High Fe Content Research Articles

Structure and Oxidation Behavior of NiAl-Based Coatings Produced by Non-Vacuum Electron Beam Cladding on Low-Carbon Steel

NiAl-based intermetallic coatings were obtained using non-vacuum electron beam cladding on low-carbon steel. The structure of the coatings was investigated using optical microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD). The coatings mostly consisted of grains elongated perpendicular to the substrates, with a strong <100> texture along the grain growth direction. The coatings contained about 14 at. % Fe, which appeared due to the partial melting of the steel substrate. At the bottom of the coatings, an inhomogeneous mixing zone with an increased concentration of Fe was formed; at the “substrate–coating” interface, a thick layer with a Fe50-Ni25-Al25 at. % composition was observed. The samples exhibited weight gains of 0.1, 0.8, 2.14, and 3.4 mg/cm2 after 100 h of oxidation at 700, 800, 900, and 1000 °C, respectively. The oxide layer contained α-Al2O3 and θ-Al2O3, and the presence of iron atoms contributed to the formation of a small amount of spinel. During the oxidation process, a layer with a high Fe content (~60 at. %) formed along the boundary between the oxide film and the NiAl-based material, which had a positive effect on the formation of a non-porous “oxide–coating” interface.

Effect of B addition on the formation of Fe-rich phases in Al-Si-Fe alloys

Boron (B) is an effective grain refiner in Al-Si alloys, but the mechanism responsible for the effect of B on the formation and growth of Fe-rich phases is still in debate. In this paper, we used in-situ synchrotron X-ray radiography, combined with optical microscopy, scanning electron microscopy, thermodynamics and first-principles calculations, to study the influence of B on the nucleation and growth of Fe-rich phases in Al-7Si-xFe (x = 1.2–3.0) alloys. The results showed that B had an excellent influence on the grain refinement of Al-7Si-1.2Fe alloys, but it had no obvious effect on the morphology and distribution of Fe-rich phases due to the eutectic reaction to form Al-AlB2. B had a certain refining effect on primary Fe-rich phases in Al-Si-Fe alloys with high Fe content (≥2.36 wt. %), but it cannot completely inhibit the formation of these plate-like Fe-rich phases. The in-situ synchrotron X-ray radiography results showed that the addition of B significantly reduced the formation temperature of primary Fe-rich phases. First-principles calculations showed that the adsorption energy of B on the nucleation sites , e.g., α-Al2O3 (0001), was significantly higher than that of Fe, which inhibited the nucleation of the primary Fe-rich phase above the Al-AlB2 eutectic temperature and promoted its undercooling of nucleation. Furthermore, many α-Al nuclei formed during the transition to the Al-AlB2 eutectic; their subsequent growth hindered the development of the primary Fe-rich phase. The results of this study provide insights for designing new recycled Al-Si alloys and fundamental knowledge of Fe-rich phase modification by B addition.

KNO3, Nano-Zn, and Fe Foliar Application Influence the Growth and Physiological Responses of Aloe vera under Salinity

Aloe vera L. is a perennial drought-tolerant plant that is commonly used in the pharmaceutical, food, and cosmetic industries. To evaluate the effects of the foliar application of KNO3, nano-Zn, and Fe (0 and 2 mgL−1) on Aloe vera plants under NaCl salinity stress (0, 50, 100 mM), a factorial experiment was conducted based on a completely randomized design. The results revealed that foliar applications influenced the root dry weight. The chlorophyll b content was affected by the salinity plus the foliar application. The total soluble solids content, chlorophyll a, phenolics, and flavonoids of the leaves, the gel content, catalase and superoxide dismutase activity, malondialdehyde, proline, and mineral nutrients content were impacted by the treatments as well. The highest values for the gel content (0.37 g per leaf) and plant dry weight (13.1 g per pot) were recorded at 0 mM NaCl + KNO3 + nano-Fe. The top K/Na ratio (35.2), and the largest K (69 g kg−1), P (6.6 g kg−1), Ca (31 g kg−1), and Mg (2.5 g kg−1) contents were recorded after the 0 mM NaCl + KNO3 treatment. The highest Fe content (383 g kg−1) was observed with 0 mM NaCl + nano-Fe treatment, and the maximum Zn content (37.6 mg kg−1) was measured after the 0 mM NaCl + nano Zn treatment. One hundred mM NaCl increased the malondialdehyde and Na contents. The largest amount of catalase activity was measured after the 50 mM NaCl + KNO3 + nano-Zn treatment. Salinity stress had adverse effects on the growth and physiological responses of Aloe vera. However, the foliar application of KNO3, nano-Zn and Fe mitigated the damaging effects of salinity. The results from more detailed studies would be advisable for pioneer farmers and the agricultural sector.

