3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Geochemical characterisation of mine drainage from a copper mine operations at Phalaborwa (South Africa) and Kitwe (Zambia)(2022) Mwelwa KitondoMining and processing of copper minerals form a solid and dependable base for infrastructure, social and economic development of most countries in the Southern African region to which South Africa and Zambia belong, with Phalaborwa and Kitwe as their respective centers of copper mine operations. Copper and its auxiliary metals have benefited man in electrical, electronics, medicine and other spheres associated with modern and easy life. At the far side of societal benefits from an extended copper extractive mining, negative impacts of its operations degrade the environment of which water has always been regarded as the worst impacted target. Phalaborwa and Kitwe study sites are characterised by Cu-sulphide minerals coexisting with carbonate minerals in host ore rocks of volcanic and sedimentary origins, respectively. Phalaborwa is supplemented by large amounts of exploitable iron minerals (Magnetite) and phosphate minerals (Apatite), a recognized residence of REEs. In Kitwe, the exploitable ore deposits are rich in Cu-Co metals. Geochemistry was used, both as a path and a tool, to describe distinct features of a copper mine waste samples, assess potential hazards posed by contaminants resulting from their interaction with oxygen and water, evaluate metal speciation resulting from fractionation of sediments. Analytical results were further complemented by PHREEQC geochemical diagnostic simulations of surface water mixing and predictive simulations of surface water loss through evaporation. Adsorption studies were also used to investigate the recovery capacity of natural magnetite (Mgt) for rare earth elements (REEs) with essential properties for applications in electronics and medicine. Samples, consisting of stream water and sediments, and tailings (dumps) were collected at Kitwe study area. River and dam water and sediments, and a variety of mine solid waste consisting of rocks (Rk), sand, phosphogypsum (PG), carbonatite (Cbt), copper-crust (Cu_crust), magnetite (Mgt) and and tailings ex-concentrator (TexCon) were collected at Phalaborwa study area. Physical (dry) and chemical (wet) sample preparation, of which Toxicity Characteristics Leaching Procedure. (TCLP) and Sequential Extraction (SE) form part, paved the way for qualitative and quantitative analytical determination. A combination of analytical techniques (XRD, XRF, SEM-EDS, LPS, IC, ICP-OES (ICP-MS) and CHNS Analyser) were employed to identify minerals and quantify contaminants. Tailings dumps and sediments samples, from Kitwe, were digested (aqua regia, 3HCl:1HNO3) and leached (TCLP) to assess the effects of vigorous and mild extraction conditions. For both techniques, there were more release of major and trace elements from tailings dumps than sediments. Comparisons of digestion results, (tailings sediments), were: Al (12434<24774 mg kg-1), Ca (58368>5594 mg kg-1), K (6374>1379 mg kg-1), Mg (44622>6153 mg kg-1), Co (407.0>126.7 mg kg-1), Cu (3368>1320 mg kg-1), Fe (24753<27600 mg kg-1), Mn (3790>494.2 mg kg-1) and Zn (40.8<150.0 mg kg-1). The presence of SO42- in phosphogypsum (PG) and copper crust (Cu-crust) minerals, PO43- in sand (Sand) and rock (Rock1) minerals, and CO32- in carbonatite (Cbt) minerals of respective geologic samples was indicative of their association with the amorphous reactive phase whereas quartz, aluminosilicates and magnetite (Mgt) signaled the prominent presence of the crystalline inert phase. The extent of minerals dissolution and their accompanying release of inherent trace elements had a huge bearing on the composition of sample leachates. Cu was abundantly leached out from Cu-crust (45100 mg kg-1), Mgt (424.9 mg kg-1) and TexCon (141.8 mg kg-1). Non geologic samples, in perticular elephant dung (ED), produced leachates with elevated major ions concentration than Mgt, e.g. Ca2+ (1.93>0.33%), Mg2+ (0.78>0.18%), SO42- (964>228 mg L-1), Cl- (124>64 mg L-1). Metal species and positive saturation indices (SI > 1) of mineral precipitates, calculated from PHREEQC computation of surface water parameters, were abundant and more varied in WRD than in rivers. Furthermore, pH and Eh provided a favourable environment for the immobilization of trace metals via adsorption to, and subsequent deposition of scavengers such as iron- and Mn- oxyhydroxides. River sediments, from Phalaborwa, were crystalline (Si, Al, Fe) with silt to silty loam texture and high C/S ratio. Their leaching was reflective of these characteristics and their fractionation consistently released more bioavailable Mn and Cu. Sediments