Occurrences at mineral-bacteria interface during oxidation of arsenopyrite by Thiobacillus ferrooxidans

The combination of an improved bacterial desorption method, scanning electron microscopy (SEM), diffuse reflectance and transmission infrared Fourier transform spectroscopy, and a desorption-leaching device like high-pressure liquid chromatography (HPLC) was used to analyze bacterial populations (adhering and free bacteria) and surface-oxidized phases (ferric arsenates and elemental sulfur) during the arsenopyrite biooxidation by Thiobacillus ferrooxidans. The bacterial distribution, the physicochemical composition of the leachate, the evolution of corrosion patterns, and the nature and amount of the surface-oxidized chemical species characterized different behavior for each step of arsenopyrite bioleaching. The first step is characterized by a slow but strong adhesion of bacteria to mineral surfaces, the appearance of a surface phase of elemental sulfur, the weak solubilization of Fe(II), As(III), and As(V), and the presence of the first corrosion patterns, which follow the fragility zones and the crystallographic orientation of mineral grains. After this short step, growth of the unattached bacteria begins, while ferrous ions in solution are oxidized by them. Ferric ions produced by the bacteria can oxidize the sulfide directly and are regenerated by Fe(II) bacterial oxidation. At this time, a bioleaching cycle takes place and a coarse surface phase of ferric arsenate (FeAsO(4) . xH(2)O where x approximately 2) and deep ovoid pores appear. At the end of the bioleaching cycle, the high concentration of Fe(III) and As(V) in solution promotes the precipitation of a second phase of amorphous ferric arsenate (FeAsO(4) . xH(2)O where x approximately 4) in the leachate. Then the biooxidation process ceases: The bacteria adhering to the mineral sufaces are coated by the ferric arsenates and the concentration of Fe(III) on the leachate is found to have decreased greatly. Both oxidation mechanisms (direct and indirect oxidation) have been stopped. (c) 1995 John Wiley & Sons, Inc.     

Oxygen Dependency of Neutrophilic Fe(II) Oxidation by Leptothrix Differs from Abiotic Reaction

Neutrophilic Fe(II) oxidizing microorganisms are found in many natural environments. It has been hypothesized that, at low oxygen concentrations, microbial iron oxidation is favored over abiotic oxidation. Here, we compare the kinetics of abiotic Fe(II) oxidation to oxidation in the presence of the bacterium Leptothrix cholodnii Appels isolated from a wetland sediment. Rates of Fe(II) oxidation were determined in batch experiments at 20°C, pH 7 and oxygen concentrations between 3 and 120 μmol/l. The reaction progress in experiments with and without cells exhibited two distinct phases. During the initial phase, the oxygen dependency of microbial Fe(II) oxidation followed a Michaelis-Menten rate expression (K_M = 24.5 ± 10 μmol O₂/l, v_max = 1.8 ± 0.2 μmol Fe(II)/(l min) for 10⁸ cells/ml). In contrast, abiotic rates increased linearly with increasing oxygen concentrations. At similar oxygen concentrations, initial Fe(II) oxidation rates were faster in the experiments with bacteria. During the second phase, the accumulated iron oxides catalyzed further oxidative iron precipitation in both abiotic and microbial reaction systems. That is, abiotic oxidation also dominated the reaction progress in the presence of bacteria. In fact, in some experiments with bacteria, iron oxidation during the second phase proceeded slower than in the absence of bacteria, possibly due to an inhibitory effect of extracellular polymeric substances on the growth of Fe(III) oxides. Thus, our results suggest that the competitive advantage of microbial iron oxidation in low oxygen environments may be limited by the autocatalytic nature of abiotic Fe(III) oxide precipitation, unless the accumulation of Fe(III) oxides is prevented, for example, through a close coupling of Fe(II) oxidation and Fe(III) reduction.     

