Pyritic Sulfur Research Articles

Late Quaternary marine transgressions inferred from the pyrite sulfur content and isotopes within core sediments from the southeast coast of China

Paleoenvironmental reconstructions of coastal areas during geological history are critical for understanding past responses to marine transgression. Identifying transgressive layers in sedimentary strata is therefore of great importance. To this end, we examined the content and isotopic composition of pyrite sulfur, in combination with classical organic geochemical indicators (e.g., C/N ratio and the δ13C of organic carbon), to trace the marine transgressions along the southeast coast of China since Marine Isotope Stage (MIS) 5. Our results suggest that the mass ratio of total organic carbon and pyrite sulfur (C/S ratio) is sensitive to seawater intrusion. Three transgressive layers were identified by low C/S ratios in core NDGK2, which correspond to sea level rise during MIS5, MIS3, and MIS1. Sediments deposited during MIS1 are represented by low C/S ratios with an average of 2.31, while those deposited during MIS5 and MIS3 have slightly higher C/S ratios, indicating a less extensive influence of seawater. Pyrite production in sediments deposited during MIS5 and MIS3 may have been limited by sulfate supply, as reflected by more positive values of δ34Spyr, whereas pyrites deposited during MIS1 were likely formed without sulfate limitation, as reflected by more negative values of δ34Spyr. The isotopic signals of pyrite sulfur thus further confirm the inference based on the C/S ratio. The magnitude of the transgression increased from MIS5 to MIS1, which is in agreement with the findings from classical organic geochemical indicators examined in this study, as well as geochemical and micropaleontological salinity indicators from previous studies. Our findings provide a promising method for identifying marine transgressions and their magnitude from the depositional record, especially when sedimentary strata lack diagnostic micropaleontological and sedimentological characteristics.

Distribution of Se in Floating Coals with Densimetric Fractions in China

Scholars at home and abroad have studied the concentrations of Se in coal and the relationship between Se and sulfur assignment. However, little attention has been paid to the study of Se in floating coal, especially the distribution pattern of Se in floating coal of densimetric fractions and the influencing factors. A total of 138 coal samples were collected from 14 provinces and cities in China to test the Se and sulfur concentrations in coal, and we carried out the comparison of Se with forms of sulfur with 81 of them. A total of 10 coal samples were selected for float-and-sink analyses to investigate the distribution pattern of Se in floating coal. The results showed that the average Se concentration of Chinese coal was 2.26 μg/g, which is identical with the results of previous research studies, which found an average Se concentration of 2~3 μg/g. Selenium was not uniformly distributed in floating coals of densimetric fractions but it had some regularity. The main controlling factor was the sulfur content in the coal. The Se concentrations of the high-sulfur coal showed a “linear growth” distribution with an increasing density, the Se concentrations of the floating coal in each densimetric fraction increased slowly and the Se concentrations of the floating coal of a densimetric fraction > 2.00 g/cm3 increased sharply. The other controlling factor was the ash yield of the coal. The Se concentrations of the low–medium-sulfur floating coal showed a “parabolic-like” distribution, i.e., low Se concentrations at both ends and high Se concentrations at the middle densimetric fraction. With the increase in the ash content of the coal from 18.23% to 51.92%, the densimetric fraction with the highest Se concentration gradually progressed from 1.40 g/cm3 to 1.50 g/cm3, 1.60 g/cm3 and 1.80 g/cm3 in order. The correlation between the selenium of the raw coal from different regions and the total sulfur, pyrite sulfur and organic sulfur was not significant. However, there existed a significant correlation between Se, total sulfur, pyrite sulfur and organic sulfur in floating coals from the same mining area and depositional environment, among which pyrite sulfur was the most correlated with Se, followed by total sulfur and organic sulfur.

Genetic mechanism of super-large karst bauxite in the northern North China Craton: Constrained by diaspore in-situ compositional analysis and pyrite sulfur isotopic compositions

