Bacterial Pyrite Oxidation Research Articles

Remediation of Caldas site by natural attenuation

Acid mine drainage (AMD) is one of the main environmental issue caused by chemical and bacterial oxidation of pyrite (FeS2) and other sulfite minerals when exposed to atmospheric conditions during mining. In Brazil, AMD occurs in a former uranium mine and contains radionuclides and other elements, which are precipitated from acidic water by liming. Due to the inefficiency of the treatment, contaminants overflow to the water reservoir of Indústrias Nucleares do Brasil – INB in Caldas. The multiplicity of interactions that can occur between the contaminants and the sediments of the reservoir requires a broader approach in order to understand the fixation and/or transport of these elements. In this work the natural remediation approach is reviewed and an initial chemical and radiochemical characterization of the reservoir sediments is presented. Uranium was determined by spectrophotometry, Ra-226, Ra-228 and Pb-210 by gamma spectrometry and zinc by ICP-OES. Twenty-six sediment samples were collected in the reservoir and a bathymetry survey by sonar was performed to determine the thickness of the sediment layer. All the data were processed using the ArcGIS program. To assess the potential mobility and bioavailability of contaminants and to study the role of bacterial sulfate reduction in the immobilization of these contaminants, Acid-volatile sulfide (AVS) analyzes will be performed as a further step.

Iberian Pyrite Belt Subsurface Life (IPBSL), a Drilling Project of Biohydrometallurgical Interest

The geomicrobiological characterization of Río Tinto, an extreme acidic environment, has proven the importance of the iron cycle, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic heavy metals) but also in maintaining the high level of microbial diversity detected in the water column and the sediments. The extreme conditions detected in the Tinto basin are not the product of industrial contamination but the consequence of the presence of an underground bioreactor that obtains its energy from the massive sulfide minerals of the Iberian Pyrite Belt (IPB). To test this hypothesis, a drilling project (IPBSL) to intersect ground waters interacting with the mineral ore is under way, to provide evidence of subsurface microbial activities. A dedicated geophysical characterization of the area selected two drilling sites due to the possible existence of water with high ionic content. Two wells have been drilled in Peña de Hierro, BH11 and BH10, with depths of 340 and 630 meters respectively, with recovery of cores and generation of samples in anaerobic and sterile conditions. The geological analysis of the retrieved cores showed an important alteration of mineral structures associated with the presence of water, with production of expected products from the bacterial oxidation of pyrite. Ion chromatography of water soluble compounds from uncontaminated samples showed the existence of putative electron donors, electron acceptors, as well as variable concentration of metabolic organic acids, which suggest the presence of an active subsurface ecosystem associated to the high sulfidic mineral content of the IPB. Enrichment cultures from selected samples showed evidences of an active iron and sulfur cycle, together with unexpected methanogenic, methanotrophic and acetogenic activities. The geological, geomicrobiological and molecular biology analyses which are under way, should allow the characterization of this ecosystem of biohydrometallurgical interest

Aerobic bacterial pyrite oxidation and acid rock drainage during the Great Oxidation Event

The enrichment of redox-sensitive trace metals in ancient marine sedimentary rocks has been used to determine the timing of the oxidation of the Earth's land surface. Chromium (Cr) is among the emerging proxies for tracking the effects of atmospheric oxygenation on continental weathering; this is because its supply to the oceans is dominated by terrestrial processes that can be recorded in the Cr isotope composition of Precambrian iron formations. However, the factors controlling past and present seawater Cr isotope composition are poorly understood. Here we provide an independent and complementary record of marine Cr supply, in the form of Cr concentrations and authigenic enrichment in iron-rich sedimentary rocks. Our data suggest that Cr was largely immobile on land until around 2.48 Gyr ago, but within the 160 Myr that followed--and synchronous with independent evidence for oxygenation associated with the Great Oxidation Event (see, for example, refs 4-6)--marked excursions in Cr content and Cr/Ti ratios indicate that Cr was solubilized at a scale unrivalled in history. As Cr isotope fractionations at that time were muted, Cr must have been mobilized predominantly in reduced, Cr(III), form. We demonstrate that only the oxidation of an abundant and previously stable crustal pyrite reservoir by aerobic-respiring, chemolithoautotrophic bacteria could have generated the degree of acidity required to solubilize Cr(III) from ultramafic source rocks and residual soils. This profound shift in weathering regimes beginning at 2.48 Gyr ago constitutes the earliest known geochemical evidence for acidophilic aerobes and the resulting acid rock drainage, and accounts for independent evidence of an increased supply of dissolved sulphate and sulphide-hosted trace elements to the oceans around that time. Our model adds to amassing evidence that the Archaean-Palaeoproterozoic boundary was marked by a substantial shift in terrestrial geochemistry and biology.

