Chenyan Ma

Sulfur oxidation activities of pure and mixed thermophiles and sulfur speciation in bioleaching of chalcopyrite

The sulfur oxidation activities of four pure thermophilic archaea Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared. Meanwhile, the relevant surface sulfur speciation of chalcopyrite leached with the mixed thermophilic archaea was investigated. The results showed that the mixed culture, with contributing significantly to the raising of leaching rate and accelerating the formation of leaching products, may have a higher sulfur oxidation activity than the pure cultures, and jarosite was the main passivation component hindering the dissolution of chalcopyrite, while elemental sulfur seemed to have no influence on the dissolution of chalcopyrite. In addition, the present results supported the former speculation, i.e., covellite might be converted from chalcocite during the leaching experiments, and the elemental sulfur may partially be the derivation of covellite and chalcocite.

Investigation of Elemental Sulfur Speciation Transformation Mediated by Acidithiobacillus ferrooxidans

The speciation transformation of elemental sulfur mediated by the leaching bacterium Acidithiobacillus ferrooxidans was investigated using an integrated approach including scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, and X-ray absorption near edge spectroscopy (XANES). Our results showed that when grown on elemental sulfur powder, At. ferrooxidans ATCC23270 cells were first attached to sulfur particles and modified the surface sulfur with some amphiphilic compounds. In addition, part of the elemental sulfur powder might be converted to polysulfides. Furthermore, sulfur globules were accumulated inside the cells. XANES spectra of these cells suggested that these globules consisted of elemental sulfur bound to thiol groups of protein.

Characteristics of secondary inorganic aerosol and sulfate species in size-fractionated aerosol particles in Shanghai

Sulfate, nitrate and ammonium (SNA) are the dominant species in secondary inorganic aerosol, and are considered an important factor in regional haze formation. Size-fractionated aerosol particles for a whole year were collected to study the size distribution of SNA as well as their chemical species in Shanghai. SNA mainly accumulated in fine particles and the highest average ratio of SNA to particulate matter (PM) was observed to be 47% in the fine size fraction (0.49-0.95 μm). Higher sulfur oxidation ratio and nitrogen oxidation ratio values were observed in PM of fine size less than 0.95 μm. Ion balance calculations indicated that more secondary sulfate and nitrate would be generated in PM of fine size (0.49-0.95 μm). Sulfur K-edge X-ray absorption near-edge structure (XANES) spectra of typical samples were analyzed. Results revealed that sulfur mainly existed as sulfate with a proportion (atomic basis) more than 73% in all size of PM and even higher at 90% in fine particles. Sulfate mainly existed as (NH4)2SO4 and gypsum in PM of Shanghai. Compared to non-haze days, a dramatic increase of (NH4)2SO4 content was found in fine particles on haze days only, which suggested the promoting impact of (NH4)2SO4 on haze formation. According to the result of air mass backward trajectory analysis, more (NH4)2SO4 would be generated during the periods of air mass stagnation. Based on XANES, analysis of sulfate species in size-fractionated aerosol particles can be an effective way to evaluate the impact of sulfate aerosols on regional haze formation.

Sulfur Species Investigation in Extra- and Intracellular Sulfur Globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus

The sulfur chemical speciation in extracellular and intracellular sulfur globules of Acidithiobacillus ferrooxidans and Acidithiobacillus caldus were investigated with an integrated approach including scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy and sulfur K-edge X-ray absorption near edge structure spectroscopy (XANES). The results indicated that both strains can accumulate extracellular sulfur globules when grown on thiosulfate, and the major sulfur chemical speciation of which were S8 for A. ferrooxidans and mixture of ring sulfur and polythionate for A. caldus, respectively. In contrast, A. ferrooxidans can accumulate both linear sulfur and S8 internally when grown with sulfur powder and thiosulfate, whereas A. caldus did not accumulate intracellular sulfur globules. In addition, the fitted results of sulfur K-edge XANES spectra indicated that the reduced glutathione (containing thiols groups) were involved in sulfur bio-oxidation of both strains and the tetrathionate were the intermediate products during thiosulfate metabolism by two strains.

Sulfur speciation and bioaccumulation in camphor tree leaves as atmospheric sulfur indicator analyzed by synchrotron radiation XRF and XANES

Analyzing and understanding the effects of ambient pollution on plants is getting more and more attention as a topic of environmental biology. A method based on synchrotron radiation X-ray fluorescence and X-ray absorption near edge structure spectroscopy was established to analyze the sulfur concentration and speciation in mature camphor tree leaves (CTLs), which were sampled from 5 local fields in Shanghai, China. Annual SO2 concentration, SO4(2-) concentration in atmospheric particulate, SO4(2-) and sulfur concentration in soil were also analyzed to explore the relationship between ambient sulfur sources and the sulfur nutrient cycling in CTLs. Total sulfur concentration in mature camphor tree leaves was 766-1704 mg/kg. The mainly detected sulfur states and their corresponding compounds were +6 (sulfate, include inorganic sulfate and organic sulfate), +5.2 (sulfonate), +2.2 (suloxides), +0.6 (thiols and thiothers), +0.2 (organic sulfides). Total sulfur concentration was strongly correlated with sulfate proportion with a linear correlation coefficient up to 0.977, which suggested that sulfur accumulated in CTLs as sulfate form. Reduced sulfur compounds (organic sulfides, thiols, thioethers, sulfoxide and sulfonate) assimilation was sufficed to meet the nutrient requirement for growth at a balanced level around 526 mg/kg. The sulfate accumulation mainly caused by atmospheric sulfur pollution such as SO2 and airborne sulfate particulate instead of soil contamination. From urban to suburb place, sulfate in mature CTLs decreased as the atmospheric sulfur pollution reduced, but a dramatic increase presented near the seashore, where the marine sulfate emission and maritime activity pollution were significant. The sulfur concentration and speciation in mature CTLs effectively represented the long-term biological accumulation of atmospheric sulfur pollution in local environment.