>5 billion tons of karstic bauxites were formed during the Late Carboniferous in the North China Craton (NCC). However, the metallogenic mechanism of bauxite is still obscure due to the unclear formation process of the main ore mineral, diaspore. We conducted geological, mineralogical, δ34Spyrite, and in-situ diaspore trace element analyses on the Baode-Xingxian large bauxite deposit in the northern NCC, aiming to clarify the diaspore-forming mechanism and explore the genesis of bauxite. Generally, bauxites in northern NCC contains three layers from bottom to top: Fe-bearing claystone, bauxite ore, and claystone. The bauxite ore is mainly diaspore, kaolinite, and illite; the Fe-bearing claystone is illite and berthierine; and the claystone is primarily kaolinite. The broadly distributed high positive δ34Spyrite values (10‰–40‰) indicate that bauxites in the northern NCC formed in shallow-water environments. Total 216 diaspore grains have similar trace element compositions, and are obviously enriched in Cr, V, Re and U, but not in Mo, indicating that diaspore was formed in the subreduced facies. Diaspore with Fe/Al up to 4 mol% has slightly large cells, indicated that small-scale larger ions, Fe, entered the diaspore lattice to form Fe-diaspore. The favorable temperature and water activity of Fe-diaspore precipitation is similar to that of Al-hematite+ boehmite. We thus propose a probable diaspore formation mechanism: the small scale of Fe for Al substitution in the diaspore lattice and stabilize it to induce Fe-diaspore formation. Fe-diaspore is metastable with respect to diaspore and tends to convert into it during the diagenesis process.

Pyrite Sulfur Isotope Systematics Suggest Low Marine Sulfate Levels across the Ediacaran–Cambrian Transition

The Ediacaran–Cambrian (E–C) transition was a critical period in Earth’s history, and it was characterized by variable but potentially significant increases in atmospheric oxygen levels (pO2). Sulfate is an essential oxidant and plays a key role in regulating Earth’s surface redox conditions. However, there is uncertainty regarding seawater sulfate levels during the E–C transition. To address this issue, organic carbon (δ13Corg) and pyrite sulfur isotope (δ34Spy) analyses of the Heyu section (the Dengying Formation) in the Sichuan Basin, South China, were carried out. The δ13Corg varies between −36.4‰ and −27.4‰, and δ34Spy ranges from −6.6‰ to 27.3‰. The TOC and pyrite content ranges from 0.13 wt.% to 4.28 wt.% and from 0.01 wt.% to 0.94 wt.%, respectively. The marine sulfate concentration was modeled using a one-dimensional diffusion–advection–reaction model (1D-DAR). The modeling results indicate that the seawater sulfate level remained at a relatively low level of ~2–6 mM. The increased pyrite burial at extensive marine anoxia during the terminal Ediacaran period was likely a driver of such a low sulfate level.

Expansion of Reducing Marine Environments During the Ireviken Biogeochemical Event: Evidence From the Altajme Core, Gotland, Sweden

AbstractNew δ34Spy (pyrite) and δ34SCAS (carbonate‐associated sulfate) across the Llandovery‐Wenlock boundary (∼432 Ma) provide evidence for the expansion of reduced marine environments during the Ireviken Biogeochemical Event. This event consists of a major positive carbon isotope excursion, increased biotic turnover, and other major perturbations and changes within biogeochemical cycles. This interval of time has been hypothesized to coincide with an expansion of reducing marine environments that caused increased organic carbon burial and led to the Ireviken positive carbon isotope excursion (ICIE). Previous high‐resolution carbon isotope work in the Altajme core from Gotland, Sweden provides the highest resolution record of the ICIE yet documented and provides an ideal expanded stratigraphic section to study this event. Local expansion of reduced marine environments within the deeper shelf setting of the Altajme core is indicated by a positive shift in δ34Spy values and increase in pyrite sulfur concentrations at the onset of the ICIE. These data are indicative of increased microbial sulfate reduction within this portion of the Baltic Basin. Combined with new δ34SCAS data from this core, as well as additional data from distant basins, the new data presented here suggest a global expansion of reduced environments led to an increase in organic carbon burial and the ICIE.

Isolation and Characterization of A Novel Iron–Sulfur Oxidizing Bacterium Acidithiobacillus Ferrooxidans YQ-N3 and its Applicability in Coal Biodesulfurization

Acidithiobacillus ferrooxidans is a chemotrophic, aerobic, acidophilic, and Gram-negative bacterium that plays a key role in iron and sulfur cycling and has a wide range of applications in the industrial field. A novel A. ferrooxidans strain, hereinafter referred to as strain “YQ-N3”, was isolated from sediments of a river polluted by acid mine drainage (AMD) of an abandoned mine in Shanxi, China. The whole genome sequencing results revealed that A. ferrooxidans YQ-N3 has a 3,217,720 bp genome, which is comprised of one circular chromosome and five circular plasmids (Plasmid A, Plasmid B, Plasmid C, Plasmid D, Plasmid E). Plasmid E, a new plasmid, had not been annotated in the reference database. A. ferrooxidans YQ-N3 had a close evolutionary relationship with A. ferrooxidans ATCC23270 and A. ferridurans JCM18981 and exhibited higher similarity in its genomic structure with A. ferrooxidans ATCC23270. Multiple genes related to environmental resistance and iron and sulfur metabolism were predicted from its genome. A. ferrooxidans YQ-N3 can remarkably increase the oxidation rate of Fe2+ and S0 and enhance the hydrophilicity of S0, which was supported by functional gene analysis and laboratory experiments. The biological desulfurization experiment demonstrated that A. ferrooxidans YQ-N3 can reduce the sulfur content in coal by removing pyrite sulfur and organic sulfur.

