Iron Sulfide Precipitation Research Articles

Apatite as a Record of Magmatic–Hydrothermal Evolution and Metallogenic Processes: The Case of the Hongshan Porphyry–Skarn Cu–Mo Deposit, SW China

Apatite, as a common accessory mineral found in magmatic–hydrothermal deposits, effectively yields geochemical insights that facilitate our understanding of the mineralization process. In this research, multiple generations of magmatic and hydrothermal apatite were observed in the Hongshan porphyry–skarn Cu–Mo deposit in the Yidun Terrane in SW China. The geochemical compositions of the apatite were studied using in situ laser ablation–inductively coupled plasma mass spectrometry and an electron probe microanalysis to understand the magmatic–hydrothermal processes leading to ore formation. The apatite (Ap1a) occurs as subhedral to euhedral inclusions hosted in the phenocrysts of the granite porphyry. The Ap1b occurs later than Ap1a in a fine-grained matrix that intersects the earlier phenocrysts. Increases in F/Cl, F/OH, and F/S and decreases in ΣREE and (La/Yb)N from Ap1a to Ap1b suggest the exsolution of a volatile-rich phase from the magma. The skarn hosts three types of hydrothermal apatite (Ap2a, Ap2b, and Ap3), marking the prograde, retrograde, and quartz–sulfide stages of mineralization, respectively. The elemental behaviors of hydrothermal apatite, including the changes in Cl, Eu, As, and REE, were utilized to reflect evolutions in salinity, pH, oxygen fugacity, and fluid compositions. The composition of Ap2a, which occurs as inclusions within garnet, indicates the presence of an early acidic magmatic fluid with high salinity and oxygen fugacity at the prograde skarn stage. The composition of Ap2b, formed by the coupled dissolution-reprecipitation of Ap2a, indicates the presence of a retrograde fluid that is characterized by lower salinity, higher pH, and a significant decrease in oxygen fugacity compared to the prograde fluid. The Ap3 coexists with quartz and sulfide minerals. Based on studies of Ap3, the fluids in the quartz–sulfide stage exhibit relatively reducing conditions, thereby accelerating the precipitation of copper and iron sulfides. This research highlights the potential of apatite geochemistry for tracing magmatic–hydrothermal evolution processes and identifying mineral exploration targets.

Characterizing and modeling hydrogen sulfide production in anaerobic digestion of livestock manure, agro‐industrial wastes, and wastewater sludge

AbstractHydrogen sulfide (H2S) is the most undesirable inorganic gas in biogas from anaerobic digestion (AD). However, H2S production in AD is complex and understanding of its processes is still limited. This study performed six controlled batch anaerobic co‐digestion experiments to investigate H2S production. Materials were obtained from four field anaerobic digester systems and co‐digestion feedstocks from agroindustry. An additional precipitation experiment was conducted to further examine H2S production dynamics. Digesters containing highly soluble, carbohydrate‐based wastes had a high H2S final specific production (FSP) value. Additionally, the FSP values were negatively correlated with the initial Fe(II):S ratios in the digester liquid of the batch tests. The precipitation experiment indicated that iron sulfide precipitation was preferred in the presence of an anaerobic community. The H2S production as a time series was successfully modeled using a generalized additive model (R2 > 0.82). This study revealed that sulfate, phosphorus, and iron concentrations are important predictors and potential inhibitors of H2S production in AD. Further examination of real‐time H2S modeling in AD is warranted.

Bioturbation and the δ56Fe signature of dissolved iron fluxes from marine sediments.