Role of ferric ions in bioleaching of uranium from low tenor Indian ore

The role of biogenic ferric ions in leaching of uranium by Acidithiobacillus ferrooxidans from a low grade ore of Turamdih mines, India, has been investigated. Using the enriched culture of bacterial isolate containing mainly A. ferrooxidans from the source mine water, biorecovery of 98% uranium at 20% (w/v) pulp density, pH 1·7 and 35°C temperature using <76 μm particles in 40 days was obtained. The effect of temperature on bioleaching of uranium showed higher recovery at 35°C. The uranium dissolution was facilitated by iron(III) available in the leach liquor because of bacterial oxidation of pyrite and chemical dissolution of magnetite present in the ore under acidic conditions. The biogenically generated Fe(III) ions enhanced uranium dissolution from the uraninite ore. The bioleaching of uranium appeared to follow a chemical control kinetic model with the reaction of lixiviant, Fe(III) and acid on the surface of the solid in the temperature range 25–35°C. Phase identification by XRD and the study of surface morphology of the ore and the residue by SEM study corroborated the above mechanism of uranium leaching.On a étudié le rôle des ions ferriques biogènes dans la lixiviation de l’uranium par A. ferrooxidans d’un minerai pauvre des mines de Turamdih, en Inde. En utilisant la culture enrichie d’isolat bactérien contenant principalement Acidithiobacillus ferrooxidans de l’eau de source de la mine, on a obtenu une biorécupération de 98% d’uranium à 20% de densité de la pulpe (poids/vol), avec un pH de 1·7 et une température de 35°C, en utilisant des particules de <76 μm, en 40 jours. L’effet de la température sur la biolixiviation de l’uranium montrait une récupération plus élevée à 35°C. La dissolution de l’uranium était facilitée par le fer(III), disponible dans la liqueur de lixiviat grâce à l’oxydation bactérienne de la pyrite et à la dissolution chimique de la magnétite présentes dans le minerai en conditions acides. Les ions Fe(III) engendrés biogéniquement augmentaient la dissolution de l’uranium du minerai d’uraninite. La biolixiviation de l’uranium semblait suivre un modèle cinétique à contrôle chimique avec la réaction du lixiviant – Fe(III) et de l’acide à la surface du solide dans la gamme de température de 25 à 35°C. L’identification de phase par XRD et l’étude de la morphologie de la surface du minerai et du résidu par étude au SEM corroboraient le mécanisme ci-dessus de lixiviation de l’uranium.

Bacterial leaching of manganese ores

Leaching of various types of ores, containing 12-30% manganese, by the thiobacterium Acidithiobacillus ferrooxidans was studied. Leaching of reduced ores (manganocalcite and manganiferous limestone) was mediated mainly by degradation of manganiferous minerals (by sulfuric acid produced in the course of bacterial oxidation of pyrite or sulfur). Bacterial treatment of the ores for 144 and 192 h allowed solubilization of 96-98% of manganese. Inoculation of bacteria into pulp with pyrite increased the rate of leaching of oxide ore (psilomelane) by 37%, and the degree of its extraction within 180 h increased from 80 to 97%.

Studies on kinetics of biodissolution of metals from Indian Ocean nodules

This paper describes the studies on kinetics of bio-dissolution of valuable metals such as copper, nickel and cobalt from the Indian Ocean nodules using Thiobacillus ferrooxidans and Thiobacillus thiooxidans in the presence of pyrite and sulphur. The bacterial oxidation of pyrite and sulphur produces ferrous sulphate and sulphurous acid respectively which reduce Mn(IV) of the nodules to Mn(II), thereby dissolving the metals through indirect mechanism. The leaching data collected in the temperature range 293–308 K at a pH of 2 and 5% pulp density with the particle size of 300 to −75 μm, show that the dissolution of the metals follows shrinking core kinetic model. The leaching is controlled by the diffusion of the lixiviant through the product layer which is also indicated by the activation energy values.

The EPS of Acidithiobacillus ferrooxidans - a model for structure-function relationships of attached bacteria and their physiology

To dissolve pyrite or sulphur, leaching bacteria like Acidithiobacillus ferrooxidans attach to these substrata by extracellular polymeric substances (specifically, lipopolysaccharides). The primary attachment to pyrite at pH 2 is mediated by exopolymer-complexed iron(III) ions in an electrostatic interaction with the negatively charged pyrite surface. Cells grown on sulphur exhibit a different composition of the extracellular lipopolysaccharides, namely with increased hydrophobic properties, and do not attach to pyrite. Thus, the cells adapt the chemical composition of their exopolymers to the substrate/substratum. It is concluded that the mechanism of bacterial pyrite oxidation is basically indirect. The actual corrosive agents are iron(III) ions. Preliminary data indicate that active strains complex more iron(III) ions in their EPS than less active ones. Obviously, the exopolymeric layer comprises a reaction space for the regeneration of these ions by the activity of the iron oxidising bacteria.

