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Ectomycorrhizal (ECM) fungi play a major role in forest ecosystems and managed tree plantations. Particularly, they facilitate mineral weathering and nutrient transfer towards colonized roots. Among nutrients provided by these fungi, potassium (K) has been understudied compared to phosphorus (P) or nitrogen (N). The ECM fungus Paxillus ammoniavirescens is a generalist species that interacts with the root of many trees and can directly transfer K to them, including loblolly pine. However, the forms of K that ECM fungi can store is still unknown. Here, we used synchrotron potassium X-ray fluorescence (XRF) and K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy on P. ammoniavirescens growing in axenic conditions to investigate the K chemistries accumulating in the center and the edge of the mycelium. We observed that various K forms accumulated in different part of the mycelium, including K-nitrate (KNO 3), K-C-O compounds (such as K-tartrate K 2 (C 4 H 4 O 6) and K-oxalate (K 2 C 2 O 4)), K-S and K-P compounds. Saprotrophic fungi have been shown to excrete carboxylic acids, which in turn play a role in soil mineral weathering. Our finding of several K counter-ions to carboxylic acids may suggest that, besides their direct transfer to colonized roots, K ions can also be involved in the production of compounds necessary for sourcing nutrients from their surrounding environment by ECM fungi. Additionally, this work reveals that XANES spectroscopy can be used to identify the various forms of K accumulating in biological systems. • We use XANES to identify the K chemistries in the ECM fungus Paxillus ammoniavirescens. • Hotspots of various K forms accumulate in the hyphae P. ammoniavirescens. • K-nitrate, K-C-O, K-S, and K-P compounds were found in P. ammoniavirescens hyphae. • K ions can be involved in compounds needed for mineral weathering by ECM fungi. [ABSTRACT FROM AUTHOR]

The lanthanide (Ln) elements are critical materials that are typically extracted/mined together. Their separation by use of solvent extraction from acidic media is well known; however, there are few studies in basic media with carbonate anions. We investigated the complexation of Eu(III) and Tb(III) carbonates as solids and solutions in alkaline K2CO3, wherein we sought to access a Tb(IV) carbonate complex through ozonolysis. L3‐edge XANES of Eu and Tb carbonate solids, colorless solutions, and a red‐hued Tb solution (obtained by ozonolysis) all showed Ln(III) cations. The absence of evidence for a Tb(IV) complex was confirmed through XAS and EPR analyses, despite the solution exhibiting a deep red color. For solids and solutions, EXAFS results indicate molecular Ln(III)‐carbonato anions. In terms of the Eu(III) carbonate coordination number, the coordination does not change upon dissolution of the solid sample. Furthermore, EXAFS for the solutions revealed evidence for the association of potassium cations with the Ln(III)‐carbonato anions. This direct observation of contact ion pairing by EXAFS at room temperature is rare. The insights into Ln(III) carbonate complexation and solution speciation afforded by XANES‐EXAFS, FT‐IR, and EPR provides perspectives that serve as benchmarks for future computational and experimental efforts focused on caustic‐side solvent extraction of Ln(III) ions. [ABSTRACT FROM AUTHOR]

The viscosities of Ce‐free and Ce‐bearing (∼1.3 mol%, ∼6.5 wt.% Ce2O3) soda lime silicate (window glass) melts were measured with respect to oxidation state. Experiments were performed isothermally using a concentric‐cylinder viscometer on melts equilibrated with successively reducing CO–CO2 gas mixtures within a gas tight vertical tube furnace at 1 atm. Viscosity measurement and sampling were performed at the end of each melt reduction step. Further, viscosities in the glass transition temperature range were estimated using the shift factor method applied to glass transition temperature values determined using differential scanning calorimetry (DSC) measurements on quenched glasses. The Ce speciation at each stepwise melt reduction was probed using Ce L3‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy, while structural information upon Ce addition and reduction was provided by Raman spectroscopy. The viscosities of these materials remain constant at this level of Ce addition and do not vary significantly with redox state at high temperature. Conversely, viscosity values in the glass transition temperature range increase upon both Ce addition and reduction. Our analysis, based on the glass composition analyses obtained via electron probe microanalyzer (EPMA), viscosity calculations, and observations of silicate structural changes, leads to the conclusion that the observed viscosity increase around the glass transition temperature is explained by the high ionic field strength of Ce ions as well as the polymerization behavior of the silicate matrix occurring during reduction of Ce. Because of its low concentration, resulting from its low solubility, Ce redox changes exert only minimal effects on the viscosity of this melt. [ABSTRACT FROM AUTHOR]

Titanium occurs as Ti3+, in addition to the more usual Ti4+, in extraterrestrial materials such as Lunar basalts and chondritic meteorites. The proportion of Ti as Ti3+ was investigated by Ti K-edge X-ray absorption near edge structure (XANES) spectroscopy for five silicate glass compositions quenched from melts equilibrated at 1400 °C, atmospheric pressure, and oxygen fugacities (f O 2) in log units relative to the fayalite-magnetite-quartz (FMQ) buffer from FMQ+3.3 to FMQ-10.2 (+6.6 to −6.9 log units relative to the iron-wüstite, IW, buffer). All spectra could be well fit using a linear combination of the spectra recorded from the most oxidised and reduced samples of the same composition, indicating that the samples only contain two Ti species. Ti3+/ΣTi (where ΣTi = Ti3+ + Ti4+) = 0 for the most oxidised samples but is unknown for the most reduced. Thus, the linear combination fit results were used in a regression model in which Ti3+/ΣTi of the reduced end-member was varied to give Ti3+/ΣTi values of the other samples that best fit the thermodynamically expected dependence of Ti3+/ΣTi on f O 2. The most reduced samples were found to have Ti3+/ΣTi ∼ 0.6. The resulting modified equilibrium constants of the Ti oxidation reaction, log K ', are linearly correlated with the optical basicity (Λ) parameterisation of melt composition, such that as Λ increases, Ti3+/ΣTi decreases, at constant f O 2. This correlation allows Ti3+/ΣTi to be predicted for other compositions and, assuming that the temperature dependence of Ti3+/Ti4+ is parallel to FMQ, a general equation relating Ti3+/Ti4+ to f O 2 was obtained: log(Ti3+/Ti4+) = −0.25ΔFMQ − 0.32(19) − 3.44(32) Λ. This equation was used to predict Ti3+/ΣTi as a function of f O 2 for high-Ti Mare basalt, chondrule (CV and CM), and calcium aluminium inclusion (CAI; Type A and B) compositions. For melts of these compositions Ti3+ = Ti4+ at ∼ FMQ-10.8, −9.5, −9.3, −10.6, and −10.2 (∼IW-7.5, −6.2, −6.0, −7.3, and −6.9), respectively, independent of temperature. [ABSTRACT FROM AUTHOR]

The interaction of NiO clusters with a graphene layer of a nanotube in NiOx/CNT composites is simulated based on a theoretical analysis of Ni K-edge XANES spectra. Various cases of orientation of crystallographic planes relative to the nanotube wall are considered. It was determined that Ni in the composite is predominantly in the 2+ state, NiO particles are oriented towards the tube wall by the (200) plane. Accounting for carbon atoms even in the first sphere of the nickel environment makes it possible to achieve good agreement between the theoretical spectrum and experiment. [ABSTRACT FROM AUTHOR]

