Solid Sulfur Research Articles

Oxidative transformation of iron monosulfides and pyrite in estuarine sediments: Implications for trace metals mobilisation

Iron monosulfides are the initial iron sulfide minerals that form under reducing conditions in organic-rich sediments. Frequently referred as monosulfidic black ooze (MBO), these sediments exists in a range of anoxic systems including estuaries, coastal wetlands and permeable reactive barriers. The objective of this study was to investigate the transformation of solid phase sulfur, iron fractions and trace metals mobilisation in organic-rich hypersulfidic sediments during dredging. Two sediments from geographically contrasting sites in the Peel-Harvey Estuary were collected and subjected to oxidation through resuspension over 14 days. During oxidation, redox potential rapidly and continuously increased, although minimal change in pH was observed in both sediments. The majority of FeS was oxidised within 48 h. Although not as dynamic as FeS, unusually high rates of FeS2 oxidation were measured in both sediments at circumneutral pH, with between 39 and 58% of FeS2 oxidised over 14 days. The rapid oxidation of FeS2 may be attributed to the presence of nano-size FeS2 crystals (≈550–860 nm) with a high surface area. Before resuspension, solid bound Fe(total) was most abundant as measured by HCl-extractable Fe(II), followed by organic bound Fe(total) and oxide bound Fe(total). There was a marked decrease in these three fractions in both sediments during resuspension, with an increase in Fe(III) fraction. No significant release of trace metals was observed during resuspension of sulfidic sediments. However, disturbance to these estuarine sediments increases Fe(III) formation and further deteriorates the environment through smothering biological surfaces, deteriorating food sources and the quality of benthic habitats.

Sulfur-bearing molecules observed in the massive star-forming regions, DR21(OH) and G33.92+0.11

Recent high sensitive and high angular resolution observations are providing unprecedented amount of chemical data, especially, on the massive star-forming regions. It will greatly extend our understandings on the complicated star formation process, if we can digest those huge amount of information. We discuss here on the properties of the sulfurbearing species observed with high angular resolutions toward two massive star-forming regions, DR21(OH) and G33.92+0.11. H2S may not exist as a solid form in the grain mantles, but OCS is believed to be one of major solid sulfur species, as suggested before. In addition, the bipolar-like outflow of the H2CS emission observed in DR21(OH) may suggest that H2CS is also one of solid sulfur species on the grain mantles. Depending on the chemical environment, the competition between hydrogenation and oxidization on the grain surface may lead to formation of specific solid forms to dominate, which could be either H2CS or OCS. SO and SO2 are often observed to be associated with ionized gas, such as the UC HII regions. These species seem to be formed in the high temperature turbulent gas in a later stage of star formation after the hot core phase. Fractional abundances of these sulfur-bearing species appear to be consistent to a certain extent in several star-forming regions. The physical and chemical evolution of massive star formation seems to pass through very similar stages in most star-forming regions. Consequently, it may indicate that there exists a consistent and coherent pattern of processes experienced by the massive star formation, in spite of the large variations in small scale locational differences.

The effect of pressure on sulphur speciation in mid- to deep-crustal arc magmas and implications for the formation of porphyry copper deposits

Piston cylinder experiments are used to investigate the effect of oxygen fugacity (ƒO2) on sulphur speciation and phase relations in arc magmas at 0.5–1.5 GPa and 840–950 °C. The experimental starting composition is a synthetic trachyandesite containing 6.0 wt% H2O, 2880 ppm S, 1500 ppm Cl and 3800 ppm C. Redox conditions ranging from 1.7 log units below the Ni–NiO buffer (NNO − 1.7) to NNO + 4.7 were imposed by solid-state buffers: Co–CoO, Ni–NiO, Re–ReO2 and haematite–magnetite. All experiments are saturated with a COH fluid. Experiments produced crystal-bearing trachydacitic melts (SiO2 from 60 to 69 wt%) for which major and volatile element concentrations were measured. Experimental results demonstrate a powerful effect of oxidation state on phase relations. For example, plagioclase was stable above NNO, but absent at more reduced conditions. Suppression of plagioclase stability produces higher Al2O3 and CaO melts. The solid sulphur-bearing phases and sulphur speciation in the melt are strong functions of ƒO2, as expected, but also of pressure. At 0.5 GPa, the anhydrite stability field is intersected at NNO ≥ +2, but at 1.0 and 1.5 GPa, experiments at the same ƒO2 produce sulphides and the stability field of sulphate moves towards higher ƒO2 by ~1 log unit at 1.0 GPa and ~1.5 log units at 1.5 GPa. As a result, models that appeal to high oxidation state as an important control on the mobility of Cu (and other chalcophiles) during crustal differentiation must also consider the enhanced stability of sulphide in deep- to mid-crustal cumulates even for relatively oxidized (NNO + 2) magmas. Experimental glasses reproduce the commonly observed minimum in sulphur solubility between the S2− and S6+ stability fields. The solubility minimum is not related to the Fe content (Fe2+/Fe3+ or total) of the melt. Instead, we propose this minimum results from an unidentified, but relatively insoluble, S-species of intermediate oxidation state.

