Fe Fraction Research Articles

Soil organic matter stabilization during early stages of Technosol development from Ca, Mg and pyrite-rich parent material

The mechanisms underlying soil organic matter (SOM) accrual in Technosols are still poorly understood. Here we studied a 20-year chronosequence of three Technosols constructed with dolomitic limestone mining waste: two cultivated with sugarcane (for 3 and 7 years) and one under pasture (for ∼20 years). Through a combination of SOM physical fractionation and wet-chemical extractions, we aimed to unravel the processes driving SOM accumulation in these soils and developed a conceptual model for embryonic soils developed from Ca, Mg and pyrite-rich parent material. Our results revealed that the weathering of comminuted waste rocks (e.g., shale, siltstone) provided 2:1 minerals (especially smectite) to participate in mineral-organic associations. The weathering of primary minerals also promoted the formation of secondary minerals, which interacted with SOM and increased the amount of mineral associated organic matter (MAOM) up to 20 g SOC kg−1. Pyrite oxidation produced highly reactive secondary Fe phases, while the dolomite dissolution increased the concentrations of Ca2+ and Mg2+ and maintained near-neutral pH conditions, favoring the formation of cation-bridges. The progressive increase in the different operational Fe fractions (Fe in organomineral complex, poorly crystalline, and crystalline Fe oxides) along the Technosol chronosequence was strongly correlated with MAOM, highlighting the significant role of Fe in SOM accumulation. Furthermore, we observed substantial increase in particulate organic matter (POM), up to 22 g SOC kg−1, which was associated with increased aggregate formation and stability. These processes collectively contribute to the protection of SOM during early stages of soil development from in Ca, Mg, and pyrite-rich parent material, and thus indicate a high potential for carbon sequestration.

Spatiotemporal Variability in Soil Properties and Composition in Mangrove Forests in Baía de Todos os Santos (NE Brazil)

Soil properties and components in mangrove ecosystems influence their geochemical processes and services. Despite the extensive mangrove areas present in Brazil, few studies focusing on these themes are under development. In this sense, this work aimed to investigate the spatial variability in soil attributes and composition, the geochemistry of Fe, and the isotopic characteristics of organic matter in mangroves in Baía de Todos os Santos (Cacha Prego, Ponta Grossa, Ilha de Maré, Pitinga), which constitutes Brazil’s second largest bay. The soils investigated showed spatial and temporal changes affecting their properties (pH, Eh) and composition (TOC, Fe fractions), as well as clear spatial changes in the redox potential values (+30–+188 mV), with higher values in PT. Soil textures ranged from predominantly sandy (CP, PT, PG: sand, >70%) to a finer granulometry (IM: sand, 33–64%). These characteristics influenced Fe partitioning and organic matter content, with higher TOC and pyrite values observed in IM (FeS2: 2720–9233 mg kg−1; TOC: 4.4–6.6%) and lower sulfide values found in PT, mainly in the dry season (FeS2: 85–235 mg kg−1). The soil δ13C and N/C ratios seem to suggest a mixed origin of organic matter.

Physiological effects of some engineered nanomaterials on radish (Raphanus sativus L.) intercropped with pea (Pisum sativum L.).

Intercropping leguminous plant species with non-legume crops could be an effective strategy to maintain soil fertility. Additionally, the application of nano-Zn and Fe in trace amounts can substantially improve the bioavailable fractionof Zn and Fe. We studied the effect of foliar application of some nanomaterials on the agronomic, physio-biochemical attributes under a radish/pea intercropping system. The radish and pea were sprayed with different nanomaterials (Zn-Fe nanocomposite, nZnO, and nanobiochar) at 0 and 50mg L-1 concentrations. Results indicated that the growth parameters of radish were higher in intercropping than in monocropping, while pea growth was inhibited in intercropping compared with monocropping. The shoot and root length, fresh weight, and dry matter of radish were increased by 28-50%, 60-70%, and 50-56% by intercropping than monocropping. Foliar spray of nano-materials further increased the growth traits of intercropped radish, such as shoot and root length, fresh weight, and dry matter, by 7-8%, 27-41%, and 50-60%, respectively. Similarly, pigments such as chlorophyll a, b, and carotenoids and the concentration of free amino acids, soluble sugars, flavonoids, and phenolics were differentially affected by intercropping and nanomaterials. The yield of the non-legume crop was increased by intercropping, whereas the legume crop exhibited significant growth inhibition due to competitive interactions. In conclusion, both intercropping and foliar spray of nanomaterials could be used as a combined approach to benefit plant growth and enhance the bioavailable Fe and Zn fractions of both crops.