Distribution characteristics and controlling factors of reduced inorganic sulfur forms in Three Gorges Reservoir sediment and its influence on the release of endogenous phosphorus

还原性无机硫(RIS)包括硫酸盐还原产物和活性铁(Fe_HR)形成的酸可挥发性硫(AVS)、硫的中间产物元素硫(S⁰)及沉积物中硫铁元素的最终积累物质黄铁矿硫(S_py),RIS不仅可以影响沉积物重金属的生物有效性,还控制铁还原及内源磷的释放等生源要素的地球化学行为。为了研究三峡库区沉积物中RIS分布特征及其环境意义,于2017年7-8月和12月采集三峡库区云阳至秭归段17个点的表层沉积物样品并测定其RIS含量。结果表明: 与其他湖泊、河流相比,三峡库区表层沉积物RIS含量较低,其中,AVS的含量为0.06~0.65 μmol/g,S⁰为0.50~1.66 μmol/g,S_py为0.96~17.54 μmol/g. AVS和S⁰含量夏季高于冬季,云阳至秭归段RIS变化趋势大致为先降低后增加再降低,有较明显的季节和地域差异。相关性分析、主成分分析和聚类分析表明,研究区沉积物生物可利用磷(BAP)、Fe_HR及上覆水体SO^2-₄含量为沉积物RIS的主要限制因子。库区冬季RIS与有机磷(Org-P)和可交换态磷(Ex-P)呈显著相关性,当硫化物含量增加时,会促进Org-P的矿化分解和Ex-P向上覆水体迁移,增加释磷风险。同时,本研究从硫驱动富营养化的角度评估了三峡库区存在污染风险的水域。除库区内已发生过典型水华的重点支流外,长滩河和九畹溪也存在富营养化问题。;Reduced inorganic sulfur (RIS) includes acid volatile sulfur (AVS) formed from sulfate reduction products and reactive iron (Fe_HR), elemental sulfur (S⁰), an intermediate product of sulfur, and pyrite sulfur (S_py), the ultimate accumulation material of elemental sulfur and iron in sediments. RIS can affect not only the biological effectiveness of sediment heavy metals, but also control the geochemistry of biogenic elements such as iron reduction and release of endogenous phosphorus behavior. In order to study the distribution characteristics of RIS in the sediments of the Three Gorges Reservoir area and its environmental significance, surface sediment samples were collected from 17 points in the section from Yunyang to Zigui in the Three Gorges Reservoir area in July-August and December 2017, and the RIS content was measured. The results showed that, compared with other lakes and rivers, the RIS content of surface sediments in the Three Gorges Reservoir area was lower, with AVS content ranging from 0.06 to 0.65 μmol/g, S⁰ from 0.50 to 1.66 μmol/g, and S_py from 0.96 to 17.54 μmol/g. The AVS and S⁰ contents are higher in summer than in winter, and the trend of RIS in the section from Yunyang to Zigui is roughly decreasing, then increasing and then decreasing, with obvious seasonal and regional difference. Correlation analysis, principal component analysis and cluster analysis showed that bioavailable phosphorus (BAP), Fe_HR and SO^2-₄ content in the overlying water were the main limiting factors of sediment RIS in the study area. The winter RIS in the reservoir area was significantly correlated with organic phosphorus (Org-P) and exchangeable phosphorus (Ex-P), and when the sulfide content increased, it promoted the mineralized decomposition of Org-P and the migration of Ex-P to the overlying water column, increasing the risk of phosphorus release. Meanwhile, this study assessed the waters at risk of pollution in the Three Gorges Reservoir area from the perspective of sulfur-driven eutrophication. In addition to the key tributaries in the reservoir area where typical water blooms have occurred, the Changtan River and Jiuwan River also have eutrophication problems.

