3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Temporal variation in the allocation of acid mine drainage contaminants in the waters and sediments of the engineered remediation reed beds along the Varkenslaagte stream: an autum - winter study(2016-01-19) Omo-Okoro, Patricia NdidiamakaAcid Mine Drainage (AMD) refers to the seepage or runoff of acidic water from abandoned mines into the surrounding environment. Acid mine drainage is considered a serious long term environmental threat associated with mining. This study was conducted on the Varkenslaagte canal or stream which flows from north to south within the AngloGold Ashanti West Wits gold mining operation, 75 km west of Johannesburg, and receives AMD from tailings storage facilities (TSFs) located on both the northern aspect and the western aspect of the catchment. On the Varkenslaagte, 17 reed beds were planted between 1-12-2011 and 12-9-2012, in a series of shallow excavated depressions. This study was conducted in 2013 and 2014, and aimed to ascertain: (i) whether there is any temporal difference (autumn – end of the rainy season, versus winter – mid-dry season, for 2013 and 2014 combined) in selected fresh-water quality parameters and concentrations of AMD contaminants in the flowing waters in the engineered reed beds; - this was observed, as higher concentrations were recorded in winter than in autumn, for some of the selected water quality parameters, in both survey years; (ii) to determine if vertical changes exist in the elements down the sediment profile from the surface to a depth of approximately half a metre; - conspicuous vertical changes were not evident; and also; (iii) to provide a baseline for monitoring the post clean-up state of the upper Varkenslaagte, and conclude whether the reed bed system is retaining AMD contaminants (major ions, trace and major elements). Chemical variations in water and sediment samples were measured in situ in April/May 2013 and July 2014, and water samples and sediment cores collected for laboratory analyses. Water samples were collected from three points (inflow, middle and outflow) at each of 15 reed beds (RBs, numbered RB 1 -15) in receipt of AMD from two directions (downstream and laterally from TSFs on the northern and western aspects). Ion Chromatography was used to detect chloride (Cl-) and sulphate (SO42-), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used to identify major and trace elements; iron (Fe), magnesium (Mg), manganese (Mn), potassium (K), cobalt (Co), nickel (Ni), lead (Pb), copper (Cu) and zinc (Zn) in the water samples whereas X-Ray Fluorescence (XRF) analysis for elements was conducted on surface sediments (0-2cm; additional analyses of sediment core samples at depths 2-5 cm, 5-10 cm, 10-20 cm and 20 -30 cm were analyzed but were not considered further). The water in the reed beds was moderately acidic to within the target range. It ranged from pH 5.17 to 6.51 in April, 2014 (approaching the end of the wet season) (P < 0.05) (P = 0.0001) to slightly higher values of pH 5.45 to 6.82 in July, 2014 (mid-dry season) (P = 0.0053). Marginal acidity is above pH 6. A pH of 6.5 – 7.5 is within the target water quality range (TWQR) on the Highveld. High electrical conductivity (EC) values were found, ranging from 3500 – 4600 μs/cm in April and 2600 – 5500 μs/cm in July, though EC values can be higher on much of the South African gold mining Highveld. Lateral influx of AMD from the western TSFs was visually observed into two of the southernmost Varkenslaagte stream reed beds (at RBs13 and 15) during both April and July sampling. In 2014, the Varkenslaagte was still flowing from reed bed to reed bed, although very slowly, similar to 2013. Chloride, sulphate and metal concentrations were high relative to target water quality ranges in most of the reed beds in during April and July, 2014. Although higher concentrations in the sediment suggest that the reed beds are effective in capturing and retaining contaminants in sediment and root mass, the concentrations in the water in reed beds 1-15 still exceeded the target water quality ranges for aquatic ecosystems in South Africa (DWAF, 1996) and the World Health Organization (WHO) guidelines for drinking water quality (WHO, 2004). However use of the water from the Varkenslaagte by humans and livestock is prohibited by the Department of Water and Environmental Affairs, and the National Nuclear Regulator. The bar charts comparing 2013 and 2014 selected water quality data showed that during winter/drier periods with no rains, the rate of evaporation exceeded dilution; this was observed by the slightly lower pH values recorded across the reed beds in July, 2013 and 2014, in comparison with the slight higher pH values recorded across the reed beds in May, 2013 and April, 2014. The bar charts also showed that the highest EC was recorded in the winter of 2014. It was also observed from the principal component analyses (PCAs) that EC, sulphate