The release of arsenic from biologically formed arsenic-containing FeS under aerobic environment: Implications for the stability and species variation of nano-sized iron sulfide in remediation

The low temperature phase relation of iron sulfide compounds Fe1-xS, with composition ranging from FeS to Fe7S8, has been investigated extensively over the past several decades. Despite these efforts conflicting reports on the stability of low temperature phases still exist and major disagreements between proposed phase diagrams remain unresolved. In this paper we report preliminary findings of our effort to determine whether the low temperature iron sulfide compounds form a homologous series Fen-l,Sn n≥ 8 [1] or a solid solution [2]. We have examined the stability of iron sulfide crystal of composition Fe9S10 using in situ heating experiment and image contrast transmission electron microscopy. We have found that Fe9S10 decomposes to two distinct phases. These two phases are labelled as H and K phases.

Download Full-text

Greigite (Fe3S4) is thermodynamically stable: Implications for its terrestrial and planetary occurrence

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2017312117 ◽

2020 ◽

Vol 117 (46) ◽

pp. 28645-28648

Author(s):

Tamilarasan Subramani ◽

Kristina Lilova ◽

Mykola Abramchuk ◽

Kurt D. Leinenweber ◽

Alexandra Navrotsky

Keyword(s):

High Pressure ◽

Monoclinic Phase ◽

Iron Sulfide ◽

Enthalpies Of Formation ◽

Stable Phase ◽

Fine Grained ◽

Low Surface Energy ◽

Iron Sulfide Minerals ◽

The Common ◽

The Stability

Iron sulfide minerals are widespread on Earth and likely in planetary bodies in and beyond our solar system. Using measured enthalpies of formation for three magnetic iron sulfide phases: bulk and nanophase Fe3S4spinel (greigite), and its high-pressure monoclinic phase, we show that greigite is a stable phase in the Fe–S phase diagram at ambient temperature. The thermodynamic stability and low surface energy of greigite supports the common occurrence of fine-grained Fe3S4in many anoxic terrestrial settings. The high-pressure monoclinic phase, thermodynamically metastable below about 3 GPa, shows a calculated negative P-T slope for its formation from the spinel. The stability of these three phases suggests their potential existence on Mercury and their magnetism may contribute to its present magnetic field.

Download Full-text

Soft chemical approaches to inorganic nanostructures

Pure and Applied Chemistry ◽

10.1351/pac200678091619 ◽

2006 ◽

Vol 78 (9) ◽

pp. 1619-1650 ◽

Cited By ~ 18

Author(s):

C. N. R. Rao ◽

Ved Varun Agrawal ◽

Kanishka Biswas ◽

Ujjal K. Gautam ◽

Moumita Ghosh ◽

...

Keyword(s):

Iron Sulfide ◽

Exchange Process ◽

Inorganic Materials ◽

Organic Layer ◽

Metal Chalcogenides ◽

Nanocrystalline Films ◽

One Pot ◽

Metal Nanocrystals ◽

Crystalline Films ◽

The Stability

Chemical approaches have emerged as the preferred means to synthesize nanostructures of various inorganic materials due to superior control over size, shape, and surface functionality. This article provides an overview of the contributions made in the authors' laboratory toward the synthesis of nanocrystals, nanowires, nanotubes, nanowalls, and other nanostructures of several inorganic materials. Thus, thiolized monodisperse metal nanocrystals have been obtained by a ligand exchange process and the stability of their 2D assemblies studied. Nanocrystals of pure CoO and ReO3 have been synthesized, for the first time, employing a one-pot solvothermal technique. The solvothermal method has also been used to obtain organic soluble nanocrystals of semiconducting materials such as CdS, CdSe, and GaN. Inorganic nanowires and nanotubes have been prepared by several soft chemical routes, including surfactant-assisted synthesis and hydrogel templating. A simple reaction between elemental Se and Te with NaBH4 in water has been utilized to obtain nanowires of Se and Te. We also describe the nebulized spray pyrolysis (NSP) technique to synthesize carbon nanotubes and nanowires of metals and III-V nitride semiconductors with improved yields. An important new technique for preparing nanocrystalline films of materials is by the reaction of the metal precursors in the organic layer at the interface of two immiscible liquids, with appropriate reagents. Nanocrystalline films of metals, alloys, and semiconductors and ultra-thin single-crystalline films of metal chalcogenides and oxides have been obtained by this technique. Apart from these, we discuss single precursor routes to iron sulfide, GeSe2, and III-V nitride nanostructures as well as the first synthesis of GaS and GaSe nanowalls and nanotubes obtained through exfoliation by laser irradiation and thermal treatment.

