Reduction Of Elemental Sulfur Research Articles

Molecular mechanism of elemental sulfur dissolution in H2S under stratal conditions.

Resulting from the solubility reduction of elemental sulfur during the development of high sulfur gas formations, sulfur deposition often occurs to reduce the gas production and threaten the safety of gas wells. Understanding the dissolution mechanism of elemental sulfur in natural gas is essential to reduce the risk caused by sulfur deposition. Because of the harsh conditions in the high-sulfur formations, it remains challenging to in situ characterize the dissolution-precipitation processes, making deficient the knowledge of sulfur dissolution mechanism. The dissolution of sulfur allotropes (SN, N = 2, 4, 6 and 8) in H2S, the main solvent of sulfur in natural gas, is studied in this work by means of first-principles calculations and molecular dynamics simulations. While S6 and S8 undergo physical interaction with H2S under the conditions corresponding to those at 1-6 km stratigraphic depths, S2 and S4 react with H2S and form stable polysulfides. Unravelling the mechanism would be helpful for understanding and controlling the sulfur deposition in high-sulfur gas development.

Molecular mechanism in the solubility reduction of elemental sulfur in H2S/CH4 mixtures: A molecular modeling study

The solubility evolution of elemental sulfur in sour gas is key to study the occurrence and inhibition of sulfur deposition in the exploitation of high-sulfur gas reservoirs. Elemental sulfur mainly dissolves in H2S, and its solubility decreases dramatically in the presence of methane. As both methane and H2S are the main components in high-sulfur gas, it is essential to understand the molecular mechanism of the solubility reduction in H2S/CH4 mixtures. Molecular dynamics simulations are carried out for the S8, H2S and CH4 mixtures to reproduce the solubility reduction upon methane addition, and then used to reveal the reduction mechanism at the level of intermolecular interaction. The simulations reveal that both the strong competitiveness and high collision probability of H2S–CH4 pairs reduce the average densities of H2S–S(S8) and H2S–H2S pairs, which reduce the sulfur solubility in a direct/indirect but cooperative way. The role of methane in the solubility reduction is then discussed and the molecular mechanism of sulfur dissolution and precipitation in the sour gasses is addressed.

New insights into sulfur input induced methylmercury production and accumulation in paddy soil and rice

Sulfur has a high affinity for mercury (Hg) and can serve as effective treating agent for Hg pollution. However, conflict effects between reducing Hg mobility and promoting Hg methylation by sulfur were found in recent studies, and there is a gap in understanding the potential mechanism of MeHg production under different sulfur-treated species and doses. Here, we investigated and compared the MeHg production in Hg-contaminated paddy soil and its accumulation in rice under elemental sulfur or sulfate treatment at a relatively low (500 mg·kg−1) or high (1000 mg·kg−1) level. The associated potential molecular mechanisms are also discussed with the help of density functional theory (DFT) calculation. Pot experiments demonstrate that both elemental sulfur and sulfate at high exposure levels increased MeHg production in soil (244.63–571.72 %) and its accumulation in raw rice (268.73–443.50 %). Coupling the reduction of sulfate or elemental sulfur and decrease of soil redox potential leads to the detachment of Hg-polysulfide complexes from the surface of HgS which can be explained by DFT calculations. Enhancement of free Hg and Fe release through reducing Fe(III) oxyhydroxides further promotes soil MeHg production. The results provide clues for understanding the mechanism by which exogenous sulfur promotes MeHg production in paddies and paddy-like environments and give new insights for decreasing Hg mobility by regulating soil conditions.

