School of Physical Sciences (Phys-Sciences) Collections

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    Epoxidation of olefins over supported bimetallic catalysts using oxygen as oxidant and carbon dioxide as moderator
    (Makerere university, Kampala, Uganda, 2025) Yikii, Letibo Collins
    The conversion of olefins, into value-added products such as epoxides is of academic and industrial interest. The epoxides have various industrial applications although they are usually produced using environmentally unfriendly processes. This study presents a green approach for production of epoxides from readily available olefins catalyzed by a heterogeneous gold and silver-based polyoxometalate (Au-Ag@POM). The Au-Ag@POM catalyst was characterized using different techniques such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), Zetasizer, powder X-ray diffraction (PXRD), Transmission electron microscope (TEM) and Inductively coupled plasma-mass spectroscopy (ICP-MS). The catalyzed epoxidation process was carried out in a Schlenk line setup connected to round bottomed flasks through which oxygen and carbon dioxide where bubbled and the products were analyzed using GC-MS and GC-FID against biphenyl as the internal standard. The optimal reaction conditions were determined using response surface methodology with norbonene as the model substrate, tert-butyl hydroperoxide (TBHP) as the initiator, carbon dioxide (CO2) as promoter and oxygen (O2) as the oxidant. Under optimal condition of catalyst load (0.075 g), reaction time (24 hours), O2 (1 atm), CO2 pressure (1 atm), and reaction temperature (80 ℃), the process achieved a norbonene conversion of 71.5 %, norbonene oxide selectivity of 98.4 % and yield of 70.4 %. When the Au-Ag@POM catalyst was tested on other olefins such styrene, cyclooctene, cyclohexene and 1-hexene, the catalytic system produced the desired epoxide in 79.9 %, 41.9 %, 14.8 % and 14.4 % yield respectively. On the other hand, when that catalyst was tested in different solvent systems of acetonitrile, in absence of a solvent, 1,2-dichloroethane, acetonitrile 1,2-dichloroethane ratio of 1:15, the epoxide yields produced were 19.84 %, 17.2 %, 25.6 %, and 70.4 % respectively. The Au-Ag@POM catalyst efficiently produced epoxides under mild, with high selectivity and yields, especially for norbonene and styrene. It showed reusability over multiple cycles and adaptability to different olefins with variable reaction times. Future work should expand substrate scope, explore greener oxidants, and assess economic and environmental viability for industrial application.
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    Assessment of per- and polyfluoroalkyl substances in wastewater from selected wastewater treatment plants in Kampala and Jinja Cities, Uganda
    (Makerere University, 2025) Miiro, Ashirafu
    Over the past two decades, the rapid urbanization and industrialization in Uganda have generated wastewater containing emerging contaminants such as per- and polyfluoroalkyl substances (PFASs). This study assessed PFASs contamination from Bugolobi (Kampala) and Kirinya (Jinja) wastewater treatment plants (WWTPs) by analysing 80 influent and effluent samples for 15 PFASs using LC-MS/MS. Ten PFASs were detected, ranging from nondetectable levels (n.d) to 372.4 ng/L (mean: 20.94 ± 0.42 ng/L), levels that are comparable in magnitude to those reported for WWTPs in other African countries. At Bugolobi, influent concentrations ranged from n.d to 190.01 ng/L (mean: 60.85 ± 1.03 ng/L), while effluent concentrations varied from n.d to 372.4 ng/L (mean: 237.91 ± 7.06 ng/L). At Kirinya, levels ranged from n.d to 29.37 ng/L (mean: 17.58 ± 3.54 ng/L; influent) and n.d to 30.21 ng/L (mean: 7.79 ± 0.85 ng/L; effluent), dominated by short-chain compounds (PFBS, PFBA). Mass loadings were higher at Bugolobi (5,353.56 mg/day, 1.95 kg/year) than at Kirinya (93.62 mg/day, 0.034 kg/year). Despite discharge loads falling below permissible thresholds, the persistence and mobility of short-chain PFASs underscore the need for strict pollution control strategies. PFSAs exhibited higher removal (72.45% Bugolobi; 36.45% Kirinya) than PFCAs (-127.38% Bugolobi; -20.50% Kirinya), with negative efficiencies likely reflecting precursor transformation, desorption, or apparent concentration increases due to volume reduction rather than true production of PFASs. Bugolobi (~82.59%; aggregate) outperformed Kirinya (~25.19%) due to the advanced conventional treatment technology used. Ecological risk assessment revealed higher risks at lower trophic levels (many RQs >1; algae), at Bugolobi (impacting Daphnia and fish) compared to Kirinya (most RQs <1), potentially due to lower influx and partial mitigation by its pond-based system. These findings underscore WWTPs as point sources of PFASs that may find their way into neighbouring aquatic ecosystems, resulting in ecological risks to organisms.
