The issue of deflagration to detonation transition (DDT) is one of the key factors influencing safety standards, risk assessment and risk managements in the petrochemical industries. It is also one of the most outstanding problems in combustion theory. Despite the efforts from a number of scientists around the world, numerical predictions of DDT is still an un-resolved problem due to the high level of complexities involved. Although there have been relatively more experimental efforts, a comprehensive database to assist model validation and development is still lacking. The present thesis includes numerical analysis of a wide range of combustion regimes to establish the critical conditions under which transition from deflagration to detonation occurs. In order to facilitate the study, new correlations for hydrogen burning velocity are derived from curve-fitting to experimental data from literature and implemented in the code for simulation of initial stages of flame acceleration and deflagration propagation. DetoFOAM, a code for solving transient and fully compressible Euler equations, has been developed within the framework of the OpenFOAM toolbox for numerical simulations of gaseous detonation. The detonation solver uses the total variation diminishing (TVD) numerical schemes which are suitable for shock capturing. A one step reaction mechanism has been developed following first principle and tuned for both small and large scale simulations. Since the numerical solver for DDT simulations must be capable of handling both deflagration and detonation as well as the transition, a new solver, DDTFOAM, which is based on solving fully compressible and transient Navier-Stokes equations has also been developed. DDTFOAM also uses the TVD numerical schemes for shock capturing and uses the Implicit Large Eddy Simulation (ILES) approach as a compromise for accuracy and computational efficiency [131]. Implementing an adequate chemical reaction mechanism in the DDTFOAM has been challenging to ensure that the right amount of chemical energy release is supplied in the right place and at the right time. Incorrect models for chemical energy release can significantly modify the flow behaviour. The available reactions in the literature are very limited and valid for limited range of conditions, e.g. for laminar flames only. A single step Arrhenius type reaction has been designed, tuned and implemented in DDTFOAM. The reaction mechanism has been carefully designed to reproduce flame properties e.g. laminar flame speed and thickness as well as detonation properties such as detonation thickness, propagation velocity, etc. The main difference between DetoFOAM and DDTFOAM that the former is designed for supersonic combustions (detonations) only; therefore it neglects the diffusive effects and solves reactive Euler Equations, whereas in DDTFOAM full Navier Stokes Equations are solved. The detonation solver is mainly designed for large scale detonation simulations therefore the derived reaction mechanism for this solver is obtained trough slightly different procedure compared to the DDT solver. Obtaining the reaction mechanism for DDTFOAM is more challenging as it has to reproduce properties of deflagrations as well as detonations correctly. The computational power which is required to carry out the simulations is extremely high. Different techniques have been employed to reduce the computational cost without compromising accuracy. These include using the ILES approach in cooperation with adaptive mesh refinement and multiple meshes. Numerical predictions have been conducted for different combustion regimes including laminar flames, turbulent flames and detonations as well as the actually DDT processes. The predictions of deflagrations waves are found to be In reasonably good agreement with some published experiment data. In case of detonations, detailed studies have been conducted on the detonation front structure, cellular structures as well as large industrial scenarios. This work involved contributions to Buncefield explosion investigations [109-110]. Finally, numerical simulations of some standard DDT tests have been carried out. The predictions have again achieved reasonable agreement with published experimental data and previous simulations. Successful simulations of large scale detonation in the present work represent the capability of the present study to address the increasing demands from the industries to study real scale accidental scenarios. Furthermore the obtained results for DDT simulations compare well with the medium scale experimental works and provide a step forward towards large scale and unconfined DDT studies.

This thesis aims to describe the ultra-rapid synthesis of a number of important transition metal carbides as well as investigating their reaction mechanisms. 4 binary systems are discussed; Nb-C, Mo-C, Ta-C and W-C, and work carried out on the ternary system, Nb-Ta-C, is also evaluated. Carbide production was investigated from both the oxide and elemental precursors. Ultra-rapid synthesis has been achieved through the development of a reproducible experimental technique and the investigation into a plethora of reaction variables as well as microwave applicators and powers. This resulted in, specifically within the single mode cavity, the completion of the majority of reactions within 20 s. Further development was then built upon the direct relationship observed between phase fraction results (obtained from Powder X-ray Diffraction (PXD) data), in-situ temperature and ex-situ dielectric property measurements; allowing reaction profiles of the various carbides to be mapped, as well as a crucial understanding of the effects of microwave energy on materials at various temperatures. Powder Neutron Diffraction (PND) was also used to evaluate product purity and the C occupancy of the final products, revealing non-stoichiometry which relates directly to the Tc onset observed for the superconducting transition metal carbides. This, in turn, allowed the trends observed for the ternary carbides to be explained, a linear trend does not exist between Tc and C occupancy. In an effort to develop on the understanding of solid state microwave heating, in-situ reaction monitoring techniques were investigated. Through the use of thermal imaging and high speed photography, the W-C system was observed during the crucial initial stages of the reaction process. The information obtained both corroborated previously collected data and allowed a possible reaction mechanism to be alluded to. The observation of localised heating, prior to the beginning of carbide formation, suggests possible high temperatures far exceeding those observed by optical pyrometry. This could well explain the rapid reaction times as well as suggest an interaction mechanism between carbon, an efficient microwave absorber, and tungsten, a low dielectric loss metal.

