Masters Degrees (Chemical Engineering)

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Browsing Masters Degrees (Chemical Engineering) by Author "Augustyn, Andre Rossouw"

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    An initial investigation into the application of surfactin, a biosurfactant, as an alternative desulphurisation agent, for the prevention of acid mine drainage, via froth flotation
    (Stellenbosch : Stellenbosch University, 2020-12) Augustyn, Andre Rossouw; Tadie, Margreth; Pott, Robert William M.
    ENGLISH ABSTRACT: Coal mining plays a significant part in the South African economy. One of the largest problems associated with coal mining is acid mine drainage (AMD), which is produced through the oxidation of sulphide-minerals, in the presence of water and a suitable oxidant. AMD is toxic to the surrounding environment and causes lasting damage. Froth flotation is a viable option for the desulphurisation of coal tailings which cause AMD. Global trends towards more sustainable and environmentally friendly surfactants have led to the investigation of biosurfactants as replacements for synthetic surfactants used in flotation. Surfactin, a microbial biosurfactant, may be promising as a desulphurisation agent, due to its molecular structure and the anionic nature of its functional groups, indicating the potential for preferential chelation of pyrite. The aim of this research was to determine the effectiveness of surfactin as a collector in desulphurisation of coal through froth flotation, as a mitigation strategy for the formation of acid mine drainage. The first objective was achieved using surface tension to determine the critical micelle concentration of the surfactin sample, found to be 4.5 mg/L, to determine a practical surfactin concentration range, which was used for further experimentation. Surfactin adsorption on both the surface of coal and pyrite was confirmed through zeta potential and FTIR analysis and indicated a greater interaction with both the surface of coal and pyrite in the neutral and alkaline pH ranges, signifying that ionisation of the surfactin carboxylic groups plays a significant role in adsorption. The attachment mechanism of surfactin to the surface of coal was confirmed to be hydrophobic physisorption between the aliphatic functional groups of surfactin molecules and the carbonaceous surface functional groups of coal, but results indicated that there was a limited number of surfactin adsorption sites. In contrast, the attachment mechanism of surfactin onto the surface of pyrite was chemisorption to either Fe-hydroxide sites or through interaction of the amide groups on surfactin with sulphur on the pyrite surface. Surfactin demonstrated a cleaning effect on both the surface of coal and pyrite, which may contribute to the increase in hydrophobicity. Surfactin acted as a collector of both coal and pyrite at most operating conditions, however, there were instances at which surfactin had little to no effect on the hydrophobicity of coal or pyrite, and in the case of coal, surfactin acted as a depressant at pH 8. Generally, surfactin was a more effective collector of coal in the acidic pH range, and of pyrite in the alkaline pH range. This differential activity allows for the preferential flotation of either coal or pyrite. The final objective was to determine the coal desulphurisation system operating conditions, and based on this preliminary study, those were determined to be at pH 10 and 5 mg/L surfactin concentration. This provided a 56.2% pyrite recovery and 47.8 % coal recovery. As a preliminary study, this research achieved its aim and indicated that surfactin shows great potential as an effective agent for the desulphurisation of coal through froth flotation.