Sulfide Phases Research Articles

Electron probe microanalysis of trace sulfur in experimental basaltic glasses and silicate minerals

Abstract Sulfur (S) in the mantle is conventionally assumed to be exclusively stored in accessory sulfide phases, but recent work shows that the major silicate minerals that comprise >99% of the mantle could be capable of hosting trace amounts of S. Assessing the incorporation of trace S in nominally S-free mantle minerals and determining equilibrium S partitioning between these minerals and basaltic melt requires analyzing small experimental phases with low S contents. Here, we develop a protocol for EPMA analysis of the trace levels of S in silicate phases. We use a suite of natural and experimental basaltic glass primary and secondary standards with S contents ranging from 44 ppm to 1.5 wt%. The effects of beam current and counting time are assessed by applying currents ranging from 50 to 200 nA and total counting times between 200 and 300 s at 15 kV accelerating voltage. We find that the combination of 200 nA beam current with a 200 s counting time (80 s peak, 60 s each for upper and lower background, respectively) achieves precise yet cost-effective measurements of S down to a calculated detection limit of ~5 ppm and a blank-derived, effective detection limit of ~17 ppm. Close monitoring of the S peak intensity and position throughout the duration of each spot also shows that high currents and extended dwell times do not compromise the accuracy of measurements, and even low S contents of 44 ppm can be reproduced to within one standard deviation. Using our developed recipe, we analyzed a small suite of experimental clinopyroxenes (Cpx) and garnets (Gt) from assemblages of silicate partial melt + Cpx ± Gt ± sulfide, generated at 1.5 to 3.0 GPa and 1200 to 1300 °C. We find S contents of up to 71 ± 35 ppm in Cpx and 63 ± 28 ppm in Gt and calculate mineral-melt partition coefficients (Dsmin/melt) of up to 0.095 ± 0.064 and 0.110 ± 0.064 for DsCpx/melt and DsGt/melt, respectively. The sulfur capacity and mineral-partitioning for Cpx are in good agreement with SXRF measurements in a prior study by Callegaro et al. (2020), serving as an independent validation of our EPMA analytical protocol.

Validating the rhenium proxy for rock organic carbon oxidation using weathering profiles

Chemical weathering over geological timescales acts as a source or sink of atmospheric carbon dioxide (CO2), while influencing long-term redox cycling and atmospheric oxygen (O2) at Earth's surface. There is a growing recognition that the oxidative weathering of rock organic carbon (OCpetro) can release more CO2 than is locally drawn down by silicate weathering, and may vary due to changes in erosion and climate. The element rhenium (Re) has emerged as a proxy to track the oxidative weathering of OCpetro, yet uncertainties in its application remain namely that we lack a systematic assessment of the comparative mobility of Re and OCpetro during sedimentary rock weathering. Here we measure Re and OCpetro loss across gradients in rock weathering at 9 global sites, spanning a range of initial OCpetro values from ∼0.2 % to >10 %. We use titanium to account for volume changes during weathering and assess Re and OCpetro loss alongside major elements that reflect silicate (Na, Mg), carbonate (Ca, Mg) and sulfide (S) weathering. Across the dataset, Re loss is correlated with OCpetro loss but not with loss of any other major element. Across the weathering profiles, the average molar ratio of OCpetro to Re loss was 0.84 ± 0.15, with 8 out of 9 sites having a ratio >0.74. At one site (Marcellus Shale), the average ratio was lower at 0.58 ± 0.11. The excess loss of Re matches expectations that, typically, between ∼0 and 20 % of the Re liberated by sedimentary rock weathering derives from silicate or sulfide phases, while some OCpetro may be physically or chemically protected from weathering. Overall, our measurements provide validation for the Re proxy of OCpetro oxidation and allow future work to further improve our knowledge of regional and global-scale rates of this important source of CO2 in the geochemical carbon cycle.