Continuous single-stage elemental sulfur reduction and copper sulfide precipitation under thermoacidophilic conditions

Metal sulfide precipitation is a viable technology for high-yield metal recovery from hydrometallurgical streams, with the potential to streamline the process design. A single-stage elemental sulfur (S0)-reducing and metal sulfide precipitating process can optimize the operational and capital costs associated with this technology, boosting the competitiveness of this technology for wider industrial application. However, limited research is available on biological sulfur reduction at high temperature and low pH, frequent conditions of hydrometallurgical process waters. Here we assessed the sulfidogenic activity of an industrial granular sludge previously shown to reduce S0 under hot (60–80 °C) and acidic conditions (pH 3.6). A 4 L gas-lift reactor was operated for 206 days and fed continuously with culture medium and copper. During the reactor operation, we explored the effect of the hydraulic retention time, copper loading rates, temperature, and H2 and CO2 flow rates on the volumetric sulfide production rates (VSPR). A maximum VSPR of 274 ± 6 mg·L−1·d−1 was reached, a 3.9-fold increase of the VSPR previously reported with this inoculum in batch operation. Interestingly, the maximum VSPR was achieved at the highest copper loading rates. At the maximum copper loading rate (509 mg·L−1·d−1), a 99.96% copper removal efficiency was observed. 16 s rRNA gene amplicon sequencing revealed an increased abundance of reads assigned to Desulfurella and Thermoanaerobacterium in periods of higher sulfidogenic activity.

Adaptations to high pressure of Nautilia sp. strain PV-1, a piezophilic Campylobacterium (aka Epsilonproteobacterium) isolated from a deep-sea hydrothermal vent.

Physiological and gene expression studies of deep-sea bacteria under pressure conditions similar to those experienced in their natural habitat are critical for understanding growth kinetics and metabolic adaptations to in situ conditions. The Campylobacterium (aka Epsilonproteobacterium) Nautilia sp. strain PV-1 was isolated from hydrothermal fluids released from an active deep-sea hydrothermal vent at 9° N on the East Pacific Rise. Strain PV-1 is a piezophilic, moderately thermophilic, chemolithoautotrophic anaerobe that conserves energy by coupling the oxidation of hydrogen to the reduction of nitrate or elemental sulfur. Using a high-pressure-high temperature continuous culture system, we established that strain PV-1 has the shortest generation time of all known piezophilic bacteria and we investigated its protein expression pattern in response to different hydrostatic pressure regimes. Proteogenomic analyses of strain PV-1 grown at 20 and 5MPa showed that pressure adaptation is not restricted to stress response or homeoviscous adaptation but extends to enzymes involved in central metabolic pathways. Protein synthesis, motility, transport, and energy metabolism are all affected by pressure, although to different extents. In strain PV-1, low-pressure conditions induce the synthesis of phage-related proteins and an overexpression of enzymes involved in carbon fixation.

Polysulfide-assisted urea synthesis from carbon monoxide and ammonia in water

Efficient conversion of carbon monoxide into urea in an aqueous ammonia solution was demonstrated through coupling with the elemental sulfur reduction to polysulfides. This reaction starts with a simple mixture of carbon monoxide, ammonia, elemental sulfur, and a small amount of hydrogen sulfide for polysulfide formation, enabling an almost complete conversion of 1 atm of carbon monoxide to urea (95–100% yield) within 216, 64, and 32 h at 35 °C, 50 °C, and 65 °C, respectively. Polysulfides control the overall reaction rate while suppressing the accumulation of a by-product, hydrogen sulfide, to less than 1 Pa. These functions follow simple kinetic and thermodynamic theories, enabling prediction-based reaction control. This operational merit, together with the superiority of water as a green solvent, suggests that our demonstrated urea synthesis is a promising option for sulfur utilization beneficial for agricultural production.