We developed a reaction-transport model capable of tracing iron isotopes in marine sediments to quantify the influence of bioturbation on the isotopic signature of the benthic dissolved (DFe) flux. By fitting the model to published data from marine sediments, we calibrated effective overall fractionation factors for iron reduction (-1.3‰), oxidation (+0.4‰), iron-sulfide precipitation (+0.5‰) and dissolution (-0.5‰) and pyrite precipitation (-0.7‰) that agree with literature values. Results show that for bottom-water oxygen concentrations greater than 50 µM, higher bioturbation increased the benthic DFe flux and its δ 56Fe signature. By contrast, for oxygen concentrations less than 50 µM, higher bioturbation decreased the benthic DFe flux and its δ 56Fe signature. The expressed overall fractionation of the benthic DFe flux relative to the δ 56Fe of the iron oxides entering the sediment ranges from -1.67‰ to 0.0‰. On a global scale, the presence of bioturbation increases sedimentary DFe release from approximately 70 G mol DFe yr-1 to approximately 160 G mol DFe yr-1 and decreases the δ 56Fe signature of the DFe flux.

Sequential removal of nitrate and sulfate in woodchip and hematite – coated biochar bioreactor

The article demonstrates a method for the adaptation of denitrifying woodchip bioreactors for the removal of sulfate as well. Sulfate is removed by sulfate reduction and subsequent iron sulfide precipitation.

Early diagenetic processes in an iron-dominated marine depositional system

The early diagenetic interplay between reactive iron, sulfur, and organic matter in the bathymetrically isolated Santa Monica Basin (SMB) sediments are investigated in this study. We explore solid-phase and porewater profiles from the basin, supplemented with a transect from 71 to 907 m water depth that includes oxygenated (>60 μM O2) bottom waters near the coast and oxygen-deficient waters (∼4 µM O2) in the basin. The geochemical data of the basin sediments are further scrutinized by means of reactive transport modeling.The results show that the basin sediments do not follow the traditional geochemical signatures of oxygen-deficient settings. A lack of dissolved sulfide accumulation and sulfurized iron persists despite the sediments being deposited under reducing conditions (without bioturbation/bioirrigation), strong organic carbon input (TOC up to 5.0 wt%), and active dissimilatory sulfate reduction. Not only did we find an exceptional enrichment in highly reactive Fe in the surface sediments (∼45 % of total Fe), but the enrichment of reactive Fe, including ferrihydrite, persists downcore and coexists with high levels of dissolved Fe. The enhanced preservation of Fe oxides and lack of iron-sulfide precipitation is in part explained by detection via Mössbauer spectra of iron oxides bounded to organic matter (Fe[III]-OM coprecipitates).The modeled Fe budget shows that most of the Fe oxides in the surface sediments are internally recycled by upward diffusion and subsequent oxidation of Fe2+. Sulfide oxidation coupled to Fe reduction effectively precludes sulfide accumulation while enhancing build-up of dissolved Fe, fueling the Fe cycle within the first 5 cm depth. Continuous reoxidation of Fe2+ enhances the formation of Fe(III)-OM coprecipitates, limiting the amount of reactive organic matter. In the unavailability of labile organic matter, other than within the uppermost layers, the organic-rich sediment profiles are dominated by Fe cycling that limits the production and preservation of sulfides and enhances the preservation of Fe oxides and organic carbon. This study highlights key local controls on Fe availability in marginal basins and describes an intricate biogeochemical C-Fe-S cycling in modern and possibly ancient marine systems with important implications for Fe availability in the marine realm.

A novel chemical model for burial diagenesis and Zn–Pb sulphide precipitation within the Carboniferous Waulsortian Limestone, Ireland

