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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

X-ray Computed Tomography of Irradiated and Unirradiated AGR-3/4 Compacts

X-ray Computed Tomography (XCT) has been utilized to image and characterize compacts from the combined third and fourth irradiation of the Advanced Gas Reactor (AGR) Program, AGR-3/4, fuel. The experiment contained tristructural isotropic (TRISO)-coated fuel particles as well as designed-to-fail (DTF) fuel particles. Two irradiated compacts, representing the lower and higher range of AGR-3/4 burnup (4.85% and 14.92% fissions per initial heavy metal atom FIMA) were examined. These represent the first known highly irradiated TRISO fuel compacts to be examined via X-ray CT. Additionally, two unirradiated compacts from the same production batch as the examined irradiation compacts were also imaged for a baseline comparison. As XCT of irradiated TRISO compacts is not a commonly implemented characterization technique, a significant portion of the report focuses on developed methodology and imaging conditions. A specialized sample shielding device was developed and fabricated specifically to limit received dose to staff during sample preparation for XCT and to minimize excess gamma radiation dose to sensitive electronic components with the utilized X-ray system. Significant penetration through the uranium oxycarbide fuel kernels by significantly hardening the X-ray beam with specialized proprietary filters acquired from Carl Zeiss NTS Ltd. The filter utilized resulted in an average X ray photon energy of ~110 keV which approaches uranium’s K-edge (~115 keV), maximizing penetration for a microfocus X-ray source. The gamma-radiation emitted from the irradiated AGR-3/4 TRISO compacts, has the same properties and mechanisms for interaction with matter as X-rays, thus the detection of gamma-radiation by the utilized X-ray detectors was initially a concern. However, although ?-rays did produce an observable signal on the X-ray detector, its contribution to the overall imaging results appeared negligible upon 3D reconstruction. The neglibile impact on the resulting 3D reconstructed volumes were likely the result of: (1) a significantly lower detection efficiency for ?-rays relative to X-rays; (2) An X-ray flux at the detector several orders of magnitude higher than that of the impinging ?-rays from the irradiated compacts. These results suggest that irradiated compacts with significantly higher radiation fields can be examined in the future if an acceptable route for sample handling and preparation can be determined. Additionally, the 3D imaging results of XCT can provide a valuable means of assessing compacts. While in many ways complimentary to traditional post irradiation examination techniques such as optical ceramography, XCT can provide additional insight into compact features traditionally difficult to discern directly from cross-sectional imaging alone. Preliminary analyses on kernel size, morphology (aspect ratio and sphericity), and kernel orientation were presented. Sphericity, a simple morphological shape descriptor, was utilized to screen for kernel extrusions within the high burnup compact. The number of kernel extrusions identified via XCT represented an approximate two-fold increase from the quantity of extruded particles observed (via optical ceramography) in adjacent compacts from the same irradiation capsule. While numerical analysis of the compact datasets was highly preliminary, initial results show promise for providing complimentary metrics to current AGR-3/4 PIE and potentially additional insight into the processes driving TRISO fuel degradation during reactor operation. Additional analyses to be performed at a later date include a more detailed examination of kernel size, kernel sphericity (and observed kernel extrusions), and sphericity. Given all particles can be observed in a single data volume possible correlation of spatial position with observed kernel features will also be made at a later date.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2016

K-Shell Photoabsorption and Photoionisation of Trace Elements I. Isoelectronic Sequences With Electron Number 3< or = N < or = 11

Context. With the recent launching of the Hitomi X-ray space observatory, K lines and edges of chemical elements with low cosmic abundances, namely F, Na, P, Cl, K, Sc, Ti, V, Cr, Mn, Co, Cu and Zn, can be resolved and used to determine important properties of supernova remnants, galaxy clusters and accreting black holes and neutron stars.Aims. The second stage of the present ongoing project involves the computation of the accurate photoabsorption and photoionisation cross sections required to interpret the X-ray spectra of such trace elements.Methods. Depending on target complexity and computer tractability, ground-state cross sections are computed either with the close-coupling Breit-Pauli R-matrix method or with the autostructure atomic structure code in the isolated-resonance approximation. The intermediate-coupling scheme is used whenever possible. In order to determine a realistic K-edge behaviour for each species, both radiative and Auger dampings are taken into account, the latter being included in the R-matrix formalism by means of an optical potential.Results. Photoabsorption and total and partial photoionisation cross sections are reported for isoelectronic sequences with electron numbers 3< or = N< or = 11. The Na sequence (N=11) is used to estimate the contributions from configurations with a 2s hole (i.e. [2s]) and those containing 3d orbitals, which will be crucial when considering sequences with N 11.Conclusions. It is found that the [2s/u] configurations must be included in the target representations of species with N> 11 as they contribute significantly to the monotonic background of the cross section between the L and K edges. Configurations with 3d orbitals are important in rendering an accurate L edge, but they can be practically neglected in the K-edge region.

