In the increasingly competitive coal market, it is becoming more important for coal operators to develop mathematical models for surface mining which can estimate mining costs before the actual mining begins. The problem becomes even more acute with the new reclamation laws, as they affect surface coal mining methods, productivity, and costs. This study presents a computer simulator for a mountaintop removal type of surface mining operation. It will permit users to compare the costs associated with different overburden handling and reclamation plans. It may be used to minimize productivity losses, and, perhaps, to increase productivity and consequently to reduce operating costs through design and implementation of modified mountain top removal methods. / M.S.

M.Phil. (Mineral Economics) / The energy crises in the seventies and eighties had led to an awareness in the world's business community about the profit potential in the energy mineral supply market. All the sectors in this industry came under scrutiny, also the coal export sector. This awareness and rising interest in the world's coal export market caused amongst others, two major developments : a) a significant rise in investments in coal exporting ventures b) a higher expectation by shareholders with respect to capital returns and future growth Most companies participated in this expansion campaign, and committed resources to achieving the higher objectives. The downturn in'the world's economy , and the resultant diminished demand for energy minerals, caused the coal export market to come under pressure. The long lead time existing in the establishment of mining projects, and the fact that mines under construction cannot be mothballed until times improve, also contributed to the over-capacity situation that eventuated in the coal export industry worldwide. Many companies faced a battle for survival, and participants in the industry had to re-appraise their long term strategies. Established coal producing companies had to determine which strategies would best answer their requirements : a) whether it be to divest from coal production b) whether they should diversify their operational base and many others...

M.Sc. / The decommissioning of mines and mining-related activities brings about the onset of rehabilitation. A legacy that most coal mines must address is the rehabilitation of the coal discard dumps that are generated by the beneficiation process of the raw coal. Rehabilitation involves the shaping and covering with a topsoil layer of these coal discard dumps. The topsoil layer is then revegetated to provide a stable form of protection against erosion. Considerations taken into account regarding the rehabilitation of coal discard dumps include the final slope angle, physical constraints i.e. railways or rivers, a source of topsoil and the grass species to be sown. Once the dump has been shaped, capped and seeded, regular applications of fertilizer take place for a defined period of time. This is to accelerate the growth of the grasses, as well as to stabilise the nutrient levels in the topsoil capping. Ingwe Mine Closure Operations (MCO), part of Ingwe Collieries Limited, is the business unit entrusted with the management and successful rehabilitation of Ingwe’s defunct operations. All of the coal discard dumps sampled in this study are found on such defunct operations. These coal discard dumps have been rehabilitated to a very high standard by MCO, and in most cases exceed the minimum requirements stipulated by law and guideline documents. This study and the results obtained from it reflect this. This study investigated, in terms of defined types of cover, whether or not there is a statistically significant difference between the: • six coal discard dumps from which data were collected; • five different defined slope aspects; • two groups of slope angles; and • slope angle and slope aspect in terms of cover. The data collected was analysed statistically, so as to determine whether significant differences (95 percentile confidence level), in terms of cover, exist. The purpose of this was to determine whether or not a preferred slope aspect or slope angle group could be identified for the six coal discard dumps sampled. By identifying a preferred slope aspect or slope angle group, companies could alter the design of operational or defunct dumps so as to maximise these. This would make the rehabilitation of the dump more sustainable and could possibly reduce aftercare costs. Through statistical analysis of the data collected it was determined that: • of the six coal discard dumps sampled, significant differences did exist between some of the dumps regarding basal cover, plant litter cover and bare ground. As each dump is different with its own specific micro-climate, this can be expected. The age of the dumps could also have played a role in terms of development; • of the five different defined slope aspects analysed, no significant differences existed between any of them; • of the two groups of slope angles analysed, no significant difference existed between them; and • no relationship between slope angle and slope aspect, in terms of cover, could be established. The analysis of the data collected was done by means of ANOVA one-way tests, coupled with Post Hoc Tests and Contrast Tables. The results of the statistical analysis were evaluated by the STATCON Department of the Rand Afrikaans University for accuracy. The data and the statistical analysis thereof were found to be satisfactory and correct. Various other statistical analyses were conducted on the data, but the results obtained from these tests were all the same as that of the original data analysis. These analyses included the Univariate Analysis of Variance, T-tests and Mann-Whitney tests.

