Iron-bearing Minerals Research Articles

The coupling effect and ecological risk assessment of iron, manganese, and arsenic in the water environment of the central Yangtze River Basin, China.

Excessive heavy metal in drinking water are harmful to human body. Groundwater was still the drinking water resource in most of rural areas in the central of the Yangtze River Basin. Heavy metals of Fe, Mn, and As in the low plain region of the Yangtze River Basin significantly exceeded the standard, resulting in 16.67% and 5.00% of water samples in the area reaching moderate and severe heavy metal pollution states. However, the coupling effect and ecological risks of iron, manganese, and arsenic in the water environment are unknown. This paper found that the dissolution of iron-bearing and manganese-bearing minerals into groundwater affected each other, when the burial depth of groundwater was less than 20m. Conversely, the dissolution of minerals containing iron and arsenic into the groundwater interacted with each other when the groundwater depth was greater than 20m. The precipitation of siderite (FeCO3) and rhodochrosite (MnCO3) may control the dissolved Fe and Mn in groundwater. The area between Yangtze River and Han River was more affected by industrial activities, and the south area of the Yangtze River was more affected by agricultural activities. This paper not only strengthened the understanding of the risk of heavy metal pollution in local groundwater, but also provided important scientific basis for the protection of regional groundwater ecological environment.

Effects of nanoplastics on the growth, transcription, and metabolism of rice (Oryza sativa L.) and synergistic effects in the presence of iron plaque and humic acid

Nanoplastics (NPs) can adversely affect living organisms. However, the uptake of NPs by plants and the physiological and molecular mechanisms underlying NP-mediated plant growth remain unclear, particularly in the presence of iron minerals and humic acid (HA). In this study, we investigated NP accumulation in rice (Oryza sativa L.) and the physiological effects of exposure to polystyrene NPs (0, 20, and 100 mg L−1) in the presence of iron plaque (IP) and HA. NPs were absorbed on the root surface and entered cells, and confocal laser scanning microscopy confirmed NP uptake by the roots. NP treatments decreased root superoxide dismutase (SOD) activity (28.9–44.0%) and protein contents (31.2–38.6%). IP and HA (5 and 20 mg L−1) decreased the root protein content (20.44–58.3% and 44.2–45.2%, respectively) and increased the root lignin content (22.3–27.5% and 19.2–29.6%, respectively) under NP stress. IP inhibited the NP-induced decreasing trend of SOD activity (19.2–29.5%), while HA promoted this trend (48.7–50.3%). Transcriptomic and metabolomic analysis (Control, 100NPs, and IP-100NPs-20HA) showed that NPs inhibited arginine biosynthesis, and alanine, aspartate, and glutamate metabolism and activated phenylpropanoid biosynthesis related to lignin. The coexistence of IP and HA had positive effects on the amino acid metabolism and phenylpropanoid biosynthesis induced by NPs. Regulation of genes and metabolites involved in nitrogen metabolism and secondary metabolism significantly altered the levels of protein and lignin in rice roots. These findings provide a scientific basis for understanding the environmental risk of NPs under real environmental conditions.

Deciphering the biodegradation of thiamethoxam by Phanerochaete chrysosporium with natural siderite: Synergistic mechanisms, transcriptomics characterization, and molecular simulation

Fungi play vital roles in the fate of organic pollutants, particularly when interacting with minerals in aquatic and soil environments. Mechanisms by which fungi may mitigate pollutions in fungus-mineral interactions are still unclear. Inspired by biogeochemical cycling, we constructed a range of co-culture systems to investigate synergistic effects of the white-rot fungus Phanerochaete chrysosporium and the iron-bearing mineral siderite on thiamethoxam (THX) transformation, a common neonicotinoid pesticide. Co-culturing with siderite significantly enhanced THX transformation during the initial 10 days with a dose effect, achieving 86 % removal within 25 days. Fungi could affect siderite’s dissolution, transformation, and precipitation through their biological activities. These interactions triggered physiological adaptation and resilience in fungi. Siderite could enhance the activity of fungal ligninolytic enzymes and cytochrome P450, facilitating biotransformation. Genes expression related to growth, energy metabolism, and oxidative stress response upregulated, enhancing fungal resilience to THX. The primary THX degradation pathways included nitro-reduction, C-N cleavage, and de-chlorination. Molecular dynamics simulations provided insights into catalytic mechanisms of enzyme-THX interactions. Together, siderite could act as natural enhancers that endowed fungi to resist physical and chemical stresses in environments, providing insights into contaminants attenuation, fungal biomineralization, and the coevolution of the Earth's lithosphere and biosphere.