Hydrogeochemical characterization of groundwater and their associated potential health risks.

The present study assessed the human health risk exposure from the consumption of poor quality groundwater in the Lucknow area, a part of Central Ganga alluvial plain in India. Around 27 (n = 27) groundwater samples were collected from the study area. The analytical results of the samples (n = 27) collected indicate silicate and carbonate weathering is the dominant process along with cation exchange, sulfide oxidation, and reverse ion exchange. The type of groundwater is Ca2-Na-HCO3- type having all cations and anions within permissible WHO limits except for iron (Fe2+) and nitrate (NO3-). The high concentrations of Fe2 and NO3- in samples indicate the possibility of a non-geogenic point source for the same in an urban-influenced environment. The ionic concentration of dissolved constituents is used in weighted overlay analysis to generate the water quality index (WQI). WQI indicates that most urban areas (~ 98.52%) have fallen in the good to excellent category except few situated in the highly populated parts of Lucknow. The ionic concentrations of Fe2+ and NO3- have been further used to estimate human health risk by integrating regional urban population density data in Lucknow. The risk map shows alarming risks in the west-central part, where nearly ~ 35% of the total area is at moderate to high health risk.

Self-Assembled Multiphase Nanocomposite SrCo1–xFexO3-δ Thin Films with Voltage-Controlled Magnetism for Spintronic Applications

SrCo1–xFexO3-δ (SCFO) grown on SrTiO3 substrates using pulsed laser deposition forms either a single-phase film or a two-phase self-assembled nanocomposite film depending on the oxygen partial pressure, PO2. A high PO2 of 150 mTorr during growth promotes phase separation of SCFO into a nanocomposite comprising Co oxide pillars embedded epitaxially in a Fe-rich SCFO matrix made up of brownmillerite and oxygen-deficient perovskite, despite the average composition of Sr/(Co + Fe) = 1. The SCFO matrix in the nanocomposite consists of a brownmillerite structure at a high Co content and an oxygen vacancy ordered perovskite at a high Fe content. In contrast, single-phase SCFO films grow at 20 mTorr. Ionic liquid gating of the nanocomposites oxidizes brownmillerite into perovskite with interlayer defects and renders the matrix phase magnetic with a saturation magnetization of 200 emu cm–3 at 173 K when x = 0.30.

Rhyolitic melt production in the midst of a continental arc flare-up—The heterogeneous Caspana ignimbrite of the Altiplano-Puna volcanic complex of the Central Andes

Abstract The ~5 km3, 4.54–4.09 Ma Caspana ignimbrite of the Altiplano-Puna volcanic complex (APVC) of the Central Andes records the eruption of an andesite and two distinct rhyolitic magmas. It provides a unique opportunity to investigate the production of silicic magmas in a continental arc flare-up, where small volumes of magma rarely survive homogenization into the regional magmatic system that is dominated by supereruptions of monotonous dacitic ignimbrites. The fall deposit and thin flow unit that record the first stage of the eruption (Phase 1) tapped a crystal-poor peraluminous rhyolite. The petrological and geochemical characteristics of Phase 1 are best explained by partial melting of or reheating and melt extraction from a granodioritic intrusion. Phase 2 of the eruption records the emplacement of a more extensive flow unit with a crystal-poor, fayalite-bearing rhyolite and a porphyritic to glomeroporphyritic andesite containing abundant plagioclase-orthopyroxene-Fe-Ti oxide (norite) glomerocrysts. The isotopic composition of Phase 2 is significantly more “crustal” than Phase 1, indicating a separate petrogenetic path. The mineral assemblage of the noritic glomerocrysts and the observed trend between andesite and Phase 2 rhyolite are reproduced by rhyolite-MELTS–based models. Pressure-temperature-water (P-T-H2O) estimates indicate that the main (Phase 2) reservoir resided between 400 and 200 MPa, with the andesite recording the deeper pressures and a temperature range of 920–1060 °C. Rhyolite phase equilibria predict an estimated temperature of ~775 °C and ~5 wt% H2O. Pressures derived from phase equilibria indicate that the rhyolite was extracted directly from the noritic cumulate at ~340 MPa and stored at slightly shallower pressures (200–300 MPa) prior to eruption. The rhyolite-MELTS models reveal that latent-heat buffering during the extraction and storage process results in a shallow liquidus during the extensive crystallization that produced a noritic cumulate in equilibrium with a rhyodacitic residual liquid. Spikes in latent heat facilitated the segregation of the residual liquid, creating the pre-eruptive compositional gap of ~16 wt% SiO2 between the andesite and the Phase 2 rhyolite. Unlike typical Altiplano-Puna volcanic complex (APVC) magmas, low fO2 conditions in the andesite promoted co-crystallization of orthopyroxene and ilmenite in lieu of clinopyroxene and magnetite. This resulted in relatively high Fe concentrations in the rhyodacite and Phase 2 rhyolite. Combined with the co-crystallization of plagioclase, this low oxidation state forced high Fe2+/Mg and Fe/Ca in the Phase 2 rhyolite, which promoted fayalite stability. The dominance of low Fe3+/FeTot and Fe-Ti oxide equilibria indicates low fO2 (ΔFMQ 0 − ΔFMQ − 1) conditions in the rhyolite were inherited from the andesite. We propose that the serendipitous location on the periphery of the regional thermal anomaly of the Altiplano-Puna magma body (APMB) permitted the small-volume magma reservoir that fed the Caspana ignimbrite eruption to retain its heterogeneous character. This resulted in the record of rhyolitic liquids with disparate origins that evaded assimilation into the large dacite supereruption-feeding APMB. As such, the Caspana ignimbrite provides a unique window into the multi scale processes that build longlived continental silicic magma systems.

