Doctoral Degrees (Earth Sciences)

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Browsing Doctoral Degrees (Earth Sciences) by Author "Babedi, Lebogang"

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    An investigation of the molecular-level mineral chemistry of metal-bearing pyrite and its electrochemical behaviour under flotation related conditions
    (Stellenbosch : Stellenbosch University, 2023-03) Babedi, Lebogang; Von der Heyden, Bjorn; Tadie, M.; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Pyrite (FeS₂) is an iron disulphide mineral found in hydrothermal ore deposits, including gold ore deposits, each having its unique physicochemical conditions (e.g., pH, temperature, salinity) at the emplacement site. Pyrite can incorporate several trace elements into lattice sites, making it an n- or p-type semiconductor in nature. Due to this semiconducting variance, numerous investigations have observed diverse flotation responses for pyrite from different ore sources. This study investigates how lattice-incorporated metals (As, Au, Co, and Ni) affect electronic structure and flotation collector (xanthate) response in an alkaline media. This is done by compiling a global dataset of pyrite trace element data to understand its trace element signatures and then utilizing these signatures to guide chemical vapour transport synthesis of high-purity crystals. This work uses X-ray photoelectron spectroscopy and rest potential analysis to investigate the impact of metal geochemical type and concentration on pyrite valence bands and reactivity. Valence band assessments demonstrate that metals in the pyrite lattice shift orbital contributions and Fermi levels depending on geochemical origin and concentration. The metal's nature dictates whether it effects valence band contributions around the Fermi level (Au, Co, Ni) or deeper ones (As). Pyrite's changing chemistry affects its oxidation and interaction with xanthate collector under alkaline conditions. Pyrites (pure, Co, Ni, and Au + Co-bearing) are noble and do not induce mineral surface oxidation, while As- bearing pyrite is the least noble and promotes oxidation. Noble pyrites (pure, Co, and Ni) associated with n-type semiconducting have a weaker collector interaction than the least noble (As-bearing) associated with p-type. The lack of dixanthogen on As-bearing pyrite compared to Co- and Ni-bearing pyrite shows that a greater collector-mineral interaction does not oxidize the collector on the mineral surface. Dixanthogen is present at low Ni concentrations but absent at higher concentrations, showing that collector oxidation on the mineral surface depends on metal concentration. Reactivity and electronic structural trends are correlated. The potency of collector-mineral interactions and the size of Fermi level variations as a function of metal concentration and geochemical nature are comparable. This thesis shows how synthetic minerals grown experimentally may answer important questions regarding the molecular chemistry and reactivity of sulphide minerals like pyrite. This study shows how metals impact pyrite's valence band contributions and how they affect the collector interaction. The behavior of pyrite with a xanthate collector gives important knowledge that may be used to adjust flotation collectors to best show minerals' selectivity and reactivity independent of their semiconducting qualities controlled by chemistry.