In-Situ Raman Spectroscopy of Lithium-Sulfur Cells

With the increasing demand for higher capacity and energy density, new batteries are being developed to meet these demands. Among the most promising chemistries, Lithium-Sulfur (Li-S) is one of the most popular. This is because of its excellent theoretical energy density (2600 Wh/kg, active materials) [1]. There are challenges that prevent Li-S cells from being commercialized, including adverse impact on cell performance due to lithium polysulfide (PS) formation/dissolution, volume changes during cycling and lithium dendrite formation. The issue that retains the focus of many researchers is the formation and shuttling of PSs as it directly impacts the practicality of the cell in terms of longevity and efficiency. There have been various approaches to mitigate PS shuttling including the use of specially designed cathode materials. One such material is sulfur-polyacrylonitrile (S-PAN) where PAN acts as a backbone [1, 2, 3]. The structure of this material supports the full reduction of elemental sulfur to Li2S upon discharging. This full reduction prevents the formation of intermediate PSs and loss of sulfur through PS shuttling, thus improving the sulfur utilization of S-PAN cathodes. The hypothesis is that there are little to no intermediate PSs present in S-PAN cathodes. To prove this, we used Raman spectroscopy to compare the quantitative results between the S-PAN electrode and conventional sulfur electrode. Specifically, with Raman spectroscopy, the features of the spectra that we are comparing are the Raman peaks of intermediate PSs that may be present in the samples [4, 5]. If the hypothesis is correct, the intensities of the Raman peaks for intermediate PSs for S-PAN should be less pronounced than conventional sulfur. In other words, the S-PAN electrode should exhibit significantly fewer intermediate polysulfides than the conventional sulfur electrode. The test is conducted by discharging the Raman cell to a set of incremental potentials where Raman spectra are taken at each potential. This will allow for the comparison of the polysulfide compositions and concentrations at different potential levels.We will present the effect of S-PAN on the charge-discharge cycle and compare it to a conventional Li-S cell. We will also utilize Raman Spectroscopy and in-situ Raman cells to characterize and compare PS species in both S-PAN and conventional S based cells. References Mukkabla, R.; Buchmeiser, M. R., Cathode materials for lithium–sulfur batteries based on sulfur covalently bound to a polymeric backbone. Journal of Materials Chemistry A, 2020, 8 (11), 5379-5394.Wang, J.; Yang, J.; Wan, C.; Du, K.; Xie, J.; Xu, N., Sulfur Composite Cathode Materials for Rechargeable Lithium Batteries. Advanced Functional Materials, 2003, 13 (6), 487-492.Warneke, S.; Eusterholz, M.; Zenn, R. K.; Hintennach, A.; Dinnebier, R. E.; Buchmeiser, M. R., Differences in Electrochemistry between Fibrous SPAN and Fibrous S/C Cathodes Relevant to Cycle Stability and Capacity. Journal of The Electrochemical Society, 2018, 165 (1), A6017-A6020.Zhang, L.; Qian, T.; Zhu, X.; Hu, Z.; Wang, M.; Zhang, L.; Jiang, T.; Tian, J.-H.; Yan, C., In situ optical spectroscopy characterization for optimal design of lithium–sulfur batteries. Chemical Society Reviews, 2019, 48 (22), 5432-5453.McBrayer, J. D.; Beechem, T. E.; Perdue, B. R.; Apblett, C. A.; Garzon, F. H. Polysulfide Speciation in the Bulk Electrolyte of a Lithium SULFUR BATTERY. Journal of The Electrochemical Society, 2018, 165 (5). Acknowledgement This work was supported in part by the U.S. Department of Energy, Office of Science, Office Workforce Development for Teachers and Scientists (WDTS) under the Science Community College Internship (CCI) Program as well as the Office of Energy Efficiency and Renewable Energy, Energy Storage Graduate Internship Program at the National Renewable Energy Laboratory.

Predicting the solubility of elemental sulfur in hydrogen sulfide through a molecular dynamics approach

Solubility reduction of elemental sulfur in H2S is the main reason of sulfur deposition in natural gas exploitation. In contrast to the usual approach in which the dissolution and diffusion processes of solid sulfur are simulated, a new computational model in which the aggregation process of S8 molecules starting with a well-dispersed solution is proposed to predict the solubility of S8 in H2S. Molecular dynamics simulations based on the new model produce reliable results compared to the measurements. Moreover, this model exhibits good efficiency and reproducibility, providing a useful tool for studying the sulfur deposition mechanism.

