Sulfidic Conditions Research Articles

Comparison of the aggressiveness of hydrogen sulfide media to steel in the vapor and water phases

Corrosion resistance in hydrogen sulfide-containing environments of the main structural steels used in infrastructure facilities of gas fields has been studied. Gas objects are distinguished by the fact that most of the internal space of equipment and pipelines is in contact with the vapor phase, the internal corrosion of which under hydrogen sulfide conditions has been little studied. The corrosion rates and the composition of the formed corrosion products, which differ depending on the type of medium (water or steam), are determined. The phase composition (crystalline or X-ray amorphous) of the resulting products affects their protective ability and differs in the vapor and aqueous phases. It has been established that under gaseous conditions of moisture condensation, local pitting lesions are formed under fragile corrosion products. The thickness of the iron sulfide film in the vapor phase turned out to be lower than in the aqueous medium. It was revealed that dangerous corrosion consequences (in the form of blisters and cracking) appear on the studied samples of carbon and low-alloy steels, which are characteristic of the process of hydrogenation under conditions of hydrogen sulfide corrosion.

Significance of pH and iron-sulfur chemistry for molybdenum sequestration under sulfidic conditions

Molybdenum (Mo), a redox-sensitive trace metal, plays an important role in recording ancient oxygenation and deoxygenation events as a paleoredox proxy. The mobility and reactivity of Mo in aqueous conditions are closely tied to the chemistry of reduced sulfur and iron species. However, our current knowledge on the formation, structure, stability, and condensation pathways of FeMoS clusters in aqueous settings remains limited, which has driven the current study. In this study, we conducted systematic experiments investigating the interactions between dissolved Mo (initially introduced as molybdate, MoO42−, or tetrathiomolybdate, MoS42−), ferrous iron (Fe2+), and sulfide (ΣH2Saq) in variously defined abiotic sulfidic systems to determine the external conditions (i.e., pH, and reactant concentrations and ratios) necessary for the formation of solid-phase Fe-Mo sulfides. Solution samples of each system were monitored using ultraviolet-visible spectroscopy (UV–vis) to track the degree of thiolation of dissolved Mo species. Precipitates were analyzed using X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to determine their elemental compositions and valences, and structure (i.e., crystalline or amorphous), respectively. All FeMoS precipitates were amorphous and contained 76–90% Mo(IV) and 10–24% Mo(V) with a trend toward lower Mo(IV):Mo(V) ratios with increasing pH. The degree of Mo thiolation, which was strongly dependent on solution pH and Fe2+ concentrations, greatly affected the amount of Mo sequestered (i.e., an increased degree of Mo thiolation in solution led to an increased amount of Mo in the final FeMoS precipitate). These findings suggest that changes in pH and Fe2+ concentrations may be responsible for the sulfide-independent variations in Mo behavior observed in euxinic basins.

Corrosion law of cement paste under hydrogen sulfide conditions in natural gas wells

Downhole anticorrosion in sour gas (H2S or CO2) wells is one of the technical problems in petroleum engineering, and the corrosion law of cement paste, which is the “first barrier of the wellbore,” needs to be focused on. Aiming at the problems existing in the current research on the corrosion of underground cement paste, a curing method for interfacial corrosion is proposed. X-ray diffraction and scanning electron microscopy are used to investigate the corrosion mechanism of cement paste cured under hydrogen sulfide (H2S) conditions in natural gas wells. Experimental results showed that the corrosion depth of cement paste is proportional to the partial pressure of H2S and the corrosion time, and the compressive strength of cement paste after corrosion is inversely proportional to the H2S partial pressure value and the corrosion time. Due to the gradual enrichment, accumulation, and migration of products after the cement paste is corroded by H2S, the cement paste forms a relatively stable dense layer or corrosion transition zone. The porosity and permeability of cement paste after corrosion increased with corrosion time, showing the characteristics of first increasing and then decreasing and finally making it more difficult for the corrosive medium to enter the interior of the cement paste. It is an important method stable corrosion transition zone forms as soon as possible, which is important to maintain the long-term sealing and chemical integrity of the cement sheaths in natural gas wells containing H2S.

