Sulfidation Behavior Research Articles

Sulfidation Behaviour of Blast Furnace Dust at High Temperatures

Sulfidation Behaviour of Blast Furnace Dust at High Temperatures

Spectral behavior of sulfides in simulated daytime surface conditions of Mercury: Supporting past (MESSENGER) and future missions (BepiColombo)

To detect the mineral diversity of a planet's surface, it is essential to study the spectral variations over a broad wavelength range at relevant simulated laboratory conditions. The MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging) mission to Mercury discovered that irrespective of its formation closest to the Sun, Mercury is richer in volatiles than previously expected. This is especially true for sulfur (S), with an average abundance of 4 wt%. It has been proposed that sulfur in the interior of Mercury can be brought to the surface through volcanic activity in the form of sulfides as slag deposits in Mercury hollows and pyroclastic deposits. However, comprehensive spectral library of sulfide minerals measured under vacuum conditions in a wide spectral range (0.2–100 μm) was lacking. This affects the detectability and understanding of the distribution, abundance, and type of sulfides on Mercury using remote-sensing spectral observations. In the case of Mercury, the effect of thermal weathering affecting the spectral behavior of these sulfides must be studied carefully for their effective detection. In this study, we present a spectral library of synthetic sulfides including MgS, FeS, CaS, CrS, TiS, NaS, and MnS. For each sample, we performed emissivity measurements in the thermal infrared range (TIR: ∼7–14 μm) for sample temperatures from 100°C–500°C, covering the daytime temperature cycle on Mercury's surface. In addition, for each sample we measured the spectral reflectance of fresh and thermally processed sulfides over a wide spectral range (0.2–100 μm) and at four different phase angles, 26°, 40°, 60°, 80°. This spectral library facilitates the detection of sulfides by past and future missions to Mercury by any optical spectrometer of any spectral range. Specifically, the emissivity measurements in this study will support the Mercury Radiometer and Thermal Imaging Spectrometer (MERTIS) instrument on the ESA/JAXA BepiColombo mission, which will study the surface mineralogy over a wavelength range of 7–14 μm at a spatial resolution of 500 m/pixel. The measured reflectance of these sulfides in 0.2–100 μm at various phase angles will support the interpretation of measurements from past (MDIS, MASCS on MESSENGER) and future missions (SIMBIO-SYS on BepiColombo).

Copper Sulfides: Earth‐Abundant and Low‐Cost Thermoelectric Materials

The depletion of nonrenewable energy sources insisted the search for new types of energy solutions. Thermoelectric conversion is one possible energy solution which converts waste heat into useful electricity. In the past several years, thermoelectric research developed many novel materials. Among these, most of the practically useful materials with better performance are based on Bi, Pb, Te, and Sb, but are toxic and expensive. There is a need of earth‐abundant, low‐cost, and less‐toxic compounds with superior thermoelectric performance so as to realize the large‐scale commercial applications. Recent studies have identified eco‐friendly thermoelectric materials based on the alloys of copper and sulfur, suggesting an alternative to the well‐established expensive thermoelectric materials. These compounds exhibit interesting electronic properties with better thermoelectric efficiency (zT). The structural properties permit to decouple electrical and thermal conductivities, which is an essential requirement to get improved efficiency. Several approaches, such as phase tuning, doping, nanostructure/microstructure designing, compound formation, etc., are chosen to increase the performance. On the whole, the present review summarizes the strategies and techniques that have been adopted to improve the thermoelectric behavior of copper sulfides and its compounds.

Physico-chemical Behavior of Hydrogen Sulfide Induced by Reactions with H and D Atoms on Different Types of Ice Surfaces at Low Temperature

Abstract To elucidate the physico-chemical behavior of hydrogen sulfide (H2S) on icy grains in dense molecular clouds, we investigated the surface reactions of solid H2S with H and D atoms in low-temperature laboratory experiments. We confirmed that H2S was lost from the surface by reaction with H atoms via chemical desorption. We found no strong association between the effective desorption cross section and the ice structure (porous amorphous, non-porous amorphous, or crystalline) or temperature (10–30 K). At 10 K, the reaction rate constant for the H–D substitution of solid H2S with D atoms almost matched that for the D–H substitution of solid D2S with H atoms. The present experimental results clearly suggest that the observed abundances of H2S and its deuterated isotopologues (HDS and D2S) in the interstellar medium are controlled, at least partly, by surface reactions on interstellar icy grains.