quality, assessed using bioavailable concentrations of trace elements as probable effect quotients (PEQs), was poor (mean PEQ > 0.5) and posed a risk to benthos. Predictive evaporation simulations of Cu_crust leachates indicated, in commensuration with percentages evaporation, worrisome exponential increases in concentration (ca 32%, 120% and 1900% increase at 10%, 50% and 95% evaporation, respectively), and deposition of metal species that could precipitate the deterioration of the aquatic system. Isotherms and kinetics models of REEs adsorption onto natural magnetite together with their thermodynamics were determined. Based on results, Langmuir isotherm model gave the best description of this adsorption process, and every indication pointed at the adsorption as obeying the pseudo-second order kinetic model. Thermodynamics adsorption studies were unanimous in determining the mechanism of REEs adsorption onto Mgt. The percentage recovery was 94.8%. The heats of adsorption, ΔHo (av = 22, min = 17, max = 41 kJ mol-1) and ΔHx, (av = 24, min = 18, max = 40 kJ mol-1), the activation energy, Ea, (av = 51, min = 16, max = 40 kJ mol-1), the activation energy Ea (av = 51, min = 16, max = 102 kJ mol-1), and the adsorption energy obtained from D-R isotherm Es (12 – 15 kJ mol-1) fell, generally, within the category of physisorption/ion exchange mechanism limits found in literature (ΔHo and ΔHx < 80, Ea < 40 and Es < 16 kJ mol-1). Furthermore, REEs adsorption onto Mgt was spontaneous (ΔGo < 0) with dissipative entropy (ΔSo > 0). This study did not seek to compare the two study areas by looking at results of one study site in parallel with results of the other study site, but to allow the evidence of similarities and differences, where possible, to come out with no demanding efforts by searching for aspects that are comparable.Item Simulataneous water and energy optimization in shale exploration(2019) Oke, Doris OluwafunmilayoBecause of several environmental challenges associated with the development of shale resources around the world especially in the area of water management as well as flaring of co-produced gas. It is important to find a better strategy that can alleviate these environmental issues by developing a more integrated approach to address the challenges of the water-energy nexus in shale exploration. This thesis presents a mathematical framework for simultaneous optimization of water and energy usage in hydraulic fracturing using superstructure-based optimization technique. First, a continuous time formulation for scheduling is developed for the hydraulic fracturing activities. Recycle/reuse of fracturing water (flowback water) is achieved through purification of flowback wastewater using thermally driven membrane distillation (MD). A detailed design model for this technology is incorporated within the water network superstructure in order to account for the design specifications and the energy requirement of the system. The feasibility of utilizing the co-produced gas that is traditionally flared as a potential source of energy for MD is also examined. The applicability of the proposed model is determined using a case study which is a representative of Marcellus shale play. Next, the mathematical formulation is extended to account for shale gas production, processing, distribution, usage in power generation, and transmission of produced power in which the effect that the type of gas to be produced in a particular shale play/region will have on the infrastructure development is investigated. The study considers natural gas as fuel for commercial, industrial and residential customers, as well as fuel for electric power generation, with the goal of maximizing the overall profit. The resultant model is applied to a case study, which is a representative of Marcellus shale play. The application of the model results in 23.2 % reduction in freshwater consumption, 18.6 % savings in the total cost of freshwater and 42.7 % reduction in the energy requirement of the regenerator. The thermal energy consumption is in the order of 160×103 kJ/m3 of water. Two types of gas are considered: wet gas and dry gas. The results indicate that the cost incurred in the network involving wet gas is 41.76 % higher than the network involving dry gas due to the processing requirement of wet gas. In addition, the multi-contaminant property of flow back water is investigated through implementation of an on-site pre-treatment technology to remove contaminants like total suspended solid (TSS), Total organic compound (TOC), oil, grease and scaling materials whereby, specification for water reuse can be achieved. This is achieved by considering detailed ultrafiltration model in order to evaluate the sustainability