Bio-oxidation of iron using Thiobacillus ferrooxidans

The effects of pH, ferrous and ferric ion concentrations on iron oxidation by Thiobacillus ferrooxidans were examined. The initial temperature and bacterial concentration were maintained at 37°C and 2±1×104cells/ml, respectively. The iron oxidation rate increased with increased initial ferrous iron concentration to 4g/l and thereafter decreased. The presence of iron(III) showed a negative effect on the bacterial iron oxidation rate. The increase of pH also showed an increase in the oxidation rate up to pH 1.75. The oxidation rate followed first order kinetics for the parameters studied. A rate equation has been developed.     

Anaerobic growth on elemental sulfur using dissimilar iron reduction by autotrophic Thiobacillus ferrooxidans

Abstract Anaerobic growth on elemental sulfur using dissimilar iron reduction by Thiobacillus ferrooxidans has been demonstrated. The ferric ion reducing activity (FIR) of the anaerobic cells was double that of the aerobic cells. Significant differences in inhibition of FIR by respiratory inhibitors were observed between aerobic and anaerobic cells. A higher amount of cytochrome was detected in anaerobic cells compared to aerobic cells. Absorption minima developed with the addition of ferric sulfate in the dithionite reduced cell suspension demonstrated that the ferric ion could accept electrons from the cytochrome system of this bacterium. The possibility of two different electron transport chains in ferric ion reduction is discussed.     

Use of Thiobacillus ferrooxidans for iron oxidation and precipitation

Fe(II) oxidation reaction was carried out using an acidophilic microorganism, Thiobacillus ferrooxidans. Four different parameters such as pH, Fe(II), Fe(III) and biomass concentration were studied. The oxida-tion reaction follows a pseudo first order rate equation. Apparent reaction rate constants were calculated. Unified rate equation was developed using the four parameters. Along with oxidation, a part of the iron also was precipitated. The extent of Fe(III) precipitation in each case was calculated. © Rapid Science 1998     

Ferrous iron oxidation and uranium extraction by Thiobacillus ferrooxidans

The microbiological oxidation of ferrous iron in batch and continuous systems has been investigated in relation to uranium extraction from a low-grade ore by Thiobacillus ferrooxidans. The influence of the parameters, agitation, and aeration on oxygen saturation concentration, rate of oxygen mass transfer, and rate of ferrous iron oxidation was demonstrated. The kinetic values, V_max and K were determined using an adapted Monod equation for different dilution rates and initial concentrations of ferrous iron. The power requirements for initial leaching conditions were also calculated. Uranium extraction as high as 68% has been realized during nine days of treatment. Regrinding the leach residue and its subsequent leaching yielded 87% uranium solubilization.     

Thiobacillus ferrooxidans pili

The surface structures of Thiobacillus ferrooxidans were studied. When growing on a medium containing elemental sulphur, the cells possess peritrichously located filaments (piles) whose diameter varies from 4.5 to 7.0 nm and length, from 0.7 to 3.0 mcm. The cells of T. ferrooxidans do not have piles on a medium with ferrous iron. The physiological role of these structures for thiobacilli is discussed.     

Ferric iron reduction by Thiobacillus ferrooxidans at extremely low pH-values

When ferrous iron and sulfur were supplied, cells of T. ferrooxidans in a well-aerated medium started growth by oxidizing ferrous iron. After ferrous iron depletion a lagphase followed before sulfur oxidation started. During sulfur oxidation at pH-values below 1.3 (±0,2) the ferrous iron concentration increased again, although the oxygen saturation of the medium amounted to more than 95%. The number of viable cells did not increase. Thus resting cells of T. ferrooxidans, which are oxidizing sulfur to maintain their proton balance, reduce ferric to ferrous iron. The ferrous iron-oxidizing system seemed to be inhibited at pH-values below 1.3. At a pH-value of 1.8 the ferrous iron was reoxidized at once. A scheme for the linkage of iron- and sulfur metabolism is discussed.     

A structured model for Thiobacillus ferrooxidans growth on ferrous iron

A structured model for Thiobacillus ferrooxidans growth dependence on ferrous and ferric iron, arsenic, oxygen, carbon dioxide, pH, and temperature is presented. A new kinetic mechanism for ferrous oxidation by T. ferrooxidans is introduced. Data from several earlier experimental studies of T. ferroaxidans growth are used for model development. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 310-319, 1997.     