Effect of Fe and C Contents on the Microstructure and High-Temperature Mechanical Properties of IN625 Alloy Processed by Laser Powder Bed Fusion.

Two alloys with different Fe and C contents were studied to assess the influence of their compositions on the microstructure and mechanical properties of Ni-based Inconel 625 superalloy processed by laser powder bed fusion and subjected to stress relief annealing (870 °C) and a solution treatment (1120 °C). It was concluded that the alloy with a higher Fe content (~4 wt.% as compared to ~1 wt.%) manifests a greater propensity to segregate Nb and Mo elements during printing and form δ phase particles during the stress relief annealing. On the other hand, the alloy with a higher C content (~0.04 wt.% compared to ~0.02 wt.%) exhibits a greater tendency to form M6C carbides during the solution treatment. No effects of the Fe and C content variations on the room temperature mechanical properties were observed. On the contrary, an increase in the C content resulted in a 40% lower high-temperature (760 °C) ductility of the laser powder bed fused and post-processed IN625 alloy, without affecting its strength characteristics.

Lithostratigraphy, Origin, and Geodynamic Setting of Iron Formations and Host Rocks of the Anyouzok Region, Congo Craton, Southwestern Cameroon

In Cameroon, most of the iron formation occurrences reported are found within the Nyong and Ntem Complexes. The Anyouzok iron deposit is located in the Nyong Complex greenstone belts, which represent the NW margin of this Congo craton. The main lithological units comprise the iron formations (IFs) unit, consisting of banded IFs (BIFs) and sheared BIFs (SBIFs), and the associated metavolcanic rocks unit consisting of mafic granulite, garnet amphibolite, and biotite gneiss. Within the Anyouzok area, BIFs are rare, while SBIFs are ubiquitous. This study reports the petrography, mineralogy, and whole rock geochemistry of IFs and interbedded metavolcanic rocks of the Anyouzok iron deposit. The abundance of cavities, higher Fe contents (49.60–55.20 wt%), and strong Eu anomalies (Eu/Eu* = 2.14–3.17) within the SBIFs compared to the BIFs suggest that SBIFs were upgraded through post-depositional hydrothermal alteration activities. REE signatures indicate the contribution of both seawater and hydrothermal fluids during BIFs precipitation. Mafic granulite and garnet amphibolite protoliths were derived from the partial melting of a metasomatized spinel lherzolite depleted mantle source. The overall compositional variations of the Anyouzok IFs and interbedded metavolcanic rocks endorse an Algoma-type formation deposited in the back-arc basin under suboxic to anoxic conditions.

