[Effect of temperature on activity of Acidithiobacillus ferrooxidan and formation of biogenic secondary iron minerals]

In this study, batch experiments were performed to investigate the effect of temperature on the Fe (II) oxidation and the formation of biogenic secondary iron minerals by Acidithiobacillus ferrooxidan. Results showed that the low temperature significantly inhibited the oxidation activity of A. ferrooxidan. In the FeSO4-H2O biological oxidation system facilitated by A. ferrooxidan, it was found that after 5 days culture, the oxidation rates of Fe (II) in treatments of 10 degrees C and 28 degrees C were 11.81% and 100%, respectively. In addition, it rapidly rose to 95.10% when the temperature was adjusted from 10 degrees C (cultured for 7 days) to 28 degrees C in 1 day, and the maximum oxidation rates were as follows: 10 degrees C (cultured for 7 days) +28 degrees C (2.25 h(-1)) > 28 degrees C (1.42 h(-1)) >10 degrees C (0.81 h(-1)). Furthermore, the XRD patterns showed that the lower Fe (III) supply rate was more conducive to the formation of amorphous schwertmannite in 9K medium at 10 degrees C. Correspondingly, the generation of amorphous schwertmannite was preceded to ihleite at 28 degrees C, and the crystallinity degree of ihleite was getting better with the extension of culture time. Combined with the SEM characteristics, it was judged that the 28 degrees C sample contained jarosite and schwertmannite.

Elimination of high concentration hydrogen sulfide and biogas purification by chemical-biological process

A chemical-biological process was performed to remove a high concentration of H2S in biogas. The high iron concentration tolerance (20gL(-1)) of Acidithiobacillus ferrooxidans CP9 provided sufficient ferric iron level for stable and efficient H2S elimination. A laboratory-scale apparatus was setup for a 45 d operation to analyze the optimal conditions. The results reveal that the H2S removal efficiency reached 98% for 1500ppm H2S. The optimal ferric iron concentration was kept between 9 and 11gL(-1) with a cell density of 10(8)CFUg(-1) granular activated carbon and a loading of 15gSm(-3)h(-1). In pilot-scale studies for biogas purification, the average inlet H2S concentration was 1645ppm with a removal efficiency of up to 97% for a 311d operation and an inlet loading 40.8gSm(-3)h(-1). When 0.1% glucose was added, the cell density increased twofold under the loading of 65.1gSm(-3)h(-1) with an H2S removal efficiency still above 96%. The analysis results of the distribution of microorganisms in the biological reactor by DGGE show that microorganism populations of 96.7% and 62.7% were identical to the original strain at day 200 and day 311, respectively. These results clearly demonstrate that ferric iron reduction by H2S and ferrous iron oxidation by A. ferrooxidans CP9 are feasible processes for the removal of H2S from biogas.

[Isolation, identification and oxidizing characterization of an iron-sulfur oxidizing bacterium LY01 from acid mine drainage]

An acidophilic iron-sulfur oxidizing bacterium LY01 was isolated from acid mine drainage of coal in Guizhou Province, China. Strain LY01 was identified as Acidithiobacillusferrooxidans by morphological and physiological characteristics, and phylogenetic analysis of its 16S rRNA gene sequence. Strain LY01 was able to grow using ferrous ion (Fe2+), elemental sulfur (S0) and pyrite as sole energy source, respectively, but significant differences in oxidation efficiency and bacterial growth were observed when different energy source was used. When strain LY01 was cultured in 9K medium with 44.2 g x L(-1) FeSO4.7H2O as the substrate, the oxidation efficiency of Fe2+ was 100% in 30 h and the cell number of strain LY01 reached to 4.2 x 10(7) cell x mL(-1). When LY01 was cultured in 9K medium with 10 g x L(-1) S0 as the substrate, 6.7% S0 oxidation efficiency, 2001 mg x L(-1) SO4(2-) concentration and 8.9 x 10(7) cell x mL(-1) cell number were observed in 21 d respectively. When LY01 was cultured with 30 g x L(-1) pyrite as the substrate, the oxidation efficiency of pyrite, SO4(2-) concentration and cell number reached 10%, 4443 mg x L(-1) and 3.4 x 10(8) cell x mL(-1) respectively in 20 d. The effects of different heavy metals (Ni2+, Pb2+) on oxidation activity of strain LY01 cultured with pyrite were investigated. Results showed that the oxidation activity of strain LY01 was inhibited to a certain extent with the addition of Ni2+ at 10-100 mg x L(-1) to the medium, but the addition of 10-100 mg x L(-1) Pb2+ had no effect on LY01 activity.