Masters of Science / Eskom supplies to 95% of South Africa’s energy needs and it primarily comes from coal combustion at their coal–fired power stations. Large volumes of fly ash are generated at these coal-fired power stations as a by-product of the coal combustion process. Fly ash is disposed onto landfills at the respective power stations and these landfills are currently running out of storage space. Subsequently, there are concerning environmental impacts upon the natural water environment resulting from coal mining. More specifically, the discharge of acid mine (AMD) water from historical coal mines impact negatively on the water quality in the nearby rivers and dams in the Witbank area. Therefore, as a consequence of the limited space at fly ash landfills, Eskom has embarked on finding alternative ways to re-use fly ash in different applications such as: soil amelioration and land reclamation, road construction as well as brick and cement development. This study focussed on the feasibility of disposing fly ash into the backfill of historical and future coal mines with the intention to firstly reduce fly ash disposal at existing landfills and secondly to improve the decant water quality of the coal mines in the Witbank area. Globally, fly ash has been successfully used in mine backfilling and AMD treatment in countries such as United States of America and India, due to cementitious properties of their fly ash. However, there is limited knowledge on how South African fly ash would behave under backfilled conditions of opencast coal mines where it will be exposed to acidic water environments. This is due to the fact that South African fly ash is considered a Level 3 type hazardous waste, due to its heavy metal concentrations. This waste classification is unique and the strictest compared to global classifications and these methodologies specify that fly ash should be disposed onto lined waste disposal sites due to the potential leaching of heavy metals from these waste sites. It is important to understand the hydrogeological and hydro-geochemical properties of fly ash over time once it is exposed to acid mine water. Field and laboratory tests were conducted to understand these hydrogeological and hydro-geochemical properties of fly ash. Falling head hydraulic tests were conducted at two existing ash landfill sites to determine the hydraulic conductivity (K) of ash of different age. The results exhibit a decreasing trend in K with increasing age. This is due to the pozzolanic nature of fly ash and secondary mineralization of gypsum which causes the fly ash to harden in the presence of water from irrigation for dust suppression together with precipitation over time. Laboratory testing included the use of constant head Darcy column tests to determine the change in K and geochemical properties of the leachate over time. Natural AMD with a pH of 2.5 and a metal composition was used as influent and the leachate were routinely collected and analysed for metal concentrations. The hydraulic conductivity of the fly ash showed a decreasing trend over time. During the placement of coal ash, the moisture allows pozzolanic reactions to solidify the coal ash and lowers the K, towards 10-1 m/d, relative to fresh ash. Secondary mineralization of calcium minerals, in the coal ash contributes to a further decrease in the K, by another order of magnitude from 10-1 m/d towards 10-2 m/d. Sulphate and iron minerals from the AMD also played a major role in the decreasing K as they accumulate in void spaces and having a clogging effect, decreasing the K to 10-3 m/d. The alkaline nature of the coal ash initially neutralizes the acidic levels of AMD from an inflow pH = 2.5 to an outflow pH = 11. Acidification of the outflow towards a pH = 4 was observed, due to large volumes of AMD (>80 000 mL) flowing through short coal ash columns. The K decreased to 3 orders of magnitude, from an initial 10-1 m/d to 10-3 m/d, with the AMD iron (>150 mg/L) and sulphate concentration (>2000 mg/L) playing the dominant role in reducing the hydraulic conductivity. From the geochemical leach test results, it was observed that most of the leachate water was of a better quality than the influent AMD water quality. The outflow pH (pH = 11 to pH = 4) was higher than the pH of the inflow AMD (pH = 2.5). Overall EC reduced in discharge compared to inflow AMD (ECinflow: 535 – 545 mS/m versus ECoutflow: 350 – 490 mS/m), although Na and K in the leachate exhibited higher concentrations (10+2 mg/L) compared to the AMD inflow concentrations (10+1 mg/L). However, most of the other chemical elemental concentrations such as Fe (10-2 – 10+1 mg/L), Si (10-2 – 100 mg/L), Al (10-2 – 10+1 mg/L), Mn (10-2 – 10+1 mg/L), Cr (10-3 – 100 g/L) and SO4 (10+2 – 1+3 mg/L) in the discharge showed lower concentrations when compared to the inflow Fe (10+2 mg/L), Si (100 mg/L), Al (10+1 mg/L), Mn (10+1 mg/L), Cr (10-2 mg/L) and SO4 (10+3 mg/L) concentrations. These results show how fly ash backfill may impact on the current coal mining environment. Overall, the laboratory hydraulic conductivity and geochemical testing showed promising results for fly ash backfilling. Based on this research, fly ash can be used to alter the existing coal mining environment as it is currently known in the Witbank area. The topography, hydraulic conductivity and the water table within the backfill can be altered to improve decant water quality of ash backfilled coal mines.