95/03241 Bacterial pyrite oxidation: Influence of morphological, physical and chemical properties

95/03241 Bacterial pyrite oxidation: Influence of morphological, physical and chemical properties

Bacterial pyrite oxidation: Influence of morphological, physical and chemical properties

Physical and chemical characteristics of six types of pyrite isolated from ores and coals as well as the mechanism of their oxidation by Thiobacillus ferrooxidans and Sulfobacillus thermosulfidooxidans were investigated. The effect of monocrystallinity, orientation of crystals, and microaggregation on the oxidation degree of polish rock section was clearly revealed. The investigation of the surface of powdered pyrite particles showed the ratio S 2−/Fe 2+ of pyrite to be equal to 2.7. This indicates that the surface of the pyrite particles was deficient in metal or redundant in sulfur. This ratio holds in the coarse of pyrite oxidation by T. ferrooxidans, indicating that Fe 2+ and S 2− are oxidized simultaneously. In the presence of S. thermosulfidooxidans the ratio S 2−/Fe 2+ is reduced to 1.0 for some types of pyrite indicating preferential oxidation of S 2−. The kinetics and mechanism of bacterial oxidation of pyrites are discussed.

Thermal analysis of controlled-release elastomeric formulations: Part 2. A DSC study of the effect of sodium lauryl sulphate loading on vulcanization

Controlled release of sodium lauryl sulphate (SLS) from monolithic elastomeric pellets represents one way of achieving long-term inhibition of bacterial oxidation of pyrite. The degree of cure of elastomeric formulations influences the rate of release of SLS. Vulcanization decreases the permeability of the elastomeric matrix and results in slower release of SLS. The effect of SLS loading on the vulcanization of natural rubber and synthetic cis-1,4-polyisoprene has been studied by DSC. Dynamic temperature scans show that the heat of reaction (Δ H), which is a measure of the area of the exothermic peak, decreases with increasing SLS content. The decrease in Δ H is not very significant at SLS levels up to 15%, but is clearly noticeable at levels of 25%. In the case of formulations which contain 35% SLS, no curing exotherms are observed. It is therefore concluded that rubber formulations which contain 35% or more SLS are unvulcanized. Analysis of curing exotherms by means of the Borchardt and Daniels DSC kinetics data analysis program gives inconclusive results. It is suggested that the complex chemistry of the accelerated sulphur vulcanization of olefinic rubbers makes it difficult to obtain reliable quantitative reaction kinetics information for this particular type of reaction.

Thermal analysis of controlled-release elastomeric formulations: Part 1. Determination of the solubility limits of sodium lauryl sulphate in elastomers by differential scanning calorimetry

Controlled-release formulations for attaining long-term inhibition of bacterial oxidation of pyrite and the concomitant acid mine drainage were prepared from natural and synthetic rubbers used as binding matrices and sodium lauryl sulphate (SLS) as the active ingredient. The kinetics of release of an active agent from a polymeric matrix depend on several solute-dependent and solute-independent variables. This study focuses on one of the solute-dependent variables, namely, the solubility limit. Since no data on the solubility limits of SLS in natural and synthetic rubbers could be traced, techniques for determining these solubility values were investigated. In this study natural rubber (SMR 20) and synthetic cis-1,4-polyisoprene (IR-80) formulations containing from 0 to 35% SLS were analysed by differential scanning calorimetry (DSC). The thermograms obtained show the appearance of a characteristic melting endotherm when the solubility limit of SLS is exceeded, and this allows the amounts of dissolved and dispersed SLS in the controlled-release formulations to be estimated. The results of the study demonstrate the usefulness of DSC as a convenient and reliable method for determining the solubility limits of solids in elastomers.