Froth flotation is a widely used, cost effective particle separation process. However, its high performance is limited to a narrow particle size range, e.g., between 50 µm and 600 µm for coal and between 10 µm and 100 µm for minerals. Outside this range, the efficiency of froth flotation decreases significantly, especially for difficult-to-float particles of weak hydrophobicity (e.g., oxidized coal). Nanobubbles integrated into a specially designed column flotation expanded the particle size range for efficient froth flotation as a result of increased probabilities of particle- bubble collision and attachment and reduced probability of detachment. The major advantages of nanobubble enhanced flotation include lower collector and frother dosages since nanobubbles that are mostly smaller than 1 µm can be formed selectively on hydrophobic coal particles from dissolved air in coal slurry. Nanobubbles act as a secondary collector on particle surfaces, thereby resulting in considerably lower operating costs. A systematic parametric investigation of the proposed technology was performed to understand the effects of process variables on separation performance with a typical coal sample using a specially designed flotation column and three 10-liters conventional flotation cells. Results indicate that the combustible recovery of a -150 µm coal increased by 5-50% in the presence of nanobubbles, depending on process operating conditions. Nanobubbles also significantly improved process separation efficiency and increased the flotation rate constant by more than 40%. Theoretical evaluation of the innovative flotation technology was employed using specially designed apparatus to study the nanobubbles stability and the roles of nanobubbles on particle-bubble interactions, froth stability, and surface area flux. In addition, a detailed technical performance and economic evaluation was performed.

This dissertation presents the findings of a project where, following investigation and assessment, a million tonnes of sand and gravel at a contaminated former US Air Force Base was excavated for use as aggregate. The process required on-site screening for petroleum hydrocarbons of over 7,000 soil samples and provided an opportunity to assess the efficiency of the investigation, assess the application of geophysics of hydrocarbon contaminated sites, and look at the role of aggregate extraction in the contaminated land industry.

This thesis presents research into the binding, extraction and transport of the hexachloroplatinate anion, [PtCl6]2-, by organic receptors in a solvent extraction process. The target anion is produced during the processing of platinum-containing ores and the aim was to develop reagents that can selectively extract [PtCl6]2- to optimise the recovery of platinum. Chapter One outlines reasons for the interest in [PtCI6]2-and provides an overview of the processes and techniques used to refine precious metals. An introduction to anion coordination chemistry relevant to the research project is also presented. Chapter Two discusses the design features incorporated into organic receptors to enable strong and selective binding of [PtCl6]2-. These features include a tertiary amine protonation site, hydrogen-bond donor groups and organic solubilising moieties. The synthesis of a series of functionalised tripodal tris(2-aminoethyl)amine based receptors with sulfonamide, amide, urea, thiourea or pyrrole NH hydrogenbond donor groups are reported. Complexation reactions between the receptors and H2PtCl6 to form [(LH)2PtCl6] ion pairs are discussed. Crystallographic analysis of the [(LH)2PtCl6]complexes with TREN-based sulfonamide, urea and amide receptors confirms the presence of hydrogen-bonds between the NH donor groups and the outer-sphere of [PtCl6]2-. The low organic solubility of the complexes prevented the study of these systems in solvent extractions. Chapter Three describes the variation of terminal substituents of the tripodal receptors with the aim of improving the organic solubility of the extractants and their [PtCl6]2-complexes. In these "second generation" receptors the terminal substituents assessed include 3, 5-dimethylphenyl, 4-iso-propylphenyl, 4-tert-butylphenyl, 3, 5- dimethoxyphenyl, 3, 4 dimethoxypheynl and 3, 4, 5-trimethoxyphenyl. Through reaction of the receptors with H2PtCl6 the solubility of the resultant complexes are assessed. Chapter Four describes the development of an optimised solvent extraction method to study the extractive behaviour receptors. A pH swing mechanism is utilised to control the uptake and release of [PtCl6]2-. The extraction results for trioctylamine and the soluble tripodal urea and amide receptors are compared. Attempts are also made to confirm the stoichiometry of the complex in solution. Chapter Five describes the synthesis of tris(2-aminoethyl)amine based receptors with hydrogen- and halogen-bond donor groups with the aim of increasing the strength of the interaction between a receptor and [PtCI6]2-. Receptors with an extended tripodal scaffold based on a tris(3-aminopropyl)amine with urea and amide moieties are also presented. The results of the complexation reactions and solvent extraction studies with these modified extractants are presented. Chapter Six presents the design and synthesis of bipodal and monopodal receptors in order to assess the role of the number of hydrogen-bond donor functionalised arms. The results of the solvent extraction studies with these receptors are discussed and comparisons made between tripodal, bipodal and monopodal extractants. The crystallographic analysis of the [(LH)2PtCl6] complexes formed between the bipodal urea and amide receptors is described. Chapter Seven highlights the important findings from this work. Conclusions are drawn as to the optimum receptor system developed and this is compared to the extractant system thought to be in current use for the extraction and transport of [PtCl6]2-.