Mechanical properties of foamed long glass fiber reinforced polyphenylene sulfide integral sandwich structures manufactured by direct thermoplastic foam injection molding

To achieve high levels of lightweight design in automotive or aerospace industry, it is necessary to optimize certain composite material systems concerning their lightweight potential. With sandwich composites, which generally consist of a core which is coated with two face-layers, it is possible to reduce the overall part weight while increasing the specific mechanical properties under inhomogeneously distributed loads. Hereby the sandwich core ensures the load transmission while the face layers absorb the tensile and compressive loads occurring at bending stress. The aim is to increase the efficiency of said sandwiches while minimizing the weight per area by using for example (fiber-) reinforced face layers and foamed core materials. Polyphenylene sulfide (PPS) is an important high temperature, engineering thermoplastic polymer. Because of its properties it is used in the automotive, aerospace and electronics industry. As polyphenylene sulfide has a high processing temperature and requires processing know-how, there a few scientific studies on its foaming behavior. To understand the process-structure-property relationship of this material system, an experimental study on the foaming behavior of neat polyphenylene sulfide and long glass fiber reinforced polyphenylene sulfide using the high-pressure foam injection molding process is conducted. As it is also attractive from a manufacturing point of view to reduce the number of manufacturing steps and to operate with the source materials from the beginning of the process an in-line compounding and foam injection molding process is used. This allows the manufacturing of integral sandwich structures with connected, fiber reinforced face and foamed core layers in one shot via “direct thermoplastic foam injection molding”. With the findings of this study researchers and manufacturers of neat and fiber reinforced PPS parts are able to identify process parameter boundaries and the influence of these parameters on the sandwich structure and mechanical properties.

Thermal behavior and kinetics of sulfide concentrates

Thermal behavior of sulfide concentrates can give rise to many serious problems in its storage and transportation. In order to uncover the thermal behavior of sulfide concentrates, as well as obtain the kinetic parameters, four representative samples were tested using TG-DTG-DSC techniques in the presence of oxygen from 20? to 1000? and with three different heating rates of 5, 10, and 15? per minute. Meanwhile, corresponding activation energies of sulfide concentrates were also determined by the Coats-Redfern method (199.4-234.9 kJmol?1 for Sample 1, 203.6-235.9 kJmol?1 for Sample 2, 234.7-255.6 kJmol?1 for Sample 3, and 199.7-254.9 kJmol?1 for Sample 4). Results indicate that the heating rate is an important factor affecting the thermal behavior of sulfide concentrates. The peak temperature corresponding to the maximum mass loss rate of the ore sample at different heating rates is different and the sulfide concentrates at heating rate of 5? per minute is more prone to spontaneous combustion. Furthermore, this thermodynamic method was demonstrated to be effective for investigating and predicting the thermal behavior of sulfide concentrate and the activation energy index was reasonable for determining its spontaneous combustion tendency.

