氧化亚铁硫杆菌对黄铜矿的氧化作用

结合德兴铜矿堆浸厂的生产实践 ,研究了氧化亚铁硫杆菌在浸出黄铜矿过程中的直接、间接作用和铁的行为。氧化亚铁硫杆菌在生长繁殖过程中 ,不断将Fe2 +氧化为Fe3+,同时Fe3+又发生一系列的水解反应 ,Fe2 +的细菌氧化主要以O2 为最终的电子受体 ,氧化亚铁硫杆菌对黄铜矿的直接氧化作用占主导地位。

Electrochemical oxidation behavior of pyrite bioleaching by Acidthiobacillus ferrooxidans

The electrochemical oxidation behavior of pyrite in bioleaching system of Acidthiobacillusferrooxidans was investigated by cyclic voltammetry （CV）, polarization curve and electrochemical impedance spectroscopy （EIS）. The results show that in the presence or absence of A. ferrooxidans, the oxidation reaction of pyrite is divided into two steps： the first reaction step involves the oxidation of pyrite to S, and the second reaction step is the oxidation of S to SO4^2-. The oxidation mechanism of pyrite is not changed in the presence of A. ferrooxidans, but the oxidation rate of pyrite is accelerated. With the extension of reaction time of A. ferrooxidan with pyrite, the polarization current density of pyrite increases and the breakdown potential at which the passive film dissolves decreases. The impedance in the presence ofA. ferrooxidans is obviously lower than that in the absence of A. ferrooxidans, further indicating that microorganism accelerates the corrosion process of pyrite.

Enhancement of bio-oxidation of refractory arsenopyritic gold ore by adding pyrolusite in bioleaching system

Pyrolusite was added in the bioleaching process to enhance the bio-oxidation process. Bioleaching tests at different dosages of pyrolusite ore, pH and inoculation amounts of Acidithiobacillus ferrooxidans were studied. The results showed that the time of the bio-oxidation process was decreased obviously and the arsenic leaching rate reached 94.4% after the bioleaching. The bio-oxidation of arsenopyrite and the effective extraction of manganese from pyrolusite were achieved by the bioleaching process. After bioleaching, the leaching rate of gold from the reaction residues reached 95.8% by cyanide leaching. In the bio-oxidation process, pyrolusite increased the redox potential of the solution to accelerate the bioleaching rate. The experiment showed that there were two reaction modes in the bioleaching process.

Relationship and effect of redox potential,jarosites and extracellular polymeric substances in bioleaching chalcopyrite by acidithiobacillus ferrooxidans

The changes of pH,redox potential,concentrations of soluble iron ions and Cu^2＋ with the time of bioleaching chalcopyrite concentrates by acidithiobacillus ferrooxidans were investigated under the different conditions of initial total-iron amount as well as mole ratio of Fe（III） to Fe（II） in the solutions containing synthetic extracellular polymeric substances （EPS）.When the solution potential is lower than 650 mV （vs SHE）,the inhibition of jarosites to bioleaching chalcopyrite is not vital as EPS produced by bacteria can retard the contamination through flocculating jarosites even if concentration of Fe（III） ions is up to 20 g/L but increases with increasing the concentration of Fe（III） ions;jarosites formed by bio-oxidized Fe3＋ ions are more easy to adhere to outside surface of EPS space on chalcopyrite;the EPS layer with jarosites acts as a weak diffusion barrier to further rapidly create a high redox potential of more than 650 mV by bio-oxidizing Fe^2＋ ions inside and outside EPS space into Fe^3＋ ions,resulting in a rapid deterioration of ion diffusion performance of the EPS layer to inhibit bioleaching chalcopyrite severely and irreversibly.