ZnO:Fe nanoparticles with Fe fraction up to 10%mol – growth and characterization

ZnO nanoparticles (NPs) doped with iron were synthesized by the microwave-hydrothermal method using various reagents. The properties of these NPs were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL), cathodoluminescence (CL) measurements. In the article, we discuss the surprising results of optical studies of ZnO:Fe NPs. The phenomenon of luminescence quenching by the magnetic ion, characteristic for bulk materials, was not observed. We examined three potential reasons for this observation.

Screening redox stability of iron rich by-products for effective phosphate immobilisation in freshwater sediments

Iron (Fe) rich by-products can be added to lake or river sediments to immobilise phosphate (PO4) and lower eutrophication risks. These Fe materials differ in mineralogy and specific surface area, hence differing in PO4 sorption capacity and stability under reducing conditions. This study was set up to identify key properties of these amendments in their capacity to immobilise PO4 in sediments. Eleven Fe rich by-products, collected from drinking water treatment plants and acid mine drainage, were characterised. The PO4 adsorption to these by-products was first determined under aerobic conditions and the solid-liquid distribution coefficient KD for PO4 correlated strongly to oxalate extractable Fe content. A static sediment-water incubation test was subsequently used to evaluate the redox stability of these by-products. The reductive processes gradually released Fe to solution and more Fe was release from the amended than from the control sediments. The total Fe release to solution was positively related to ascorbate reducible Fe fractions in the by-products, suggesting that such fractions indicate potential loss of P retention capacity on the long term. The final PO4 concentration in the overlying water was 5.6 mg P L−1 in the control and was successfully lowered by factor 30–420 depending on the by-product. The factor by which solution PO4 was reduced in Fe treatments increased with increasing KD determined under aerobic conditions. This study suggests that efficient by-products to trap P in sediments are characterised by a high oxalate Fe content and a low reducible Fe fraction.

Trace Elements in Soy-Based Beverages: A Comprehensive Study of Total Content and In Vitro Bioaccessibility.

Soy-based beverages are one of the most consumed plant-based beverages, which have been used as a substitute for dairy products. Soy is a source of several nutrients (vitamins, minerals, and phenolic compounds, etc.) and its consumption is usually associated with several benefits, such as the prevention of cardiovascular diseases, cancer, and osteoporosis. However, non-essential trace elements can be found in these beverages. Thus, a comprehensive study concerning trace elements Al, As, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sb, Se, Sn, Sr, and Zn in soy-based beverages was proposed. In vitro digestion allowed to simulate the gastrointestinal juice (bioaccessibility) and the Caco-2 cells culture model was applied for the bioavailability assay. Trace elements measures were performed by inductively coupled plasma optical emission spectrometry (ICP OES). Multivariate analysis classified soy-based beverages according to their soy source (isolate protein, hydrosoluble extract, and beans); Al, Cu, Fe, Mn, Sr, Se, and Zn bioaccessible fractions corresponded to approximately 40%-80% of their total content, and soy-based beverages were found to be a good Fe, Se, and Zn source. However, our results showed risk exposure assessment from daily consumption of one glass of soy-based beverage can contribute to 3.5% and 0.9% of Al Provisional Tolerable Weekly Intake (PTWI) for children and adults, respectively.