Manganese and Arsenic Oxidation Performance of Bacterium-Yunotaki 86 (BY86) from Hokkaido,Japan, and the Bacterium's Phylogeny

We examined the Mn(II) oxidation performance of a bacterium, BY86, collected at Yunotaki Falls Hokkaido, Japan. The bacterium showed rapid oxidation of Mn(II), and brown precipitates containing Mn formed within a few days of incubation. The presence of higher oxidation states of Mn than Mn(II) was ascertained by the UV-vis and XANES sutdy. This bacterium did not oxidize As(III) to As(V) in the absence of Mn. In the presence of Mn, however, As(III) was rapidly oxidized to As(V) on the cell surfaces. These findings indicate that BY86 does not have the ability to directly oxidize As(III) to As(V) within a short period of contact, but indirectly oxidizes it by the Mn oxides generated on the cell surfaces. A phylogenetical study disclosed that BY86 was most closely related to Bacillus cereus with an identity of 99.90%. It is expected that our findings in this study will contribute to the study of Mn(II)-oxidizing bacteria, which play an important role in the biogeochemical cycling of Mn as well as other trace elements including As.     

Fe(III)-enhanced anaerobic transformation of 2,4-dichlorophenoxyacetic acid by an iron-reducing bacterium Comamonas koreensis CY01

This work studied the ability of Comamonas koreensis CY01 to reduce Fe(III) (hydr)oxides by coupling the oxidation of electron donors and the enhanced biodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by the presence of Fe(III) (hydr)oxides. The experimental results suggested that strain CY01 can utilize ferrihydrite, goethite, lepidocrocite or hematite as the terminal electron acceptor and citrate, glycerol, glucose or sucrose as the electron donor. Strain CY01 could transform 2,4-D to 4-chlorophenol through reductive side-chain removal and dechlorination. Under the anaerobic conditions, Fe(III) reduction and 2,4-D biodegradation by strain CY01 occurred simultaneously. The presence of Fe(III) (hydr)oxides would significantly enhance 2,4-D biodegradation, probably due to the fact that the reactive mineral-bound Fe(II) species generated from Fe(III) reduction can abiotically reduce 2,4-D. This is the first report of a strain of C. koreensis capable of reducing Fe(III) (hydr)oxides and 2,4-D, which extends the diversity of iron-reducing bacteria associated with dechlorination.     

Enhancing pozzolana colonization by As(III)-oxidizing bacteria for bioremediation purposes

The colonization of pozzolana by an As(III)-oxidizing bacterial consortium was monitored from the first hours of bacterial adhesion to 6 weeks of development under fed-batch conditions, using adapted ultrasonic dislodging and crystal-violet staining procedures to determine the biofilm adhering to the complex surfaces. The effect of temperature, arsenic concentration, and presence or absence of yeast extract (YE) on the amount of biofilm biomass and on the As(III)-oxidation were assessed to test the biofilm’s resilience and optimize the colonization. Fed-batch cultures allow twice as much pozzolana colonization as that obtained under batch conditions. In addition, As(III) oxidation and the quantities of biomass under fed-batch culture conditions were the same at 14°C and 25°C. Whereas YE improves (+150%) bacterial adhesion during the first 2 h, its impact in the longer term appears to be less significant—biofilm formation in presence of YE after 5 weeks was no greater than biofilm formation in the absence of YE. Finally, YE involves a drastic (−70%) decrease of As(III) oxidation. Preliminary tests for drinking-water bioremediation revealed the ability of Chéni Arsenic Oxidizing 1 biofilms to remain and retain As(III) oxidation activity at low As(III) concentrations (50 μg l⁻¹).     