Reconstructing redox variations in a young, expanding ocean basin (Cretaceous Central Atlantic)

The redox sensitive elements (RSE) are indicators of organic matter (OM)-rich rocks and provide valuable information on paleoenvironmental parameters, including organic productivity, chemical evolution of water masses, ocean residence times and sea-bottom redox conditions. Yet, their potential to understand global environmental changes is hindered by the scarcity of continuous geological records, often highly fragmented in space and time. In this contribution, a large dataset from five closely spaced sedimentary sections in the Western African margin is used to reconstruct a 40 myr-long record of the redox conditions in a time spanning from the early Aptian to early–middle Campanian. Studied intervals were originally located in different positions of the embryonic Atlantic Ocean, and intercept four separated oceanic anoxic events (OAE1c, OAE1d, OAE2 and OAE3). The complete geochemical characterization revealed the changes of Mn, V, Ni, Cu, Zn, Mo, U and Se during the deposition of OM-rich sediments, as a function of their depositional environments, redox conditions, and time. It is shown that, although enrichments of RSE are triggered by increasingly reducing seafloor conditions, the extent to which these elements are retained within the sedimentary record depend on both local variations in detrital inputs and global perturbations of the marine RSE inventories. The analyses show that RSE are characteristically enriched with respect to global shale values, having geochemical characteristics (i.e., high Mo/TOC and high Mo/U) suggestive of suboxic to sulfidic conditions from the late Albian to Campanian.

Enhancement of hydrotreating activity of oil-soluble CoMo6 heteropolyacid for 4,6-dimethyldibenzothiophene and vacuum residue by controlling sulfurization degree

An oil-soluble CoMo6 heteropolyacid was synthesized by modifying the heteropolyacid with a surfactant dioctadecyl dimethyl ammonium chloride, and then was used to prepare highly active sulfided catalyst. The effect of sulfurization degree on the hydrotreating activity of the catalyst was investigated, and the results show that the incompletely sulfurized catalyst exhibited high reactivity for 4,6-dimethylbenzothiophene (4,6-DMDBT) and vacuum residue (VR). The unusual finding was attributed to more CoMoS species and surface oxysulfides, and the latter were probably generated in the partial replacement of O atoms with S atoms during the sulfurization. The acidic oxysulfides (SO42- groups) not only improved the activation of 4,6-DMDBT but also facilitated the cleavage of C-C bonds of the intermediate product 3,3′-dimethylcyclohexylbenzene according to the reaction data and DFT calculation. Besides, the catalysts with incomplete sulfide state exhibited outstanding catalytic performance on the upgrading of VR. The proposed incomplete sulfurization strategy provided a new way to prepare bifunctional hydrogenation catalysts with both desulfurization and cracking activities.

Mo–Ni, Mo–Fe and Mo–Ni–W nanoparticles for down-hole upgrading

Patented in situ (in reservoir) upgrading technology (ISUT) converts a portion of the reservoir into a “catalytic reactor” by irreversibly attaching a low percentage of nanoparticles to the reservoir's sand/rock. The nanoparticles are prepared as a dispersion in hot vacuum residue and the hot dispersion is injected into the reservoir with low quantities of hydrogen.MoNi, MoFe and MoNiW nanoparticles suspended in bitumen were prepared, in similar way as in ISUT, and the suspensions treated in a batch reactor. Two different sulfiding agents (ammonium sulfide and thiocarbamide) were added during the preparation of the nanoparticles-bitumen suspension. Particle diameters obtained for the suspensions were determined by NTA. The particles were recovered after reaction and its surface composition determined by XPS. Reaction products were analyzed by high temperature simulated distillation, density, viscosity, sulfur and nitrogen content and stability (P-value). MoNi, MoFe and MoNiW with average sizes of 84, 101 and 93 nm, respectively, were produced. XPS characterization of the Mo–Ni–W particles before reaction showed that Mo and Ni are only partly sulfided, while W was present as WO3. The proportion of the metals in the sulfided state increases after reaction from 39 to 94, 35 to 77 and a 0 to 50 (atomic %) for Mo, Ni and W, respectively. In addition, VR conversions were similar by comparing the thermal and catalytic tests, indicating that VR cracking is mainly thermal. However, viscosity, MCR and S contents were lower, and API gravity was higher when a catalyst was used. Also, catalytic products proved more stable than products obtained from thermal reaction. The reaction carried out using dispersions where thiocarbamide was the sulfiding agent provided products with slightly betterer properties in spite of showing larger particle diameters.

Organic-rich bimineralic ooids record biological processes in Shark Bay, Western Australia.