Efficiency and mechanism of micro- and nano-plastic removal with polymeric Al-Fe bimetallic coagulants: Role of Fe addition

The occurrence of microplastics (MPs) and even nanoplastics (NPs) in tap water has raised considerable attention. As a pre-treatment and also the most important process in drinking water treatment plants, coagulation has been widely studied to remove MPs, but few studies focused on the removal pattern and mechanism of NPs, especially no study paid attention to the coagulation enhanced by prehydrolysed Al-Fe bimetallic coagulants. Therefore, in this study, polymeric species and coagulation behaviour of MPs and NPs influenced by Fe fraction in polymeric Al-Fe coagulants were investigated. Special attention was given to the residual Al and the floc formation mechanism. The results showed that asynchronous hydrolysis of Al and Fe sharply decreases the polymeric species in coagulants and that the increase of Fe proportion changes the sulfate sedimentation morphology from dendritic to layered structures. Fe weakened the electrostatic neutralization effect and inhibited the removal of NPs but enhanced that of MPs. Compared with monomeric coagulants, the residual Al decreased by 17.4 % and 53.2 % in the MP and NP systems (p < 0.01), respectively. With no new bonds detected in flocs, the interaction between micro/nanoplastics and Al/Fe was merely electrostatic adsorption. According to the mechanism analysis, sweep flocculation and electrostatic neutralization were the dominant removal pathways of MPs and NPs, respectively. This work provides a better coagulant option for removing micro/nanoplastics and minimizing Al residue, which has promising potential for application in water purification.

Contrasting Effects of Nitrogen and Organic Fertilizers on Iron Dynamics in Soil after 38–Year Fertilization Practice

Various environmental factors and anthropogenic practices can affect the Fe biogeochemical cycles in soils. Nitrogen and carbon states are closely associated with Fe dynamics. However, we still have a limited understanding of the complex response of Fe biogeochemical processes to long–term nitrogen– and organic–fertilization regimes. This study investigated the Fe fraction and distribution, as well as the link between Fe and nitrogen/carbon, in bulk soil and in soil aggregates. The results showed that the long–term application of the nitrogen fertilizer increased the contents of water–soluble iron (Ws–Fe) and carbonate–bound iron (Ca–Fe) in the bulk soil and various sizes of aggregates, as well as the iron contents in soybeans. The decreased pH and enhanced Feammox reaction in response to the nitrogen–fertilizer treatments were responsible for the increase in the Ws–Fe and Ca–Fe fractions. By contrast, the long–term application of the organic fertilizer decreased the contents of Ws–Fe and Ca–Fe, while it increased the contents of Ox–Fe and Or–Fe. Moreover, the contents of Ox–Fe and Or–Fe were positively correlated with the organic–carbon contents in the micro–aggregates of 0.053–0.25 mm and &lt;0.053 mm. These results indicated that the long–term use of the organic fertilizer encouraged Fe immobilization in organo–inorganic compounds. However, the application of the nitrogen fertilizer alleviated the Fe retention induced by the organic fertilizer. In conclusion, long–term nitrogen and organic fertilization have contrasting influences on the mineralogy and availability of Fe in soil. This study is useful for understanding the mechanism underlying the interaction between Fe and nitrogen/carbon, as well as Fe’s phytoavailability in response to different fertilization practices in brown soil.

Spatial co-occurrence patterns of benthic microbial assemblage in response to trace metals in the Atacama Desert Coastline.