Mineralogická charakteristika barytové mineralizace z lokality Ruda-hájenka (hornoměstský rudní revír, silezikum)

The previously unknown remnants of old mining activity were recently found at the locality Ruda-hájenka in the SW part of the Horní Město Ore District (Northern Moravia, Czech Republic). Partly weathered fragments of baryte mineralization in association with acid metavolcanites of the Vrbno Group (Devonian, Silesicum) were found in the dump material. Baryte mineralization exhibits a fine-grained marble-like appearance and locally contains minor disseminated pyrite. A detailed mineralogical study also revealed the presence of trace amount of other hypogene sulphides (galena and sphalerite), whose chemical composition is similar to those reported from the Horní Město Ore District. In addition, baryte also contains individual grains or aggregates of quartz, K-feldspar, and muscovite, which are often corroded and replaced by baryte. The silicates contain negligible amount of Ba (up to 0.02 apfu), which is only slightly higher than those in the same mineral phases from the host metavolcanic rock. The isotope composition of sulphur in baryte and pyrite indicates at least two different sources of sulphur (marine sulphate and likely sulphur leached from wall rocks) and isotope disequilibrium between co-existing minerals. The texture and mineral composition of the studied mineralization resemble metamorphosed baryte mineralizations occurring in the wider area (including local stratiform baryte bodies), but the absence of elevated contents of Ba in feldspars and especially in mica contradicts with an idea of Variscan metamorphic re-crystallization of the studied mineralization together with its host rock environment under the greenschist facies conditions. Therefore, one cannot exclude the possibility that it can be a post-metamorphic vein mineralization, which experienced intense deformation and recrystallization at very low temperatures, associated with rejuvenation of fault-related tectonic activity. The supergene mineral phases are represented especially by limonite, less frequent are minerals of the hollandite group (hollandite, coronadite, cryptomelane), anglesite, cerussite, and a not very well identified Ce-mineral, most likely cerianite-(Ce). Supergene origin is also presupposed for rarely found acanthite.

Simultaneous nitrification and autotrophic denitrification in fluidized bed reactors using pyrite and elemental sulfur as electron donors

In this study, simultaneous nitrification and autotrophic denitrification (SNAD) with either elemental sulfur or pyrite were investigated in fluidized bed reactors in mesophilic conditions. The reactor performance was evaluated at different ammonium (12–40 mg/L of NH4+-N), nitrate (35–45 mg/L of NO3−-N), and dissolved oxygen (DO) (0.1–1.5 mg/L) concentrations, with a hydraulic retention time of 12 h. The pyrite reactor supported the SNAD process with a maximum nitrogen removal efficiency of 139.5 mg/(L⸱d) when the DO concentration was in the range of 0.8–1.5 mg/L. This range, however, limited the denitrification efficiency of the reactor, which decreased from 90.0% ± 5.3% in phases II–V to 67.9% ± 7.2% in phases VI and VII. Sulfate precipitated as iron sulfate (FeSO4/Fe2(SO4)3) and sodium sulfate (Na2SO4) minerals during the experiment. The sulfur reactor did not respond well to nitrification with a low and unstable ammonium removal efficiency, while denitrification occurred with a nitrate removal efficiency of 97.8%. In the pyrite system, the nitrifying bacterium Nitrosomonas sp. was present, and its relative abundance increased from 0.1% to 1.1%, while the autotrophic denitrifying genera Terrimonas, Ferruginibacter, and Denitratimonas dominated the community. Thiobacillus, Sulfurovum, and Trichlorobacter were the most abundant genera in the sulfur reactor during the entire experiment.

Causes of variation in the concentration and distribution of H2S in carbonate reservoirs of the Feixianguan Formation, Lower Triassic in the eastern Sichuan Basin