Marine ooids have formed in microbially colonized environments for billions of years, but the microbial contributions to mineral formation in ooids continue to be debated. Here we provide evidence of these contributions in ooids from Carbla Beach, Shark Bay, Western Australia. Dark 100-240 μm diameter ooids from Carbla Beach contain two different carbonate minerals. These ooids have 50-100 μm-diameter dark nuclei that contain aragonite, amorphous iron sulfide, detrital aluminosilicate grains and organic matter, and 10-20 μm-thick layers of high-Mg calcite that separate nuclei from aragonitic outer cortices. Raman spectroscopy indicates organic enrichments in the nuclei and high-Mg calcite layers. Synchrotron-based microfocused X-ray fluorescence mapping reveals high-Mg calcite layers and the presence of iron sulfides and detrital grains in the peloidal nuclei. Iron sulfide grains within the nuclei indicate past sulfate reduction in the presence of iron. The preservation of organic signals in and around high-Mg calcite layers and the absence of iron sulfide suggest that organics stabilized high-Mg calcite under less sulfidic conditions. Aragonitic cortices that surround the nuclei and Mg-calcite layers do not preserve microporosity, iron sulfide minerals nor organic enrichments, indicating growth under more oxidizing conditions. These morphological, compositional, and mineralogical signals of microbial processes in dark ooids from Shark Bay, Western Australia, record the formation of ooid nuclei and the accretion of magnesium-rich cortical layers in benthic, reducing, microbially colonized areas.

Review of Molybdenum Disulfide Research in Slurry Bed Heavy Oil Hydrogenation.

With the growing demand for gasoline and diesel fuel and the shortage of conventional oil reserves, there has been extensive interest in upgrading technologies for unconventional feedstocks such as heavy oil. Slurry bed reactors with high tolerance to heavy oil have been extensively investigated. Among them, dispersive MoS2 is favored for its excellent hydrogenation ability for heavy oil even under harsh reaction conditions such as high pressure and high temperature, its ability to effectively prevent damage to equipment from deposited coke, and its ability to meet the requirement of high catalyst dispersion for slurry bed reactors. This paper reviews the relationship between the structure and hydrogenation effectiveness of dispersive molybdenum disulfide, the hydrogenation mechanism, and the improvement of its hydrogenation performance by adding defects and compares the application of molybdenum disulfide in heavy oil hydrogenation, desulfurization, deoxygenation, and denitrification. It is found that the current research on dispersive molybdenum disulfide catalysts focuses mostly on the reduction of stacking layers and catalytic performance, and there is a lack of research on the lateral dimensions, microdomain regions, and defect sites of MoS2 catalysts. The relationship between catalyst structure and hydrogenation effect also lags far behind the application of MoS2 in the precipitation of hydrogen, etc. Oil-soluble and water-soluble MoS2 catalysts eventually need to be converted to a solid sulfide state to have hydrogenation activity. The conversion history of soluble catalysts to solid-type catalysts and the key to their improved catalytic effectiveness remain unclear.

Sulfidized state and formation: Enhancement of nanoscale zero-valent iron on biochar（S-nZVI/BC） in activating peroxymonosulfate for Acid Red 73 degradation

To improve the performance of the nanoscale zero-valent iron (nZVI)-based advanced oxidation process (AOPs), a sulfidation pre-modification endowed nZVI with stable reduction nature mechanism was proposed, and a coupled system of activating PMS with sulfidized nanoscale zero-valent iron supported by biochar(S-nZVI/BC@PMS) was constructed in this study. It could be found that sulfidation state and formation, largely dependent on the sulfidized modification method, had a great impact on the enhancement for nZVI/BC in activating PMS for Acid Red 73 degradation. Compared with original nZVI/BC, the formed FeS shell blocked the external air to protect the internal Fe0, and S-nZVI/BC became relatively hydrophobic, which could slow down the material corrosion by water and dissolved oxygen to enhance the reaction durability. Appropriate sulfidation reduced the electrochemical impedance and enhanced the electrical conductivity of the catalyst, which facilitated the electron transfer in the system, and the participation of reducing sulfur species enabled the reaction to form a positive cycle and ensure a prolonged duration. Excessive sulfidation caused the material to become unstable and thus susceptible to air erosion, reducing the efficiency of contaminant removal. Due to the FeS protective shell, hydrophobicity of S-nZVI/BC and the promoted electron transfer in the system, S-nZVI/BC@PMS system secured more free radicals and had longer reaction time under the same conditions. In addition, S-nZVI/BC had good antioxidant properties, universality, and reusability for practical applications. These findings not only elucidated the superiority of S-nZVI/BC@PMS system but also provided new insights into cost-saving and efficient advanced oxidation processes.