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, .tohannesburg, ill fulfilment of the requirements for the degree or Mester of Science in Engineering Johannesburg, 1992 / Pillar extraction using 'handgot' methods has been practised in South African collieries fOJ' many years. During the late Sixties pillar extraction with mechanized conventional equipment commenced, and approximately a decade later, continuous miners were introduced into pillar and rib pillar extraction panels. During the years that these mining methods were practised, a vast amount of experience was gained on the various collieries. Problems were experienced by various mines and the management of these mines made numerous alterations to the mining methods with varied degrees of success, Research was 0.150 conducted by COMRO and by V,\ri01l5 mines and mining house". Apart from the recommendations of Salamon and Oravecz (1976) on pillar design in stooping sections, little information has been published and, thus, little is generally available to mine managers, planners and operators to assist them in the layout and design for plllar and rib pillar extraction. A survey of all the pillar and rib pillar practises, past and present, has been conducted for collieries in South Africa and abroad and the successes, failures, problems experienced, changes made to the mining methods and the results of these changes have been documented. The problems and successes experienced, t~ similarities and difference between mines and mining methods, and the research flndlngs have been assessed and evaluated. Design guidelines relevant to the various methods of pillar and rib pillar extraction have been established to improve the safety and performance of pillar extraction operations. These guldellnea ate not intended to be prescriptive but are designed more to bring to the attention of the mine manager, planner and operator those fllctors which should be taken into consideration during the planning and operation \)f a pillar Ot rib pillar extraction panel. In addition to the strata related factors, the economics of the mining method is important to determine if it is beneficial to do secondary ext-action, and also to assist in optimlsing the secondary extraction. The design prlnclplns were therefore appUed to diffcrtmt panel layouts, pillar sizes and extraction sequences to determine the effect on the production costs.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2016 / The blind headings created in room and pillar mining are known to be the high risk areas of the coal mine, since this is where the coal production is actually taking place and hence the liberation of maximum quantity of methane. The ventilation of this region called the localized ventilation is carried out using auxiliary ventilation devices. This ventilation may be planned and be the subject of mine standards, but it is not very well understood and implementation on a day to day basis is usually left to the first level of supervisory staff. Majority of the methane explosions have been found to occur in these working areas and blind headings. The correct use of auxiliary ventilation devices can only be carried out once the effect of the system variables associated with each device is very well understood and can be calculated mathematically. Presently, no mathematical models or empirical formulas exist to estimate the effect of the associated system variables on the flow rates close to the face of the heading. The extent of ventilation of a heading ventilated without the use of any auxiliary device is not clear. Furthermore, to design additional engineering solutions, the flow patterns inside these heading ventilated with the auxiliary ventilation devices needs to be understood. The study of the face ventilation systems and the effect of the system variables associated system with each auxiliary ventilation device can be carried out experimentally, but doing a large number of experiments underground is very difficult as it disturbs the mine production cycles. Furthermore, studying the flow patterns experimentally is even more cumbersome, and can only be done to some extent using smoke or tracer gas. Therefore, Computational Fluid Dynamic‟s (CFD) advanced numerical code ANSYS Fluent was used to study the effect of a number of system variables associated with the face ventilation systems used in blind headings. As part of the procedure, the CFD model used was validated using four validation studies, in which the numerical results were compared with the actual experimental results. The numerical results differed to a maximum of 10% for all the experimental results. The system variables associated with ventilation of a heading, without the use of any auxiliary device, with the use of Line Brattice (LB) and fan with duct were selected. A range of values was chosen for each variable, and scenarios were created using every possible combination of these variables. All the scenarios were simulated in Ansys Fluent, the air flow rates, air velocities, velocity vectors, and velocity contours were calculated and drawn at different locations inside the heading. The effect of each system variable was found using a comparative analysis. The results were represented in simple user-friendly form and can be used to estimate the air flows at the exit of the LB and face of the heading for various settings of the LB and fan and duct face ventilation