N,S‐Doped Zeolite‐Templated Carbon Like Supported NixFeySz as an Efficient Bifunctional Catalyst for Rechargeable Zinc Air Batteries

AbstractA still unexplored class of heterostructured bifunctional catalysts for oxygen evolution (OER) and reduction (ORR) reactions is investigated: Ni−Fe sulfides deposited onto a N,S‐co‐doped zeolite‐templated carbon (ZTC) substrate achieved upon the impregnation of a ZTC with thiourea and Ni and Fe precursors (Ni/Fe atomic ratio of 1). By heat‐treating the impregnated ZTC substrate at 700 °C under N2 atmosphere the efficient bifunctional catalyst is generated. A difference of only 0.76 V is measured between the potential required to drive an OER current density of 10 mA cm−2 and the ORR half‐wave potential. Using electrochemical measurements and physico‐chemical characterizations, it is evidenced that OER activity results from the presence of a sulfide containing both Fe and Ni whereas the ORR activity originates from the N,S‐doped ZTC substrate. The selectivity of the ORR process is improved through the presence of sulfide phases. Compared to more conventional carbon substrate such as N,S‐co‐doped reduced graphene oxide, high specific surface area ZTC favors high ORR performances. The functional ZTC material was further successfully implemented as bifunctional air electrode in a coin‐type Zn‐air battery.

Density functional theory study of cobalt sulfide as a counter electrode material for dye-sensitized solar cells

Abstract Dye-sensitized solar cells (DSSCs) are viewed as potential substitutes for traditional silicon-based solar cells due to their affordability, impressive performance in low-light conditions, eco-friendly energy production, and adaptability in solar product integration. The use of noble metals such as platinum as counter electrodes in DSSCs was initially limited by their high cost; however, cobalt sulfide has been recognized as a viable alternative due to its abundance, non-toxic properties, and cost-effectiveness. In this work, the crystal structure, electronic, optical characteristics and electrocatalytic activity of the tetragonal phases of cobalt sulfide are investigated through density functional theory with a quantum espresso package. The results obtained for the lattice parameter are a = b = 3.53 Å and c = 4.80 Å. The generalized gradient approximation and hybrid exchange correlation function yield bandgaps of 1.63 and 1.69 eV, respectively, which are consistent with the reported experimental values. An analysis of the density of states and the projected density was carried out to validate the accuracy of the calculated band gaps. Additionally, significant information was obtained from the optical properties through the calculation of the dielectric function. The findings reveal real and imaginary static dielectric constants of 11.85 and 0.13, respectively. Furthermore, the measured absorption and conductivity spectra exhibit promising attributes in the UV–visible range and good electrical conductivity. Moreover, the electrocatalytic activity was studied to analyze the adsorption energy of CoS and the electrolyte. Generally, the calculated electronic and optical properties of CoS crystals indicate their potential application as counter electrodes in dye-sensitized solar cells.

Atomic decoration of MoS2 using Fe, Co or Ni for highly efficient and selective hydrodesulfurization

Hydrodesulfurization (HDS) is one of the most efficient processes for removing sulfur-containing molecules such as dibenzothiophene (DBT) from oil, whatever fossil based or bio-based. However, hydrodesulfurization using molybdenum sulfides (MoS2) as catalytic active centers and transition metals (X) as promoters is seriously challenged by the insufficient catalytic activity and selectivity because of the separate phases of sulfides, and sparse X-Mo-S active sites, leading to poor synergistic effect between the X promoter and MoS2 active centers. Herein, atomically doped MoS2 catalysts (denoted as XMo, X = Fe, Co or Ni) were synthesized by using polyoxometalate template-based synthetic strategy were proposed. The pre-organized Anderson-type POMs, [XMo6O24H6]n− (X = Fe, Co or Ni), acted as a pre-assembled molecular platform with intimate X-Mo interactions, ensure the uniform formation of X-Mo-S active sites after sulfuration. The promoter atoms, including Fe, Co and Ni, enhanced the efficiency of hydrodesulfurization of MoS2. Particularly, NiMo exhibits the highest HDS activity, while CoMo shows a moderate HDS activity with the highest DDS selectivity (∼85 %). Despite the lowest HDS activities, FeMo with the cheapest Fe promoter, shows good DDS selectivity (∼70 %). Further study reveal NiMo has the most laminated morphology and highest stacking slabs, resulting in the highest HDS activity. Benefiting from the Co(Fe)-Mo-S structure and abundant sulfur vacancy, CoMo and FeMo showed great enhancement in the DDS selectivity. Moreover, the DDS selectivity of these designed catalysts were supported energetically by first principle calculations. This research will expand on the ability to improve the HDS activities and DDS selectivity by precisely engineering catalytic active sites to achieve significant synergistic effect in atomic scale.