Download Full-text

Oxidation of pyrite (FeS2) and troilite (FeS) impurities in kaolinitic clays after calcination

Materials and Structures ◽

10.1617/s11527-021-01858-9 ◽

2021 ◽

Vol 55 (1) ◽

Author(s):

Franco Zunino ◽

Karen Scrivener

Keyword(s):

Quality Control ◽

Iron Sulfide ◽

Negative Influence ◽

Alkaline Media ◽

Iron Sulfides ◽

Clay Particles ◽

Blended Cements ◽

Complete Decomposition ◽

Adequate Quality ◽

The Stability

AbstractValorisation of locally available clays for producing blended cements is crucial for a widespread adoption of sustainable binders incorporating these materials. In some places, clays can be intermixed with small amounts of iron sulfides, which could eventually expand in the alkaline media of concrete and lead to cracking if clay particles are sufficiently fine. This study explored the stability of iron sulfides, namely troilite and pyrite, during calcination of clays and their influence in reactivity. It was found that both troilite and pyrite decompose and oxidize into hematite under typical calcination conditions for clays. Furthermore, there is no negative influence of the presence of iron sulfide phases on the reactivity of calcined clays. This shows that these clays are suitable for use in blended cements, provided that adequate quality control is conducted to ensure a complete decomposition of the iron sulfide phases.

Download Full-text

Geotechnical implications of diagenetic iron sulfide formation in Champlain Sea sediments

Canadian Journal of Earth Sciences ◽

10.1139/e79-052 ◽

1979 ◽

Vol 16 (3) ◽

pp. 575-584 ◽

Cited By ~ 12

Author(s):

Joseph J. Donovan ◽

Ginette Lajoie

Keyword(s):

Iron Sulfide ◽

Ferric Hydroxide ◽

Geochemical Data ◽

Stable Phase ◽

Iron Hydroxides ◽

Reducing Conditions ◽

Decomposition Of Organic Matter ◽

Bacterial Decomposition ◽

The Stability ◽

High Sulfide

It has been proposed that iron hydroxides act as cementing agents in Champlain Sea clays, causing brittle behaviour and high sensitivities. Study of interbedded turbiditic sandy and clayey strata of the Champlain Sea disputes this contention. Ground waters flowing through these sandy interbeds have high pH and are sodium bicarbonate dominant and strongly reduced, with a calculated Eh of −276 to −343 mV, using the sulfate–sulfide redox couple. During movement from recharge to discharge, sulfate is reduced by bacterial decomposition of organic matter in the clays, producing high sulfide and bicarbonate activities. In terms of Eh and pH, these waters fall within the stability fields of Fe2+ and FeS2.No pyrite was detected in the sediments, but in borehole samples and very fresh exposures of both clay and sand lithologies a very finely-disseminated black mineral phase, interpreted as iron monosulfides, was observed which is highly unstable in an aerobic environment, oxidizing rapidly to red-brown ferric hydroxide. The presence of these monosulfides, along with the aqueous geochemical data, indicate strongly reducing conditions in the clay strata, in which iron hydroxides are not a stable phase. Ferric hydroxides can therefore not be called upon as cementing agents; past studies which identified these ferric compounds as such cementing agents based their conclusions on samples out of equilibrium with their natural environment and are not directly relevant to the behaviour of the clay under natural conditions. The effects of these iron monosulfides and associated organic material on clay behaviour have not yet been studied.

Download Full-text

Fe5S2 identified as a host for sulfur in Earth’s core

10.31223/x5h337 ◽

2021 ◽

Author(s):

Claire Zurkowski ◽

Barbara Lavina ◽

Abigail Case ◽

Kellie Swadba ◽

Stella Chariton ◽

...

Keyword(s):

Iron Sulfide ◽

Inner Core ◽

Outer Core ◽

Iron Sulfides ◽

Earth’S Core ◽

Earth's Core ◽

Planetary Cores ◽

Wide Range ◽

Metal Metal ◽

The Stability

Planetary habitability, as we experience on Earth, is linked to a functioning geodynamo which is in part driven by the crystallization of the liquid iron-nickel-alloy core as a planet cools over time. Cosmochemical considerations suggest that sulfur is a candidate light alloying element in rocky planetary cores of varying sizes and oxidation states; such that, iron sulfide phase relations at extreme conditions contribute to outer core thermochemical convection and inner core crystallization in a wide range of planetary bodies. Here we experimentally investigate the structural properties of the Fe-S system and report the discovery of the sulfide, Fe5S2, crystallizing in equilibrium with iron at Earth’s outer core pressures and high temperatures. Using single-crystal X-ray diffraction techniques, Fe5S2 was determined to adopt the complex Ni5As2-type structure (P63cm, Z = 6). These results conclude that Fe5S2 is likely to crystallize at the interface of Earth’s core and mantle and will begin to crystallize during the freezing out of Earth and Venus’ core overtime. The increased metal-metal bonding measured in Fe5S2 compared to the other high P-T iron sulfides may contribute to signatures of higher conductivity from regions of Fe5S2 is crystallization. Fe5S2 could serve as a host for Ni and Si as has been observed in the related meteoritic phase, perryite, (Fe, Ni)8(P, Si)3, adding intricacies to elemental partitioning during inner core crystallization. The stability of Fe5S2 presented here is key to understanding the role of sulfur in the multicomponent crystallization sequences that drive the geodynamics and dictate the structures of Earth and rocky planetary cores.