atomic data / X-rays: general↗
DOE OSTI2023

Wave vector and field vector orientation dependence of Fe K pre-edge X-ray absorption features in clinopyroxenes

Abstract Pre-edge X-ray absorption features are commonly used to derive redox states for transition metal oxides in crystals and glasses. Several calibrations for Fe2+ and Fe3+ in silicate glasses have utilized the general relationships among pre-edge peak intensity, energy, and redox state. However, absorption variations complicate those relationships in anisotropic crystals. Although absorption anisotropy at and above the energy of the rising edge adheres to the typical cos2 relationship observed in absorption spectroscopies at other energies, the anisotropy of the pre-edge is far more complicated. Prior studies focusing on pre-edge absorption anisotropy demonstrate a 1-cos4φ dependence of absorption magnitudes with rotation. Experiments presented here show that absorption magnitudes of the pre-edge vary as a function of both electric field vector orientation and wave vector direction. However, rotations around the field vector axis or wave vector axis individually result in cos2 dependence of absorption magnitudes. Rotations where both wave vector and field vector orientation are varied are not well fit by either model in the pre-edge. The resulting anisotropy complicates the process of measuring characteristic absorption in the pre-edge, making valence state determinations challenging for strongly anisotropic crystal structures such as pyroxene.

Geochemistry & Geophysics↗
DOE OSTI2021

Effect of 3d/4p Mixing on 1s2p Resonant Inelastic X-ray Scattering: Electronic Structure of Oxo-Bridged Iron Dimers

1s2p resonant inelastic X-ray scattering (1s2p RIXS) has proven successful in the determination of the differential orbital covalency (DOC, the amount of metal vs ligand character in each d molecular orbital) of highly covalent centrosymmetric iron environments including heme models and enzymes. However, many reactive intermediates have noncentrosymmetric environments, e.g., the presence of strong metal-oxo bonds, which results in the mixing of metal 4p character into the 3d orbitals. This leads to significant intensity enhancement in the metal K-pre-edge and as shown here, the associated 1s2p RIXS features, which impact their insight into electronic structure. Binuclear oxo bridged high spin Fe(III) complexes are used to determine the effects of 4p mixing on 1s2p RIXS spectra. In addition to developing the analysis of 4p mixing on K-edge XAS and 1s2p RIXS data, this study explains the selective nature of the 4p mixing that also enhances the analysis of L-edge XAS intensity in terms of DOC. These 1s2p RIXS biferric model studies enable new structural insight from related data on peroxo bridged biferric enzyme intermediates. The dimeric nature of the oxo bridged Fe(III) complexes further results in ligand-to-ligand interactions between the Fe(III) sites and angle dependent features just above the pre-edge that reflect the superexchange pathway of the oxo bridge. Lastly, we present a methodology that enables DOC to be obtained when L-edge XAS is inaccessible and only 1s2p RIXS experiments can be performed as in many metalloenzyme intermediates in solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Deciphering the Oxygen Absorption Pre-edge: A Caveat on its Application for Probing Oxygen Redox Reactions in Batteries

The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal (TM) oxide studies in various fields, especially on the fervent topic of oxygen redox states in battery electrodes. However, critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions, which has been a popular practice in the battery field. This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements, structures, and electrochemical states through combined experimental and theoretical analyses. It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states. Furthermore, the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window, leading to a summary map of the relative energy positions of the low-lying TM states, with higher TM oxidation states at lower energies, corresponding to higher electrochemical potentials. The results naturally clarify some unusual redox reactions, such as Cr 3+/6+ . This work provides a critical clarification on O-K pre-edge interpretation and more importantly a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.