Redox Properties of Structural Fe in Clay Minerals: 4. Reinterpreting Redox Curves by Accounting for Electron Transfer and Structural Rearrangement Kinetics.

Iron-bearing smectite clay minerals can act as electron sources and sinks in the environment. Previous studies using mediated electrochemical analyses to determine the reduction potential (EH) values of smectites observed that the relationship between the structural Fe2+(s)/FeTotal ratio in the smectite and EH varied based on the redox history of the smectite. We hypothesize that this behavior, referred to as redox hysteresis, results from the smectite particles not equilibrating with the applied EH over the course of the experiment (∼30 min). To test this hypothesis, we developed a model incorporating interfacial electron transfer kinetics and charge redistribution within the particle to simulate the mediated electrochemical experiments from previous studies. The simulated redox curves accurately matched the previously reported experimental redox curves of the smectite SWa-1, demonstrating that longer equilibration periods led to a decrease in redox hysteresis. We validated this experimentally by measuring the redox curve of SWa-1 after an equilibration period of at least 12 h. Furthermore, we extended the simulations to three other smectites (NAu-1, NAu-2, and SWy-2) and extracted their respective thermodynamic and kinetic parameters. This work offers a framework for interpreting and modeling redox reactions on clay surfaces, along with key parameters for four commonly studied smectites.

Reconstructing the redox environment of the Cambrian Harkless Formation, Nevada, USA: Navigating the effects of iron-rich clay minerals on the iron speciation redox proxy

Understanding the oxygenation of ancient oceans is critical for contextualizing evolutionary events throughout Earth's history. While there are many geochemical proxies available for evaluating paleoredox state, iron speciation is one of the most robust and widely applied recorders of local bottom water redox. The proxy uses a series of sequential extractions which are operationally designed to target redox active iron in different mineral groups, including carbonates, oxides, magnetite, and sulfides. However, clay minerals that contain iron are not specifically targeted but can be important reservoirs of redox active iron. These clay minerals are abundant during many times in Earth's history, so it is critical to understand how they are extracted during iron speciation and their impact on paleoenvironmental interpretations.Here we apply the iron speciation proxy in combination with other geochemical proxies (FeT/Al, Mn enrichments) and mineralogical analyses to determine local bottom water redox conditions during deposition of the early Cambrian Harkless Formation exposed near Gold Point, Nevada, USA. The Harkless Formation contains one of the last occurrences of archaeocyathan reefs before their extinction, thus studying the underlying strata can provide information about the environmental conditions which led to reef development. Iron speciation results indicate oxic to potentially anoxic conditions in the water column. The presence of FeT/Al enrichments, Mn depletion, and the Fe-rich redox sensitive clay minerals chamosite and glauconite suggest intermittent anoxia in the water column and porewaters during some intervals of Harkless deposition. Further, by combining iron speciation extractions with petrographic and x-ray diffraction analyses, we demonstrate that glauconite and chamosite were likely formed at or below the sediment water interface and are also not consistently or fully removed by the standard sequential iron reagents, as noted by previous work.The presence of these authigenic Fe-bearing clay minerals overall results in an underestimation of the proportion of redox active iron during deposition and early sediment diagenesis that may lead to incorrect environmental characterization. We therefore advocate for caution and careful examination of the mineralogy of samples when applying the iron speciation proxy, particularly when authigenic and/or early diagenetic iron-bearing clay minerals are suspected to be present. Based upon these findings, we suggest that the Harkless Formation experienced variable local bottom water redox conditions ranging from oxic to anoxic during deposition. Changes in the relative abundances of chamosite and glauconite may also indicate an increase in oxygenation up section, suggesting that local water column oxygenation played a role in archaeocyathan reef development.