Re-Os isotope geochemistry of komatiite-hosted Ni-Cu-PGE deposits in Finland

We have studied the Re-Os isotope systematics of komatiite-related Ni-Cu-PGE sulfide deposits in Finland, including the Archean Ruossakero Ni-(Cu), Vaara Ni-(Cu-PGE), Tainiovaara Ni-(Cu-PGE) deposits and Ni-PGE sulfide mineralization related to a dunitic body at Tulppio, and the Paleoproterozoic Lomalampi PGE-(Ni-Cu) deposit. We analyzed chromite separates from both mineralized and non-mineralized komatiitic rocks, bulk-sulfide separates, and country-rock black schist from one deposit, and for comparison, chromite separates from non-mineralized Archean komatiitic rocks from the Kovero and Kuhmo greenstone belts.We have observed open-system behavior of sulfides in three deposits, with their Re-Os isotope compositions indicating resetting at ca. 1.83–1.87 Ga by metamorphic events related to the Svecofennian orogeny. Most of the chromite separates, especially those with >10 ppb Os, retain their primary isotope compositions with near-chondritic initial 187Os/188Os ratios, indicating that their Os was derived from a mantle source with a chondritic Re-Os isotope evolution. These include the Vaara deposit, which yielded a chromite Re-Os isochron age of 2719 ± 140 Ma and low initial γOs of −1.2 ± 0.02, in spite of the evidence for the presence of mass-independent S isotope fractionation in this deposit, suggesting a low-Os, sulfur-bearing contaminant. In the case of the Lomalampi deposit, chromites yield an isochron with an age of 2058 ± 93 Ma and initial γOs of +0.9 ± 0.02, consistent with earlier isotope data from Central Lapland komatiites. However, one chromite from a mineralized cumulate gave a γOs(2050 Ma) value of +24 ± 18, indicating a minor/moderate degree of crustal contamination involving material from country rock black schists. This is also supported by earlier S isotope data. In the Archean Tainiovaara deposit, chromite also suggests crustal contamination (γOs + 13 ± 1), but country rocks are Os-poor Archean gneisses, leaving the source of radiogenic Os unclear, though it is possible that contamination occurred at a greater depth. Our results also provide evidence that the Re-Os age of the Ruossakero deposit is ca. 2.9 Ga, with the deposit likely representing komatiitic magmatism that is older than the komatiitic magmatism elsewhere in Finland. Re-Os results also confirmed that the mineralized Tulppio Dunite is Archean in age.

Visual MINTEQ model, ToF–SIMS, and XPS study of smithsonite surface sulfidation behavior: Zinc sulfide precipitation adsorption

Abstract In this study, we investigate the smithsonite surface sulfidation by zinc sulfide precipitation adsorption. Smithsonite solubility experiments indicated that the CZnT in Na2S solution (1.0 × 10−3 mol/L) was 1–2 orders of magnitude lower compared with the corresponding experiment results in deionized water. Na2S addition benefited the dissolution rate of smithsonite in deionized water. Visual MINTEQ model results confirmed that the zinc sulfide precipitation formed after the main sulfidation reaction between Zn(OH)2(aq) and HS− ions at pH 10, compared with the conversion from ZnS(aq), Zn2S32− ions, and Zn4S64− ions to sphalerite. Moreover, X-ray diffraction and X-ray photo-electron spectroscopy (XPS) analysis showed that the average crystallite sizes of zinc sulfide precipitation particle obtained by co-precipitation technique were approximately 2.32 nm in size. These particles were composed of zinc monosulfide and zinc polysulfide. Time-of-flight secondary ion mass spectrometry and XPS analysis provided strong evidence for zinc sulfide precipitation adsorption on the smithsonite surfaces. Furthermore, more mass signals of S−, ZnS−, S2−, and Zn2S− were observed from the zinc sulfide precipitation than from natural sphalerite, and the monosulfide in the zinc sulfide precipitation was easily adsorbed on the smithsonite surfaces. Results elucidate the smithsonite surface sulfidation behavior during zinc sulfide precipitation adsorption.

Sulfidation mechanism of ZnO roasted with pyrite

Sulfidation is a widely used technology to improve the floatability of oxidized metal minerals or to stabilize the heavy metals in various wastes. The sulfidation mechanism of ZnO with pyrite was detailedly studied by thermodynamic calculation and roasting experiments. The sulfidation behaviors, phase transformations, microscopic morphology and surface properties were investigated by TG-DSC, ICP, XRD, SEM-EDS, and XPS analysis. The results indicate that the nature of the sulfidation is the reaction of ZnO with the gaseous sulfur generated by the decomposition of pyrite. Pyrite instead of sulfur as the sulfidizing agent can not only relieve the volatilization loss of sulfur but also enhance the formation of liquid phase and thus facilitate the growth of ZnS particles. The sulfidation reaction belongs to surface chemical reaction and relates to the migration of oxygen from the inside of ZnO to its surfaces. The presence of carbon not only eliminates the release of SO2, but also decreases the decomposition temperature of pyrite and promotes the sulfidation of ZnO. The addition of Na2CO3 promotes the sulfidation of ZnO at lower temperatures (below 850 °C) and enhances the growth of ZnS particles but has a negative effect on the sulfidation at higher temperatures.