PHOTOLYTIC HAZES IN THE ATMOSPHERE OF 51 ERI B

ABSTRACT We use a 1D model to address photochemistry and possible haze formation in the irradiated warm Jupiter, 51 Eridani b. The intended focus was to be carbon, but sulfur photochemistry turns out to be important. The case for organic photochemical hazes is intriguing but falls short of being compelling. If organic hazes form, they are likeliest to do so if vertical mixing in 51 Eri b is weaker than in Jupiter, and they would be found below the altitudes where methane and water are photolyzed. The more novel result is that photochemistry turns H2S into elemental sulfur, here treated as S8. In the cooler models, S8 is predicted to condense in optically thick clouds of solid sulfur particles, while in the warmer models S8 remains a vapor along with several other sulfur allotropes that are both visually striking and potentially observable. For 51 Eri b, the division between models with and without condensed sulfur is at an effective temperature of 700 K, which is within error its actual effective temperature; the local temperature where sulfur condenses is between 280 and 320 K. The sulfur photochemistry we have discussed is quite general and ought to be found in a wide variety of worlds over a broad temperature range, both colder and hotter than the 650–750 K range studied here, and we show that products of sulfur photochemistry will be nearly as abundant on planets where the UV irradiation is orders of magnitude weaker than it is on 51 Eri b.

Probing Polysulfide Shuttle Effect in the Li-S Battery

The lithium-sulfur battery is a strong contender among the beyond Li-ion chemistries due to its superior capacity and energy density as compared to the conventional Li-ion cells. However, experimental evidences suggest that even the first discharge capacity is appreciably lower than the theoretical limit. This non-ideality is usually associated with the so-called “polysulfide shuttle effect”. On the cathode side, solid sulfur dissolves in the electrolyte and undergoes successive reduction to different intermediate and reduced-order sulfide ions. Due to the underlying potential and concentration gradients, these negative ions travel toward the anode and chemically oxidize the lithium metal, while being reduced simultaneously. Theoretical capacity is achieved when sulfur undergoes complete electrochemical reduction; hence the above chemical reaction(s) limit the available capacity. Lithium sulfide (Li2S) is the final discharge product which forms when the ionic product exceeds the solubility limit. This can passivate the surface, block the porous structure and may lead to the reacting species starvation in the cathode. The shuttle effect is a resultant manifestation of these coupled phenomena. In this work, a computational study is presented in order to quantify the influence of shuttle effect on the Li-S cell capacity. The model correlates concentration evolution and microstructural changes with cell performance. Based on this understanding, electrode modifications such as, cathode coating and microstructure properties are studied in order to fundamentally understand the deleterious influence of the “shuttle effect” on cell performance. Figure 1

Poromechanical effect in the lithium–sulfur battery cathode

In lithium–sulfur (Li–S) batteries, during discharge, solid sulfur (S8(s)) gets dissolved and undergoes successive reduction and finally precipitates as lithium sulfide (Li2S) in a typical carbon-based, porous cathode. Deposition of Li2S leads to 80% volume expansion compared to solid S8(s). During the dissolution–precipitation process, the total volume change of the electrolyte in the pore space can be attributed to two factors: (a) precipitation/dissolution of the solid sulfur phase; and (b) the cathode microstructure shrinks or swells to accommodate the changes in the pore volume resulting from the electrolyte induced hydrostatic pressure. Current lithium–sulfur performance models neglect this contribution. In this work, a computational methodology has been developed to quantify the impact of precipitation induced volume change, pore morphology and confinement attributes in a Li–S cathode. Impact of volume expansion on cell voltage has also been analyzed using a performance model. It is found that the poromechanical interaction significantly affects the second voltage plateau. Cathode microstructures with relatively smaller pores tend to experience less volume expansion, for the same operating conditions. It has been found that non-uniform precipitation may lead to significant pore confinement, which has the potential to cause microcrack formation in the pore walls of a typical carbon-based cathode microstructure.