Hydrogen sulfide (H2S) has been encountered in many oil and gas fields worldwide, causing potentially various health and safety issues; thus, it is crucial to assess its concentration before drilling. Natural gas from the Feixianguan carbonates in the Jiannan gas field is predominantly composed of methane with various H2S concentrations varying from very minor to 3.71%. However, the H2S concentrations display obvious difference, ranging from 0.18% to 0.81% in the southern zone and 0.21–3.71% in the northern zone, with high concentrations (>1%) occurring selectively in dolomitized reservoirs in the northern zone. Based on petrographic and geochemical data and reactive transport numerical modeling, the H2S origin and sulfate sources were analyzed for understanding factors controlling the H2S concentration and distribution.In the northern zone containing high H2S concentrations, there is a common mineral assemblage of pyrobitumens, burial calcite cements, pyrite, and hemispherical elemental sulfur in dolomite reservoirs. Burial calcite cements, often coated by pyrobitumens, have higher precipitation temperatures (>106 °C), and lighter δ13C ratios than host dolostones, suggesting the incorporation of organic carbon into the precipitation of these high-temperature burial calcites supplied by thermochemical sulfate reduction (TSR). Numerical modeling indicates the SO42− concentrations of pore waters would increase significantly in dolomitized domains during seawater-involved dolomitization, consisting with the fact of the higher SO42− concentrations of pore waters in the northern zone. The dolomitizing fluids delivered sulfates into reservoirs which were inevitably reduced by hydrocarbons, once the reaction temperature was reached. Comparatively, in the southern zone where carbonates were not subjected to intensive dolomitization and the SO42− concentrations of pore waters were low, the H2S originated only from the thermal decomposition of oil and organic matter (<1%). This study implies that hydrocarbon exploration in dolomitized reservoirs should be given greater caution because of the more favorable conditions for H2S generation.

Metallogenic process of Permian Taiping karstic bauxite deposit in Youjiang Basin, China

More than 1 billion tons of bauxite was formed on the karstic surface of the Permian Maokou Formation limestone in the western Guangxi area of Youjiang Basin (YB). However, its formation mechanism is still a matter of debate. In this study, the Taiping bauxite deposit, a representative large deposit in this area, was selected to carry out detailed mineral microanalysis and pyrite sulfur isotope analysis to further understand the metallogenic process of bauxite in this region. Taiping bauxite contains two layers: the lower bauxite layer and the upper claystone layer. Bauxite ore was mainly composed of diaspore, pyrite, anatase, kaolinite, minor pyrophyllite, parisite, and bastnäsite. Small amounts of detrital moissanite, native boron, and zircon were also found in the ore. The claystone was dominated by kaolinite, diaspore, pyrite, and chlorite. The occurrence of detrital zircon, moissanite, and native boron suggests that they were most likely derived from volcanic ash or lava, further confirming the contribution of volcanoes. The mineral assemblages of diaspore, pyrite, anatase, parisite, and bastnäsite in the bauxite ore indicate alkaline and reducing depositional environments. The extensive development of ovoid microorganisms and the significant negative δ34S values of pyrite (−42.80 ‰ to −12.54 ‰) indicate that microorganisms were involved in the formation of bauxite. This view was further confirmed by the wide development of fine pyrite (∼1 μm) cemented by cryptocrystalline diaspore in the ore. Extensive volcanism promotes the weathering of parent rocks, releasing Al3+, Fe3+, Ti4+, and REE3+ ions into the weathering system. Under strongly acidic and oxidizing conditions in the upper part of the weathering profile, these ions can migrate downward until they reach an alkaline and reducing environment on the carbonate surface. A large amount of diaspore, pyrite, anatase, parisite, and bastnäsite was formed near the karstic surface with the participation of microorganisms. Epigenetic modifications were also evident in the widespread development of kaolinite and pyrophyllite formed by the silicification of diaspore.

Method of Identifying Total Sulfur Content in Coal: Geochemical and Geophysical Logging Data from the Upper Paleozoic in North China.

The research of sulfur content and logging parameters in coal seams is of great significance for accurate mining and efficient utilization of coal. Taking 81 coal samples collected from the Upper Paleozoic in North China as an example, coulometric titration and chemical reagent methods were used to determine the contents of total sulfur and morphological sulfur in coal seams, and correlation analysis and multivariate linear fitting methods were used to analyze the relationship between total sulfur in coal and the shape and peak value of logging curve. The results show that the content of total sulfur in the Upper Paleozoic coal seams ranges from 0.19% to 12.36%. The morphological sulfur in coal is mostly pyrite sulfur, followed by organic sulfur and sulfate sulfur. The logging curves of the deep lateral resistivity log (LLD), natural gamma ray (GR), short-distance gamma gamma (CGS), and spontaneous potential (SP) in coal seams from Shanxi Formation are funnel-shaped, tooth-shaped, box-shaped, and flat-shaped, respectively. The shapes of LLD corresponding to a few coal seams with a sulfur content of less than 3.0% are finger-shaped and bell-shaped, and GR is finger-shaped. The GR, CGS, acoustic (AC), and density (DEN) curves corresponding to Taiyuan Formation coal seams with a total sulfur content more than 3.0% (St,d ≥ 3.0%) are mainly box-shaped, and the LLD curve corresponding to high-sulfur coal seams is mostly tooth-shaped. The LLD, GR, CGS, and AC curves are second only to funnel-shaped, and the DEN curve is tooth-shaped. The LLD, GR, AC, CGS, and DEN curves of coal seams with a total sulfur content less than 3.0% are mainly box-shaped. GR, AC, and DEN curves are next to tooth-shaped, LLD is bell-shaped, and CGS curve is finger-shaped. The total sulfur content in coal has a negative correlation with LLD and CGS values and a positive correlation with GR, AC, DEN,and SP values. The prediction model of total sulfur in coal is established by using a multivariate linear fitting method through geophysical logging parameter values, which can provide a method for comprehensively quantifying the change of total sulfur content in coal seams.