Copper and zinc sulfides bioleaching by an extremely thermophilic archaeon in high NaCl concentration

Chloride bioleaching has received attention of several mineral processing industries, particularly in countries where there is scarcity of freshwater and only chloride-containing waters can be used. Therefore, the present work investigated the effect of NaCl (1.0 mol L−1) on the bioleaching of three sulfide minerals: chalcopyrite, bornite, and sphalerite by the thermophilic archaea Sulfolobus acidocaldarius. Chalcopyrite dissolution was only 25 % in the biotic experiment in the absence of chloride, but reached 90 % in the presence of both microorganisms and chloride, while less than 60 % extraction was observed in the abiotic experiment with chloride. In the experiments of bornite bioleaching, 86 % and 77 % of copper were extracted in the biotic and abiotic tests with chloride, respectively. In the absence of NaCl, the biotic and abiotic experiments presented similar copper dissolution (∼35 %). Finally, bioleaching experiments carried out with sphalerite showed zinc extractions below 35 % in all conditions tested. The main contribution from the archaea was its ability to produce low concentrations of ferric ion, which was partially precipitated as jarosite, resulting in low redox potential values (< 450 mV vs. Ag/AgCl), and efficiently bioleached bornite and chalcopyrite. Furthermore, XRD and SEM-EDS analyses demonstrated that sphalerite was practically not leached while bornite was transformed into new copper sulfide phases (CuS and Cu3FeS4). Jarosite and elemental sulfur were products of chalcopyrite and bornite bioleaching in the presence of chloride.

Synthesis and consequence of three-dimensionally ordered macroporous Beta zeolite supported NiW catalyst for efficient hydrocracking of 1-methylnaphthalene to BTX

The three-dimensionally ordered macroporous Beta (3DOM-Beta) zeolite was prepared and used as support of NiW sulfide catalyst for hydrocracking. The as-prepared NiW/3DOM-Beta catalyst possessed a high specific surface area and external specific surface area up to 499 m2/g and 241 m2/g, respectively, and a small average layer length (3.62 nm), a high highest average stacking number (4.64) and dispersion (fW=0.24) of metal sulfide phase, which are characteristic of high hydrogenation activity. Its high mesopore volume (0.25 cm3/g) and the highly ordered interconnected macro-meso-microporosity hierarchical structure significantly facilitated diffusive mass transfer. Compared to the NiW sulfide supported on conventional Beta (C-Beta), alkali-treated Beta (A-Beta) and nanosized Beta (Nano-Beta) zeolites, NiW/3DOM-Beta catalyst showed the highest BTX selectivity and yield of 40.7 % and 40.2 % (33.2 % and 32.6 % on NiW/C-Beta, 34.8 % and 33.9 % on NiW/A-Beta, 37.2 % and 36.6 % on NiW/Nano-Beta), and the highest hydrocracking activity (TOF=2.11 × 10-2∙s−1) as well as the smallest coking content (6.7 wt%). This work not only reveals the promotion effects of the ordered mesopore structure of supports on metal dispersion, accessibility of acid sites, diffusion of reactants and products for designing hydrocracking catalyst, but also shows the potential practical application of 3DOM zeolites with interconnected macro-meso-microporosity for the efficient catalytic conversion of macro-hydrocarbons via hydroupgrading.