36 MATERIALS SCIENCE↗
NASA NTRS1994

Optical, IUE, and ROSAT observations of the eclipsing nova-like variable V347 Puppis (LB 1800)

Using time-resolved optical spectroscopy and UBVRI and high-speed photometry obtained at Mount Stromlo Observatory, Mount John University Observatory, and the South African Astronomical Observatory; International Ultraviolet Explorer (IUE) ultraviolet spectroscopy; and Roentgen Satellite (ROSAT) survey X-ray fluxes, we present a study of the accretion disk, hot spot, and emission line regions in the bright eclipsing nova-like variable V347 Pup (LB 1800). In the optical and UV, V347 Pup is a strong emission line source with a continuum spectrum which is remarkably red for a high-M cataclysmic variable. Consistent with its high inclination, we interpret the continuum spectrum as the superposition of the spectrum of the cool (T(sub eff) approximately 7000 K) outer edge and the hot (T(sub eff) approximately 100,000 K) inner regions of a self-eclipsed accretion disk. For the assumed parameters, the model matches the level and shape of the observed spectrum for an inclination of approximately 88 and a distance of approximately 300 pc. The prominent hump in the optical and UV light curves just before eclipse manifests the presence of the hot spot where the accretion stream strikes the edge of the disk. The wavelength dependence of the amplitude of the hump is best modeled by a spot having an effective temperature of approximately 25,000 K and an area of approximately 3 x 10(exp 18) sq cm if the spot radiates like a blackbody, or an effective temperatue of approximately 14,000 K and an area of approximately 3 x 10(exp 19) sq cm if it radiates with a stellar spectrum. In either case, the hot spot produces only one-tenth of the predicted luminosity for the assumed mass-transfer rate of 10(exp -8) solar mass/yr. Either the hot spot is 'buried' in the edge of the accretion disk, or a significant fraction of its luminosity is radiated away in lines. The difference in azimuth between the peak of the hump and the dynamically expected location of the hot spot suggests that the spot's emitting surface is rotated forward by approximately 36 deg relative to the edge of the disk.

Mauche, Christopher W.↗
NASA NTRS1997

Simultaneous X-ray and Far-Ultraviolet Spectra of AGN with ASCA and HUT

We obtained ASCA spectra of the Seyfert 1 galaxy NGC 3516 in March 1995. Simultaneous far-UV observations were obtained with the Hopkins Ultraviolet Telescope on the Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law of energy index 0.78. The low energy absorbing column is significantly less than previously seen. Prominent 0 VII and 0 VIII absorption edges are visible, but, consistent with the much lower total absorbing column, no Fe K absorption edge is detectable. A weak, narrow Fe K(alpha) emission line from cold material is present as well as a broad Fe K(alpha) line. These features are similar to those reported in other Seyfert 1 galaxies. A single warm absorber model provides only an imperfect description of the low energy absorption. In addition to a highly ionized absorber with ionization parameter U = 1.66 and a total column density of 1.4 x 10(exp 22)/sq cm, adding a lower ionization absorber with U = 0.32 and a total column of 6.9 x 10(exp 21)/sq cm significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to less than 160 km/s at 90% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fit to the X-ray spectrum can match the observed equivalent widths of all the UV absorption lines. Accounting for the X-ray and UV absorption simultaneously requires an absorbing region with a broad range of ionization parameters and column densities.

Kriss, Gerard A.↗
NASA NTRS2002

A Chandra Spectroscopic Survey of Persistent Black Hole Candidates

We present results from observations of persistent black hole candidates with the High-Energy Transmission Gratings on board the Chandra X-Ray Observatory. The sources include LMC X-1, LMC X-3, GRS 1758-258, and Cyg X-1. Along with the published results on 1E 1740.7-2942, we have completed a high-resolution spectroscopic survey of such systems. The observed X-ray spectra of LMC X-1 and LMC X-3 show no prominent discrete features, while absorption edges (Mg K and Si K) are detected in the spectrum of GRS 1758-258. The edges are likely to be of interstellar origin. In most cases, the X-ray continuum can be described well by models that are often adopted in low-resolution studies of black hole candidates: a multitemperature disk spectrum plus a Comptonization component. However, the relative contribution of the two components varies greatly among different sources. For instance, only the disk component is present for LMC X-1 and GRS 1758-258, while the Comptonized component is required for other sources. We discuss general issues related to obtaining disk parameters from modeling X-ray continuum.