The HydS C-terminal domain of the Thiocapsa bogorovii HydSL hydrogenase is involved in membrane anchoring and electron transfer

Thiocapsa bogorovii BBS (former name Thiocapsa roseopersicina) contains HydSL hydrogenase belonging to 1e subgroup of NiFe hydrogenases (isp-type). The operon of these hydrogenases contains gene for small subunit (hydS), gene for large subunit (hupL), and genes isp1 and isp2 between them. It is predicted that last two genes code electron transport careers for electron transfer from/to HydSL hydrogenase. However, the interaction between them is unclear. The aim of this study was to determine structural and functional role of T. bogorovii HydS C-terminal end. For this purpose, we modelled all subunits of the complex HydS-HydL-Isp1-Isp2. Hydrophobicity surface analysis of the Isp1 model revealed highly hydrophobic helices suggesting potential membrane localization, as well as the hydrophilic C-terminus, which is likely localized outside of membrane. Isp1 model was docked with models of full length and C-terminal truncated HydSL hydrogenases and results illustrate the possibility of HydSL membrane anchoring via transmembrane Isp1 with essential participation of C-terminal end of HydS in the interaction. C-terminal end of HydS subunit was deleted and our studies revealed that the truncated HydSL hydrogenase detached from cellular membranes in contrast to native hydrogenase. It is known that HydSL hydrogenase in T. bogorovii performs the reaction of elemental sulfur reduction (S0 + H2 = ≥H2S). Cells with truncated HydS produced much less H2S in the presence of H2 and S0. Thus, our data support the conclusion that C-terminal end of HydS subunit participates in interaction of HydSL hydrogenase with Isp1 protein for membrane anchoring and electron transfer.

The Paleoarchean Northern Mundo Novo Greenstone Belt, São Francisco Craton: Geochemistry, U–Pb–Hf–O in zircon and pyrite δ34S-Δ33S-Δ36S signatures

Greenstone belts contain several clues about the evolutionary history of primitive Earth. Here, we describe the volcano-sedimentary rock association exposed along the eastern margin of the Gavião Block, named the Northern Mundo Novo Greenstone Belt (N-MNGB), and present data collected with different techniques, including U–Pb–Hf–O isotopes of zircon and multiple sulfur isotopes (32S, 33S, 34S, and 36S) of pyrite from this supracrustal sequence. A pillowed metabasalt situated in the upper section of the N-MNGB is 3337 ± 25 Ma old and has zircon with εHf(t) = −2.47 to −1.40, Hf model ages between 3.75 Ga and 3.82 Ga, and δ18O = +3.6‰ to +7.3‰. These isotopic data, together with compiled whole-rock trace element data, suggest that the mafic metavolcanic rocks formed in a subduction-related setting, likely a back-arc basin juxtaposed to a continental arc. In this context, the magma interacted with older Eoarchean crustal components from the Gavião Block. Detrital zircons from the overlying quartzites of the Jacobina Group are sourced from Paleoarchean rocks, in accordance with previous studies, yielding a maximum depositional age of 3353 ± 22 Ma. These detrital zircons have εHf(t) = −5.40 to −0.84, Hf model ages between 3.66 Ga and 4.30 Ga, and δ18O = +4.8‰ to +6.4‰. The pyrite multiple sulfur isotope investigation of the 3.3 Ga supracrustal rocks from the N-MNGB enabled a further understanding of Paleoarchean sulfur cycling. The samples have diverse isotopic compositions that indicate sulfur sourced from distinct reservoirs. Significantly, they preserve the signal of the anoxic Archean atmosphere, expressed by MIF-S signatures (Δ33S between −1.3‰ to +1.4‰) and a Δ36S/Δ33S slope of −0.81 that is indistinguishable from the so-called Archean array. A BIF sample has a magmatic origin of sulfur, as indicated by the limited δ34S range (0 to +2‰), Δ33S ~ 0‰, and Δ36S ~ 0‰. A carbonaceous schist shows positive δ34S (2.1‰–3.5‰) and elevated Δ33S (1.2‰–1.4‰) values, with corresponding negative Δ36S between −1.2‰ to −0.2‰, which resemble the isotopic composition of Archean black shales and suggest a source from the photolytic reduction of elemental sulfur. The pillowed metabasalt displays heterogeneous δ34S, Δ33S, and Δ36S signatures that reflect assimilation of both magmatic sulfur and photolytic sulfate during hydrothermal seafloor alteration. Lastly, pyrite in a massive sulfide lens is isotopically similar to barite of several Paleoarchean deposits worldwide, which might indicate mass dependent sulfur processing from a global and well-mixed sulfate reservoir at this time.

