Browsing 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
Compost-assisted phytoremediation of mine tailings and footprint areas using chrysopogon zizanioides (l) roberty enhanced with moringa leaf extract biostimulant in the Witwatersrand goldfields of South Africa: a sustainability initiative
(University of the Witwatersrand, Johannesburg, 2024) Mlalazi, Nkanyiso; Chimuka, Luke; Simatele, Mulala Danny
In the Witwatersrand goldfields of South Africa, mine tailings and footprint areas are significant environmental problems because they are major sources of toxic metals. These metals can leach into soils, and both surface and ground water, causing serious risks to human, animal, and plant life. In this study, the compost-assisted phytoremediation of tailing storage facilities (TSFs) and footprint soil using Chrysopogon zizanioides (vetiver grass) enhanced with moringa leaf extract (MLE) was investigated. A greenhouse experiment was conducted to identify the most favorable parameters, and was followed by a field study to test the optimized parameters under real-environment settings. For the greenhouse experiment, a 3×2×2 fully crossed factorial design was used to determine the optimum variables. Vetiver growth was assessed under three compost concentrations (0%, 30% and 60%), two types of MLE (laboratory extracted MLE and commercial MLE) and two application regimens (once a week and twice a week) were used. The biomass and metal concentrations in the vetiver grass roots and leaves were measured after sixteen weeks followed by a two-way ANOVA analysis and the post-hoc tests. All the vetiver that was planted in 0% compost died within four weeks regardless of the MLE treatment. Vetiver grass planted on the 60% compost amendments and sprayed with laboratory extracted MLE had the highest biomass production, followed by plants grown in 30% compost amendments and sprayed with commercial biostimulant. However, the heavy metal removal or uptake data by the plant was inconclusive, as most of the toxic metals were not removed by vetiver grass which was attributed to the effect of compost. Based on biomass data, the 30% compost amendment and commercial bio-stimulant was the ideal treatments for the phytoremediation of gold mine tailings using vetiver grass. Although metal accumulation by plants is one of the attributes considered in phytoremediation, it is not the most significant factor in the phytostabilisation process. Plant growth and biomass production are the most significant, therefore it is concluded that vetiver, MLE and compost can be used in the phytostabilisation of gold mine tailings, however reduction in compost may be considered in future to improve the accumulation of metals in the roots for improved results. Following the conclusion of the greenhouse study, a field study was conducted during the rainy season of 2021. Two field experiments were carried out concurrently at two sites: the footprint area (that was used as a rock dump) and the tailings storage facility (TSF 4). A split-plot design was used in this study. The experiment at each site assumed a 3×1×2 factorial design, with three levels of compost treatment (0%, 15% and 30%), 1 level of vetiver cultivar (Chrysopogon zizanioides), and 2 levels of MLE treatment (commercial MLE and tap water, both sprayed once a week). Three blocks measuring 1 m × 2 m, each with 20 holes filled with equal amounts of soil amended with the different compost levels were prepared in triplicates. A single vetiver grass slip was planted in each hole. The blocks were then divided into 2 sections, each with 10 holes, and commercial MLE was sprayed on one section, while only water was sprayed on the other section once a week. After sixteen weeks, three plants were harvested from each section and the number of leaves, leaf length, number of tillers, biomass for roots and leaves and element concentrations were measured. Data analysis was done using two-way ANOVA
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
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
The Impact of different levels of organic plant-based compost on the macro and micro elements, secondary metabolites and water soluble vitamins content of Moringa oleifera leaves
(University of the Witwatersrand, Johannesburg, 2023) Ngwenya, Nkazimulo; Risenga, Ida M.; Chimuka, Luke
Moringa oleifera leaves are a high source of phytochemicals and nutrients inclusive of macro and micro elements, secondary metabolites and water-soluble vitamins. All the M. oleifera plant parts inclusive of its leaves have been widely utilised for nutritional and/ medicinal properties because of its high levels of minerals and phytochemicals. Studies have been conducted targeting the improvement of the quantity of M. oleifera nutrient content. However, with increased consumer awareness of high quality organic, consumer and environmentally safe products there is increased need to improve the quality of M. oleifera products. One of the major factors impacting the quality and quantity of M. oleifera leaf nutrients is cultivation practices. Particularly soil amendments applied to improve plant biomass have also