Formation of polymetallic ores in the metasedimentary rocks of Rangpo area, Sikkim Lesser Himalaya, India: Mineralogical and geochemical attributes

Present work investigates the ore mineralogy, geochemistry of host metasedimentary rocks, and the mineral chemistry of the main sulphide minerals, namely, sphalerite, chalcopyrite, galena, and pyrite from the Rangpo sulphide mineralization, Sikkim. Based on the textural relationships of the oxide and sulphide minerals such as mutual boundary, exsolution blebs, and replacement features, three stages including two stages of primary ore mineral formation, and an alteration stage of secondary mineral development is established. Oxide and sulphide minerals predominantly magnetite, chalcopyrite, sphalerite, galena, pyrrhotite, and cobaltite occur as stage‐I ore minerals, and the sulphide minerals namely galena, pyrrhotite chalcopyrite, arsenopyrite, sphalerite, and pyrite are identified as stage‐II minerals. The alteration minerals malachite and azurite represent stage‐III. The geochemistry of host metasedimentary rocks is characterized by SiO2 in the range of 53.28 to 85.62 wt%, Mg# values between 25.48 and 49.60, MgO and K2O having a strong negative correlation with SiO2, high values of Zr/Sc (32.5) versus Th/Sc (3.44), and enrichment of trace elements like Cr (30–87 ppm), V (27–81 ppm), Ni (13–49 ppm), and Sc (3–12 ppm). The Th/Sc versus Zr/Sc, K2O/Na2O versus SiO2, and Th/Co versus La/Sc plots attribute that the host metasedimentary rocks are recycled sediments largely of passive continental margin with a felsic source. However, the Mg# versus SiO2 and K2O/Na2O versus SiO2 point to the incorporation of mantle material from the orogenic margin, possibly arc‐related and mafic in nature. The features such as the mineral assemblage, the simultaneous crystallization shown by mutual boundaries and exsolution blebs, and the mineral chemical data of ore minerals favour a high‐temperature hydrothermal environment of ore deposition. This inference is substantiated by general high Fe concentration in sphalerite and other ore minerals, 800 to 2,400 ppm Cd in sphalerite, Ag and Sb in galena from 1,000 to 2,500 ppm and 400 to 800 ppm respectively, and noticeable Ag in chalcopyrite. The inferred depositional and tectonic environment of host metasedimentary rocks, the petrographic features of ores, and their mineral chemical data altogether invoke that the Rangpo ore mineralization in metasedimentary rocks was formed at high temperature in an environment where mafic mantle material from the active arc was amalgamated with the passive margin sediments derived from the felsic source rocks.

Nature and evolution of diagenetic fluids in the deeply buried Cambrian Xiaoerbulake Formation, Tarim Basin, China

Significant amounts of petroleum are found in the deeply buried Cambrian Xiaoerbulake Formation in the Tarim Basin. However, limited understanding of origin of diagenetic fluids hampers petroleum exploration. In this study, petrological and high-resolution geochemical methods have been performed to understand the origin and evolution of diagenetic fluids, and their effects on the formation of dolostone reservoir. The Xiaoerbulake Formation is characterised by microbialites. The matrix is characterised by modern seawater-like rare earth element and yttrium (REY) patterns and δ18O values of −6.02 ± 2.11‰ Vienna Pee Dee Belemnite (VPDB). Fine-crystalline dolomite cements have similar δ13C values and heavy rare earth element enrichment patterns to that of matrix dolomite, yet with lower δ18O values of −7.47 ± 1.2‰ VPDB. In the deep-burial regimes, medium- to coarse-crystalline dolomite cements and saddle dolomites were precipitated at temperatures of 90–120 and 130–190 °C, respectively, lower δ18O values, distinct middle rare earth element enrichment, and high Fe and Mn contents compared with matrix and fine-crystalline dolomite cements. These imply thermochemical reduction of Fe- or Mn-rich oxides and/or hydrothermal fluids. Compared with other types of dolomite cements, calcite cements are characterised by low δ13C values (as low as −6‰ VPDB), light rare earth elements enrichment and significantly elevated Y/Ho ratios (86 ± 59.3), likely related to the oxidation of organic matter during thermochemical sulfate reduction (TSR). Consequently, diagenetic fluid may have evolved from: Cambrian seawater, meteoric water, shallow-buried seawater-dominated pore water, medium-deep-buried ferrous-rich pore water, lately high-salinity hydrothermal fluid-dominated pore water and finally to acidic fluids related to TSR dissolution. Reservoir quality is enhanced by hydrothermal pulses and TSR in deep-burial settings. This study is significant for those concerned with the formation of deep-buried carbonate reservoirs.