Triclosan transformation and impact on an elemental sulfur-driven sulfidogenic process

Elemental sulfur reduction has recently been demonstrated to be a promising sulfidogenic process for cost-effective treatment of various wastewaters. However, it remains unknown if sulfur reduction is capable of pharmaceuticals and personal care products (PPCPs) removal. Thus, this study investigated the feasibility of such process to remove PPCPs and how PPCPs influence the system performance during a long-term operation. Triclosan (TCS), a typical broad-spectrum antibacterial agent and a ubiquitous emerging organic contaminant in environments was chosen as the model compound. Results showed that TCS was removed principally via fast sorption followed by slow biodegradation. Amides, polysaccharides and hydroxyl groups in extracellular polymeric substances (EPS) provided adsorption sites. Both metabolism and co-metabolism of TCS with organic carbon removal were responsible for TCS biodegradation. Reductive dechlorination and hydroxylation of TCS were inferred during TCS biodegradation. The genera Georgenia, Soehngenia, Comamonas, Pseudomonas, Desulfovibrio and Sulfurospirillum were the potential TCS degraders in the sulfur-reducing system. Additionally, the presence of TCS at environmentally relevant concentrations did not negatively impact the performance of organic carbon removal, but altered functional bacteria groups (i.e. fermentative and sulfur-reducing genera). In summary, the sulfur-reducing system could be sufficiently robust to transform organohalide antimicrobials of PPCPs (e.g. triclosan) without compromising the performance.

Structures and Energetics of Elemental Sulfur in Hydrogen Sulfide

Severe safety concerns arise from sulfur deposition that occurs frequently in the development of high sulfur-content natural gas formation. Solubility reduction of elemental sulfur in H2S is the main reason of sulfur deposition. To understand how elemental sulfur, which exists in the form of sulfur clusters (Sn), interacts with H2S, quantum chemistry calculations are performed to study the structures and thermodynamic properties of Sn–H2S complexes. Weak interaction resulting mainly from intermolecular sulfur–sulfur interaction is revealed for these complexes. The complexes formed by S4, S6 and S8 have similar binding energies that are relatively higher than that of S2–H2S. Because of their small binding energies and Gibbs free energies, these complexes may coexist in formation, but are however easily decomposed or formed depending on stratigraphic or pipeline conditions. Our calculations reveal the status of elemental sulfur in H2S, which is useful for subsequent predictions on sulfur solubility and sulfur deposition in high sulfur-content natural gas formation.

A pilot-scale sulfur-based sulfidogenic system for the treatment of Cu-laden electroplating wastewater using real domestic sewage as electron donor

Elemental sulfur (S0) reduction process has been demonstrated as an attractive and cost-efficient approach for metal-laden wastewater treatment in lab-scale studies. However, the system performance and stability have not been evaluated in pilot- or large-scale wastewater treatment. Especially, the sulfide production rate and microbial community structure may significantly vary from lab-scale system to pilot- or large-scale systems using real domestic sewage as carbon source, which brings questions to this novel technology. In this study, therefore, a pilot-scale sulfur-based sulfidogenic treatment system was newly developed and applied for the treatment of Cu-laden electroplating wastewaters using domestic sewage as carbon source. During the 175-d operation, >99.9% of Cu2+ (i.e., 5580 and 1187 mg Cu/L for two types of electroplating wastewaters) was efficiently removed by the biogenic hydrogen sulfide that produced through S0 reduction. Relatively high level of sulfide production (200 mg S/L) can be achieved by utilizing organics in raw domestic sewage, which was easily affected by the organic content and pH value of the domestic sewage. The long-term feeding of domestic sewage significantly re-shaped the microbial community in sulfur-reducing bioreactors. Compared to the reported lab-scale bioreactors, higher microbial community diversity was found in our pilot-scale bioreactors. The presence of hydrolytic, fermentative and sulfur-reducing bacteria was the critical factor for system stability. Accordingly, a two-step ecological interaction among fermentative and sulfur-reducing bacteria was newly proposed for sulfide production: biodegradable particulate organic carbon (BPOC) was firstly degraded to dissolved organic carbon (DOC) by the hydrolytic and fermentative bacteria. Then, sulfur-reducing bacteria utilized the total DOC (both DOC degraded from BPOC and the original DOC present in domestic sewage) as electron donor and reduced the S0 to sulfide. Afterwards, the sulfide precipitated Cu2+ in the post sedimentation tank. Compared with other reported technologies, the sulfur-based treatment system remarkable reduced the total chemical cost by 87.5‒99.6% for the same level of Cu2+ removal. Therefore, this pilot-scale study demonstrated that S0 reduction process can be a sustainable technology to generate sulfide for the co-treatment of Cu-laden electroplating wastewater and domestic sewage, achieving higher Cu2+removal and higher cost-effectiveness than the conventional technologies.