Basin-scale processes such as regional fluid flow and organic maturation are commonly associated with the precipitation of Pb–Zn sulphide minerals. Despite extensive study, the origin of carbonate-hosted Pb–Zn mineralisation (Mississippi Valley-type and Irish-type) remains controversial, with deposits viewed as exceptional features derived from unusual basin conditions (e.g. regional hydrothermal fluid flux). In order to explore the links between mineralisation and broader-scale basinal processes, we have examined the relationship of base metal sulphides to regional diagenetic phases in the Waulsortian Limestone (Feltrim Formation) of the world-class Irish Midlands Zn–Pb province. Using combined sedimentology, petrography, and trace/rare earth element chemistry of regional calcite cements, we have reconstructed the basinal fluid history before, during and after sulphide mineralisation. The non-bright‐dull cathodoluminescence and trace metal composition of calcite cements indicates that the Waulsortian Limestone was subjected to three major chemical environments during progressive burial diagenesis: 1. Near-surface/shallow-burial oxic conditions; 2. subsurface euxinic conditions; and 3. subsurface ferruginous (ferrosulphidic) conditions. Zn–Pb mineralisation occurred under stage 2 euxinic conditions. We suggest that euxinic conditions were initiated when hydrocarbons entered the Waulsortian succession regionally, associated with the introduction of sour gas (H2S) accumulations. Mixing between more oxic base metal-bearing and H2S-bearing fluids produced ideal conditions for voluminous Zn–Pb sulphide precipitation. Increasing fluid anoxia then led to iron oxide dissolution with consequently increased iron sulphide precipitation, causing eventual depletion of H2S, and marked the onset of ferruginous conditions that terminated metal sulphide precipitation. Base metals were potentially derived from a range of sources that include Carboniferous seawater (and the dissolution of associated Mn/Fe oxyhydroxides), hydrocarbons, and basement-interacted basinal brines. The chemical model proposed by this study is compatible with existing data on the Irish Zn–Pb Orefield and indicates that sulphide mineralisation is linked to normal basin-scale processes such as subsidence, aquifer redox evolution and hydrocarbon generation. These results may explain many other global occurrences of carbonate-hosted Zn–Pb mineralisation and provide new insights into the chemical and redox processes that occur during burial diagenesis.

Enhancement of methanogenic activity by micronutrient control: Micronutrient availability in relation to sulfur transport

The main purpose of this research was to clarify the influence of the addition of iron (Fe) alone (0–100 mg/L) or 50 mg/L of Fe with 2 mg/L each of cobalt (Co), copper (Cu) and nickel (Ni) on the methanogenic activity of a mesophilic two-stage UASB system treating ethanol wastewater at a fixed chemical oxygen demand (COD) loading rate of 16 kg/m3/day under a continuous mode of operation and steady state condition. The addition of Fe provided the dual benefits of a reduction in both the dissolved sulfide and the hydrogen sulfide (H2S) content in produced gas, resulting in marginally improved hydrogen (H2) and methane (CH4) productivities. When the Fe dosage was increased beyond the optimum value of 50 mg/L, the process performance drastically declined, as a consequence of the high total volatile fatty acid (VFA) concentrations that inhibited both the acidogens and methanogens predominantly present in the 1st and 2nd reactors, respectively. The chemical precipitation of iron sulfide was responsible for the reduction of produced H2S in both the aqueous and gaseous phases as well as the minimization of added amounts of all other micronutrients to fulfil the sufficiency of all micronutrients for anaerobic digestion (AD). The addition of 2 mg/L each of Co, Cu and Ni together with 50 mg/L Fe resulted in the greatest enhancement in process performance, as indicated by the improved CH4 yield (mL/g COD applied) to about 42.3%, compared to that without micronutrient supplement.

Effect of sediment deposition on phosphate and hydrogen sulfide removal by granulated coal ash in coastal sediments

Granulated coal ash (GCA) is a strong in-situ capping material for removing PO4-P and H2S-S in contaminated coastal sediments. Although GCA performance is weakened by sediment deposition, related research is rare. To evaluate sediment deposition effects on PO4-P and H2S-S removal by GCA, GCA was placed on the top of sediment (C-GCA), was partially mixed with sediment (M-GCA), and was fully covered by sediment (N-GCA). Effective PO4-P and H2S-S removal from sediments occurred in the order of C-GCA > M-GCA > N-GCA. C-GCA and M-GCA significantly decreased PO4-P and H2S-S concentrations by 84– 90% and 100%, respectively, through calcium phosphate and iron sulfide precipitation. N-GCA was less effective in PO4-P and H2S-S removal than the control after 2.5 months, as fine sediment particles blocked the GCA pores, decreasing calcium and iron elution. The results provide a better understanding of how sediment deposition negatively impacted GCA performance.