The Middle Paleozoic Magmatism of the Central Tuvinian Trough (Eastern Altai–Sayan Fold Area): Petrogenesis, Tectonics, and Geodynamics

Abstract —The Tuvinian trough is one of the large grabens of the rift system formed in the Devonian–Carboniferous in the eastern part of the Altai–Sayan fold area. Based on the results of comprehensive studies, the age was refined, and the geochemical features of igneous rocks formed during two stages of tectonic and magmatic activity within the Tuvinian trough were studied. In the Early Devonian (397 Ma, Emsian), at the stage of the initiation of the Tuvinian trough in the stretching setting, the volcanic and subvolcanic rocks of the Kendei Formation formed, which make a bimodal series. The Early Devonian igneous rocks of mafic composition have geochemical features of both intraplate (low values of Mg#, high contents of K2O (up to 2.9 wt.%) and TiO2 (up to 2.2 wt.%), and enrichment in LREE relative to HREE) and suprasubductional (enrichment in Pb and Sr and depletion in Ta and Nb) formations and are characterized by high values of εNd(T) (+5.9 to +8.0). They are assumed to have formed from a mixed source including the depleted mantle and components modified by subduction. The Early Devonian felsic volcanic rocks, which are the extreme member of the bimodal sequence, also combine the geochemical features of rocks of intraplate (high Fe, low Sr, P, and Ti contents, Zr and Hf enrichment) and island arc (Ta and Nb depletion) origin. These rocks with εNd(T) values from +4.0 to +7.0 resulted from the melting of a heterogeneous source corresponding in composition to the lower continental crust. In the Middle Devonian–early Carboniferous (390–350 Ma), the Tuvinian rift trough evolved into a mature stage, at which the mafic rocks of the Torgalyk complex were intruded. The Middle Devonian–early Carboniferous mafic rocks are similar in isotope and geochemical characteristics, including the Nd isotopic composition (εNd(T) = +6.7), to the Early Devonian formations. In contrast to the Early Devonian rockes, the magmas for the Middle Devonian–early Carboniferous mafic rocks were generated a relatively homogeneous mantle source without significant metasomatic transformations, the features of which are better manifested in the Kendei rocks.

Groundwater arsenic poisoning in a primary educational institution: health risks to school-going children

This study aimed to estimate arsenic (As) and iron (Fe) content in tubewell water (n = 58) in primary educational institutions and subsequently assess the health risks to school-going children. Results described that the As concentration ranged between 0.002 and 0.994 mg L−1 with an average value of 0.044 mg L−1; which exceeded the World Health Organization (WHO) provisional guideline value of 0.01 mg L−1. Similarly, the Fe content varied from 0.05 to 10 mg L−1 averaging to 2.84 mg L−1. Samples of 55.17% contained a greater As concentration than 0.01 mg L−1 and 18.97% greater than Bangladesh drinking water quality (BDWQ) standard of 0.05 mg L−1, respectively. Meanwhile, 75.86% of samples contained a higher Fe concentration than the maximum Bangladesh permissible limit of 1 mg L−1. Health risk assessment indicated that girls are more vulnerable than boys are. The average hazard quotients (HQs) for As intake through drinking water were 6.01 ± 17.85 and 7.41 ± 22.03 for boys and girls, respectively, implying non-carcinogenic health risks to both genders. The HQs for Fe intake were less than threshold value of 1 indicating no health issues may arise from Fe intake alone. However, consumption of As and Fe may trigger health risks to students as indicated by the hazard index (HI), which was higher than 1. The average cancer risk (CR) values for both boys (0.0027 ± 0.008) and girls (0.0033 ± 0.0099) exceeded the threshold limit of 10–6–10–4, suggesting a possibility of lifetime cancer risks to the school-going children. Consequently, school authorities should find alternative ways to ensure safe drinking water for school-going children to avoid possible cancer and non-cancer health risks through consumption of As-poisoning water.

Biogeochemical processes of arsenic transformation and redistribution in contaminated soils: Combined effects of iron, sulfur, and organic matter

• As(V)-reducing bacteria may reduce and release arsenic bound to all soil fractions. • The redistribution pathway of released As is dominated by soil Fe and S contents. • In soil with low Fe, As sequestration depends largely on the formation of As-sulfide. • In Fe-rich soil, released As preferentially adsorb on Fe-oxides, despite S content. • Microbial reduction of solid-phase As(V) was enhanced in organic-rich soils. Microbially-mediated mobilization of soil arsenic (As) is greatly influenced by the soil properties. However, in soils with contrasting iron (Fe), sulfur (S), and organic matter (OM) contents, the biogeochemical pathways controlling As transformation and distribution remain unclear. Using sequential soil As extraction and X-ray absorption spectroscopy (XAS), we investigated the causal mechanisms of As reduction and redistribution in five soils during microbial incubation. Incubation of arsenate (As(V))-reducing bacteria resulted in a significant arsenite (As(III)) release (21.6–61.9% of total soil As (As total )). Thereafter, the re-immobilization of released As(III) was controlled by contrasting biogeochemical pathways, which were mainly dominated by soil Fe and S. For soil with high Fe content (191.1 g/kg), As immobilization is attributed to As(III)-readsorption by (neoformed) Fe-(oxyhydr)oxides, despite the presence of abundant S (10.3 g/kg); while in soils with relatively low Fe content (25.9–35.6 g/kg) and high S content (1.4–1.7 g/kg), As-sequestration depends largely on As-sulfide formation (5–47% of solid-phase As), including realgar and orpiment-like phases. In contrast, released As remains in solution in soils with relatively low Fe (27.5–52.4 g/kg) and S contents (0.6–1.0 g/kg). Arsenic-XAS results show that all soil As fractions, including residual As(V), can potentially be reduced (34–92% of As total ), and solid-phase As(V) reduction was enhanced at higher OM content. Collectively, these results elucidate the dominant biogeochemical pathways controlling As fate in soils with different Fe, S, and OM contents.