Accelerated reduction and solubilization of elemental sulfur by 1,2-aminothiols.

Nucleophilic 1,2-aminothiol compounds readily reduce typically-insoluble elemental sulfur to polysulfides in both water and nonpolar organic solvents. The resulting anionic polysulfide species are stabilized through hydrogen-bonding interactions with the proximal amine moieties. These interactions can facilitate sulfur transfer to alkenes.

Long Chain Fatty Acid Degradation Coupled to Biological Sulfidogenesis: A Prospect for Enhanced Metal Recovery.

This research assessed the microbiological suitability of oleate degradation coupled to sulfidogenesis by enriching communities from anaerobic sludge treating dairy products with S0, , , and S2 as electron acceptors. The limiting factor hampering highly efficient oleate degradation was investigated in batch reactors. The best sulfidogenic performance coupled to specialization of the enriched bacterial community was obtained for S0- and S2-reducing enrichments, with 15.6 (± 0.2) and 9.0 (± 0.0) mM of sulfide production, respectively. Microbial community analyses revealed predominance of Enterobacteraceae (50.6 ± 5.7%), Sulfurospirillum (23.1 ± 0.1%), Bacteroides (7.5 ± 1.5%) and Seleniivibrio (6.9 ± 1.1%) in S0-reducing cultures. In S2-reducing enrichments, the genus Desulfurella predominated (49.2 ± 1.2%), followed by the Enterobacterales order (20.9 ± 2.3%). S0-reducing cultures were not affected by oleate concentrations up to 5 mM, while S2-reducing cultures could degrade oleate in concentrations up to 10 mM, with no significant impact on sulfidogenesis. In sequencing batch reactors operated with sulfide stripping, the S0-reducing enrichment produced 145.8 mM sulfide, precipitating Zn as ZnS in a separate tank. The S2 fed bioreactor only produced 23.4 mM of sulfide precipitated as ZnS. The lower sulfide production likely happened due to sulfite toxicity, an intermediate of thiosulfate reduction. Therefore, elemental sulfur reduction represents an excellent alternative to the currently adopted approaches for LCFA degradation. To the best of our knowledge, this is the first report of oleate degradation with the flux of electrons totally diverted toward sulfide production for metal precipitation, showing great efficiency of LCFA degradation coupled to high levels of metals precipitated as metal sulfide.

Elemental sulfur reduction by a deep-sea hydrothermal vent Campylobacterium Sulfurimonas sp. NW10.