and pH, in combination with Mg and Fe, were responsible for most of the variation in the water quality data for the two survey years, 2013 and 2014. Following the findings from this study, it is recommended that monitoring of the site should also address whether the reed beds and other control measures that have been put in place (riparian woodlands and windmill pumps) will be adequate to control the lateral seepage from the Western TSFs at some of the southernmost reed beds.Item The utilisation of cellulosic biomass in the treatment of acid mine drainage and the subsequent production of fermentable sugars for bioprocessing(2015-02-16) Magowo, WebsterSugar cane bagasse and switch grass were used to investigate their potential in the remediation (decreasing metal ion concentration and increasing pH) of Acid Mine Drainage (AMD) and the possibility that the AMD residue sludge containing cellulose could be further hydrolysed using a commercial cellulase enzyme system to produce glucose for bioprocesses. In general both the feedstocks series appeared to increase pH and reduce dissolved iron concentration after being incubated with AMD for a period of 14 weeks at room temperature. The milled switch grass was shown to have a greater remediating effect on AMD, raising the pH from 2.11 to 5.46, and decreasing iron concentration from 500mg/l to 174mg/l, a decrease of 62%. The sugar cane bagasse was shown to have the least remedial effect, increasing pH from 2.11 to 2.38, and only reducing iron concentration by 30%. The 2‐5cm switch grass raised the pH from 2.11 to 3.86, and the iron concentration was reduced from 500mg/l to 283mg/l, a 42% reduction. The milled grass series was chosen for further enzymatic hydrolysis. The milling reduced the size of the switch grass and destroyed the cell structure making it more accessible to AMD treatment. This also allowed the enzyme in the hydrolysis to penetrate to the fibres and reach the sugar oligomers. The sludge of the AMD treated switch grass was incubated with cellulases enzymes for 24 hours at 50oC, producing glucose concentration of up to 4,86mg/ml.Item Assessment of algae as mercury bioindicators in acid mine drainage waters and their potential for phytoremediation(2014-07-22) Tshumah-Mutingwende, Rosamond Rosalie Marigold SetswaThe use of algae as heavy metal bioindicators in aquatic environments has received much attention. In this study, the performance of a common freshwater living green alga, Cladophora sp. as a mercury bioindicator and its potential for phytoremediation applications was assessed by various parameters which included the influence of contact time, pH, initial mercury concentration and the presence of competing metal cations. A rapid uptake of mercury by Cladophora sp. was displayed. More than 99% of mercury in solution was removed within the first 5 min of contact and equilibrium was attained after 10 min. High adsorption capacities of 800 mg kg-1, 530 mg kg-1 and 590 mg kg-1 at pH 3, 6.5 and 8.5 respectively were obtained at the optimum mercury concentration of 1.0 mg l-1. Competitive adsorption studies showed that the selectivity of heavy metal cations by Cladophora sp. was in the following order: Hg2+ ˃Fe2+˃Cu2+˃ Zn2+ ˃ Co2+. These results indicate that living Cladophora sp. algae are suitable for use as mercury bioindicators in AMD waters and are also suitable for the removal of mercury in AMD conditions.Item Preparation of magnetic nano-composite-beads and their application to remediation of Cr(VI) and U(VI) from acid mine drainage(2013-08-07) Tavengwa, Nikita TawandaOccurring parallel to the developments in imprinting technology are magnetic materials which are being applied increasingly in environmental remediation, medicine, biotechnology and many other fields. Combining the imprinting effects of the polymer and nano magnetic particles yields composite materials which are both selective to the template and magneto responsive for easy polymer removal from aqueous solutions. In this study, magnetic ion imprinted polymers with high recognition for uranyl ion (UO2 2+) in the presence of competing ions were synthesized by bulk and precipitation polymerizations. The uranyl template was removed from the magnetic polymer matric by 1M HCl and 1M NaHCO3 leachants to form cavities which were complimentary in shape and size to the template. Full characterization of the magnetite and magnetic polymers was achieved by use of the following characterization techniques: Raman spectroscopy (RS), Transmission electron microscopy (TEM), Energy dispersive spectrometry (EDS), Powder X-ray diffraction (PXRD) analysis, Brunauer, Emmett and Teller (BET) analysis, Ultraviolet visible (UV-vis) spectroscopy, Fourier-transform infrared (FTIR), Thermo-gravimetric analysis (TGA), Carbon, hydrogen, nitrogen and sulphur (CHNS) analysis, Diffuse reflectance spectroscopy (DRS) and Atomic force microscopy (AFM). Parameters which were optimized included sample