http://hdl.handle.net/10386/26 2026-04-17T10:58:43Z http://hdl.handle.net/10386/5407 Geology, mineralogy and the occurrence of rare earth elements in the coal deposit at the Uitkomst Colliery (Utrecht Coalfield), Kwazulu-Natal, South Africa Maseko, Sibusiso The Utrecht Coalfield is one of the coalfields of the Main Karoo Basin, which is currently underexplored and there is no information regarding the REEs concentration. Before extracting the REEs, it is significant to examine the distribution and concentration of REEs within the host rock, in this case, coal. The purpose of the study is to explore the mineralogical and geochemical characteristics and occurrence of REEs in the coal deposits at the Utrecht Coalfield (Uitkomst Colliery). Seventeen samples from three different seams (Gus, Alfred, and Fritz) were analysed using petrography, ultimate analysis, proximate analysis, and X-ray diffraction (XRD) analysis. The REEs concentration in the samples was determined by inductively coupled plasma (ICP-MS) techniques, whereas scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) as a direct method and Pearson’s correlation as an indirect method was used to determine the mode of occurrence of the REEs in the samples from the Utrecht Coalfield. The Vryheid Formation in the Utrecht Coalfield consists of sandstones, siltstones, shale, and mudstone, with minor coal seams. The average thickness of the Eland, Fritz, Alfred, and Gus seams is 0.30 m, 0.21 m, 1.21 m, 1.12 m, and 1.26 m, respectively. The samples were dominantly inertinite rich with lesser liptinite and vitrinite macerals and were categorised as medium-rank- C. The Gus, Alfred and Fritz seams had an average ash content of 14.9%, 29.9% and 18.4%, respectively. Few of the samples were low sulphur coals whereas others were medium sulphur coals. The dominant minerals detected by the XRD are quartz and kaolinite with lesser pyrite. The sum concentration of REEs ranged from 23.15 to 173.50 ppm, with an average of 101.43 ppm. The average REEs concentration for the Gus Seam was 79.47 ppm, 120.79 ppm for the Alfred seam, and 137.63 ppm for the Fritz seam. The samples had REEs concentrations higher than that of Worlds and USA Coals except for samples CMB-L1, CB2-L1, CB1-L2, CB2-L2, and CB2-S1. Furthermore, samples CB1-L1, CMB-D, JCBH08B, and JCBH20 had REEs concentrations higher than that of Chinese Coals. The Pearsons’ correlation indicated a mixed inorganic-organic affinity of REEs as shown by the positive correlation. The SEM-EDS analysis in the samples revealed that the REEs have inorganic and organic affinities. The coal-forming environment was weakly reducing to oxidizing, favouring REEs enrichment. The provenance is predominantly a felsic source region, likely a mixture of Archean and post-Archean rocks, including sedimentary sources with granitic, tholeiitic, and alkalic basalt. The Utrecht Coalfield is not promising for REEs extraction. Thesis (M.Sc. (Geology)) -- University of Limpopo, 2025 2025-01-01T00:00:00Z http://hdl.handle.net/10386/5204 Computational and experimental studies of transition metal carbonate precursors as cathodes for lithium-ion batteries Morukuladi, Mogahabo Tebogo This study investigates the layered oxide cathode with NMC-type LiNixMnyCozO2 as the alternative cathode material for lithium ion batteries. This material has attracted the researcher’s interest as alternative cathode material due to its low cost and less toxicity as compared to the most widely commercialised lithium cobalt oxide (LCO). Lithium nickel manganese cobalt oxide (often abbreviated as NMC) is a type of cathode material used in lithium-ion batteries. It's a popular choice because it offers a balance of high energy density, good cycling stability and relatively low cost compared to other cathode materials. In this study we investigate the stability properties of Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2, respectively. In particular, we focus on the manganese rich compositions and minor amounts of nickel and cobalt. We further doped both system (Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2) with fluorine, titanium, niobium and chromium to check if their contributions could improve or disprove the behaviour of Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2 materials. Firstly, the structural, electronic, mechanical and vibrational properties of Ni0.3Mn0.5Co0.2CO3, Ni0.3Mn0.5Co0.2O2 and their doped systems have been calculated using the density functional theory employing the pseudo-potential plane-wave approach within the local gradient approximation with the Hubbard parameter U for strongly correlated transition metals. The structural property calculations included the equilibrium lattice parameters, density and energy of formations while electronic properties included the partial density of states (PDOS), total density of states (TDOS) and band structures for all the systems. Furthermore, mechanical properties investigated the elastic constants, Pugh ratio and anisotropy while vibrational properties investigates the phonon dispersion curves for Ni0.3Mn0.5Co0.2CO3, Ni0.3Mn0.5Co0.2O2 and their doped systems. The calculated lattice parameters