Taxonomic and functional microbial communities may respond differently to anthropogenic coastal impacts, but ecological quality monitoring assessments using environmental DNA and RNA (eDNA/eRNA) in response to pollution are poorly understood. In the present study, we investigated the utility of the co-occurrence network approach's to comprehensively explore both structure and potential functions of benthic marine microbial communities and their responses to Cu and Fe fractioning from two sediment deposition coastal zones of northern Chile via 16S rRNA gene metabarcoding. The results revealed substantial differences in the microbial communities, with the predominance of two distinct module hubs based on study zone. This indicates that habitat influences microbial co-occurrence networks. Indeed, the discriminant analysis allowed us to identify keystone taxa with significant differences in eDNA and eRNA comparison between sampled zones, revealing that Beggiatoaceae, Carnobacteriaceae, and Nitrosococcaceae were the primary representatives from Off Loa, whereas Enterobacteriaceae, Corynebacteriaceae, Latescibacteraceae, and Clostridiaceae were the families responsible for the observed changes in Mejillones Bay. The quantitative evidence from the multivariate analyses supports that the benthic microbial assemblages' features were linked to specific environments associated with Cu and Fe fractions, mainly in the Bay. Furthermore, the predicted functional microbial structure suggested that transporters and DNA repair allow the communities to respond to metals and endure the interacting variable environmental factors like dissolved oxygen, temperature, and salinity. Moreover, some active taxa recovered are associated with anthropogenic impact, potentially harboring antibiotic resistance and other threats in the coastal zone. Overall, the method of scoping eRNA in parallel with eDNA applied here has the capacity to significantly enhance the spatial and functional understanding of real-time microbial assemblages and, in turn, would have the potential to increase the acuity of biomonitoring programs key to responding to immediate management needs for the marine environment.

Enhancement mechanism of magnetite on the ball-milling destruction of perfluorooctane sulfonate by iron

Zero-valent iron (Fe) is commonly employed as an additive for the mechanochemical destruction (MCD) of organic pollutants. The poly- and perfluoroalkyl substances (e.g., perfluorooctane sulfonate, PFOS) are a class of toxic environmental pollutants that are difficult to effectively degrade due to their thermodynamic and chemical stability. In this study, magnetite (Fe3O4) was applied to improve the milling performance of Fe to PFOS and its promoting mechanisms were emphatically explored. The desulfurization rate was in ahead of the defluorination rate because the C–S bond is less stable than the C–F bonds in PFOS. Fe3O4 had an excellent reinforcement effect on the milling performance of Fe, which was mainly through accelerating the electron transfer as a conductor, reacting with Fe to produce FeO, and facilitating the formation of HO●. During the MCD of PFOS with Fe/Fe3O4 as an additive, HO● played a dominant role in the defluorination process (accounting for >67%). After the elimination of sulfonate group (−SO3−), the produced radical (C7F15CF2●) continued to react through two main pathways: one was the stepwise defluorination after hydrogenation, and the other one was oxidation reaction after alcoholization to yield the corresponding aldehydes and carboxylic acids. The optimum Fe fraction (MFe) was 30%, and air atmosphere was more effective than oxygen and nitrogen conditions. This study helps to comprehensively understand the role of Fe3O4 in defluorination and fills the gap of Fe/Fe3O4 application in the MCD of PFASs.

In Vitro Bioaccessibility and Health Risk Assessment of Arsenic and Zinc Contaminated Soil Stabilized by Ferrous Sulfate: Effect of Different Dietary Components.

Iron-based materials have good stability in reducing the mobility and toxicity of heavy metals, but the behavior and human health risks of heavy metals could be affected by dietary components. This study investigated the effect of typical diets (lettuce, cooked rice and apples) on the bioaccessibility and morphological changes of arsenic (As) and zinc (Zn) in contaminated site after stabilization by ferrous sulfate (FeSO4). The results showed that the bioaccessibility of As and Zn were increased in a co-digestion system of food. The augmented effect on As bioaccessibility mainly occurred in the gastric phase: apple > lettuce > cooked rice (p < 0.05), while the augmented effect on Zn bioaccessibility mainly occurred in the intestinal phase: lettuce > apple > cooked rice (p < 0.05). FeSO4 weakened the dissolution effect of dietary components on As bioaccessibility, and reduced As bioaccessibility in the gastric and intestinal phases by 34.0% and 37.9% (p < 0.05), respectively. Dietary components and Fe fractions influenced the speciation and distribution of As and Zn. FeSO4 reduced the hazard quotient (HQ) and carcinogenic risk (CR) values of the contaminated soil by 33.97% and 33.59%, respectively. This study provides a reference for a better understanding of more realistic strategies to modulate exposure risks of heavy metal-contaminated sites.