pH, which gave an optimum value of 4. Magnetic IIP and NIP amounts which gave maximum adsorption capacities were found to be 50 mg for both of these adsorbents. The optimum contact time was found to be 45 minutes. The performance of all magnetic ion imprinted polymers (IIPs) was expectedly superior to that of the corresponding non imprinted polymers (NIPs) in all adsorption studies. The first rate constant (k1) and correlation coefficient (R2) values evaluated for the pseudo first order were found to be between 0.048-0.093 min-1 and 0.602-0.991 min-1, respectively. For the pseudo second order, second rate constant (k2) and correlation coefficient (R2) were found to be between 0.273- 0.678 and 0.9811-0.9992, respectively. The selectivity order observed was as follows: UO2 2+ > Fe3+ > Pb2+ > Ni2+ > Mg2+. The magnetic polymers selective to Cr(VI) were also synthesized and were leached with HCl to remove the template. The synthesized Cr(VI) magnetic polymers, the optimum pH obtained was 4 for both the magnetic IIP and the corresponding NIP. The amount of the adsorbent which gave the maximum adsorption was determined to be 20 and 65 mg for the magnetic IIP and NIP, respectively. A Cr(VI) concentration which was adsorbed maximally was from 5 mg L-1 which was therefore taken as the optimum. The maximum adsorption capacities for the magnetic polymers were 6.20 and 1.87 mg g-1 for the magnetic IIP and NIP, respectively. The optimum time for the adsorption of the Cr(VI) analyte was determined as 40 minutes. Investigation of the order of selectivity of anions followed the trend: Cr2O7 2- SO4 2- F- NO3- -.Item Use of remote sensing and GIS in a risk assessment of gold and uranium mine residue deposits and identification of vulnerable land use(2013-04-29) Sutton, Malcolm WilliamAcid rock drainage (ARD) and dust are potential consequences of gold and uranium mine residue deposits (MRDs) on the Witwatersrand basin. Urbanisation has taken place around mines and, with the curtailing of mining activities and clearing of land previously covered by MRDs, there is pressure to use this land for residential, industrial and agricultural purposes. However, mining companies historically were not required to provide pollution control measures and there is evidence for contamination of land and water. Thus, there is a need to prioritise contamination sources for mitigation and to understand the extent of contamination and potential risks associated with different categories of land-use on mining land. The aim of my study was to conduct a first-order risk assessment to aid in identifying vulnerable land use in the vicinity of gold and uranium mining, and prioritising MRDs, including footprints, for mitigation. To achieve this I constructed a Geographical Information System (GIS) using publicly available spatial data, and then tested the usefulness of historical aerial photographs and remote sensing imagery for mapping MRDs and impacts of MRD origin under Highveld conditions (i.e. a seasonal climate with summer rainfall and annual evapotranspiration of >2.5 times mean annual precipitation). The Ekurhuleni Metropolitan Municipality (EMM; 1923 km2) is an area of extensive historical mining with major urbanisation, while retaining areas for agricultural land use; thus it was selected as a representative study site. I used a numerical rating scheme, which combined a number of parameters in two separate stages to calculate a risk index. The first stage involved the classification of hazards associated with MRDs while the second involved an assessment of land use vulnerability based on exposure pathways and proximity. Historical aerial photographs (1938, 1964 and 2003) and the Chamber of Mines (CoM) Dump Indexes were used to identify and classify MRDs in terms of basic geotechnical properties, current status and historical failure. Multi-spectral data, acquired over two years (2002 and 2003) in two seasons (spring and summer) by the TERRA satellite’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor, were used to compile thematic images, indicating potential contamination of surrounding land. It was intended that a zone of influence could be distinguished for each MRD enabling me to rate the hazard severity. The thematic images I selected included primary minerals (pyrophyllite and chlorite), secondary minerals (copiapite and jarosite), an indicator of uranium-bearing ore (referred to as mincrust) and the normalised difference vegetation index (NDVI). These minerals were chosen as potential indicators of different transport routes of contaminants and I tested their associations with different features and land use. I also tested for seasonal differences in the detection of these minerals, and used NDVI to examine the masking effect of active vegetation. I found GIS to be well suited for combining the various forms of spatial data and providing information about MRDs, aqueous pathways, proximity to vulnerable land uses and impacted