Rate Equations and Kinetic Parameters of the Reactions Involved in Pyrite Oxidation by Thiobacillus ferrooxidans

Rate equations and kinetic parameters were obtained for various reactions involved in the bacterial oxidation of pyrite. The rate constants were 3.5 muM Fe per min per FeS(2) percent pulp density for the spontaneous pyrite dissolution, 10 muM Fe per min per mM Fe for the indirect leaching with Fe, 90 muM O(2) per min per mg of wet cells per ml for the Thiobacillus ferrooxidans oxidation of washed pyrite, and 250 muM O(2) per min per mg of wet cells per ml for the T. ferrooxidans oxidation of unwashed pyrite. The K(m) values for pyrite concentration were similar and were 1.9, 2.5, and 2.75% pulp density for indirect leaching, washed pyrite oxidation by T. ferrooxidans, and unwashed pyrite oxidation by T. ferrooxidans, respectively. The last reaction was competitively inhibited by increasing concentrations of cells, with a K(i) value of 0.13 mg of wet cells per ml. T. ferrooxidans cells also increased the rate of Fe production from Fe plus pyrite.

Feasibility of a dutch process for microbial desulphurization of coal

Abstract The technical and economical feasibility of microbial coal desulphurization has been studied with attention on the removal of finely dispersed inorganic sulphidic minerals which cannot be removed by sink-float processes. Data have been collected on the suitability of various low-sulphur coals representative of future Dutch imports. It was possible to remove 90% of the pyrite present within 8 to 10 days by using a mesophilic, pyrite-oxidizing, microbial system. No removal of organic sulphur was observed. Depending on the type of coal, a considerable reduction in the contents of ash-forming minerals and heavy metals was achieved. To determine the optimal dimensions of a reactor system, the kinetics of bacterial growth and pyrite oxidation were studied. The kinetics of bacterial pyrite oxidation appear to be first order in the amount of pyrite present, indicating a plug flow reactor is most appropriate. However, because almost all of the bacterial biomass is attached to the solids, incoming coal in a continuous working system can be inoculated only by intensive contact with particles already loaded with bacteria. For this purpose, a plug flow reactor is not adequate, and a configuration consisting of a mixed flow reactor followed by a plug flow is proposed. To prevent biomass limitation, the residence time in the mixed flow reactor must be longer than the reciprocal value of the specific growth rate of the pyrite oxidizing bacteria, 0.05 h −1 at pH 1.8. The slow kinetics and the enormous amounts of coal to be treated require huge reactors. To make the process economical, the reactors must be simple and cheap. The choice is a cascade of Pachuca tank reactors. The first tank functions as the mixed flow reactor. The following tanks, in series, approximate a plug flow. Studies on oxygen mass transfer, mixing and settling in laboratory scale Pachuca tank reactors revealed that the air flow required for the oxygen supply of the pyrite-oxidizing microflora is enough for adequate suspension and mixing of the coal in the water and to prevent settling. From the kinetic and technological studies a process design has been derived. This has been adopted by an engineering consultancy firm to calculate the cost of the process. It appears that, depending on the coal types to be cleaned, the location and governmental environmental regulations, microbial desulphurization might be a realistic option.

Distribution of Iron-Oxidizing Bacteria in the Nordic Uranium Tailings Deposit, Elliot Lake, Ontario, Canada

Iron-oxidizing bacteria are present within the top 2 m (but not always at the surface) and near the water table-capillary fringe of the vegetated Nordic uranium deposit, Elliot Lake, Ontario, Canada. They are distributed uniformly in the top 0.5 m of unvegetated tailings. The locations of these bacteria correlate with zones of pyrite oxidation as delineated in previous studies by the formation of soluble iron and sulfate. Heterotrophic bacteria are also present in the tailings, with greatest concentrations at the surface and near the water table-capillary fringe. Sulfate-reducing bacteria were detected in the soil and peat at the base of the tailings. The results of this study suggest that the establishment of vegetation directly upon the tailings surface does not arrest bacterial pyrite oxidation.

Analysis of soluble iron compounds in the bacterial oxidation of pyrite

Bacterial solubilization and oxidation of iron from pyrite were determined with the use of analytical methods which differentiated between total iron and reduced and oxidized forms of soluble iron. About 70% precipitation of Fe(III) was apparent in six-week old cultures. Yeast extract (0.2 and 2%) inhibited the bacterial oxidation of pyrite. Incomplete (∼50%) bacterial oxidation of iron dissolved from pyrite was attributed to the inhibition of the bacterial iron-oxidation at pH 1.2–1.3. Sample pretreatments with ion-exchange resins before analysis indicated that cationic iron concentration was almost identical with that of total iron in bacterial cultures; anionic forms of Fe amounted to about 7% of the total soluble iron.

