Sulfide Flotation in Complexing Media and Bacterial Degradation of the CU(II)-TETA Complex in an Aqueous Environment
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Production of flotation concentrates from ores require a variety of reagents that include complexing agents such as cyanide and triethylenetetramine (TETA). These chemicals, while being useful for the process, can cause environmental issues. In this thesis, the batch flotation of selected ores was investigated together with the surface chemical phenomena related to the use of three complexants, namely TETA, cyanide and chloride. The ores consisted of Ni-Cu sulfides, rich in pyrrhotite and a galena-pyrite sample, both of which involved the use of TETA and a pyrite-based sample. Investigations with the first group indicated that the metabisulfite SMBS/TETA combination in synthetic seawater performed better in comparison with tap water. The synergistic effect of SMBS/TETA was superior due to enhanced complexing activity in chloride-rich medium. The pyrite sample that had been pre- contacted with cyanide was successfully desulfurized to minimize acid production potential in the environment. These investigations were coupled with fundamental investigations on electrochemistry of pyrrhotite, pyrite and galena through cyclic voltammetry, electrical impedance spectroscopy, contact angle measurements under applied electrochemical potential, as well as Raman spectroscopy and UV studies. The electrochemical studies provided evidence for the synergistic effect of the SMBS/TETA combination. The contact angle measurements provided support for formation metastable sulfur causing hydrophobicity in the absence of collector, which was largely masked on iron sulfides due to dominance of their surfaces with ferric hydroxide/oxide. Raman spectroscopy of the flotation concentrates provided clear evidence for the formation of metastable elemental sulfur/polysulfide on cyanide-contacted pyrite, which was a key factor explaining its unusual floatability. UV spectroscopy of ethanol extracts from the flotation concentrates provided further evidence of elemental sulfur forming on the mineral surfaces. Overall, these results represent a unique linkage between surface chemical phenomena and genuine flotation behaviour of several ore samples. Proper use of the SMBS/TETA combination is demonstrated to be a potential solution to rectify poor flotation of sulfide ores in seawater. The sulfurous acid-copper sulfate treatment is demonstrated to be a potential solution for desulfurization of cyanide tailings. In the environmental area, the microorganism Paecilomyces sp. (KC790497.1) demonstrated to biodegrade over 90% Cu-TETA complex in aqueous solutions.
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