Optimizing mixed culture of two acidophiles to improve copper recovery from printed circuit boards (PCBs)

In the previous research, the effects of different addition time and amount of printed circuit boards (PCBs) on cells growth and metals recovery in separated and mixed culture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans were investigated. This paper aimed to optimize mixed culture of both acidophiles for maximizing PCBs addition amounts and copper leaching percentage simultaneously. Initially, influences of inoculums ratio between two acidophiles on their cells growth were studied. Then, initial medium pH and concentrations of FeSO4 · 7H2O and elemental sulfur (S(0)) were optimized by response surface methodology (RSM) to improve copper recovery. Finally, multiple-point PCBs addition was tested to determine maximal amounts. Results showed that with initial inoculums ratio (Af:At) 1:2, pH 1.56, FeSO4 · 7H2O and S(0) at 16.88 and 5.44 g/L, and PCBs addition 28.8 g/L, copper recovery reached 92.6% after 240 h cultivation. It was indicated that copper could be efficiently leached out from increased PCBs addition amount and FeSO4 · 7H2O was remarkably reduced from 22.1 to 16.88 g/L.

Using biochemical system to improve cinnabar dissolution

In order to evaluate the leaching of cinnabar, a chemobiological reactor system with Acidithiobacillus ferrooxidans for cinnabar dissolution was investigated. The results demonstrated cinnabar dissolution had relation to bioprocess of A. ferrooxidans and iron concentration tightly. The optimal dilution rate and iron concentration were 0.4/h and 2-3 g/L in chemobiological reactor. The process may be contributed to the indirect catalyzing of ferric iron generated with A. ferrooxidans and direct adherence oxidation function. This research shows the new microbiological technique may be a feasible and economical method in application.

Degradation of inhibitory substances in sludge by Galactomyces sp. Z3 and the role of its extracellular polymeric substances in improving bioleaching

This study sought to elucidate the effect and mechanism of Galactomyces sp. Z3 in improving the bioleaching of heavy metals from sludge. Results showed that co-inoculation of Galactomyces sp. Z3 and two Acidithiobacillus strains (Acidithiobacillus ferrooxidans LX5 and Acidithiobacillus thiooxidans TS6) reduced the period required for sludge bioleaching by 4.5days compared to Acidithiobacillus alone. Further, removal efficiencies of Cu, Zn and oxidation rate of Fe(2+) and S(0) were higher in co-inoculation system than the Acidithiobacillus alone. Galactomyces sp. Z3 consumed the acetate, propionate, iso-butyrate, butyrate, and iso-valerate in sludge from the initial concentrations of 109.50, 28.80, 7.70, 34.30, and 18.40mg/L to 10.20, 0.61, 0.63, 19.40 and 1.30mg/L, respectively, after 12h in the co-inoculation system, significantly lower than the concentrations observed in the Acidithiobacillus alone. Meanwhile, the surfactant properties of the extracellular polymeric substances produced by the Galactomyces accelerated the rate of sulfur oxidization by A. thiooxidans.

Oxidation of hydrogen sulfide in biogas using dissolved oxygen in the extreme acidic biofiltration operation

This work aimed to investigate the interactive effects of empty bed retention time (EBRT), specific hydraulic loading rate (q) and initial pH (pHi) of the aerated recirculating liquid to remove H2S in extreme acidic biofiltration. Biogas containing H2S 6395±2309ppm and CH4 79.8±2.5% was fed to the biofilter as pH of the high dissolved oxygen recirculating liquid swung between pHi to 0.5. Response surface methodology was employed that gave the H2S removal relationship model with R(2) 0.882. The predicted highest H2S removal within the studied parameter ranges was 94.7% at EBRT 180.0s, q 4.0m(3)/m(2)/h and pHi 3.99. Results from separate runs at a random condition were not statistically different from the model prediction, signifying a validity of the model. Additionally, CH4 content in the exit biogas increased by 4.7±0.4%. Acidithiobacullus sp. predominance in the consortia of this extreme acidic condition was confirmed by DGGE.