Al2O3 Concentration Effect on Deep Hydrodesulfurization of 4,6-Dimethyldibenzothiophene over NiWS/Al2O3-ZrO2 Catalysts.

The Al2O3 concentration effect over NiWS/Al x Zr100-x catalysts was investigated for deep hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DMDBT). The sol-gel method changed the wt % Al2O3 concentrations used to synthesize the Al x Zr100-x supports. The NiWS/Al x Zr100-x catalysts were prepared with ammonium metatungstate hydrate and nickel(II) nitrate hexahydrate by sequential incipient impregnation, calcination, and H2S/H2 activation. The catalytic evaluation data fit a pseudo-first-order trend in the 4,6-DMDBT HDS reactions. In the oxide phase, the catalysts presented Ni and W species in tetrahedral (td) and octahedral (oh) coordination, with the oh species prevailing as a function of the Al2O3 amount. The lower amount of Al2O3 can facilitate the "Type II" NiWS phase formation by weakening the interaction of the W-O-Al bond and promoting W and Ni species sulfidation. In the sulfide phase, catalysts with (oh) coordination and surface WO X species promote the formation of WS2 and NiWS species during the catalyst activation step. This species favors the reaction yield, where the hydrogenation route is predominant, with the highest initial reaction rate using the NiWS/Al25Zr75 catalyst. A direct correlation was found between high hydrogenation/hydrogenolysis ratio values and low Al2O3 concentrations.

Nanosheet-interwoven structures and ion-electron decoupling storage enable Fe1-xS fast ion transport in Li+/Na+/K+ batteries

Fe1-xS, known for its high theoretical capacity, abundant resources, and intrinsic safety, has become a focal point as a universal anode for Li+/Na+/K+ batteries. However, its fast-charging capability is unsatisfactory due to sluggish ion transport rate and low electrical conductivity. Furthermore, its Li+/Na+/K+ storage mechanisms are still unclear. Here, we fabricate a single-crystal Fe1-xS/N-doped carbon composite nanosheet interwoven structure, in which N-doped carbon layers onto surface of Fe1-xS nanosheets ameliorate the electrical conduction and the interwoven nanosheets form open pore channels that favor permeation of electrolytes to boost ion transport. In-situ magnetometry reveals that ion-electron decoupling storage and transport occur in two-phase composites of Fe/Li2S, Fe/Na2S, and Fe/K2S, in which Fe phase stores and transports electrons and sulfide phase stores and transports ions in a space-charge form, resulting in extra ion storage and fast ion transport. Consequently, the nanosheet interwoven structure delivers high capacities (1320.1/652.2/350.6 mAh g−1), outstanding fast-charging performances (679.6/295.4/106.4 mAh g−1 at 20 A g−1), and long cycling life over 5000 cycles as Li+/Na+/K+ battery anodes, respectively

Interplay of luminescence and magnetic phenomena in Mn-doped ZnS zinc blende nanocrystals: Influence of magnetic doping

This research comprehensively investigates the interplay between luminescence and magnetic phenomena in the zinc blende phase of manganese-doped and undoped zinc sulfide. The study involves the synthesis of zinc sulfide nanocrystals through a soft chemical method, followed by an in-depth experimental characterization. Theoretical studies were conducted using a 2 × 2 × 2 supercell model with 64 atoms to explore the impact of native defects and manganese doping on zinc sulfide's the electronic, magnetic, and optical properties. The research findings offer a detailed physical description of magnetic and optic phenomena observed, underpinned by a strong correlation between theoretical predictions and experimental results. An essential contribution of this work is developing a depiction that elucidates the relationship between optical transitions and spin-exchange in the context of these phenomena.