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    Environmental effects of Gold mining in Burundi : a case study of Butihinda Commune, Muyinga Province, North Eastern Burundi
    (Makerere University, 2025) Nkeshimana, Ernest
    The study was conducted in Butihinda Commune, Northeastern Burundi, to evaluate the environmental effects of gold mining by assessing contamination levels of selected heavy metals in springs, streams, and soils proximal to mining waste and tailings. A total of 10 rock, 15 soil (seven from near the mining waste, the other seven from near the tailings stockpiles, and one baseline soil sample), and five water samples were collected during the wet season. Mapping, petrographic analysis, X-Ray Fluorescence (XRF), and Atomic Absorption Spectrometry (AAS) were used to establish the lithology, identify gold-associated minerals, and determine the Contamination Factor (CF) and Heavy Metal Pollution Index (HPI). Quartzite was the dominant lithology, composed mainly of quartz with minor sulphide minerals such as arsenopyrite, chalcopyrite, and pyrite. The X-Ray Fluorescence results showed elevated concentrations for Fe₂O₃ (16.24-39.47 wt.%), As₂O₃ (0.01-0.26 wt.%), Cr₂O₃ (0.05-0.09 wt.%), NiO (0.04 wt.%), CuO (0.01-0.18 wt.%), PbO (0.13 wt.%), and SiO₂ (64.90-97.28 wt.%) in most rock samples, reflecting both natural geochemical enrichment and hydrothermal recrystallization within shear zones. Soil samples near mining waste exhibited very high CF values for As (CF = 15.71) and Cu (CF = 7.42), while those near tailings had high CF values for Ni (CF = 18.59), As (CF = 58.57), and Cu (CF = 14.57), indicating strong anthropogenic input. Water quality assessment revealed that spring waters had an HPI of 1.92, classifying them as excellent potable water (HPI < 50), whereas the Rugomero stream recorded an HPI of 3,709.58, rendering it unsuitable for human consumption (HPI > 300) according to WHO (2017) standards. The extreme HPI in the stream was attributed to elevated concentrations of Fe (3.80-79.12 mg/L), As (0.040 mg/L), Cd (0.216 mg/L), and Hg (0.140 mg/L), mainly from artisanal gold extraction introducing these toxic elements in Rugomero stream. Overall, the findings demonstrate that Butihinda’s bedrock naturally contains high levels of Fe, As, Cu, Ni, and Cr due to its quartzite-sulphide mineral assemblage, while Hg contamination is primarily anthropogenic. Poor management of mining waste and tailings significantly exacerbates soil and water pollution in the Butihinda gold mining areas, posing environmental and public health concerns.