Study on the desulfurization effect of coal by microwave–Fenton system

AbstractBACKGROUNDMicrowave‐assisted and Fenton reagents were combined to enhance the removal effect of sulfur from coal. The coal samples before and after desulfurization were characterized by various testing methods such as X‐ray photoelectron spectroscopy, X‐ray diffraction and scanning electron microscopy.RESULTSThe microwave–Fenton system showed the best desulfurization effect with a desulfurization rate of 77.52% at a microwave power of 800 W and irradiation time of 5 min, which was 82.96% higher than the maximum desulfurization rate of Fenton reagents alone. The desulfurization rates of pyrite sulfur, organic sulfur and sulfate sulfur can reach 88.76%, 58.77% and 59.33%, respectively.CONCLUSIONThe minerals in the treated coal samples were significantly reduced. The microwave–Fenton system can generate a large number of hydroxyl radicals to break the CS bond, while exposing more sulfur‐containing groups to the reagents, resulting in more oxidation of low‐valent sulfur and sulfoxide to high‐valent sulfone and sulfate sulfur. The model compound removal effect was measured, dibenzyl sulfide &gt; diphenyl sulfoxide &gt; diphenyl sulfoxide &gt; dibenzothiophene, while the microwave–Fenton system could significantly enhance the desulfurization effect of the above four model compounds. It was found that with the increase in applied electric field, the reaction energy barrier decreased and the CS bond was more easily broken, which was favorable to the reaction. © 2022 Society of Chemical Industry (SCI).

Occurrence Characteristics of Fine-Grained Pyrite in Coal and Its Scaling Effect on Flotation Desulfurization.

To explore the occurrence and distribution characteristics of fine-grained pyrites in coal and the effect of pyrite particle size on flotation efficiency, coal samples from Guizhou province and Shanxi province, China, were selected for pyrite morphology observation and sulfur content test before and after flotation desulfurization experiments with different coal particle sizes. Experimental results showed that the fine-grained fine pyrites in coal have various occurrence forms and complex connections with the coal matrix. The fragmentation process can change the distribution of pyrite content in coal. Flotation desulfurization experiments showed that the sum of pyrite content in the cleaned coal and middlings gradually became significantly higher in coal particles with size 15-37 μm compared with particle sizes 37-44 and 44-75 μm. The complex occurrence morphology and crystal structure of fine-grained pyrite make it difficult to be removed from the coal matrix by ore grinding during flotation. Fine-grained pyrite mainly occurs in the form of framboïdal pyrite, disseminated pyrite, and monomer pyrite with a size of 0.69-33.94 μm in the middlings and cleaned coal. Therefore, 37 μm is considered as the critical dimension for ore grinding to improve the effective flotation desulphurization efficiency in this study, and some more effective methods should be used to increase the desulfurization efficiency of fine-grained pyrite.

Textures, trace elements, sulfur, lead and He-Ar isotope analyses of pyrite: Implications for ore-forming processes and the origin of the Shenjiayao gold deposit, southern margin of the North China Craton