of the system in terms of energy consumption and associated costs. The study also looks into the feasibility of using the gas that would otherwise be flared to generate electrical energy for the membrane system via an onsite gas generator. The application of the proposed model in a case study results in 21.4 % reduction in the amount of water required for fracturing and 10.3 % reduction in the amount of energy needed by the regenerator. The system consumes 0.109 kWh/m3 of energy at an operating pressure of 3.69 bar. This indicates a very low-energy consumption compared to a typical energy requirement for wastewater reclamation which usually ranges between 0.8 and 1.0 kWh/m3 for membrane filtration. The study indicates the possibility of reducing the operating cost of the regeneration network by 61 % if the electrical energy needed is generated onsite using the gas that would otherwise be flared. The effect of using multiple/ hybrid treatment technologies in maximizing hydraulic fracturing wastewater reuse while accounting for the sustainability of the process in terms of energy and associated cost is also investigated. The study considers ultrafiltration and membrane distillation processes as possible pre-treatment and desalination technologies for flowback water management. Two different scenarios are considered to cover possible flowback water composition in hydraulic fracturing in terms of salinity. Application of the proposed model to a case study leads to 24.13 % reduction in the amount of water required for fracturing. In terms of energy requirements, the approach led to 31.6 % reduction in the required thermal energy in membrane distillation and 8.62 % in the energy requirement for UF. For flowback water with moderate TDS concentration, 93.6 % of the wastewater reuse comes from pre-treated water by ultrafiltration and 6.4 % from membrane distillation. However, as the flow back water salinity becomes higher, the percentage of pre-treated water that could be reused reduced to 81.1 % and the percentage supply through membrane distillation increased to 18.9 %. In all cases, the results indicate that the decision to allow the pre-treated water to pass through desalination technology strictly depends on the volume of water required by a particular well pad and the salinity of the wastewater. In general, although the obtained results may not generally applicable to all shale plays, the proposed framework and supporting models aid in understanding the potential impact of using scheduling and optimization techniques in addressing flow back wastewater management.Item Contaminant fate in Searsia Lancea woodlands on acid mine drainage in the Witwatersrand Basin Goldfields(2017) Joubert, Maxine KellyThere has been increasing research into plants used for phytoremediation, specifically for phytoextraction and phytostabilisation of heavy metals in soil. There has been little research on trees for their large biomass, especially field studies. There is also a lack of research on trees in South Africa specifically. This study evaluated the fate of contaminants (Na, Mg, Al, S, Cl, Cd, Cr, Mn, Fe, Cu, Zn, and Pb) in Searsia lancea, a tree native to South Africa, planted in woodland trials for phytostabilisation and hydrological control on AngloGold Ashanti mining properties, at the base of tailings storage facilities as part of the Mine Woodlands Programme – a collaboration between the University of the Witwatersrand and AngloGold Ashanti. Trees of average height were harvested from three out of four S. lancea plots at four different sites; two sites at the West Wits mining operations (Madala and Redsoils), and two sites at the Vaal River mining operations (West Complex and Mispah). One site at each mining operation had nutrient-poor soil, and one site had nutrient-rich soil for plant growth. Harvesting of above-ground biomass took place first, in which the tree compartments were separated into wood (stems), twigs, and leaves. These were bagged and weighed, and then dried naturally. Sub-samples of wood, twigs, and leaves were taken after weighing the bulk samples. These sub-samples were washed, freeze-dried, and ground using ceramic burr grinders for analysis. Tree roots were excavated using a backacter (TLB), which then proceeded to dig soil pits roughly 2.5 x 3 x 3 m for soil sample collection. Sub-samples of coarse roots and fine roots were taken, but roots were bagged and weighed together. Sub-samples of roots were also washed, freeze-dried, and ground using a ceramic burr grinder for analysis. Soil samples were taken at certain depths within the pits (0-2, 2-5, 5-10, 10-15, 15-20, 20-30, 40-50, 50-60, 60-70, 70-80, 90-100, 120-130, 145-155, 170-180, 190-210, 240-260 and 