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in batch cultures was examined, using on-line off-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 specific 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 specific growth rate, μ, is derived by applying the Pirt equation for bacterial substrate consumption and growth. The maximum specific growth rate, μ _max, measured in the batch culture agrees with the dilution rate at which washout occurs in continuous cultures. The maximum oxygen consumption rate, q _O2,max, 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 differ from those in continuous cultures, such that, at equal ferric to ferrous iron concentration ratios, biomass-specific rates are up to 1.3 times higher in continuous cultures. Received: 8 February 1999 / Accepted: 17 February 1999     

Solubilization and speciation of iron during pyrite oxidation by Thiobacillus ferrooxidans

Various species of soluble iron in pyrite‐grown cultures of Thiobacillus ferrooxidans were determined by colorimetry, atomic absorption spectrometry, and ultraviolet spectroscopy. All the cultures were incubated for six weeks before iron analysis. The effects of the following factors were investigated: particle size, initial pH, shaking (aeration), concentration of pyrite, and concentration of yeast extract. Shaking, but not initial pH nor particle size, influenced the relative proportion of different iron species. Polynomial regressions could be used to describe the functional relationship between the different iron species and concentration of pyrite; fewer relationships were evident with respect to concentration of yeast extract. The variance‐covariance matrices indicated a linear dependence among the different iron species. Canonical correlations indicated perfect correlations between group variables of iron, copper, and zinc, with the exception of an absence of significant correlation with the hydroxy complex of iron (FeOH²⁺).

The dissolved ferrous iron (dissociated and weakly chelated) always remained less than 7% of the total iron in solution. The total ferrous iron, which included complexed species, amounted to 7–34% of the total iron in solution. The concentrations of dissociated ferrous and ferric iron and their weak chelates (the dissolved iron) remained mostly constant, irrespective of the concentration of the total iron in solution. Most of the total iron was complexed as ferric species and the amount correlated with culture conditions. The hydroxy complex (FeOH²⁺), which was indicative of the relative amount of hydrolyzable ferric iron upon dilution in CO₂‐free water, usually ranged between 60 and 80% of the total iron. The amount of the total iron in uninoculated controls was less than 12% of that solu‐bilized in the presence of iron‐oxidizing thiobacilli.

T. ferrooxidans was enumerated by a most‐probable‐number technique after three and six weeks of growth on pyrite. The counts after three weeks indicated an increase in the number of free and loosely attached bacteria, followed by a decline of about one order of magnitude in bacterial numbers after six weeks. The technique for bacterial enumeration was deemed unsatisfactory because it could not account for cells attached on pyrite.     

The ferrous iron oxidation kinetics of Thiobacillus ferrooxidans in continuous cultures

The oxidation and growth kinetics of ferrous iron with Thiobacillus ferrooxidans in continuous cultures was examined at several total iron concentrations. On-line off-gas analyses of O₂ and CO₂ were used to measure the oxygen and carbon dioxide consumption rates in the culture. Off-line respiration measurements in a biological oxygen monitor (BOM) were used to measure directly the maximum specific oxygen consumption rate, qO₂,max, of cells grown in continuous culture. It was shown that these reproducibly measured values of qO₂,max vary with the dilution rate. The biomass-specific oxygen consumption rate, qO₂, is dependent on the ratio of the ferric and ferrous iron concentrations in the culture. The oxidation kinetics was accurately described with a rate equation for competitive ferric iron inhibition, using the value of qO₂,max measured in the BOM. Accordingly, only the kinetic constant Ks/K _i needed to be fitted from the measurements. A new method was introduced to determine the steady-state kinetics of a cell suspension in a batch culture that only takes a few hours. The batch culture was set up by terminating the feeding of a continuous culture at its steady state. The kinetic constant K _s/K _i determined in this batch culture agreed with the value determined in continuous cultures at various steady states. Received: 8 February 1999 / Accepted: 17 February 1999     

Decrease in iron oxidizing activity of Thiobacillus ferrooxidans adsorbed on activated carbon

It was observed that about 90% of free-swimming Thiobacillus ferrooxidans in 9 K medium was adsorbed on added activated carbon when the concentration of the cultivated bacteria reached about 4 x 10(13) cells m(-3). The oxidation of ferrous iron and the leaching of copper ore were carried out in shake flasks and in aerated columns. The rates of oxidation and leaching increased when bacteria adsorbed on activated carbon were used. However, the evaluation of the reaction rates by eliminating the catalytic effect of activated carbon showed that the contribution to the reaction by the adsorbed microorganism was very small.     

Anaerobic Growth of Thiobacillus ferrooxidans

The obligately autotrophic acidophile Thiobacillus ferrooxidans was grown on elemental sulfur in anaerobic batch cultures, using ferric iron as an electron acceptor. During anaerobic growth, ferric iron present in the growth media was quantitatively reduced to ferrous iron. The doubling time in anaerobic cultures was approximately 24 h. Anaerobic growth did not occur in the absence of elemental sulfur or ferric iron. During growth, a linear relationship existed between the concentration of ferrous iron accumulated in the cultures and the cell density. The results suggest that ferric iron may be an important electron acceptor for the oxidation of sulfur compounds in acidic environments.     