No description available.

No description available.

A Dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the Degree of the Master of Science / Drilled specimens from four types of rocks, namely Quartzite, Norite, Sandstone and Coal encountered in the South African mining environment were tested to determine their fracture toughness coefficients, using International Society for Rock Mechanics (I...) standards. The tests were conducted using a MTS servo-controlled testing machine in displacement control mode. (Abbreviation abstract) / Andrew Chakane 2018

A research report submitted to the Faculty of Engineering and the Build Environment, University of the Witwatersrand, in partial fulfillment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2014 / The South African power crisis and corresponding rising costs experienced since 2008, created a paradigm shift in terms of electricity use. The mining sector is the second highest consumer of electricity with metalliferous mines being accountable for 80% of the total power. Recent studies revealed that underground ventilation and cooling accounts for 30% to 40% of total electricity costs in an underground metalliferous mine. Hence the need to look at ways to reduce electricity consumption in ventilation and cooling. Work has been done on optimising efficiencies of ventilation and refrigeration systems of underground mines. Currently, the high energy consumption is driven by efforts to achieve a thermally acceptable environment for workers (manned) in deep metalliferous mines which is currently between 27ºC (wb) and 29ºC (wb). However, no detailed study has been done looking at increasing thermally acceptable environments for deep level metalliferous mine. In this study the impact of increasing rejection temperature to 40ºC (db) was assessed in the automated (unmanned) scenario at a maximum depth of 2811 metres. Then the power demand was compared with the manned scenario. The results proved that automation in an underground mine has the potential of reducing electricity cost of ventilation and cooling by more than 50%. For example, the production rate of about 200 kilo-tons per month yield an annual cost saving of R71 million on electricity. These cost savings can be used to justify automation systems. Automation removes workers from the hazardous environment and replaces them with equipment which can withstand harsher conditions. The introduction of an automation system in underground mines would not come risk-free. Currently, automation systems have not yet reached a level of removing workers completely from underground.There are instances that would require workers to enter production zones. A Bow-Tie risk analysis was used to show the hazards that workers would be exposed to and prevention controls and responses to mitigate the impact the risks. / MT2017

The participation of indigenous communities and use of indigenous knowledge systems (IKS) in environmental governance is provided for in several international and national environmental legislation and policies. In South Africa, the National Environmental Management Act 107 of 1998 (NEMA) in Chapter 1, Principle 4g requires that decisions must take into account the interests, needs and values of all interested and affected parties, and this includes recognising all forms of knowledge, including traditional and ordinary knowledge. This study investigated the Environmental Impact Assessment process (EIA) in mining developments in three rural communities in Limpopo Province, South Africa with regards to the effectiveness of public participation in fostering the incorporation of IKS. The qualitative research design used in this study employed several research methods through the utilisation of 3 villages as a case study. Semi-structured interviews, a focus group discussion and document analysis were used to collect information regarding the public participation process and the integration of IKS into EIAs. This report illustrates that IKS exists in rural communities and some of it is relevant to be incorporated in EIAs. This research study has shown that while expert knowledge dominates the EIA process, there is no indication that this is done deliberately to exclude IKS. This study has also revealed that the public participation process has a number of weaknesses such as in the selection and composition of community stakeholders and communication procedures. Suspicions also developed amongst the villagers of community representatives being bribed by the mine, and infighting started within community committees resulting in some community members losing trust in the committees. The disagreements with regards to the integrity of community committees created divisions and this negatively impacted on the public participation process. However, despite these weaknesses, if capacity building for both EIA experts and rural communities is done, the public participation process has potential as a tool to aid the integration of IKS into EIAs.