280-300 cm). These were bagged and sent for analysis of pH, Electrical Conductivity (EC), and Reduction-Oxidation Potential (Eh). All samples were analysed by X-Ray Fluorescence (XRF). The Mann-Whitney U Test and a non-parametric analysis of variance (Kruskal-Wallis) were used to test for significant differences in contaminant distribution. Post-hoc pairwise comparisons were performed using Dunn’s procedure with a Bonferroni correction for multiple comparisons to test for specific differences between soils (sites), tree compartments and soil using IBM SPSS statistics 24. Bioconcentration Factors (BCF) and Translocation Factors (TF) were calculated to assess the phytostabilisation and phytoextraction abilities of S. lancea. The fate of contaminants was found to be different for different contaminants. Sulphur and Mn were highest in the leaf compartment; Chlorine, Cu, and Zn were highest in the twig compartment; no elements were found to be highest in the wood compartment; Mg and Fe were highest in the coarse roots; and Ca was highest in the fine root compartment. It was also found that S. lancea is an accumulator of S, Cl, and Ca with levels of 2 508.92, 2 500.96 and 16 733.46 mg/kg respectively. Searsia lancea appears to be a Al, Fe, and Cr stabiliser with TFs < 1 and translocates metals in the sequence Ca > Na > Fe > Mg > Zn > S > Mn > Pb > Cu > Al > Cl > Cr. BCF results show that S. lancea is more of an accumulator than a stabiliser as BCF root: soil pattern was found to be Cl > S > Cu > Cr > Zn > Mn > Mg > Na > Pb > Ca > Al > Fe; while BCF shoot: soil pattern was found to be > 1 in the sequence Cl > S > Ca > Na > Mg > Zn > Cu > Mn > Pb > Cr > Fe > Al, with Al, Cr, Fe, and Pb higher in soil compared to shoot concentrations. This study demonstrates that certain indigenous tree species are capable of phytoremediation of contaminated sites and that larger biomass species can take up great elemental masses of certain elements. Key words: phytoremediation, phytostabilisation, phytoextraction, native trees, mine pollution, Searsia lanceaItem Investigation of the Ramotswa Transboundary Aquifer area, groundwater flow and pollution(2017) Modisha, Reshoketswe Caroline OudiGroundwater is a principal source of water for many semi-arid countries, including Botswana and South Africa. This is especially true for the rural communities within these regions that lie on the periphery of local water scheme pipelines and make direct use of groundwater. The Ramotswa transboundary aquifer, which supplies local communities and nearby cities with fresh groundwater, is a highly productive and unique karst sequence shared by South Africa and Botswana. The objective of the study was to contribute to the available hydrogeological data by means of evaluating groundwater flow, nitrate pollution and the median recession index and master recession curve for the aquifer. The interpreted airborne geophysical data revealed the presence of collapsed features in the northeastern area corresponding to the karst morphology. A piezometric map of the area shows the groundwater flow is towards the north-northeast, which is supported by salinity increase across the study area. Increased nitrate concentrations were identified in areas with increased rainfall, shallow groundwater and a mature karst system. Only 3% of the 36 sample sites had nitrate concentrations exceeding the WHO guideline limit of 50 mg/l. This was attributed to the legacy of unlined pit latrines in karstified areas. Pollution is entirely anthropogenic and generally from non-point sources. A median recession index computed by RECESS program from the Dinokana spring discharge data was 295.7 days per log cycle and the generated master recession curve’s gentle slope alludes to massive storage potential within the karst compartment. The results of the study can alert stakeholders alike of the health risk of direct consumption of the groundwater without pretreatment. Establishing an understanding of the nitrate pollution sources and groundwater flow direction, and estimating the recession index provides informed groundwater pollution and vulnerability management options. This can improve the aquifer resource assessment and the livelihoods of local communities in the face of increasing climate change.Item Groundwater and surface water interaction in the Uitenhage Artesian Basin, Eastern Cape, South Africa: case study of the Swartkops and Coega aquifer(2017) Nyawo, Bongizenzo LangelihleThe state of water quality in the Swartkops River catchment in the Uitenhage area, Eastern Cape Province, South Africa, continues to be degraded by anthropogenic activities, which include municipal waste water, industrial waste and agricultural runoff. The study area consists