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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Lattice Mie resonances and emissivity enhancement in mid-infrared iron pyrite metasurfaces

High-refractive-index antennas with characteristic dimensions comparable to wavelength have a remarkable ability to support pronounces electric and magnetic dipole resonances. Furthermore, periodic arrangements of such resonant antennas result in narrow and strong lattice resonances facilitated by the lattice. We design iron pyrite antennas operating in the mid-infrared spectral range due to the material’s low-energy bandgap and high refractive index. We utilize Kirchhoff’s law, stating that emissivity and absorptance are equal to each other in equilibrium, and we apply it to improve the thermal properties of the iron pyrite metasurface. Through the excitation of collective resonances and manipulation of the antenna lattice’s period, we demonstrate our capacity to control emissivity peaks. These peaks stem from the resonant excitation of electric and magnetic dipoles within proximity to the Rayleigh anomalies. In the lattice of truncated-cone antennas, we observe Rabi splitting of electric and magnetic dipole lattice resonances originating from the antennas’ broken symmetry. We demonstrate that the truncated-cone antenna lattices support strong out-of-plane magnetic dipole lattice resonances at oblique incidence. We show that the truncated-cone antennas, as opposed to disks or cones, facilitate a particularly strong resonance and bound state in the continuum at the normal incidence. Our work demonstrates the effective manipulation of emissivity peaks in iron pyrite metasurfaces through controlled lattice resonances and antenna design, offering promising avenues for mid-infrared spectral engineering.

Islam, Md Sakibul↗
DOE OSTI2019

Soil Microbiome Dynamics During Pyritic Mine Tailing Phytostabilization: Understanding Microbial Bioindicators of Soil Acidification

Challenges to the reclamation of pyritic mine tailings arise from in situ acid generation that severely constrains the growth of natural revegetation. While acid mine drainage (AMD) microbial communities are well-studied under highly acidic conditions, fewer studies document the dynamics of microbial communities that generate acid from pyritic material under less acidic conditions that can allow establishment and support of plant growth. This research characterizes the taxonomic composition dynamics of microbial communities present during a 6-year compost-assisted phytostabilization field study in extremely acidic pyritic mine tailings. A complementary microcosm experiment was performed to identify successional community populations that enable the acidification process across a pH gradient. Taxonomic profiles of the microbial populations in both the field study and microcosms reveal shifts in microbial communities that play pivotal roles in facilitating acidification during the transition between moderately and highly acidic conditions. The potential co-occurrence of organoheterotrophic and lithoautotrophic energy metabolisms during acid generation suggests the importance of both groups in facilitating acidification. Taken together, this research suggests that key microbial populations associated with pH transitions could be used as bioindicators for either sustained future plant growth or for acid generation conditions that inhibit further plant growth.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRSDate not supplied

Triple Oxygen Isotope Kinetics of Sulfate From Pyrite Oxidation

Sulfates from low temperature terrestrial and marine environments are out of equilibrium with their oxygen sources. Instead, oxygen isotope compositions of sulfate imply they are dominated by kinetic signatures of oxidative and reductive processes (Killingsworth et al., 2022) that are under-constrained compared to equilibrium effects (Hayles and Killingsworth, 2022). Consequently, the specific role of pyrite oxidation in setting the oxygen isotope composition of sulfate is also under-constrained. This scenario inhibits a more nuanced understanding of small variations in the oxygen isotopes of sulfate and their implications for tracing oxygen sources and sulfur cycle transformations, particularly in low-temperature relatively sulfate-limited freshwater systems such as rivers, lakes, aquifers, and mining-affected environments. To alleviate these knowledge gaps, we conduct pyrite oxidation experiments at time scales spanning minutes to years, analyze the triple oxygen isotope compositions (∆ 17 O and δ 18 O) of sulfate products, and interpret results using molecular modeling. Our preliminary results show isotopic relationships of 1) pyrite-derived sulfate ∆ 17 O reaching above the meteoric water line as its δ 18 O becomes lighter than water, and 2) sulfate ∆ 17 O and δ 18 O extending between water and O 2 . From these results we interpret a kinetic isotope effect between sulfate and water and mixing between sulfate end members containing most of their oxygen atoms from water and from O 2 .