Fundamental controls on organic matter preservation in organic- and sulfur-rich hydrocarbon source rocks

Incorporation of reduced inorganic sulfur (S) into organic matter (OM) in euxinic environments is considered a vital route through which OM is preserved for millions of years. However, precipitation of iron sulfides is believed to compete with OM preservation via sulfurisation. High resolution geochemical, petrographic, and electron microprobe (EMPA) analyses were employed to better understand S controls on OM preservation with particular focus on iron sulfides precipitation in organic S-rich mudstones from the Kimmeridge Clay (KCF), Monterey (MF), and Whitby Mudstone [Grey Shale (GS) and Jet Rock (JR) Members] Formations. Analyses indicated that S in the KCF and MF is mostly bound to OM as shown by the relatively high abundance of organic sulfur compounds (OSCs) in their pyrolysates. The relatively low amounts of iron (Fe) in these mudstones permitted extensive reaction of S and OM to occur efficiently, promoting preservation of high amounts OM through sulfurisation. State-of-the-art EMPA imaging of total S and Fe indicated that the S was mainly bound to organics, supporting the geochemical analyses. In contrast, S in the GS and JR was predominantly sequestered as pyrite (FeS2) rather than organically bound, as indicated by the relatively low quantity/absence of OSCs in their pyrolysates, hence, preservation through sulfurisation was less significant in these settings. EMPA imaging of S in these mudstones shows discrete shapes ranging in geometry and size and in most cases correlated with Fe in the corresponding Fe EMPA images, confirming that the S exists in discrete authigenic FeS2. Overall, in line with previous research, this study indicates that preservation of OM through sulfurisation is an important pathway for sequestration of OM. However, an abundance of reactive Fe could hinder this process by preferentially reacting with reduced S, to form iron sulfides (mainly FeS2), thus impeding reactions between OM and S to occur efficiently.

Treating acid mine drainage with decomposed organic soil: Implications for peatland rewetting

Acidification and salinisation of groundwater and surface water bodies are worldwide problems in post-mining landscapes due to acid mine drainage (AMD). In this study, we hypothesised that highly decomposed peat offers a suitable substrate for mitigating AMD pollution of water bodies and that hydraulic load affects the removal efficiency of iron and sulphate. A lysimeter experiment was conducted mimicking peatland rewetting to quantify iron and sulphate removal and pH changes at different loading rates. The low initial pH of 4 rose to 6 and electrical conductivity declined by up to 47%. The initially high concentrations of iron (>250 mg/L) and sulphate (>770 mg/L) declined by, on average, 87 and 78%, respectively. The removal efficiency of sulphate was negatively correlated with either the hydraulic or the sulphate load, respectively, i. e. the lower the hydraulic load, the higher the removal efficiency of sulphate. However, the removal of iron was not explained by the load. The results imply that desulphurication and thus subsequent precipitation of iron sulphides was the main removal process and that peatland rewetting is an effective measure to mitigate AMD pollution of freshwater systems. For the heavily AMD-polluted studied section of the River Spree, we estimated by combining experimental with field data that a sulphate load reduction of the river by about 20% (36,827 tons/yr) will occur if all peatlands in the sub-catchment (6067 ha; 6.7% of the total area) are rewetted. Future investigations must show if the pollutant removal is declining over time in decomposed peat layers due to acidification and/or lack of bioavailable carbon and how the rewetting of peatland with AMD will affect the restoration of their ecosystem functioning in the long term.