Synergistic adsorption mechanism of novel combined collector in flotation separation of fayalite from magnetite: Experiments and MD simulations

As an iron-bearing silicate mineral, fayalite has similar surface properties to magnetite, which makes it challenging to efficiently separate fayalite from magnetite by flotation. In this study, magnetite and fayalite were separated using novel combined collector polyoxyethylene alkyl amine (PAE) and terpinol (AT) through reverse flotation. Combined with a variety of characterization analysis and molecular dynamics (MD) simulation, the synergistic adsorption mechanism of the combined collector on mineral surface was revealed from multiple perspectives. The optimum scheme and pH response range of the combined collector were determined by micro-flotation test. Compared with PAE alone, the difference value of flotation recovery between fayalite and magnetite using combined collector was increased by 10.16%, and the dosage was reduced by 20%. Additionally, an effectively adsorption of combined collector onto fayalite surface to improve its surface hydrophobicity. Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and MD simulations results showed synergistic adsorption was produced onto fayalite surface using combined collector mainly through non-polar interaction, hydrogen bond association and bridge adsorption. Furthermore, the spatial distribution and diffusion behavior of water molecules provide microscopic evidence for the enhancement of surface hydrophobicity of fayalite by combined collector.

Land-Use Pattern-Based Spatial Variation of Physicochemical Parameters and Efficacy of Safe Drinking Water Supply along the Mahaweli River, Sri Lanka

Exploration of the pollution status of river-based water sources is important to ensure quality and safe drinking water supply for the public. The present study investigated physicochemical parameters of surface water in the upper segment of River Mahaweli, which provides drinking water to the Nuwara Eliya and Kandy districts of Sri Lanka. River surface water from 15 intakes and treated water from 14 Water Treatment Plants (WTPs) were tested for pH, water temperature, turbidity, EC, COD, 6 anions, 21 cations, 3 pesticides, and 30 antibiotics once every 3 months from June 2022 to July 2023. Except for turbidity and iron concentrations, all other parameters were within the permissible range as per the Sri Lanka Standard Specification for Potable Water (SLS 614:2013). The uppermost Kotagala WTP raw water had a high concentration of iron due to runoff from areas with abundant iron-bearing minerals. Turbidity increased as the river flowed downstream, reaching its highest value of 13.43 NTU at the lowermost Haragama. Four intakes had raw surface water suitable for drinking as per the Water Quality Index (WQI). Pollution increased gradually towards downstream mainly due to agricultural runoff, industrial effluents, and urbanization. Poor water quality at the upstream Thalawakale-Nanuoya intake was due to highly contaminated effluent water coming from Lake Gregory in Nuwara Eliya. Cluster analysis categorized WTP locations in the river segment into 3 clusters as low, moderate, and high based on contaminations. Principal component analysis revealed that the significance of the 41.56% variance of the raw water was due to the pH and the presence of heavy metals V, Cr, Ni, Rb, Co, Sr, and As. All treated water from 15 WTPs had very good to excellent quality. In general, heavy metal contamination was low as indicated by the heavy metal pollution index (HPI) and heavy metal evaluation index (HEI). The treatment process could remove up to 94.7% of the turbidity. This is the first attempt to cluster the river catchment of the Mahaweli River based on physicochemical parameters of river water. We present here the land-use pattern-based pollution of the river and efficacy of the water treatment process using the Mahaweli River Basin as a case study. Regular monitoring and treatment adjustments at identified points are recommended to maintain the delivery of safe drinking water.

Abiotic transformation of chlorinated organics at the active surface of iron-bearing minerals in soils and sediments

Abiotic transformation of chlorinated organics at the active surface of iron-bearing minerals in soils and sediments

Promotion of aromatic amino acids of extracellular polymeric substance targeted transformation via sulfite mediated iron redox cycling in sludge solid-liquid separation

Highly hydrophilic extracellular polymeric substance (EPS) with gel-like structure seriously plagues the development of sludge deep dewatering. Oxysulfur radicals-based oxidation driven by iron-bearing mineral proposes a promising strategy for effective EPS decomposition. However, the transformation and involved interaction mechanisms of aromatic proteins are still controversial due to the complex EPS structure. Herein, sulfite mediated siderite (denoted as Fe(II)/S(IV)) was developed for targeted transformation aromatic amino acids in EPS oxidation to strengthen sludge solid-liquid separation. The enhanced sludge dewaterability were benefited from the Fe(II)/S(IV) bonded interaction assisted by Fe3+/Fe2+ as redox interface that facilitating the release of intracellular bound water via diminish the hydrophily and bind strength with solid protons. The amide region nitrogen of aromatic amino acids (especially tyrosine and tryptophan) originating from EPS presented looser structure and lower spatial site resistance, which were attributed to the exposure of hydrophobic sites in amino groups after Fe(II)/S(IV) treatment. Furthermore, the effective decline of aromatic amino acids in inner layer-EPS (loosely bound EPS and tightly bound EPS) was directed from Fe-N targeted interaction by triggering a series of sulfate-based radical chain reactions. The good correlation between electron transfer amount (R2 = 0.926) and Fe-N (R2 = 0.925) with bonding interaction demonstrated that the complexation of aromatic amino acids with Fe sites on siderite/sulfite via Fe-N bonds, accounting for efficient sludge solid-liquid separation. This study deepens the understanding of sludge organic matter targeted transformation and provides a tactic for iron-based conditioning of sludge.