Influence of Biogenic Fe(II) on Bacterial Crystalline Fe(III) Oxide Reduction

Bacterial crystalline Fe(III) oxide reduction has the potential to significantly influence the biogeochemistry of anaerobic sedimentary environments where crystalline Fe(III) oxides are abundant relative to poorly crystalline (amorphous) phases. A review of published data on solid-phase Fe(III) abundance and speciation indicates that crystalline Fe(III) oxides are frequently 2- to S 10-fold more abundant than amorphous Fe(III) oxides in shallow subsurface sediments not yet subjected to microbial Fe(III) oxide reduction activity. Incubation experiments with coastal plain aquifer sediments demonstrated that crystalline Fe(III) oxide reduction can contribute substantially to Fe(II) production in the presence of added electron donors and nutrients. Controls on crystalline Fe(III) oxide reduction are therefore an important consideration in relation to the biogeochemical impacts of bacterial Fe(III) oxide reduction in subsurface environments. In this paper, the influence of biogenic Fe(II) on bacterial reduction of crystalline Fe(III) oxides is reviewed and analyzed in light of new experiments conducted with the acetate-oxidizing, Fe(III)-reducing bacterium (FeRB) Geobacter metallireducens . Previous experiments with Shewanella algae strain BrY indicated that adsorption and/or surface precipitation of Fe(II) on Fe(III) oxide and FeRB cell surfaces is primarily responsible for cessation of goethite ( f -FeOOH) reduction activity after only a relatively small fraction (generally < 10%) of the oxide is reduced. Similar conclusions are drawn from analogous studies with G. metallireducens . Although accumulation of aqueous Fe(II) has the potential to impose thermodynamic constraints on the extent of crystalline Fe(III) oxide reduction, our data on bacterial goethite reduction suggest that this phenomenon cannot universally explain the low microbial reducibility of this mineral. Experiments examining the influence of exogenous Fe(II) (20 mM FeCl 2 ) on soluble Fe(III)-citrate reduction by G. metallireducens and S. algae showed that high concentrations of Fe(II) did not inhibit Fe(III)-citrate reduction by freshly grown cells, which indicates that surface-bound Fe(II) does not inhibit Fe(III) reduction through a classical end-product enzyme inhibition mechanism. However, prolonged exposure of G. metallireducens and S. algae cells to high concentrations of soluble Fe(II) did cause inhibition of soluble Fe(III) reduction. These findings, together with recent documentation of the formation of Fe(II) surface precipitates on FeRB in Fe(III)-citrate medium, provide further evidence for the impact of Fe(II) sorption by FeRB on enzymatic Fe(III) reduction. Two different, but not mutually exclusive, mechanisms whereby accumulation of Fe(II) coatings on Fe(III) oxide and FeRB surfaces may lead to inhibition of enzymatic Fe(III) oxide reduction activity (in the absence of soluble electron shuttles and/or Fe(III) chelators) are identified and discussed in relation to recent experimental work and theoretical considerations.     

Further Readings in Geomicrobiology

Microbial biofilms preferentially colonized pyrite surfaces of black shale incubated in groundwater in the Newark Basin (northeastern United States) for 1 month. SEM observation revealed the co-occurrence of bacteria-shaped pits and secondary iron minerals on pyrite, which indicate biological involvement in pyrite weathering and secondary solid formation. Of the 24 16S rDNA sequences obtained from bacterial communities on pyrite, arsenopyrite and quartz sand, 22 belonged to the phylum proteobacteria, including 5 identified as β or ?-proteobacteria capable of oxidizing iron or sulfur, 16 identified as members of the Fe(III)-reducing Geobacteraceae in the δ-proteobacteria and one identified as the Fe(III)-reducing Ferribacterium. Results indicate that microbes play an essential role in the oxidation of iron sulfides (via direct contact and indirect pathways) and the reduction of iron oxides in pyrite-bearing substrata of a slightly acidic black shale aquifer.     