Oxygen isotopes↗
DOE OSTI2023

Development of molecular cluster models to probe pyrite surface reactivity

Abstract The recent discovery that anaerobic methanogens can reductively dissolve pyrite and utilize dissolution products as a source of iron and sulfur to meet their biosynthetic demands for these elements prompted the development of atomic‐scale nanoparticle models, as maquettes of reactive surface sites, for describing the fundamental redox steps that take place at the mineral surface during reduction. The given report describes our computational approach for modeling n (FeS 2 ) nanoparticles originated from mineral bulk structure. These maquettes contain a comprehensive set of coordinatively unsaturated Fe (II) sites that are connected via a range of persulfide (S 2 2− ) ligation. In addition to the specific maquettes with n = 8, 18, and 32 FeS 2 units, we established guidelines for obtaining low‐energy structures by considering the pattern of ionic, covalent, and magnetic interactions among the metal and ligand sites. The developed models serve as computational nano‐reactors that can be used to describe the reductive dissolution mechanism of pyrite to better understand the reactive sites on the mineral, where microbial extracellular electron‐transfer reactions can occur.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

X-Ray Diffraction Line Broadening in Shock Modified Pyrite [Book Chapter]

Powder compacts of a commercially-available pyrite, FeS 2 , have been subjected to controlled, quantitative high pressure shock loading at peak pressures from 7.5-22 GPa. The profiles of the x-ray diffraction lines have been examined to determine the reduction of the crystallite (domain) size and the introduction of residual microstrain due to defects and dislocations resulting from the transmission and interaction of the shockwave. Pyrite experience a surprisingly smaller profile broadening than observed for all other materials under similar shock conditions, suggesting a much more refractory character. Such small changes are consistent with low defect densities and with the relative low reaction activity (oxidation of sulfide to sulfate by humid air) observed on this material in the complementary studies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Chemical beneficiation of cobaltiferous pyrite: a thermodynamic and parametric study

Despite ongoing efforts to identify substitute materials, cobalt remains indispensable for the production of rechargeable batteries essential to the global energy transition. Currently, most cobalt is sourced as a by-product of nickel and copper extraction from politically and ethically unstable regions. To address this vulnerability, certain primary cobalt deposits—where cobalt occurs within the crystal lattice of pyrite (FeS 2 )—have been identified as potential alternatives. Nonetheless, conventional beneficiation methods have proven largely ineffective for the potential processing of these minerals. This study investigated the thermal decomposition of cobaltiferous pyrite contained in flotation concentrates as a subsequent chemical beneficiation stage aimed at (i) selectively removing sulfur to further increase cobalt grades and (ii) producing a ferromagnetic product suitable for downstream magnetic separation. A thermodynamic analysis was first conducted to evaluate the feasibility of the decomposition reactions and the temperature-dependent evolution of sulfur species. A parametric experimental study then assessed the influence of temperature, residence time, and gas flow rate under N 2 and CO 2 atmospheres. Under the most favorable experimental conditions tested (650 °C, 15 min), cobalt grades increased by up to 15% with negligible cobalt losses and the co-production of high-purity sulfur (>95%). Magnetic separation of the resulting calcine yielded a final concentrate containing 2.09% cobalt at 82.5% recovery, representing a 16–74% improvement over previous baseline studies on similar feedstocks.

Beneficiation↗
NASA NTRS1993

Venus mountain-top mineralogy: Misconceptions about pyrite as the high radar-reflecting phase

Altitude-dependent, high radar-reflectivity surfaces on Venus are observed on most mountainous volcanic terranes above a planetary radius of about 6054 km. However, high radar-reflectivity areas also occur at lower altitudes in some impact craters and plain terranes. Pyrite (FeS2) is commonly believed to be responsible for the high radar reflectivities at high elevations on Venus, on account of large dielectric constants measured for sulfide-bearing rocks that were erroneously attributed to pyrite instead of pyrrhotite. Pentlandite-pyrrhotite assemblages may be responsible for high reflectivities associated with impact craters on the Venusian surface, by analogy with Fe-Ni sulfide deposits occurring in terrestrial astroblemes. Mixed-valence Fe(2+)-Fe(3+) silicates, including oxyhornblende, oxybiotite, and ilvaite, may contribute to high radar reflecting surfaces on mountain-tops of Venus.