Synthesis of Alpha Ferrous Oxalate Dihydrate from Ferrotitaniferous Mineral Sands via Hot Pressurized Aqueous Oxalic Acid: Kinetics and Characterization

Ferrous oxalate dihydrate is a versatile organic mineral with applications across fields. However, little is known about the feasibility of its synthesis directly from iron-bearing minerals using binary subcritical water (sCW) systems and its associated kinetics. In this study, the sCW+oxalic acid system at either 115 °C or 135 °C was investigated as a reaction medium for ferrous oxalate dihydrate (α-FeC2O4∙2H2O) synthesis, starting from ferrotitaniferous sands. The kinetics of the synthesis reaction were studied, and the physicochemical characterization of the as-synthetized ferrous oxalates was performed. Overall, the sCW synthesis was temperature-dependent, following second-order reaction kinetics according to the proposed precipitation pathway. A high reaction rate constant, significantly high yields (up to 89%), and reduced reaction times (2–8 h) were evident at 135 °C. The as-synthetized product corresponded to the monoclinic α-FeC2O4∙2H2O, showed relatively high specific surface areas (from 31.9 to 33.7 m2∙g−1), and exhibited band gap energies within the visible light range (~2.77 eV). These results suggest that α-FeC2O4∙2H2O can be synthesized using an organic dicarboxylic acid and iron-rich, widely available, low-cost mineral precursors. In addition, the as-prepared α-FeC2O4∙2H2O could be further optimized and tested for catalytic and visible light photocatalytic applications.

Effects of mineral adsorption on the molecular composition of soil dissolved organic matter: Evidence from spectral analyses

The adsorption of soil dissolved organic matter (DOM) by minerals is crucial for long-term carbon storage and has been extensively studied. However, the variations in soil DOM composition resulting from adsorption by different minerals have rarely been investigated from a spectral perspective. This study examined the impact of non‑iron (kaolinite) and iron-bearing (ferrihydrite) minerals on the concentration and characteristics of DOM from dark brown soil during a 60-h-long incubation experiment. Soil dissolved organic carbon was removed more efficiently by ferrihydrite (66.2 %) than by kaolinite (14.8 %). UV–Vis spectroscopic analysis indicated that DOM with high aromaticity and molecular weight exhibited a strong affinity for both ferrihydrite and kaolinite. The fluorescence of soil DOM decreased in the ferrihydrite treatment, with a notable reduction in humic-like fluorescent components identified through fluorescent excitation-emission matrix coupled parallel factor analysis. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy revealed that carboxyl groups were critical in DOM adsorption on ferrihydrite, participating in ligand exchange, hydrogen bonding, and electrostatic attraction. This study highlights the important role of iron-bearing minerals in soil carbon sequestration and demonstrates how different mineral alter soil DOM composition, potentially influencing the cycling of organic carbon in terrestrial systems.

The Clay-SRB (sulfate-reducing bacteria) system: Dissolution and fractionation of REY

Rare earth elements (REYs) originate from the weathering of parent granite, whose clay-sized fractions are pivotal in the regolith-hosted rare earth elements (REEs) deposits. Regarding microbial action on REY mobilization and fractionation, their patterns remain unclear. Chemical extraction and bio-leaching experiments utilizing sulfate-reducing bacteria (SRB) were performed to exemplify the chemical and microbial effects on REY mobilization among the clay-sized phases. Our results indicate that the REYs occur primarily in the three fractions: i.e., amorphous FeMn phase, crystalline Fe phase, and carbonate in chemical reactors wherein the mineral phase was critical to the adsorption of REY. The 30-day SRB-leaching experiments led to an increase in the percentage of REY from 6% to 45% in the residue phase, implying that the residue phase, RAmor iron phase, and ROrg phase hosted the REYs. The disorder of iron-bearing minerals, formation of iron-organic matters (Fe-OM), and secondary iron-bearing minerals represented a significant bio-leaching mechanism. Compared to chemical extraction, relatively higher MREY and HREY release efficiencies were obtained via bio-leaching, with average LREY/HREY ratios of 1.34–5.91 and 0.2–2.24 in chemical and bio-reactors, respectively. Our findings exhibited high potential microbial effects on the mobilization and fractionation of REY among mineral phases, offering real insights into the biogeochemical processes between minerals and bacteria.