Evolution of Cu and Zn speciation in agricultural soil amended by digested sludge over time and repeated crop growth

Metals such as Zn and Cu present in sewage sludge applied to agricultural land can accumulate in soils and potentially mobilise into crops. Sequential extractions and X-ray absorption spectroscopy results are presented that show the speciation changes of Cu and Zn sorbed to anaerobic digestion sludge after mixing with soils over three consecutive 6-week cropping cycles, with and without spring barley (Hordeum vulgare). Cu and Zn in digested sewage sludge are primarily in metal sulphide phases formed during anaerobic digestion. When Cu and Zn spiked sludge was mixed with the soil, about 40% of Cu(I)-S phases and all Zn(II)-S phases in the amended sludge were converted to other phases (mainly Cu(I)-O and outer sphere Zn(II)-O phases). Further transformations occurred over time, and with crop growth. After 18 weeks of crop growth, about 60% of Cu added as Cu(I)-S phases was converted to other phases, with an increase in organo-Cu(II) phases. As a result, Cu and Zn extractability in the sludge-amended soil decreased with time and crop growth. Over 18 weeks, the proportions of Cu and Zn in the exchangeable fraction decreased from 36% and 70%, respectively, in freshly amended soil, to 28% and 59% without crop growth, and to 24% and 53% with crop growth. Overall, while sewage sludge application to land will probably increase the overall metal concentrations, metal bioavailability tends to reduce over time. Therefore, safety assessments for sludge application in agriculture should be based on both metal concentrations present and their specific binding strength within the amended soil.

High Capacity NbS2-Based Anodes for Li-Ion Batteries.

We have investigated the lithium capacity of the 2H phase of niobium sulfide (NbS2) using density functional theory calculations and experiments. Theoretically, this material is found to allow the intercalation of a double layer of Li in between each NbS2 layer when in equilibrium with metal Li. The resulting specific capacity (340.8 mAh/g for the pristine material, 681.6 mAh/g for oxidized material) can reach more than double the specific capacity of graphite anodes. The presence of various defects leads to an even higher capacity with a partially reversible conversion of the material, indicating that the performance of the anodes is robust with respect to the presence of defects. Experiments in battery prototypes with NbS2-based anodes find a first specific capacity of about 1,130 mAh/g, exceeding the theoretical predictions.

Laser-Induced Synthesis of Tin Sulfides.

Various polytypes of van der Waals (vdW) materials can be formed by sulfur and tin, which exhibit distinctive and complementary electronic properties. Hence, these materials are attractive candidates for the design of multifunctional devices. This work demonstrates direct selective growth of tin sulfides by laser irradiation. A 532nm continuous wave laser is used to synthesize centimeter-scale tin sulfide tracks from single source precursor tin(II) o-ethylxanthate under ambient conditions. Modulation of laser irradiation conditions enables tuning of the dominant phase of tin sulfide as well as SnS2/SnS heterostructures formation. An in-depth investigation of the morphological, structural, and compositional characteristics of the laser-synthesized tin sulfide microstructures is reported. Furthermore, laser-synthesized tin sulfides photodetectors show broad spectral response with relatively high photoresponsivity up to 4 AW-1 and fast switching time (τ rise = 1.8ms and τ fall = 16ms). This approach is versatile and can be exploited in various fields such as energy conversion and storage, catalysis, chemical sensors, and optoelectronics.

Decomposition of Sulfide Phases and Subsequent Matte Collection in the Black Top of a Platinum Group Metal Smelter

ABSTRACT This study explored, on a laboratory scale, how matte separates from the gangue in the black top of a PGM smelter. Two PGM concentrates, one with high sulfide content (17.3 mass%, Platreef concentrate) and the other with low sulfide content (1.3 mass%, UG-2 concentrate), were studied in the temperature range of 800°C to 1480°C, which is the temperature gradient across the black top. The results showed that effective matte separation occurs at temperatures when the matte is completely molten, and a substantial amount of liquid silicate phase has formed. The main matte separation mechanism is the coalescence of sulfide prills and their gravitational settling through the continuous path created by the liquid silicate phase. Complete matte separation occurs at lower temperatures in Platreef concentrate (1400°C in Platreef concentrate vs. 1480°C in UG-2 concentrate), due to the higher concentration of liquid silicate phase of lower viscosity, as well as the higher amount of sulfide minerals in this concentrate. PGMs already dissolve and collect in a nickel-iron-based alloy associated with the matte at temperatures as low as 900°C.