Disentangling the pedogenic factors controlling active Al and Fe concentrations in soils of the Cameroon volcanic line

Active Al, Fe and Si (i.e., oxalate extractable fraction: Alo, Feo, Sio) strongly affect soil physical, chemical and biological properties. This study examined the pedogenic factors affecting Alo, Feo and Sio contents across a soil weathering sequence in the Cameroon volcanic line. We investigated the B horizon (∼50-cm depth) from 26 soils formed in basaltic materials at different elevations (110–2570 m) incorporating a wide range of temperature (14–27 °C) and precipitation (1520–3130 mm). The weathering sequence ranged from weakly weathered Andisols in the southwest region grading to strongly weathered Oxisols on the central highlands. We assumed pyrophosphate extractable Al/Fe (Alp/Fep) as organo-Al/Fe complexes, and Sio, (Alo − Alp) and (Feo − Fep) as short-range-order (SRO) minerals. Factor analysis of climatic (e.g., temperature and precipitation/leaching metrics) and soil geochemical properties (e.g., weathering indices) identified three independent factors representing temperature/dry season intensity, weathering degree and precipitation/leaching as the primary determinants of Alo, Feo and Sio concentrations. Organo-metal complexes (Alp and Fep) were negatively correlated with the temperature/dry season intensity factor, whereas the SRO mineral phases (Sio, Alo − Alp and Feo − Fep) were negatively correlated with weathering degree. The precipitation/leaching factor positively correlated with Alo, Feo and Sio. Our analysis infers that low temperature promotes the formation and preservation of organo-Al/Fe complexes, whereas weathering degree is more critical for SRO minerals. Further, increased weathering and a drier climate enhance the formation of crystalline clay minerals at the expense of SRO minerals. Allophanic materials (Sio) were evident (Sio: 9–43 g kg−1) only in weakly weathered soils. However, low allophanic contents were found in more highly weathered soils (Sio: 2–7 g kg−1) accompanied by high Alp and Fep, suggesting the importance of volcanic parent materials as a direct source of Al and Fe via weathering for the formation of organo-metal complexes. In sum, we clarified the discriminatory effects of climatic factors and degree of weathering in regulating the composition of the active Al, Fe and Si fractions along the Cameroon volcanic line.

Bioactive levels of Zn, Pb, Cu, Cd and Mg, Fe in pollution sensitive and tolerant Scots pines needles – Is survival mineral-dependent?

Pine species are considered worldwide as developing various mechanisms counteracting industrial pollution specifically with Zn, Pb, Cu, and Cd. We assumed that the survival of plants should involve also the active concentrations of plant-born heavy metals as well as the mineral elements (Mg, Fe) crucial for normal photosynthetic activity of needles. The needles were collected from 100 randomly selected trees, which were divided into 50 specimens of sensitive (S) and 50 specimens of tolerant (T) species. In the study, the needles were also separated by age into 1 and 2 year-old needles. Two solutions of pH 3.5 and 6.0, mimicking acid rains (AR) were applied for extracting the bioactive forms of Zn, Pb, Cu, Cd and Mg and Fe. The elaborated mineral photosynthetic indices (12 in total), SPI (Single Phytotoxicity Indices), IPI (Integrated Phytotoxicity Indices) and TIPI (Total Integrated Phytotoxicity Indices) revealed that bioactive concentrations of Mg and Fe should be specifically regulating Zn, Pb, Cu, Cd fluxes in Scots pine needles. Such mechanism appears crucial for the survival of pine needles, both 1 and 2-years old, since Mg and Fe are directly activated in the photosynthesis process. The concentrations of bioactive Mg and Fe fractions were higher in sensitive (S) as compared to tolerant (T) pines, explaining thus the basis of their response - stronger for S and weaker for T - to adverse effects induced by the particular heavy metals. We stipulated that magnesium and iron should emerge promptly and permanently as toxicity mitigation factors, acting as a Mineral Toxicity Fence (MTF), supporting thus the survival mineral-dependent hypothesis.