Novel Hyper Antimony-Oxidizing Bacteria Isolated from Contaminated Mine Soils in China

Antimony (Sb)-oxidizing bacteria play an important role in environmental Sb bioremediation because of their ability to convert the more toxic Sb(III) to the less toxic Sb(V). So far, the information about the Sb(III)-oxidizing bacteria species is still limited. In this study, three highly Sb(III)-resistant bacterial strains were isolated from contaminated mine soils after aerobic enrichment culturing with Sb(III) (1 mM). The morphological, biochemical, and 16S rRNA gene sequencing analysis suggested that the three novel bacterial isolates fell within Cupriavidus, Moraxella, and Bacillus, respectively. Among the strains, Moraxella sp. S2 isolated from soils with the highest Sb content exhibited the highest minimum inhibitory concentration for Sb(III) but the lowest Sb(III) oxidation efficiency, which could not completely oxidize 50 μM Sb(III) in 15 days. Cupriavidus sp. S1 was able to oxidize 50 μM Sb(III) completely in 12 days, but could not oxidize 100 μM Sb(III) even with extended time of incubation, while Bacillus sp. S3 with the lowest resistance to Sb(III) could aerobically oxidize 100 µM Sb(III) within 2 days, showing high Sb(III) oxidation efficiency. Our research demonstrated that indigenous microorganisms associated with Sb mine soils were capable of Sb oxidation, and the novel bacteria isolated could represent good candidates for Sb remediation in heavily polluted sites.     

Microbial Metabolism of Benzene and the Oxidation of Ferrous Iron under Anaerobic Conditions: Implications for Bioremediation

Benzene and toluene were biodegraded when chelated Fe(III) served as the terminal electron acceptor in aquifer sediments contaminated by a petroleum refinery. Benzene biodegradation ceased when Fe(III) was depleted but resumed upon reamendment. Microorganisms from the same sediments degraded toluene, but not benzene, under nitrate reducing conditions. However, the anaerobic oxidation of Fe(II) to Fe(III) was also observed in toluene-degrading incubations. Fe(II) oxidation was dependent on the presence of nitrate and enhanced when organic electron donors were provided. Microbial nitrate-linked Fe(II) oxidation was also documented in other petroleum-contaminated aquifer sediments, sludge from an oil–water separator, a landfill leachate-impacted aquifer and a garden soil. These observations suggest that some of the reported effects of nitrate on hydrocarbon biodegradation may be indirect through the reoxidation of Fe(II).     

The influence of chelating agents upon the dissimilatory reduction of Fe(III) by Shewanella putrefaciens

The ability of S. putrefaciens to reduce Fe(III) complexed by a variety of ligands has been investigated. All of the ligands tested caused the cation to be more susceptible to reduction by harvested whole cells than when uncomplexed, although some complexes were more readily reduced than others. Monitoring rates of reduction by a ferrozine assay for Fe(II) formation proved inadequate using Fe(III) ligands giving Fe(II) complexes of low kinetic lability (e.g. EDTA). A more suitable assay for Fe(III) reduction in the presence of such ligands proved to be the observation of associated cytochrome oxidation and re-reduction. Where possible, an assay for Fe(III) reduction based upon the disappearance of Fe(III) complex was also employed. Reduction of all Fe(III) complexes tested was totally inhibited by the presence of O₂, partially inhibited by HQNO and slower in the absence of a physiological electron donor. Upon cell fractionation, Fe(III) reductase activity was detected exclusively in the membranes. Using different physiological electron donors in assays on membranes, relative reduction rates of Fe(III) complexes complemented the data from whole cells. The differences in susceptibility to reduction of the various complexes are discussed, as is evidence for the respiratory nature of the reduction.     

Potential for Microscale Bacterial Fe Redox Cycling at the Aerobic-Anaerobic Interface