Cui, Wei↗
DOE OSTI2025

Thermal Performance of a Conduction-Cooled CCT Dipole ReBCO Magnet: Several Cycles of Cool-Down and Thermal Gradient Measurements

Here, this paper presents experimental results from conduction-cooled thermal testing of a ReBCO canted cosine theta (CCT) magnet (C2), originally designed and fabricated at LBNL using CORC cables. While the performance of the coil under liquid helium and nitrogen environments has been previously established, this study explores its behavior under conduction cooling using a large test cryostat at The Ohio State University. The magnet, measuring 613 mm in length and weighing ∼75 kg, consists of four helical layers wound with ReBCO-based CORC wire and was thermally anchored to a copper cold ring supported by a G-10 strongback. Cooling was provided by two Sumitomo RDK-415D cryocoolers, offering a combined 3 W at 4.2 K and 150 W at 77 K. Multiple thermal cycles were performed, with cooldown durations of up to 45 hours. Final base temperatures of approximately 10.8 K (at the coil edge) and 12.0 K (at the coil center) were achieved, with an axial temperature difference of approximately 1.2 K. The warm-up period extended over approximately 24.6 hours. Voltage measurements from all four layers were recorded during cooldown and warmup. The system demonstrated stable cooldown performance, repeatable gradients, and good thermal anchoring. These results support the feasibility of conduction cooling in large-scale HTS magnets, aligning with broader goals for “green” cryogen-free accelerator technologies and paving the way for more sustainable, scalable, and energy-efficient high-field magnet systems in next-generation particle accelerators.

Canted cosine theta magnets↗
DOE OSTI2025

M-Edge Spectroscopy of Transition Metals: Principles, Advances, and Applications

M-edge X-ray absorption spectroscopy (XAS), which probes 3p→3d transitions in first-row transition metals, provides detailed insights into oxidation states, spin-states, and local electronic structure with high element and orbital specificity. Operating in the extreme ultraviolet (XUV) region, this technique provides sharp multiplet-resolved features with high sensitivity to ligand field and covalency effects. Compared to K- and L-edge XAS, M-edge spectra exhibit significantly narrower full widths at half maximum (typically 0.3–0.5 eV versus >1 eV at the L-edge and >1.5–2 eV at the K-edge), owing to longer 3p core-hole lifetimes. M-edge measurements are also more surface-sensitive due to the lower photon energy range, making them particularly well-suited for probing thin films, interfaces, and surface-bound species. The advent of tabletop high-harmonic generation (HHG) sources has enabled femtosecond time-resolved M-edge measurements, allowing direct observation of ultrafast photoinduced processes such as charge transfer and spin crossover dynamics. This review presents an overview of the fundamental principles, experimental advances, and current theoretical approaches for interpreting M-edge spectra. We further discuss a range of applications in catalysis, materials science, and coordination chemistry, highlighting the technique’s growing impact and potential for future studies.

M-edge XANES↗
DOE OSTI2024

Validation of the Scientific Program for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) was designed to conduct a survey covering 14,000 deg$^{2}$ over 5 yr to constrain the cosmic expansion history through precise measurements of baryon acoustic oscillations (BAO). The scientific program for DESI was evaluated during a 5 month survey validation (SV) campaign before beginning full operations. This program produced deep spectra of tens of thousands of objects from each of the stellar Milky Way Survey (MWS), Bright Galaxy Survey (BGS), luminous red galaxy (LRG), emission line galaxy (ELG), and quasar target classes. These SV spectra were used to optimize redshift distributions, characterize exposure times, determine calibration procedures, and assess observational overheads for the 5 yr program. In this paper, we present the final target selection algorithms, redshift distributions, and projected cosmology constraints resulting from those studies. We also present a One-Percent Survey conducted at the conclusion of SV covering 140 deg$^{2}$ using the final target selection algorithms with exposures of a depth typical of the main survey. The SV indicates that DESI will be able to complete the full 14,000 deg$^{2}$ program with spectroscopically confirmed targets from the MWS, BGS, LRG, ELG, and quasar programs with total sample sizes of 7.2, 13.8, 7.46, 15.7, and 2.87 million, respectively. These samples will allow exploration of the Milky Way halo, clustering on all scales, and BAO measurements with a statistical precision of 0.28% over the redshift interval z < 1.1, 0.39% over the redshift interval 1.1 < z < 1.9, and 0.46% over the redshift interval 1.9 < z < 3.5.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Utilization of Novel (KNbO 3 ) 1− x (Ba 2 FeNbO 6 ) x ( x = 0.1, 0.2, 0.3) Solid Solutions for Efficient Photo‐Assisted Fenton Degradation of Methylene Blue Dye