Characterization of direct coal liquefaction catalysts by their sulfidation behavior and tetralin dehydrogenation activity

Direct coal liquefaction (DCL) involves complex catalytic reactions and catalyst transformation. These catalyst behaviors are not well revealed and correlated with the DCL results in the past due to large errors in conventional high-pressure autoclave experiments, which are slow in heating rate and complex in product separation and quantification. To better understand transformation of DCL catalysts and evaluate their activity, this paper studies activity of seven DCL catalysts in dehydrogenation of tetrahydronaphthalene (THN or tetralin) using a high throughput method and compare the results with the catalytic activity in DCL in a conventional high-pressure autoclave. The catalysts' activities in THN dehydrogenation and in DCL are correlated with their sulfidation behaviors observed in temperature-programmed heating in a 5%H2S/H2 atmosphere. It is found that the catalysts show the same activity order in THN dehydrogenation and in DCL. The rate constant of THN dehydrogenation and coal conversion and oil yield in DCL correlate well with S content of the catalysts at reaction conditions. Regardless of the metal forms and the catalysts' preparation methods, linear trends are observed: the higher the catalysts' S content, the lower the activation energy for THN dehydrogenation, and the higher the coal conversion and oil yield in DCL. This finding provides a general role as well as easy methods for assessing the catalysts' activity in the direct coal liquefaction, i.e. the catalysts' DCL activity can be evaluated by their S contents or by their activities in THN dehydrogenation.

Release behavior of allyl sulfide from cyclodextrin inclusion complex of allyl sulfide under different storage conditions

The stability of allyl sulfide, an organosulfur compound present in garlic oil, in its α-, β-, and γ-cyclodextrin inclusion complexes was investigated under various storage conditions. The complexes of cyclodextrins and allyl sulfide were prepared by spray drying. The storage temperature, relative humidity, and initial moisture content of the inclusion complex had different effects on the release rate of allyl sulfide. Allyl sulfide in α-cyclodextrin complexes had a lower release rate than in β- and γ-cyclodextrin complexes at 100°C and at 50°C under 6, 40, 54, and 73% relative humidity. The initial moisture content affected only the release rate of allyl sulfide from α-cyclodextrin complexes. The release behavior of allyl sulfide can be correlated with the first-order release rate equation with a normal Gaussian distribution of free energy of activation of release rate constant. The results indicated α-cyclodextrin is a suitable material for controlled release of allyl sulfide.

Phase transition and thermoelastic behavior of cadmium sulfide at high pressure and high temperature

The phase transition and thermal equation of state of cadmium sulfide (CdS) were studied at high pressure and temperature conditions up to 21.9 GPa and 650 K, by using in situ synchrotron angle-dispersive X-ray diffraction and an externally-heated diamond anvil cell (DAC). A pressure-induced phase transition from wurtzite structure (WZ) to rocksalt structure (RS) was observed at about 2.6 GPa, which was agreed with previous studies (2.0–3.5 GPa). In addition, fitting of the experimental data by means of the third-order Brich-Murnaghan equation of state (III-BM EoS) gives the bulk modulus K0 = 81.6 (13) GPa, its pressure derivative K′0 = 3.68 (13), and the volumetric thermal expansion coefficient α0 = 2.97 (25) × 10−5 K−1 for RS phase of CdS. Simultaneously, the thermal expansion coefficient (α0 = 1.51 × 10−5 K−1), and its axial thermal expansivities (8.30 × 10−6 K−1 and 5.96 × 10−6 K−1) along a-axis and c-axis for WZ phase of CdS at ambient conditions were obtained, respectively. Moreover, it was found that the phase transition pressure from WZ (or ZB) type to RS type of cadmium chalcogenides (CdS, CdSe and CdTe) is quite similar by comparing their phase transition pressures. Furthermore, the elastic properties of metal sulfides (ZnS, CdS, HgS, PbS) with the same crystal structure but different metal cations were also discussed, and found that the bulk moduli for the RS phase of metal sulfides (ZnS, CdS, HgS, PbS) have a negative correlation with the cation radius, but a positive correlation with the electronegativity.