Decomposition mechanism of pentlandite during electrochemical bio-oxidation process

Electrochemical measurements were carried out to elucidate decomposition mechanism of pentlandite using modified powder microelectrode with Acidithiobacillus ferrooxidans attached or without on the mineral powder surface.Cyclic voltammetry（CV） results show that at a low potential of about-0.2 V（vs SCE）,the pentlandite was transformed to an intermediated phase like Fe4.5-yNi4.5-xS8-z when Fe and Ni ions were evacuated from mineral lattice;when the potential was changed from-0.2 V to 0.2 V,the unstable violarite（Fe3Ni3S4） and FeNi2S4 were formed which was accompanied by element sulfur formed on the mineral surface;when the potential increased over 0.2 V,the unstable intermediated phase decomposed entirely;at a higher potential of 0.7 V,the evacuated ferrous ion was oxidized to ferric ion.The presence of Acidithiobacillus ferrooxidans made the oxidation peak current increase with initial peak potential negatively moving,and the bacteria also contributed to the sulfur removing from mineral surface,which was demonstrated by the reduction characteristic at potential ranging from-0.75 to-0.5 V.Leaching experiments and electrochemical results show that the solution acidity increasing when pH2 may impede the oxidation process slightly.

Relationships among bioleaching performance, additional elemental sulfur, microbial population dynamics and its energy metabolism in bioleaching of chalcopyrite

To estimate the relationships among bioleaching performance, additional elemental sulfur （S0）, microbial population dynamics and its energy metabolism, bioleaching of chalcopyrite by three typical sulfur- and/or iron-oxidizing bacteria, Acidithiobacillus ferrooxidans, Leptospirillum ferriphilum and Acidithiobacillus thiooxidans with different levels of sulfur were studied in batch shake flask cultures incubated at 30 °C. Copper dissolution capability （71%） was increased with the addition of 3.193 g/L S0, compared to that （67%） without S0. However, lower copper extraction was obtained in bioleaching with excessive sulfur. Microbial population dynamics during chalcopyrite bioleaching process was monitored by using PCR-restriction fragment length polymorphism （PCR-RFLP）. Additional S0 accelerated the growth of sulfur-oxidizing bacteria, inhibited the iron-oxidizing metabolism and led to the decrease of iron-oxidizing microorganisms, finally affected iron concentration, redox potential and bioleaching performance. It is suggested that mixed iron and sulfur-oxidizing microorganisms with further optimized additional S0 concentration could improve copper recovery from chalcopyrite.

Comparison of Fe^(2+) oxidation by Acidithiobacillus ferrooxidans in rotating-drum and stirred-tank reactors

Fe2＋ oxidation by Acidithiobacillus ferrooxidans（At.ferrooxidans） under different solid contents by adding inert Al2O3 powder was examined in rotating-drum and stirred-tank reactors.The results show that the bioactivity of At.ferrooxidans in the stirred-tank is higher than that in the rotating-drum in the absence of Al2O3 powder,but the biooxidation rate of Fe2＋ decreases markedly from 0.23 g/（L·h） to 0.025 g/（L·h） with increasing the content of Al2O3 powder from 0 to 50%（mass fraction） in the stirred-tank probably due to the deactivation of At.ferrooxidans resulting from the collision and friction of solid particles.The increase in Al2O3 content has a little adverse effect on the bioactivity of At.ferrooxidans in the rotating-drum due to different mixing mechanisms of the two reactors.The biooxidation rate of Fe2＋ in the rotating-drum is higher than that in the stirred-tank at the same content of Al2O3 powder,especially at high solid content.The higher bioactivity of At.ferrooxidans can be maintained for allowing high solid content in the rotating-drum reactor,but its application potential still needs to be verified further by the sulfide bioleaching for the property differences of Al2O3 powder and sulfide minerals.

Bio-decomposition of rock phosphate containing pyrites by Acidithiobacillus ferrooxidans

Leaching soluble phosphorus from rock phosphate containing pyrites by Acidithiobacillus ferrooxidans (A.f.) is feasible, and the reaction mechanism is as follows. Pyrites are oxidized by A.f. to produce H_2SO_4 and FeSO_4; the rock phosphate is decomposed by H_2SO_4, forming soluble phosphorus compounds; and Fe2+ from FeSO_4 is oxidized to Fe^3+, providing energy for the growth of A. f.. In this process, as H_2SO_4 is produced in the reaction, an acidic condition in the culture medium is formed, which benefits the growth of A. f. and aids both continuous oxidation of pyrites and leaching of soluble phosphorus from rock phosphate. The fraction of phosphorous leached can reach the largest in the presence of 1.0 g/L Fe^3+, 200 mg/L Mg^2+ and 400 mg/L NH_4^+. The optimal technological parameters on the fraction of phosphorous leached are as follows: the volume fraction of inocula of A. f., the mass ratio of pyrites to rock phosphate and the pH value are in ranges of 5%-25%, 3:1-5:1 and 1.8-2.2, respectively.