Burns, Roger G.↗
NASA NTRS1993

The rate of chemical weathering of pyrite on the surface of Venus

This abstract reports results of an experimental study of the chemical weathering of pyrite (FeS2) under Venus-like conditions. This work, which extends the earlier study by Fegley and Treiman, is part of a long range research program to experimentally measure the rates of thermochemical gas-solid reactions important in the atmospheric-lithospheric sulfur cycle on Venus. The objectives of this research are (1) to measure the kinetics of thermochemical gas-solid reactions responsible for both the production (e.g., anhydrite formation) and destruction (e.g., pyrrhotite oxidation) of sulfur-bearing minerals on the surface of Venus and (2) to incorporate these and other constraints into holistic models of the chemical interactions between the atmosphere and surface of Venus. Experiments were done with single crystal cubes of natural pyrite (Navajun, Logrono, Spain) that were cut and polished into slices of known weight and surface area. The slices were isothermally heated at atmospheric pressure in 99.99 percent CO2 (Coleman Instrument Grade) at either 412 C (685 K) or 465 C (738 K) for time periods up to 10 days. These two isotherms correspond to temperatures at about 6 km and 0 km altitude, respectively, on Venus. The reaction rate was determined by measuring the weight loss of the reacted slices after removal from the furnace. The reaction products were characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy on the SEM.

Fegley, B., Jr.↗
NASA NTRS1993

The role of CO2 in weathering reactions and the presence of S2 on Venus: Implications for the pyrite stability field

The stability of pyrite has become the focal point of study, since regions of low radio thermal emissivity were detected during the Pioneer Venus and Magellan radar mapping missions of Venus. Thermodynamic calculations and experimental studies have been performed assuming CO2 is a major contributor to the weathering of sulfides, as CO2 is the major gas species in the Venusian atmosphere. The purpose of the present study, however, is to demonstrate that CO2 is a non-reactive gas and that a minor species, S2, is the most important gas in determining whether pyrite is stable in the high radar reflectivity regions.

Straub, Darcy W.↗
NASA NTRS1994

A comparison of iron extraction methods for the determination of degree of pyritisation and the recognition of iron-limited pyrite formation

Measurements of degree of pyritisation require an estimate of sediment iron which is capable of reaction with dissolved sulphide to form pyrite, either directly or indirectly via iron monosulphide precursors. Three dissolution techniques (buffered dithionite, cold 1 M HCl, boiling 12 M HCl) were examined for their capacity to extract iron from a variety of iron minerals, and iron-bearing sediments, as a function of different extraction times and different grain sizes. All the iron oxides studied are quantitatively extracted by dithionite and boiling HCl (but not by cold HCl). Both HCl techniques extract more iron from silicates than does dithionite but probably about the same amounts as are potentially capable of sulphidation. Modern sediment studies indicate that most sedimentary pyrite is formed rapidly from iron oxides, with smaller amounts formed more slowly from iron silicates (if sufficient geologic time is available). It is therefore recommended that the degree of pyritisation be defined with respect to the dithionite-extractable (mainly iron oxide) pool and/or the boiling HCl-extractable pool (which includes some silicate iron) for the recognition of iron-limited pyritisation.

NASA Discipline Exobiology↗
NASA NTRS1993

3.4-Billion-year-old biogenic pyrites from Barberton, South Africa: sulfur isotope evidence

Laser ablation mass spectroscopy analyses of sulfur isotopic compositions of microscopic-sized grains of pyrite that formed about 3.4 billion years ago in the Barberton Greenstone Belt, South Africa, show that the pyrite formed by bacterial reduction of seawater sulfate. These data imply that by about 3.4 billion years ago sulfate-reducing bacteria had become active, the oceans were rich in sulfate, and the atmosphere contained appreciable amounts (>>10(-13) of the present atmospheric level) of free oxygen.

NASA Discipline Exobiology↗
DOE OSTI2013

Method of synthesizing pyrite nanocrystals

A method of synthesizing pyrite nanocrystals is disclosed which in one embodiment includes forming a solution of iron (III) diethyl dithiophosphate and tetra-alkyl-ammonium halide in water. The solution is heated under pressure. Pyrite nanocrystal particles are then recovered from the solution.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Initial Laboratory Measurements Probing Hydrogen Interactions with Eagle Ford Shale and Pyrite: Potential Implications for Subsurface Hydrogen Storage