Recent studies of bacterial Fe(II) oxidation at circumneutral pH by a newly-isolated lithotrophic β-Proteobacterium (strain TW2) are reviewed in relation to a conceptual model that accounts for the influence of biogenic Fe(III)-binding ligands on patterns of Fe(II) oxidation and Fe(III) oxide deposition in opposing gradients of Fe(II) and O₂. The conceptual model envisions complexation of Fe(III) by biogenic ligands as mechanism which alters the locus of Fe(III) oxide deposition relative to Fe(II) oxidation so as to delay/retard cell encrustation with Fe(III) oxides. Experiments examining the potential for bacterial Fe redox cycling in microcosms containing ferrihydrite-coated sand and a coculture of a lithotrophic Fe(II)-oxidizing bacterium (strain TW2) and a dissimilatory Fe(III)-reducing bacterium (Shewanella algae strain BrY) are described and interpreted in relation to an extended version of the conceptual model in which Fe(III)-binding ligands promote rapid microscale Fe redox cycling. The coculture systems showed minimal Fe(III) oxide accumulation at the sand-water interface, despite intensive O₂ input from the atmosphere and measurable dissolved O₂ to a depth of 2 mm below the sand-water interface. In contrast, a distinct layer of oxide precipitates formed in systems containing Fe(III)-reducing bacteria alone. Voltammetric microelectrode measurements revealed much lower concentrations of dissolved Fe(II) in the coculture systems. Examination of materials from the cocultures by fluorescence in situ hybridization indicated close physical juxtapositioning of Fe(II)-oxidizing and Fe(III)reducing bacteria in the upper few mm of sand. Together these results indicate that Fe(II)-oxidizing bacteria have the potential to enhance the coupling of Fe(II) oxidation and Fe(III) reduction at redox interfaces, thereby promoting rapid microscale cycling of Fe.     

Dissimilatory Fe(III) reduction by an electrochemically active lactic acid bacterium phylogenetically related to Enterococcus gallinarum isolated from submerged soil

AIMS: The isolation and identification of a glucose-oxidizing Fe(III)-reducing bacteria (FRB) with electrochemical activity from an anoxic environment, and characterization of the role of Fe(III) in its metabolism. METHODS AND RESULTS: A Gram-positive (Firmicutes), nonmotile, coccoid and facultative anaerobic FRB was isolated based on its ability to reduce Fe(III). Using the Vitek Gram-positive identification card kit and 16S rRNA gene sequence analysis, the isolate was identified as Enterococcus gallinarum, designated strain MG25. On glucose this isolate produced lactate plus small amounts of acetate, formate and CO2 and its growth rates were similar in the presence and absence of Fe(O)OH. These results suggest that MG25 can couple glucose oxidation to Fe(III) reduction, but without conservation of energy to support growth. Cyclic voltammetry showed that strain MG25 was electrochemically active. CONCLUSIONS: An electrochemically active and FRB, E. gallinarum MG25, was isolated from submerged soil. Fe(III) is used in the bacterial metabolism as an electron sink. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report concerning the electrochemical activity of glucose-oxidizing FRB, E. gallinarum. This organism and others like it could be used as new biocatalysts to improve the performance of a mediator-less microbial fuel cell.     

Kinetics of arsenic(III) oxidation by iron(III) catalysed by pyrite in the presence ofThiobacillus ferrooxidans

Summary A simple kinetic model of As(III) oxidation by Fe(III) in the presence of pyrite andThiobacillus ferroxidans is described based on the stoichiometry of the reaction and bioproduction of Fe(III). The environmental consequences of this reaction were considered.     

Ferric iron-reducing Shewanella putrefaciens and N2-fixing Bradyrhizobium japonicum with uptake hydrogenase are unable to oxidize atmospheric H2

Abstract Bradyrhizobium japonicum and Shewanella putrefaciens were unable to oxidize hydrogen at atmospheric concentrations (0.55 ppmv), neither in suspension nor when added to sterile soil. The K _m-value of S. putrefaciens for H₂ (39 ppmv in gas phase, 0.22 μM in aqueous phase), using Fe(III) as electron acceptor, showed a 4–5-fold higher affinity for H₂ than that of B. japonicum (1200 ppmv; 0.84 μM) or other hydrogen-oxidizing bacteria. However, the V _max (4.54 fmol H₂ h⁻¹ cell ⁻¹) and threshold (> 0.5 ppmv; 0.35 nM) of S. putrefaciens and the V _max (7.19 fmol H₂ h⁻¹ cell⁻¹) and threshold (> 0.5 ppmv; 0.35 nM) of B. japonicum were in the same order of magnitude as data for Knallgas bacteria from relevant literature. To enable hydrogen oxidation in soil the soil-samples with S. putrefaciens even had to be supplemented with Fe(III). Fresh soil, on the other hand, oxidized hydrogen very efficiently below atmospheric mixing ratios, demonstrating that there must be other oxidation activities in soil.     