systems. The analysis of the ventilation of a heading without the use of LB shows that a maximum penetration depth is found with the Last Through Road (LTR) velocity of 1.35m/s. The flow rates and the maximum axial velocities increase with the increase in the LTR velocity up to a depth of 10m (maximum air flowing into a heading of 1.26m3/s and 1.58m3/s is found for the 3m and 4m high heading using 2m/s LTR velocity). For the LB ventilation system the LTR velocities, heading height, length of the LB in the LTR and heading, angle of the LB in LTR, and distance of the LB to the wall of the heading (side wall) were varied to identify clearly the effect of these control variables, on the flow rate at the exit of the LB, and close to the face of the heading. The flow rate at the exit of the LB is found to be proportional to the product of the distance of the LB to the wall in the LTR and heading. The flow rate at the exit of the LB, face of the heading, and inside the heading is found proportional to the LTR velocity and height of the heading. It is found that a minimum length of LB is associated with each distance of the LB to the wall in the heading, to maximize the delivery of air close to the face of the heading. This length is found to be equal to 15m for 1m LB to wall distance, and 10m for 0.5m LB to wall distance. Mathematical models were developed to estimate the effect of each studied system variables on the flow rates at the exit of the LB and close to face of the heading. For the fan and duct systems the length, diameter, and the fan design flow rates were varied. It is found that for a force fan duct system only a maximum of 50% of the total air that reaches the face is fresh and the remaining 50% is recirculated air. The flow rate with the exhaust fan system is found to be much lower than the force fan duct system. It increases with the reduction in duct mouth to heading face distance, and increase in duct diameter. Mathematical models are developed to calculate the flow rates at the face of the heading using the effect of each studied system variable. The research reveals that the ANSYS numerical code is an appropriate tool to evaluate the face ventilation of a heading in a three dimensional environment using full scale models. The South African coal mining industry can benefit from the outcomes of this study, specially the mathematical models, in a number of ways. Ventilation engineers can now estimate the flow rates close to the face of the heading for different practical mining scenarios and ensure sufficient ventilation by using the appropriate auxiliary ventilation settings. The results can easily be developed into training aids using easy to use excel spread sheets to ensure that mineworkers at the coal face have a better understanding of the working of the auxiliary ventilation devices. It can also serve Academia as part of the curriculum to teach the future mining engineers how the different variables associated with the auxiliary ventilation system affect the ventilation in a heading. The research therefore, has the potential to provide a significant step toward, understanding airflow rates delivered by the auxiliary devices close to the face of the heading and the air flow patterns inside the heading as a basis for improving the working environment for underground mineworkers. / MT2017

Thesis (M.Sc. (Engineering))--University of the Witwatersrand, Faculty of Engineering, 1987.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requir tents for the degree of Master of Science in Engineering. Johannesburg 1996. / The design of bord and pillar working in South African collieries is based on the pillar strength formula developed by Salamon and Munro1967 and which has been used widely since then for designing pillars. This formula is based on the statistical analysis of 27 collapsed and 98 intact coal pillar cases from collieries located in the Transvaal and the Free state. The main objective of this study is to establish the difference in the strength of the coal material in ditferent seams by means of laboratory testing. In this manner, some 753 coal samples from 10 collieries from 4 seams were tested. The size and width to height ratio effects on strength were analysed. The size effect showed that the difference between the seams was obvious, with a difference of 59,4 per cent between the strongest and weakest coal. The statistical re-analysis showed that the strength of the six blocks from the No 2 seam, Witbank Coalfield occurred in a fairly tight strength range; and that laboratory coal strengths from individual seams or mines could deviate to a significant although relatively small extent from the overall average. / AC2017