Copper is a redox variable element that may occur as Cu0, Cu+, and Cu2+ in the Earth's crust. The oxidation state will affect its partitioning between coexisting minerals, melts and fluids and hence its behaviour in magmatic processes. Copper bearing silicate glasses were quenched from melts with 23 synthetic compositions (19 CaO-Na 2 O-MgO-Al 2 O 3 -SiO 2 (CNMAS), two "granites" containing K 2 O ± H 2 O, and Fe-bearing "MORB" and "andesite") equilibrated at oxygen fugacities (f O 2), expressed in log units relative to the fayalite-magnetite-quartz (FMQ) buffer, ranging from −0.7 to 14, temperatures from 900 to 1500 °C and pressures from 0 to 2.5 GPa. Cu K -edge X-ray absorption near edge structure (XANES) spectra were recorded from the glasses and a pre-edge feature in the XANES spectra was found to scale with the proportion of Cu+. Cu+/ΣCu (where ΣCu = Cu+ + Cu2+) was quantified by fitting the intensity of the pre-edge feature as a function of f O 2 to the thermodynamically expected relationship. Cu+/ΣCu was found to only weakly depend on melt composition, with more basic melts (e.g., basalts rather than granites) preferentially stabilising Cu2+. Increasing temperature stabilises Cu+, while increasing pressure had little effect on Cu+/ΣCu in CNMAS melts but preferentially stabilised Cu2+ in granite melts. Cu+/ΣCu can be predicted in silicate melts by the empirical equation: log(Cu2+/Cu+) = 0.25(ΔFMQ + 8.58 − 25050/T + 940P/T – 0.02P) − 4.73 + 5400/T + 1.99 Λ + (280P – 90P2) where T is temperature in K, P is pressure in GPa and Λ is the optical basicity of the composition. The effects of f O 2 , melt composition, temperature and pressure on Cu+/ΣCu indicate that Cu+ will be the dominant oxidation state in terrestrial silicate melts (e.g., Cu+/ΣCu = 99% in an andesitic melt at 900 °C, 1 GPa and ΔFMQ = 1). The electron exchange reaction Cu2+ + Fe2+ → Cu+ + Fe3+ occurs on cooling and, given the abundance of Fe in natural melts, the oxidation state of Cu in natural glasses is unlikely to correspond to that in the original melt. [ABSTRACT FROM AUTHOR]

The Ti content of zircon (ZrSiO 4) can be used as a geothermometer. Ti could substitute for Si or Zr in zircon, which would result in opposing responses of Ti solubility to (i) the activities of SiO 2 (a SiO 2 quartz/coesite) and TiO 2 (a TiO 2 rutile) and (ii) changes in pressure due to differences in the molar volumes of the components ZrTiO 4 and TiSiO 4 relative to ZrSiO 4. Previous calibrations of the Ti-in-zircon thermometer assumed that Ti occupies the Si-site. X-ray absorption near edge structure (XANES) spectroscopy has confirmed that Ti is tetrahedrally coordinated on the Si-site at atmospheric pressure, however, Ti is predicted to change to the Zr-site at higher pressures. Ti-bearing zircons were prepared at 1400 °C and pressures from 0.0001 to 6.5 GPa using a flux-method that produced crystals up to 50 μm in size. Ti K- edge XANES spectra of zircons prepared at < 4.0 GPa are characterised by an intense pre-edge peak (attributed to the 1 s → 3 d transition), which is consistent with Ti in tetrahedral coordination on the Si-site. The intensity of this peak is proportional to the amount of Ti on the Si-site, and decreases abruptly > 4.0 GPa (accompanied by a change in the energy and shape of the absorption edge), indicating a change in the coordination of Ti. Ti-O bond lengths determined from extended X-ray absorption fine structure (EXAFS) spectra of 1.788(7) Å at 1.0 GPa and both 1.87(4) Å and 2.21(2) Å at 6.5 GPa are consistent with Ti changing from the Si-site to the larger Zr-site. The proportion of Ti on each site varies systematically with pressure, with equal proportions of Ti on both sites at ∼ 4.4 GPa. Sole occupancy of Ti on the Zr-site is predicted to occur at pressures coinciding with the transition of zircon to reidite (∼ 8.0 GPa). This change in site is consistent with a systematic decrease in the Ti content of these zircons with increasing pressure when a SiO 2 quartz/coesite and a TiO 2 rutile = 1. As a result, an updated model for estimating zircon crystallisation temperatures from the Ti content was derived: l o g T i f = 5.84 7 - 4800 86 T - 0.12 1 P - 0.0056 15 P 3 - l o g a S i O 2 q u a r t z / c o e s i t e f + l o g a T i O 2 r u t i l e where Ti is in ppm, f is the fraction of Ti on the Si-site given by 1/(1 + 10−(3.37(13) − 0.77(5) P)), T is temperature in K, P is pressure in GPa, and the uncertainties are 1σ. For zircons with independent estimates of temperature, pressure, a SiO 2 quartz/coesite and a TiO 2 rutile this new model predicts crystallisation temperatures within 40 °C (or 8 %) of the independent temperature estimates at all pressures. This contrasts with previous models for which predicted temperatures are within certainty of nominal temperatures at ∼ 1.0 GPa, but underestimated (by up to 70 °C) at pressures < 1.0 GPa and underestimated (by up to 300 °C) at higher pressures where the proportion of Ti on the Zr-site should be significant. [ABSTRACT FROM AUTHOR]

[Display omitted] • Scapolite hosts S in oxidised (SO 3 and SO 2) and reduced forms (polysulfides and minor sulfide). • Most reduced S was found in scapolites formed under amphibolite facies. • S in scapolite can buffer ore fluid oxidation state to sulphate/sulphide coexistence. Scapolite is a common S-, Cl-, and C-bearing mineral in metamorphic terranes, especially those that include meta -evaporites. Fluid interaction with scapolite-bearing rocks can result in albitisation of scapolite, and release of volatile components such as Cl−, CO 3 2–, SO 2 and/or SO 4 2−. Hence, scapolite may play an important role in buffering the oxidation state, salinity and sulfur speciation of the rock and fluids in such terranes, and since Cl, S, and the redox state of S are vital for the transport and deposition of metals, scapolite may exert an important influence on hydrothermal mineralisation processes. We investigated the oxidation state of S and concentrations of S and Cl from 17 scapolite-bearing samples collected from various metamorphic and hydrothermal environments. The highest concentrations of S and Cl in the samples set are respectively 1.11 ± 0.04 wt% S (reported as SO 3, n = 10 points measurements) and 3.84 ± 0.17 wt% (n = 11 points measurements). µ-XANES spectroscopy demonstrates that S chemistry in scapolite is complex, S being present in both oxidised (as sulfate and sulfite) and reduced forms (polysulfides and minor sulfide) in most scapolites. These results confirm that scapolite can buffer fluid oxidation state to sulfate/sulfide coexistence, at acidic to neutral pH. The proportion of reduced S in scapolite increases with increasing metamorphic grade from greenschist to amphibolite facies. Since scapolite contains highly reactive polysulfide and sulfite, its breakdown may promote alteration of sulfide minerals and release of hosted metals. Thus, the presence of scapolitic calc-silicate rocks can strongly influence regional syn -orogenic metallogeny and should allow the mobilisation of metals differently from other bulk compositions. [ABSTRACT FROM AUTHOR]

Niobium (Nb) is one of the most immobile elements during supergene weathering, widely used for mass-balance calculations, despite elusive information on the mechanisms controlling its dynamics in the critical zone. Here, a multiscale approach, from weathering profile to atomic-scale, is developed to monitor Nb speciation along a thick (about 50 m) lateritic regolith formed over the Pitinga pluton (Amazonas, Brazil). In the A-type parent granite, Nb is mainly hosted in ilmenite (1.5–2 wt% Nb 2 O 5) and, to a lesser extent, in rutile (2–3 wt% Nb 2 O 5). A quantitative assessment of the average Nb speciation from the parent rock to the upper horizons has been carried out by combining spectroscopic and spatially-resolved chemical techniques. The contribution of Nb-bearing Ti oxides (2–6 wt% Nb 2 O 5) and Fe oxides (0.1–0.3 wt% Nb 2 O 5) in the average Nb speciation increases with the degree of weathering and reaches 80% in the most altered horizon. This unusual Nb speciation results from the nature of the primary Nb carriers, less resistant to weathering than common Nb ore minerals such as pyrochlore. X-ray absorption spectroscopy demonstrates that Nb released from the weathering of ilmenite substitutes for Fe and Ti in goethite and Ti oxides, respectively, providing atomic-scale evidence of the high affinity of Nb for these phases. Elemental mobility of Nb, Ta and Sn followed by geochemical mass-transfer calculations evidences lateral transport from Nb-Sn-enriched laterites developed over the surrounding Nb-enriched facies of the Pitinga granite to the studied profile. Elements such as Ti, Zr and Hf, often considered immobile, are leached or redistributed in the studied profile. Our results demonstrate Nb remobilization during intense weathering. Although Nb scavenging by secondary Fe and Ti oxides limits Nb mobility at the mineral scale, this work questions the unrestricted use of Nb as a chemical invariant during surficial alteration processes. [ABSTRACT FROM AUTHOR]