Precipitation Induced Stress and Degradation in the Lithium-Sulfur Battery Cathode

Lithium-sulfur (Li-S) batteries display significantly higher practical energy density (~500Wh/kg) as compared to commercially available lithium ion based battery systems (~150Wh/kg)1. This improved energy density arises from the fact that each mole of sulfur (S8) reacts with sixteen moles of electron. In the long term, the lithium-sulfur based cells have the potential to be cheaper due to the usage of lower cost active materials. Hence, these light weight lithium-sulfur cells can significantly increase the range experienced by electric vehicles. However, at present the lithium-sulfur cells display modest cycle life only under low power and low rates of operation1. The staged, multi-step reaction during the discharge process causes performance limitation in Li-S batteries2. In addition, shuttling of the long-chain polysulfides from the cathode to the anode and reaction with the lithium film not only reduces the effective capacity of the cell, but also forms a passivating layer on top of the lithium anode, which can significantly increase the anode overpotential1. Deposition of insoluble lithium-sulfides on top of pristine solid sulfur can passivate the active material and result in capacity fade at higher rates of operation1. During the discharge of a lithium-sulfur battery, a major product is lithium-sulfide (Li2S) which is insoluble in the electrolyte solvent and precipitates at cathode-electrolyte interface2 , 3. When a mole of S8(s) completely coverts to Li2S(s), it occupies 80% more volume2. This volume expansion is accommodated by the cathode system in two ways: a) By decreasing the pore space, and b) By increasing the total volume of the electrode which results in a higher value of porosity4. Computational models developed to capture the performance of lithium-sulfur cells do not take into account the effect of swelling of the entire electrode2 , 3. Also depending on the mechanical stability of the cathode microstructure, this precipitation induced volume expansion can give rise to significant stress and fracture of the cathode substrate. Subsequent detachment of the ruptured cathode microstructure form the conducting network can severely deteriorate the overall capacity of the lithium-sulfur cell1. A poromechanics based computational study has been conducted to elucidate the effect of cathode material (in terms of elastic and fracture properties) and microstructure (in terms of pore shape and size) on the overall volume expansion and performance of lithium sulfur cells. Preliminary studies indicate that both pore shape and size can significantly impact the overall volume expansion and mechanical integrity experienced by the cathode microstructure. From the effective stiffness point of view, small sized pores are preferred, because large pores experience higher volume expansion. However, extremely small pores contain very thin pore-walls, which can be prone to microcracking under a precipitation induced stress. A thorough analysis of the influence of cathode microstructure, including the pore morphology, size, and volume fraction, will be elucidated in this presentation.

Towards a uniform and large-scale deposition of MoS2 nanosheets via sulfurization of ultra-thin Mo-based solid films

Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor–solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm2-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (<750 °C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000 °C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.

Optimization of sulfur adsorption over Ag-zeolite nanoadsorbent by experimental design method

Environmental protection has mentioned the need to cut out all of fuels sulfur compounds. One of the most important processes that affect sulfur removal in atmospheric condition is the interaction of liquid fuels with solid sulfur removal adsorbents such as zeolites. To investigate the nano-AgX-zeolite efficiency for the sulfur adsorption process, a set of experimental tests was arranged and conducted by Box–Behnken design software, in an adsorption laboratory setup. The selected variables comprised metal percent, adsorption temperature and calcination temperature. The parameter levels were 0.5–10 %, 30–120 and 200–500 °C, respectively. The experiment results were used to find the statistical model. The results demonstrate that the sulfur concentration level is 48.36 ppm in the last product at 83 °C for adsorption temperature, 5.53 % for metal percent and 436 °C for calcination temperature in constant pH and constant process time.

Covellite CuS nanocrystals: realizing rapid microwave-assisted synthesis in air and unravelling the disappearance of their plasmon resonance after coupling with carbon nanotubes.

