Browsing by Author "Babedi, Lebogang"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    A Fundamental study on the effects of cation substitution on the molecular chemistry and surface reactivity of sphalerite
    (Stellenbosch : Stellenbosch University, 2018-12) Babedi, Lebogang; Von der Heyden, Bjorn; Tadie, Margreth; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Sphalerite exhibits multiple flotation responses because of its intricate mineral chemistry which arises from its ability to incorporate different metal impurities. Historical work has focussed largely on the influences of Fe impurities on the flotation behaviour of sphalerite. This has created a broad knowledge gap related to the influence of associated metal impurities (e.g. Cd, Co etc.) on the structure and surface chemistry and the consequent flotation response of sphalerite. The current study seeks to address the knowledge gap using sets of analytical techniques (XRD, Raman spectroscopy, UV-vis and zeta potential) to build a molecular-level link between the crystal structure distortions, surface characteristics, and electronic structure alteration. These properties are related to the ultimate flotation response of synthetic sphalerite doped with variable amounts (0-4 wt.%) of Cd, Co and Fe. Sets of impurity (Cd, Co, Fe) bearing sphalerite samples were synthesised using a dry experimental method to ensure a controlled sphalerite composition when evaluating the influence of individual cation substitutions. The structural evaluations with XRD revealed that each metal impurity induced lattice distortion, as reflected by the varied unit cell constants with increasing impurity concentration. The magnitude of the lattice distortions can be correlated with impurity concentration and ionic size of each metal impurity. Raman spectroscopy showed that the different metal impurities induce new surface features in the form of an impurity mode, the position of which reflects the chemical nature of the metal impurity bond formed within sphalerite molecular cluster. The stronger bonds (Co and Fe) require higher vibrational energies thus occur at higher wavenumber (Fe 300 cm-1, Co 303 cm-1) compared to the weaker bonds of Cd (295 cm-1). The intensity ratios between the Zn-S mode (TO) and the impurity mode can be correlated (r2 = 0.9403 Cd, r2 = 0.7915 Fe, r2 = 0.961 Co) as a function of increases in impurity concentration. My UV-Vis data indicates that the variations in the band gap of sphalerite changed as a function of cation substitution (Cd>Fe>Co), and these were found to correlate well (r2 = 0.99) with the measured position of the Raman impurity mode of the corresponding cation substituent. The influence of each individual cation on the surface charge, Cu-activation and collector adsorption was assessed using electro-kinetic techniques (zeta potential), which provided valuable information on the surface reactivity of impurity bearing sphalerite. The study illustrates different electro kinetic characteristics of sphalerite depending on the nature of the substituting metal, which resulted in the formation of multiple surface products. The zeta potential responses varied between the different trace element substituted sphalerite reflecting differences in their nucleophilic and electrophilic properties. The results presented herein thus provide a systematic correlation between the structure and surface chemistry and illustrate how such changes manifest to the variation to the electronic structure and consequently the flotation response. This illustrates that maximum recovery of zinc can only be achieved through multidisciplinary study and fundamental understanding of the effects of cation substitution on mineral structure and surface chemistry, the latter necessarily affecting the flotation response.
  • Thumbnail Image
    Item
    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.