In-operando imaging of polysulfide catholytes for Li–S batteries and implications for kinetics and mechanical stability
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Polysulfide
Iron sulfide
Deposition
Carbon fibers
Bacteria that disproportionate elemental sulfur fractionate sulfur isotopes such that sulfate is enriched in sulfur-34 by 12.6 to 15.3 per mil and sulfide is depleted in sulfur-34 by 7.3 to 8.6 per mil. Through a repeated cycle of sulfide oxidation to S0 and subsequent disproportionation, these bacteria can deplete sedimentary sulfides in sulfur-34. A prediction, borne out by observation, is that more extensive sulfide oxidation will lead to sulfides that are more depleted in sulfur-34. Thus, the oxidative part of the sulfur cycle creates circumstances by which sulfides become more depleted in sulfur-34 than would be possible with sulfate-reducing bacteria alone.
Sulfur Cycle
Sulfate-Reducing Bacteria
Isotopes of sulfur
Sulfur Metabolism
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Four model constructed wetlands (CWs) were designed to investigate the effects of sulfate load on sulfate and sulfide removal. The results showed that as the sulfate load increased from 1.42 to 7.01 g S m–3 d–1, the sulfate removal rate increased from 1.42 to 3.16 g S m–3 d–1, and the sulfide discharge rate increased from 0.08 to 1.46 g S m–3 d–1. The total sulfur removal rate ranged between 1.29 and 1.74 g S m–3 d–1. The sulfide in the effluent only accounted for 5.55%–46.9% of the removed sulfate. This indicated that CWs can effectively reduce sulfide discharge while removing sulfate. The conversion of dissolved sulfide into deposited sulfur by CW matrix was a main way for sulfide removal. Elemental sulfur, acid volatile sulfide (AVS), and pyrite-sulfur were the main forms of sulfur deposition in this study. The accumulations of these three sulfur compounds were 16.6–36.2, 22.3–36.0, and 49.7–63.6 mg S kg–1 gravel, respectively. Sulfur balance analysis showed that 42.9%–71.1% of the removed sulfate was deposited in the matrix, and only 0.84%–2.34% was absorbed by the plant.
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Zero-valent sulfur is a key intermediate in the microbial oxidation of sulfide to sulfate. Many sulfide-oxidizing bacteria produce and store large amounts of sulfur intra- or extracellularly. It is still not understood how the stored sulfur is metabolized, as the most stable form of S(0) under standard biological conditions, orthorhombic α-sulfur, is most likely inaccessible to bacterial enzymes. Here we analyzed the speciation of sulfur in single cells of living sulfide-oxidizing bacteria via Raman spectroscopy. Our results showed that under various ecological and physiological conditions, all three investigated Beggiatoa strains stored sulfur as a combination of cyclooctasulfur (S8) and inorganic polysulfides (Sn(2-)). Linear sulfur chains were detected during both the oxidation and reduction of stored sulfur, suggesting that Sn(2-) species represent a universal pool of bioavailable sulfur. Formation of polysulfides due to the cleavage of sulfur rings could occur biologically by thiol-containing enzymes or chemically by the strong nucleophile HS(-) as Beggiatoa migrates vertically between oxic and sulfidic zones in the environment. Most Beggiatoa spp. thus far studied can oxidize sulfur further to sulfate. Our results suggest that the ratio of produced sulfur and sulfate varies depending on the sulfide flux. Almost all of the sulfide was oxidized directly to sulfate under low-sulfide-flux conditions, whereas only 50% was oxidized to sulfate under high-sulfide-flux conditions leading to S(0) deposition. With Raman spectroscopy we could show that sulfate accumulated in Beggiatoa filaments, reaching intracellular concentrations of 0.72 to 1.73 M.