Plants rely on potassium for many critical biological processes, but most soils are potassium limited. Moving potassium from the inaccessible, mineral-bound pool to a more bioavailable form is crucial for sustainably increasing local potassium concentrations for plant growth and health. Here, we use a synthetic soil habitat (mineral doped micromodels) to study and directly visualize how the saprotrophic fungus, Fusarium sp. DS 682, weathers K-rich soil minerals. After 30 days of fungal growth, both montmorillonite and illite (secondary clays) had formed as surface coatings on primary K-feldspar, biotite, and kaolinite grains. The distribution of montmorillonite differed depending on the proximity to a carbon source, where montmorillonite was found to be associated with K-feldspar closer to the carbon (C) source, which the fungus was inoculated on, but associated with biotite at greater distances from the C source. The distribution of secondary clays is likely due to a change in the type of fungal exuded organic acids; from citric to tartaric acid dominated production with increasing distance from the C source. Thus, the main control on the ability of Fusarium sp. DS 682 to weather K-feldspar is proximity to a C source to produce citric acid via the TCA cycle. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is an indispensable nutrient for arable crops, but at the same time, contributes to excessive eutrophication in aquatic ecosystems. Knowledge about P is essential to assess the possible risks of P being transported towards vulnerable aquatic ecosystems. Our objective was to characterize P along a catena from arable and wetland soils towards aquatic sediments of a shallow lagoon of the Baltic Sea. The characterization of P in soil and sediment samples included a modified sequential P fractionation and P K-edge X-ray absorption near edge structure (XANES) spectroscopy. The concentrations of total P ranged between 390 and 430 mg kg−1 in the arable soils, between 728 and 2258 mg kg−1 in wetland soils and between 132 and 602 mg kg−1 in lagoon sediments. Generally, two sinks for P were revealed along the catena. The wetland soil trapped moderately stable P, Al-P and molybdate-unreactive P (MUP), which are most likely organically bound phosphates. Sediments at the deepest position of the catena acted as a sink for, MUP compounds among the lagoon sediments. Thus, wetlands formed by reed belts can help to prevent the direct transfer of P from arable soils to adjacent waters and deeper basins and help to avoid excessive eutrophication in shallow aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Herein, we describe the synthesis, crystal structure, and electronic properties of {[K2(dmso)(H2O)5][Ni2(H2mpba)3]·dmso·2H2O}n (1) and [Ni(H2O)6][Ni2(H2mpba)3]·3CH3OH·4H2O (2) [dmso = dimethyl sulfoxide; CH3OH = methanol; and H4mpba = 1,3-phenylenebis(oxamic acid)] bearing the [Ni2(H2mpba)3]2− helicate, hereafter referred to as {NiII2}. SHAPE software calculations indicate that the coordination geometry of all the NiII atoms in 1 and 2 is a distorted octahedron (Oh) whereas the coordination environments for K1 and K2 atoms in 1 are Snub disphenoid J84 (D2d) and distorted octahedron (Oh), respectively. The {NiII2} helicate in 1 is connected by K+ counter cations yielding a 2D coordination network with sql topology. In contrast to 1, the electroneutrality of the triple-stranded [Ni2(H2mpba)3] 2− dinuclear motif in 2 is achieved by a [Ni(H2O)6]2+ complex cation, where the three neighboring {NiII2} units interact in a supramolecular fashion through four R22(10) homosynthons yielding a 2D array. Voltammetric measurements reveal that both compounds are redox active (with the NiII/NiI pair being mediated by OH– ions) but with differences in formal potentials that reflect changes in the energy levels of molecular orbitals. The NiII ions from the helicate and the counter-ion (complex cation) in 2 can be reversibly reduced, resulting in the highest faradaic current intensities. The redox reactions in 1 also occur in an alkaline medium but at higher formal potentials. The connection of the helicate with the K+ counter cation has an impact on the energy levels of the molecular orbitals; this experimental behavior was further supported by X-ray absorption near-edge spectroscopy (XANES) experiments and computational calculations. [ABSTRACT FROM AUTHOR]

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm−1) and 760 nm (13,160 cm−1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe–Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm−1 and B = 800 cm−1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications. [ABSTRACT FROM AUTHOR]

Two sodium vanadium phosphates, synthetic analogues of the minerals kosnarite, Na3V2(PO4)3, and yurmarinite, Na7V4(PO4)6, were obtained by hydrothermal synthesis simulating a natural hydrothermal solution. While the Na3V2(PO4)3 phase belongs to the NASICON family and is well-known for its high-ionic conductivity, the new Na7V4(PO4)6 compound is a rare case of V2+-containing oxosalts, which are hard to prepare due to their instability in air. Here we report the crystal structure of heterovalent vanadium phosphate studied by single crystal X-ray diffraction, XANES spectroscopy, and topological ion migration modelling. A discussion of divalent vanadium compounds of both natural and synthetic origin is also given, with a review of the methods for their synthesis and a comparative analysis of V–O bond lengths. [ABSTRACT FROM AUTHOR]

Platelets and their subcellular components (e.g., dense granules) are essential components in hemostasis. Understanding their chemical heterogeneities at the sub-micrometer scale, particularly their activation during hemostasis and production of platelet-derived extracellular vesicles, may provide important insights into their mechanisms; however, this has rarely been investigated, mainly owing to the lack of appropriate chemical characterization tools at nanometer scale. Here, the use of scanning transmission X-ray microscopy (STXM) combined with X-ray absorption near edge structure (XANES) to characterize human platelets and their subcellular components at the carbon K-edge and calcium L2,3-edge, is reported. STXM images can identify not only the spatial distribution of subcellular components in human platelets, such as dense granules (DGs) with sizes of ~200 nm, but also their granule-to-granule chemical heterogeneities on the sub-micrometer scale, based on their XANES spectra. The calcium distribution map as well as the principal component analysis of the STXM image stacks clearly identified the numbers and locations of the calcium-rich DGs within human platelets. Deconvolution of the carbon K-edge XANES spectra, extracted from various locations in the platelets, showed that amide carbonyl and carboxylic acid functional groups were mainly found in the cytoplasm, while ketone-phenol-nitrile-imine, aliphatic, and carbonate functional groups were dominant in the platelet DGs. These observations suggest that platelet DGs are most likely composed of calcium polyphosphate associated with adenosine triphosphate (ATP) and adenosine diphosphate (ADP), with significant granule-to-granule variations in their compositions, while the cytoplasm regions of platelets contain significant amounts of proteins.