Exploring the Efficiency of Magnetic Separation and Gravity Concentration for Valorizing Pb-Zn Smelter Slag in a Circular Economy Framework.

The presented work offers an innovative process scheme for valorizing Pb-Zn slag, which involves crushing, grinding, and separation techniques to concentrate valuable components (non-ferrous metals). This methodology could have a significant impact on the global beneficiation of metallurgical slags since it is significantly more simple, environmentally friendly, and cost-effective than standard pyro- and hydrometallurgical procedures. According to previous physicochemical and mineralogical studies, Pb-Zn slag is a valuable secondary raw material. This inhomogeneous technogenic resource contains substantial amounts of non-ferrous metals (Pb, Zn, Cu, and Ag). However, laboratory tests have indicated that the Pb-Zn slag contains highly uneven amounts of valuable metals, ranging from several g/ton to tens of g/ton. The main issue is that traditional metallurgical procedures for releasing beneficial elements are not commercially viable since the elements are "trapped" within the amorphous aluminosilicates or intergrowths of alloy grains and glassy phases. Gravity concentration (Wilfley 13 shaking table) and magnetic separation (Davis separator and disk separator) were used to obtain the final concentrate following comminution and grindability testing. The gravity concentration proved more effective. Namely, magnetic separators could not process nor adequately separate beneficial non-ferrous elements because they were merged together with iron-bearing minerals and aluminosilicates in amorphous Pb-Zn slag grains. With the gravity concentration approach, 12.99% of the processed slag belonged to ∆T fraction (concentration of non-ferrous metal alloys), while remaining 87% corresponded to the tailings fraction (∆L). The total amounts of recovered Pb, Zn, Cu, and Ag from ∆T and ∆L fractions were 5.28%, 6.69%, 0.58%, and 76.12 ppm and 1.22%, 6.05%, 0.43%, and 15.26 ppm, respectively. This streamlined approach to valorizing Pb-Zn slag can reduce the need for hazardous chemicals used in hydrometallurgical refinement operations, as well as the extremely high temperatures required for pyrometallurgical processing. This is the first study to investigate the viability of this novel methodology, which involves the direct examinations of the Pb-Zn slag feed with various alternative technologies for separation and concentration. After extracting the valuable metals, the amorphous aluminosilicate part of the Pb-Zn slag can be reapplied as an alternative raw material in the building sector, adding to the circularity of the suggested approach.

Constraints on the spin-state transition of siderite from laboratory-based Raman spectroscopy and electrical conductivity under high temperature and high pressure

The vibrational and electrical transport properties of natural siderite are systematically investigated by means of in-situ Raman spectroscopy and alternating current impedance spectroscopy under conditions of 0.6–55.6 GPa, 298–873 K and different hydrostatic environments using a diamond anvil cell (DAC). Upon non-hydrostatic compression, all of these observable characteristic variations of siderite including the appearance of three absolutely new Raman peaks (L’, v4′ and v1′), the disappearance of Raman peaks (T, L and v4) and the discontinuity in the pressure-dependent electrical conductivity can provide robust evidence of electronic spin transitions of Fe2+ from high-spin to mixed-spin to low-spin states at the respective pressures of 42.5 GPa and 48.5 GPa. As far as hydrostatic condition, the electronic spin states from high-spin to mixed-spin to low-spin states occurred at the higher pressures of 45.7 GPa and 50.4 GPa, respectively, which implied the highly sensitive hydrostaticity of electronic spin transition pressures. Upon decompression, the reverse electronic spin transitions from low-spin to mixed-spin to high-spin states were detected at the respective pressures of 47.2 GPa and 28.7 GPa under non-hydrostatic condition, and as well as at the pressures of 49.4 GPa and 25.1 GPa under hydrostatic condition, respectively. The huge pressure hysteresis of 13.8 GPa and 20.6 GPa for the electronic spin state transition was revealed under non-hydrostatic and hydrostatic environments, respectively. In order to explore the effect of temperature on the electronic spin transition, a series of electrical conductivity experiments on siderite were performed over the temperature range of 323–873 K under conditions of three typical pressures of 47.7, 49.8 and 51.6 GPa. Furthermore, the functional relationships between the temperature and pressure describing the high-spin to mixed-spin to low-spin transitions for siderite were successfully established: P1 (GPa) = 39.318 + 0.015 T (K) and P2 (GPa) = 41.277 + 0.018 T (K), respectively. In conclusion, our acquired phase diagram of the electronic spin transition on siderite is beneficial to deep insight into the electronic spin behavior for those of iron-bearing carbonate minerals under high-temperature and high-pressure conditions.