Damming Induced Natural Attenuation of Hydrothermal Waters by Runoff Freshwater Dilution and Sediment Biogeochemical Transformations (Sochagota Lake, Colombia)

The volcanic area of the Paipa system (Boyacá, Colombia) contains a magmatic heat source and deep fractures that help the flow of hot and highly mineralized waters, which are further combined with cold superficial inputs. This mixed water recharges the Salitre River and downstream feeding Sochagota Lake. The incoming water can contribute to substantial increases in hydrothermal SO42−-Na water in the water of the Salitre River basin area, raising the salinity. An additional hydrogeochemical process occurs in the mix with cold Fe-rich water from alluvial and surficial aquifers. This salinized Fe-rich water feeds the Sochagota Lake, although the impact of freshwaters from rain on the hydrochemistry of the Sochagota Lake is significant. A series of hydrogeochemical, biogeochemical, and mineralogical processes occur inside the lake. The aim of this work was to study the influence of damming in the Sochagota Lake, which acts as a natural attenuation of contaminants such as high concentrations of metals and salty elements coming from the Salitre River. Damming in the Sochagota Lake is considered to be an effective strategy for attenuating highly mineralized waters. The concentrations of dissolved elements were attenuated significantly. Dilution by rainfall runoff and precipitation of iron sulfides mediated by sulfate-reducing bacteria in deposits rich in organic material were the main processes involved in the attenuation of concentrations of SO42−, Fe, As Cu, and Co in the lake water. Furthermore, the K-consuming illitization processes occurring in the sediments could favor the decrease in K and Al.

Identification of magnetic enhancement at hydrocarbon-fluid contacts

Identifying the depths of the hydrocarbon-fluid contacts in a reservoir is important for determining hydrocarbon reserves and production planning. Using core samples from the Tay Sandstone reservoir in the central North Sea, we show that there is a magnetic enhancement at the hydrocarbon-fluid contacts that is detectable through both magnetic susceptibility measurements and magnetic hysteresis measurements. We observed this magnetic enhancement at both gas-oil and oil-water contacts, which have been independently identified using nonmagnetic methods; we did not consider gas-water contacts in this study. We demonstrate that this magnetic enhancement is caused by the precipitation of new nanometric iron oxide (magnetite) and iron sulfide (greigite) phases. The magnetic enhancement may be caused by diagenetic changes or preferential biodegradation at the top of the oil column during early filling and at the oil-water contact. Our findings have the potential to be used to identify paleo-hydrocarbon-fluid contact in both structurally modified fields and failed wells. The technique can also be used to infer the fill history of a basin and calibrate petroleum systems models. Magnetic susceptibility measurements have the advantage that they can easily and quickly be measured in the field on whole core material.

Using magnetic techniques to calibrate hydrocarbon migration in petroleum systems modelling: A Case Study from the Lower Tertiary, UK Central North Sea

Summary Magnetic minerals form or alter in the presence of hydrocarbons, making them a potential magnetic proxy for identifying hydrocarbon migration pathways. In this paper we test this idea by magnetically measuring core samples from the Tay Fan in the Western Central Graben in the Central North Sea. In a companion paper, 3D petroleum systems modelling has been carried out to forward model migration pathways within the Tay Fan. Rock magnetic experiments identified a range of magnetite, maghemite, iron sulphides, siderite, goethite and titanohematite, some of which are part of the background signal, and some due to the presence of hydrocarbons. Typical concentrations of the magnetic minerals were ∼10–200 ppm. Importantly, we have identified an increasing presence of authigenic iron sulphides (likely pyrite and greigite) along the identified lateral hydrocarbon migration pathway (east to west). This is likely caused by biodegradation resulting in the precipitation of iron sulphides, however, though less likely, it could alternatively be caused by mature oil generation, which subsequently travelled with the migrating oil to the traps in the west. These observations suggest mineral magnetic techniques could be a rapid alternative method for identifying the severity of biodegradation or oil maturity in core sample, which can then be used to calibrate petroleum systems models.