Effect of Fe(III) Modification on the Phosphorus Removal Behavior of Ce(III) Carbonate Adsorbents.

Excessive phosphorus (P) in water is the main reason for eutrophication, which has been a global problem for many years. For the adsorption treatment of phosphorus-containing wastewater, adsorbents are key research topics. In this study, we develop the synthesis of a series of Ce/Fe adsorbents by modifying the commercial cerium carbonate with Fe2(SO4)3. By conducting comprehensive analysis with XRD, FTIR, and SEM, we find that the amorphous granular structure and large chunky structure created by the high and low Fe content, respectively, both had a negative effect on the adsorption capacity of phosphate. Among different adsorbents, Ce/Fe-15/3, with Ce loading of 28.33 wt % and Fe loading of 5.66 wt %, exhibits high P adsorption capacity of 58 mg P/g (in pH = 7, 30 mg P/L solution). It also demonstrates excellent selectivity toward phosphate adsorption in Cl–, SO42–, and NO3– solution (up to 20 times of the phosphate molarity) and good adsorption stability in acidic environments (pH = 3–6). The adsorption behavior of Ce/Fe-15/3 can be modeled well by the Langmuir model and pseudo-second-order (PSO) model. By conducting the XPS analysis, we conclude that the adsorption mechanism is a combination effect of Ce/PO43– and Fe/PO43– chemical interactions.

Experimental serpentinization of iron-rich olivine (hortonolite): Implications for hydrogen generation and secondary mineralization on Mars and icy moons

Serpentinization of olivine-rich ultramafic rocks is recognized to have been widespread across the solar system throughout its history, with substantial implications for the chemical and physical properties of planetary lithospheres, atmospheric compositions, and astrobiology. One especially significant product of serpentinization is molecular hydrogen (H2), whose generation is closely linked to the oxidation of Fe as serpentinization proceeds. While numerous experimental simulations of serpentinization have been conducted over the years, these studies have been performed almost exclusively using reactant minerals that contain relatively high Mg and low Fe contents representative of terrestrial mantle rocks. In contrast, very few studies have been conducted with the more Fe-enriched mineral compositions that may predominate on other solar system bodies. In this study, an experiment was conducted to investigate mineral alteration and H2 generation during serpentinization of Fe-rich olivine (hortonolite; Fo∼62) at 230 °C and 35 MPa. After 3500 h of reaction, ∼55 % of the hortonolite reacted to secondary minerals composed of serpentine (chrysotile) and magnetite. Chrysotile contained proportionally less Fe than the original hortonolite, reflecting the partitioning of some Fe into magnetite; however, it contained substantially more Fe than serpentine precipitated from alteration of Mg-rich, Fe-poor terrestrial mantle olivine (Fo∼90) under the same reaction conditions. Reaction of hortonolite also produced more than four times as much magnetite as Mg-rich olivine. Generation of H2 occurred steadily throughout the experiment, with more than five times as much H2 generated per mole of hortonolite reacted than observed for Fe-poor olivine at the same conditions. The results suggest that serpentinization of Fe-rich ultramafic rocks on Mars and other planetary bodies may have a substantially greater capacity to generate H2 and to precipitate magnetite than their Fe-poor terrestrial counterparts, which would enhance their potential to support H2-based biological communities, contribute to atmospheric warming, and augment local magnetic signatures in planetary lithospheres.