Increasing mass transfer of volatile organic compounds in air scrubbers: a fundamental study for different gas–liquid systems

AbstractBACKGROUNDAir scrubbers are commonly used as treatment techniques for industrial waste gases containing volatile organic compounds (VOCs). Mass transfer of hydrophobic compounds to liquid can be increased using water soluble additives in the scrubbing liquid or applying water‐miscible or immiscible solvents. The design of air scrubbers requires reliable partition data, which are limited in the literature. This manuscript provides partitioning data of new scrubber liquids and subsequent research will link the partitioning data with mass transfer characteristics in a pilot‐scale scrubber.RESULTSThe DynAb method was applied for the first time to a broad set of gas–liquid systems to study the partitioning behaviour of volatile organic sulphides and aldehydes. Cyclodextrins (CD) were chosen as water soluble additives. Silicone oil (SO) and isopropylmyristate (IPM) were used as water immiscible solvents, whereas dipropylene glycol methyl ether was applied as a water‐miscible solvent. The inclusion of VOCs into the CD structure is very compound specific. Binding constants were calculated to quantify the CD‐VOC affinity and the partitioning behaviour of the VOCs with oils and solvents was quantified. The air‐to‐water partition coefficient of hexanal could be reduced more than 50 times with a concentration of 72 g L‐1 α‐CD. IPM (100% v/v) could reduce the air‐to‐IPM partitioning coefficient by a factor of 120 for dimethyl disulphide.CONCLUSIONThe determined partition coefficients can be used for suitability evaluation for the design and modelling of air treatment systems. A broad range of evaluated gas–liquid systems provides quantitative knowledge about VOC behaviour. © 2017 Society of Chemical Industry

Effects of Doping Rare Earth Elements (Y, La, and Ce) on Catalytic Performances of CoMo/MgAlM for Water Gas Shift Reaction

Rare earth element (La, Y, and Ce) modified MgAl-hydrotalcites of MgAlM were synthesized from coprecipitation and calcination, and further loaded with CoMo active species to give CoMo/MgAlM catalysts. X-ray powder diffraction, inductively coupled plasma, and N2 adsorption isotherms indicate that MgAlM possess large BET surface areas (58–91 m2/g), and rare earth elements were successfully introduced into samples. CO2-TPD (temperature-programmed desorption), NH3-TPD, H2-TPR (temperature-programmed reduction), H2S-TPS (temperature-programmed sulfidation), and Raman spectra indicate the presence of unique interactions between rare earth elements and Mo active species, which strongly affect the reduction and sulfidation behaviors of these catalysts. High resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analysis suggest that the addition of rare earth elements decreases the slab length and stacking numbers of MoS2 and promotes the sulfidation degree of Mo oxides. Th...

Pseudocapacitive-battery-like behavior of cobalt manganese nickel sulfide (CoMnNiS) nanosheets grown on Ni-foam by electrodeposition for realizing high capacity.

Hierarchical interconnected nanosheets (HIN) of cobalt manganese nickel sulfide (CoMnNiS) were synthesized on Ni foam by a simple and economical electrodeposition technique for energy storage application. Sulfonated thin nanosheets of Co, Mn and Ni provide stability of chemical activity, surface functionalization and surface reactivity to the electrode. The fabricated electrode shows a specific capacity of 257.4 mA h g−1 (at 2.5 A g−1), measured by galvanostatic charging–discharging (GCD). Both diffusion and capacitive mechanisms in the sulfide layer contribute to the high electrical conductivity. Asymmetric devices CoMnNiS/NiCuO and CoMnNiS/CNT (CNT = carbon nanotubes) were fabricated, providing a maximum operating voltage of 1.7 V and 1 V, specific capacity of 20.8 and 50.8 mA h g−1, and energy density of 8.4 and 6.3 W h kg−1 corresponding to a power density of 985 and 211 W kg−1, respectively, at a current density of 0.5 and 0.63 A g−1. These results demonstrate a novel material for application in energy storage devices as an electrode.