Semiconductor nanocrystals that show plasmonic resonance represent an emerging class of highly promising plasmonic materials with potential applications in diverse fields, such as sensing and optical and optoelectronic devices. We report a new approach to synthesizing homogeneous covellite CuS nanoplatelets in air and the almost complete disappearance of their plasmonic resonance once coupled with multiwalled carbon nanotubes (MWCNTs). These nanoplatelets were rapidly synthesized by a simple microwave-assisted approach at a relatively low reaction temperature in air, instead of under N2 as reported previously. These less severe synthesis conditions were enabled by appropriately selecting a Cu precursor and preparing a precursor sulfur solution (instead of using solid sulfur) and by using microwave radiation as the heat source. The advantages of utilizing microwave irradiation, including uniform and rapid heating, became clear after comparing the results of the synthesis with those achieved using a conventional oil-bath method under N2. The CuS nanoplatelets prepared in this way showed very strong plasmon resonance at c. 1160 nm as a result of their free charge carriers at the calculated density of nh = 1.5 × 10(22) cm(-3) based on the Drude model. With the aim of exploring their potential for near-infrared responsive optoelectronic devices, they were hybridized with functionalized MWCNTs. Their strong plasmon resonance almost completely disappeared on hybridization. Detailed investigations excluded the effect of possible structural changes in the CuS nanoplatelets during the hybridization process and a possible effect on the plasmon resonance arising from the chemical bonding of surface ligands. Charge transfer was considered to be the main reason for the almost complete disappearance of the plasmon resonance, which was further confirmed by terahertz (THz) time-domain spectrometry and THz time-resolved spectrometry measurements performed on the CuS-MWCNT nanohybrids. By extracting the rising and relaxation constants through fitting a single-exponential rising function and a bi-exponential relaxation function, in combination with the results of THz differential transmission as a function of the NIR pump fluence, it was found that hole injection changed the electronic properties of the MWCNTs only subtly on a short picosecond time scale, whereas the nature of the band structure of the MWCNTs remained largely unchanged. These findings aid our understanding of recently emerging semiconductor plasmonics and will also help in developing practical applications.

Sol–gel encapsulated lithium polysulfide catholyte and its application in lithium–sulfur batteries

Careful control of sol–gel chemistry allows for the encapsulation of water-reactive lithium polysulfides

Recovery of solid sulfur from hydrogen sulfide gas by an electrochemical membrane cell

Sulfides are hazardous chemicals which endanger the lives of humans. Electrochemical oxidation of sulfides is a predominant method for sulfur removal from wastewater. A major limitation of the electrochemical method of sulfur removal is the deposition of sulfur on the anode surface which retards the electrochemical reaction. In the present study, sulfides were oxidized consequently in an electrochemical membrane process to generate elemental sulfur in a powdered form. Sulfide oxidation was achieved by employing flattened and standard titanium substrate insoluble anode (TSIA) meshes with low energy inputs (20 mA cm−2). The shape of the electrode (standard) consequently determines the electrochemical oxidation of the metal sulphide. The irreversible reaction of the sulfide oxidation reaction was explained by a cyclic voltammetry study. This investigation explains that the current distribution of the standard TSIA may be the reason for the sulfur recovery process by an electrochemical membrane reactor, and the recovered product was confirmed through X-ray diffraction and Raman spectroscopy. The spherical shape of the sulfur particles was observed by field emission scanning electron microscopes (FE-SEM and EDAX).

Towards Next Generation Lithium-Sulfur Batteries: Non-Conventional Carbon Compartments/Sulfur Electrodes and Multi-Scale Analysis

In this work, a novel heterofunctional, bimodally-porous carbon morphology, termed the carbon compartment (CC), is utilized as a sulfur host within a lithium-sulfur battery cathode. A multi-scale model explores the physics and chemistry of the lithium-sulfur battery cathode. The CCs are synthesized through a rapid, low cost process to improve electrode-electrolyte interfacial contact and accommodate volumetric expansion associated with sulfide formation. The CCs demonstrate controllable sulfur loading and ca. 700 mAh g−1 (at 47%-wt S) reversible capacity with high coulombic efficiency due to their unique structures. Density functional theory and ab initio molecular dynamics characterize the interface between the C/S composite and electrolyte during the sulfur reduction mechanism. Stochastic realizations of 3D electrode microstructures are reconstructed based on representative SEM micrographs to study the influence of solid sulfur loading and lithium sulfide precipitation on microstructural and electrochemical properties. A macroscale electrochemical performance model is developed to analyze the performance of lithium-sulfur batteries. The combined multi-scale simulation studies explain key fundamentals of sulfur reduction and its relation to the polysulfide shuttle mechanism: how the process is affected due to the presence of carbon substrate, thermodynamics of lithium sulfide formation and deposition on carbon, and microstructural effects on the overall cell performance.