Really active form of fluorine toxicity affecting Acidithiobacillus ferrooxidans activity in bioleaching uranium

In order to determine the mechanism of bacterial tolerance to fluorine,Acidithiobacillus ferrooxidans ATCC 23270 was domesticated and studied under the conditions of different fluorine concentrations and pH values with or without treatment by Proteinase K.The bacterial activities were observed through measuring the changes of solution potentials by platinum electrode with Ag/AgCl reference electrode and the intracellular fluorine was determined by-uorine ion-selective electrode.The results indicated that the tolerance of Acidithiobacillus ferrooxidans ATCC 23270 to fluorine could be obviously improved by domestication,HF was the effective form of fluorine to affect the bacterial activity,and pH increase or concentration change of ions of strong complex ability with fluorine ions in solution could result in false appearance of high fluorine-resistant strain.Some proteins located in cell wall or cell membrane were intimately relative with the bacterial fluorine tolerance.

Formation of jarosite and its effect on important ions for Acidithiobacillus ferrooxidans bacteria

The precipitation of jarosite adversely affects the bio-leaching of copper sulfides in the Sarcheshmeh heap bio-leaching process. The variables of the initial concentration of ferrous iron in the growth medium, pH, and temperature were examined in the laboratory to determine how they affect the precipitation of jarosite in the presence of Acidithiobacillus ferrooxidans bacteria. It was found that the maximum ferric precipitate occurred at a ferrous sulfate concentration of 50 g/L, a temperature of 32 ℃, and an initial pH value of 2.2. The effects of the precipitation of ferric iron on the quantities of ions that are important for A. ferrooxidans bacteria in aqueous phase, i.e., ferric, sulfate, potassium, phosphate, and magnesium ions, also were assessed. The results showed relatively similar patterns for the ferric and potassium ions, and then reason might have been the co-precipitation of these ions as constituent elements of jarosite mineral. At pH values greater than 1.6, the solubility of phosphate ions decreased dramatically due to the co-precipitation of phosphate ions with the jarosite precipitate and due to the significant growth rate of A. ferrooxidans bacteria in this pH range. Due to the dissolution of a gangue constituent in the ore, the magnesium levels increased in the first few days of the bio-leaching process;thereafter, it decreased slightly.

Catalytic effect of visible light and Cd^2+on chalcopyrite bioleaching

The effects of visible light and Cd^2+ion on chalcopyrite bioleaching in the presence of Acidithiobacillus ferrooxidans(A.ferrooxidans)were studied by scanning electron microscopy(SEM),synchrotron radiation X-ray diffraction(SR-XRD),and X-ray photoelectron spectroscopy(XPS).The results of bioleaching after 28 days showed that the copper dissolution increased by 4.96%with only visible light,the presence of Cd2+alone exerted slight inhibition effect on chalcopyrite dissolution and the concentration of dissolved copper increased by 14.70%with visible light and 50 mg/L Cd^2+.The results of chemical leaching showed that visible light can promote the circulation of iron.SEM results showed that Cd^2+promoted the attachment of A.ferrooxidans on chalcopyrite surface under visible light.SR-XRD and XPS results indicated that visible light and Cd^2+promoted chalcopyrite dissolution,but did not inhibit the formation of passivation.Finally,a model of synergistic catalysis mechanism of visible light and Cd2+on chalcopyrite bioleaching was proposed.