A kinetic model for biological oxidation of ferrous iron by Thiobacillus ferrooxidans

The kinetics of bacterial oxidation of ferrous iron in the presence of Thiobacillus ferrooxidans cells were studied using an initial-rate method. Measurements of the redox potential of the solution during the oxidation of ferrous iron were used to assess the initial rate of the reaction. Effects on the rate of reaction were determined for ferrous iron concentration in the range 0.25 to 30 kg m(-3), bacterial concentration in the range 3.25 x 10(7) to 4.47 x 10(8) cells mL(-1), and temperature in the range 20 to 35 degrees C. Using these experimental results and an approach based on Michaelis-Menten kinetics, a model for biological oxidation of ferrous iron was developed. The model, which incorporates terms for the effect of temperature and substrate and cell inhibition, was successfully used to simulate the full range of experimental data obtained. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 478-486, 1997.     

A novel mineral flotation process using Thiobacillus ferrooxidans.

Oxidative leaching of metals by Thiobacillus ferrooxidans has proven useful in mineral processing. Here, we report on a new use for T. ferrooxidans, in which bacterial adhesion is used to remove pyrite from mixtures of sulfide minerals during flotation. Under control conditions, the floatabilities of five sulfide minerals tested (pyrite, chalcocite, molybdenite, millerite, and galena) ranged from 90 to 99%. Upon addition of T. ferrooxidans, the floatability of pyrite was significantly suppressed to less than 20%. In contrast, addition of the bacterium had little effect on the floatabilities of the other minerals, even when they were present in relatively large quantities: their floatabilities remained in the range of 81 to 98%. T. ferrooxidans thus appears to selectively suppress pyrite floatability. As a consequence, 77 to 95% of pyrite was removed from mineral mixtures while 72 to 100% of nonpyrite sulfide minerals was recovered. The suppression of pyrite floatability was caused by bacterial adhesion to pyrite surfaces. When normalized to the mineral surface area, the number of cells adhering to pyrite was significantly larger than the number adhering to other minerals. These results suggest that flotation with T. ferrooxidans may provide a novel approach to mineral processing in which the biological functions involved in cell adhesion play a key role in the separation of minerals.     

Mechanism of microbial flotation using Thiobacillus ferrooxidans for pyrite suppression

Microbial desulfurization might be developed as a new process for the removal of pyrite sulfur from coal sluries such as coal-water mixture (CWM). An application of iron-oxidizing bacterium Thiobacillus ferrooxidans to flotation would shorten the periods of the microbial removal of pyrite from some weeks by leaching methods to a few minutes. The floatability of pyrite in flotation was mainly reduced by T. ferrooxidans itself rather than by other microbial substances in bacterial culture as additive of flotation liquor. Floatability was suppressed within a few seconds by bacterial contact. The suppression was proportional to increasing the number of cells observed between bacterial adhesion and the suppression of floatability. If 25% of the total pyrite surface area covered with the bacteria, pyrite floatability would be completely depressed. Bacteria that lost their iron-oxidizing activities by sodium cyanide treatment were also able to adhere to pyrite and reduced pyrite floatability as much as normal bacteria did. Thiobacillus ferrooxidans ATCC 23270, T-1, 9, and 11, which had different iron-oxidizing abilities, suppressed floatability to similar-levels. The oxidizing ability of bacteria did not influence the suppressing effect. These results showed the mechanism of the suppression of pyrite floatability by bacteria. Quick bacterial adhesion to pyrite induced floatability suppression by changing the surface property from hydrophobic. The quick adhesion of the bacterium was the novel function which worked to change the surface property of pyrite to remove it from coal. (c) 1993 John Wiley & Sons, Inc.     

Phenotypic switching of Thiobacillus ferrooxidans

Two solid medium formulations, designated 100:10 and 10:10, were developed for the growth of Thiobacillus ferrooxidans. The new media contain a mixture of both ferrous iron and thiosulfate as available energy sources, permitting the detection of colony morphology variants that arise spontaneously in a wild-type population. Several morphological and physiological characteristics of a class of T. ferrooxidans variants, termed LSC for large spreading colony, are described. LSC variants lack the ability to oxidize iron but retain the capacity to utilize thiosulfate or tetrathionate as energy sources. An LSC colony spreads on the surface of solid 100:10 medium as a monolayer of cells in a fashion resembling that of certain swarming or gliding bacteria. The LSC variant reverts to a parental wild type at frequencies that vary in different independently arising isolates. The identity of the LSC variant as a derivative of the parental wild-type T. ferrooxidans was established by Southern blot hybridization.