion along a dynamic (vibrating) inclined plane. Central to this understanding is the notion that granular systems exhibit a unique rheology that is not observed in fluids; i.e. neither Newtonian nor non-Newtonian. It is thus imperative to fully quantify the granular rheology, which is determined by the depth of the particle bed along the screen, the solids concentration, and the average velocity of the granular avalanche on the screen. The concept of granular rheology is important. Existing empirical models of vibrating screens tend to be extremely dependent on boundary conditions of a particular machine design. The concept of granular rheology is important because, akin to fluid flow, granular flow exhibits different flow regimes depending on the extent of energy input in the system. This work employed DEM to quantify the granular rheology of particles moving along a vibrating inclined screen in order to begin the development of a phenomenological model of screening. The model extends the visco-plastic rheology formation of Pouliquen et al. (2006) to capture the kinetic and turbulent stresses obtained in granular flow on an inclined vibrating screen. In general, DEM was employed to develop a mechanistic model of screening which includes a description of the rheology of granular flow on a vibrating screen. Microscopic properties of granular flow were used in DEM to simulate screening of particulate materials. Granular mixtures of two particle constituents (3 mm and 5 mm) were simulated on an inclined vibrating screen of 3.5 mm apertures. For the base case, frequency and amplitude are 4 Hz and 1 mm, respectively. While microscopic properties were employed for the simulation, the properties extracted from the simulations are macroscopic fields which are consistent with the continuum equations of mass, momentum and energy balance. From the continuum equations, a micro-macro transition method called the coarse-graining approach was employed to obtain the volume fraction and the tangential velocity as a function of the depth of flow along the inclined surface. This approach is suitable for this work because the produced fields satisfy the equations of continuum mechanics; even near the base of the flow. The continuum analysis of the flowing layer reveals a coexistence of flow regimes- (i) quasi-static, (ii) dense (liquid-like), and (iii) inertial. The regimes are consistent with the measured solids concentrations spanning these regimes on inclined vibrating screens. The quasi-static regime is dominated by frictional stress and corresponds to low inertial number (I). Beyond the quasi-static regime, the frictional stress chains break and the collisional-kinetic and turbulent stress begin to dominate. The variation of the effective frictional coefficient with the inertial number (I) characterises the flow. Finally, an effective frictional coefficient model that is based on frictional, collisionalkinetic and turbulent stress was developed. Data analyses for this model were done at a steady flow in the base case where a coexistence of three flow regimes were observed. It was observed that each regime of flow is dominated by corresponding shear stresses. While the quasi-static regime is dominated by frictional stress, the kinetic and the inertial regimes are dominated by kinetic and turbulent shear stresses, respectively. This model was tested by varying the intensity of vibration in the base case and it was observed that at higher frequencies and amplitudes, the quasi-static regime gradually disappeared. Furthermore, the inertial number at which transition occurs to different regimes varies in response to the intensity of vibration. This is an important step in developing a phenomenological model of screening. The model presents a fundamental understanding of the mechanisms governing transport of granular matter on an inclined vibrating screen.