Constraints on marine phosphate availability and cycling directly inform our understanding of long‐term biological evolution. However, early Earth phosphate records are sparse, biased toward siliciclastic samples, and susceptible to post‐depositional modification. Well‐preserved shallow marine inorganic carbonate precipitates provide a complementary yet understudied record of phosphate cycling. We combined micro‐X‐ray fluorescence mapping, X‐ray absorption, and Nuclear Magnetic Resonance spectroscopy on samples of Precambrian syndepositional herringbone calcite (HBC) and microspar to characterize phosphorus speciation and distribution in these carbonate fabrics. Phosphorus spectroscopy from synthetic calcite, HBC, and microspar, is qualitatively consistent with a disordered distribution of phosphate. These characteristics are diagnostic of calcite‐hosted phosphate, which is pervasive at low concentrations in HBC and microspar. This study provides evidence that ancient, well‐preserved carbonate fabrics retain phosphate sourced from seawater and highlights the potential for an unaltered archive of marine phosphate concentration over geologic time. Plain Language Summary: Phosphorus is a critical nutrient to sustain life on Earth as we know it. Understanding the form and source of phosphorus on the early Earth will enhance our knowledge of the origins and early evolution of life. However, there is no way to directly measure the source, form and abundance of phosphorus in the environment when life was evolving over 2.5 billion years ago. The rock record provides a potential archive to indirectly measure phosphorus from ancient marine environments, yet there are a number of considerations, for example; (a) which minerals are able to record information about marine phosphorus? (b) How do we know those minerals have not been altered over time? In this work, we have identified well‐preserved, unaltered carbonate minerals from ∼2.5 billion and 800 million years ago, that preserve marine phosphate within their mineral structure using micron‐scale techniques. The characterization of this form of phosphorus is important to our understanding of the evolution of the phosphorus cycle over Earth's history. Key Points: Synchrotron analyses identify calcite‐hosted phosphate in well‐preserved Precambrian carbonate fabricsHerringbone calcite and synsedimentary microspar serve as an unaltered archive for ancient marine dissolved inorganic phosphateMicrite retains abundant apatite mineral micro‐inclusions that may bias bulk calcite‐hosted phosphate or P/Ca records [ABSTRACT FROM AUTHOR]

Recovering phosphorus (P) and sulfur (S) from biowaste is a key strategy to address the current P resources shortage and soil S deficiency. Food waste digestate (FWD) contains high contents of P and S, while its direct application is severely limited by available nutrient leaching loss and pollutant exposure. Hydrothermal treatment (HT) is an effective technique for biowaste disposal, enabling detoxification and resource recovery. The study systematically investigated the speciation transformation of P and S in FWD during HT, using chemical extraction and in-situ X-ray absorption near-edge structure (XANES) spectroscopy. The results revealed that up to 98% of P in FWD was enriched in the solid product (hydrochar) after HT, with organic P and labile P being converted into stable Ca-bound forms, predominantly hydroxyapatite. This transformation reduced the risk of P leakage loss compared to untreated FWD. Interestingly, the S speciation evolution exhibited more complexity. The highest S proportion in hydrochar of 73.6% was observed at 140 °C under HT. As the temperature increased from 140 °C to 180 °C, S in the hydrochar gradually dissolved into the liquid phase, attributed to unstable aliphatic compounds (mercaptan) and the sulfides oxidizing to sulfates. Above 180 °C, intermediate oxidation states and sulfates were reduced and formed metal sulfides. These findings have important implications for understanding the viability of HT for FWD disposal and the value-added utilization of FWD., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Abstract Constraints on marine phosphate availability and cycling directly inform our understanding of long‐term biological evolution. However, early Earth phosphate records are sparse, biased toward siliciclastic samples, and susceptible to post‐depositional modification. Well‐preserved shallow marine inorganic carbonate precipitates provide a complementary yet understudied record of phosphate cycling. We combined micro‐X‐ray fluorescence mapping, X‐ray absorption, and Nuclear Magnetic Resonance spectroscopy on samples of Precambrian syndepositional herringbone calcite (HBC) and microspar to characterize phosphorus speciation and distribution in these carbonate fabrics. Phosphorus spectroscopy from synthetic calcite, HBC, and microspar, is qualitatively consistent with a disordered distribution of phosphate. These characteristics are diagnostic of calcite‐hosted phosphate, which is pervasive at low concentrations in HBC and microspar. This study provides evidence that ancient, well‐preserved carbonate fabrics retain phosphate sourced from seawater and highlights the potential for an unaltered archive of marine phosphate concentration over geologic time.

Platelets and their subcellular components (e.g., dense granules) are essential components in hemostasis. Understanding their chemical heterogeneities at the sub-micrometer scale, particularly their activation during hemostasis and production of platelet-derived extracellular vesicles, may provide important insights into their mechanisms; however, this has rarely been investigated, mainly owing to the lack of appropriate chemical characterization tools at nanometer scale. Here, the use of scanning transmission X-ray microscopy (STXM) combined with X-ray absorption near edge structure (XANES) to characterize human platelets and their subcellular components at the carbon K-edge and calcium L2,3-edge, is reported. STXM images can identify not only the spatial distribution of subcellular components in human platelets, such as dense granules (DGs) with sizes of ~200 nm, but also their granule-to-granule chemical heterogeneities on the sub-micrometer scale, based on their XANES spectra. The calcium distribution map as well as the principal component analysis of the STXM image stacks clearly identified the numbers and locations of the calcium-rich DGs within human platelets. Deconvolution of the carbon K-edge XANES spectra, extracted from various locations in the platelets, showed that amide carbonyl and carboxylic acid functional groups were mainly found in the cytoplasm, while ketone-phenol-nitrile-imine, aliphatic, and carbonate functional groups were dominant in the platelet DGs. These observations suggest that platelet DGs are most likely composed of calcium polyphosphate associated with adenosine triphosphate (ATP) and adenosine diphosphate (ADP), with significant granule-to-granule variations in their compositions, while the cytoplasm regions of platelets contain significant amounts of proteins. [ABSTRACT FROM AUTHOR]

Plants rely on potassium for many critical biological processes, but most soils are potassium limited. Moving potassium from the inaccessible, mineral-bound pool to a more bioavailable form is crucial for sustainably increasing local potassium concentrations for plant growth and health. Here, we use a synthetic soil habitat (mineral doped micromodels) to study and directly visualize how the saprotrophic fungus, Fusarium sp. DS 682, weathers K-rich soil minerals. After 30 days of fungal growth, both montmorillonite and illite (secondary clays) had formed as surface coatings on primary K-feldspar, biotite, and kaolinite grains. The distribution of montmorillonite differed depending on the proximity to a carbon source, where montmorillonite was found to be associated with K-feldspar closer to the carbon (C) source, which the fungus was inoculated on, but associated with biotite at greater distances from the C source. The distribution of secondary clays is likely due to a change in the type of fungal exuded organic acids; from citric to tartaric acid dominated production with increasing distance from the C source. Thus, the main control on the ability of Fusarium sp. DS 682 to weather K-feldspar is proximity to a C source to produce citric acid via the TCA cycle.

Modeling metal sorption in soils is of great importance to predict the fate of heavy metals and to assess the actual risk driven from pollution. The present study focuses on adsorption of HM ions on two types of hydromorphic soils, including calcaric fluvisols loamic and calcaric fluvic arenosols. The individual and competitive adsorption behaviors of Cu and Zn on soils and soil constituents are evaluated comprehensively. It is established that the sorption processes were best described with the Langmuir model. The results suggest that the calcaric fluvic arenosols are more vulnerable to heavy metal input compared to fluvisols loamic. In all cases, Cu had a higher range of values of the adsorption process parameters relative to Zn. The Zn is likely to be the most critical environmental factor in such soils since it exhibited a decreased sorption under competitive conditions. The retention mechanisms of HM in hydromorphic soils are considered. Based on theoretical calculations of ion activity in soil solutions using solubility diagrams of Cu and Zn compounds, the possibility of precipitation of Cu hydroxide and Zn carbonate in the studied soils is shown. Direct physical methods of nondestructive testing (XAFS and XRD) are applied to experimentally prove the formation of these HM compounds on the surface of montmorillonite, the dominant mineral in hydromorphic soils, and calcite. Thus, the combination of both physicochemical methods and direct physical methods can provide a large amount of real information about the mechanisms of HM retain with solid phases. [ABSTRACT FROM AUTHOR]

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%. [ABSTRACT FROM AUTHOR]

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%.