Jurassic Au–Ag mineralization of the Linjiasandaogou deposit in the Liaodong Peninsula, northeast China: Evidence from apatite U–Pb dating and the in situ geochemistry of sulfides

The Liaodong Peninsula in northeast China hosts visible and invisible Au-dominated mineralization. Compared with visible Au, age and mechanisms of invisible Au-dominated mineralization are still unclear. The Linjiasandaogou deposit in the Liaodong Peninsula comprises disseminated and veinlet ores hosted in Paleoproterozoic schist and Triassic granite porphyry and lamprophyres. Three mineralization stages were identified in this deposit: the early pyrite (Py1), arsenian pyrite (Py2)–arsenopyrite–sphalerite (Sp1)–quartz–apatite, and freibergite–sphalerite (Sp2)–galena–quartz stages. Gold mineralization is mainly in invisible forms and was deposited during the second stage, whereas Ag was deposited during the third stage. Uranium-Pb dating of hydrothermal apatite from the second stage indicates that Au mineralization occurred at ca. 184 Ma, when the Yaojiagou granite was emplaced. In situ S isotope analysis shows that sulfides which formed during the mineralization stages have a narrow range of δ34SV-CDT values (4.80 ‰–8.53 ‰) that are typical of a magmatic–hydrothermal system. Py2 has higher As, Au, and Ag contents of 15,100–95,576, 15.4–183, and 20.8–129 ppm, as compared with Py1 (As <0.9–11,050 ppm, Au <0.03–11.1 ppm, and Ag <0.05–48.5 ppm). The negative correlations between As–S and Au–Fe in pyrite are indicative of As substitution for S and Au substitute for Fe in the pyrite. The pyrite and sphalerite trace element compositions indicate that the formation temperatures of the three stages were >250 °C, 154–252 °C, and 167–197 °C, respectively. The evolution of the hydrothermal system indicates that the deposition of Au is due to cooling and fluid-rock interaction, whereas the precipitation of Ag results from an increase in the sulfidation state. Results suggest the invisible Au-dominated mineralization in the Linjiasandaogou deposit was associated with the Early Jurassic intrusion. This study supplements the ore-forming epoch framework of the Qingchengzi ore field and improves the understanding of the Au–Ag mineralization in this area.

A 20-million-year reconstruction to decipher the enigmatic Cambrian extinction – Ordovician biodiversification transition

The late Cambrian extinction – Early Ordovician biodiversification represents one of the crucial lower Paleozoic biological changes. However, the mechanisms responsible for this transition remain poorly understood. Here, we reconstructed the paleoenvironmental changes based on a model that integrated the atmospheric-oceanic-biological inputs and provided the first detailed assessment of the Cambro-Ordovician biological turnover. The results show depositional environments evolved into extremely sulfidic conditions with lower nutrient inputs and more restricted water circulation from the Miaolingian to early Furongian, leading to the Steptoean Positive Carbon Isotope Excursion event. The intense volcanic activity in the early Jiangshanian appears to be responsible for the recurrent bio-calamity. Later in the mid-late Furongian (mid-Jiangshanian to Stage 10), enhanced terrestrial weathering contributed to the Earth's cooling and higher inputs of terrestrial nutrients, beneficial to the subsequent biological recovery. In the Early Ordovician and despite reduced terrestrial nutrient input, massive oceanic water upwelling alleviated sulfidic conditions and brought nutrients, laying the foundation for the Great Ordovician Biodiversification Event.

Critical assessment of U, Ba and Ni as redox and productivity proxies in organic-rich sediments underneath dynamic, highly productive waters

