A gradual depletion of high-grade ores, coupled with the growing demand for mineral commodities across the world has culminated in the increased exploitation of lean-grade ores with complex mineralogy. The mineral processing industry commonly uses an extensive range of inorganic, naturally derived or synthetic organic reagents in the separation of valuable minerals from the ore. Froth flotation is a commonly used separation technique to float or depress different sulfide minerals from the ore, based on their surface properties. In recent times, biological processes have been attracting attention in mineral processing and metal recovery operations due to a number of factors, especially lower operating costs, lesser energy consumption and their environment friendly nature. The use of microorganisms and their direct derivatives in mineral processing, hydrometallurgy and in the bioremediation of mineral industry discharges has led to the emerging area of “Mineral Bioprocessing”.
In this study, a family of four microorganisms belonging to the Bacillus species, viz., Paenibacillus polymyxa, Bacillus circulans, Bacillus megaterium and Bacillus subtilis was used to ascertain the selective floatability of sphalerite from a sphalerite-galena mineral mixture. These bacteria are Gram positive, mesophilic, neutrophilic, aerobic and spore forming.
The major objectives of the investigation include:
a) Identification and characterization of bioreagents derived from Bacillus species for the flotation of sphalerite from a sphalerite-galena mixture
b) Optimization of the flotation process for the enhanced recovery of sphalerite using specific bioreagent combinations
c) Modes and mechanisms of bacterial adaptation to minerals and their consequent effects on the flotation of sphalerite and galena
d) Elucidation of the mechanisms of microbe-mineral interactions and the role of extracellular secretions in sphalerite flotation column and their N-terminal residues were identified using Edmann N-terminal sequencing. Additionally, sequences of several internal peptides from both the proteins were determined using Tandem Mass Spectrometric techniques. A database search revealed that the sequences of these peptides are unique and have not been reported earlier.
It was established that the bacterial cells give high flotation recovery of sphalerite under buffered conditions and that it took place only in the presence of anionic buffers. Additionally, the viability of the bacterial cells was not required for the flotation of minerals. A major finding of this study was that other than extracellular DNA (eDNA), none of the other bacterial surface components like teichoic acids, surface proteins, polysaccharides played a positive role in the flotation process. Nucleic acids, more particularly single stranded DNA (ssDNA), facilitated sphalerite flotation relative to double stranded DNA (dsDNA). A probable mechanism of ssDNA -mediated selective flotation of sphalerite has been presented. A negative role for non-DNA surface components was also observed. This led to the realization of the need for an optimum ratio of DNA to non-DNA components in the selective flotation of sphalerite from a sphalerite-galena mixture.
It was found that the surface physiochemical properties of the mineral adapted bacteria differed significantly from that of the unadapted bacteria. Adaptation enhanced the flotation recoveries of the corresponding mineral vis-à-vis the unadapted bacteria. Sphalerite adapted bacteria secreted more extracellular proteins while the galena adapted bacteria secreted more polysaccharides compared to the unadapted bacteria. Sphalerite adapted bacteria selectively floats more sphalerite from the mineral mixture than the galena adapted as well as the unadapted bacteria. It was evident from the electrokinetic studies that the surface charge of the chosen sulfide mineral adapted bacteria was less negative relative to the unadapted bacteria. This phenomenon was observed with all the four bacterial species used in this study. A noteworthy finding was that the bacteria especially B.circulans induce a change in morphology from rod to sphere as a strategy during adaptation to a toxic mineral such as galena. This phenomenon has been shown to involve changes in crucial cell wall components as well as changes in the levels of expression of bacterial cytoskeleton elements involved in the maintenance of the rod shape. This aspect of the study involved the partial sequencing of the B.circulans homolog of the key cytoskeleton gene, mreB (B gene in murien cluster e), using the Polymerase Chain Reaction
(PCR) followed by DNA sequencing. A Genbank search indicated that this is the first report of the sequence of B.circulans mreB gene. This was followed by measuring the hypothesized downward changes in the levels of expression of the mreB gene by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). The possible mechanisms of the adaptive morphological changes and of the interaction of the chosen sulfide minerals with the family of microorganisms studied have been discussed with respect to their bioflotation efficiency.
| Identifer | oai:union.ndltd.org:IISc/oai:etd.ncsi.iisc.ernet.in:2005/2427 |
| Date | 12 1900 |
| Creators | Vasanthakumar, B |
| Contributors | Subramanian, S |
| Source Sets | India Institute of Science |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Relation | G25093 |
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