Novel (KNbO 3 ) 1− x (Ba 2 FeNbO 6 ) x ( x = 0.1, 0.2, 0.3) solid solutions corresponding to K 0.82 Ba 0.18 Fe 0.09 Nb 0.91 O 3 , K 0.64 Ba 0.36 Fe 0.18 Nb 0.82 O 3 , and K 0.46 Ba 0.54 Fe 0.27 Nb 0.73 O 3 compounds have been synthesized via molten salt method. X‐ray diffraction confirms the formation of solid solutions, while transmission electron microscopy combined with energy‐dispersive spectroscopy results demonstrates a homogeneous distribution of elements. The obtained solid solutions crystallized in a cubic crystal structure, whereas the parent KNbO 3 possesses an orthorhombic structure. The wide bandgap semiconductor KNbO 3 transformed into a visible‐light‐active material, with its bandgap energy reduced from 3.56 eV to ≈2.4 eV. The substitution of K in KNbO 3 with Ba is responsible for structural modification from orthorhombic to cubic symmetry, whereas both structural modification and the substitution of Nb with Fe correlated with optical properties. The photocatalytic activities of all obtained solid solutions are improved compared with the parent KNbO 3 and Ba 2 FeNbO 6 compounds for photocatalytic degradation of methylene blue (MB) dye. Among the series of solid solutions, K 0.82 Ba 0.18 Fe 0.09 Nb 0.91 O 3 photocatalysts show the highest MB removal efficiency owing to its relatively higher surface area, suppressed charge carrier recombination, and more negative conduction band edge. Moreover, K 0.82 Ba 0.18 Fe 0.09 Nb 0.91 O 3 photocatalyst (0.1 g) combined with hydrogen peroxide (H 2 O 2 ) to form a novel photo‐Fenton system, achieving almost complete degradation of 100 mL of 10 mg L −1 MB dye in 30 min.

Avcıoğlu, Celal [Technische Universität Berlin, Fa↗
NASA NTRS1984

Transient dips of Cygnus X-1 observed from Tenma

The transient intensity dips of the binary system Cyg X-1 have been observed, using the gas scintillation proportional counter (GSPC) array onboard the Tenma X-ray astronomy satellite. The duration of the dips was in the range from several seconds to 10 minutes, with several dips occurring as much as 15 h before the superior conjunction. Within the dips, complex structures were observed with time scales of several seconds, and, in at least one case, shorter than two seconds. For a dip lasting longer than 10 minutes, a high-quality spectrum was obtained which reveals the K-absorption edge of iron at 7.18 + or - 0.18 keV. On the basis of the observed absorption, it is suggested that the dips are caused by absorption due to relatively cool matter (less than about 30,000 k); the low-energy excess observed during the dips is due either to an extended soft X-ray emitting corona or to partial obscuration of the X-ray source by multiple blobs. From the time structure of the dip, a blob size of the order of 10 to the 9th cm is derived.

Kitamoto, S.↗
DOE OSTI2021

X-ray spectroscopic identification of strain and structure-based resonances in a series of saturated carbon-cage molecules: Adamantane, twistane, octahedrane, and cubane