Sediments of the continental shelf anoxic zones of the Benguela upwelling system (BUS) and the Peruvian upwelling system are present-day hotspots of trace element accumulation. However, contribution of the lithogenic trace element fraction and early diagenetic transformation processes are poorly constrained. The identification of source and accumulation mechanisms is necessary for the validation of trace elements as proxies for productivity and redox cycling, notably in highly dynamic upwelling systems such as the BUS. Here, we analyzed redox- and biosensitive elements (U, Ba, Ni), lithogenic tracers (Al, Ti, Zr), total organic carbon (TOC) and P in eleven short sediment cores from the Namibian shelf (ca. 22–25°S) as well as grain size fractionated hinterland samples from the Tsauchab Valley at Sossusvlei (∼25°S). These samples help to constrain the lithogenic trace element contributions, a prerequisite for a realistic interpretation of marine authigenic trace element data. Our findings corroborate previous findings that Zr is a sensitive tracer of the coarse fraction in marine sediment for dust input and/or sediment reworking. Hence, the combined analysis of the coarse fraction (Zr), organic matter, and P enrichments (TOC/P) differentiates between a calm, organic matter-rich central shelf environment and a more energetic phosphorite-rich southern shelf environment. A significant correlation of U with P in cores from the southern shelf corroborates previous findings of U incorporation into apatite, the initial formation of which requires oscillating oxic to sulfidic redox conditions. Non-apatite associated U dominates in the cores from the central shelf, where it is only enriched in the buried, anoxic parts of the sediment. This also supports oscillating oxic to sulfidic redox conditions in surface sediment, where U may be recycled. Hence, U accumulates either (i) in apatite under oscillating oxic to sulfidic conditions or (ii) in buried anoxic sediment sections. This strongly questions the use of U as indicator of suboxic conditions but rather anoxic conditions. While lithogenic fractions of U were negligible, the lithogenic fractions of Ba and Ni were found to be elevated. The calculation of authigenic Ba when accounting for lithogenic Ba from the Sossusvlei fine fractions gives more realistic authigenic Ba values. The high Ba enrichment in the BUS is interpreted as uptake of Ba by diatoms and/or nucleation of barite in P-rich diatom remains, as suggested previously. Given the shallow water depth of the cores, barite formation must already take place in subsurface waters (<50 m water depth) as opposed to previous suggesting greater water depths. The lithogenic background of Ni strongly varies from 23°S to 25°S based on Sossusvlei data and the literature. When authigenic Ni contents are calculated accordingly and plotted versus TOC, more systematic trends are seen (compared to total Ni versus TOC). Essentially all cores show an increase in the authigenic Ni/TOC ratio with sediment depth suggesting better preservation and retention of Ni as compared to TOC consistent with previous observations in sediments from the Peruvian upwelling system. This trend corroborates the use of Ni as a productivity indicator for upwelling sediments.

Integrated effects of bioturbation, warming and sea-level rise on mobility of sulfide and metalloids in sediment porewater of mangrove wetlands

Global warming and sea-level rise exert profound impacts on coastal mangrove ecosystems, where widespread benthic crabs change sediment properties and regulate material cycles. How crab bioturbation perturbs the mobilities of bioavailable arsenic (As), antimony (Sb) and sulfide in sediment-water systems and their variability in response to temperature and sea-level rise is still unknown. By combining field monitoring and laboratory experiments, we found that As was mobilized under sulfidic conditions while Sb was mobilized under oxic conditions in mangrove sediments. Crab burrowing greatly enhanced oxidizing conditions, resulting in enhanced Sb mobilization and release but As sequestration by iron/manganese oxides. In control experiments with non-bioturbation, the more sulfidic conditions triggered the contrasting situation of As remobilization and release but Sb precipitation and burial. Moreover, the bioturbated sediments were highly heterogeneous for spatial distributions of labile sulfide, As and Sb as presented by 2-D high-resolution imaging and Moran's Index (patchy at the <1 cm scale). Warming stimulated stronger burrowing activities, which led to more oxic conditions and further Sb mobilization and As sequestration, whilst sea-level rise did the opposite via suppressing crab burrowing activity. This work highlights that global climate changes have the potential to significantly alter element cycles in coastal mangrove wetlands by regulating benthic bioturbation and redox chemistry.

Fluid-rock interaction, skarn genesis, and hydrothermal alteration within an upper crustal fault zone (Island of Elba, Italy)

