K.A. Natarajan

Studies on interaction of Paenibacillus polymyxa with iron ore minerals in relation to beneficiation

Interaction between Paenibacillus polymyxa with minerals such as hematite, corundum, quartz and kaolinite brought about significant surface chemical changes on all the minerals. Quartz and kaolinite were rendered more hydrophobic, while hematite and corundum, became more hydrophilic after biotreatment. The predominance of bacterial polysaccharides on interacted hematite and corundum and of proteins on quartz and kaolinite was responsible for the above surface-chemical changes. Bio-pretreatment of the above iron ore mineral mixtures resulted in the selective separation of silica and alumina from iron oxide, through bioflotation and bioflocculation. The utility of bioprocessing in the beneficiation of iron ores is demonstrated.

Interaction of Bacillus polymyxa with some oxide minerals with reference to mineral beneficiation and environmental control

Interaction of Bacillus polymyxa with calcite, hematite, corundum and quartz resulted in significant surface chemical changes not only of the cells but also in the minerals. Both the cell surfaces as well as quartz particles were rendered more hydrophobic after mutual interaction, whilst the rest of the minerals exhibited enhanced hydrophilicity after interaction with the bacteria. The bacteria were also observed to be capable of dissolving calcite, hematite and corundum and biosorbing the dissolved metal ions to varying extents. An excess of polysaccharides could be observed on biotreated calcite, hematite and corundum while the predominance of a protein-based metabolic product was evident on quartz surfaces. The utility of bioprocessing in the beneficiation of the above minerals through bioflotation and bioflocculation is demonstrated.

Biobeneficiation of bauxite using Bacillus polymyxa: calcium and iron removal

Calcium and iron removal from a bauxite ore by Bacillus polymyxa has been demonstrated. Within a period of 7 days, the above organism could remove all the calcium and about 45% of iron from the ore in the presence of 2% sucrose in a Bromfield medium. The highest removal of calcium and iron corresponded with the maximum in extracellular polysaccharide production by the organism. Scanning electron microscopy of the biobeneficiated bauxite surfaces indicated tenacious attachment of the bacteria onto the ore particle. Some calcium and iron removal was observed even in the presence of bacterial metabolites such as polysaccharides, organic acids and slime. However, the calcium removal in the absence of microorganism (by metabolites alone) was found to be 50% of that obtained in its presence. These observations clearly indicate that both a direct mechanism through bacterial attachment to the ore and an indirect mechanism through leaching with metabolites are involved in the biobeneficiation process.

Role of bacterial interaction and bioreagents in iron ore flotation

Interaction between Paenibacillus polymyxa and iron ore minerals such as hematite, corundum, calcite, quartz and kaolinite brought about significant surface chemical changes on all the minerals. Quartz and kaolinite were rendered more hydrophobic, while the other three minerals became more hydrophilic after bacterial interaction. Predominance of bacterial polysaccharides on interacted hematite, corundum and calcite and of proteins on quartz and kaolinite was responsible for the surface chemical changes. The bacterial strains could be preadapted to different mineral substrates. Corundum-adapted strains were seen to secrete mineral-specific proteins which could be used to separate alumina from iron ores. The utility of bioprocessing in the beneficiation of iron ores for removal of silica and alumina is demonstrated.

Mechanisms of adhesion of Paenibacillus polymyxa onto hematite, corundum and quartz

Adhesion of bacteria onto solid surfaces is a necessary event in nature for the utilization of inorganic and organic values and for the enhanced growth of bacteria. Interactions between Paenibacillus polymyxa, with different minerals such as hematite, corundum and quartz are examined in this work in the light of Derjaguin, Landau, Verwey and Overbeek theory, popularly known as DLVO theory and possible chemical interactions. The adhesion process is normally controlled initially by physicochemical interactions between cells and mineral substrates and subsequently by the production of extra cellular polymers to make the attachment stronger, From this study, it is clear that maximum adsorption of cells on hematite and corundum occurs at a pH below the isoelectric point, whereas in the case of quartz the adsorption of cells remained almost constant in the entire pH range studied. From adhesion tests, it is also clear that the above bacteria adsorb preferentially on hematite and corundum than on quartz. It is obvious from the interaction energy calculations that the columbic forces play a major role in the interaction of P. polymyxa with hematite, corundum and quartz. Although the columbic forces do play such a role, it is evident from the Fourier Transform Infrared Spectroscopy (FTIR) results that other forces such as chemical forces are also involved simultaneously.