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, for the Degree of Master of Science. / storage and waste dumps from coal mining tend to spontaneously combust. This is mainly as a result of the oxidation process which is accelerated by the availability of oxygen and the exothermic nature of the oxidation process. In cases of poor ventilation the heat accumulation within the bed is thought to lead to the spontaneous combustion of coal. The work in this dissertation aims to investigate the change in oxygen concentration in a bed of coal and also measure the rate of oxidation (oxygen absorption) in a closed reactor under isothermal conditions. Drying rate of coal under nitrogen was also looked into. An analysis of the oxygen concentration profile in a three metre 20 cm ID plastic column filled up with coal has been carried out. As the coal ages (becomes oxidised) its reactivity towards oxygen decreases and changes in the oxygen concentration profile are noticed. Experiments have been carried out up to 8 months and from the results obtained, a simple pseudo-steady-state model has been developed to describe the diffusion of oxygen into a reacting coal bed. The findings could prove useful in trying to find a solution to coal and waste dump fire control. The second experiment is a simple isothermal oxygen absorption experiment in which the rate of absorption of oxygen on a given coal sample is measured at different initial concentrations of oxygen. The initial concentration of oxygen is varied over a fairly wide range in order to determine the dependence of the rate of oxidation on the oxygen concentration. The rate- limiting step in low temperature oxidation of coal is found to be the absorption of oxygen. Moisture also plays a role in coal oxidation. Drying experiments were also carried out so as to quantify and investigate the rate of loss of moisture. Models have been developed which try to explain the mechanisms involved in the drying process. The modelling suggest that the bound water model is more appropriate to the type of behaviour exhibited during the drying process / Andrew Chakane 2018

Master of Science in Engineering by advanced coursework and research: A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering Johannesburg, 2016 / The mining sector plays a significant role in the economy of Zimbabwe. The mining sector is the second largest contributor to the country’s GDP at over 20%. Zimbabwe as a country is endowed with abundant mineral resources. The top three commodities in terms of estimated resources are iron ore, coal and platinum with resources of 30 billion tonnes, 26 billion tonnes and 2.8 billion tonnes respectively. Zimbabwe’s vast mineral resources and reserves are of strategic importance to the Zimbabwe economy. Coal mining is one of the major economic contributors to the mining industry in Zimbabwe. The purpose of the study is to determine the optimal operational model for Makomo Resources from a mining and processing point of view. The study is based on a coal-mining project in the Zimbabwean mining industry. Makomo Resources is the largest privately owned coal mining company in the country, which has a mining licence to perform coal-mining activities in the north-west part of the Bulawayo Mining District of Zimbabwe. Makomo Resources applies a conventional strip mining method by means of truck and shovel to extract the coal reserves. Makomo Resources is supplying over 200,000 tonnes of coal per month to the local and export market. The mine has invested in USD20 million capital to commission a wash plant. The study investigates how to optimise the plant throughput by comparing two mining options: Mining Option 1 - crush and screen 2m power coal, crush & screen and wash a full 7m low ash coal seam and wash 2m of coking coal. Mining Option 2 – crush and screen 2m power coal, crush & screen a 3m low sulphur coal seam and wash low ash coal and coking coal of 4m and 2m respectively. The study investigated all the marketing, geology, mining and financial parameters in the Zimbabwean coal mining context. The study determines the appropriate mining methodology and explore to optimise the coal processing. Two financial models were developed to evaluate and compare the two proposed mining options, determine their feasibility and conclude the optimal mining model. Financial techniques were used to analyse and evaluate the two mining options. The financial models were used to analyse and evaluate the following:  The cashflow over the 10-year period.  The Net Present Value (NPV) and Internal Rate of Return (IRR) of each mining option.  The payback period of the washing plant.  Profitability Index per mining option. The NPV of a project determines the economic value of the mining project. The decision on a mining investment is mostly related to the NPV and IRR of the project. Discounted Cash flow (DCF) models were developed for both mining options that shows project cash in and out flows and calculates economic indicators, such as IRR and NPV. The NPV and IRR were the main methods for the evaluation of the two mining options. The resulting DCF models were developed in an Excel spreadsheet format designed for a 10-year Life of Mine (LOM) period. Mining Option 1 has a higher NPV of USD38.2 million in comparison to USD9.7 million for Mining Option 2. The IRR for Mining Option 1 was calculated at 48%, which is bigger than the IRR for Mining Option 2 of 26%. Mining Option 1 has a simple payback period and discounted payback period of 2.7 years and 4.9 years respectively. Mining Option 2 has a simple payback period and discounted payback period of 3.9 years and 11.9 years respectively. Mining Option 1 has a shorter payback period than Mining Option 2. Both mining options have a Profitability Index (PI bigger than one with Mining Option 1 and Mining Option 2 recording values of 1.87 and 1.18 respectively. Mining Option 1 has the better PI value and is therefore more profitable. Based on the economic evaluation, Mining Options 1 is by far more attractive than Mining Option 2, which results in a better return on the investment and profitability, therefore the preferred option. / MT2017