Novel nanocarbons such as fullerenes, nanotubes, graphene, and nanodiamond reside at the cutting edge of nanoscience and technology. Along with chemical functionalization, geometric constraints (such as extreme curvature in nanotubes or defects within or at the surfaces of diamond nanoparticles) significantly alter the electronic states of the nanocarbon material. Understanding the effects of steric strain on the electronic structure is critical to developing nanoelectronic applications based on these materials. This paper presents a fundamental study of how strain affects the electronic structure in a benchmark series of some fundamental saturated carbon cage compounds. Adamantane, C10H16, the smallest diamondoid and arguably the smallest nanodiamond crystallite, has carbon atoms essentially commensurate with diamond lattice positions and possesses by far the least molecular strain of this series. Twistane also is a C10H16 isomer but the fixed cyclohexane twist conformation of the central ring introduces additional strain into the cage. Octahedrane [(CH)12] and cubane [(CH)8] are considerably more strained, culminating in cubane where carbon–carbon bonds lie either parallel or orthogonal to one another. Using gas-phase near-edge x-ray absorption fine structure spectroscopy to probe the unoccupied electronic states, we observe two major progressions across this series. First, a broad C–C σ* resonance in the absorption splits into two more narrow and intense resonances with increasing strain. Second, the first manifold of states previously associated with tertiary C–H σ* in the diamondoid series appears to broaden and shift to lower energy. This feature is more than twice as intense in cubane than in octahedrane, even though these two molecules have only tertiary carbons, with the chemical formula (CH)x. The spectral differences are entirely due to the shape of the molecules; in particular, in cubane, the features arise from a high degree of p-p interaction between parallel C–C bonds. In contrast to the conventional wisdom that near-edge x-ray absorption is primarily an atomically localized spectroscopy, molecular shape and associated strain lead to the dominant features in spectra acquired from this fundamental series of carbon cage structures.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Anomalous X-Ray Scattering and Extended X-Ray Absorption Fine Structure Study of the Local Structure of CrFeCoNiMo x (x = 0.11, 0.18, and 0.23) High-Entropy Alloys

Anomalous x-ray scattering (AXS) and extended x-ray absorption fine structure (EXAFS) were used to determine the local structure of Mo in CrFeCoNiMo x (x = 0.11, 0.18, and 0.23), a high-entropy alloy with a face-centered cubic (FCC) lattice. No superlattice peaks were observed down to the 10 -4 intensity level. This observation along with the nearly constant decrease of the FCC diffraction peaks above the Mo K absorption edge suggests that Mo atoms have no preferred site occupancy in the FCC lattice. Modeling of the EXAFS data suggests a local chemical order in CrFeCoNiMo x , where in Mo-rich samples (e.g., x = 0.23), Mo atoms are preferably surrounded by lighter atoms, such as Cr.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Phosphate-modulated transformation of Sb(V)-bearing ferrihydrite under microbial iron- and sulfate-reducing conditions

Antimony (Sb) is a toxic metalloid that poses environmental risks in terrestrial and aquatic systems. The fate of the Sb(V) oxyanion, Sb(OH) 6 − , is governed by complex biogeochemical processes, including immobilization by ferric (Fe(III)) oxides, reduction by sulfide, and the less-explored competitive adsorption with other anions such as phosphate (PO 4 3− ). Here, this study investigates the interplay between such mechanisms in controlling the behavior of Sb(V) associated with ferrihydrite (Fh) under Fe(III)- and sulfate-reducing conditions, with a particular emphasis on the role of phosphate in influencing Sb(V) mobility and transformation. Anoxic reactors that contained Sb(V)-coprecipitated Fh, varying PO 4 3− concentrations (0, 0.2, and 2 mM), and sulfate, were inoculated with a microbial community sourced from Sb-contaminated soil. Additionally, abiotic reactors with either Sb(V)-adsorbed or Sb(V)-coprecipitated Fh and different PO 4 3− loadings (0–100 mM) were created to investigate the competitive adsorption mechanisms in the absence of microbial activity. Results from the abiotic reactors suggest that Sb(V) is likely incorporated into the Fh structure, with only minor amounts remaining surface-bound and extractable by PO 4 3− . In the biotic reactors, microbial Fe(III) and sulfate reduction were more extensive in the presence of PO 4 3− . At 0.2 mM PO 4 3− , microbial activity transformed Fh into siderite and led to the complete reduction of Sb(V) to Sb(III) as stibnite (Sb 2 S 3 ). At 2 mM PO 4 3− , the greater coverage by PO 4 3− stabilized Fh and decreased the extent of both Fe(III) and Sb(V) reduction, and shifted the reduced products to mackinawite and Sb(III) adsorbed onto Fh, in addition to stibnite formation. This study demonstrates that while PO 4 3− may not directly compete with Sb(V) for sorption sites, it can influence Sb mobility in Fe(III)- and sulfate-reducing environments by enhancing microbial activity and altering the mineralization pathways.

Microbial Fe(III) and sulfate reduction↗