Iron Removal from Low-Grade Pyrophyllite Ore by Microwave Irradiation and Dry Magnetic Separation

Owing to its unique properties, pyrophyllite is an economical alternative to many minerals in different applications. The presence of iron-bearing minerals in Saudi pyrophyllite hampers its industrial uses. The aim of this study was to examine the removal of iron from Saudi low-grade pyrophyllite ore using two approaches. The first approach involves dry high-intensity magnetic separation, whereas the second approach involves microwave pretreatment of the ore before dry magnetic separation. For the first approach, the studied operating parameters were roll speed; feed rate, field intensity, and feed particle size. For the alternative approach, microwave treatment followed by dry magnetic separation, the microwave irradiation time and the magnetic field intensity were studied. The results show that the combined microwave treatment and dry separation method could provide high-purity pyrophyllite for filler industries. Microwave irradiation for 30 min was optimal to change impurity phases (i.e., pyrite, hematite) into ferromagnetic phases in microwave-treated pyrophyllite samples. At a magnetic field intensity of 2000 Gauss, the 30 min microwave-irradiated pyrophyllite sample achieved an iron recovery of 11.2% in non-magnetic fractions, with a removal efficiency of 89% with an alumina recovery of 91.31%.

Effect of iron bearing minerals on iron ore processing

In the current study, elemental analysis and microscopic investigations were conducted to characterize the minerals present in an iron ore sample. The iron content was below 24%, with the dominant iron-bearing minerals being hematite and magnetite. Consequently, gravity and magnetic separation methods were employed to enhance the iron content. However, the processing results less than what was expecting due to incomplete sample characterization. The sample was further analyzed using quantitative X-ray diffraction analysis. This more comprehensive examination revealed additional iron-bearing minerals as goethite, ankerite, and limonite. The behavior of these minerals likely contributed to the unsuccessful separation process which was thoroughly explored in this article. Understanding the mineralogical composition of iron ores is paramount for optimizing processing operations and achieving successful outcomes.

Iron species and sulfur isotopic compositions of authigenic pyrite in deep-sea sediments at southern Hydrate Ridge, Cascadia margin (ODP Leg 204): implications for non-steady-state depositional and diagenetic processes

Two accretionary sediment sequences from Sites 1245 and 1252 recovered during Ocean Drilling Program (ODP) Leg 204 at southern Hydrate Ridge were investigated to explore the response of geochemical partitioning of iron and sulfur isotopic composition of authigenic pyrite to non-steady-state depositional and diagenetic scenarios. Five iron species were characterized by a modified sequential extraction procedure that covers almost all iron-bearing minerals in sediment cores, including: (1) iron-bearing carbonates, mainly siderite; (2) ferric (hydr)oxides, probably ferrihydrite and/or lepidocrocite; (3) magnetite; (4) iron-bearing silicates; and (5) pyrite. Highly reactive iron has been accumulated for a long-term steady-state history and its pyritization, to varying degrees, is limited by availability of dissolved sulfide. This causes pyrite and siderite occurred in the same sedimentary layer and shows an inverse relationship between their concentrations. From this, their proportions to highly reactive iron can be chosen for evaluating the degree of sulfidization. A significant change in sulfur isotopic composition of pyrite (-42.4 to +16.8‰ VCDT) indicates that the steady-state conditions are dramatically limited, where the δ34S values higher than -20‰ may result from an upward shift of SMT zone close to the seafloor or a sudden, massive depositional event. To explain the downcore sulfidization effects and pyrite δ34S values, we developed two categories of conceptual scenarios based on variations in sedimentation rate and methane flux. The geochemical features similar to those derived from each scenario were searched in the sediment columns and the non-steady-state events behind the scenarios were proved to be consistent with the real observations. Thus, iron species and pyrite δ34S values can be regarded as a proxy to differentiate different non-steady-state depositional and diagenetic controls on the sedimentary record.