Differential utilization and transformation of sulfur allotropes, μ-S and α-S8, by moderate thermoacidophile Sulfobacillus thermosulfidooxidans.

The utilization of amorphous μ-S and orthorhombic α-S8 by thermoacidophile Sulfobacillus thermosulfidooxidans was firstly investigated in terms of cell growth and sulfur oxidation behavior. The morphology and surface sulfur speciation transformation were evaluated by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), Raman spectroscopy and sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. The results showed that the strain grown on μ-S entered slower (about 1 day later) into the exponential phase, while grew faster in exponential phase and attained higher maximal cell density and lower pH than on α-S8. After bio-corrosion, both sulfur samples were evidently eroded, but only μ-S surface presented much porosity, while α-S8 maintained glabrous. μ-S began to be gradually converted into α-S8 from day 2 when the bacterial cells entered the exponential phase, with a final composition of 62.3% μ-S and 37.7% α-S8 on day 4 at the stationary phase. α-S8 was not found to transform into other species in the experiments with or without bacteria. These data indicated S. thermosulfidooxidans oxidized amorphous μ-S faster than orthorhombic α-S8, but the chain-like μ-S was transformed into cyclic α-S8 by S. thermosulfidooxidans.

Effect of oxygen stoichiometry in LuFe2O4−δ and its microstructure observed by aberration-corrected transmission electron microscopy

A series of oxygen deficient LuFe(2)O(4-δ) materials have been prepared under a controlled oxygen partial-pressure atmosphere. Measurements of magnetization reveal that the increase of oxygen deficiencies could evidently depress the ferrimagnetic phase transition temperature (T(N)). In additional to the well-known charge ordering within the (11(-)0) crystal plane, a visible structural modulation with q = (0,1/4.2,7/8) commonly appears on the (100) plane in the oxygen deficient samples. An aberration-corrected transmission electron microscopy study on the oxygen deficient samples demonstrates the presence of oxygen vacancies and local structural distortion. The atomic structural features in correlation with the structural modulation, distortion of the FeO(5) polyhedron and the (001) twinning domains have been also examined.

Cu/Te substitution effects on superconductivity and microstructure of phase-separated K0.8Fe1.75Se2

Two series of K0.8Fe1.75−xCuxSe2 () and K0.8Fe1.75Se2−yTey () single crystals of nominal composition have been prepared and their physical properties and microstructural features have been studied. Resistivity measurements demonstrate that the superconducting transition temperature decreases gradually with the increase of the substitution level and zero resistivity finally disappears in both systems. Systematic TEM, SEM and XRD structural analyses, in combination with the magnetic experimental data, reveal a rich variety of structural phenomena resulting from different types of substitution. Cu substitution gives rise to the volume of a new non-superconducting Cu-rich phase with modulation coexisting with the superconducting stripe domain. With the increase of the ratio of the new non-superconducting phase along with doping, the superconducting path is finally cut off, and results in the absence of zero resistivity. In contrast, the absence of superconductivity in Te-substituted materials is correlated with the complete disappearance of the q2 superconducting phase due to the suppression of phase separation.

Microstructural properties of K0.8 Fe1.6 S2, K0.8 Fe1.75 Se2-y Sy(0???y???2) and K0.8 Fe1.5+x S2(0?<?x???0.5) single crystals

The structural features of the antiferromagnetic K0.8Fe1.6S2 have been studied in the temperature range from 300K up to 700K by means of in situ transmission electron microscopy (TEM). The superstructure with a wave vector q(1) = 1/5(3a* + b*) originating from a Fe-vacancy order has been clearly observed; moreover, the structural analysis shows that K0.8Fe1.6S2 undergoes a transition from the Fe-vacancy order to disorder at about 585K. The S substitution effect on the phase separation and superconductivity in the K0.8Fe1.75Se2-ySy materials has been systematically investigated by SEM and TEM structural analyses, as well as by electrical resistivity measurements. Our experimental results reveal that the S element adopts a homogeneous distribution in all investigated materials, and the essential phase-separation nature is very similar to what was observed in the K0.8Fe1.75Se2 superconductor. A phase-separated state formed by the coexistence of two Fe-vacancy orders with wave vectors q(1) = 1/5(3a*+b*) and q(3) = 1/4(3a*+b*) in K0.8Fe1.5+xS2 (0 < x < 0.1) has been briefly discussed. Copyright (C) EPLA, 2013

Oxygen-vacancy ordering in multiferroic Bi1?xCaxFeO3?x/2 (0.1???x???0.5)

Multiferroic Bi1-xCaxFeO3-x/2 (0.1 <= x <= 0.5) materials have been synthesized via a high-temperature sintering method. The structural properties have been studied using transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). The EELS measurements reveal that the oxidation state of Fe ions in these compounds is Fe+3, and oxygen vacancies are created as Ca substitutions for Bi. A series of superstructure modulations appear along the a-axis direction, and their wavelength can be written as L = na (n = 4, 5, 6 and 7) depending on the Ca contents. Based on our structural analysis, we interpret these superstructures in terms of oxygen-vacancy ordering associated with local structural distortions. Copyright (C) EPLA, 2013