Two step meso-acidophilic bioleaching of chalcopyrite containing ball mill spillage and removal of the surface passivation layer

Meso-acidophilic bacterial leaching of ball mill spillage (containing chalcopyrite >80%) was carried out in an innovative two-step bioleaching method. The major drawback of meso-acidophilic bioleaching limiting industrial application is the passivation phenomenon over the ore surfaces in iron-sulfur rich environments. In the present study, we present a novel wash solution that efficiently removed the passivation layer. FTIR characterization of the bioleached sample indicated that the residues could be further leached to recover extra copper after wash solution application. XRD study indicated accumulation of sulfates (SO(4)(-)) of Na, K, Fe and oxy hydroxides of iron [FeO(OH)] in the form of jarosite outlining the passivation layer. SEM, FESEM-EDS studies indicated severe corrosion effects of the wash solution on the passivation layer. Two step bioleaching of the ore sample yielded 32.6% copper in 68days in the first interlude and post wash solution application yielded 10.8% additional copper.

Influence of H2SO4 and ferric iron on Cd bioleaching from spent Ni-Cd batteries

The paper is concerned with biohydrometallurgical methods of cadmium recovery from spent Ni-Cd batteries. Cd leaching efficiency from electrode material in different media (H(2)SO(4) and Fe(2)(SO(4))(3) solutions), at different Fe(III) concentrations and using the bacteria Acidithiobacillus ferrooxidans were investigated. The main aim of this study was to understand which from the bioleaching products (sulphuric acid or ferric sulphate) play a main role in the bioleaching process of Cd recovery. The influence of Fe ions on Cd leachability was confirmed. The best leaching efficiency of Cd (100%) was reached by bioleaching and also by leaching in Fe(2)(SO(4))(3) solution. The results of X-ray diffraction confirmed that no cadmium was present in solid residuum obtained after the Cd bioleaching as well as Cd leaching using solely ferric iron. The use of H(2)SO(4) solution resulted in the lowest efficiency of Cd leachability, the presence of hydroxides in electrode materials caused neutralization of the leaching solution and inhibition of Cd leaching.

A novel and highly efficient system for chalcopyrite bioleaching by mixed strains of Acidithiobacillus

An integrated bioleaching system (stable pH-silver ion-chloride ion) was firstly proposed to for improving the efficiency of chalcopyrite bioleaching by mixed strains of Acidithiobacillus. The individual effects of stable pH, silver ion, and chloride ion on bioleaching were respectively studied. The highest copper ion concentrations in each system were 45.8, 50.2, and 45.2 mg/l, respectively, when it was only 28.0 mg/l the blank system. Compared with the individual stable pH, silver or chloride ion systems, the relevance of biological and chemical reactions achieved a better balance in the integrated system (stable pH 1.3, 2.0 mg/l silver ion, and 2.5 g/l chloride ion). Moreover, the highest ferrous and sulfate ion concentrations implied less production of S0 membrane and jarosite precipitation. It was also demonstrated by the highest copper ion concentration 55.5 mg/l. These results all indicated that this system was a novel and believable strategy for effectively operating chalcopyrite bioleaching.

Microbial processing of apatite rich low grade Indian uranium ore in bioreactor

Bioreactor leaching using enriched culture of Acidithiobacillus ferrooxidans and Leptosprillium ferrooxidans was investigated for the apatite rich Indian (Narwapahar) uranium ore. Bioreactor leaching of Narwapahar ore of <45 μm size at pH 2.0 and 10% (w/v) PD using 10% (v/v) inoculum of the bacterium at 35 °C (A. ferrooxidans) and 40 °C (L. ferrooxidans), solubilised 57% and 63% uranium in 5 days, respectively; the E(SCE) values being 561 and 588 mV. Leaching kinetics improved so much so that ~83% uranium was recovered in just 10h with 10% inoculum of A. ferrooxidans containing biogenic Fe(3+); at 20% PD uranium recovery rose to 87%. Role of temperature (25-40 °C) was noticed with 90.3% uranium bioleaching in 10h at 40 °C with L. ferrooxidans as against 77% leaching with A. ferrooxidans at pH 2.0, 40 °C and 20% (w/v) PD.