Evaluating the multidecadal response of historic seawater incursion events and salinity-induced meromixis at Laytons Lake, Nova Scotia, Canada

McGuire HE, Dunnington DW, Loder AL, Spooner IS, Mallory ML, McLellan NR, Su, C-C. 2021. Evaluating the multidecadal response of historic seawater incursion events and salinity-induced meromixis at Laytons Lake, Nova Scotia, Canada. Lake Reserv Manage. 37:378–390. Long-term monitoring data from freshwater lakes can be challenging to retrieve yet are valuable for assessing lakes at risk of saltwater intrusion. We demonstrate the use of an applied paleolimnological method to identify the response of a freshwater lake to seawater incursion and salinity-induced meromixis by examining the geochemistry of lake sediments deposited over the past century. Laytons Lake is located 1.5 km from the Bay of Fundy coastline, and experienced documented seawater incursion events in 1944 and 1949 leading to a period of extended meromixis (>40 yr). Our limnological measurements indicate that meromixis no longer exists at Laytons Lake, and hypolimnetic phosphorus (P) concentrations and conductivity values have declined since 1982. Meromictic conditions, the establishment of the chemocline, and high sedimentation rates collectively preserve a geochemical record of seawater incursion, which was identified as a short-duration, positive chloride (Cl-) excursion followed by the precipitation of iron sulfide (FeS2). A decline in Cl- concentration after the incursion events in the paleorecord may represent the deterioration of the chemocline, and the reestablishment of thermal stratification and mixing. We suspect that seawater incursions can have a multidecadal impact on aquatic systems, and that bulk geochemical analysis of paleolimnological records is a useful, low-cost tool that can provide a long-term perspective on the limnological consequences of such events. These long-term data can inform the assessment of aquatic systems at risk of saltwater incursion due to sea-level rise.

Rock magnetic evidence of tectonic control on the sedimentation and diagenesis in the Andaman Sea over ~1 million years

We evaluate the sedimentary (magnetic, mineralogical, geochemical, grain size) records of a long sediment core (NGHP-01-17 A) to elucidate the tectonic control on the sedimentation and diagenesis in the Andaman Sea (AS) over the past ~ 1 Ma. Two distinct sedimentary magnetic zones (Z-I and Z-II) are identified based on the rock magnetic signatures. A significant shift in the depositional environment is observed around ~90 ka which is marked by a rapid change in magnetite susceptibility (χlf), Fe, Ti and organic carbon content in Z-I. A trend of upward increase in χlf from ~90 ka to 3 ka in core NGHP-01-17 A suggest increase in detrital flux to the AS and represents the onset of a new sedimentary regime following most recent event of tectonic uplift in Indo-Burman Ranges (IBR) which occurred at ~ 150 ka. Methane influenced progressive diagenetic dissolution of detrital iron oxides and subsequent precipitation of iron sulfides in Z-II is clearly evident in the rock magnetic and mineralogical data. Multiple bands of diagenetically formed iron sulfide nodules at different periods in Z-II indicate episodic intensification of anaerobic oxidation of methane (AOM) due to enhanced methane-flux. We propose that fluid migration forced by tectonic processes facilitated episodic release of methane from deep reservoir that led to the formation of iron-sulfide nodules in the AS.

Diagenesis of Magnetic Minerals in Active/Relict Methane Seep: Constraints From Rock Magnetism and Mineralogical Records From Bay of Bengal

In this study, we conducted a comprehensive investigation of rock magnetic, mineralogical, and sedimentological records of sediment cores supplemented by a high resolution seismic data to elucidate the controls of structural and diagenetic (early vs. late) processes on the sediment magnetism in active and relict cold seep sites in the Bay of Bengal. Two distinct sediment magnetic zones (Z-I and Z-II) are defined based on the down-core variations in rock magnetic properties. The sediment magnetism is carried by complex magnetic mineral assemblages of detrital (titanomagnetite, titanohematite) and authigenic (fine-grained greigite) minerals. Overall, the magnetic susceptibility varies over one order of magnitude with highest values found in relict core. Uppermost sediment magnetic zone (Z-I) is characterized by higher concentration of magnetite as seen through elevated values of magnetic susceptibility (χlf) and saturation isothermal remanent magnetization (SIRM). A systematic gradual decrease of χlf and IRM1T in Z-I is attributed to the progressive diagenetic dissolution of iron oxides and subsequent precipitation of iron sulfides. Magnetic grain size diagnostic (ARM/IRM1T) parameter decreases initially due to the preferential dissolution of fine-grained magnetite in the sulfidic zone (Z-I), and increases later in response to the authigenic formation of magnetite and greigite in methanic zone (Z-II). Distinct low S-ratio and χlf values in methanic zone of relict core is due to increased relative contribution from highly preserved coercive magnetic (titanohematite) grains of detrital origin which survived in the diagenetic processes. A strong linkage between occurrence of authigenic carbonates and greigite formation is observed. Two plausible mechanisms are proposed to explain the formation and preservation of greigite in Z-I and Z-II: 1) decline in methane flux due to massive hydrate accumulation within the active fault system and formation of authigenic carbonate crust in the sub-surface sediments hindered the supply of upward migrating fluid/gas; thereby limiting the sulfide production which preferentially enhanced greigite formation in Z-I and 2) restricted supply of downward diffusing sulfide by the carbonate layers in the uppermost sediments created a sulfide deficient zone which inhibited the pyritization and favoured the formation of greigite in the methanic zone (Z-II).

