Solubilization and speciation of iron during pyrite oxidation by Thiobacillus ferrooxidans (original) (raw)
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Chemical Geology, 2001
Pyrite was oxidised by growth of Thiobacillus ferrooxidans aerobically at 328C by orbital shaking at 90 revolutions per Ž . Ž . minute rpm in the laboratory. The analyses of the experimental solutions showed a long period of adaptation lag phase before the onset of rapid bio-oxidation. Lag phase lasted for approximately 400 h. During this period, the dissolved iron and sulphur content increased very slowly compared with a very rapid rise during the exponential phase of growth. The molar ratio of the dissolved Fe to S in solution decreased from 1.3 to approximately 1 during the lag phase. The molar ratio continued to fall during the exponential phase and reached approximately 0.5, which is the ratio defined by the stoichiometry of pyrite. The form of dissolved iron during the lag phase was ferrous, while during the exponential phase, it was mostly ferric. On the other hand, all the dissolved sulphur was in the form of SO during both the lag and exponential phase. These 4 indicate that the Fe is preferentially leached from pyrite, but S is the main source of energy for T. ferrooxidans during the lag phase.
Mineral Products of Pyrrhotite Oxidation by Thiobacillus ferrooxidans†
Applied and Environmental Microbiology, 1993
The biological leaching of pyrrhotite (Fe 1- x S) by Thiobacillus ferrooxidans was studied to characterize the oxidation process and to identify the mineral weathering products. The process was biphasic in that an initial phase of acid consumption and decrease in redox potential was followed by an acid-producing phase and an increase in redox potential. Elemental S was one of the first products of pyrrhotite degradation detected by X-ray diffraction. Pyrrhotite oxidation also yielded K-jarosite [KFe 3 (SO 4 ) 2 (OH) 6 ], goethite (α-FeOOH), and schwertmannite [Fe 8 O 8 (OH) 6 SO 4 ] as solid-phase products. Pyrrhotite was mostly depleted after 14 days, whereas impurities in the form of pyrite (cubic FeS 2 ) and marcasite (orthorhombic FeS 2 ) accumulated in the leach residue.
Institute of Biology Bucharest, Romanian Academy, 2005
The increasing pollution of the environment raised the interest towards the resistance of microorganisms to metals and the potential of using microorganisms, not only in ore leaching and detoxifying of the environments polluted with heavy metals. The sulphur wastes deposited in dumps with high concentrations of metallic ions have the capacity of generating acid and toxic waters. A special importance in using bacteria of the genus Thiobacillus in the metal solubilization processes from the acid mine draining is represented by adapting of these microorganisms to higher concentrations of metallic ions existent in those environments. High percentages of soluble pyrite were obtained using the P5 population of Thiobacillus ferrooxidans, which made the pyrite soluble in percentages of 87-92, which confirms its higher tolerance to Fe 3+. The lowest percentages of solubilized pyrite (9.06-25.50%) were got in the presence of the Thiobacillus ferrooxidans B9 strain, this fact being correlated with the higher sensitivity of this strain to the presence of ferric iron in the environment.
Kinetics of Iron Oxidation by Thiobacillus ferrooxidans
Applied and environmental microbiology, 1991
A statistical relationship between the rate of ferric ion production by a strain of Thiobacillus ferrooxidans and various levels of cell concentration, Fe concentration, Na concentration, and temperature was studied by a direct colorimetric method at 304 nm. The relationship was linear (90 to 93%), cross-product (3 to 4%), and quadratic (1 to 2%). The levels of cell concentration and Fe concentration and their respective interactions with one another and the other factors had the most significant effects on the regression models. The solution of the quadratic response surface for optimum oxidation was a saddle point, and the predicted critical levels of temperature, cell concentration, Fe concentration, and Na concentration ranged between -6 and 2 degrees C, 0.43 and 0.62 mg/ml, 72 and 233 mM, and 29.6 mM, respectively.
The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures
Applied Microbiology and Biotechnology, 1999
The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures was examined, using on-line o-gas analyses to measure the oxygen and carbon dioxide consumption rates continuously. A cell suspension from continuous cultures at steady state was used as the inoculum. It was observed that a dynamic phase occurred in the initial phase of the experiment. In this phase the bacterial ferrous iron oxidation and growth were uncoupled. After about 16 h the bacteria were adapted and achieved a pseudo-steady state, in which the speci®c growth rate and oxygen consumption rate were coupled and their relationship was described by the Pirt equation. In pseudo-steady state, the growth and oxidation kinetics were accurately described by the rate equation for competitive product inhibition. Bacterial substrate consumption is regarded as the primary process, which is described by the equation for competitive product inhibition. Subsequently the kinetic equation for the speci®c growth rate, l, is derived by applying the Pirt equation for bacterial substrate consumption and growth. The maximum speci®c growth rate, l max , measured in the batch culture agrees with the dilution rate at which washout occurs in continuous cultures. The maximum oxygen consumption rate, q O 2 Ymax , of the cell suspension in the batch culture was determined by respiration measurements in a biological oxygen monitor at excess ferrous iron, and showed changes of up to 20% during the course of the experiment. The kinetic constants determined in the batch culture slightly dier from those in continuous cultures, such that, at equal ferric to ferrous iron concentration ratios, biomass-speci®c rates are up to 1.3 times higher in continuous cultures.
Oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans
Applied and …, 1988
The oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans that was absorbed and unabsorbed onto the surface of sulfur prills was studied. Unadsorbed sulfur-grown cells oxidized ferrous iron at a rate that was 3 to 7 times slower than that of ferrous iron-grown cells, but sulfur-grown cells were able to reach the oxidation rate of the ferrous iron-adapted cells after only 1.5 generations in a medium containing ferrous iron. Bacteria that were adsorbed to sulfur prills oxidized ferrous iron at a rate similar to that of unadsorbed sulfur-grown bacteria. They also showed the enhancement of ferrous iron oxidation activity in the presence of ferrous iron, even though sulfur continued to be available to the bacteria in this case. An increase in the level of rusticyanin together with the enhancement of the ferrous iron oxidation rate were observed in both sulfur-adsorbed and unadsorbed cells. On the other hand, sulfur oxidation by the adsorbed bacteria was not affected by the presence of ferrous iron in the medium. When bacteria that were adsorbed to sulfur prills were grown at a higher pH (ca. 2.5) in the presence of ferrous iron, they rapidly lost both ferrous iron and sulfur oxidation capacities and became inactive, apparently because of the deposition of a jarosite-like precipitate onto the surface to which they were attached.
Soluble Microbial Products Decrease Pyrite Oxidation by Ferric Iron at pH < 2
Environmental Science & Technology, 2013
Research on microbial activity in acid mine drainage (AMD) has focused on transformations of iron and sulfur. However, carbon cycling, including formation of soluble microbial products (SMP) from cell growth and decay, is an important biogeochemical component of the AMD environment. Experiments were conducted to study the interaction of SMP with soluble ferric iron in acidic conditions, particularly the formation of complexes that inhibit its effectiveness as the primary oxidant of pyrite during AMD generation. The rate of pyrite oxidation by ferric iron in sterile suspensions at pH 1.8 was reduced by 87% in the presence of SMP produced from autoclaved cells at a ratio of 0.3 mg DOC per mg total soluble ferric iron. Inhibition of pyrite oxidation by SMP was shown to be comparable to, but weaker than, the effect of a chelating synthetic siderophore, DFAM. Two computational models incorporating SMP complexation were fitted to experimental results. Results suggest that bacterially produced organic matter can play a role in slowing pyrite oxidation.
Bacterial pyrite oxidation: release of iron and scanning electron microscopic observations
Hydrometallurgy, 1981
The dissolution of iron from pyrite was enhanced by cultures of Thiobacillus ferrooxidans. Data from different analytical methods of iron determination indicated that most of the iron in filtered leachates was in a fine-dispersed (colloidal) or chelated form. Scanning electron micrographs showed extensive pitting of pyrite surfaces after 6 weeks leaching. Hexagonal (rhombohedral) and pseudo-cubic jarosite crystals were found in leach residues of polished pyrite specimens.
Applied and Environmental Microbiology
It was found that the de novo synthesis of not only sulfur:ferric ion oxidoreductase (ferric ion-reducing system) but also iron oxidase was absolutely required when Thiobacillus ferrooxidans AP19-3 was grown on sulfur-salts medium. The results strongly suggest that iron oxidase is involved in sulfur oxidation. This bacterium could not grow on sulfur-salts medium under anaerobic conditions with Fe3+ as a terminal electron acceptor, suggesting that energy conservation by electron transfer between elemental sulfur and Fe3+ is not available for this bacterium.
Effects of the oxygen transfer rate on ferrous iron oxidation by Thiobacillus ferrooxidans
Enzyme and Microbial Technology, 1998
Ferrous iron oxidation by Thiobacillus ferrooxidans was studied in shake flasks and a bubble column under different aeration conditions. The maximum biooxidation rate constant was affected by oxygen transfer only at low aeration intensities. At oxygen transfer rates higher than 0.03 mmol O 2 l Ϫ1 min Ϫ1 , the maximum biooxidation rate constant was about 0.050 h Ϫ1 in both shake flasks of different size and the bubble column. The oxygen transfer rate could be used as a basis for scaling up bioreactors for ferrous iron biooxidation by T. ferrooxidans.