The Terranera magnetite-hematite-pyrite deposit of the Island of Elba (Italy) is an historical skarn deposit hosted by a fault zone of regional importance (Zuccale Fault) and by its hanging wall rocks.We combine field observations with petrographic data, electron probe microanalyses (EPMA), XRPD data, fluid inclusion microthermometry, and element imaging by Laser Ablation-Inductively Coupled Plasma-Time of Flight Mass Spectrometry (LA-ICP-TOFMS) to define the ore-forming process at Terranera. We show that in this location the fault is made of four levels of mineralized fault rocks having distinct mineral compositions. In these levels, a mineral association made of diopside, clinozoisite, and other Mg-rich minerals is replaced by magnetite, hematite, pyrite, Mg-hornblende, clinochlore, and other Mg-rich phyllosilicates. This paragenesis is overprinted by goethite and clay minerals. Chlorite-quartz geothermometry and fluid inclusion microthermometry show that ore precipitation occurred at 350–180 °C from fluids of distinct bulk salinities, but goethite and clay mineral overprinting progressed at lower T.We propose that Terranera is a magnesian Fe skarn formed due to the interaction between distinct hydrothermal fluids and a dolomitic protolith, which was preserved within the fault zone. These fluids mixed and cooled during protolith metasomatism, causing ore precipitation due to oxidation and desulfidation. A very similar process was described in a large deposit of Elba (Rio Marina). Argillic alteration was widespread within the fault but met permanently intermediate sulfidation conditions. Trace element composition of hematite shows that Terranera has features that overlap those of skarn and epithermal deposits. In particular, elements that are typical of epithermal deposits (Sb, Ga, Ge, As) occur at mass fractions (50–200 μg/g) that are either unreported or not typical of hematite from skarn deposits. These features identify Terranera as formed in an ore environment that was transitional between that of a skarn and of an epithermal deposit. These features are shared by other historical deposits located at Elba and in the massive pyritic ore district of south Tuscany (e.g., Gavorrano, Fenice Capanne). This indicates that a similar environment might have occurred during the Neogene beyond Elba, in a much larger ore district of south Tuscany.

Defense System of the Manila Clam Ruditapes philippinarum under High-Temperature and Hydrogen Sulfide Conditions

Hydrogen sulfide (H2S) acts as an environmental toxin. Despite its toxicity, little is known about the defense strategies of marine bivalves against it. Thus, the tolerance, behavioral characteristics, and physiological response strategies against H2S treatment in the sentinel organism Manila clam Ruditapes philippinarum were examined. We monitored the survival and behavioral status of Manila clams exposed to different combinations of temperature and H2S. The physiological response strategies were examined by measuring the enzymatic activity of cytochrome C oxidase (CCO), fumarate reductase (FRD), superoxide dismutase (SOD), and catalase enzymes (CAT). Moreover, adverse effects of H2S on the tissue and cell structure of Manila clams were also examined under a transmission electron microscope. Manila clams responded to H2S stress through behavioral and chemical defenses. With exposure to H2S alone, Manila clams primarily enhanced aerobic respiratory metabolic pathways in the beginning stages by opening the shell and increasing the CCO activity to obtain more oxygen; with increasing exposure time, when aerobic respiration was inhibited, the shell was closed, and FRD, CAT, and SOD were activated. At this point, Manila clams responded to H2S stress through the anaerobic metabolism and antioxidant defense systems. However, high temperatures (≥28 °C) altered the defense strategy of Manila clams. With co-exposure to high temperatures and high H2S concentrations (≥20 μmol/L), the Manila clams immediately closed their shells and changed from aerobic respiration to anaerobic metabolism while immediately activating antioxidant defense systems. Nevertheless, this defense strategy was short lived. In addition to this, apparent damage to tissue and cell structures, including mitochondrial ridge dissolution and many vacuoles, was observed in Manila clams exposed to high temperatures and high H2S concentrations. Thus, prolonged exposure to high temperature and H2S damages the tissue structure of Manila clams, affecting their behavioral capacity and future survival. In summary, profiling Manila clams' physiological response strategies to H2S exposure provided ecological behavioral support for our current understanding of H2S detrimental toxicity on marine bivalves.

Changing Hydrocarbon-Producing Potential of the Cambrian Niutitang Shale: Insights from Pyrite Morphology and Geochemical Characteristics.

