Bacterium Thiobacillus Ferrooxidans Research Articles

Impact of microbial diversity and sulfur chemistry on safeguarding sulfudic mine waste

A study on the microbial diversity in two uranium mine waste heaps revealed that many different physiological groups of microorganisms occurred. The acidophilic thiobacilli Thiobacillus ferrooxidans and Thiobacillus thiooxidans were the dominant microorganisms in a uranium mine waste heap with a mean pH-value of 4. Moderately acidophilic thiobacilli dominated in a second heap with carbonaceous material and a mean pH-value of 6. Tetra-and pentathionate were detected in carbonaceous ore samples. Polythionates are the main products in the case of chemical pyrite oxidation experiments at pH 7.9, explaining the source of substrate for the moderately acidophilic thiobacilli. In the case of pyrite oxidation at pH 1.9 more than 90% of the pyritic sulfur was completely oxidized to sulfate, together with 10% of elemental sulfur and traces of polythionates. Elemental sulfur is a suitable substrate for Thiobacillus thiooxidans. For remediation purposes the action of inhibitory substances on bacterial leaching was tested. An efficient inhibition of the acidophilic leaching bacteria Thiobacillus ferrooxidans, Thiobacillus thiooxidans, and Leptospirillum ferrooxidans was achieved by sodium dodecylsulfate (SDS), calcium fluoride (CaF 2), concrete, and limestone (CaCO 3). The latter three agents were suitable for a long-term protection of mine waste resulting from measurements of microbial activity, cell count, and metal solubilization. Dissolved SDS allows for a temporary treatment.

Fundamental Study on Biomachining : Machining of Metals by Thiobacillus ferrooxidans

In this work, we investigate the possibility of biological machining by bacteria as a new technique for metal removal. Some kinds of chemolithotrophic bacteria gain energy from inorganic matter and fix carbon dioxide from the air. One of them, the bacterium Thiobacillus ferrooxidans, "eats" metals. Machining of grooves on pure iron and pure copper by Thiobacillus ferrooxidans is experimentally investigated. The experimental analysis showed that biomachining was possible, since the depth of the grooves generated on the workpiece increased almost linearly with the machining time. Furthermore, electric-field-assisted biomachining proved to be even more effective, because the removed rate became much higher under an electric field.

96/00059 In-situ polymerization of pyrrole in coal

Bioleaching of pyrite (FeS2) by the thermophilic bacterium Acidianus brierleyi was studied experimentally and theoretically in a stirred-tank reactor operated continuously with respect to both mineral particles and liquid medium. Continuous bioleaching experiments were performed at 65°C and pH 1.5 over the range of dilution rates (0.4–5 d−1) and feed pyrite-liquid loading ratios (5 and 20 kg/m3). A mathematical model was developed to describe quantitatively the bioleaching process in the continuous-flow mode of operation. The reactor model assumed that the growth rate of adsorbed bacteria on the mineral surface is proportional to the product of the adsorbed-cell concentration and the fraction of adsorption sites by unoccupied by cells, and took into account a distribution of residence time for the mineral particles leaving the reactor. The model developed here and the parameter values determined previously in separate batch tests gave good predictions of the mean leaching fraction and the free cell concentration in the reactor. The present model was also consistent with previous rate data for the bioleaching of zinc sulfide by the mesophilic bacterium Thiobacillus ferrooxidans in a continuous-flow reactor.

Molecular aspects of the electron transfer system which participates in the oxidation of ferrous ion by Thiobacillus ferrooxidans.

The enzymes and redox proteins, which participate in the oxidation of ferrous ion by the acidophilic iron-oxiding bacterium Thiobacillus ferrooxidans, have been isolated and characterized. They are Fe(II)-cytochrome c oxidoreductase, cytochromes c-552(s), c-552(m) and c-550(m), rusticyanin, and cytochrome c oxidase. On the basis of the interactions of these components, an electron transfer system has been proposed which seems to function in the oxidation of ferrous ion by the bacterium.

Microbial desulfurization of coal with Thiobacillus ferrooxidans bacteria

Microbial desulfurization of Polish flame coal, characterized by high total concentration of sulfur and a high concentration of pyrite sulfur, was studied. The optimum conditions of the process were established. When using Thiobacillus ferrooxidans bacteria, the best results were obtained with desulfurization carried out on coal samples making 2.4 wt% of the extraction mixture at the initial concentration of ferrous ions of 15 g dm −3 and for a process duration of seven days. Since desulfurization of coal mainly involves oxidation of the pyrite, a kinetic model of Fe 2+ oxidation by Thiobacillus ferrooxidans bacteria was proposed. The process was found to be described well by the equation derived for autocatalytic reaction of the first-order, both towards the inorganic substrate (Fe 2+) and the biocatalyst (protein). The rate constants and induction times of Fe 2+ oxidation and protein growth were determined for different temperatures, pH values and initial concentrations of Fe 2+. The highest rate constant and the shortest induction time were obtained for 35°C and the initial Fe 2+ concentration of 3 g Fe 2+ dm −3. No effect of pH changes, in a range 2.0–3.0, on the kinetics of the process was noted.