The Relationship between Metabolic Pathways of Bacteria and Pyrrhotite Bioleaching Behavior

The effect of Sulfobacillus thermosulfidooxidans, cultured respectively in the substratum containing ferrous ion or solid elemental sulfur in a long term, on the leaching behavior of pyrrhotite was revealed through leaching test and surface analysis of pyrrhotite leaching residues using XRD and SEM. It was demonstrated that there was significant difference in growth characteristic of S. thermosulfidooxidans, the leaching behavior and surface products of pyrrhotite when pyrrhotite bioleaching was conducted using S. thermosulfidooxidans cultured in different mediums, and it suggested that the difference was chiefly due to different energy metabolism pathways. The pyrrhotite leaching behavior using S. thermosulfidooxidans grown on ferrous ion in a long term was similar to that in the sterile acidic system, and only leaching yield was slightly improved. This was attributed to the ability to oxidize sulfur of S. thermosulfidooxidans was weakened and thus the effect of the generated sulfur could not be eliminated, which leads to low iron extraction and low S. thermosulfidooxidans reproduced ability for lack of growth energy. In the case of S. thermosulfidooxidans cultured in medium containing sulfur, The ability to oxidize sulfur was enhanced, the bacterium grew rapidly in the mid-term of leaching, which weakened the suppressing effect of sulfur film and improved significantly pyrrhotite leaching. However, a large number of jarosite was generated owing to the accumulation of ferric ions with the bioleaching processing, and the formed wrapping layer by jarosite and minor sulfur on mineral surface suppressed further leaching of pyrrhotite.

Vacuum deposition of stoichiometric crystalline PbS films: The effect of sulfurizing environment during deposition

Thin film of lead sulfide (PbS) was deposited onto highly cleaned glass and quartz substrates using a vacuum thermal evaporation technique. The effect of the sulfurizing environment on the growth and properties of vacuum-deposited PbS thin film was studied. The ambient sulfurizing environment was created by thermal decomposition of thiourea inside the vacuum chamber during deposition to maintain the stoichiometry and quality of the PbS film. The sulfurizing gas H2S, produced in the thermal decomposition of the solid sulfur containing thiourea readily combines with the cations (Pb2+) without leaving any anions (S2−) at the substrates and also has not produced any excess of sulfur at the substrates. The deposited film was characterized by optical spectroscopy, x-ray diffraction patterns, scanning electron micrographs with energy dispersive analysis of x-rays, and atomic force micrographs. The physical characterization of the deposited PbS film revealed that the surface of film grown in the sulfurizing environment improved and contained more stoichiometric sulfur in comparison to film deposited without the sulfurizing environment.

Chemical vapor deposition growth and transport properties of MoS2–2H thin layers using molybdenum and sulfur as precursors

This paper introduces a feasible process to achieve the molybdenum disulfide atomic layers using chemical vapor deposition (CVD) method, with molybdenum thin film and solid sulfur as precursors. And some improvements were made to reduce the amount of metastable MoS2–3R. The morphology of the acquired MoS2 layers, existing as triangular flakes or large-area continuous films, can be controlled by adjusting the synthesis time and reacting temperature. The characterization results show that the monolayer MoS2 flakes reveal a (002)-oriented growth on SiO2/Si substrates, and its crystalline domain size is approximately 30 μm, and the thickness is 0.65 nm. Since the synthesis of MoS2–3R is restrained, the electronic transport properties of MoS2 with different layers were investigated, revealing that those properties equal with those of MoS2 samples prepared by exfoliation methods.

The growth scale and kinetics of WS2 monolayers under varying H2 concentration.