Phosphorus (P) is an indispensable nutrient for arable crops, but at the same time, contributes to excessive eutrophication in aquatic ecosystems. Knowledge about P is essential to assess the possible risks of P being transported towards vulnerable aquatic ecosystems. Our objective was to characterize P along a catena from arable and wetland soils towards aquatic sediments of a shallow lagoon of the Baltic Sea. The characterization of P in soil and sediment samples included a modified sequential P fractionation and P K-edge X-ray absorption near edge structure (XANES) spectroscopy. The concentrations of total P ranged between 390 and 430 mg kg−1 in the arable soils, between 728 and 2258 mg kg−1 in wetland soils and between 132 and 602 mg kg−1 in lagoon sediments. Generally, two sinks for P were revealed along the catena. The wetland soil trapped moderately stable P, Al-P and molybdate-unreactive P (MUP), which are most likely organically bound phosphates. Sediments at the deepest position of the catena acted as a sink for, MUP compounds among the lagoon sediments. Thus, wetlands formed by reed belts can help to prevent the direct transfer of P from arable soils to adjacent waters and deeper basins and help to avoid excessive eutrophication in shallow aquatic ecosystems.

We present an extensive study of the luminescence characteristics of Mn impurity ions in a YAl3(BO3)4:Mn crystal, in combination with X-ray fluorescence analysis and determination of the valence state of Mn by XANES (X-ray absorption near-edge structure) spectroscopy. The valences of manganese Mn2+(d5) and Mn3+(d4) were determined by the XANES and high-resolution optical spectroscopy methods shown to be complementary. We observe the R1 and R2 luminescence and absorption lines characteristic of the 2E ↔ 4A2 transitions in d3 ions (such as Mn4+ and Cr3+) and show that they arise due to uncontrolled admixture of Cr3+ ions. A broad luminescent band in the green part of the spectrum is attributed to transitions in Mn2+. Narrow zero-phonon infrared luminescence lines near 1060 nm (9400 cm−1) and 760 nm (13,160 cm−1) are associated with spin-forbidden transitions in Mn3+: 1T2 → 3T1 (between excited triplets) and 1T2 → 5E (to the ground state). Spin-allowed 5T2 → 5E Mn3+ transitions show up as a broad band in the orange region of the spectrum. Using the data of optical spectroscopy and Tanabe–Sugano diagrams we estimated the crystal-field parameter Dq and Racah parameter B for Mn3+ in YAB:Mn as Dq = 1785 cm−1 and B = 800 cm−1. Our work can serve as a basis for further study of YAB:Mn for the purposes of luminescent thermometry, as well as other applications.

Phosphorus (P) availability in soils controls critical functions and properties of terrestrial ecosystems. Vertical distribution patterns of P concentration and speciation in soil profiles provide historical records of how pedogenic processes redistribute and transform P and thus change its availability in soils, which, however, remain poorly understood. We determined the patterns in three forest soil profiles of contrasting climate, using fine sampling intervals, P K -edge X-ray absorption near edge (XANES) spectroscopy and chemical extractions. The major features of the patterns persist under the contrasting climate. The total P concentration decreases from A to B horizons, reaches a minimum in the B horizons, and then increases towards the upper C horizons, but with little variations with depth in the lower C horizons. Both calcium-bound inorganic P (Ca–P i) and organic P (P o) decrease and Fe- and Al-bound P i [(Fe + Al)–P i ] increases in proportion downward in the A horizons because dust inputs and accumulation of organic matter both decline with increasing depth. Ca–P i is negligible and (Fe + Al)–P i is dominant in the B horizons due to strong weathering. There is a strong downward increase in Ca–P i proportion and decrease in (Fe + Al)–P i proportion from the lower B to the upper C horizons. New Ca–P i seems to form in the upper C horizons where downward leaching Ca2+ and phosphate accumulate due to the low water permeability of the soils. In the lower C horizons, Ca–P i increases and (Fe + Al)–P i decreases with increasing depth due to decreasing chemical weathering. Regarding P bioavailability, the proportion of occluded P (P occ) shows an increasing and decreasing trend with increasing depth, being the highest in the B horizons; however, there are no consistent trends for non-occluded P (P n-occ). While the P vertical patterns can be understood by considering the relative importance of different pedogenic processes, climate affects the intensities of these processes and thus the details of the patterns. When depth-integrated, warmer/wetter climate results in decreases in the proportions of both Ca–P i and P n-occ but increases in the P loss and the proportions of P o , (Fe + Al)–P i , and P occ. Regardless of soil depth and climate, the P i speciation, i.e., the relative proportions of Ca–P i and (Fe + Al)–P i over total P i , correlates well with soil pH and weathering degree (Chemical Index of Alteration, CIA), and the P o concentration correlates with pedogenic Fe and Al and organic carbon concentration. The correlations suggest that the P i speciation is primarily controlled by soil geochemistry/mineralogy, and the P o concentration by both soil geochemistry/mineralogy and biological activities. P occ correlates with CIA, and thus is mainly controlled by soil mineralogy; but P n-occ correlates weakly with soil properties, probably due to its susceptibility to combined influences of dust inputs, leaching, biological activities, and adsorption on minerals. The above quantitative relationships may help predict P speciation and availability in diverse soils. We further show that soil profiles, and climate and CIA gradients are useful tools for studying P transformations, particularly for the P i pool, during pedogenesis. This study provides an integration and synthesis of controls of climatic and edaphic variables on P dynamics in forest soils. [ABSTRACT FROM AUTHOR]

Two sodium vanadium phosphates, synthetic analogues of the minerals kosnarite, Na3V2(PO4)3, and yurmarinite, Na7V4(PO4)6, were obtained by hydrothermal synthesis simulating a natural hydrothermal solution. While the Na3V2(PO4)3 phase belongs to the NASICON family and is well-known for its high-ionic conductivity, the new Na7V4(PO4)6 compound is a rare case of V2+-containing oxosalts, which are hard to prepare due to their instability in air. Here we report the crystal structure of heterovalent vanadium phosphate studied by single crystal X-ray diffraction, XANES spectroscopy, and topological ion migration modelling. A discussion of divalent vanadium compounds of both natural and synthetic origin is also given, with a review of the methods for their synthesis and a comparative analysis of V–O bond lengths.

Zinc K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy of Zn adsorbed to silica and Zn‐bearing minerals, salts and solutions was conducted to explore how XANES spectra reflect coordination environment and disorder in the surface to which a metal ion is sorbed. Specifically, XANES spectra for five distinct Zn adsorption complexes (Znads) on quartz and amorphous silica [SiO2(am)] are presented from the Zn–water–silica surface system: outer‐sphere octahedral Znads on quartz, inner‐sphere octahedral Znads on quartz, inner‐sphere tetrahedral Znads on quartz, inner‐sphere octahedral Znads on SiO2(am) and inner‐sphere tetrahedral Znads on SiO2(am). XANES spectral analysis of these complexes on quartz versus SiO2(am) reveals that normalized peak absorbance and K‐edge energy position generally decrease with increasing surface disorder and decreasing Zn–O coordination. On quartz, the absorption‐edge energy of Znads ranges from 9663.0 to 9664.1 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On SiO2(am), the absorption‐edge energy of Znads ranges from 9662.3 to 9663.4 eV for samples dominated by tetrahedrally versus octahedrally coordinated species, respectively. On both silica substrates, octahedral Znads presents a single K‐edge peak feature, whereas tetrahedral Znads presents two absorbance features. The energy space between the two absorbance peak features of the XANES K‐edge of tetrahedral Znads is 2.4 eV for Zn on quartz and 3.2 eV for Zn on SiO2(am). Linear combination fitting of samples with a mixture of Znads complex types demonstrates that the XANES spectra of octahedral and tetrahedral Znads on silica are distinct enough for quantitative identification. These results suggest caution when deciphering Zn speciation in natural samples via linear combination approaches using a single Znads standard to represent sorption on a particular mineral surface. Correlation between XANES spectral features and prior extended X‐ray absorption fine structure (EXAFS) derived coordination environments for these Znads on silica samples provides insight into Zn speciation in natural systems with XANES compatible Zn concentrations too low for EXAFS analysis. [ABSTRACT FROM AUTHOR]