Effect of bacterial adaptation on kinetics and mechanisms of bioleaching ferrous sulfides

Thiobacillus ferrooxidans bacteria were used in this work to study the effect of bacterial adaptation on bioleaching of three iron-bearing sulfide minerals, namely, pyrite (FeS 2), chalcopyrite (CuFeS 2), and arsenopyrite (FeAsS). It was found that bacterial adaptation prior to bioleaching, enhanced the degree of sulfide leaching 2–4 fold over non-adapted bacteria. Also the bacterial activity was enhanced by 2–4.8 fold. The pH of leaching solution was decreased by the increase in both adaptation period and bioleaching time. A mechanistic model for bioleaching of sulfides with T. ferrooxidans is described. The model explains the role of bacteria in direct and indirect biochemical leaching reactions. It also reconciles such observed behaviors and phenomena as lag time, adaptation, pH increase lag time, and electrochemistry of bioleaching. The model shows how direct and indirect biochemical interactions are involved in bioleaching of ferrous sulfides.

Ferrous Sulphate Oxidation Using Thiobacillus ferrooxidans: a Review

The ability of the chemolithotrophic bacterium Thiobacillus ferrooxidans to oxidise ferrous sulphate has been exploited in the process of bioleaching, treatment of acidic mine drainage and removal of H2S from sour gases. Over the years, much attention has been paid to this organism and the process it catalyses. Unfortunately, inconsistent and ambiguous results have been reported in the literature. Therefore, further studies need to be undertaken in order to verify the optimal pH and temperature ranges of 2·0–3·3 and 30–33°C respectively and the optimal levels of O2 and CO2 as well as 4the values of the basic kinetic parameters and the effect of substrate and product inhibition. On the process side, the work has mainly been aimed at improving the rate of ferrous iron oxidation and numerous immobilisation matrices and bioreactors systems have been tested.

Ferrous sulphate oxidation using thiobacillus ferrooxidans: a review

The ability of the chemolithotrophic bacterium Thiobacillus ferrooxidans to oxidise ferrous sulphate has been exploited in the process of bioleaching, treatment of acidic mine drainage and removal of H 2S from sour gases. Over the years, much attention has been paid to this organism and the process it catalyses. Unfortunately, inconsistent and ambiguous results have been reported in the literature. Therefore, further studies need to be undertaken in order to verify the optimal pH and temperature ranges of 2·0–3·3 and 30–33°C respectively and the optimal levels of O 2 and CO 2 as well as 4the values of the basic kinetic parameters and the effect of substrate and product inhibition. On the process side, the work has mainly been aimed at improving the rate of ferrous iron oxidation and numerous immobilisation matrices and bioreactors systems have been tested.

Microbial desulfurization of coal by Thiobacillus ferrooxidans and thermophilic archaea

Several different microorganisms have been suggested for coal desulfurization. In the present investigation, the thermophilic archaea Acidianus brierleyi (DSM 1651), Sulfolobus acidocaldarius (DSM 639) and Sulfolobus solfataricus (DSM 1616) were compared with the mesophilic bacterium Thiobacillus ferrooxidans (DSM 583) concerning their capability of removing sulfur from coal. The desulfurization rate as well as the amount of sulfur removed by the microorganisms was studied. Two of the investigated microorganisms, Thiobacillus ferrooxidans and Acidianus brierleyi, were capable of oxidizing pure pyrite as well as oxidizing sulfur in coal. A kinetic analysis was performed assuming first order reactions. The rate constant for oxidation of pure pyrite by A. brierleyi was observed to be higher than for T. ferrooxidans. The values of the rate constants for sulfur removal from coal were comparable for the two microorganisms, but were higher than for oxidation of pure pyrite.

The chemolithotrophic bacteriumThiobacillus ferrooxidans

The iron-oxidizing bacterium Thiobacillus ferrooxidans is the most important microorganism in mineral leaching. It plays the dominant role in bioextractive processes because of its ability to oxidize both iron and reduced sulfur compounds. T. ferrooxidans is also an important microorganism in acid rock/mine drainage, a serious environmental problem. In this article, the current status of this bacterium is described with particular emphasis on the biomining industry.

