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Microbial Processing
Published in S. Komar Kawatra, Advanced Coal Preparation and Beyond, 2020
Selective flocculation using bacteria is a different proposition than either froth flotation or oil agglomeration. In this case, the bacteria are used to selectively attach to the coal, rather than to the pyrite (Misra et al., 1992; Raichur et al., 1995). The bacteria are an integral part of the process, as they are responsible for the flocculation of the coal particles. The organism used is Mycobacterium phlei, which is one of the few bacteria that is strongly hydrophobic. The hydrophobic nature of the cell causes it to selectively attach to multiple coal particles, binding them together into flocs that can be separated from pyrite and ash minerals by their higher settling rate.
Biotechnological Avenues in Mineral Processing: Fundamentals, Applications and Advances in Bioleaching and Bio-beneficiation
Published in Mineral Processing and Extractive Metallurgy Review, 2023
Srabani Mishra, Sandeep Panda, Ata Akcil, Seydou Dembele
In order to carry out vital metabolic interactions, microbes attach themselves to the surface of the minerals. For example, minerals act as terminal electron acceptor in the respiratory cycle for Shewanella oneidensis. Likewise, minerals act as energy storehouse for Acidithiobacilli group of bacteria. The bacterial cell surface bears a negative charge under most physiological conditions, while other factors such as electrostatic forces, van der Waals interactions, hydrophobic, entropic, H-bonding and acid-base properties play a significant role in the bacterial attachment (Rao, Vilinska and Chernyshova 2010). For example, the negative charge attributed to the fatty acid composition in Mycobacterium phlei is majorly responsible for the preliminary attachment of the bacteria to coal and pyrite surfaces (Dwyer et al. 2012).
A Review on Bioflotation of Coal and Minerals: Classification, Mechanisms, Challenges, and Future Perspectives
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Kaveh Asgari, Qingqing Huang, Hamid Khoshdast, Ahmad Hassanzadeh
On the other hand, pH can enhance or weaken the properties of bacteria as a bioreagent. For example, if the pH is close to the IEP of the bioreagent, the bioreagent surface would be uncharged, and floc formation would occur. Besides, pH affects the behavior of different ions and metals, thereby inducing either inhibitory or growth-promoting impacts (Sanwani et al. 2021). One example is the adhesion of Mycobacterium phlei and Bacillus subtilis onto dolomite and apatite at different pH values (Zheng, Arps, and Smith 2001). Both bacteria adsorb onto apatite and dolomite and act as their depressants. At acidic and near-neutral pH values, the attachment of both species on dolomite is more readily than onto apatite. By increasing pH, the adhesion and depression effect of Bacillus subtilis on dolomite becomes more dominant than for apatite. On the other hand, at basic pH conditions, the adsorption of Mycobacterium phlei onto apatite is more than onto dolomite and, compared to Bacillus subtilis, acts as a weaker depressant for dolomite but a stronger depressant for apatite. Another instance is apatite and quartz hydrophobicity in contact with Rhodococcus opacus bacteria (Merma et al. 2013). In addition, it was shown that prior to interacting with microorganisms, the surfaces of both minerals were hydrophilic, and the contact angle values were relatively low. After bacterial interaction with the mineral surface, an increase in contact angle of both minerals has been seen, with the largest change at near pH 5. At this pH contact angle of biotreated apatite and quartz experienced an increase about 30 and 15 degree, respectively. However, a further increase in pH decreases the hydrophobicity of minerals, demonstrating that pH plays a vital role in separating minerals in the presence of microorganisms.
Fusion of the Microbial World into the Flotation Process
Published in Mineral Processing and Extractive Metallurgy Review, 2022
Derya Öz Aksoy, Serhat Özdemir, Pınar Aytar Çelik, Sabiha Koca, Ahmet Çabuk, Hüseyin Koca, Pablo Brito-Parada
Collectors: In this group of microbial reagent studies, microorganisms, metabolites, or cell components serve as collectors. In a study in which the microorganism itself was used as a collector conducted by Misra et al. (1993), it was observed that Mycobacterium phlei was used as a collector in hematite flotation and there was a correlation between flotation efficiency and adhesion of bacteria to hematite. In another study dealing with the microorganism itself published by de Mesquita, Lins and Torem (2003) the Rhodococcus opacus is selectively adsorbed only on the hematite surface around pH 5 and it is possible to separate hematite from quartz with an efficient hematite flotation. In a similar study, it was stated that Rhodococcus ruber has an important potential for use as a biocollector in metal sulfide flotation (Lopez et al. 2015). In another research by Patra and Natarajan, it was shown that pyrite can be separated from quartz and calcite by flocculation or flotation after its interaction with P. polymyxa or bacterial metabolites (Patra and Natarajan 2003). Among the studies in which bioreagents are used as biocollectors, a study conducted by Curtis et al. in 2009 is remarkable in terms of the path followed in the production of the bioreagent. This study was the first virus (bacteriophage) study to involve cloning a peptide that is claimed to be sufficiently hydrophobic and selective toward the sphalerite and chalcopyrite minerals. This peptide has been cloned into a nonpathogenic bacteriophage. Subsequent experiments on a synthetic mixture containing pure sphalerite, chalcopyrite and quartz showed that the produced peptide selectively binds only to sphalerite and chalcopyrite but does not interact with silica. However, this study remains the only example in the bioflotation literature where the biocollector is virus-derived (Curtis et al. 2009). Bioflotation studies in which bioreagents in the literature were used as collectors are summarized in (Table 4).