Spectral features of Fe and organic carbon in estimating low and moderate concentration of heavy metals in mangrove sediments across different regions and habitat types

Soil or sediment spectral reflectance do not directly reflect information of spectrally featureless heavy metals. With mangrove sediment samples collected in five regions and four habitat types, this study aimed to explore the spectral features related to spectrally active constituents (Fe and organic carbon (OC)) in estimating low and moderate concentrations of four heavy metals (Cr, Ni, Cu and Pb). A total of 27 modeling strategies using XGBoost (extreme gradient boosting) model were compared for estimating each heavy metal: three types of spectral features (Fe, OC and heavy metal) * three spectral transformation methods (Log(1/R), first derivative (FD) and continuous wavelet transform (CWT)) * three variable selection methods (genetic algorithm (GA), successive projection algorithm (SPA) and recursive feature elimination (RFE)). The results showed that the combination of CWT and RFE was recommended for heavy metal estimation, and the ranking of model accuracy was Cu > Pb > Ni > Cr. The optimal XGBoost model was found using spectral features related to Fe for Cr (RVal2(determination coefficient of independent validation) = 0.42, RMSE (root mean square error) = 0.32 and RPIQ (the ratio of performance to interquartile range) = 1.53) and Cu estimation (RVal2 = 0.87, RMSE = 0.19 and RPIQ = 2.20), spectral features related to OC for Ni estimation (RVal2 = 0.63, RMSE = 0.26 and RPIQ = 2.38) and spectral features related to Pb itself for Pb estimation (RVal2 = 0.82, RMSE = 0.23 and RPIQ = 2.59). Moreover, the XGBoost model transferability across different habitat types outperformed that across different regions and data ranges of Fe and OC. We conclude that the modeling strategy using spectral features related to spectrally active constituents has great potentials in quantifying low and moderate concentration of sediment heavy metals, and the samples with high Fe concentration (31.62–37.29 g kg−1) are recommended to improve estimation accuracy of low and moderate concentrations of heavy metals, which could provide sampling strategy development and early warning of heavy metal pollution in mangrove ecosystem.

Study on the chemical adsorption of gaseous As2O3 by ash

Arsenic (As) transformation during flue-gas cooling process determines terminal As emission. In this study, the dominant role of chemical adsorption in gaseous As transformed to ash was confirmed. Dynamic curves of As2O3 adsorption by ash at 500–900 °C were obtained. The adsorbed As amount increased linearly with time, far from reaching saturation, and the maximum amount was approximately 10 times the As content in ash collected from power plant dust collectors, indicating that the actual capacity of ash was far higher. Analysis of As form and elemental distribution directly proved that chemical adsorption by ash was mainly through the joint action of Ca and Fe, and its correlation with other components was weak. At 500–900 °C, as temperature increased, the amount of As adsorbed by CaO gradually increased, whereas that of Fe2O3 first increased and then decreased. The adsorption product of CaO was stable, whereas certain forms of products of Fe2O3 released at 800 °C. Therefore, as temperature increased, the amount of As adsorbed by ash with high Fe content first increased and then decreased, reaching a maximum at 800 °C °C, whereas that of ash with higher Ca content kept increasing. The strong adsorption capacity of ash with high Ca and Fe contents helps reduce terminal As emission.

New insights into the archives of redox conditions in seep carbonates from the northern South China Sea

Modern cold seeps are of fluctuant flux, which could result in variabilities of geochemical archives through intensively influencing the redox condition in pore fluids. However, the geochemical archives are not fully understood when the redox condition changes. Here, tubular carbonates from the Shenhu Sea Area were used to reconstruct the formation environment and redox conditions. The moderately negative δ13C values of the carbonates (−40.1‰ to −30.8‰, VPDB) indicate a mixed carbon source of thermogenic and biogenic methane. The low δ18O values (−2.7‰ to 1.0‰, VPDB) suggest a type of 18O-depleted pore fluid possibly influenced by gas hydrate formation. Co-variation of MoEF, WEF, CoEF, and CrEF suggests that high Fe contents in the rims of samples R1 and R2 are induced by Fe (oxyhydr)oxidation enrichment, while the positive correlation between MoEF and Mn/Al ratio indicates that high Mn contents in the rims of samples R3 and R4 are induced by Mn (oxyhydr)oxidation enrichment. The occurrence of Fe or Mn enrichment in the rims and the absence of Fe/Mn enrichment in the cores suggest Fe/Mn (oxyhydr)oxides forming in pore fluid rather than in bottom seawater. The carbonate phases of the rims enriched in Fe (oxyhydr)oxides are dominated by high magnesium calcite, while those of the rims enriched in Mn (oxyhydr)oxides are dominated by aragonite. The occurrence of Fe or Mn (oxyhydr)oxides corresponds to the previously proposed formation depth for the carbonate phase. The occurrence of dissolution textures in these rims indicates episodic oxic conditions, which would facilitate Fe2+/Mn2+ oxidation. We suppose that the Fe2+ and Mn2+ could be supplied through fluid seepage or diffusion from underlying sediments when the flux decreased. Similar archives may be applied to qualitatively reflect the changes of redox conditions in seep systems. Similar scenarios may help us understand the geochemical records in seeps of fluctuant flux.