Prognosis of the stability of arsenic in the biotop of the brown-coal dump

In the nature there is a large number of various microorganisms which participate in the process of transformation of minerals and other materials, in their corrosion, disintegration decomposition or even formation of new components. Many of the microorganisms gain the energy for their metabolic processes trough oxidation of anorganic compounds. Interaction of microorganisms or their metabolites with deposited components, which may be toxid, can take place directly in the dump biotop. In fly-ashes produced by burning the Slovak brown coal a higher arsenic content is present, the arsenic in the original coal being bound in a very stable FeAsS compound (arsenopyrite). However this compound is decomposed by burning and so we were interested in the stability of newly formed arsenic compounds found in the fly-ash. Their stability was tested by leaching experiments in an environment of nutrient medium for bacteria Thiobacillus ferrooxidans 9KA (pH 1.5) at a concentration of cells 7x10 ml and simultaneously also without bacterial culture at the same condition. Apart from this, the extraction of arsenic from fly-ash was monitored also in the environment of metabolites of fungi Aspergillus niger (citric acid) at pH 1.8.

Mineral properties and bacterial leaching of intensively ground sphalerite and sphalerite-pyrite mixture

The intensive grinding of sphalerite or sphalerite-pyrite mixtures accelerates the extraction of zinc from sphalerite by the bacteria Thiobacillus ferrooxidans and as a consequence shorten the process of bacterial leaching. This grinding affects the solid-state properties of the sulphides. It increases not only the specific surface but also the defects in sphalerite that have a positive influence on the progress of bacterial leaching. Such intensive grinding modifies in complement the electrochemical properties by increasing the anodic behaviour of sphalerite in a sphalerite-pyrite mixture. The extent of the changes in leaching is influenced by agglomeration effects of small particles obtained by intensive grinding as well as by the presure of pyrite that increase the galvanic effect and the surface properties.

Bioleaching of molybdenum from coal liquefaction catalyst residues

It has been shown that the bacterium Thiobacillus ferrooxidans can solubilize MoS 2 from coal liquefaction catalyst residues. The MoS 2 is formed during the liquefaction process from a molybdenum catalyst precursor. MoS 2 is insoluble; in order to be recovered and reused, it must be converted to a soluble form. T. ferrooxidans can oxidatively solubilize the molybdenum in MoS 2 to molybdate, in which form it can be recovered as a soluble or HCl extractable material. Bioleaching experiments show that with a starting cell concentration of 1.0 × 10 7 cells ml −1, or greater, a significant amount of the molybdenum in the residue was solubilized. These experiments indicate that the amount of molybdenum biologically solubilized from the liquefaction residues is dependent on inoculum size, with all strains of T. ferrooxidans tested having equal ability, and on the particle size of the residue. An important factor in the solubilization of MoS 2 by T. ferrooxidans is the inhibitory effect of molybdate. Literature reports that as little as 10 ppm molybdate is inhibitory to growth or ferrous iron oxidation. However, leachates containing in excess of 70 ppm molybdenum (equivalent to 116 ppm molybdate) were generated as a result of bioleaching of the liquefaction residue. When cells from previous leaching experiments were used to inoculate flasks containing fresh media and additional liquefaction residue, the bacteria were able to bioleach the fresh residue. Recent experiments have focused on the ability of T. ferrooxidans to produce protective agents in the leachate that minimize the inhibitory effects of molybdate. We found that production of the protective factor(s) did not depend on previous exposure of the cells to molybdenum or liquefaction residue.

Electrochemistry ofthiobacillus ferrooxidans interactions with pyrite

A cyclic voltammetry technique was used to study the interactions of mineral-pyrite during bioleaching with the bacteriumThiobacillus (T.) ferrooxidans over its entire growth cycle. Invariably, the pyrite surface drastically changed its properties on the second day of bacterial rowth (bioleaching). After 2 days, the cyclic voltammograms (CVs) were insensitive to convective diffusion produced by stirring. The product layer was examined by scanning electron microscopy (SEM), X-ray diffraction, and chemical analysis. The SEM study revealed an extremely high density of bacteria on the pyrite surface. The high density of bacteria, along with the solid reaction products formed on the pyrite surface, created conditions for crack/pore diffusion, explaining why the CVs became insensitive to convective diffusion (stirring) in solution. X-ray diffraction study confirmed jarosite as a product layer. A mechanism is proposed by whichT. ferrooxidans cells serve as nucleation sites for jarosite formation.

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.

Desulphuring of natural gas and petroleum oil by autotrophic Thiobacillus ferrooxidans

Hydrogen sulphide is a common toxic contaminant in natural gas and oil. In this study, the strictly autotrophic bacterium Thiobacillus ferrooxidans, which oxidizes reduced sulphur compounds, was used to desulphur petroleum oil and gas. The reaction was carried out in a closed vessel containing substrate mixed with a bacterial suspension. The significance of the hydrogen sulphide oxidizing activity of T. ferrooxidans is discussed.