Mechanism of bioleaching chalcopyrite by Acidithiobacillus ferrooxidans in agar-simulated extracellular polymeric substances media

The mechanism of leaching chalcopyrite by Acidithiobacillus ferrooxidans （,4. ferrooxidans） in agar-simulated extracellular polymeric substances （EPS） media was investigated. The results indicate that bacterial EPS can release H＋ and concentrate Fe3＋; Fe2＋ is movable between agar-simulated EPS phase and bulk solution phase, but it is difficult for Fe3＋ to move due to its hydroxylation and EPS complex action; A. ferrooxidans first prefer Fe2＋ as energy to metabolize compared with chalcopyrite, and a suitable simulated EPS environment for bacterial living is at about pH 1.8; the iron precipitates and jarosites formed by a lot of biologically oxidized Fe3 cover the simulated EPS easily and form an impermeable deposit acting as a limited barrier of ion transport that attenuates the aggressiveness of the bioleaching attack. The EPS layer blocked by iron precipitates or jarosites is responsible for the chalcopyrite passivation.

Bioleaching of chalcopyrite by UV-induced mutagenized Acidiphilium cryptum and Acidithiobacillus ferrooxidans

The original strains Acidithiobacillusferrooxidans GF and Acidiphilium cryptum DXI-1 were isolated from the drainage of some caves riched in chalcopyrite in Dexing Mine in Jiangxi Province of China. The optimum temperature and pH for growth were 30 ℃ and 3.5 for Ac. cryptum DXI-1, and 30 ℃ and 2.0 for At. ferrooxidans GF, respectively. For Ac. cryptum DXI-1, the optimum UV radiating time was 60 s and the positive mutation rate was 22.5%. The growth curves show that Ac. cryptum after mutagenesis reached stationary phase within 60 h, which was 20 h earlier than the original strain. For At. ferrooxidans GF, the optimum mutation time was 60 s and the positive mutation rate was 35%. The most active UV-mutated strain At. ferrooxidans GF oxidized all the ferrous after 48 h. The bioleaching experiments showed that bioleaching with the mixture of UV-mutated strains of At. ferrooxidans GF and A c. cryptum DX1-1 （1：1） could extract 3.01 g/L of copper after 30 d, while the extracted copper was 2.63 g/L with the mixture of the original strains before UV-mutation. At the end of the bioleaching experiments, the proportion of the cell density in the cultures ofAc. cryptum DXI-1 andAt.ferrooxidans GF was approximately 1：5.

Microaerobic iron oxidation and carbon assimilation and associated microbial community in paddy soil

Iron oxidation is a prevalent and important biogeochemical process in paddy soil,but little is known about whether and how microbially mediated iron oxidation is coupled with carbon assimilation,particularly under microaerobic conditions.Here,we investigated kinetics of CO_2 assimilation and Fe(Ⅱ)oxidation in an incubation experiment with paddy soil under suboxic conditions,and profiled the associated microbial community using DNA-stable isotope probing and 16S r RNA gene-based sequencing.The results showed that CO_2 assimilation and Fe(II)oxidation in the gradient tubes were predominantly mediated by the microbes enriched in the paddy soil,primarily Azospirillum and Magnetospirillum,as their relative abundances were higher in the^( 13)C heavy fractions compared to^( 12)C heavy fractions.This study provided direct evidence of chemoautotrophic microaerophiles linking iron oxidation and carbon assimilation at the oxic–anoxic interface in the paddy soil ecosystem.

Microbial Characterization of Denitrifying Sulfide Removal Sludge Using High-Throughput Amplicon Sequencing Method

The denitrifying sulfide removal(DSR) process has recently been studied extensively from an engineering perspective. However, the importance of microbial communities of this process was generally underestimated. In this study, the microbial community structure of a lab-scale DSR reactor was characterized in order to provide a comprehensive insight into the key microbial groups in DSR system. Results from high-throughput sequencing analysis revealed that the fraction of autotrophic denitrifiers increased from 2.34 % to 10.93% and 44.51% in the DSR system when the influent Na Cl increased from 0 g/L, to 4 g/L and 30 g/L, respectively. On the contrary, the fraction of heterotrophic denitrifiers decreased from 61.74% to 39.57%, and 24.12%, respectively. Azoarcus and Thiobacillus were the main autotrophic denitrifiers, and Thauera was the main hetetrophic denitrifier during the whole process. This study could be useful for better understanding the interaction between autotrophs and heterotrophs in DSR system.