Fungal-Transformation of Surrogate Sulphides and Carbonaceous Matter in Refractory Gold Ores: Revisited

In the recovery of gold from refractory gold ores, pretreatment is required to decompose sulphides and liberate occluded gold before cyanidation, and to deactivate carbonaceous matter and prevent it from adsorbing dissolved gold. Until the past three decades, most commercial pretreatment processes had been by abiotic means. Biological pretreatment methods on commercial basis is therefore a recent phenomenon, and several researches are underway to assess the ability of different biological agents in the breakdown of sulphur and carbonaceous matter (CM) in gold ores. This paper, which is a revisit of an earlier one, presents an overview of on-going research aimed at assessing the capability of the fungus, Phanerochaete chrysosporium, to degrade sulphides and CM. Surrogate carbonaceous materials (lignite, bituminous and anthracite coals) and pure sulphides (pyrite and arsenopyrite) were used to model the behavior of CM and sulphides in refractory gold ores. To monitor the extent of biotransformation, preg-robbing test was conducted on the as-received and treated CM, and sulphide sulphur in the residual sulphidic materials was also determined. From an initial preg-robbing effect of 125 µg of gold per gram of CM, the ability of CM to preg-rob gold reduced by 70-95% in the order of lignite<bituminous <anthracite within 21 days of treatment, whereas there were 18% and 39% oxidation of sulphide sulphur in pyrite and arsenopyrite respectively. XRD examination of the treated anthracite confirmed reduction in the graphitic structure of carbon following fungal transformation. Similarly, there was a decline in the major sulphide peak after microbial pretreatment. The results indicate that the fungus biotransforms through destruction of the ordered structure, followed by introduction of oxygen groups. The amorphous nature, thus generated, inhibits the uptake of aurocyanide ions by CM, while enhancing the affinity of cyanide for the oxidised sulphide material in subsequent cyanidation treatment. The findings contribute to knowledge on novel and technically viable alternative methods for oxidative pretreatment of refractory gold ores. Keywords: Phanerochaete Chrysosporium, Carbonaceous Matter, Metal Sulphides, Biotransformation

Sulfidation behavior and mechanism of zinc silicate roasted with pyrite

Sulfidation roasting followed by flotation is widely known as a possible generic technology for enriching valuable metals in low-grade Zn-Pb oxide ores. Zn2SiO4 is the primary Zn phase in willemite. Zn4Si2O7(OH)2(H2O), the main Zn phase in hemimorphite, transforms into Zn2SiO4 at temperatures above 600 °C. To enrich the Zn in willemite and hemimorphite, the Zn species should first be converted to ZnS. Therefore, a thorough understanding of the sulfidation reaction of Zn2SiO4 during roasting with pyrite is of vital important. In this study, the sulfidation behavior and reaction mechanisms of a Zn2SiO4-pyrite roasting system were determined using HSC 5.0 software, TG-FTIR spectroscopy, XRD, XPS and SEM-EDS. The results indicate that the sulfidation process can be divided into three steps: the decomposition of pyrite and formation of a sulfur-rich environment, the sulfur-induced migration of O2− and transformation of sulfur vapor, and the sulfidation reaction via oxygen-sulfur exchange. During the sulfidation roasting process, pyrite was converted to loose and porous Fe3O4, whereas Zn2SiO4 was transformed into ZnS and SiO2 in situ. These findings provide theoretical support for controlling the sulfidation roasting process of willemite and hemimorphite.

The role of sulfide minerals in the genesis of groundwater with elevated geogenic arsenic in bedrock aquifers from western Quebec, Canada