been found to significantly improve nutrient content of M. oleifera leaves. However, the popularly used soil amendments which are in the form of synthetic fertilisers or animal based compost have raised environmental and product safety concerns. They contain, among other contaminants, traces of heavy metals and other toxins which are harmful to both the environment and consumers of the produce. Producers of herbal plants such as M. oleifera are looking for sustainable, environmental safe ways of improving the quantity and quality of the produce. Application of organic plant based compost was therefore investigated as a potential soil amendment source in improving M. oleifera nutrients in an organic, clean sustainable way, and thus improving the quality of the produce. The use of plant based compost to improve the nutritional content of M. oleifera grown in South Africa was reported in this thesis. The primary objective of the study was to assess the impact of the plant-based organic compost on the macro and micro elements composition, secondary metabolite accumulation and distribution and water soluble vitamins content in M. oleifera leaves. This work is novel and worth exploring as it seeks to investigate for the first time the correlation between the use of plant-based organic compost and quality improvement in terms of nutrient content of M. oleifera leaf biomass. Furthermore, this research is the first of its kind which looks at the impact of compost on the nutritional content encompassing, macro and micro nutrients, secondary metabolites and water soluble vitamins in M. oleifera grown in South Africa. In addition, the developed and validated high performance liquid chromatography (HPLC) method for the simultaneous quantification of five B vitamins was successfully used in the identification and quantification of the vitamins. Clay soil and M. oleifera seeds used in the study were obtained from the M. oleifera community farm in Hammanskraal, Gauteng, South Africa. The clay soil was amended with plant-based organic compost purchased from the local nursery store. The amendments achieved four treatment levels namely 15 % compost / soil amendment, 30 % compost / soil amendment, 45 % compost / soil amendment and 60 % compost / soil amendment. Moringa oleifera seeds used were obtained from the same farm. Plant samples were grown in the School of Animal, Plant and Environmental Sciences (APES), University of the Witwatersrand, greenhouse under ambient temperatures. Harvesting of the leaf biomass was done after six months and nutrient analysis was carried out. Analytical techniques such as Spectroscopy and Chromatography were used for the nutrient analysis. Presence and quantity of macro and micro elements in the soil and leaves was analysed using the Inductively Coupled Plasma Optical Emission spectroscopy (ICP-OES). Whilst, the Ultra high-performance liquid chromatography coupled with electrospray ionization quadrupole time-of-flight mass spectrometry (UHPLC-ESI-QTOF-MS) was used to determine plant metabolites, and for the quantification of water-soluble vitamins by coupling it with the diode array detector (DAD). The nutrient analysis revealed that the use of organic plant-based compost for the amendment of clay soil improved the quality of the soil and M. oleifera leaves harvested from each soil amendment. The addition of the organic plant-based compost improved the macro and micro nutrients. Comparison of the different compost levels revealed that addition of plant based compost increased the bioavailability of macro and micro nutrients in the soil and increased their accumulation in M. oleifera leaves. Metabolic fingerprinting of M. oleifera leaf samples using UHPLC-ESI-QTOF-MS followed by untargeted compound analysis exposed variation in the identified metabolites. Further use of multivariate analysis in the form of PCA clustered the samples into five distinct clusters indicating diversity in the distribution of secondary metabolite as influenced by the addition of plant-based compost to the soil. The developed HPLC method was suitable for the simultaneous quantification of five B vitamins based on the low LOD and LOQ values, recovery of 97.8- 99.58% and good linearity. Application of the validated method revealed that, the addition of plant based compost significantly improved the quantity of the tested vitamins (Vitamin B1, B2, B3, B6 and B9). The 30% plant-based organic compost and clay soil combination was identified and recommended as the best compost-soil combination in improving nutrients in M. oleifera leaf biomass. It had the highest level of macro and micro nutrients. Leaves harvested from this soil/compost combination had higher concentration of Ca (45 042.5 mg/Kg), Mg (17 430 mg/Kg), P (8802. 5 mg/Kg). In addition leaves, harvested from 30% compost treatment exhibited the highest number of identified secondary metabolites and had the highest concentration of two of the five tested water soluble vitamins. This knowledge will make great contribution in the M. oleifera industry in South Africa and worldwide particularly for farmers who are into organic M. oleifera production.