School of Chemistry (ETDs)

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Browsing School of Chemistry (ETDs) by Author "Chimuka, Luke"

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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) Michael Rampfumedzi, Tshilidzi; 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
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    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
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    Quantitative analysis of gold in low-grade tailings from different matrices, coupled with a study into the associated uncertainties
    (University of the Witwatersrand, Johannesburg, 2023) Mashale, Kedibone Nicholine; Tshilongo, James; Chimuka, Luke
    Gold is one of the precious group elements that is used for various purposes, such as jewellery, auto catalysts and as a form of investment. Various countries have gold reserves, with South Africa being the leading gold producer between 1980 and 2007. However, as of 2022, it is ranked as the eighth largest producer of gold, contributing 3% to the global contribution. The majority of gold is mainly mined from the Witwatersrand Basin in Johannesburg. It is well known that mining has been ongoing for decades, which means that a significant amount of land has been mined across the country. During gold mining, a large proportion of the ore material from which the gold is extracted is waste, together with the chemicals that were used, and this waste is termed mine tailings. This implies that based on the years that gold mining has occurred for and the depth of mining, a significant amount of the tailings have been deposited into free land around the mines, some of which are close to communities. The tailings consist of traces of gold that were left due to inefficient extraction processes and other components, such as base metals. The disadvantage of this is that due to the other chemical composition of these tailings, they have the potential to be dangerous to the environment. Some tailings contain minerals such as jarosite (KFe2(SO4)2(OH)6) that cause acid mine drainage, while heavy metals such as lead, mercury, arsenic and chromium can leach into surface and ground waters, causing pollution. Furthermore, they pose a danger if the dams that they are stored in collapse, which was recently witnessed in South Africa. Because of these factors, there have been various advances made towards the beneficiation of tailings, such as utilizing them to make glass or bricks for construction. A major advancement was the reprocessing of these mine tailings to recover or extract the remaining gold, which benefits both the environment and the mining houses. Therefore, in a move to support this initiative, scientists have taken to the laboratory to develop new or optimize existing methods for the extraction and quantification of gold, which is expected to be of a low grade over time. Various methods can be used for the quantification of gold, including the conventional fire assay, wet and dry chlorination and acid digestion. Most of these are suitable for medium- to high-grade gold ores but are known to experience challenges in regard to low-grade ores. The aim of this research was therefore to find the optimum method for the quantification of gold from mine tailings emanating from the Ventersdorp Contact Reef (VCR) and Barberton Greenstone Belt (GBS). Subsequent to chemical analysis, the samples were characterized for mineralogy using X-ray diffraction (XRD) and Brunauer‒Emmett‒Teller (BET) surface area