of two aquifers (Swartkops and Coega) that are separated by the fault (Coega fault). In the study area there are two main rivers, namely: Swartkops River and Coega River, which are situated in the Swartkops Aquifer and Coega Aquifer, respectively. Most of the degrading anthropogenic activities are situated in the vicinity of the Swartkops River. The focus of the study was on the pollution of the stream water and aquifer (groundwater), with particular emphasis on the groundwater management. The study objectives were to establish the relationship between groundwater levels and surface topography using Bayesian interpolation method and groundwater and surface water interaction using environmental isotope and hydrogeochemical techniques. The bacteriological assessment was also conducted to determine if hydraulic connections exist between groundwater and the polluted streams. The results of the Bayesian Interpolation Method indicated that there was a strong relationship between the groundwater level elevation and surface topography with the correlation coefficient of 0.9953. The results also indicated that the fault is permeable; hence it did not have influence on groundwater circulation; however, groundwater does not flow from Swartkops River to Coega Aquifer due to groundwater flow gradient. The environmental isotope results indicated that both Swartkops Aquifer and Swartkops River were characterised by heavy isotopes signatures, which indicated the correlation between the two water components. The results further showed that the Swartkops River was recharging the Swartkops aquifer. However, no correlation was established between Swartkops River and Coega aquifer due to flow gradient. Although the flow gradient allows the flow of groundwater from Coega Aquifer to Swartkops Aquifer, Coega aquifer is a Government Water Controlled Area, which could have a very low to none impact on the other aquifer. Piper diagram and stiff diagrams indicated one water type found in the Swartkops and Coega aquifers, which was: Na-Cl type. The water in the Coega aquifer indicated high salinity in the chemical properties, which was typical old marine water derived from deep groundwater source. It was noted that the electrical conductivity values in the Waste Water Treatment Work were closest to those of the Swartkops River and Aquifer, which was in central to those of Coega Aquifer. The bacterial analysis results indicated that during the wet season most of the bacterial counts were high as compared to dry season. It was noted; however, that during the wet season the bacterial counts appeared similar in both aquifers. It is unlikely that the similarities emanated from the interaction of the two aquifers as the analysis of the results indicated that the bacterial counts found in the Coega Aquifer emanated from the farming activities. The study concluded that the fault act as a pathway for migration of groundwater flow. It was established that the groundwater only flows from Coega Aquifer to Swartkops Aquifer due to difference in the hydraulic gradient.Item Ground water pollution at sanitary landfill sites: geohydrological, environmental isotope and hydrochemical studies(1998) Butler, Michael JohnThis study determines the potential of prerncting pollution to ground water by sanitary landfills. The tracing capabilities of both stable and radioactive environmental isotopes are also evaluated. Four landfills were selected, the Linbro Park and Waterval sites in Johannesburg, and the Bloemfontein northern and southern landfill sites. The sites all differ in geological environment, size. age and physiographic setting. [Abbreviated Abstract. Open document to view full version]Item Application of fate and transport models to evaluate the efficiency of a Cr(VI) remediation pump and treat system(2016) Nkosi, Sifiso CollenGroundwater treatment by chemical precipitation is a popular form of remediation at mines that are in operation. The water quality status at the implementation of the PAT in this study was compared to the water quality status after a six-month period of active remediation. Chromium is very important as an industrial metal owing to its numerous uses in a variety of industries. The objective of the remedial action is to intercept the Cr(VI) plume, abstract contaminated groundwater and chemically treat it on the surface. The long-term (15-year) objective is to eventually reduce Cr(VI) concentrations in the aquifer(s) to below 0.05 mg/ℓ. The PAT system was implemented as a mediumterm (5-year) strategy to intercept the Cr(VI) contamination plume during migration to prevent it from negatively impacting on groundwater users downstream of the mine. In the vicinity of the three PAT systems’ abstracting