and energy of formation could be used for benchmarking in the future since no similar work was found in literature for comparison. Moreover, the calculated energy of formations revealed the relatively low and negative values for all the systems, suggesting thermodynamic stability. With the band structures, we found that Ni0.3Mn0.5Co0.2CO3 and Ni0.3Mn0.5Co0.2O2 structures were semiconductors with a direct gap of 0.004 eV and 0.036 eV with their doped systems also indicating metallic characteristics. Moreover, the partial density of states for our materials and their doped systems were also found to be metallic as there was no energy band gap observed at the Fermi line. Furthermore, the elastic constants revealed that all our systems recorded 21 independent elastic constants which falls within the triclinic lattice systems. For a material to be considered mechanically stable within the triclinic system, there are conditions to be satisfied, hence Ni0.3Mn0.5Co0.2CO3 satisfied all the conditions suggesting mechanical stability while Ni0.3Mn0.5Co0.2O2 did not satisfy all the conditions implying mechanical instability. The phonon dispersion curves revealed that Ni0.3Mn0.5Co0.2CO3 was vibrationally stable while Ni0.3Mn0.5Co0.2O2 was vibrationally unstable due to the presence of negative vibrations along the Brillouin zone. Furthermore, the phonon dispersion curves for doped systems revealed that some are vibrationally stable while some are vibrationally unstable. Secondly, since the study focuses on manganese rich systems, cluster expansion technique was used to generate phases in the manganese rich side. From the results, various phases with varied concentrations and symmetries were produced by the ground-state phase diagram. The accuracy of new structures during cluster expansion fitting is indicated by the cross validation score (CVs) for all of the generated new structures being less than 5meV per active atom position. Since all of the developed structures have CVs below 5meV, this indicate that our calculations were valid and the newly generated structures will work realistically. From the phase diagram, we noticed that all the predicted phases are in the negative energy of formations side (miscible constituent) which indicate thermodynamic stability. Moreover, of all the phases generated within the diagram, only phases in the manganese rich side were explored by using first principles calculations to further confirm their stability properties by determining their structural, electronic, mechanical and vibrational properties. The energy of formation results revealed that all the phases are thermodynamically stable while electronic properties revealed metallic characteristic for all the phases in the Mn-rich side. For mechanical properties, we found that few phases did not satisfy the triclinic conditions which implies mechanical instability while other phases were found to satisfy the conditions, indicating mechanical stability. Lastly, the carbonate co-precipitation method was used in this study to synthesize the transition metal carbonate precursors using a 4L stirred tank reactor (CSTR) under steady state circumstances. We produced Ni0.28Mn0.53Co0.19CO3 and Ni0.17Mn0.67Co0.17CO3 which was later lithiated to form LiNi0.33Mn0.53Co0.14O2 and LiNi0.17Mn0.67Co0.17O2 as our layered cathodes. Both the lithiated samples were further characterized for thermogravimetric analysis, x-ray diffractions, morphologies, EDX and XRF. Thermogravimetric analysis revealed thermodynamic stability for both samples while XRD’s also managed to produce the most crystalline peak at 003 indexing. The scanning electron microscopy was also tested to determine the particle size and distribution for both samples and the results revealed a homogeneous particle distribution in each sample. We further collaborated with University of Kent for the usage of the synchrotron beam of the Diamond light source to determine the effect of fluorination on our NMC samples. In particular, we wanted to check if fluorination reduces or increases the oxidation states of metals within our samples and results revealed that fluorination does not change the oxidation state of our samples. Thesis (Ph.D. (Physics)) -- University of Limpopo, 2025 2025-01-01T00:00:00Z http://hdl.handle.net/10386/5200 Computational study on interaction of heterocyclic, triazine and thionocarbamate collectors with pentlandite (Fe,Ni)9S8 mineral surfaces Zavala, Nontobeko Nondumiso Due to the demands of nickel, substantial effort has been put into the recovery of pentlandite. Enhancing the separation of pentlandite minerals from the gangue in the extracted ores remains a problem. Pentlandite is the major source of nickel as well as a major carrier of platinum group elements (PGEs). Nickel is utilised in a wide range of industrial applications such as stainless steel, coinage, and rechargeable batteries. There is a need for selective collectors that can supplement the available xanthates, dithiophosphate and dithiocarbamate collectors for recovery of pentlandite and nickel ores. This study adopted density functional theory (DFT) with dispersion correction by Grimme to investigate the interaction