Controls of mass transport deposit and magnetic mineral diagenesis on the sediment magnetic record from the Bay of Bengal

We conducted rock magnetic, mineralogical, sedimentological and geochemical analyses on a sediment core (MD161/Stn-11) retrieved from a complex marine sedimentary system of Krishna-Godavari (K-G) basin to delineate the control of mass transport deposits (MTD's) and methane-induced diagenesis on the sediment magnetic record. Four sediment magnetic zones (Z-I, Z-II, Z-III, Z-IV) were defined based on rock magnetic signatures. The sediment magnetic signal is mainly carried by complex magnetic mineral assemblages of detrital (titanomagnetite, titanohematite) and diagenetic (pyrite) minerals. Changes in rock magnetic properties are mainly controlled by fluctuations in supply of detrital magnetic particles, onset of MTD's and differential rate of methane-influenced magnetic minerals diagenesis in the studied sediment core. Downcore reduction in magnetic susceptibility followed by subsequent precipitation of iron sulfides within sediment magnetic zone (Z-I) representing the period of normal sedimentation can be attributed to diagenetic dissolution caused by anaerobic oxidation of methane coupled to sulfate reduction. Decline in magnetic susceptibility and increase in sediment grain size within MTD-rich sediment intervals (Z-II, Z-III, Z-IV) is linked to loss of finer magnetic grains due to diagenetic dissolution and dilution caused by increase in concentration of diamagnetic minerals. Lower values of magnetic grain size diagnostic (ARM/SIRM) parameter indicate loss of finer and selective retention of coarser magnetic particles due to diagenetic dissolution beyond 12 mbsf. Elevated content of total organic carbon (TOC) content in Z-III and Z-IV can be attributed to the efficient preservation of labile organic matter due to rapid sediment deposition. A conceptual model is presented to explain the control of mass transport deposit and magnetic mineral diagenesis on the sediment magnetic record.

Biogeochemical cycling of sulfur, manganese and iron in ferruginous limnic analog of Archean ocean