The optical and electronic properties of tungsten disulfide monolayers (WS2) have been extensively studied in the last few years, yet growth techniques for WS2 remain behind other transition metal dichalcogenides (TMDCs) such as MoS2. Here we demonstrate chemical vapor deposition (CVD) growth of continuous monolayer WS2 films on mm2 scales and elucidate effects related to hydrogen (H2) gas concentration during growth. WS2 crystals were grown by reduction and sulfurization of WO3 using H2 gas and sulfur evaporated from solid sulfur powder. Several different growth formations (in-plane shapes) were observed depending on the concentration of H2. Characterization using atomic force microscopy (AFM) and scanning electron microscopy (SEM) revealed etching of the SiO2 substrate at low concentrations of H2 and in the presence of an Ar carrier gas. We attribute this to insufficient reduction of WO3 during growth. High H2 concentrations resulted in etching of the grown WS2 crystals after growth. The two dimensional X-ray diffraction (2D XRD) pattern demonstrates that the monolayer WS2 was grown with the (004) plane normal to the substrate, showing that the WS2 conforms to the growth substrate.

Engineering of Hollow Core-Shell Interlinked Carbon Spheres for Highly Stable Lithium-Sulfur Batteries.

We report engineered hollow core-shell interlinked carbon spheres that consist of a mesoporous shell, a hollow void, and an anchored carbon core and are expected to be ideal sulfur hosts for overcoming the shortage of Li-S batteries. The hollow core-shell interlinked carbon spheres were obtained through solution synthesis of polymer spheres followed by a pyrolysis process that occurred in the hermetical silica shell. During the pyrolysis, the polymer sphere was transformed into the carbon core and the carbonaceous volatiles were self-deposited on the silica shell due to the blocking effect of the hermetical silica shell. The gravitational force and the natural driving force of lowering the surface energy tend to interlink the carbon core and carbon/silica shell, resulting in a core-shell interlinked structure. After the SiO2 shell was etched, the mesoporous carbon shell was generated. When used as the sulfur host for Li-S batteries, such a hierarchical structure provides access to Li(+) ingress/egress for reactivity with the sulfur and, meanwhile, can overcome the limitations of low sulfur loading and a severe shuttle effect in solid carbon-supported sulfur cathodes. Transmission electron microscopy and scanning transmission electron microscopy images provide visible evidence that sulfur is well-encapsulated in the hollow void. Importantly, such anchored-core carbon nanostructures can simultaneously serve as a physical buffer and an electronically connecting matrix, which helps to realize the full potential of the active materials. Based on the many merits, carbon-sulfur cathodes show a high utilization of sulfur with a sulfur loading of 70 wt % and exhibit excellent cycling stability (i.e., 960 mA h g(-1) after 200 cycles at a current density of 0.5 C).

Ion Association in Hydrothermal Sodium Sulfate Solutions Studied by Modulated FT-IR-Raman Spectroscopy and Molecular Dynamics

Saline aqueous solutions at elevated pressures and temperatures play an important role in processes such as supercritical water oxidation (SCWO) and supercritical water gasification (SCWG), as well as in natural geochemical processes in Earth and planetary interiors. Some solutions exhibit a negative temperature coefficient of solubility at high temperatures, thereby leading to salt precipitation with increasing temperature. Using modulated FT-IR Raman spectroscopy and classical molecular dynamics simulations (MD), we studied the solute speciation in solutions of 10 wt % Na2SO4, at conditions close to the saturation limit. Our experiments reveal that ion pairing and cluster formation are favored as solid saturation is approached, and ionic clusters form prior to the precipitation of solid sulfate. The proportion of such clusters increases as the phase boundary is approached either by decreasing pressure or by increasing temperature in the vicinity of the three-phase (vapor-liquid-solid) curve.

Purification of hydrogen sulfide from oxygen

A technique for determining the concentration of oxygen in hydrogen sulfide is developed on passing the tested hydrogen sulfide through the stainless steel chips and determining the amount of solid sulfur formed over the catalyst’s surface as a result of hydrogen sulfide oxidation by impurities of oxygen. A method for the deep purification of hydrogen sulfide of oxygen is developed. It is shown that under certain conditions, two chemical reactions for the conversion of hydrogen sulfide into two different modifications of sulfur (solid and gaseous) can proceed independently and simultaneously on the catalyst’s surface.