Regular ArticleThe Rate of Iron Sulfide Formation in the Solar Nebula
Abstract
The kinetics and mechanism of the reaction H2S(g) + Fe(s) = FeS(s) + H2(g) was studied at temperatures and compositions relevant to the solar nebula. Fe foils were heated at 558–1173 K in H2S/H2gas mixtures (∼25 to ∼10,000 parts per million by volume (ppmv) H2S) at atmospheric pressure. Optical microscopy and X-ray diffraction show that the microstructures and preferred growth orientations of the Fe sulfide scales vary with temperature and H2S/H2ratio. Initially, compact, uniformly oriented scales grow on the Fe metal. As sulfidation proceeds, the scales crack and finer grained, randomly oriented crystals grow between the metal and the initial sulfide scale. The composition of the scales varies from Fe0.90S to FeS with temperature and H2S/H2ratio, in agreement with thermodynamic calculations. The weight gain and thickness change of the samples give nearly identical measures of the reaction progress. Sulfide layers formed in 25–100 ppmv H2S grow linearly with time. Iron sulfides formed in ∼1000 ppmv H2S originally grow linearly with time. Upon reaching a critical thickness growth follows parabolic kinetics. Iron sulfide formation in 10,000 ppmv H2S also follows parabolic kinetics. The linear rate equation for sulfidation of Fe grains (≤20 μm diameter) in the solar nebula isd(FeS)/dt=kfPH2S−krPH2(cm hour−1). The forward and reverse rate constants are (cm hour−1atm−1)kf= 5.6(±1.3)exp(−27950(±7280)/RT) andkr= 10.3(±1.0)exp(−92610(±350)/RT), respectively. The activation energies for the forward and reverse reactions are ∼28 kJ mole−1and ∼93 kJ mole−1, respectively. FeS formation in the solar nebula is rapid (e.g., ∼200 years at 700 K and 10−3bars total pressure for 20 μm diameter Fe grains) as predicted by simple collision theory models of FeS formation.
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Correlated IR-SEM-TEM studies of three different grains from Ryugu: From the initial material to post-accretional processes
2024, Geochimica et Cosmochimica ActaIn order to better constrain the alteration history of the Ryugu parent body, we performed a multi-analytical study combining scanning electron microscopy, transmission electron microscopy and infrared spectroscopy on sections extracted from the three fragments A0064-FO019, A0064-FO021 and C0002-FO019 returned from Ryugu by the Hayabusa2 space mission. The three sections show large differences in terms of structure, mineralogy and infrared signature. Section A0064-FO019 resembles the major Ryugu lithology with the presence of both fine-grained phyllosilicates (fg-phyllos) with embedded nanosulfides and coarse-grained phyllosilicates (cg-phyllos), whereas section C0002-FO019 belongs to the group of the less altered lithologies with the presence of anhydrous minerals embedded in a partially amorphous matrix. Section A0064-FO021 also belongs to this group but shows two different lithologies, a compact amorphous one and a more porous and very fractured one showing the presence of Na-rich phosphate, calcite and olivine. The two less altered lithologies (sections A0064-FO021 and C0002-FO019) show the presence of numerous mineralogical features similar to those observed in cometary interplanetary dust particles, ultra-carbonaceous Antarctic micrometeorites or in the CM Paris meteorite, i.e. amorphous and partially crystallized matrix with GEMS-like ghosts objects, whisker olivine, phosphide, or FeNi metal. This supports an outer solar system origin common with that of cometary material for the Ryugu parent body. Combined with the results of Nakamura et al. (2022b) reporting the presence of a lithology showing the presence of GEMS-like objects, we propose that section C0002-FO019 represents the onset of aqueous alteration of such primitive materials. The cg-phyllos and fg-phyllos of section A0064-FO019, i.e. of the major Ryugu lithology, representing the advanced stage of alteration, exhibit distinctive IR signatures with a higher abundance of oxygen-rich functional groups in the organic matter (OM) from the cg-phyllos. We thus suggest the following chronology of formation and evolution for Ryugu: (1) accretion of highly porous aggregate of GEMS-like units with fine-grained high-temperature anhydrous silicates, (2) onset of alteration with the dissolution of primary nanosulfides and development of amorphous/partially crystallized material in the pores, (3) crystallization of fg-phyllos with a second generation of sulfides, (4) later formation of cg-phyllos devoid of nanosulfides and their associated oxygen-rich OM in a more water-rich environment.