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    Characterization of quartzite rocks of the Congo-Nile Ridge in Mugongo-Ryarusera Area, North-West of Burundi
    (Makerere University, 2025) Nshimirimana, Benjamin
    The quartzite rocks from the Mugongo-Ryarusera are an important potential resource as they can directly be used industrially. The study aim was to evaluate the physical, petrographic and chemical properties of the Mugongo-Ryarusera quartzite for its value-added uses and industrial applications in glassmaking, ferrosilicon and silicon production. Forty samples were collected and subjected to various analyses. Colour analysis shows that all samples exhibit light colours (white, light grey and very light grey). The evaluation of the density shows an average of 2.64 g/ml which is close to the density value of 2.65 obtained using the specific gravity. The mean porosity value of quartzite rocks of the study area is 3.98 % whereas the particle size analysis shows that the rocks are mostly made up of coarse grains. Petrographic analysis also shows that the quartzite is mainly composed of coarse grains with some fine grains, anhedral to subhedral in many samples. This means that crystals are completely irregular and angular in shape which facilitates an effective melting process. Chemical analysis shows that the mean concentration of SiO2 is about 98.515% and the other oxides include Al₂O₃, Fe₂O₃, WO₃, K₂O, CuO, TiO2, SO₃ and CaO with a mean concentration of 0.681%, 0.2585%, 0.22%, 0.1715%, 0.008%, 0.0095%, 0.034% and 0.00075% respectively. The estimated volume of the outcrop found using GIS (ArcMap) is 11,287,895,590.675 m³ (11.3 km3). Considering the silica content, these rocks can be used for the production of all types of glass, except optical glass, as recommended by the American Ceramic Society and the National Bureau of Standards, as well as by Indian specifications. They can also be utilized for certain types of glass production, as outlined by the British Standard for Glass Sand used in glass manufacturing. Additionally, these quartzite rocks could be used for ferrosilicon production after reducing the average Al2O3 content from 0.6% to 0.4%. However, they are not suitable for silicon production without prior beneficiation. Once impurities are removed by reducing the ratios of trace elements, the quartzite can meet the specifications for all types of glass and silicon production.
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    Origin and hydrogeochemical characteristics of geothermal fluids from the Buranga Area, Western Uganda
    (Makerere University, 2025) Ayesiga, Ambrose
    Buranga area is located in the western branch of the East African Rift System. The geophysical and geological studies conducted in the area suggest that Buranga area is the most suitable area for geothermal development. However, the origin and hydrogeochemical characteristics of the geothermal fluids are poorly understood. The hydrochemical and stable isotope characteristics have been examined in this study to identify and determine the source of the main dissolved components and the hydrogeochemical characteristics of the geothermal fluids. Methods applied in the analysis of the origin and hydrogeochemical characteristics include isotope tracers, major ion ratios, geothermometers and graphical methods as well as hydrogeochemical simulations. Based on the δ18O and δ2H values, geothermal waters were found to be meteoric mixed with palaeo-waters. The gas isotope analysis indicates that CO2 mainly originates from the mantle. Based on the total dissolved solids (TDS) values, the Buranga hot springs are high salinity Na-Cl waters. The hydrogeochemical assessments indicate that Na+ and Cl- are derived from silicate dissolution that occurs within the sedimentary rock formation. The silicate dissolution is responsible for the concentration of Ca2+, Mg2+ and HCO3- while SO42- concentration results from oxidation of inorganic sulphides of volcanic origin. Further, K+ originates from the dissolution of silicate rocks with potassium-bearing minerals such as K-feldspar. The hydrogeochemical processes of the fluids suggest that most of the common cations and anions found in the Buranga hot spring waters originate from high-temperature water/rock interaction processes. The geothermal fluids are in full equilibrium with host rock. Therefore, the estimated reservoir temperature range between 160.8 ℃ to 163.9 ℃ determined using Na-K (1988) geothermometer was considered the most reliable. The reservoir temperatures determined using Quartz-vapour loss range from 116.6 to 125.5 ℃, Quartz-no vapour loss ranges from 118.2 to 128.7 ℃, K-Mg (1988) ranges from 177.0 to 190.7 ℃, Na-K (1979) ranges from 143.1 to 146.5 ℃, Na-K (1988) ranges from 160.8 to 163.9 ℃ and Na-K (1983b) ranges from 145.3 to 148.4 ℃. The inferred estimated circulation depth of the geothermal water is at 2,812 to 2,876 m below ground level.