Studies on multi-metal ion tolerance of Thiobacillus ferrooxidans

The influence of different concentrations of base metal ions, such as CU2+, Zn2+ and Fe3+, when present either alone or in different possible binary and ternary combinations in a 9K medium, on the fel rous ion oxidation ability of Thiobacillus ferrooxidans was studied. Levels and degree of toxicity of these ions have been quantified in terms of toxicity index (TI). Copper and zinc tolerant strains of the bacteria were developed through serial subculturing and their activity tested in the presence of the above metal ions in comparison with the behavior of wild unadapted cells under similar conditions. Copper tolerant strains (25 g/L Cu2+) were found to be more efficient in the bioleaching of both copper and zinc concentrates than wild unadapted strains, while zinc tolerant strains (40 g/L Zn2+) exhibited better leaching efficiency only in the bioleaching of sphalerite concentrates. The significance and relevance of multi-metal ion tolerance in Thiobacillus ferrooxidans has been highlighted with respect to bioleaching of sulphide mineral concentrates

Surface Chemical Studies on Galena and Sphalerite in the Presence of Thiobacillus Thiooxidans with Reference to Mineral Beneficiation

Adsorption and electrokinetic studies were carried out to examine the surface chemical changes on galena and sphalerite before and after interaction with Thiobacillus thiooxidans (T. thiooxidans). The adsorption density of bacterial cells onto the two sulphide minerals was found to be independent of pH, although an increased number of cells was adsorbed onto galena compared to sphalerite. The adsorption isotherms of the cells with respect to the two minerals conform to the Langmuir equation. Zeta potential measurements revealed that the isoelectric points of the sulphide minerals were shifted to higher pH values after bacterial interaction, suggestive of specific adsorption. Both the sulphide minerals as well as the cells became less electronegative as a function of time after interaction with each other. Selective flotation and flocculation studies highlighted that galena could be separated from sphalerite after bacterial interaction. These tests confirmed that galena was depressed while sphalerite was made hydrophobic after interaction with the cells. Fourier transform infrared spectroscopic studies provided evidence in support of hydrogen bonding for the mineral-cell adsorption process. Possible mechanisms of interaction between galena/sphalerite and the cells of T. thiooxidans are discussed.

Surface chemical characterisation of Paenibacillus polymyxa before and after adaptation to sulfide minerals

A heterotroph Paenibacillus polymyxa bacteria is adapted to pyrite, chalcopyrite, galena and sphalerite minerals by repeated subculturing the bacteria in the presence of the mineral until their growth characteristics became similar to the growth in the absence of mineral. The unadapted and adapted bacterial surface have been chemically characterised by zeta-potential, contact angle, adherence to hydrocarbons and FT-IR spectroscopic studies. The surface free energies of bacteria have been calculated by following the equation of state and surface tension component approaches. The aim of the present paper is to understand the changes in surface chemical properties of bacteria during adaptation to sulfide minerals and the projected consequences in bioflotation and bioflocculation processes. The mineral-adapted cells became more hydrophilic as compared to unadapted cells. There are no significant changes in the surface charge of bacteria before and after adaptation, and all the bacteria exhibit an iso-electric point below pH 2.5. The contact angles are observed to be more reliable for hydrophobicity assessment than the adherence to hydrocarbons. The Lifschitz–van der Waals/acid–base approach to calculate surface free energy is found to be relevant for mineral–bacteria interactions. The diffuse reflectance FT-IR absorbance bands for all the bacteria are the same illustrating similar surface chemical composition. However, the intensity of the bands for unadapted and adapted cells is significantly varied and this is due to different amounts of bacterial secretions underlying different growth conditions.

Electrochemical effects of mineral-mineral interactions on the flotation of chalcopyrite and sphalerite

The role of mineral-mineral interactions on the flotation of chalcopyrite and sphalerite has been discussed with respect to different sulphide mineral combinations involving chalcopyrite, galena and sphalerite. Rest potential, combination potential and galvanic current measurements were made to understand the electrochemical behaviour of the above sulphide minerals when present individually and in different combinations. Galvanic interactions between a noble mineral such as chalcopyrite and active minerals such as galena and sphalerite significantly affect the floatability of the noble mineral, the effect on the active mineral being minimal. The deleterious effect of ageing of a single sulphide mineral, especially in the presence of oxygen, on its floatability could be minimized if it is present in galvanic combinations in a flotation medium. ESCA studies were carried out to identify the reaction products on the sulphide minerals after different types of mineral-mineral interactions. Probable electrochemical reaction mechanisms are outlined.

Microbial aspects of acid mine drainage and its bioremediation

The role of chemolithotrophs such as Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans which were isolated from some abandoned mines and processed waste tailings in the generation of acid mine drainage and toxic metal dissolution was discussed. Mechanisms of acid formation and dissolution of copper, zinc, iron and arsenic from copper, lead-zinc and arsenopyrite-bearing sulfide ores and tailings were established in the presence of Acidithiobacillus group of bacteria. Sulphate Reducing Bacteria(SRB) isolated from the above mine sites could be used to precipitate dissolved metals such as copper, zinc, iron and arsenic. Arsenic bioremediation was demonstrated through the use of native microorganisms such Thiomonas spp. which could oxidize arsenite to arsenate. Bioremoval of arsenic through the use of jarosite precipitates generated by Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans was also found to be very effective. Biotechnological processes hold great promise in the remediation of acid mine drainage and efficient removal of toxic metal ions such as copper, zinc and arsenic.