Migration of arsenic(III) during bacterial oxidation of arsenopyrite in chalcopyrite concentrate by Thiobacillus ferrooxidans

During bacterial oxidation of the arsenopyrite that contaminated a chalcopyrite concentrate, the bioextraction of arsenic from the concentrate was examined. A long-term constant As(III) concentration, representing a large portion of the total arsenic, occurred in the leaching medium. As(III) was not further oxidized, either under bioextraction conditions or by Fe(III) in the presence of the mesophilic bacterium Thiobacillus ferooxidans. These results are discussed in relation to the influence of leaching microorganisms on the form of arsenic in the solution. Dissolved As(III) could be reversed into a solid phase by adsorption of As(III) by forming an iron precipitate. Correspondence to: M. Mandl     

A mathematical model for the bacterial oxidation of a sulfide ore concentrate

The effect of dilution rate and feed solids concentration on the bacterial leaching of a pyrite/arsenopyrite ore concentrate was studied. A mathematical model was developed for the process based on the steady-state data collected over the range of dilution rates (20 to 110 h) and feed solids concentrations (6 to 18% w/v) studied. A modified Monod model with inhibition by arsenic was used to model bacterial ferrous ion oxidation rates. The model assumes that (i) pyrite and arsenopyrite leaching occurs solely by the action of ferric iron produced from the bacterial oxidation of ferrous iron and (ii) bacterial growth rates are proportional to ferrous ion oxidation rate. The equilibrium among the various ionic species present in the leach solution that are likely to have a significant effect on the bioleach process were included in the model. (c) 1994 John Wiley & Sons, Inc.     

Biological effects of anionic meso-tetrakis (para-sulfonatophenyl) porphyrins modulated by the metal center. Studies in rat liver mitochondria

In this paper, we present a study about the influence of the porphyrin metal center and meso ligands on the biological effects of meso-tetrakis porphyrins. Different from the cationic meso-tetrakis 4-N-methyl pyridinium (Mn(III)TMPyP), the anionic Mn(III) meso-tetrakis (para-sulfonatophenyl) porphyrin (Mn(III)TPPS4) exhibited no protector effect against Fe(citrate)-induced lipid oxidation. Mn(III)TPPS4 did not protect mitochondria against endogenous hydrogen peroxide and only delayed the swelling caused by tert-BuOOH and Ca²⁺. Fe(III)TPPS4 exacerbated the effect of the tert-BuOOH, and both porphyrins did not significantly affect Fe(II)citrate-induced swelling. Consistently, Fe(III)TPPS4 predominantly promotes the homolytic cleavage of peroxides and exhibits catalytic efficiency ten-fold higher than Mn(III)TPPS4. For Mn(III)TPPS4, the microenvironment of rat liver mitochondria favors the heterolytic cleavage of peroxides and increases the catalytic efficiency of the manganese porphyrin due to the availability of axial ligands for the metal center and reducing agents such as glutathione (GSH) and proteins necessary for Compound II (oxomanganese IV) recycling to the initial Mn(III) form. The use of thiol reducing agents for the recycling of Mn(III)TPPS4 leads to GSH depletion and protein oxidation and consequent damages in the organelle.     