The preferential oxidation of CO (CO-PROX) has been identified as one route of further reducing the trace amounts of CO (approx. 0.5 – 1 vol%) in the H2-rich reformate gas after the high- and low-temperature water-gas shift reactions. CO-PROX makes use of air to preferentially oxidise CO to CO2, reducing the CO content to below 10 ppm while minimising the loss of H2 to H2O. In this study, a Co3O4/γ-Al2O3 model catalyst was investigated as a cheaper alternative to the widely used noble metal-based ones. The CO oxidation reaction in the absence of hydrogen has been reported to be crystallite size-dependent when using Co3O4 as the catalyst. However, studies looking at the effect of crystallite size during the CO-PROX reaction are very few. Metal-support interactions also play a significant role on the catalyst’s performance. Strong metal-support interactions (SMSI) in Co3O4/Al2O3 catalysts give rise to irreducible cobalt aluminate-like species. Under CO oxidation and CO-PROX reaction conditions, such strong interactions in a similar catalyst can have a negative effect on the performance of Co3O4 but can keep its chemical phase intact i.e., help prevent the reduction of the Co3O4 phase. The catalysts used to investigate these two effects (i.e., crystallite size and metal-support interactions) were synthesised using the reverse micelle technique from which nanoparticles with a narrow size distribution were obtained. Certain properties of the microemulsions prepared were altered to obtain five catalysts with varying Co3O4 crystallite sizes averaging between 3.0 and 15.0 nm. Four other catalysts with different metal-support interactions were also synthesised by altering the method for contacting the support with the cobalt precursor. The crystallite size of Co3O4 in these four catalysts was kept in the 3.0 – 5.0 nm size range. Catalytic tests for the first series of catalysts showed that the mass-specific CO oxidation activity increased with a decrease in the starting crystallite size of Co3O4. However, the surface area-specific CO2 formation rate increased with an increase in the crystallite size up to 8.5 nm. Above 8.5 nm, the crystallites possess relatively few surface active sites due to their low massspecific surface areas. In situ characterisation in the UCT-developed magnetometer and PXRD capillary cell instruments at temperatures between 50 and 350 °C revealed that at elevated temperatures the catalysts were partially reduced to metallic Co with CoO being the other cobalt phase present. The formation of metallic cobalt resulted in the formation of methane and in the decrease of the CO2 selectivity. Larger crystallites were reduced to a greater extent compared to smaller crystallites possibly due to the existence of weaker metal-support interactions in the catalysts with the large crystallites. Upon decreasing the reaction temperature to below 350 °C, both in situ techniques also revealed that all the catalysts were partially re-oxidised to CoO with no Co3O4 observed. The complete re-oxidation of the surface metallic Co species terminated the formation of methane and restored the exclusive conversion of CO to CO2. It is possible that at the end of each experiment the catalysts possess crystallites with a double-shell structure i.e., crystallites with a CoO core, a metallic Co inner-shell and a CoO outer-shell. For the second series of catalysts, those that had SMSI were much harder to reduce to metallic Co as expected, with the methane yields observed barely reaching 20% at 350 °C (as opposed to reaching 100% as observed with the first series of catalysts). When decreasing the reaction temperature to below 350 °C, the CO oxidation activity over these catalysts was restored but was unexpectedly higher than the activity initially observed along the heating profile. The reason for this enhanced activity may be that the nanoparticles had segregated from the support along the heating profile as they were being partially reduced. The segregation weakened the metal-support interactions availing more active surface area. The catalysts with weaker metalsupport interactions displayed higher mass-specific CO oxidation activities but were much easier to reduce to metallic Co and as a result, formed much more methane along the heating profile (i.e., 50 - 350 °C). These catalysts were later partially re-oxidised at decreased reaction temperatures (i.e., below 350 °C) and were also thought to have crystallites with a double-shell structure at the end of the tests.

A study was undertaken on the decay of acid ion exchange resin from both a qualitative and quantitative perspective. The qualitative study concentrated on observing the impact on resin strength of varying electrolyte concentrations and varying di-vinyl benzene contents, during the loading phase. The phenomenon of osmotic shock in addition to resin cracking and swelling is clearly observed. A further qualitative study bore out the change in resin rigidity as the resin is artificially degraded through repeated loadings and regenerations performed by using a specially constructed device that cyclically loads and regenerates resin up to 1000 times in a three week period. Loss of resin rigidity was observed under these circumstances and was measured by means of observing changes in degree of swelling/contraction and changes in translucence. Quantitative study of the resin was limited to its characterisation through measurement of the equilibrium through the Mass-Action Law, capacity and resin kinetics. A study, of existing kinetic rigorous modelling methods and in particular the extensively published challenge of the multiple mechanism adsorption process, was undertaken. A rigorous model, that divorces the external and internal mass-transport parameters from the traditionally utilised lumped parameter, is proposed. All kinetic measurements were performed in a 1 litre closed circuit (finite system) consisting of a variable-pump, a five mL zero length column (ZLC) and a reservoir, allowing for the insertion of probes and sample extraction. An original method of model simulation for the purposes of fitting to kinetic data was developed and consists of determining the resin surface concentration from flux data assuming the applicability of Newton’s Law of Cooling to the ionic flux through the external laminar layer. Simulation of flux inside the resin was achieved by assuming an internal homogeneous environment and the applicability of the Nernst-Plank equation that combines transport effects of both Fick’s Law of Diffusion and inter-ion electrical forces to the flux of both the adsorbing and desorbing ions simultaneously, during the transient adsorption process. The parameters of the rigorous model are the intra-particle diffusion of both the adsorbing and desorbing ions (Di, DD) in addition to the mass transfer coefficient (KL) in the laminar layer at the surface at the resin/liquid interface. A full simulator was produced using Turbo Pascal software which was fitted to raw kinetic data using the Hook-Jeeves search algorithm.