The primary arsenic-bearing minerals and their relation to the mobilization of arsenic in groundwater are investigated in a mineralized area of the Canadian Shield (Province of Quebec, Canada). Bedrock core and groundwater samples were collected from three mining exploration boreholes completed in the fractured bedrock aquifer. Chemical analyses of groundwater reveal that the boreholes contain high arsenic concentrations ranging from 0.11 to 0.46mg/l. Mineralogical analyses of core samples indicate that arsenic is mainly present as arsenopyrite (FeAsS) and gersdorffite (NiAsS), with arsenic and sulfur contents ranging from a few mg/kg to more than 3.1 and 1.3wt%, respectively. Core leaching experiments show that the release of arsenic in oxidizing and weak alkaline water largely depends on the mineralogy of arsenic. Gersdorffite-rich samples release larger amount of arsenic than arsenopyrite-rich samples, which is mainly attributed to the high reactivity of gersdorffite compared to arsenopyrite. However, the high arsenic concentrations in groundwater are not associated with the occurrence and extent of gersdorffite-rich zones in the bedrock. These results are interpreted as evidence that the local weathering of sulfide minerals is not the main mechanism of arsenic mobilization in borehole waters. The groundwater composition strongly suggests that the mobilization of arsenic is related to the reductive dissolution of Fe and Mn oxyhydroxides in the downgradient part of the aquifer. Thus, it is proposed that the high arsenic concentrations in groundwater are mainly driven by (1) the initial release of arsenic through sulfide oxidation under oxidizing conditions (recharge areas), (2) the sequestration by sorption onto Fe-Mn oxyhydroxides and clay minerals, (3) the transport of arsenic in dissolved and particulate forms in groundwater through fractures, and (4) the (re)mobilization by dissolution of Fe-Mn oxyhydroxides under reducing conditions (downgradient areas). This study highlights the potential role of sulfide stability and the importance of redox conditions in the mobilization of arsenic in groundwater from areas of sulfide mineralization. More detailed information is needed regarding the geochemical behavior of arsenic-bearing sulfides in bedrock aquifers under natural conditions and its implication for geogenic arsenic in groundwater.

Sulfur resistant WGS catalyst for hydrogen production based on CoMo supported by Nb modified MgAl mixed oxide

In this paper, CoMo supported on Nb modified MgAl mixed oxide by calcination of layered double hydroxides (LDHs) were prepared using wet impregnation method. The fresh calcined catalysts were further sulfided by H2S/H2 and tested for water-gas shift reaction (WGSR). The physicochemical properties of fresh calcined catalysts were characterized by various adsorption and bulk techniques like XRD, ICP, N2-physisorption, CO2-TPD, H2-TPR, H2S-TPS and HRTEM. It is found that the addition of Nb does not affect the formation of LDHs, but changes the reduction and sulfidation behavior of Mo species on oxidic catalyst as well as the dispersion of MoS2 phase on the sulfided catalyst. The CoMo/Nb(5%)MgAl catalyst shows the lowest apparent sulfidation activation energy, consumes the highest amount of H2S and thus has the highest catalytic activity in WGS reaction.

Phase transition of tetragonal copper sulfide Cu2S at low temperatures

The low-temperature behavior of tetragonal copper sulfide, ${\mathrm{Cu}}_{2}\mathrm{S}$, was investigated by powder and single-crystal x-ray diffraction, calorimetry, electrical resistance measurements, and ambient temperature optical absorption spectroscopy. The experiments were complemented by density-functional-theory-based calculations. High-quality, polycrystalline samples and single crystals of tetragonal copper sulfide were synthesized at 5 GPa and 700 K in a large volume multianvil press. Tetragonal ${\mathrm{Cu}}_{2}\mathrm{S}$ undergoes a temperature-induced phase transition to an orthorhombic structure at around 202 K with a hysteresis of $\ifmmode\pm\else\textpm\fi{}21$ K, an enthalpy of reaction of 1.3(2) $\mathrm{kJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}$, and an entropy of reaction of 6.5(2) $\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{mol}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$. The temperature dependence of the heat capacity at the transition temperature indicates that the transition from the tetragonal to the low-temperature polymorph is not a single process. The structure of the low-temperature polymorph at 100 K was solved in space group $Pna{2}_{1}$. The structure is based on a slightly distorted cubic close packing of sulfur with copper in threefold coordination similar to the structure of tetragonal copper sulfide. The electrical resistance changes several orders of magnitude at the transition following the temperature hysteresis. The activation energy of the conductivity for the tetragonal phase and the low-temperature polymorph are 0.15(2) and 0.22(1) eV, respectively. The direct band gap of the tetragonal polymorph is found to be 1.04(2) eV with the absorption spectrum following Urbach's law. The activation energies and the band gaps of both phases are discussed with respect to the results of the calculated electronic band structures.