Behavior of sulfur during pyrolysis of waste tires: A critical review
2022, Journal of the Energy InstituteWaste tires (WT) are known as "black pollution", and their quantity is growing year by year. The rational disposal of WT has become an urgent problem. Pyrolysis is an economical method to treat WT, and the pyrolysis products can be further utilized. A large number of studies have reported on the effects of various parameters of pyrolysis on the yield and quality of pyrolysis products, as well as the further utilization of pyrolysis products. It is worth noting that WT contain a certain amount of sulfur. The sulfur will be released during the treatment process and may further cause secondary pollution. This paper approaches multidisciplinary aspects for the evaluation of sulfur in the process, such as the sulfur content in WT and pyrolysis products, the type of sulfur-containing compounds, transformation mechanism of sulfur, relevant influencing factors and sulfur-containing pollutants control methods. Moreover, the behavior of sulfur during co-pyrolysis is also reviewed. The challenges of the pyrolysis process were suggested. Finally, helpful suggestions and feasible research directions are presented in this paper. This paper can provide a theoretical reference for the enhancement of the pyrolysis process.
Search for meteoritic GEMS II: Comparison of inclusions in amorphous silicates from the Paris chondrite and from anhydrous chondritic interplanetary dust particles
2021, Geochimica et Cosmochimica ActaAmorphous silicates containing abundant nano-inclusions have been reported in the Paris CM chondrite (Leroux et al., 2015). They have chemical and morphological similarities to glass with embedded metal and sulfides (GEMS) found in interplanetary dust particles (IDPs) and micrometeorites believed to originate from comets. We used scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy (EDS) and nanodiffraction to study the chemistry and mineralogy of these inclusions in order to understand the origin of the GEMS-like material in Paris and its possible relationships to other materials found in primitive chondritic materials including IDP GEMS. EDS and diffraction analyses indicate compositional and mineralogical differences between the nanophase inclusions in cometary GEMS and Paris GEMS-like material. Metal inclusions are notably absent within Paris amorphous silicate. Ni-rich sulfides, including pentlandite, are common in even the least altered matrix material of Paris, while they are absent in GEMS-bearing IDPs and Ultracarbonaceous Antarctic Micrometeorites (UCAMMs). From examination of the inclusions, we cannot yet confirm or refute the possibility that GEMS-like material in Paris is related to cometary GEMS. The distinct compositions and mineralogy of the Paris material may be due to aqueous alteration of cometary GEMS precursors, but they may also denote an independent origin for meteoritic GEMS-like assemblages.
The Fe/S ratio of pyrrhotite group sulfides in chondrites: An indicator of oxidation and implications for return samples from asteroids Ryugu and Bennu
2021, Geochimica et Cosmochimica ActaCitation Excerpt :Troilite ideally has an at. % Fe/S ratio of 1 but can have Fe/S ratios between 1 and 0.98 (e.g., Lauretta et al., 1996, 1997), while Fe-depleted pyrrhotite has Fe/S ratios between 0.98 and 0.8 (e.g., Naldrett, 1989; Haldar, 2017). Low-Ni Fe sulfides are particularly important because they are more susceptible to alteration than high-Ni sulfides in the CM and CR chondrites (Singerling and Brearley, 2020).