Enhanced separation of pyrite from oxidized coal by froth flotation using biosurface modification

Bacterial conditioning prior to froth flotation has been used to enhance the separation of pyrite from naturally oxidized coal. The pyrite surface in the coal slurry was selectively made more hydrophilic by adapted Thiobacillus ferrooxidans bacteria, thereby depressing the floatability of pyrite, but not that of coal. After bioconditioning and removal of the bacterial culture, the coal slurry was subjected to froth flotation at pH 8. The bioconditioning of oxidized coal ahead of flotation improved pyritic sulfur rejection significantly while not greatly affecting coal recovery. The results indicated that biosurface modification is largely unaffected by the state of oxidation of the pyrite and coal, and that the process of bioconditioning followed by flotation works equally well on fresh and oxidized high sulfur coals.

Interfacial phenomena affecting the adhesion of Thiobacillus ferrooxidans to sulphide mineral surface

The electrokinetic and hydrophobic properties of the autotrophic bacteria Thiobacillus ferrooxidans as well as selected minerals have been studied by microelectrophoresis, contact angle and hexadecane/aqueous phase partition measurements. Adhesion measurements were conducted on sized fractions of quartz, pyrite, chalcopyrite and other copper sulphides in order to establish the relationships between cell surface properties and cell adhesion to specific mineral surfaces. It was found that the bacteria had an isoelectric point at pH 3.0 and that they were slightly hydrophobic, showing a water contact angle of 20–24 and extraction recoveries into hexadecane in the range 14–22 wt.% Adhesion mechanisms involved in the interaction between Thiobacillus ferrooxidans and mineral surfaces as a function of the electrokinetic and hydrophobic properties of bacteria and minerals are illustrated. Calculated free energies of bacterial adhesion to quartz, chalcopyrite and pyrite indicated that adhesion appears to occur at the secondary minimum according to the Derjaguin—Landau—Verwey—Overbeek theory.

Physiological characteristics ofthiobacillus ferrooxidansandleptospirillum ferrooxidansand physicochemical factors influence microbial metal leaching

Ore samples from sulfidic mines in Romania were analyzed quant. for the occurrence of the ferrous-ion-oxidizing bacteria Thiobacillus ferrooxidans and Leptospirillum ferrooxidans. Thiobacillus ferrooxidans was detected regularly, whereas L. ferrooxidans occurred only at sites with a temp. above 20 DegC and with sufficient humidity. Accordingly, L. ferrooxidans survived preservation expts. only in nutrient soln. with and without pyrite for 56 days at 17 DegC. Thiobacillus ferrooxidans also survived this period of time in liq. nitrogen, frozen at -70 DegC with and without protective buffer, and after freeze-drying, although the cell nos. and activity were reduced. Thiobacillus thiooxidans survived all techniques. After growth on ferrous sulfate, the ferrous-ion-oxidizing activity of L. ferrooxidans was about 40% of the activity of T. ferrooxidans. After growth on sulfidic ore, both species exhibited a lower but similar activity. Cells of L. ferrooxidans exhibited 35% activity and cells of T. ferrooxidans 15%. Lab. expts. with pure cultures of these lithotrophs and mixed with strains of Acidiphilium sp. demonstrated that chemoorganotrophic microorganisms enhanced only the metabolic activity of L. ferrooxidans. Furthermore, in mixed culture with Acidiphilium sp., cells of L. ferrooxidans formed microcolonies or flocks. Flocks did not appear in pure cultures nor in mixed cultures of T. ferrooxidans and Acidiphilium strains. Considering the porous system of an ore particle in a humid environment, high ferric ion concn., and a low pH value, the results indicate that L. ferrooxidans is as important as T. ferrooxidans for metal solubilization and thus for microbial leaching.

Effect of biotreatment with Thiobacillus ferrooxidans on the floatability of sphalerite and galena

The bacterium Thiobacillus ferrooxidans triggers the surface modification of sulfide minerals to provide hydrophilicity or hydrophobicity for the flotation of sphalerite and galena. The effects of initial cell concentration, period of biotreatment and pulp density on the floatability of the minerals are discussed. With galena, flotation enhancement obtained through sulfuric acid treatment was retarded by biotreatment at all cell concentrations due to chemical effects. Such a decrease occurred for sphalerite only at cell concentrations sufficiently high for bacterial attachment to the mineral surface. The variables affecting surface modification (and, thus, flotation response of the minerals) include the cell concentration used for bacterial conditioning, the period of biotreatment and the pulp density. Although bacterial growth during biotreatment was observed even in the absence of nutrients, such growth was more common in the sphalerite suspension than in the galena suspension. Cell protein estimations suggest that more cells are attached on galena than on sphalerite. Probable reaction mechanisms associated with bacterial modification are discussed.