with selective thiol collectors: S-allyl-N-diethyl-dithiocarbamate (ADEDTC), O-isopropyl-N-diethyl-thionocarbamate (IPDETC), Sodium mercaptobenzothiazole (MBT) and Sodium-2,6-Dithio-4-Butylamino-1,3,5-Triazine (SDTBAT) collectors. The bulk Fe5Ni4S8 pentlandite was previously determined as the most stable compound from cluster expansion which was tetragonal with space group of P42/nmc. The optimised structure had lattice dimensions of a = b = 7.020 Å and c = 9.930 Å. The XRD was used to predict the most dominant surface which were found as (111), (211), (224), and (311) surface, with the (311) surface displaying the highest intensity. These were cleaved from the relaxed bulk structure and their surface energies were computed as 1.622 J/m2 (111 surface) 1.843 J/m2 (211 surface) 1.844 J/m2 (224 surface) and 1.484 J/m2 (311 surface). The most stable surface was found to be the (311) surface which was in agreement with the experimental X-ray diffraction pattern. The adsorptions were performed on Ni and Fe atoms of Fe5Ni4S8 (311) surface as preferred adsorptions sites. It was found that ADEDTC gave the most exothermic adsorption energy of –460.581 kJ/mol compared to MBTNa (–249.59 kJ/mol), IPDETC (–161.012 kJ/mol) and SDTBAT (–352.481 kJ/mol). Most significantly these collectors preferred to bind on Ni atoms than Fe atoms, which indicated their selectivity towards the pentlandite mineral. These suggested that ADEDTC was the best co-collector compared to IPDETC, SDTBAT and MBTNa collectors for utilisation in the flotation of pentlandite mineral. The adsorption strength decreasing in order: ADEDTC > MBTNa > SDTBAT > IPDETC. This suggests that the ADEDTC collector has the potential to replace and/or be a co-collector with the widely used collectors in the recovery of pentlandite minerals. Thesis (M. Sc. (Physics)) -- University of Limpopo, 2025 2025-01-01T00:00:00Z http://hdl.handle.net/10386/5191 Modification and adsorption of triazine collectors of sperrylite (PtAs2), platarsite (PtAsS) and palladoarsenide (Pd2As) mineral surfaces Nemutudi, Bradley There are still difficulties in separating valuable minerals from gangue minerals, especially when it comes to extracting arsenides, or platinum group minerals (PGMs), like “sperrylite, platarsite and palladoarsenide, which are mostly found in the Platreef Bushveld Complex. According to reports, the flotation of PGMs resulted in low recovery when using traditional xanthates. This was owed to the report that the arsenides PGMs minerals are not easy to float, and therefore new collectors are required to enhance the recovery and separation of hard to float arsenide minerals. In minerals flotation, the pH effect is crucial in maximizing the recovery of PGMs. The study on the performance of and sodium hydroxide (NaOH) molecule and normal butyl xanthate (NBX), normal butyl dithiocarbamate (NBDTC) and the novel 2,6- dithio-4-butylamino-1,3,5-triazine (DTBAT) collectors onto sperrylite, platarsite and palladoarsenide mineral surfaces were performed using computational density functional theory with dispersion correction (DFT-D3) and experimental (microcalorimetry and microflotation) approaches. Experimentally, microcalorimetry and microflotation tests were conducted using pure synthesised sperrylite mineral. The collectors were adsorbed computationally on dry sperrylite, platarsite and palladoarsenide surfaces under neutral, alkaline and acidic conditions. Sodium hydroxide adsorption was also performed to determine the adsorption capacity with the sperrylite, platarsite and palladoarsenide (100) surfaces compared to the collector adsorptions. To compare the structural properties of each PtAs2, PtAsS and Pd2As structures, geometry optimisations were carried out. The bulk PtAs2 benefited from a hydrostatic pressure of 2.0 GPa, which resulted in lattice parameters of a = 5.967 Å and a band gap of 0.264 eV, which were in agreement with experiments. At 14.0 GPa, the lattice parameter a = 5.787 Å was determined for PtAsS, which agreed well with the experimental findings. For computational aspect, the PtAs2, PtAsS and Pd2As models were evaluated using the most stable surface plane of (100), which was found to give the lowest surface energy compared to the other surface planes. This was also complemented by the plotted X-ray diffraction (XRD), where the (200) plane for PtAs2 and PtAsS and the (300) plane for Pd2As, which are similar to the (100) plane/surface, were displayed the most dominant planes due to the highest intensity.” The computed surface energies for (100) PtAs2, PtAsS and Pd2As were 1.05 J/m2, 0.56 J/m2 and 1.46 J/m2, respectively. Several adsorption sites were considered in order to identify the most stable exothermic preferred site. “It was observed that the SNBX, SNBDTC and SDTBAT collectors preferred to adsorb on the surface Pt and As atoms through S atoms on sperrylite and platarsite, while on palladoarsenide they adsorbed on the 3-coordinated Pd atoms through S and N atoms.” For dry sperrylite surface under neutral and alkaline conditions the collectors preferred a Pt-bidentate (SNBX and SNBDTC) and Pt-tridentate (SDTBAT) adsorption modes. Under acidic conditions all the