High pressure-temperature phase equilibrium studies on Martian basalts: Implications for the failure of plate tectonics on Mars

Mars lacks ongoing tectonic activities such as volcanism and mountain-building processes. Modern plate tectonic movements on the Earth's surface are driven primarily by the descent of subducted slabs into the mantle. Slab crust made of dense eclogite metamorphosed from the Mid-Ocean Ridge Basalt provides an important driving force for slab subduction. Thus, mantle convection inside Mars can be hindered if the density contrast between Martian slab crust and the ambient Martian mantle is sufficiently smaller than that of Earth. To evaluate this hypothesis, we carried out high pressure-temperature phase equilibrium experiments on three different Martian basalts: Yamato 980459, NWA 8159, and GUSEV basalt (Humphrey). The GUSEV basalt and NWA 8159 undergo partial or complete melting along the Martian areotherm due to their high Fe content, suggesting that both compositions are geochemically evolved. Yamato 980459, the nearly primitive Martian basalt, on the other hand, would transform to a low-density eclogite at a depth of ∼250 km. The density contrast between a Martian crustal slab made of Yamato 980459, and the ambient Martian mantle is much smaller than that for Earth's mantle. Calculated slab sinking torques and velocities further suggest that sustained buoyancy-driven subduction of thin slabs was unlikely early in Martian history. Additional experiments exploring wider composition and pressure-temperature ranges are needed to fully understand the consequences of Martian mantle compositions and cooling history for the tectonic history of Mars.

The Shallow Magmatic Plumbing System of the Deccan Traps, Evidence from Plagioclase Megacrysts and Their Host Lavas

AbstractWe investigate the shallow plumbing system of the Deccan Traps Large Igneous Province using rock and mineral data from Giant Plagioclase Basalt (GPB) lava flows from around the entire province, but with a focus on the Saurashtra Peninsula, the Malwa Plateau, and the base and top of the Western Ghats (WG) lava pile. GPB lavas in the WG typically occur at the transition between chemically distinct basalt formations. Most GPB samples are evolved basalts, with high Fe and Ti contents, and show major and trace elements and Sr-Nd-Pb isotopic compositions generally similar to those of previously studied Deccan basalts. Major element modeling suggests that high-Fe, evolved melts typical of GPB basalts may derive from less evolved Deccan basalts by low-pressure fractional crystallization in a generally dry magmatic plumbing system. The basalts are strongly porphyritic, with 6–25% of mm- to cm-sized plagioclase megacrysts, frequently occurring as crystal clots, plus relatively rare olivine and clinopyroxene. The plagioclase crystals are mostly labradoritic, but some show bytownitic cores (general range of anorthite mol%: 78–55). A common feature is a strong Fe enrichment at the plagioclase rims, indicating interaction with an Fe-rich melt similar to that represented by the matrix compositions (FeOt up to 16–17 wt%). Plagioclase minor and trace elements and Sr isotopic compositions analyzed by laser ablation inductively coupled plasma mass spectrometry show evidence of a hybrid and magma mixing origin. In particular, several plagioclase crystals show variable 87Sr/86Sri, which only partially overlaps with the 87Sr/86Sri of the surrounding matrix. Diffusion modeling suggests residence times of decades to centuries for most plagioclase megacrysts. Notably, some plagioclase crystal clots show textural evidence of deformation as recorded by electron back-scatter diffraction analyses and chemical maps, which suggest that the plagioclase megacrysts were deformed in a crystal-rich environment in the presence of melt. We interpret the plagioclase megacrysts as remnants of a crystal mush originally formed in the shallow plumbing system of the Deccan basalts. In this environment, plagioclase acquired a zoned composition due to the arrival of chemically distinct basaltic magmas. Prior to eruption, a rapidly rising but dense Fe-rich magma was capable of disrupting the shallow level crystal mush, remobilizing part of it and carrying a cargo of buoyant plagioclase megacrysts. Our findings suggest that basaltic magmas from the Deccan Traps, and possibly from LIPs in general, are produced within complex transcrustal magmatic plumbing systems with widespread crystal mushes developed in the shallow crust.