Generation of ferric Lixiviant by bio‐oxidation of pyrite for in‐situ leaching

Abstract Acidic ferric ion, an effective and important oxidizing agent for mineral leaching, is usually produced by direct dissolution of the corresponding salts into the solution or can be prepared in‐situ or in separate aerated batch reactors by chemical oxidation of iron sulfide through a number of different processes. The purpose of this paper is to present the idea and the results of generating the useful ferric leaching medium by bacterial oxidation of pyrite under the commercial leaching conditions in an underground copper mine. The information presented deals mainly with factors promoting the continuous oxidation of pyrite by iron‐oxidizing bacteria and the related factors influencing the extraction of copper from the enargite. This is the first attempt to produce a ferric leaching medium in an underground mine by a microbiological process. The generation technology and engineering layout are also discussed.

Bacterial pyrite oxidation III. Adsorption of Thiobacillus ferrooxidans cells on solid surfaces and its effect on iron release from pyrite.

The cells of Thiobacillus ferrooxidans were rapidly adsorbed on the solid surfaces of an agitated flask containing 1% pulp density of pyrite particles. More than ca. 99% of the inoculated cells were adsorbed. However, considerably fewer cells were adsorbed on pyrite particles than on the glass wall of the flask. Scanning electron microscope observation revealed that T. ferrooxidans cells were adsorbed aggregatively on restricted areas of the pyrite particles. The surfaces of the pyrite particles were characteristically eroded to show etched polyhedral pits, but without prominent cell adsorption of the extensively eroded surfaces during markedly enhanced leaching. When T. ferrooxidans cells were adsorbed on the solid surfaces, the iron-oxidizing activity of the bacteria was strongly inhibited, resulting in a failure to enhance pyrite oxidation. Adsorbed cells did not proliferate on the solid surfaces. When the adsorbed cells were released into an aqueous phase by the addition of the surface active agent Tween 20, the bacterial iron-oxidizing activity inhibited by adsorption was recovered and, as a result, pyrite oxidation was markedly promoted. Significant enhancement of pyrite oxidation by T. ferrooxidans was ascribed to the development and iron-oxidizing activity of the freely dispersed cells in an aqueous phase. The function of the surface active agent is to prevent tenacious adsorption of the bacterial cells to solid surfaces and organic substances examined, such as protein, nucleic acid, yeast extract, peptone, and cell free extracts, operate in the same way as the surface active agent. The enhancement of the bacterial pyrite oxidation by the intact cells of Thiobacillus thiooxidans is thought to be attributable to the organic substances excreted from T. thiooxidans cells and/or to the exchange adsorption of cells of both thiobacilli. The present results indicate that bacterial concentration in an aqueous phase rather than on pyrite particles plays major role in the enhanced oxidation of pyrite by T. ferrooxidans and that the bacteria contribute indirectly to pyrite oxidation through the regeneration reaction of ferric iron.

Bacterial pyrite oxidation. II. The effect of various organic substances on release of iron from pyrite by Thiobacillus ferrooxidans.

The role of Thiobacillus thiooxidans was investigated in the enhancement of pyrite oxidation by the mixtures of Thiobacillus ferrooxidans and T. thiooxidans. The oxidation of pyrite by T. ferrooxidans was remarkably enhenced by the addition of dead cell suspensions and cell-free extracts of both chemolithotrophic thiobacilli and heterotrophic bacteria. The same promoting effect on the bacterial pyrite oxidation was recognized with various substances such as protein, nucleic acid, yeast extract, peptone, and also surface-active agent. These results indicate that the enhancement of bacterial pyrite oxidation by the intact cells of T. thiooxidans is attributed at least partly to the organic substances excreted from T. thiooxidans cells into the pyrite medium, and that cellular organic substances have a physico-chemical effect on a direct interaction between iron-oxidizing bacteria and solid particles

Bacterial pyrite oxidation I. The effect of pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans on release of iron.

Fundamental investigations were made on the oxidation of pyrite and consequent dissolution of iron by pure and mixed cultures of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. The release of iron from pyrite was remarkably enhanced with large inocula above ca. 109 cells per flask (or 1% pulp density) of 2-day (active) cultures of T. ferrooxidans, but not with inoculum of 108 cells or less. Furthermore, a phenomenon was observed that the enhanced oxidation of pyrite always proceeded with the coexistence of a 108 cells or less inoculum of T. ferrooxidans and T. thiooxidans incapable of oxidizing pyrite. During the bacterial oxidation of pyrite, high iron oxidation ratios (Fe3+/total Fe) above 90% were maintained, coincident with the enhanced release of iron from pyrite. Contrarily, in the absence of T. ferrooxidans, a major portion of iron was in the ferrous form and iron release was not promoted. Thus, it was thought that T. ferrooxidans contributes to the oxidation of pyrite through the regeneration reaction of ferric iron.

Bacterial pyrite oxidation: release of iron and scanning electron microscopic observations

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.