The Shenjiayao gold deposit (8.50 t Au, average grade of 2.21 g/t), hosted in a Precambrian metamorphic terrane, is located in the Xiaoshan region on the southern margin of the North China Craton. The gold mineralization is characterized by vein ores comprising native gold and gold-bearing pyrite. Paragenesis of the Shenjiayao deposit can be divided into four stages. Stage I is pyrite – milky quartz veins; Stage II consists of grey quartz – pyrite veins; Stage III is characterized by quartz – polymetallic sulfide veins; and Stage IV minor pyrite – carbonate – quartz veins. Native gold and electrum grains are mainly distributed in the fractures of quartz, pyrite, chalcopyrite, and other sulfides. In this study, three types of pyrite were distinguished based on textural and geochemical results. Py1 has silicate inclusions and mainly occurs as euhedral–subhedral grains formed in the Stage I. Py2 within quartz veins from Stage II shows oscillatory zoning and can be distinguished into two subtypes by their distinct textures (Py2a and Py2b). Py3 coexisting with native gold, chalcopyrite, sphalerite, and galena is characterized by sulfide and silicate inclusions and is divided into two subtypes (Py3a and Py3b). The porosity and heterogeneous textures of Au-bearing pyrite indicate a process of dissolution and reprecipitation. The replacement was likely the result of dissolution–reprecipitation. However, Py1 has very low lattice-bound gold contents, indicating that obtaining high-grade gold orebodies through remobilization of lattice-bound gold is unreasonable. We suggest that the deposition of abundant native gold was induced by a new volume of Au-rich ore-forming fluids and triggered by extensive fluid phase separation during Stage II and Stage III. The δ34S values for the sulfides are similar, ranging from +0.9 ‰ to +5.8 ‰, and the lead isotope compositions of Stage II and Stage III sulfides are consistent. Fluid inclusions extracted from gold-bearing pyrite have elevated 3He/4He ratios (0.18–1.13 Ra) and 40Ar/36Ar (329.5–848.5), indicating the presence of mantle-derived fluids in the ore system.

Autotrophic denitrification of nitrate rich wastewater in fluidized bed reactors using pyrite and elemental sulfur as electron donors

This study compared denitrification performances and microbial communities in fluidized bed reactors (FBRs) carrying out autotrophic denitrification using elemental sulfur (S 0 ) and pyrite (FeS 2 ) as electron donors. The reactors were operated for 220 days with nitrate loading rates varying between 23 and 200 mg N-NO 3 − /L ⋅ d and HRT between 48 and 4 h. The highest denitrification rates achieved were 142.2 and 184.4 mg N-NO 3 − /L ⋅ d in pyrite and sulfur FBRs, respectively. Pyrite-driven denitrification produced less SO 4 2 − and no buffer addition was needed to regulate the pH. The sulfur FBR needed instead CaCO 3 to maintain the pH neutral and consequentially more sludge was produced (CaSO 4 precipitation). The active community of pyrite-based systems was investigated and Azospira sp ., Ferruginibacter sp. , Rhodococcus sp. and Pseudomonas sp. were the predominant genera, while Thiobacillus sp. and Sulfurovum sp. dominated the active community in the sulfur FBR. However, Thiobacillus sp. became more dominant when operating at elevated nitrogen loading rate. Patterns of diversity and microbial community assembly were assessed and revealed three distinct stages of microbial community succession which corresponded with the operation of a period of high influent nitrate concentration (135 mg N-NO 3 − /L). It is proposed that a high degree of functional redundancy in the initial microbial communities may have helped both reactors to respond better to such high influent nitrate concentration. • Max denitrification rates were 142.2 and 184.4 mgN-NO 3 − / L ⋅ d in the FeS 2 and S 0 FBRs. • FeS 2 -driven denitrification produced low SO 4 2 − and no buffer addition was needed. • Microbial community succession was observed in response to NLR increased. • Functional redundancy in the AD microbiome resulted in resilience to increased NLRs. • The active community of FeS 2 FBR had Azospira and Pseudomonas as dominant genera.

Extremely variable sulfur isotopic compositions of pyrites in carbonate pipes from the northern South China Sea: Implications for a non-steady microenvironment

To further constrain the microenvironment during the growth of carbonate pipes at cold seeps, we present the whole-rock carbon and oxygen, and in situ pyrite sulfur isotopic compositions along the cross-sections in pyrite-bearing carbonate pipes from the northern South China Sea. The whole-rock geochemical data suggest that these carbonate pipes were formed in an anoxic and methane-rich environment. Furthermore, in situ δ34S values in pyrites across the carbonate pipe display an extremely wide range on a centimetre scale. The majority of pyrites have δ34S values ranging from 19.4‰ to 45.8‰, reflecting the dominance of sulfate-driven anaerobic oxidation of methane (AOM) at and below the sulfate methane transition zone (SMTZ). Two abnormal areas show heavier or lighter δ34S values than the majority of pyrites, respectively. Pyrites in the abnormal area I have δ34S values ranging from 62.2‰ to 130.3‰, suggesting an extremely 34S-enriched microenvironment produced via Rayleigh fractionation of limited sulfate in a closed system. The model calculation indicates that the maximum positive δ34S value could be produced when ∼93% sulfate is consumed. Pyrites in the abnormal area II have δ34S values ranging from −32.7‰ to −18.0‰, and are interpreted as a result of early organiclastic sulfate reduction with a low proportion of later sulfate-driven AOM above the SMTZ. Collectively, the extreme variations in δ34S values point to locally migrating SMTZ in a non-steady microenvironment during the growth of carbonate pipes. This study reveals that the in situ pyrite δ34S value is a diagnostic tool for tracing the change in the local microenvironment, and could be a step towards a more comprehensive picture of biogeochemical cycles at continental margins.