The role of heterotrophic microorganism Galactomyces sp. Z3 in improving pig slurry bioleaching

The feasibility of removing heavy metals and eliminating pathogens from pig slurry through bioleaching involving the fungus Galactomyces sp. Z3 and two acidophilic thiobacillus (A. ferrooxidans LX5 and A. thiooxidans TS6) was investigated. It was found that the isolated pig slurry dissolved organic matter (DOM) degrader Z3 was identified as Galactomyces sp. Z3, which could grow well at pH 2.5-7 and degrade pig slurry DOM from 1973 to 942 mg/l within 48 h. During the successive multi-batch bioleaching systems, the co-inoculation of pig slurry degrader Galactomyces sp. Z3 and the two Acidithiobacillus species could improve pig slurry bioleaching efficiency compared to the single system without Galactomyces sp. Z3. The removal efficiency of Zn and Cu exceeded 94% and 85%, respectively. In addition, the elimination efficiencies of pathogens, including both total coliform and faecal coliform counts, exceeded 99% after bioleaching treatment. However, the counts of Galactomyces sp. Z3 decreased with the fall of pH and did not restore to the initial level during successive multi-batch bioleaching systems, and it is necessary to re-inoculate Galactomyces sp. Z3 cells into the bioleaching system to maintain its role in degrading pig slurry DOM. Therefore, a bioleaching technique involving both Galactomyces sp. Z3 and Acidithiobacillus species is an efficient method for removing heavy metals and eliminating pathogens from pig slurry.

Facilitating role of biogenetic schwertmannite in the reduction of Cr(VI) by sulfide and its mechanism

The efficient conversion of Cr(VI) to Cr(III) has attracted an increasing concern in recent years owing to its threat to the environment. In the present paper, the catalytic role of biogenetic schwertmannite in the reduction of Cr(VI) by sulfide and its mechanism were investigated under different conditions through batch experiments. The results demonstrated that schwertmannite markedly accelerated the removal of Cr(VI) by sulfide, and the rates of the reaction were enhanced by 11, 8 and 6 times, respectively at pH 7.5, 8.0 and 8.8 as compared with control (no schwertmannite). In addition, the conversion of Cr(VI) into Cr(III) increased with schwertmannite loading and temperature. However, the facilitating role of schwertmannite in the reduction of Cr(VI) by sulfide was markedly suppressed by an introduction of F(-), a complex agent for Fe(III). It is concluded that the catalysis of schwertmannite results from the activated Fe(III) on the surface of schwertmannite, serving as a "bridge" in the transportation of electrons between sulfide and Cr(VI), and leading to the improving reduction of Cr(VI) by sulfide.

[Mineralogical characteristics of biogenic schwertmannite amended with different pretreatment methods and the effects on As(III) absorption]

Biogenic schwertmannite has better absorption performance for As(III) than other adsorbents, but there is obvious agglomeration of mineral particles due to the polysaccharides secreted by the bacteria during the synthesis of schwertmannite. The aim of this study was to find out a best pretreatment method to further reduce the agglomeration of mineral particles and enhance the As(III) absorption capacity by comparing the effects of different pretreatment methods on the mineralogical characteristics and adsorption performance of schwertmannite. The pretreatment methods of the biogenic schwertmannite induding the treatments with NaOH, NaCl, thermal activation at 200 degrees C and ethanol-ultrasound. The results showed that the mineral phases were not altered after pretreatment, however, different physical and chemical properties of schwertmannite were found after different pretreatment methods were used. Compared with the original mineral, the mineral surface area, Fe/S molar ratio, SEM image and As(III) adsorption were significantly changed. The highest As(III) sorption capacity was obtained for the pH 12 NaOH treated schwertmannite with the maximum absorbance at room temperature increased from 101.9 mg x g(-1) to 143.3 mg x g(-1), and the surface area enhanced from 45.63 m2 x g(-1) to 325.18 m2 x g(-1). Besides, aggregation of mineral particles was remarkably decreased.