Surface Oxidation and Wettability of Fe–Mn and Fe–Mn–Si-Alloyed Steel After Annealing

The surface oxidation and wettability of Mn and Si-alloyed steel after annealing at different conditions are studied with scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and a so-called de-wetting method. After exposure at 950 °C for 1 hour in an Ar + 5 vol pct H2 gas atmosphere with dew points (DP) ranging from – 40 °C to 10 °C, oxides were observed along the grain boundaries or dispersed on the surface for the Fe–1.8 Mn steels while a continuous oxides layer was formed on Fe–1.9 Mn–0.94 Si steels (composition in weight fractions). The oxides formed at different DPs were predicted based on thermodynamic calculations. (Fe,Mn)O was formed on Fe–1.8 Mn steel at the whole range of DPs, while the oxide phase on Fe–1.9 Mn–0.94 Si steel depends on the DP. At low-DP SiO2 were formed and with increasing the DP (Fe,Mn)SiO3 or (Fe,Mn)SiO3 + (Fe,Mn)2SiO4 were formed and finally (Fe,Mn)2SiO4 were formed. An increase of the fraction of Fe in the oxide with increasing DP for both steels was observed with XPS analysis. As a measure for the surface wettability, the contact angle of Pb droplets on the annealed steels surfaces was determined with SEM and image analysis software. Also, the contact angle of Pb on pure Fe and on the Mn and Si alloyed steels free of surface oxides was measured for comparison. The results show that the contact angle of Pb on the steel surfaces after annealing decreases with increasing DP. This improved wettability with increasing dew point is related to the Fe fraction of the oxides formed on the surface.

A process-based model for describing redox kinetics of Cr(VI) in natural sediments containing variable reactive Fe(II) species

Sediment-associated Fe(II) is a critical reductant for immobilizing groundwater contaminants, such as Cr(VI). The reduction reactivity of sediment-associated Fe(II) is dependent on its binding environment and influenced by the biogeochemical transformation of other elements (i.e., C, N and Mn), challenging the description and prediction of the reactivity of Fe(II) in natural sediments. Here, anaerobic batch experiments were conducted to study the variation in sediment-associated Fe(II) reactivity toward Cr(VI) in natural sediments collected from an intensive agricultural area located in Guangxi, China, where nitrate is a common surface water and groundwater contaminant. Then, a process-based model was developed to describe the coupled biogeochemical processes of C, N, Mn, Fe, and Cr. In the process-based model, Cr(VI) reduction by sediment-associated Fe(II) was described using a previously developed multirate model, which categorized the reactive Fe(II) into three fractions based on their extractabilities in sodium acetate and HCl solutions. The experimental results showed that Fe(II) generation was inhibited by NO3- and/or NO2−. After NO3− and NO2− were exhausted, the Fe(II) content and its reduction rate toward Cr(VI) increased rapidly. As the Fe(II) content increased, the three reactive Fe(II) fractions exhibited approximately linear correlations with aqueous Fe(II) concentrations (CFe2+), which was probably driven by sorptive equilibrium and redox equilibrium between aqueous and solid phases. The model results indicated that the reaction rate constants of the three Fe(II) fractions (kn) significantly increased with incubation time, and log(kn) correlated well withCFe2+ [log(k1)=2.84CFe2+−0.17, log(k2)=5.90CFe2+−2.49 and log(k3)=3.09CFe2+−3.37]. The numerical model developed in this study provides an applicable method to describe and predict Cr(VI) removal from groundwater under dynamic redox conditions.