Mineral carbonation is a carbon sequestration technology that entails the reaction of CO2 with oxides or silicates of magnesium, calcium or iron to produce stable carbonate compounds. Magnesium-rich tailings from the platinum industry in South Africa have been identified as a potentially viable and attractive feedstock for CO2 sequestration through mineral carbonation. Many of the strategies proposed to enhance the dissolution kinetics of silicate minerals, such as the use of elevated temperatures and pressures and chemical additives, as well as pretreatment through mechanical and thermal activation, are energy intensive and will thus reduce the net CO2 sequestration capacity of the overall mineral carbonation process. As a result, there is growing recognition of the need to evaluate the processes using life-cycle based approaches and tools to ensure they result in net CO2 reduction. However, to date, research and development has focused primarily on the optimisation of extraction and/or carbonation efficiencies, with specific emphasis on the relatively reactive silicate minerals, such as olivine and serpentine. This project seeks to investigate the viability of using pyroxene-rich PGM tailings for the sequestration of CO2, with specific emphasis on net carbon neutrality. Promising mineral carbonation processes have been identified on the basis of an extensive literature review, and include the: ammonium salts pH swing, Lackner’s HCl multi-stage, gas-solid Åbo Akademi University process, direct aqueous process, and mineral acid pH swing. Material and energy balances were then conducted for these processes on the basis of the sequestration of 1 ton of carbon dioxide, using Aspen Plus v8 simulation software package. The material and energy data were then used to determine the total carbon footprint contributions, through the use of SimaPro v 7.7.3. life cycle assessment software. The selected carbonation processes were found to release more carbon dioxide than the process sequesters. The carbonation process resulting in the most emissions released was found to be Lackner’s multi-stage process (18 295 kg-CO2e), followed by the ammonium salts process (8 798 kg-CO2e), per ton carbon dioxide sequestered. The carbonation process resulting in the least emissions released was the solid Åbo Akademi University process (1 354 kg-CO2e), followed by the gas-solid direct aqueous process (2 364 kg-CO2e), as well as the mineral acid pH swing process (3 126 kg-CO2e). The most carbon emissions intensive contributions to the carbon footprint were found to be heat requirements and chemical reagent make-up, which generally accounted for more than 85% of total emissions when combined. Aqueous processes generally incurred a much higher carbon footprint, despite using relatively lower temperatures than the gas-solid ÅAU process. This was attributed to the higher quantities of water used in the aqueous processes that, in some cases, were subject to phase change via, for example, evaporation. Additionally, the production of make-up chemical reagent, alone, was found to result in emissions that exceeded the carbon dioxide sequestered for four of the five selected processes (ammonium salts process, Lackner’s HCl multi-stage, direct aqueous, mineral acid pH swing). The potential to reduce emissions associated with heat generation could be achieved through the exploration of heat integration and cleaner alternative sources of heat, for the potentially feasible processes. On the other hand, the carbon dioxide emissions associated with make-up reagent could be reduced through the use of cleaner input materials as well as by increasing the recycle ratios to reduce external reagent requirement.