Sulfurimonas species (class Campylobacteria, phylum Campylobacterota) were globally distributed and especially predominant in deep-sea hydrothermal environments. They were previously identified as chemolithoautotrophic sulfur-oxidizing bacteria (SOB), whereas little is known about their potential in sulfur reduction. In this report, we found that the elemental sulfur reduction is quite common in different species of genus Sulfurimonas. To gain insights into the sulfur reduction mechanism, growth tests, morphology observation, as well as genomic and transcriptomic analyses were performed on a deep-sea hydrothermal vent bacterium Sulfurimonas sp. NW10. Scanning electron micrographs and dialysis tubing tests confirmed that elemental sulfur reduction occurred without direct contact of cells with sulfur particles while direct access strongly promoted bacterial growth. Furthermore, we demonstrated that most species of Sulfurimonas probably employ both periplasmic and cytoplasmic polysulfide reductases, encoded by genes psrA1 B1 CDE and psrA2 B2 , respectively, to accomplish cyclooctasulfur reduction. This is the first report showing two different sulfur reduction pathways coupled to different energy conservations could coexist in one sulfur-reducing microorganism, and demonstrates that most bacteria of Sulfurimonas could employ both periplasmic and cytoplasmic polysulfide reductases to perform cyclooctasulfur reduction. The capability of sulfur reduction coupling with hydrogen oxidation may partially explain the prevalenceof Sulfurimonas in deep-sea hydrothermal vent environments.

Tracing the Early Emergence of Microbial Sulfur Metabolisms

Hydrogen sulfide (nH2S) and sulfur oxide (SO n ; n = 1, 2, 3) gases in early Earth’s globally anoxic atmosphere were subjected to gas-phase chemical transformations by UV light. A principal photolysis pathway at that time produced elemental sulfur aerosols with mass-independently fractionated (MIF) isotopic values carrying variable minor isotope (33S, 36S) compositions. These rained into the sulfate-deficient Archean (ca. 3.85–2.5 Ga) oceans to react with [Fe2+]aq and form sedimentary sulfides. The MIF-bearing sulfides were incorporated into Archean sediments, including banded iron formations (BIF). Such aerosols may also have fueled microbial sulfur metabolisms, and thus are traceable by the MIF sulfur isotopes. Yet, data show that before ∼3.5 Ga mass-dependent34S/32S values in Early Archean sediments tend to fall within a narrow (±0.1%) range even as they carry mass-independent values. By about 3.5 Ga, 34S/32S values show much greater changes (>1%) in range congruent with microbial metabolic processing. Here, we trace probable pathways of elemental sulfur aerosols into Archean sediments, and couple our study with analysis of the evolutionary relationships of enzymes involved in sulfur metabolism to explain the observed trends. Our model explains why elemental sulfur aerosols were apparently not utilized by the Eoarchean (pre-3.65 Ga) biosphere even though an immediate precursor to the required enzyme may have already been present. Highlights Evolution of microbial sulfur metabolisms is tracked by multiple sulfur isotopes Alkaline hydrothermal vents were an abode for early microbial life Sulfite detoxification prompted anaerobic respiration Reversal of respiratory electron transport chain (ETC) stimulated photothiotrophy Surplus e- acceptors permitted the emergence of elemental sulfur reduction

Biosulfidogenesis Mediates Natural Attenuation in Acidic Mine Pit Lakes.

Acidic pit lakes are abandoned open pit mines filled with acid mine drainage (AMD)—highly acidic, metalliferous waters that pose a severe threat to the environment and are rarely properly remediated. Here, we investigated two meromictic, oligotrophic acidic mine pit lakes in the Iberian Pyrite Belt (IPB), Filón Centro (Tharsis) (FC) and La Zarza (LZ). We observed a natural attenuation of acidity and toxic metal concentrations towards the lake bottom, which was more pronounced in FC. The detection of Cu and Zn sulfides in the monimolimnion of FC suggests precipitation of dissolved metals as metal sulfides, pointing to biogenic sulfide formation. This was supported by microbial diversity analysis via 16S rRNA gene amplicon sequencing of samples from the water column, which showed the presence of sulfidogenic microbial taxa in FC and LZ. In the monimolimnion of FC, sequences affiliated with the putative sulfate-reducing genus Desulfomonile were dominant (58%), whereas in the more acidic and metal-enriched LZ, elemental sulfur-reducing Acidianus and Thermoplasma spp., and disproportionating Desulfocapsa spp. were more abundant. Furthermore, the detection of reads classified as methanogens and Desulfosporosinus spp., although at low relative abundance, represents one of the lowest pH values (2.9 in LZ) at which these taxa have been reported, to our knowledge. Analysis of potential biomarker lipids provided evidence that high levels of phosphocholine lipids with mixed acyl/ether glycerol core structures were associated with Desulfomonile, while ceramide lipids were characteristic of Microbacter in these environments. We propose that FC and LZ function as natural bioremediation reactors where metal sulfide precipitation is mediated by biosulfidogenesis starting from elemental sulfur reduction and disproportionation at an early stage (LZ), followed by sulfate reduction at a later stage (FC).