Sulfur Metabolism
Sulfate-Reducing Bacteria
Oxidizing agent
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Reactions of alkaline metal carbonates with sulfur are investigated in detail. The evolution of CO and a trace of were observed in the course of reaction with major component of polysulfides. Some evidences that the reaction proceeds with breaking of terminal sulfur-sulfur bond in the sulfur polymer, and forming CO, and polysulfide are presented. Polysulfides have the role of keeping free sulfur and allow it to react with other chemicals to rather high temperatures.plexes, whereas the binuclear and mononuclear complexes of Mn and Co$^{2+}$
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Previous studies with the strictly autotrophic sulfur bacterium, Thiobacillus thioöxidans, growing on elemental sulfur have shown that the sulfur is rapidly oxidized to sulfate without the accumulation of intermediate products. The strictly autotrophic sulfur bacterium Th. thioparus transforms thiosulfate to the 2 products, sulfate and elemental sulfur. No question has arisen concerning the initial stages of transformation of thiosulfate, but, by reason of the relatively large size of the particles of elemental sulfur compared to the tiny bacterial cells (about 0.5 × 0.8μ) it has been suggested that some initial transformation to a reduced or oxidized substance may precede passage of the sulfur material through the cell membrane, after which the reactions leading to the release of energy for growth takes place. However, McCallan and Wilcoxon present evidence which shows that the vapor pressure of elemental sulfur is sufficiently high to permit sulfur vapor to enter cells which are not even in contact with the solid sulfur. Inorganic media containing sulfur or thiosulfate and supporting growth of these 2 bacteria have been examined for the presence of sulfide. No sulfide or other reducing substance was detected in cultures of Th. thioöxidans by titration with 0.01N iodine. No substance formed from thiosulfate by Th. thioparus was found by titration with iodine. Tests for sulfide with nitroprusside were negative in both cases. The results do not support the contention of von Deines that the sulfur material precipitated by Th. thioparus during growth on thiosulfate is a highly sulfured polysulfide. Although sulfide does not appear in detectable amounts in the media, sulfide is produced by both organisms during growth.
Tetrathionate
Sodium thiosulfate
Polysulfide
Sulfur Metabolism
Sulfate-Reducing Bacteria
Sulfur Cycle
Thiobacillus
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There are three kinds of sulfur bacteria (filaceous sulfur bacteria, synthetic sulfur bacteria and colorless sulfur bacteria), and they could consume sulfide and excrete sulfur intracellularly or extracellularly. The characteristics of these sulfur bacteria, the operational conditions for sulfur producing, and the latest research status of biological sulfide removing processes home and broad were summarized in this paper. It was shown that colorless sulfur bacteria had high sulfur producing rate and twenty grams sulfur could be produced extracellularly while one gram cell weight is increased. Therefore, this kind of bacterium is suitable to be applied in the future industrialized sulfide removing process. The development trend of sulfide removing processes both in research and application, and the key standards of those processes were also summarized. In the author's viewpoint, sulfide removing process could be widely developed in the near future for its low energy consuming, low investment and suitable operational conditions. In addition, the molecular mechanism of biological sulfide removing from the points of enzymology and genetics has been discussed as well. It was indicated that the novel engineering bacteria reconstructed by gene engineering technology would have higher efficiency of sulfide removing.
Sulfide Minerals
Sulfur Metabolism
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Polysulfide
Carbon fibers
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Polysulfide
Chromatium
Sulfur Cycle
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Growing cultures of the green obligate photolithotroph, Chlorobaculum parvum DSM 263T (formerly Chlorobium vibrioforme forma specialis thiosulfatophilum NCIB 8327), oxidized sulfide quantitatively to elemental sulfur, with no sulfate formation. In the early stages of growth and sulfide oxidation, the sulfur product became significantly enriched with 34S, with a maximum delta34S above +5 per thousand, while the residual sulfide was progressively depleted in 34S to delta34S values greater than -4 per thousand. As oxidation proceeded, the delta34S of the sulfur declined to approach that of the initial sulfide when most of the substrate sulfide had been converted to sulfur in this closed culture system. No significant formation of sulfate occurred, and the substrate sulfide and elemental sulfur product accounted for all the sulfur provided throughout oxidation. The mean isotope fractionation factors (epsilon) for sulfide and sulfur were equivalent at epsilon values of -2.4 per thousand and +2.4 per thousand respectively. The significance of the experimentally-observed fractionation to the 34S/32S ratios seen in natural sulfur-containing minerals is considered.
Isotopes of sulfur
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