Background: The phosphorus (P) stocks of arable subsoils not only influence crop production but also fertilizer P sequestration. However, the extent of this influence is largely unknown. This study aimed to (i) determine the extent of P sequestration with soil depth, (ii) analyze P speciation after long-term P fertilization, and (iii) compare soil P tests in predicting crop yields. We analyzed four long-term fertilizer trials in Germany to a depth of 90 cm. Treatments received either mineral or organic P, or a combination of both, for 16 to 113 years. We determined inorganic and organic P pools using sequential extraction, and P speciation using 31P nuclear magnetic resonance (NMR) and X-ray absorption near edge structure (XANES) spectroscopy. In addition, we applied three P soil tests, double-lactate (DL), calcium acetate lactate (CAL), and diffusive gradients in thin films (DGT). Results: The results suggested that plants are capable of mobilizing P from deeper soil layers when there is a negative P budget of the topsoil. However, fertilization mostly only showed insignificant effects on P pools, which were most pronounced in the topsoil, with a 1.6- to 4.4-fold increase in labile inorganic P (Pi; resin-P, NaHCO3–Pi) after mineral fertilization and a 0- to 1.9-fold increase of organic P (Po; NaHCO3–Po, NaOH–Po) after organic P fertilization. The differences in Po and Pi speciation were mainly controlled by site-specific factors, e.g., soil properties or soil management practice rather than by fertilization. When modeling crop yield response using the Mitscherlich equation, we obtained the highest R2 (R2 = 0.61, P < 0.001) among the soil P tests when using topsoil PDGT. However, the fit became less pronounced when incorporating the subsoil. Conclusion: We conclude that if the soil has a good P supply, the majority of P taken up by plants originates from the topsoil and that the DGT method is a mechanistic surrogate of P plant uptake. Thus, DGT is a basis for optimization of P fertilizer recommendation to add as much P fertilizer as required to sustain crop yields but as low as necessary to prevent harmful P leaching of excess fertilizer P. [ABSTRACT FROM AUTHOR]

The oxidation state of Cr, Cr2+/ΣCr (where ΣCr = Cr2+ + Cr3+ = 0.35 wt%), in Fe-free silicate glasses quenched from melts equilibrated as a function of pressure to 3.5 GPa at 1500 °C, and as a function of temperature to 1500 °C at atmospheric pressure, and at oxygen fugacities (fO2, in log units relative to the quartz-fayalite-magnetite (QFM) buffer) between ∆QFM = − 1 and − 2, was determined by XANES spectroscopy. Increasing temperature stabilises Cr2+ and increasing pressure stabilises Cr3+. A general expression for Cr3+/Cr2+ in silicate melts was derived: log(Cr3+/Cr2+) = 1/4(∆QFM + 8.58 − 25,050/T + 940P/T − 0.02P) + 9770/T − 7.69 + 6.22Λ + (900P − 172P2)/T, where P is pressure in GPa, T is temperature in K, and Λ is the optical basicity of the composition. This equation reproduces 213 Cr2+/ΣCr values reported here and in the literature with an average ΔCr2+/ΣCr of 0.02. A MORB melt at 1400 °C and QFM is predicted to have Cr2+/ΣCr ~ 0.35 at the surface but Cr2+/ΣCr ~ 0 at a depth of ~ 60 km. Although Cr2+ is an important oxidation state in silicate melts it is not preserved at low temperatures due to an electron exchange reaction with Fe3+. [ABSTRACT FROM AUTHOR]

Calcium (Ca) plays a crucial role for plant nutrition, soil aggregation, and soil organic matter (SOM) stabilization. Turnover and ecological functions of Ca in soils depend on soil Ca speciation. For the first time, we used synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy at the Ca K-edge (4038 eV) to investigate Ca speciation in soils. We present Ca K-edge XANES spectra of standard compounds with relevance in soils (e.g. calcite, dolomite, hydroxyapatite, anorthite, clay mineral-adsorbed Ca; Ca oxalate, formate, acetate, citrate, pectate, phytate). Calcium XANES spectra with good signal-to-noise ratios were acquired in fluorescence mode for Ca concentrations between 1 and 10 mg g−1. Most standard spectra differed markedly among each other, allowing the identification of different Ca species in soils and other environmental samples as well as Ca speciation by linear combination fitting. Calcium XANES spectra obtained for samples from different horizons of twelve temperate forest soils revealed a change from dominating lithogenic Ca to clay mineral-bound and/or organically bound Ca with advancing pedogenesis. O layer Ca was almost exclusively organically bound. With increasing SOM decomposition, shares of oxalate-bound Ca decreased. Oxalate-bound Ca was absent in calcareous, but not in silicate subsoil horizons, which can be explained by microbial decomposition in the former vs. stabilization by association to pedogenic minerals in the latter soils. Synchrotron-based Ca XANES spectroscopy is a promising novel tool to investigate the fate of Ca during pedogenesis and—when performed with high spatial resolution (µ-XANES), to study aggregation and SOM stabilization mechanisms produced by Ca. [ABSTRACT FROM AUTHOR]

The oxidation state of iron in mantle-derived melts is commonly used to determine the oxygen fugacity (f O 2) of magmas and their related sources. The accurate and precise determination of the iron oxidation state ratio of Mid-Oceanic Ridge Basalt (MORB) glasses has been a matter of controversy for the last three decades. None of the wet chemical methods used in the literature to measure this ratio converge toward a consensus value. The same difficulties have been observed for the most recent data obtained by XANES spectroscopy, which allows the measurement of the iron oxidation state ratio at high spatial resolution. This study unravels the origin of the analytical biases observed between the colorimetric and direct titration wet chemistries used in the studies of Christie et al. (1986) and Bézos and Humler (2005), respectively. We demonstrate that colorimetric measurements overestimate the ferrous iron contents of sulfide-bearing samples whereas the direct titration method does not suffer from such sulfide interference. Because MORB glasses contain significant amount of sulfur in the +2 valence state, we re-assessed the average MORB FeO/FeO total ratio by using the bulk FeO total and FeO data from this study and from Bézos and Humler (2005), respectively. We calculated for 49 MORB glasses an average FeO/FeO total of 0.90 ± 0.02. This result agrees with colorimetric measurements corrected for sulfide interference and with the results of Bézos and Humler (2005), if corrected for the presence of plagioclase in the sample powders. The average MORB FeO/FeO total that we determined in this study agrees also within uncertainty with the most recent XANES spectroscopic data of Berry et al. (2018) (0.90 ± 0.02). [ABSTRACT FROM AUTHOR]

Although sulfur cycling in acid mine drainage (AMD)-contaminated rice paddy soils is critical to understanding and mitigating the environmental consequences of AMD, potential sources and transformations of organosulfur compounds in such soils are poorly understood. We used sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy to quantify organosulfur compounds in paddy soils from five AMD-contaminated sites and one AMD-uncontaminated reference site near the Dabaoshan sulfide mining area in South China. We also determined the sulfur stable isotope compositions of water-soluble sulfate (δ 34 S WS ), adsorbed sulfate (δ 34 S AS ), fulvic acid sulfur (δ 34 S FAS ), and humic acid sulfur (δ 34 S HAS ) in these samples. Organosulfate was the dominant functional group in humic acid sulfur (HAS) in both AMD-contaminated (46%) and AMD-uncontaminated paddy soils (42%). Thiol/organic monosulfide contributed a significantly lower proportion of HAS in AMD-contaminated paddy soils (8%) compared to that in AMD-uncontaminated paddy soils (21%). Within contaminated soils, the concentration of thiol/organic monosulfide was positively correlated with cation exchange capacity (CEC), moisture content (MC), and total Fe (TFe). δ 34 S FAS ranged from -6.3 to 2.7‰, similar to δ 34 S WS (-6.9 to 8.9‰), indicating that fulvic acid sulfur (FAS) was mainly derived from biogenic S-bearing organic compounds produced by assimilatory sulfate reduction. δ 34 S HAS (-11.0 to -1.6‰) were more negative compared to δ 34 S WS , indicating that dissimilatory sulfate reduction and abiotic sulfurization of organic matter were the main processes in the formation of HAS.