异化铁还原细菌LQ25还原重金属Cr (VI)的特性研究

[背景] 异化铁还原细菌能够在还原Fe （III）的同时将毒性较大的Cr （VI）还原成毒性较小的Cr （III）,解决铬污染的问题。[目的] 基于丁酸梭菌（Clostridium butyricum） LQ25异化铁还原过程制备生物磁铁矿,开展异化铁还原细菌还原Cr （VI）的特性研究。[方法] 构建以氢氧化铁为电子受体和葡萄糖为电子供体的异化铁培养体系。菌株LQ25培养结束时制备生物磁铁矿。设置不同初始Cr （VI）浓度（5、10、15、25和30 mg/L）,分别测定菌株LQ25对Cr （VI）还原效率以及生物磁铁矿对Cr （VI）的还原效率。[结果] 菌株LQ25在设置的Cr （VI）浓度范围内都能良好生长。当Cr （VI）浓度为15 mg/L时,在异化铁培养条件下,菌株LQ25对Cr （VI）的还原率为63.45%±5.13%,生物磁铁矿对Cr （VI）的还原率为87.73%±9.12%,相比菌株还原Cr （VI）的效率提高38%。pH变化能影响生物磁铁矿对Cr （VI）的还原率,当pH 2.0时,生物磁铁矿对Cr （VI）的还原率最高,几乎达到100%。电子显微镜观察发现生物磁铁矿表面有许多孔隙,X-射线衍射图谱显示生物磁铁矿中Fe （II）的存在形式是Fe （OH）₂。[结论] 基于异化铁还原细菌制备生物磁铁矿可用于还原Cr （VI）,这是一种有效去除Cr （VI）的途径。     

海洋沉积物中铁还原细菌组成及异化铁还原与产氢性质分析

【背景】一些铁还原细菌具有异化铁还原与产氢的能力,该类细菌在环境污染修复的同时能够解决能源问题。【目的】从海洋沉积物中富集获得异化铁还原菌群,明确混合菌群组成、异化铁还原及产氢性质。获得海洋沉积物中异化铁还原混合菌群组成,分析菌群异化铁还原和产氢性质。【方法】利用高通量测序技术分析异化铁还原菌群的优势菌组成,在此基础上,分析异化铁还原混合菌群在不同电子供体培养条件下异化铁还原能力和产氢性质。【结果】高通量数据表明,在不溶性氢氧化铁为电子受体和葡萄糖为电子供体厌氧培养条件下,混合菌群的优势菌属主要是梭菌(Clostridium),属于发酵型异化铁还原细菌。混合菌群能够利用电子供体蔗糖、葡萄糖以及丙酮酸钠进行异化铁还原及发酵产氢。葡萄糖为电子供体时,菌群累积产生Fe(Ⅱ)浓度和产氢量最高,分别是59.34±6.73 mg/L和629.70±11.42 mL/L。【结论】异化铁还原混合菌群同时具有异化铁还原和产氢能力,拓宽了发酵型异化铁还原细菌的种质资源,探索异化铁还原细菌在生物能源方面的应用。     

Integrated biological process for the treatment of a Chilean complex gold ore

Abstract: A process for gold recovery from a complex Chilean ore from Burladora (IV Region) which integrates concentration by flotation, bacterial leaching and cyanidation was studied at a laboratory scale. The chemical composition of the ore is 8.2% Fe, 0.78% Cu, 0.88% As and 3.5 g/t Au, with pyrite, hematite, covelite, arsenopyrite and chalcopyrite as the main metal-bearing minerals. The initial gold recovery by conventional cyanidation on a crushed ore sample was only 54%. The ore was ground and concentrated by flotation with a gold recovery of only 56%. The gold content of the concentrate is 17 g/I Au. Concentrate samples were leached in 1.5 l stirred reactors at 10% pulp density in 1000 ml of acid medium (pH 1.8). Some experiments were inoculated with harvested bacteria previously isolated from mining solutions. Dissolved metals, pH and bacteria concentration in the leaching solutions were periodically determined. In the presence of bacteria, oxidation of the ferrous ion produced by acid dissolution of the concentrate was observed, and after 4 days of leaching 100% of the dissolved iron was present as ferric ion. Gold recovery by cyanidation increased from 13% for the initial concentrate to 34% after 10 days of chemical acid leaching and 97% after 10 days of bacterial leaching. To increase the total gold recovery, the flotation tailings were submitted to cyanidation. A complete flowsheet of the process and a first economical evalualion are proposed. As a possible alternative process, heap bacterial leaching and further cyanidation of the ore are suggested.