The early evolution of life on Earth was intimately coupled with the evolution of ocean chemical composition and redox conditions in Archean ocean. However, the measurements of chemical and isotopic compositions of Archean sedimentary rocks does not provide sufficient information for understanding the biogeochemical processes that characterized oceans during this period. In this research, the cycling of the redox-sensitive elements in the water column and sediments of the seasonally stratified Lake Sihailongwan, China, was studied. It was found that during the stratification, the concentrations of sulfate ions in the epilimnion were <100 μmol L−1. The hypolimnion of the lake becomes anoxic and contains iron, manganese and low concentrations of hydrogen sulfide. These conditions are similar to those suggested to exist in the Archean ocean, and therefore the biogeochemical cycles in Lake Sihailongwan may be analogous to those in the Archean ocean. In Lake Sihailongwan, the chemocline is always deeper than the thermocline. The hypolimnion is supersaturated with respect to iron sulfide in August, while in May and October, this supersaturation is present only in the lower hypolimnion. The concentration profiles of the redox species in the water column and in the sediments show that dissolved iron(II) and manganese(II) diffuse from the sediments into the water column, while hydrogen sulfide and sulfate diffuse into the sediment. At the hypolimnion, the sulfur isotope fractionation values are consistent with microbial sulfate reduction, possibly combined, to a minor extent, with disproportionation of zero-valent sulfur. The absolute sulfur isotope fractionation factor increases between spring and autumn and decreases with water depth, possibly due to precipitation of iron sulfide in the lower hypolimnion. The fraction of highly reactive iron in the sediments is mainly composed of iron(II) carbonates and the most reactive iron(III) (hydr)oxide phases. Iron-based redox proxies are consistent with sediment deposition under ferruginous water column conditions. In the sediment, concentrations of sulfate and hydrogen sulfide are low, and sulfur isotope composition of sedimentary pyrite is equal to that of the epilimnetic sulfate. The obtained results demonstrated that despite a low sulfate concentration in the water column, sulfur isotope fractionation is high. However, due to the complete consumption of the sulfate reservoir, the large isotope fractionation is not preserved in the sedimentary record.

Process Improvement of a Two-Stage Upflow Anaerobic Sludge Blanket System by Micronutrient Supplement in Relation to Sulfur Transport

The main purpose of this research was to elucidate the influence of the addition of iron alone (0–100 ppm) or with 2 ppm each of cobalt, copper, and nickel on the performance of a two-stage UASB system treating ethanol wastewater. The system consisted of two reactors connected in series. The system was maintained at a fixed chemical oxygen demand loading rate (16 kg/m3d) and 37 °C with a recycle ratio of 1:1. Both Co and Ni were found to be deficient in the ethanol wastewater, while Fe and Cu became inadequate in two-stage UASB. The addition of Fe provided dual benefits of a reduction in both sulfide toxicity and hydrogen sulfide content in produced gas, resulting in marginally improved hydrogen and methane productivities. When the Fe dosage was increased beyond the optimum value of 50 ppm, the process performance drastically declined, as a result of high total volatile fatty acid concentrations that inhibited acidogens and methanogens predominantly present in the 1st and 2nd reactors, respectively. The chemical precipitation of iron sulfide was responsible for the reduction of produced H2S in both aqueous and gaseous phases. The addition of 2 ppm each of Co, Cu, and Ni together with 50 ppm Fe resulted in an enhanced process performance, as indicated by the improved CH4 yield (mL/g COD applied) to about 42.3% compared to that without micronutrient supplement. Supplementation to fulfill the sufficiency of all micronutrients was vital for the maximization of anaerobic digestion (AD) performance, as generally indicated in methanogenic activity.

Rapid pyritization in the presence of a sulfur/sulfate-reducing bacterial consortium

Sedimentary pyrite (FeS2) is commonly thought to be a product of microbial sulfate reduction and hence may preserve biosignatures. However, proof that microorganisms are involved in pyrite formation is still lacking as only metastable iron sulfides are usually obtained in laboratory cultures. Here we show the rapid formation of large pyrite spherules through the sulfidation of Fe(III)-phosphate (FP) in the presence of a consortium of sulfur- and sulfate-reducing bacteria (SRB), Desulfovibrio and Sulfurospirillum, enriched from ferruginous and phosphate-rich Lake Pavin water. In biomineralization experiments inoculated with this consortium, pyrite formation occurred within only 3 weeks, likely enhanced by the local enrichment of polysulfides around SRB cells. During this same time frame, abiotic reaction of FP with sulfide led to the formation of vivianite (Fe3(PO4)2·8H2O) and mackinawite (FeS) only. Our results suggest that rates of pyritization vs. vivianite formation are regulated by SRB activity at the cellular scale, which enhances phosphate release into the aqueous phase by increased efficiency of iron sulfide precipitation, and thus that these microorganisms strongly influence biological productivity and Fe, S and P cycles in the environment.