Transcriptional and functional studies of a Cd(II)/Pb(II)-responsive transcriptional regulator(CmtR) from Acidithiobacillus ferrooxidans ATCC 23270

The acidophilic Acidithiobacillus ferrooxidans can resist exceptionally high cadmium (Cd) concentrations. This property is important for its use in biomining processes, where Cd and other metal levels range usually between 15 and 100 mM. To learn about the mechanisms that allow A. ferrooxidans cells to survive in this environment, a bioinformatic search of its genome showed the presence of that a Cd(II)/Pb(II)-responsive transcriptional regulator (CmtR) was possibly related to Cd homeostasis. The expression of the CmtR was studied by real-time reverse transcriptase PCR using A. ferrooxidans cells adapted for growth in the presence of high concentrations of Cd. The putative A. ferrooxidans Cd resistance determinant was found to be upregulated when this bacterium was exposed to Cd in the range of 15-30 mM. The CmtR from A. ferrooxidans was cloned and expressed in Escherichia coli, the soluble protein was purified by one-step affinity chromatography to apparent homogeneity. UV-Vis spectroscopic measurements showed that the reconstruction CmtR was able to bind Cd(II) forming Cd(II)-CmtR complex in vitro. The sequence alignment and molecular modeling showed that the crucial residues for CmtR binding were likely to be Cys77, Cys112, and Cys121. The results reported here strongly suggest that the high resistance of the extremophilic A. ferrooxidans to Cd including the Cd(II)/Pb(II)-responsive transcriptional regulator.

[Effect of acidification on the dewaterability of sewage sludge in bioleaching]

Batch experiments were performed to exploit the effect and the mechanism of bioleaching on sludge dewaterability by the inoculation of Acidithiobacillus ferrooxidans LX5 in this study. Besides, chemical leaching experiments using sulphuric acid were also performed as control to study the effect of acidification on sludge dewaterability. During the processes of both biological and chemical leaching, Zeta potential, cell lyses, morphology and structure of sludge flocs were monitored. Results showed that along with the acid production and hence the decrease of pH during bioleaching, the specific resistance of bioleached sludge decreased systematically from 1.81 x 10(12) m x kg(-1) to 0.59 x 10(12) m x kg(-1), whilst Zeta potential increased from -25.2 mV to 9.6 mV, and the natural sedimentation rate increased to as high as 48% at pH 2.90. In chemical leaching, the specific resistance decreased continuously to a minimum value of 2.6 x 10(12) m x kg(-1) at pH 3.35 and then started to increase. Zeta potential increased with the decrease of pH, and reached zero at pH 2.90. At strong acid condition, sludge cells could be decomposed, resulting in the increase of total dissolved phosphorus in centrifugal liquor of chemical leached sludge. However, this phenomenon was not observed in bioleaching process because that the phosphorus was utilized by the abundant microorganism in system. Observation by SEM showed that there was no obvious change in the flocs structure of both sludge at pH 3.35 except for that some secondary minerals appeared only in bioleached sludge. These results revealed that decrease of absolute value of Zeta potential and formation of secondary minerals caused by bioleaching were responsible for the improvement of sludge dewaterability.

Targeted isolation of proteins from natural microbial communities living in an extreme environment

Microorganisms from extreme environments are often very difficult to cultivate, precluding detailed study by biochemical and physiological techniques. Recent advances in genomic sequencing and proteomic measurements of samples obtained from natural communities have allowed new access to these uncultivated extremophiles and identified abundant proteins that can be isolated directly from natural samples. Here we report the isolation of two abundant heme proteins from low-diversity biofilm microbial communities that thrive in very acidic (pH ~ 1), metal-rich water in a subsurface mine. Purification and detailed characterization of these proteins has afforded new insight into the possible mechanism of Fe(II) oxidation by Leptospirillum Group II, the dominant population in most of these biofilms, and demonstrated that the abundance and posttranslational modifications of one of these proteins is dependent on the lifecycle of the biofilm.

Extremely acidophilic sulfur-oxidizing bacteria applied in biotechnological processes for gas purification

Extreme acidophilic (pH ~ 0.25) microorganisms have been studied and applied to treat volatile sulfur emissions like carbon disulfide. These microorganisms provide opportunities for biomass control and recycling of sulfuric acid using extremely low pH operating conditions as shown in 70 L bench-scale bioreactors. Applying the extreme acidophilic bacteria in full-scale bioreactors treating carbon disulfide in combination with hydrogen sulfide emissions from industrial processes like the viscose industry was shown to be effective with average total sulfur removal efficiency above 90%.