The characteristics of shale gas enrichment conditions at different depositional positions of organic-rich shale in the Niutitang Formation of the Lower Cambrian of the Upper Yangtze in South China vary greatly. The study of pyrite provides a basis for the restoration of the ancient environment and a reference for the prediction of organic-rich shale. In this paper, the organic-rich shale of the Cambrian Niutitang Formation in the Cengong area is analyzed by means of the optical microscope, scanning electron microscope observation, carbon and sulfur analysis, X-ray diffraction whole rock mineral analysis, sulfur isotope test, and image analysis. The morphology and distribution characteristics, genetic mechanism, water column sedimentary environment, and influence of pyrite on the preservation conditions of organic matter are discussed. This study shows that the upper, middle, and lower sections of the Niutitang Formation are rich in pyrite (framboid, euhedral pyrite, subhedral pyrite, etc.). Meanwhile, the sulfur isotopic composition of pyrite (δ34Spy) shows a tight correlation with the framboid size distribution throughout the shale deposits of the Niutang Formation, and the average particle size (9.6 μm; 6.8 μm; 5.3 μm) and distribution range of framboids (2.7-28.1 μm; 2.9-15.8 μm; 1.5-13.7 μm) in the upper, middle, and lower sections show a downward trend. In contrast, the sulfur isotopic composition of pyrite shows a tendency to become heavier from above and below (mean = 0.25‰ to 5.64‰). Together with the covariant mode of pyrite trace elements (such as Mo, U, V, Co, Ni, etc.), the results showed significant differences in the oxygen levels in the water column. They show that the transgression led to long-term anoxic sulfide conditions in the lower water column of the Niutitang Formation. In addition, the main and trace elements in pyrite jointly indicated that there was hydrothermal action at the bottom of the Niutitang Formation, which led to the destruction of the preservation environment of organic matter and the decrease of TOC, which can also explain the reason why the TOC content in the middle part (6.59%) was higher than that in the lower part (4.29%). Finally, the water column became an oxic-dysoxic condition due to the decline of sea level, and the TOC content decreased (1.79%).

Dynamic oceanic redox conditions across the late Cambrian SPICE event constrained by molybdenum and uranium isotopes

The Steptoean Positive Carbon Isotope Excursion Event (SPICE) represents one of the largest carbon cycle perturbations in the Cambrian, which coincided with climatic changes and dramatic extinction of shallow-shelf faunas. This carbon perturbation has been linked to a global expansion of marine euxinia (SPICE-OAE), but the precise timing, duration and extent of changing redox conditions across the SPICE event, as well as its influences on the coeval biotic evolution, remain unclear. Here, we report paired δ98Mo–δ238U data across this event, constrained by a radioisotopically anchored astrochronology, based on Alum Shale samples from the Albjära-1 and Billegrav-2 drill-cores in Scandinavia. The δ98Mo profiles are largely invariant around 1.08±0.21‰ with short-term fluctuations parallelling changes in pyritization of iron, possibly as a result of locally varying [H2S]aq in the water column and/or fluctuating reactive iron delivery. The bottom water is interpreted to have been primarily anoxic, but with frequent local variations between oxic and sulfidic conditions in a moderately restricted basin. A novel analytic method based on variation of Mo concentrations at millimeter scale stratigraphic resolution was applied to distinguish between local and global redox signatures, revealing that cyclic redox changes are recorded in the Alum Shale sea with periods of ∼0.3 Myr, ∼0.9 Myr and ∼0.15 Myr before, during and after the SPICE-OAE, respectively. Stratigraphic profiles of Mo, U, Mo/TOC ratios and δ238U in the two cores show comparable trends, facilitating recognition of three chemically distinct stages across the SPICE event: 1) global expansion of marine euxinia (SPICE-OAE; 497.9–496.6 Ma), 2) global contraction of euxinia accompanied by enhanced carbonate weathering inputs (496.6–495.8 Ma) and 3) general global oxygenation (495.8–494.4 Ma). The first in situ correlation between the onset of the SPICE-OAE and the end-Miaolingian extinctions in Baltica corroborates that expansive anoxic and sulfidic water masses likely contributed to the biotic crisis. The time gap between the start of the extinction and the appearance of the new fauna in Baltoscandia is estimated to be ∼600 kyr.

Short-term tuning of microalgal composition by exposition to different irradiance and small doses of sulfide.

Suitability of microalgae valorization mainly depends on its biochemical composition. Overall, among all microalgal derivatives, pigments currently stand out as the major added-value component. While it is well recognized that microalgal growth conditions strongly affect biomass composition, final tuning of already grown microalgae has been scarcely studied. Herein, pigment crude extract and debris biomass composition of an already grown microalgal consortium was evaluated after a short-term exposure (90min) to different levels of irradiance (15, 50, 120μmolm-2s-1) and sulfide concentrations (0, 3.2, 16mg L-1). Although lipid, protein, and carbohydrate contents of debris biomass were not decisively modified by the short-term exposures, pigments content of the crude extracts were strongly modified after 90-min exposure at given sulfide and irradiance conditions. Particularly, a higher content of chlorophyll a, chlorophyll b, and total carotenoids was estimated at an optimal sulfide concentration of 5mg L-1, and the higher irradiance of 120μmolm-2s-1. Contrarily, the average irradiation level of 50μmolm-2s-1 and the absence of sulfide stimulated the production of phycoerythrin and phycocyanin which could be increased by 65 and 50%, respectively. Thus, a final qualitative and quantitative tuning of pigment content is plainly achievable on grown microalgal biomass, in a reduced exposure time, at given irradiance or sulfide conditions.