Geochemical cycling of phosphorus and iron in a typical reservoir in the area of Xiaoxing’an mountains, northeastern China

Reservoirs have an important impact on riverine material migration and transformation. Taking a drinking water reservoir located in the cold-temperature forest in the Xiaoxing’an mountains as an example, we comprehensively analyzed the fractions and interrelationships of phosphorus (P) and iron (Fe) from soils to riverine and reservoir sediments and discussed the coordinated migration and transformation process of regional P and Fe and the effects of dam interception. The results showed that iron-bound P (Fe-P) and aluminum-bound P (Al-P) were significantly correlated with adsorbed Fe(II), carbonate-bound Fe (Fecarb), low-activity silicate-bound Fe (Feprs), and total contents of Fe (TFe), which indicated that the geochemical cycling of these P fractions and Fe fractions is likely closely related and active in the soils and sediments. Calcium-bound P (Ca-P) was significantly correlated with magnate (Femag) and Feprs, which may be due to the correlation between their background values in this area. The contents of active P including loosely sorbed P (L-P), Al-P, and Fe-P in the reservoir’s sediments were significantly higher than those in the upstream soils and sediments (p &amp;lt; 0.05). However, Ca-P and residual P (Res-P) in soil and sediment samples showed no significant difference between the reservoir and its upstream (p = 0.309 &amp;gt; 0.05 and p = 0.748 &amp;gt; 0.05, respectively). Construction of reservoirs has played a certain role in intercepting P, especially bioavailable P, transferred from upstream soils and riverine sediments. The contents of highly active Fe fractions including easily reducible (amorphous) Fe oxide (Feox1), reducible (crystalline) Fe oxide (Feox2) and Fecarb (p &amp;lt; 0.01), and other Fe fractions (p &amp;lt; 0.05) in the sediments of the reservoir were significantly higher than those in the soil or sediment samples from upstream. This indicated that all Fe fractions migrated in the river were affected by the dam interception. The effects of dam interception would affect the bioavailability of P and Fe and enhance the cycling of nutrients in the region. Finally, this also effects the bioavailability and cycling of P and Fe in the downstream rivers and even the oceans.

Colossal permittivity, resistive and magnetic properties of zinc substituted manganese ferrites

Zinc substituted manganese ferrites, i.e., Mn1−xZnxFe2O4 (0.0 ≤ x ≤ 1.0) were synthesized by the citrate sol-gel route. Rietveld refinement of the X-ray diffraction patterns revealed the development of a single-phase cubic spinel structure with space group Fd3̅m. The stoichiometry of the prepared samples was confirmed by energy dispersive X-ray spectroscopy. The 57Fe Mössbauer study suggested the presence of Fe3+ and Fe2.5+ (mixed Fe3+ and Fe2+) ions at the tetrahedral and octahedral sites of the mixed spinel structure, respectively. However, the fraction of Fe2+/Fe3+ ions present at the octahedral site strongly depends on the site preference of Mn2+ and Zn2+ ions for both sites. Thus, the cation distribution among the tetrahedral and octahedral sites altered with increasing Zn2+ substitution (x). Impedance spectroscopy analysis displayed an enhancement in the resistive properties of MnFe2O4 with Zn2+ substitution, while the dielectric permittivity of the prepared samples exhibited a colossal value of the order of 104–107 at room temperature. This enhancement in the resistive and dielectric properties can be understood in terms of particle size, cation distributions, and conductivity inhomogeneity at the grain boundaries. The temperature-dependent ac conductivity analysis proposed that the short-range hopping of oxygen vacancies is responsible for the conduction process in the prepared samples. Here, our findings of high resistance (107), colossal permittivity (106), diminished tangent loss (0.018), and high magnetization (48 emu/g) for the Mn0.4Zn0.6Fe2O4 make this composition promising for radar absorbing applications.