Draft genome sequence of the extremely acidophilic biomining bacterium Acidithiobacillus thiooxidans ATCC 19377 provides insights into the evolution of the Acidithiobacillus genus

Acidithiobacillus thiooxidans is a mesophilic, extremely acidophilic, chemolithoautotrophic gammaproteobacterium that derives energy from the oxidation of sulfur and inorganic sulfur compounds. Here we present the draft genome sequence of A. thiooxidans ATCC 19377, which has allowed the identification of genes for survival and colonization of extremely acidic environments.

[Influence of bioleaching on dewaterability of cattle biogas slurry]

The dewaterability of cattle biogas slurry facilitated by bioleaching was investigated through batch experiments with co-inoculation of different Acidophilic thiobacilli (Acidithiobacillus thiooxidans TS6 or Acidithiobacillus ferrooxidans LX5). The experiment was set the following 5 treatments: (1) original biogas slurry (CK), (2) 4 g x L(-1) Fe(2+) (uninoculation), (3)2 g x L(-1) S(0) + 25 mL A. t, (4) 4 g x L(-1) Fe(2+) + 25 mL A. f and (5) 2 g x L(-1) S(0) + 4 g x L(-1) Fe(2+) + 12.5 mL A. t + 12.5 mL A. f. During bioleaching, dynamic changes of pH, ORP, Fe(2+), F(3+), total Fe, the settleability, the turbidity of the supernatant after settling for 12 h, and the dewaterability (expressed as specific resistance to filtration gamma or capillary suction time, CST) of biogas slurry were monitored. Results show that specific resistance gamma and CST of bioleached biogas slurry are reduced drastically for the treatments of original biogas slurry spiked with only Fe(2+), the treatment of original biogas slurry co-spiked with Fe(2+) and Acidithiobacillus ferrooxidans LX5, and the treatment of original biogas slurry co-spiked with Fe(2+), S(0) and two Acidophilic thiobacilli. Taking the dewaterability, settleability, the turbidity of the supernatant fluid after settle 12 h and economical cost into account, the treatment of original biogas slurry co-spiked with Fe(2+) and Acidithiobacillus ferrooxidans LX5 is the most suitable pattern for cattle biogas slurry bioleaching. After bioleaching, 1.14% of organic matter, 0.09% of N, 0.05% of P, and 0.1% of K are lost in the bioleaching process, but it don't affect its fertilizer efficiency. Meanwhile, the 63.2% of Cu and 91.3% of Zn are removed from the biogas slurry, and elimination efficiencies of total coliforms in bioleached slurry exceed 99%. This study might provide a new approach for treatment and disposal of biogas slurry.

Supplementation of inorganic phosphate enhancing the removal efficiency of tannery sludge-borne Cr through bioleaching

Four inorganic mineral nutrients including NH4+, K+, Mg2+ and soluble inorganic phosphate (Pi) were investigated to reveal the potential limiting nutrients for tannery sludge bioleaching process driven by Acidithiobacillus species, and the feasibility of supplementing the limiting nutrients to accelerate tannery sludge bioleaching was studied in the present study. It was found that the concentration of Pi was lower than 3.5 mg/L throughout the whole bioleaching process, which is the most probable restricting nutrient for tannery sludge bioleaching. Further experiments revealed that the deficiency of Pi could seriously influence the growth of Acidithiobacillus thiooxidans and lower its oxidization capacity for S0, and the limiting concentration of Pi for the growth of A. thiooxidans was 6 mg/L. The low concentration of soluble Pi in sludge matrix was resulted from the extremely strong sorbing/binding capacity of tannery sludge for phosphate. The supplementation of more than 1.6 g/L KH2PO4 into tannery sludge bioleaching system could effectively stimulate the growth of Acidithiobacillus species, enhance Cr removal rate and further shorten tannery sludge bioleaching period from 10 days to 7 days. Therefore, inorganic phosphate supplementation is an effective and feasible method to accelerate tannery sludge bioleaching process, and the optimum dosage of KH2PO4 was 1.6 g/L for tannery sludge with 5.1% of total solids.