Elemental sulfur-driven sulfidogenic process under highly acidic conditions for sulfate-rich acid mine drainage treatment: Performance and microbial community analysis

Elemental sulfur-driven sulfidogenic process has been demonstrated to be more economical and energy-efficient than sulfate-driven sulfidogenic process when treating metal-laden wastewater. In previous studies, we observed that the polysulfide-involved indirect sulfur reduction ensured the superiority of sulfur over sulfate as the electron acceptor in the sulfidogenic process under neutral or weak-alkaline conditions. However, realizing high-rate sulfur reduction process for acid mine drainage (AMD) treatment without pH amelioration is still a great challenge because polysulfide cannot exist under acidic conditions. In this study, a laboratory-scale sulfur-packed bed reactor was therefore continuously operated with a constant sulfate concentration (~1300 mg S/L) and decreasing pH from 7.3 to 2.1. After 400 days of operation, a stable sulfide production rate (38.2 ± 7.6 mg S/L) was achieved under highly acidic conditions (pH 2.6–3.5), which is significantly higher than those reported in sulfate reduction under similar conditions. In the presence of high sulfate content, elemental sulfur reduction could dominate over sulfate reduction under neutral and acidic conditions, especially when the pH ≥ 6.5 or ≤ 3.5. The decreasing pH significantly reduced the diversity of microbial community, but did not substantially influence the abundance of functional genes associated with organic and sulfur metabolisms. The predominant sulfur-reducing genera shifted from Desulfomicrobium under neutral conditions to Desulfurella under highly acidic conditions. The high-rate sulfur reduction under acidic conditions could be attributed to the combined results of high abundance of Desulfurella and low abundance of sulfate-reducing bacteria (SRB). Accordingly, sulfur reduction process can be developed to achieve efficient and economical treatment of AMD under highly acidic conditions (pH ≤ 3.5).

A Simple Elemental Sulfur Reduction Method for Isotopic Analysis and Pilot Experimental Tests of Symmetry‐Dependent Sulfur Isotope Effects in Planetary Processes

AbstractRecent insights into fundamental mechanisms underlying quadruple stable sulfur isotope (32S, 33S, 34S, and 36S) mass‐independent fractionation (S‐MIF) chemistry and potential implications for planetary processes highlight the urgent need of conducting laboratory experiments to delineate the chemical physics of S‐MIF. Elemental sulfur (S0), a ubiquitous component in the atmospheres of early Earth and Mars, is a major product or reactant in most experiments. Developing different chemical protocols for isotopic analysis is consequently of utility. The reduction of S0 to hydrogen sulfide (H2S) is the first step of the fluorination method for isotopic analysis, but existing S0 reduction methods require relatively long chemical reagent preparation time. Here we present an operationally simple and rapid method for reducing S0 to H2S directly by “Thode solution.” External uncertainties of our method for δ34S, Δ33S, and Δ36S measurements (associated with reduction, fluorination, purification, and mass spectrometer analysis) are 0.3‰, 0.01‰, and 0.2‰, respectively, comparable with traditional methods. This new technique was used to determine quadruple stable sulfur isotope compositions of product S0 in a set of pilot experiments designed to investigate possible symmetry‐dependent isotope effects in planetary‐relevant elemental sulfur recombination reactions. Differences in Δ33S and Δ36S between initial and produced S0 are slightly larger than analytical errors, shedding new light into the role of sulfur recombination reactions in S‐MIF. Our study offers a practical approach for measuring multiple isotopic compositions of S0 in laboratory and natural samples and creates new opportunities for deepening understanding of S‐MIF signatures in Archean rocks and Martian meteorites.