Selective adsorption mechanism of polyoxyethylene alkyl amine in reverse flotation separation of fayalite and magnetite without depressant

Effective flotation separation of magnetite from iron-bearing silicate minerals is difficult with conventional collectors because of their similar surface properties. In this work, polyoxyethylene alkyl amine (PAE), which is easy to prepare and has high surface activity, was used for the reverse flotation separation of fayalite and magnetite for the first time, and its selective adsorption mechanism was revealed. The micro-flotation tests results show that compared with dodecylamine (DDA), the separation effect of PAE on fayalite and magnetite was significantly improved. When pH was 6.5 and PAE dosage was 20 mg/L, the selective separation of fayalite and magnetite can be achieved by reverse flotation without depressant. The results of zeta potential and contact angle measurement shown that PAE was significantly adsorbed on fayalite compared with magnetite, so the hydrophobicity of fayalite treated by PAE was effectively enhanced. In addition, the differential adsorption of PAE on fayalite and magnetite was further verified by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulation, where PAE was adsorbed on the surface of fayalite by electrostatic adsorption and hydrogen bonding, while electrostatic repulsion caused PAE to be removed from the surface of magnetite. The angle between the ethylene oxide chains of PAE at adsorption equilibrium reflects the stress state of NH+ and –OH. Therefore, the selective flotation separation of magnetite and fayalite was realized based on the electrical difference of mineral surface and PAE structural characteristics.

Production of Coal Fines in Deep Coal Seam via Morphologic, Flow-Channel, Mineral Analyses: Evidence from Coalbed Methane Wells in the Qinshui Basin.

During the development of deep coalbed methane (CBM), the production of coal fines is common and suppresses the yield of CBM. This work takes the deep CBM wells in the Qinshui Basin as a case study, and the output, composition, morphology, and sources of coal fines were investigated through scanning electron microscopy, X-ray diffraction, proximate analysis, and particle size measurement including image analysis, laser diffraction, and dynamic light scattering. The results indicate that, in comparison with shallow CBM wells, deep wells produce a greater quantity of coal fines which are darker in color and have smaller particle sizes, with the majority being less than 10 μm. The coal fines exist predominantly as aggregates that contained the iron-bearing and clay minerals. Based on the Liddinger particle settling model, the water production volume required for the coal fines to return to the surface in the Wuxiang block was calculated to be 8.55 m3/d. This work can provide a scientific basis for the prevention and control of coal fines in deep CBM wells.

Microbially-mediated reductive dissolution of Fe-bearing minerals during freeze-thaw cycles

Constraining the role of microbes in the structural iron (Fe) reduction of iron-bearing minerals improves our understanding of sediments and ice sheets as a source of dissolved Fe (dFe) to the oceans. However, bio-mediated structural Fe-reduction has yet to be studied in cryospheric environments. Here, we show that the Fe reducing psychrophile bacterium Shewanella vesiculosa, isolated from sea ice in Antarctica, reduced structural Fe in nontronite (NAu-2) and maghemite (γ-Fe2O3), common mineral phases in glacial ice, and marine sediments in Antarctica, during two freeze–thaw cycles (−10 °C to +15 °C), resulting in the release of dFe. The modification of turbostratically disordered nontronite (ferric iron dominant phase) to discrete ordered illite-like structure (ferrous iron dominant phase), and the aggregation of altered small maghemite particles with neoformation of vivianite (Fe3(PO4)2·nH2O) indicated the microbially induced reductive dissolution of nontronite and maghemite, respectively. The biotic Fe-reduction gradually decreased and ceased as the temperature approached freezing (−8 °C), however the rection reactivated in the thawing cycle (−7 to +15 °C). No discernable biotic Fe-reduction was measured for either mineral under freezing conditions, suggesting that temperature limits the activity of the microbes. Further, and regardless of temperatures during two freeze–thaw cycles, Fe-reduction was not observed in abiotic control. Overall, these results highlight the importance of microbially induced Fe reduction during seasonal freeze–thaw cycles of ice and sediments in continuous supplying bioavailable dFe to cryospheric environments and the often Fe-limited polar oceans.