Determining compositional trends among individual minerals is key to understanding the thermodynamic conditions under which they formed and altered, and is also essential to maximizing the scientific value of small extraterrestrial samples, including returned samples and meteorites. Here we report the chemical compositions of Fe-sulfides, focusing on the pyrrhotite-group sulfides, which are ubiquitous in chondrites and are sensitive indicators of formation and alteration conditions in the protoplanetary disk and in small Solar System bodies. Our data show that while there are trends with the at.% Fe/S ratio of pyrrhotite with thermal and aqueous alteration in some meteorite groups, there is a universal trend between the Fe/S ratio and degree of oxidation. Relatively reducing conditions led to the formation of troilite during: (1) chondrule formation in the protoplanetary disk (i.e., pristine chondrites) and (2) parent body thermal alteration (i.e., LL4 to LL6, CR1, CM, and CY chondrites). Oxidizing and sulfidizing conditions led to the formation of Fe-depleted pyrrhotite with low Fe/S ratios during: (1) aqueous alteration (i.e., CM and CI chondrites), and (2) thermal alteration (i.e., CK and R chondrites). The presence of troilite in highly aqueously altered carbonaceous chondrites (e.g., CY, CR1, and some CM chondrites) indicates they were heated after aqueous alteration. The presence of troilite, Fe-depleted pyrrhotite, or pyrite in a chondrite can provide an estimate of the oxygen and sulfur fugacities at which it was formed or altered. The data reported here can be used to estimate the oxygen fugacity of formation and potentially the aqueous and/or thermal histories of sulfides in extraterrestrial samples, including those returned by the Hayabusa2 mission and due to be returned by the OSIRIS-REx mission in the near future.
Volatile element chemistry during accretion of the earth
2020, Chemie der ErdeWe review some issues relevant to volatile element chemistry during accretion of the Earth with an emphasis on historical development of ideas during the past century and on issues we think are important. These ideas and issues include the following: (1) whether or not the Earth accreted hot and the geochemical evidence for high temperatures during its formation, (2) some chemical consequences of the Earth’s formation before dissipation of solar nebular gas, (3) the building blocks of the Earth, (4) the composition of the Earth and its lithophile volatility trend, (5) chemistry of silicate vapor and steam atmospheres during Earth’s formation, (6) vapor - melt partitioning and possible loss of volatile elements, (7) insights from hot rocky extrasolar planets. We include tabulated chemical kinetic data for high-temperature elementary reactions in silicate vapor and steam atmospheres. We finish with a summary of the known and unknown issues along with suggestions for future work.
The selenium isotopic variations in chondrites are mass-dependent; Implications for sulfide formation in the early solar system
2018, Earth and Planetary Science LettersElement transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter. The precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains. The transfer of selenium to solids likely occurred through a similar pathway, allowing the formation of iron selenides concomitantly with sulfides. The formation rate of sulfide however remains difficult to assess. Here we investigate whether the Se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system. We present high precision Se concentration and data for 23 chondrites as well as the first , and data for a sub-set of seven chondrites. We combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites.
Our Se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites. Our overall average value for chondrites is (, 2 s.d.), or after exclusion of three weathered chondrites (, 2 s.d.). These average values are within uncertainty indistinguishable from a previously published estimate. For the first time however, we resolve distinct between ordinary (, , 2 s.d.), enstatite (, , 2 s.d.) and CI carbonaceous chondrites (, , 2 s.d.). We also resolve a Se isotopic variability among CM carbonaceous chondrites. In addition, we report on , and values determined for 7 chondrites. Our data allow evaluating the mass dependency of the variations. Mass-independent deficits ro excesses of 74Se, 76Se and 77Se are calculated relative to the observed 82Se/78Se ratios, and were observed negligible. This rules out poor mixing of nucleosynthetic components to account for the variability and implies that the mass dependent Se isotopic variations were produced in a once-homogeneous disk.
The mass-dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high H2S–H2Se contents in the region of enstatite chondrite formation. Experimental studies showed that high H2S contents favor the formation of compact sulfide layers around metallic grains. This decreases the reactive surface, which tends to inhibit the continuation of the sulfidation reaction. Under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light S and Se isotopes in solids; This hypothesis provides an explanation for our Se isotope as well as for previously published S isotope data. On the other hand, high values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration, or could reflect the contribution of ices carrying photo-processed Se from the outer solar system.
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