• At low ƒO 2 conditions sulfur acts as an important anion. • In very reduced basaltic melts (

The synthesis of carbon nanotubes (CNTs) is usually done by metallic catalysts with a gaseous carbon precursor at high temperature. Yet, mild synthesis conditions can broaden the application of CNTs and their composites. In the present work, it is unraveled why partially substituted Fe ions in 2D MnO2 nanosheets lead to the growth of CNTs at low temperatures of 400−500 °C. The local formation of Fe3C by carbon precursor explains the unusually high catalytic activity of 2D FexMn1−xO2 nanosheets for preparing CNTs. Finally, Fe3C is oxidized to Fe3C/FeOx yolk/shell morphology in ambient atmosphere after the CNT formation reaction. These results shed light on the development of novel catalyst materials that allow for efficiently prepare CNTs under mild conditions for their wider use in energy‐harvesting applications. [ABSTRACT FROM AUTHOR]

Iron oxidation state and environment in magmas affect their phase diagram and their properties, including viscosity and density, which determine magma mobility and eruptive potential. In turn, magma composition, pressure, temperature and oxygen fugacity affect iron oxidation state and coordination, potentially leading to complex feedbacks associated with magma ascent, degassing and eruption. While equilibrium experiments and models have led to a deep understanding of the role of iron in melts, our knowledge of the effects of disequilibrium processes on iron oxidation state and its structural role in lavas and magmas remains limited. Accordingly, we performed a series of dynamic disequilibrium experiments on a natural melt composition (a phonolite lava from Erebus volcano, Antarctica) at atmospheric pressure, in which oxygen fugacity and temperature were controlled and varied. During the experiments, we continuously measured iron oxidation and coordination using Fe K-edge dispersive X-ray Absorption Spectroscopy (XAS). We found that iron oxidation state changes in the phonolite melt are reversible and well reproduced by existing models. Changes in iron oxidation state are driven by joint diffusion of alkali cations and oxygen anions at magmatic temperatures (~ 1000 °C for Erebus phonolite). However, redox diffusion timescales are too slow for any significant oxygen exchange with the atmosphere at the lava/air interface or via air entrainment. Turning to iron coordination, while Fe2+ and Fe3+ are present mostly in an average five-fold coordination, complex coordination variations decoupled from redox changes were detected. The data suggest transitions between Fe3+ in four-fold and six-fold coordination prior to reduction or as a consequence of oxidation. This questions the possible implication of Fe coordination changes in triggering crystallisation of magnetite nanolites upon magma ascent, and, through such crystallisation events, in promoting magma explosivity. [ABSTRACT FROM AUTHOR]

X-ray absorption near-edge structure (XANES) spectroscopy is a powerful technique to quantitatively investigate sulfur speciation in geologically complex materials such as minerals, glasses, soils, organic compounds, industrial slags, and extraterrestrial materials. This technique allows nondestructive investigation of the coordination chemistry and oxidation state of sulfur species ranging from sulfide (2- oxidation state) to sulfate (6+ oxidation state). Each sulfur species has a unique spectral shape with a characteristic K-edge representing the s → p and d hybridization photoelectron transitions. As such, sulfur speciation is used to measure the oxidation state of samples by comparing the overall XANES spectra to that of reference compounds. Although many S XANES spectral standards exist for terrestrial applications under oxidized conditions, new sulfide standards are needed to investigate reduced (oxygen fugacity, fO2, below IW) silicate systems relevant for studies of extraterrestrial materials and systems. Sulfides found in certain meteorites (e.g., enstatite chondrites and aubrites) and predicted to exist on Mercury, such as CaS (oldhamite), MgS (niningerite), and FeCr2S4 (daubréelite), are stable at fO2 below IW-3 but rapidly oxidize to sulfate and/or produce sulfurous gases under terrestrial surface conditions. XANES spectra of these compounds collected to date have been of variable quality, possibly due to the unstable nature of certain sulfides under typical (e.g., oxidizing) laboratory conditions. A new set of compounds was prepared for this study and their XANES spectra are analyzed for comparison with potential extraterrestrial analogs. S K-edge XANES spectra were collected at Argonne National Lab for FeS (troilite), MnS (alabandite), CaS (oldhamite), MgS (niningerite), Ni1-xS, NiS2, CaSO4 (anhydrite), MgSO4, FeSO4, Fe2(SO4)3, FeCr2S4 (daubréelite), Na2S, Al2S3, Ni7S6, and Ni3S2; the latter five were analyzed for the first time using XANES. These standards expand upon the existing S XANES end-member libraries at a higher spectral resolution (0.25 eV steps) near the S K-edge. Processed spectra, those that have been normalized and "flattened," are compared to quantify uncertainties due to data processing methods. Future investigations that require well-characterized sulfide standards, such as the ones presented here, may have important implications for understanding sulfur speciation in reduced silicate glasses and minerals with applications for the early Earth, Moon, Mercury, and enstatite chondrites. [ABSTRACT FROM AUTHOR]

X-ray absorption spectroscopy (XAS) is a new highly effective nondestructive technique for diagnostics of the local atomic and electronic structure of materials, including those that do not have long-range order in their atomic arrangement. In particular, X-ray absorption near edge structure (XANES) spectroscopy makes it possible to identify materials, to assess the oxidation states of atoms, and to find the parameters of the full 3D local structure around absorbing atoms with a high degree of accuracy, up to 1 pm for bond lengths and several degrees for bond angles. This review describes the current state and capabilities of XAS spectroscopy and, in particular, XANES in studying terrestrial and extraterrestrial natural materials. Modern synchrotron centers allow the acquisition of XAS spectra of materials with high energy and time resolutions, with microfocusing and nanofocusing, and spectral measurements under real conditions (for example, directly under high pressures and temperatures). These broad possibilities make X-ray absorption spectroscopy a unique highly effective technique for the diagnostics of geological materials. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray absorption near edge spectroscopy (XANES) and extended X-ray fine structure (EXAFS) are used to study the effect of temperature in the co-precipitation synthesis of iron oxides. Nanoparticles are rod-like and agglomerate into microscale aggregates. XANES spectra complement X-ray diffractometry in the phase identification of inverse spinel structured maghemite (γ-Fe2O3). In addition to the smallest crystallite size, EXAFS analysis revealed the highly distorted structure in the sample synthesized at 90°C. The samples synthesized at lower temperatures (25OC, 60OC) are ferrimagnetic with much larger magnetizations. The variation in magnetic properties with the synthetic temperature is related to the differences in crystallite size and distortion in the structure of γ-Fe2O3 nanoparticles. [ABSTRACT FROM AUTHOR]

Interaction of Cu (II) ions with the matrix of soil and mineral phases of layered silicates was assessed by the Miller method of selective sequential fractionation and a set of synchrotron X-ray methods, including X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XANES). It was shown that the input of Cu into Calcic Chernozem in the form of monoxide (CuO) and salt (Cu(NO3)2) affected the transformation of Cu compounds and their affinity for metal-bearing phases. It was found that the contamination of soil with a soluble Cu(II) salt increased the bioavailability of the metal and the role of organic matter and Fe oxides in the fixation and retention of Cu. During the incubation of soil with Cu monoxide, the content of the metal in the residual fractions increased, which was related to the possible entry of Cu in the form of isomorphic impurities into silicates, as well as to the incomplete dissolution of exogenic compounds at the high level of their input into the soil. A mechanism for the structural transformation of minerals was revealed, which showed that ion exchange processes result in the sorption of Cu (II) ions from the saturated solution by active sites on the internal surface of the lattice of dioctahedral aluminosilicates. Surface hydroxyls at the octahedral aluminum atom play the main role. X-ray diagnostics revealed that excess Cu(II) ions are removed from the system due to the formation and precipitation of coarsely crystalline Cu(NO3)(OH)3.

