Author: Samar Almojadah
Almojadah, Samar, 2024 Investigating the Interactions between Extracellular Polymeric Substances (EPS) and Iron Sulfide Surfaces, Flinders University, College of Science and Engineering
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Precious metals such as arsenic, copper, and nickel are necessary for the advancement of contemporary technology. Since sulfide minerals contain a large proportion of valuable metals, the effectiveness of sulfide mineral beneficiation processes is important. High-grade ore is the target of currently available beneficiation processes, such as froth flotation, which uses hazardous inorganic chemicals and results in a high metal concentration in mine tailings, leading to environmental issues such as acid mine drainage. The depletion of high-grade ore necessitates the advancement of beneficiation processes to create more effective and environmentally beneficial low-grade ore refining processes.
This thesis investigates the optimisation of pyrite and arsenopyrite separation, chalcopyrite and pyrite separation, and pyrrhotite and pentlandite separation through bio-flotation in a mixed mineral system using acidophilic microbes Leptospirillum ferrooxidans (L.f) and their metabolic products. To determine the optimal conditions for separation and recovery, it is necessary to study the influence of growth conditions on the behaviour of Leptospirillum ferrooxidans and the composition of their extracellular polymeric substances (EPS). By studying this, more will be known about the bio-flotation system's parameters and how they affect the separation and recovery of these minerals.
The interactions between both L. ferrooxidans and the mineral surfaces of arsenopyrite, pyrite, chalcopyrite, pyrrhotite, and pentlandite were examined using a combination of microscopic and spectroscopic techniques. These interactions are essential to comprehending the effects of microbes and bioreagents on sulfide minerals processing. The preferred attachment and mechanisms of L. ferrooxidans were investigated using scanning electron microscopy. L. ferrooxidans preferentially adheres to pyrite and pyrrhotite mineral surfaces, with the attachment mechanism changing depending on the growth conditions and duration.
EPS generation and biofilm development were detected on the mineral surfaces; however, there were notable variations in their quantity and duration. Microflotation assays were used to examine the relationship between metabolic products and flotation behaviour. Mineral recovery is directly impacted by the presence of L. ferrooxidans bacterial cells, which increase the system's overall mineral suppression. Removing cells from the system selectively suppressed arsenopyrite, pyrite, and pentlandite, with the extent of suppression varying according to the growth conditions and time frame.
Fluorescent microscopy analysis revealed the link between bacterial growth, type of substrate, and the distribution and concentration of polysaccharide-containing EPS generation on pyrite and chalcopyrite surfaces, providing insight into pyrite suppression in bio-flotation. Raman spectroscopy revealed that most of the particles that were exposed to EPS from chalcopyrite and formed a strong bond with the polysaccharides were pyrite. This indicates that there is a relationship between the presence of copper in the EPS, pyrite surface activation, and binding more polysaccharides.
The surface states of arsenopyrite, pyrite, pyrrhotite, and pentlandite exposed to bacterial cells and extracellular polymeric compounds were analysed using X-ray photoelectron spectroscopy. Examining the surface chemical variations can provide further understanding of the observed flotation behaviour. The analysis results confirm that the EPS can interact with mineral surfaces, both with and without bacterial cells present. Changes in flotation behaviour are correlated with an increase in complex organic compounds, with polysaccharides being the main EPS component. This provides credence to the idea that the composition of EPS plays a critical role in the effective bio-flotation process that separates arsenopyrite from pyrite, chalcopyrite from pyrite, and pentlandite from pyrrhotite.
Polysaccharides in EPS demonstrate preferential attachment to arsenopyrite, pyrite, and pentlandite minerals. This attachment is primarily governed by hydrogen bonding and chemical forces between hydroxyl groups in the polysaccharides and metal hydroxides on the mineral surfaces. The selective attachment order observed is influenced by the mineral's surface properties and the composition of the EPS. The selective attachment of polysaccharides increases the hydrophilicity of the mineral surface, aiding in subsequent separation processes.
Keywords: Leptospirillum ferrooxidans, EPS, bio-flotation, selective attachment, arsenopyrite/loellingite, pyrite, pentlandite, pyrrhotite, chalcopyrite
Subject: Physics thesis
Thesis type: Doctor of Philosophy
Completed: 2024
School: College of Science and Engineering
Supervisor: Sarah Harmer