Evolution and origin of the Bairendaba Ag–Pb–Zn deposit in Inner Mongolia, China: Constraints from infrared micro-thermometry, mineral composition, thermodynamic calculations, and in situ Pb isotope

The Bairendaba deposit is a typical large-scale Ag–Pb–Zn vein-type deposit in the Southern Great Hinggan Range, Inner Mongolia, China. Vein-type orebodies are hosted within biotite–plagioclase gneiss and quartz diorite and controlled by EW- and NE-trending faults with extensive hydrothermal alteration. Three primary mineralization/alteration stages have been recognised as the early ore stage, forming ore-barren quartz veins with arsenopyrite and pyrite, the primary ore stage, forming Zn-rich sulphide veins and Pb–Ag-rich sulphide–sulfosalt veins and the late barren stage, characterised by plenty of calcite, muscovite and fluorite veins. Infrared micro-thermometric data and mineral geothermometer show temperatures of ∼300 °C and ∼180 °C for Zn mineralization and Pb–Ag mineralization, respectively. A combination of mineralogical observations and thermodynamic calculations show that Zn mineralization is at pH 5.1 to 7.2 and logfO2 of −39.7 to −35.3, whereas Pb–Ag mineralization is at pH 5.6 to 7.4 and logfO2 of −48.2 to −40.3. The sulfidation state is estimated to be intermediate-low sulfidation. Conductive heat loss and extensive wall rock alteration are inferred to cause the Zn deposition, whereas an influx of meteoric water and wall rock alteration primarily trigger the large-scale Ag deposition. Laser ablation–inductively coupled plasma–mass spectrometry analysis shows that chalcopyrite is anomalously enriched in Sn (>1000 ppm). Sn is hosted in chalcopyrite of Zn mineralization in solid solution, whereas it exists as a stannite group phase in chalcopyrite of Pb–Ag mineralization. The occurrence of stannite group minerals in chalcopyrite of Pb–Ag mineralization might imply the decomposition of the Sn-bearing chalcopyrite at low temperature. In situ Pb isotope ratios of galena (206Pb/204Pb = 18.374–18.399, 207Pb/204Pb = 15.581–15.601 and 208Pb/204Pb = 38.332–38.416) indicate that the ore metals could be derived from the Mesozoic magma. Trace element compositions of sulphides in the Bairendaba deposit share the same characteristics with magma-related systems but differ considerably from non-magmatic and epithermal deposits. These results, combined with geological and isotopic evidence, suggest that the Bairendaba deposit is a magma-related hydrothermal vein-type deposit, indicating further exploration prospects for Sn mineralization near and/or under the Bairendaba mining area.

Sulfidation of Supported Ni, Mo and NiMo Catalysts Studied by In Situ XAFS

Active sites in Mo-based hydrotreating catalysts are produced by sulfidation. To achieve insights that may enable optimization of the catalysts, this process should be studied in situ. Herein we present a comparative XAFS study where the in situ sulfidation of Mo/δ-Al2O3 and Ni/δ-Al2O3 is compared to that of δ-Al2O3 supported NiMo catalysts with different NiMo ratios. The study also covers the comparison of sulfidation of Ni and Mo using different oxide supports as well as the sulfidation conditions applied in the reactor. The XAFS spectra confirms the oxide phase for all catalysts at the beginning of the sulfidation reaction and their conversion to a sulfidized phase is followed with in situ measurements. Furthermore, it is found that the monometallic catalysts are less readily sulfidized than bimetallic ones, indicating the importance of Ni-Mo interactions for catalyst activation. Mo K-edge XAFS spectra did not show any difference related to the support of the catalyst or the pressure applied during the reaction. Ni K-edge XAFS spectra, however, show a more complete sulfidation of the Ni species in the catalyst when SiO2 is used as a support as compared to the Al2O3. Nevertheless, it is believed that stronger interactions with Al2O3 support prevent sintering of the catalyst which leads to its stabilization. The results contribute to a better understanding of how different parameters affect the formation of the active phase of the NiMo catalysts used in the production of biofuel.