three collectors favoured a Pt-monodentate adsorption mode. The adsorption energies followed the decreasing order and therefore decreasing adsorption strength as: SDTBAT > SNBDTC > SNBX, indicating that the SDTBAT had strong exothermic adsorption at neutral conditions. In alkaline conditions, the SNBX gave the most exothermic adsorption energy and the trend followed the decreasing order as: SNBX > SNBDTC > SDTBAT. The HNBDTC gave strong adsorption energy under acidic condition and the order decreased as: HNBDTC > HDTBAT > HNBX. Microcalorimetry and microflotation techniques were used to supplement the adsorption of sperrylite mineral. It was noted that the neutral condition was in agreement with the microcalorimetry (pH = 7) heats of adsorption where SDTBAT exhibited stronger adsorption. The SNBX provided the best flotation performance when compared to the SNBDTC and SDTBAT collectors, according to the microflotation recoveries conducted under alkaline conditions (pH = 9). This was in agreement with the prediction of the computational simulation. The microflotation recoveries under acidic conditions (pH = 4) showed that the HNBDTC had higher recoveries than HNBX and HDTBAT, which compared well with computational-acidic adsorptions on dry sperrylite surface. “Therefore computational-acidic and microflotation deliver similar outcomes and it was depicted that sperrylite floats better under acidic conditions using dithiocarbamate collector with higher recoveries of 41.46%. The adsorption energies on dry platarsite surface under neutral conditions for SNBX and SDTBAT collectors preferred to adsorb in a Pt-monodentate adsorption mode between the collector S atoms on surface Pt atom. The SNBDTC was found to desorb from the surface. Under alkaline conditions, the adsorption of SNBX, SNBDTC and SDTBAT preferred to form in a Pt-monodentate bonding mode. The HNBDTC preferred a Pt-monodentate bonding mode, whereas the S and N atoms of HNBX and HDTBAT desorbed from the surface. It was found that in both neutral and acidic conditions, the adsorption energies followed the decreasing order as: DTBAT > NBDTC > NBX. This suggested that DTBAT had strong affinity with the surface and therefore demonstrated that it could be utilised preferably under neutral and acidic conditions giving better performance than the NBX and NBDTC collectors. The SNBX gave strong adsorption energy under alkaline conditions on dry platarsite (100) surface, and the trend followed as: SNBX > SNBDTC > SDTBAT. This indicated that the SNBX may have better performance in improving the flotation of platarsite mineral surface at alkaline conditions. For palladoarsenide mineral surface, the collectors were observed to favour a Pd-bidentate (NBX and NBDTC) and a Pd-tridentate (DTBAT) adsorption mode under neutral, alkaline and acidic conditions. “The adsorption energies showed that SDTBAT adsorbed stronger under neutral conditions and the adsorption trend followed the decreasing order as: SDTBAT > SNBDTC > SNBX. Most significantly, it was found that the SDTBAT had strong adsorption than the SNBX and SNBDTC, suggesting a potential substitute of SNBX and SNBDTC collectors under neutral conditions. Under alkaline conditions, the SNBX gave the most exothermic adsorption energies and the trend followed the decreasing order as: SNBX > SNBDTC > SDTBAT. According to these findings, SNBX is a highly effective collector that can enhance palladoarsenide mineral recovery in alkaline environment. Under acidic conditions, the collector adsorption energies decreased in the order: HNBDTC > HNBX > HDTBAT, and clearly the HNBDTC showed the strongest exothermic adsorption. It was apparent that the HNBDTC collector displayed an ability to improve the palladoarsenide mineral recovery in acidic condition.” A variety of arsenide minerals may benefit from the flotation collectors that are designed based on the adsorption of xanthate, DTC, and s-triazine as collectors on PtAs2, PtAsS, and Pd2As. It was evident that under various pH conditions, the collectors NBX, NBDTC and DTBAT showed the capacity to enhance the recovery of sperrylite, platarsite and palladoarsenide mineral surface. Sperrylite and palladoarsenide minerals would be best floated using s-triazine under neutral, xanthate under alkaline and DTC under acidic conditions, while platarsite would be floated using s-triazine under neutral and acidic conditions and xanthate under alkaline. This demonstrated that the xanthate, DTC and s-triazine had the ability to improve the recovery of sperrylite, platarsite and palladoarsenide under different pH conditions. Interestingly, it was noted that the adsorption were more exothermic on palladoarsenide compared to the platarsite and sperrylite mineral surface. This revealed how the minerals recovered in various ways during flotation. It is clear that palladoarsenide had good collector interactions compared to sperrylite and platarsite. These findings thus paved a way for design of novel collectors for sperrylite, platarsite, palladoarsenide and other various chalcogenide minerals in order to improve their recovery. Thesis (Ph.D. (Physics)) -- University of Limpopo, 2025 2025-01-01T00:00:00Z