wells, water levels declined by an average of 2 m compared to the same period in 2014. Periodical fluctuations in the fractured aquifer are reflective of the influence of fractures on groundwater flow. In the aquifer, hydrochemical signatures show evidence of mixing between the primary and secondary aquifers. The treatment system has been successful in reducing Cr(VI) to Cr(III) and precipitating Cr(OH)3. The treatment system was designed to treat Cr(VI), other elevated constituents and generally high dissolved ions are not treated in this remedial process. Sulphate concentrations increase after treatment as a result of the addition of Fe(II)SO4 for chromate contamination treatment purposes. The simulated reaction path shows that the transformation of CrO4 2- to Cr2O3 in the treatment system is not immediate. The Cr(VI) to Cr(III) transformation is irreversible, this is beneficial as the water is abstracted from more reducing conditions, and the treatment ponds are open to the atmosphere thus the conditions following dosing with Fe(II)SO4 are oxic and chromate complexes are stable over a wider range of Eh-pH conditions than Cr(III) compounds. This ensures that the efficiency of the dosing system is not reversed in Settling Pond B. The modelled flow paths are similar to the inferred flow vectors in the plume capture zone. Fracture flow is the dominant type of flow, the fault zones and dykes create high permeability conduits to flow. Flow paths are parallel to fault lines or the lateral dimension of dykes; flow occurs along fractures and deformation zones. The reduction of Cr(VI) concentrations in some of the peripheral sampling points indicates that the PAT system has been successful in capturing the chromate contaminated water through pumping. Keywords: Hexavalent chromium, groundwater pollution, remediation, pump-and-treat, fractured aquifersItem Green element solutions for inverse groundwater contaminant problems(2016) Onyari, Ednah KwambokaIn this work two inverse methodologies are developed based on the Green element method for the recovery of contaminant release histories and reconstruction of the historical concentration plume distribution in groundwater. Unlike direct groundwater contaminant transport simulations which generally produce stable and well-behaved solutions, the solutions of inverse groundwater contaminant transport problems may exhibit non-uniqueness, non-existence and instability, with escalation in computational challenges due to paucity of data. Methods that can tackle inverse problems are of major interest to researchers, and this is the goal of this work. Basically, the advection dispersion equation which governs the transport of contaminants can be handled by analytical or numerical methods like the Finite element method, the Finite difference method, the Boundary element method and their many variants and hybrids. However, if a numerical method is used to solve an inverse problem the resulting matrix is ill-conditioned requiring special techniques to be employed in order to obtain meaningful solutions. In view of this we explore the Green element method, which is a hybrid technique, based on the boundary element theory but is implemented in an element by element manner. This method is attractive to inverse modelling because of the fewer degrees of freedom that are generated at each node. We develop two approaches, in the first approach inverse Green element formulations are developed, the ill-conditioned matrix that results is decomposed with the aid of the singular value decomposition method and solved using the Tikhonov regularized least square method. The second approach utilizes the direct Green element method and the Shuffled complex evolutionary (SCE) optimization method. Finally, the proposed approaches are implemented to solve typical problems in contaminant transport with analytical solutions besides those that have appeared in various research papers. An investigation on the capability of these approaches for the simultaneous recovery of the source strength and the contaminant concentration distribution is carried out for three types of sources and they include boundary iv sources, instantaneous point sources and continuous point sources. The assessment accounts for different transport modes, time discretization, spatial discretization, location of observation points, and the quality of observation data. The numerical results demonstrate the applicability and limitations of the proposed methodologies. It is found in most cases that the solutions with inverse GEM and the least squares approach are of comparable accuracy to those with direct GEM and the SCE approach. However, the latter approach is found to be computationally intensive.