Separation of pyritic sulfur from ultrafine coal by pyrolysis & wet high magnetic separation

ABSTRACT Coal plays a major role in the economic development of many countries, especially in metallurgical industries and conventional power generation plants. The removal of sulfur from coal has recently become even more critically important. Existence of sulfur compounds in coal limits its industrial applications due to environmental as well as technical problems. Thus, high sulfur coal is usually upgraded by desulfurization through physical, chemical, and biotechnological processes. In this study, lowering of pyritic sulfur took place after thermal treatment at 500–700°C (pyrolysis) using a wet high-intensity magnetic separation process. The samples were subjected to size reduction to −25 µm and characterized with X-ray diffraction (XRD), proximate and ultimate analysis, and differential thermal analysis (DTA). Then, the experiments were performed based on central composite rotatable design (CCRD) and response surface methodology (RSM) after thermal treatment of coal containing 3.30% total sulfur. Statistical analysis was performed to examine the significance of the effect of different operating parameters. A maximum sulfur rejection of 90.10% with the lowest sulfur content of 0.59 was obtained at 8.38% solid concentration, 4.59 g/min feed rate, and 7810 gauss magnetic field intensity. The confirmation tests at the optimum conditions produced 0.54–0.56% total sulfur with 90.25–92.33% sulfur rejection.

Multiple Sulfur Isotope Evidence for Bacterial Sulfate Reduction and Sulfate Disproportionation Operated in Mesoarchaean Rocks of the Karelian Craton

Sulfur isotope in sulfides from the Paleoarchean and the Neoarchean sedimentary rocks evidence microbial sulfur metabolism in Archean sulfur cycle. However, sulfur metabolism for the Mesoarchean interval is less obvious since evidence for a large range in sulfur isotope values has not yet been observed in Mesoarchean samples. We report the results of multiple sulfur isotope measurements for sulfide minerals from ~2.8 Ga sedimentary rocks in the southeastern part of the Karelian Craton. In situ isotope analysis of sulfide grains have been performed using a femtosecond laser-ablation fluorination method. Sulfide samples studied here yielded Δ33S values between −0.3 and +2.7‰ and δ34S values between −10 and +33‰. The Δ33S dataset was interpreted to indicate the incorporation of sulfur from two coexisting sulfur pools, photolytic sulfate and photolytically derived elemental sulfur. We suggest that the relative contributions of these Δ33S different pools to the pyritic sulfur could be controlled by the metabolic activity of coexisting sulfate-reducing and sulfur-disproportionating bacteria during pyrite formation. We therefore suggest the operation of different metabolic pathways of sulfur in Mesoarchean sedimentary environments.

Depositional control on the sulfur content and isotope of sedimentary pyrite from the southeast coast of China since MIS5

The content and isotopic composition of pyrite sulfur are significantly affected by local depositional conditions and are sensitive to environmental evolution. Here, we use core QK11, collected from Xiapu Bay, southeast coast of China, to reveal how local depositional conditions constrained pyrite formation and sulfur isotopic composition since MIS5. Our results show that the content of pyrite sulfur is mainly controlled by the TOC content during interglacial intervals and is limited by the supplement of sulfate in glacial intervals. Therefore, the C/S ratios can effectively identify three transgressions since MIS5. The sulfur isotopic composition of pyrite ranges from -36.7 to 18.4‰ in the whole core. The occurrence of isotopically “heavy” pyrite is observed at the depth of 2.2~9.2, 27.2~33.8, and 43.5~62.5 mbsf, which is attributed to the influence of sulfate reservoir effect, depositional event, unsteady diagenetic environment, and other factors, highlighting the influence of local depositional and diagenetic processes on the isotopic composition of pyrite sulfur. Pyrite sulfur in other layers is generally depleted in 34S, as low as -36.7‰, indicating that the early-stage organiclastic sulfate reduction (OSR) plays an important role in sulfur isotopic fractionation. The results also suggest that organic carbon indicators (TOC/TN ratio and δ13C) combined with the C/S ratio can effectively distinguish between freshwater and marine environments, which is of great significance to reveal depositional evolution in deep time.