Download Full-text

Variation in the stability of cockatiel (Nymphicus hollandicus) pair relationships: the roles of males, females, and mate compatibility

Behaviour ◽

10.1163/1568539042729711 ◽

2004 ◽

Vol 141 (10) ◽

pp. 1211-1234 ◽

Cited By ~ 16

Author(s):

James Millam ◽

Tracey Spoon ◽

Donald Owings

Keyword(s):

Social Interactions ◽

Emergent Properties ◽

Species Variation ◽

Monogamous Species ◽

The Social ◽

Nymphicus Hollandicus ◽

Opposite Sex ◽

Males And Females ◽

The Stability

AbstractPair relationships and their emergent properties represent potentially significant sources of proximate and ultimate influence on mating systems, but the study of such relational factors has been rare compared to the volume of literature dedicated to individual-level measures of mate quality. This study assessed variation in the stability of pair relationships in cockatiels (Nymphicus hollandicus) and sought sources for that variation in both the behavior of mated individuals and their compatibility. Pair relationships represent an especially salient aspect of the social system of cockatiels, a socially monogamous species with long-term pairing.In a semi-natural, captive setting, this study compared (1) the social interactions between cockatiel mates to those individuals' interactions with opposite-sex non-mates, (2) the roles of males and females in pair relationships, and (3) the various pairs in their displays of intrapair and extrapair interactions. We also assessed the behavioral features underlying pair relationships by examining the interrelationships among social behaviors within pairs and the degree to which emergent properties structure pair relationships. Interactions between mates, as compared to opposite-sex non-mates, were characterized by closer proximity, greater behavioral synchrony, less aggression, more allopreening, and greater sexual behavior. Males and females displayed little dimorphism in many intrapair and extrapair behaviors; however, males approached and courted their mates more than females did, and males but not females exhibited more intersexual aggression to non-mates than to their mates. Social interactions between mates varied significantly among pairs in ways that reflected variation in the degree of behavioral compatibility between mates. In other words, suites of highly correlated behaviors characterized the interactions between mates such that pairs exhibiting greater affiliative or accordant behaviors exhibited less aggressive or discordant behaviors and vice versa. Emergent properties appeared to play an especially important role in compatibility. By examining significant within-species variation in pair relationships, this study complements the increasing knowledge of mating relationships gained from comparative studies and illustrates the importance of emergent, pair-level behavior in the maintenance of long-term monogamous pair-bonds.

Download Full-text

Open discussion

Symposium - International Astronomical Union ◽

10.1017/s0074180900029533 ◽

1982 ◽

Vol 99 ◽

pp. 605-613

Author(s):

P. S. Conti

Keyword(s):

Buenos Aires ◽

Large Mass ◽

List Type ◽

Common Phenomenon ◽

Open Discussion ◽

The Stability ◽

Ring Nebulae

Conti: One of the main conclusions of the Wolf-Rayet symposium in Buenos Aires was that Wolf-Rayet stars are evolutionary products of massive objects. Some questions:–Do hot helium-rich stars, that are not Wolf-Rayet stars, exist?–What about the stability of helium rich stars of large mass? We know a helium rich star of ∼40 MO. Has the stability something to do with the wind?–Ring nebulae and bubbles : this seems to be a much more common phenomenon than we thought of some years age.–What is the origin of the subtypes? This is important to find a possible matching of scenarios to subtypes.

Download Full-text

Symmetric Multistep Methods Revisited: II. Numerical Experiments

International Astronomical Union Colloquium ◽

10.1017/s0252921100031602 ◽

1999 ◽

Vol 173 ◽

pp. 309-314 ◽

Cited By ~ 3

Author(s):

T. Fukushima

Keyword(s):

Multistep Methods ◽

Computational Time ◽

Integration Time ◽

Implicit Methods ◽

Symmetric Methods ◽

Celestial Bodies ◽

The Stability ◽

Predictor Corrector ◽

Symmetric Multistep Methods ◽

Integration Errors

AbstractBy using the stability condition and general formulas developed by Fukushima (1998 = Paper I) we discovered that, just as in the case of the explicit symmetric multistep methods (Quinlan and Tremaine, 1990), when integrating orbital motions of celestial bodies, the implicit symmetric multistep methods used in the predictor-corrector manner lead to integration errors in position which grow linearly with the integration time if the stepsizes adopted are sufficiently small and if the number of corrections is sufficiently large, say two or three. We confirmed also that the symmetric methods (explicit or implicit) would produce the stepsize-dependent instabilities/resonances, which was discovered by A. Toomre in 1991 and confirmed by G.D. Quinlan for some high order explicit methods. Although the implicit methods require twice or more computational time for the same stepsize than the explicit symmetric ones do, they seem to be preferable since they reduce these undesirable features significantly.

Download Full-text