Palaeontology relies on the description of fossil morphologies to understand the evolutionary history of life on Earth. Yet much remains unknown about the impact of fossilization processes, even though these may introduce biases into palaeobiological interpretations. Here, we report the characterization of fossilized remains of the earliest known woody plant Armoricaphyton chateaupannense preserved either in 2D (as flat carbonaceous films) or in 3D (as organo‐mineral structures) in early Devonian shales (c. 407 Ma) of the Armorican Massif on the northern margin of Gondwana. To document the fine‐scale structure and the chemistry of the tracheids of this ancient plant, we used propagation phase contrast synchrotron radiation X‐ray microcomputed tomography (PPC‐SRμCT), transmission electron microscopy (TEM) and synchrotron‐based scanning transmission X‐ray microscopy (STXM) coupled with X‐ray absorption near edge structure (XANES) spectroscopy. PPC‐SRμCT enables digital visualization of cell walls in unprecedented detail for the specimens preserved in 3D revealing structures similar to those observed in extant lignified cells, thereby strongly suggesting that the earliest woody plant A. chateaupannense originally contained lignin compounds. STXM‐based XANES and TEM data show that, whatever the preservation modes (3D vs 2D), the remaining organic matter has a chemical composition rather typical of pyrobitumen compounds, raising the possibility of an original source other than lignin. The pyrobitumen compounds also contains automorphic Ti‐nanominerals interpreted as a diagenetic feature. Altogether, the present study illustrates that anatomical and chemical preservations may not always be correlated. [ABSTRACT FROM AUTHOR]

Marine carbonate rocks are composed, in varying abundance, of cement, micrite, abiotic grains and fossils, which can provide information about the physical and chemical environments in which they formed. Geochemical analyses of these carbonates are not always interpreted alongside the wealth of geologic (including petrographic) information available, resulting in potentially faulty reconstructions of biogeochemical and environmental conditions. These concerns have prompted closer scrutiny of the effect of depositional lithofacies and diagenesis on carbonate proxies. Here, we have combined X-ray Absorption Near Edge Structure (XANES) spectroscopy and μ-X-ray Fluorescence (μ-XRF) imaging to map the speciation and abundance of sulfur in carbonate petrographic thin sections in Upper Ordovician carbonates from Anticosti Island, Canada and early Silurian carbonates from Gotland, Sweden, across multiple depositional facies. Lithofacies and fossil communities between Anticosti Island and Gotland are similar, which allows for comparison of changes in the dominant S species and their abundance in separate basins, associated with variations in (glacio)eustatic sea level. Sulfide abundance is greatest in mudstone, wackestone and packstone facies, where interstitial micrite hosts abundant pyrite. Sulfate abundance, as carbonate-associated sulfate (CAS), varies within individual fossil fragments, as well as within the same fossil phylum and is particularly high in unaltered brachiopods. In contrast, sulfate abundance is generally very low in micrite (near the detection limit) and generally arises in situ from sulfide that has been oxidized as opposed to true CAS. In different cement fabrics, sulfate abundance is greatest in drusy, pore-filling cements. Organic sulfur compounds are also detected and, although low in abundance, are mostly found within micrite. The detection and characterization of both inorganic sulfur and organic sulfur compounds provides a platform to understand early processes of biomineralization. This approach will broaden our understanding of the source of inorganically bound sulfate in ancient carbonates, as well as the effect of depositional setting and diagenesis on CAS incorporation, (re)mobilization, and ultimate abundance in sedimentary carbonates. Additionally, this work has implications for the CAS isotopic value of individual carbonate components that may affect interpretations of stratigraphic variability of numerous CAS sections throughout Earth history. [ABSTRACT FROM AUTHOR]

Refined data on the crystal structure, chemical composition and properties of jouravskite, ideally Ca3Mn4+(SO4)(CO3)(OH)6·12H2O, have been obtained on a sample from N'Chwaning 3 Mine, Kuruman, Kalahari manganese field, Northern Cape Province, South Africa. The chemical composition determined using a combination of different methods (including ICP-OES, gas chromatography of products of ignition and electron microprobe) is (wt%): CaO 25.88, SrO 0.19, BaO 0.23, B2O3 0.39, Fe2O3 1.01, MnO2 12.00, SiO2 0.06, CO2 6.8, SO3 12.44, H2O 41.8, total 100.80, which corresponds to the empirical formula (Z = 2): (Са2.98Sr0.01Ba0.01)Σ3.00(Mn4+0.89Fe3+0.08Si0.01)Σ0.98{(SO4)1.00(CO3)1.00[B(OH)4]0.07}Σ2.07(OH)5.78·11.94H2O. Tetravalent state of Mn was confirmed by Mn K-edge XANES spectroscopy. The IR spectrum of jouravskite contains characteristic bands of Mn4+(OH)6 octahedra, CO32− and SO42− anions, and H2O molecules. The crystal structure was determined using single-crystal X-ray diffraction data and refined to R = 0.0332. Jouravskite is isostructural with thaumasite. The parameters of the hexagonal (space group P63) unit cell are: a = 11.07129(14) Å, c = 10.62650(14) Å, V = 1128.02(3) Å3 and Z = 3. Investigation of other samples of ettringite-group minerals from N'Chwaning 3 Mine demonstrates wide variations of the contents of manganese, iron and boron, and possible existence of a Mn4+-dominant analogue of sturmanite with the presumed idealized formula Са6Mn4+2(SO4)2[B(OH)4](OH)10O2·nH2O. [ABSTRACT FROM AUTHOR]

Abstract Selenium is an essential trace element for which dietary intake is not sufficient in many parts of the world such as in Europe. Yeast and mushrooms may accumulate considerable amounts of selenium, but the chemical form in mushrooms has not been elucidated yet. Thus, we determined the selenium speciation of selenium-enriched button mushrooms in comparison to that of selenized yeast via Se K-edge XANES spectroscopy. Quantitative analysis of the XANES spectra revealed that the selenium in selenized yeast is mainly present as seleno-methionine but that in selenium-enriched button mushrooms, it is present predominantly as Se -methyl- l -selenocysteine. As this form is highly bioavailable and directly enters the selenium metabolic pool, selenium-enriched mushrooms may be a good food choice to improve selenium intake. [ABSTRACT FROM AUTHOR]

A comprehensive study of the Jiddat Al Harasis 055 (L4-5 type) ordinary chondrite is conducted using 2D X-ray fluorescence spectroscopy, Mössbauer spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy, X-ray diffraction, and vibrating sample magnetometry. The content of Fe, Ni, Si, Mg, S, Ca, Al, Mn, Ti, and Cr is determined; several components and areas with increased content of S, Ti, Cr, and Ni are detected along with several Ca-Al inclusions. According to XANES data, the Jiddat Al Harasis 055 sample contains iron with the average oxidation state 2.4+. This result is consistent with the data of Mössbauer spectroscopy used to identify iron phases which testifis that 46% and 54% of iron ions appear in Fe2+ and Fe3+ states, respectively. By comparing the pre-edge energy position and the area under the preedge peak of XANES spectra with literature data reported for geological materials, the average coordination number in the first coordination sphere of iron is found to be 5.3. According to the data of Xray diffraction and Mössbauer spectroscopy, the iron-containing meteorite phases consist mainly of olivine, pyroxene, hematite, and goethite. The observed magnetic properties of the sample can be attributed to small inclusions of ferromagnetic phases such as nickel nanoparticles, which cannot be reliably identified using laboratory spectral methods. [ABSTRACT FROM AUTHOR]

A review of current works on XANES spectroscopy applied for the determination of parameters of a threedimensional local atomic structure of nanostructured materials is given. Special attention is paid to a new method based on the theoretical analysis of XANES spectra by means of multivariate interpolation. The uniqueness of the technique consists not only in the highly accurate (up to 0.01 Å) determination of interatomic distances in materials without a long-range order in the atomic arrangement but also the estimation of the angular distribution of atoms (i.e. chemical bond angles) in any condensed materials. Several types of nanostructured materials, including coordination compounds, semiconductor quantum dots, nanosized structures in quasicrystals and extraterrestrial materials are given as examples. [ABSTRACT FROM AUTHOR]