Hydrogen (H 2 ) has the potential to be a transformative technology as an enabler to a low-carbon future and promoter of renewable energy. When H 2 is injected and stored in the subsurface, it has the potential to interact with the caprock (usually shale) which overlies and seals the storage reservoir. Here, this study examines geochemical reactions or changes in surface morphology to Eagle Ford Shale, a proxy for caprock, upon exposure to H 2 at 50°C and 10.3 MPa. Reactions were also performed with N 2 to provide an experimental control. Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS), Atomic Force Microscopy (AFM), and Optical Photothermal-Infrared (O-PTIR) Spectroscopy were applied to quantify changes on the microscale and nanoscale level. Fluid chemistry changes were monitored with Ion Chromatography (IC) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Exposure of Eagle Ford Shale to H 2 gas alone did not result in any alterations to the shale chemically or any changes in the surface morphology. Exposure of Eagle Ford Shale to both H 2 and water as well as N 2 and water resulted in changes to the surface morphology because of gypsum dissolution and reprecipitation, thus indicating that H 2 is not necessary to promote changes. Pure pyrite was the most reactive with H 2 possibly resulting in a reduction to pyrrhotite. These initial studies suggest that the extent of reactions activated by hydrogen with caprock are minor under the temperature and pressure conditions that would represent underground hydrogen storage.

08 HYDROGEN↗
DOE OSTI2012

Magnetron-sputter deposition of Fe{sub 3}S{sub 4} thin films and their conversion into pyrite (FeS{sub 2}) by thermal sulfurization for photovoltaic applications

The authors report on the fabrication of FeS{sub 2} (pyrite) thin films by sulfurizing Fe{sub 3}S{sub 4} that were deposited by direct current magnetron sputtering at room temperature. Under the selected sputtering conditions, Fe{sub 3}S{sub 4} nanocrystal films are obtained and the nanocrystals tend to locally cluster and closely pack into ricelike nanoparticles with an increase in film thickness. Meanwhile, the film tends to crack when the film thickness is increased over {approx}1.3 {mu}m. The film cracking can be effectively suppressed by an introduction of a 3-nm Cu intermediate layer prior to Fe{sub 3}S{sub 4} deposition. However, an introduction of a 3-nm Al intermediate layer tends to enhance the film cracking. By post-growth thermal sulfurization of the Fe{sub 3}S{sub 4} thin films in a tube-furnace, FeS{sub 2} with high phase purity, as determined by using x ray diffraction, is obtained. Optical absorption spectroscopy was employed to characterize the resultant FeS{sub 2} thin films, which revealed two absorption edges at 0.9 and 1.2 eV, respectively. These two absorption edges are assigned to the direct bandgap (0.9 eV) and the indirect allowed transitions (1.2 eV) of FeS{sub 2}, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Investigating Abiotic and Biotic Mechanisms of Pyrite Reduction

Pyrite (FeS 2 ) has a very low solubility and therefore has historically been considered a sink for iron (Fe) and sulfur (S) and unavailable to biology in the absence of oxygen and oxidative weathering. Anaerobic methanogens were recently shown to reduce FeS 2 and assimilate Fe and S reduction products to meet nutrient demands. However, the mechanism of FeS 2 mineral reduction and the forms of Fe and S assimilated by methanogens remained unclear. Thermodynamic calculations described herein indicate that H 2 at aqueous concentrations as low as 10 –10 M favors the reduction of FeS 2 , with sulfide (HS – ) and pyrrhotite (Fe 1–x S) as products; abiotic laboratory experiments confirmed the reduction of FeS 2 with dissolved H 2 concentrations greater than 1.98 × 10 –4 M H 2 . Growth studies of Methanosarcina barkeri provided with FeS 2 as the sole source of Fe and S resulted in H 2 production but at concentrations too low to drive abiotic FeS 2 reduction, based on abiotic laboratory experimental data. A strain of M. barkeri with deletions in all [NiFe]-hydrogenases maintained the ability to reduce FeS 2 during growth, providing further evidence that extracellular electron transport (EET) to FeS 2 does not involve H 2 or [NiFe]-hydrogenases. Physical contact between cells and FeS 2 was required for mineral reduction but was not required to obtain Fe and S from dissolution products. The addition of a synthetic electron shuttle, anthraquinone-2,6-disulfonate, allowed for biological reduction of FeS 2 when physical contact between cells and FeS 2 was prohibited, indicating that exogenous electron shuttles can mediate FeS 2 reduction. Here, transcriptomics experiments revealed upregulation of several cytoplasmic oxidoreductases during growth of M. barkeri on FeS 2 , which may indicate involvement in provisioning low potential electrons for EET to FeS 2 . Collectively, the data presented herein indicate that reduction of insoluble FeS 2 by M. barkeri occurred via electron transfer from the cell surface to the mineral surface resulting in the generation of soluble HS – and mineral-associated Fe 1–x S. Solubilized Fe(II), but not HS – , from mineral-associated Fe 1–x S reacts with aqueous HS – yielding aqueous iron sulfur clusters (FeS aq ) that likely serve as the Fe and S source for methanogen growth and activity. FeS aq nucleation and subsequent precipitation on the surface of cells may result in accelerated EET to FeS 2 , resulting in positive feedback between cell activity and FeS 2 reduction.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