areas. However, I found that the potential severity of the hazards posed by each MRD, as indicated by a zone of influence, could not be determined from aerial photographs and ASTER alone. I therefore utilised the findings expressed in the literature survey to assign ratings for the different classes of MRDs. The vulnerability assessment was also supplemented by literature review to rate land uses based on human exposure pathways. I determined that MRDs (including footprints) cover 4.1% of EMM, with slimes dams, totalling 3.5%, occupying the majority of this area. I found that 64% of slimes dams had failed prior to 2003 and I plotted a further 0.6% of EMM covered by visible mine residue spillage. Fifty three percent of MRDs were situated within 100 m of drainage lines or old wetlands, while 52% of these (i.e. 27% of the total) had been constructed in the watercourse. I also found that 15% were constructed on dolomites. Informal settlements were located on or bordering 6% of MRDs, with 41% of MRDs within 1 000 m. Eighty eight percent of MRDs were found within 1 000 m of formal residential areas, 71% within 500 m, and formal settlements were located on or bordering 5% of MRDs. Twenty three percent of MRDs were located within 500 m of agricultural land, while 35% were within 1 000 m; and industrial land use was on 9% of MRDs (footprints), with 40% of MRDs being within 500 m of industrial areas and 61% within 1 000 m I found that chlorite did not provide a ‘signature’ of gold and uranium mine residue, whereas the other four minerals did. I also found that, of the two seasons examined (spring and summer), the best time to take an ASTER image to detect mineral signatures of gold and uranium mine contamination is after a few dry days following the first spring rains. For this reason, I used the ASTER taken in late October (spring) 2003 to examine associations with pathways and land use. I found more pyrophyllite and copiapite on industrial and business land use than background, which I suggest is associated with the settling of windborne dust on large and flat roofs; although, in the case of copiapite this could be related to the oxidation of settled wind blown pyrite material. I found jarosite to be a reliable indicator of mine residue, which, together with mincrust, helped me identify contamination in former agricultural holdings, which are now a township. Although, chemically undefined, mincrust was a useful indicator of contamination, as I found it to be reliably detected on MRDs (including footprints), mine residue spillage, wetlands and other contaminated sites, and absent from known uncontaminated sites. Furthermore, it was not necessarily masked by active vegetation, whereas copiapite, jarosite and pyrophyllite were. Mincrust was also detected on irrigated agricultural land with an odds ratio of between 10 to 36 times greater than for rain-fed. Consequently, the most likely pathway for mincrust is the aqueous. The mincrust signature, together with historical aerial photographs, also assisted me to identify historical mining along Black Reef outcrops, through detection in a wetland upstream of known mining activities. The culmination of my study was a risk class and index for MRDs from which ‘risk maps’ were produced. These maps provide a guide to the level of risk posed by each MRD to the surrounding land use. Of the total 287 MRDs (including footprints) identified in the EMM, 50% were classified lower-risk; 40% medium-risk; 10% higher-risk and 0% as much higher risk. The lower-risk MRDs were predominantly rock dumps, whereas the higher-risk MRDs were slimes dams. The findings from my study will contribute to meaningful recommendations for future land use and enable mining companies, landowners, developers and government to allocate their resources judiciously (i.e. appropriate to the level of risk). The results of this study have been published as: Sutton, M.W., Weiersbye, I.M., Galpin, J.S and Heller, D., 2006. A GIS-based history of gold mine residue deposits and risk assessment of post-mining land uses on the Witwatersrand Basin, South Africa. In: A. B. Fourie and M. Tibbett (eds.), Mine Closure 2006: Proceedings of the 1st International Seminar on Mine Closure, Perth, ISBN: 0-9756756-6-4, pp. 667–678 (Appendix I). Sutton, M.W. and Weiersbye, I.M., 2007. South African legislation pertinent to gold mine closure and residual risk. In: A.B. Fourie, M. Tibbett and J. Wiertz (eds.), Mine Closure 2007: Proceedings of the 2nd International Seminar on Mine Closure, Santiago, ISBN: 978-0-9804185-0-7, pp. 89–102 (Appendix II). Sutton, M.W. and Weiersbye, I.M., 2008. Land use after mine closure – Risk assessment of gold and uranium mine residue deposits on the eastern Witwatersrand, South Africa. In: A.B. Fourie, M. Tibbett, I.M. Weiersbye and P.J. Dye (eds.), Mine Closure 2008: Proceedings of the 3rd International Seminar on Mine Closure, Johannesburg, ISBN: 978-0-9804185-6-9, pp. 363–374 (Appendix III).