Electronic Theses and Dissertations (Masters)

Permanent URI for this collectionhttps://hdl.handle.net/10539/38003

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Characterization, quantification, and recovery of rare earth elements(rees) in South African coal fly ash samples
(University of the Witwatersrand, Johannesburg, 2024) Rampfumedzi, Tshilidzi Michael; Chimuka, Luke
Rare earth elements (REEs) are naturally distributed throughout the Earth's crust, typically in low concentrations. They are not typically found in isolation but are rather present in various minerals, often in amounts too minute for cost-effective extraction. Fly ash is among the sources that are deemed economically viable for extracting REEs. The objective of this study was to create environmentally sustainable approaches for measuring and reclaiming rare earth elements (REEs) in coal fly ash (CAF) samples. The study involved analyzing fly ash samples collected from various coal power stations using a range of standard and advanced techniques, including X-ray fluorescence (XRF), X-ray diffraction(XRD), scanning electron microscopy (SEM), and inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The XRF only shows the presence of REEs from all three fly ash samples with a range of 40 to 100 ppm and mineral oxide ranging from 0.1 to 50 %. The XRD results show that fly ash sample is a siliceous-rich sample with abundant minerals such as quartz (SiO2), magnetite (Fe3O4), and mullite (Al4.52Si1.48O9.74). The SEM analysis of the sample confirmed the presence of rare earth minerals, including monazite which is a light atomic mass (LREE), xenotime, a heavy atomic mass (HREE), and perrierite-bearing minerals. The results obtained from the instrumental analysis show that the ICP-MS instrument is the more effective analytical technique for REE analysis in this context as compared to ICP-OES. Using certified reference materials, the results obtained by two acids digestion technique, acids digestion and sodium peroxide fusion in, CGL 111, CGL 124, and AMISO276, were compared to validate whether the methods are reliable. The acid digestion approach demonstrated greater effectiveness in comparison to the sodium peroxide fusion method. The recovery percentage (%) from ICP‒MS showed an excellent percentage yield (80 – 120%) compared to the ICP‒OES instrument (50 –120%). The ICP‒MS data indicate that all fly ash samples have a high concentration of LREEs and a lower concentration of HREEs. Excellent recovery was obtained by ICP‒MS in a developed microwave acid digestion method. The concentration of REEs obtained from ICP - MS and OES in fly ash samples ranged from 50 ppm to 200 ppm for light rare earth elements and 0.5 ppm to 20 ppm for heavy rare earth elements. The total REE (TREE) concentrations in all fly ash samples range from 400 ppm to 600 ppm
Determination of U and Th Radioisotopes in environmental samples by ICP-QMS
(University of the Witwatersrand, Johannesburg, 2023-07) Rikhotso, Xikhongelo Valentia; Sehata, James; Chimuka, Luke
Not Available
Evaluating the impact of land use activities in and around Lake Kariba on the presence and levels of anions and cations in the water body
(University of the Witwatersrand, Johannesburg, 2024-09) Monyai, Mokgaetji Andelina; Chimuka, Luke; Tutu, Hlanganani; Cukrowska, Ewa; Richards, Heidi L.
Huge seas, lakes, and rivers come to mind when we think of surface water. Surface water is vulnerable to water pollution, with consequential repercussions for the well-being of both human and aquatic environments. Furthermore, the diminishing levels of oxygen have a profound effect on the natural ecological equilibrium within river and lake ecosystems. Lake Kariba, situated in the Southern African region, is a vital freshwater ecosystem supporting local communities, wildlife, and regional economies. However, it faces threats from human activities and erratic weather. This study investigated the influence of land use activities in and around Lake Kariba on water composition and the concentration of anions and cations. The research employed a combination of field surveys and laboratory experiments to identify potential sources of ions. Sixty-nine (69) water samples (53 downstream and 16 upstream) were collected during different seasons in October 2021, July 2022 and April 2023. The Ion Chromatography, Inductively Coupled Plasma equipped with Optical Emission and Mass Spectroscopy detectors were used to concentrations of various anions (Fˉ, Clˉ, NO3ˉ, SO4 2ˉ, and PO4 3ˉ) and cations (Ca, K, Mg, Na, Si, Al, Cr, Fe, Mn, As, Cu, Ni, Ti, and Zn) respectively. Acidic water was notably observed upstream in two sampling areas, namely the Malasha and Kanzinze rivers. The Malasha River exhibited pH levels ranging from 3.71 to 4.81, while the Kanzinze River showed a pH of 6.01. The electrical conductivity (EC) for Malasha ranged from 1035 to 1484 µS/cm, whereas for Kanzinze, it measured 878.0 µS/cm. These areas exhibited significantly elevated levels of both anions and cations. In the Kanzinze River, the detected concentrations showed the following descending order: SO4 2ˉ> Clˉ > NO3ˉ> Fˉ> PO4 3ˉ (anions); Ca > Mg > Na > K > Si > Fe > Al > Zn > Cu > Mn > Ni > Cr > Ti > As (cations). Conversely, the Malasha River, exhibited the following order for anions: SO4 2ˉ > Clˉ > NO3 ˉ > Fˉ > PO4 3ˉ, and for cations: Ca > Fe > Mg > Na > Si > K > Al > Mn > Zn > Cr > Cu> Ni > Ti > As. The significant presence of SO4 2- and NO3 - indicates that human activities and agricultural practices in certain areas of Lake Kariba's catchment can have a considerable impact on the lake's water quality. Despite this, the corresponding Water Quality Index (WQI) indicated that the water quality from Kanzinze and Malasha rivers was unsuitable for drinking purposes. The findings revealed variations in ions concentration at different sampling points, with discernible patterns corresponding to specific land use types, such as mining in the upstream that elevated the levels of SO4 2- and some heavy metals and also NO3 - levels in the downstream due to commercial cage fish farming. Statistical analysis showed significant downstream variations (p < 0.05) in water chemistry parameters related to land use, while upstream areas exhibited no significant differences (p > 0.05). Water quality index ranged from 13.1 to 230.0, categorizing water quality from "excellent" to "very poor." The study underscores the complex interplay between land use activities and water chemistry in Lake Kariba, emphasizing downstream impacts. These findings contribute valuable insights for sustainable management and conservation efforts in the region, considering the dynamic nature of the ecosystem and potential threats posed by anthropogenic activities. Continuous monitoring and mitigation strategies are crucial to reserving the ecological balance of Lake Kariba and safeguarding the well-being of its surrounding communities and wildlife.