Succession of Bacterial Community Inhabited Acid Mine Drainage under High Fe（Ⅱ） Concentration

To reveal the effects of Fe2＋ on bacterial communities in the early stages of minerals dissolution, two different acid mine drainage （AMD） samples were collected at Dabaoshan Mine and Shenbu Mine. Community successions of AMD niches were analyzed by Amplified Ribosomal DNA Restriction Analysis （ARDRA）, sequencing, and phylogenetic analysis in original AMD samples and their subculture under Fe2＋ concentrations. Although geochemical properties and community structures were greatly different between the two original AMD samples, bacterial community successions were still very similar under high Fe2＋ concentrations. The results showed that Acidithiobacillus ferrooxidans have competitive relationship with other bacterial species living in the AMD, including species that were also capable of oxidizing ferrous ion. A competitive relationship among different At. ferrooxidans strains likewise existed. Some of At. ferrooxidans can grow first under conditions of high ferrous ion concentration, and other At. ferrooxidans species decreased gradually and disappeared. This suggested that these species of At. ferrooxidans are most acidophilic bacteria and afford Fe3＋ to leach other metallic ion in the early stages of minerals dissolution.

Kinetics of FeSe_2 oxidation by ferric iron and its reactivity compared with FeS_2

The mobility and bioavailability of selenium is a major health and environmental issue and a main concern for geological disposal of high-level radioactive waste. Chemically and/or microbially mediated oxidation of insoluble Se-bearing particulate, such as iron selenides, to dissolved and mobile phases controls the transport and distribution of Se in the environment. The oxidation of ferroselite （FeSe2） by ferric iron was investigated in anoxic conditions. The redox reaction can be represented by： FeSe2 ＋ 2Fe3＋ = 2Se^0 ＋ 3Fe2＋. Kinetic studies indicated that the reaction can be described by second-order rate law, with rate constants of 0.49±0.01, 0.85±0.02, 1.84±0.04, and 3.29±0.13 L mol^-1 s^-1 at pH 1.62, 1.87, 2.23, and 2.49, respectively. The positive correlation between reaction rate and pH implies that diffusion of Fe3＋ oxidant to the mineral surface is the rate-determining step. The strong reactivity of FeSe2 towards Fe^3＋ suggests that ferric iron may play a significant role in FeSe2 oxidation process （e.g., by Se^4＋, 02, etc.） and Se^0 should be the first reaction product. Also, it was shown that the reduction rate of Fe^3＋ or Se^4＋ by pyrite （FeS2） can be significantly increased in the presence of FeSe2, suggesting a stronger reactivity of FeSe2 compared with pyrite. The results obtained extend our knowledge about the subtle interaction between Se, pyrite and iron selenides in the environment, and give insight into the transfer of selenium from iron selenides to bio-available selenium （i.e., selenite and selenate） in the Se-rich environment.

Magnetic transitions in graphene derivatives

The magnetic transitions in graphene oxide （GO） have been investigated experimentally. Micron-sized GO flakes exhibit dominant diamagnetism accompanied by weak ferromagnetism at room temperature. However, when the lateral dimensions of GO flakes are reduced from micron-size to nano-size, a clear transition from dominant diamagnetism to ferromagnetism is observed. After reducing the GO chemically or thermally, the dominant magnetic properties are not altered markedly except for the gradual enhancement of ferromagnetic components. In contrast, at 2 K, significant paramagnetism is present in both the micron-sized and nano-sized GO sheets. The effects of different functional groups on magnetic transitions in graphene derivatives have been further investigated using on hydroxyl-, carboxyl-, amino- and thiol- functionalized graphene. The results reveal that significant diamagnetism with weak ferromagnetism is present at room temperature in all of these functionalized graphene derivatives and the ability of different functional groups to introduce magnetic moments follows the order -SH 〉 --OH 〉 -COOH, -NH2. Notably, at 5 K, diamagnetism, paramagnetism and ferromagnetism coexist in thiol-, hydroxyl- and carboxyl-functionalized graphene, while amino-graphene exhibits dominant paramagnetism, analogous to the low-temperature magnetism in GO. These results indicate that diamagnetism, paramagnetism and ferromagnetism can coexist in graphene derivatives and magnetic transitions among the three states can be achieved which depend on edge states, vacancies, chemical doping and the attached functional groups. The results obtained may help settle the current controversy about the magnetism of graphene-related materials.