Stable nitride precipitation in additively manufactured nickel superalloys

With negligible quantities of nitrogen, wrought and welded solid solution strengthened nickel superalloys usually contain carbides and topologically close-packed phases, such as Laves phase. However, appreciable nitrogen levels on the order of 0.1 % mass fraction drove the precipitation of a range of unanticipated nitride phases in additively manufactured Inconel 625 in the as-deposited and post process hot isostatically pressed conditions. Different nitride phases were observed with small changes in alloy chemistry. Cubic metal nitrides (MN), tetragonal Z-phase (CrNbN), and diamond-cubic metal η-nitrides (M 6 N) were found within the γ matrix of Inconel 625 containing relatively low Fe (1 %), low Ti (0.02 %), and high Si (0.39 %) mass fractions. Conversely, these phases were replaced by only MN nitrides in a similar Inconel 625 alloy with elevated mass fractions of Ti (0.21 %) and Fe (4 %). These various phases, however, were not fully predicted using state-of-the-art computational thermodynamic tools and databases, indicating a sparsity of data for nickel superalloys. Even after hot isostatic pressing, many nitrides persisted and only experienced slight changes in composition and lattice parameters in both materials. The stability of these nitride phases presents a potential pathway for achieving enhanced high temperature and creep properties within this and similar alloy systems. • Significant nitrogen contents are measured in Inconel 625 powder. • Only nitrides (MN, Z-phase, η-nitride) are observed in two as-deposited Inconel 625 alloys. • Minor alloying elements influence the type of nitride that forms. • Most nitrides persisted after post-process hot isostatic pressing.

Bimetallic Exsolved Heterostructures of Controlled Composition with Tunable Catalytic Properties.

In this paper, we show how the composition of bimetallic Fe-Ni exsolution can be controlled by the nature and concentration of oxygen vacancies in the parental matrix and how this is used to modify the performance of CO2-assisted ethane conversion. Mesoporous A-site-deficient La0.4Sr0.6-αTi0.6Fe0.35Ni0.05O3±δ (0 ≤ α ≤ 0.2) perovskites with substantial specific surface area (>40 m2/g) enabled fast exsolution kinetics (T < 500 °C, t < 1 h) of bimetallic Fe-Ni nanoparticles of increasing size (3-10 nm). Through the application of a multitechnique approach we found that the A-site deficiency determined the concentration of oxygen vacancies associated with iron, which controlled the Fe reduction. Instead of homogeneous bimetallic nanoparticles, the increasing Fe fraction from 37 to 57% led to the emergence of bimodal Fe/Ni3Fe systems. Catalytic tests showed superior stability of our catalysts with respect to commercial Ni/Al2O3. Ethane reforming was found to be the favored pathway, but an increase in selectivity toward ethane dehydrogenation occurred for the systems with a low metallic Fe fraction. The chance to control the reduction and growth processes of bimetallic exsolution offers interesting prospects for the design of advanced catalysts based on bimodal nanoparticle heterostructures.

Effect of superphosphate addition on heavy metals speciation and microbial communities during composting

Superphosphate fertilizer (SSP) as an additive can reduce the nitrogen loss and increase available phosphorus in composting but few studies investigated the effect of SSP addition on heavy metal and microbial communities. In this study, different ratios (10%, 18%, 26%) of SSP were added into pig manure composting to assess the changes of heavy metal (Cu, Mn, As, Zn, and Fe) fractions, bacterial and fungal communities as well as their interactions. SSP addition at 18% had lower ecological risk but still increased the bioavailability of Cu, Mn, and Fe in composts compared to control. Adding 18% SSP into compost decreased bacterial number and increased the fungal diversity compared to CK. Redundancy analysis indicated heavy metal fractions correlated significantly with bacterial and fungal community compositions in composting with 18% SSP. Network analysis showed adding 18% SSP increased microbial interaction and positive cooperation especially enhanced the proportion of Proteobacteria and Ascomycota.