Acoustic Velocities and Elastic Properties of Pyrite (FeS2) to 9.6 GPa

Ultrasonic interferometry was utilized in conjunction with synchrotron-based X-ray diffraction and X-radiographic imaging to determine the compressional and shear wave velocities and unit-cell volumes of pyrite (FeS{sub 2}) at room temperature and pressures up to 9.6 GPa. Fitting all of the experimental volume and velocity data to third-order finite-strain equations yielded the adiabatic zero-pressure bulk and shear moduli and their first pressure derivatives: K{sub S0}=138.9(7) GPa, G{sub 0}=112.3(3) GPa, ({partial_derivative} K{sub S0}/{partial_derivative} P){sub T} =K{sub S0'}=6.0(1), ({partial_derivative}G{sub 0}/{partial_derivative}P){sub T} =G{sub 0'}=3.0(<1), where the numbers in parentheses represent the 1{sigma} uncertainty in the last significant digit. These results are in good agreement with several previous static compression studies on this material but differ quite strongly from the results obtained via first principles calculations. This study presents the first direct measurement of the bulk shear properties of this material.

58 GEOSCIENCES↗
DOE OSTI2025

Photocatalytic Activity and Stability of Carbon Nitride‐Pyrite Composites

Abstract In photocatalysis, the photoabsorber plays a crucial role in the reaction. The most important parameters are stability, cost and optical band gap. In this work, a prominent class of absorbers, namely carbon nitrides (CN), has been investigated. In the literature, CN is most often described as stable, although photodegradation has been observed. In order to retain the beneficial properties of CN while improving stability, a crystalline phase poly(triazine imide) (PTI) of carbon nitride was investigated and compared to polymeric CN in photocatalytic hydrogen generation experiments. In order to improve the charge separation for the photoinduced hydrogen evolution reaction, pyrite (FeS 2 ) was used as a surface co‐catalyst with a loading of 1, 5 and 10 wt %. At the same time, any photodegradation products in solution were investigated by ion chromatography. Interestingly, PTI shows hardly any photocorrosion compared to defective carbon nitride, indicating its higher photostability in hydrogen evolution experiments. However, FeS 2 produces ammonium as a degradation product when synthesised from nitrogen‐containing precursors. When made from nitrogen‐free precursors, FeS 2 together with photostable PTI releases little ammonia, making it a photostable, earth‐abundant composite for photocatalytic hydrogen generation.

Kaulbersch, Julian [University of Bayreuth 95440 B↗
DOE OSTI2022

Reductive biomining of pyrite by methanogens

Pyrite (FeS 2 ) is the most abundant iron sulfide mineral in Earth’s crust. Until recently, FeS 2 has been considered a sink for iron (Fe) and sulfur (S) at low temperature in the absence of oxygen or oxidative weathering, making these elements unavailable to biology. However, anaerobic methanogens can transfer electrons extracellularly to reduce FeS 2 via direct contact with the mineral. Reduction of FeS 2 occurs through a multistep process that generates aqueous sulfide (HS – ) and FeS 2 -associated pyrrhotite (Fe 1-x S). Subsequent dissolution of Fe 1-x S provides Fe(II) (aq) , but not HS – , that rapidly complexes with HS – (aq) generated from FeS 2 reduction to form soluble iron sulfur clusters [nFeS (aq) ]. Cells assimilate nFeS (aq) to meet Fe/S nutritional demands by mobilizing and hyperaccumulating Fe and S from FeS 2 . As such, reductive dissolution of FeS 2 by methanogens has important implications for element cycling in anoxic habitats, both today and in the geologic past.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