An investigation of biooxidation ability of Acidithiobacillus ferrooxidans using NMR relaxation measurement

NMR relaxation measurements can provide a simple means for understanding biological activity of cells in solution with known composition. It has the advantage that it is an in situ, non-intrusive technique, and the acquisition is fast. The iron oxidation ability of Acidithiobacillus ferrooxidans was investigated using NMR relaxation measurements. The transversal relaxation is characterized by a time constant, T₂, which is sensitive to the chemical environment. Fe³⁺ ion has more significant T₂ shortening than Fe²⁺ ion. In the presence of A. ferrooxidans in solutions containing Fe²⁺ ion, T₂ shortening was found with increasing time as the bacteria oxidize Fe²⁺ to Fe³⁺ ions. In the optimal growth medium, the bacteria concentration increased 80 times and high iron oxidation rate was found. In 10 mM K₂SO₄ medium, however, bacteria concentration remained almost unchanged and the iron oxidation rate was significantly lower.

[Leaching of copper ore of the Udokanskoe deposit at low temperatures by an association of acidophilic chemolithotrophic microorganisms]

Pure cultures of indigenous microorganisms Acidithiobacillus ferrooxidans strain TFUd, Leptospirillum ferrooxidans strain LUd, and Sulfobacillus thermotolerans strain SUd have been isolated from the oxidation zone of sulfide copper ore of the Udokanskoe deposit. Regimes of bacterial-chemical leaching of ore have been studied over a temperature range from -10 to +20 degrees C. Effects of pH, temperature, and the presence of microorganisms on the extraction of copper have been shown. Bacterial leaching has been detected only at positive values of temperature, and has been much more active at +20 than at +4 degrees C. The process of leaching was more active when the ore contained more hydrophilic and oxidized minerals. The possibility of copper ore leaching of the Udokanskoe deposit using sulfuric acid with pH 0.4 at negative values of temperature and applying acidophilic chemolithotrophic microorganisms at positive values of temperature and low pH values was shown.

Adsorptive removal of As(III) by biogenic schwertmannite from simulated As-contaminated groundwater

This study investigates synthesis of biogenic schwertmannite by Acidithiobacillus ferrooxidans and its role and mechanism in adsorption of As(III) from water. Results indicate that schwertmannite particles formed through oxidation of ferrous sulfate by A. ferrooxidans cells for different times vary greatly in size and in morphology. The hedge-hog like schwertmannite formed after reaction for 72h are aggregative spheroid particles with a diameter of approximately 2.5μm and its chemical formula can be expressed as Fe(8)O(8)(OH)(4.42)(SO(4))(1.79). Batche studies show that both Freundlich and Langmuir model are suitable for describing the adsorption behavior of As(III) on schwertmannite at pH 7.5 and As(III) in simulated groundwater can be effectively removed by biogenic schwertmannite with a maximum adsorption capacity of 113.9mg As(III) g(-1) and the optimal pH is in the range of 7-10. The arsenic removal is hardly affected by the competing anions often observed in groundwater unless the mole concentration of PO(4)(3-) and SO(4)(2-) in groundwater are 75 or 750 times higher than As(III), respectively. The mechanism of As(III) adsorption on biogenic schwertmannite involves ligand exchanges between arsenic species and surface hydroxyl group and sulfate. In addition, experiments show that As(III)-sorbed biogenic schwertmannite aged in deionized water at 25°C exhibits no mineralogy phase changes even after ageing at pH 6.0 and 8.5 for 90d.

Column bioleaching of uranium embedded in granite porphyry by a mesophilic acidophilic consortium

A mesophilic acidophilic consortium was enriched from acid mine drainage samples collected from several uranium mines in China. The performance of the consortium in column bioleaching of low-grade uranium embedded in granite porphyry was investigated. The influences of several chemical parameters on uranium extraction in column reactor were also investigated. A uranium recovery of 96.82% was achieved in 97 days column leaching process including 33 days acid pre-leaching stage and 64 days bioleaching stage. It was reflected that indirect leaching mechanism took precedence over direct. Furthermore, the bacterial community structure was analyzed by using Amplified Ribosomal DNA Restriction Analysis. The results showed that microorganisms on the residual surface were more diverse than that in the solution. Acidithiobacillus ferrooxidans was the dominant species in the solution and Leptospirillum ferriphilum on the residual surface.