Shape-controlled electro-synthesis of pyrrhotite

Recently, iron sulfide nanomaterials have drawn increased interest, due to their novel properties and extensive applications depending on their structure. To date, various methods have been employed for the synthesis of iron sulfide nanostructures with different shapes and morphologies. The synthesis method of iron sulfide nanomaterial is a challenge, as a small variation in sulfur content can lead to formation of different phases of iron sulfide. In this study, iron sulfide nanostructures were synthesized using our fast, simple, efficient, economical and environmentally friendly method in an electrochemical cell containing two iron sheets as electrodes in an aqueous solution of sodium sulfide. This method, with many advantages such as low-toxicity, low cost and easy handling, helps to control the properties of the products through the synthesis by tuning the growth conditions. Here, the influence of applied voltage ranging from 5 V to 25 V and annealing temperatures of 200 °C and 800 °C on the structure and magnetic properties of the products were studied. The samples were analyzed by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). XRD patterns confirmed the formation of monoclinic and hexagonal pyrrhotite at 200 °C and 800 °C, respectively. Based on SEM images, pyrrhotite in different shapes, such as quasi-spherical, feathers, sheets and flower-like structures, are formed depending on the applied voltage and annealing temperature. According to VSM results, all samples annealed at 200 °C are magnetically soft with only a little hysteresis, but the magnetization increases from 2.3 emu/g to 10.1 emu/g when applied voltage varies from 5 V to 25 V. All samples annealed at 800 °C exhibit an antiferromagnetic behavior. With increasing the applied voltage, the value of remanence magnetization and coercivity increases up to ∼2000 Oe and ∼0.14 emu/g, respectively.

Structure and magnetic properties of (Ni,Fe)Fe2O4 derived from nickel slag via molten oxidation

The large amount of nickel-iron resources in nickel slag urgently needs to be recycled. In this study, (Ni,Fe)Fe2O4 was prepared by phase reconstruction of the nickel slag by molten oxidation method. The thermodynamic conditions and feasibility of the formation of (Ni,Fe)Fe2O4 during molten oxidation were analyzed by combining thermodynamic calculation and experimental research. The influence of the different NiO contents on the cation distribution and magnetic properties of (Ni,Fe)Fe2O4 was analyzed. Additionally, the mechanism governing Ni incorporation within the (Ni,Fe)Fe2O4 lattice was elucidated. The results show that the sulfide phase and silicate phase of Fe and Ni in the nickel slag were finally transformed into (Ni,Fe)Fe2O4 phase, which was preferentially precipitated during the cooling process. (Ni,Fe)Fe2O4 is formed by the replacement of Fe2+ at the octahedral site in Fe3O4 by Ni2+. As more Fe2+ is replaced by Ni2+, (Ni,Fe)Fe2O4 solid solution exhibits high permeability and low coercivity. The recoveries of Fe and Ni are up to 77.89 % and 80.8 % via the molten oxidation process, respectively. This work not only provided a theoretical foundation for the preparation of (Ni,Fe)Fe2O4 by molten oxidation but also promoted the recovery of valuable metal resources in nickel slag.

Remnant Copper Cation-Assisted Atom Mixing in Multicomponent Nanoparticles.

Nanostructured high-/medium-entropy compounds have emerged as important catalytic materials for energy conversion technologies, but complex thermodynamic relationships involved with the element mixing enthalpy have been a considerable roadblock to the formation of stable single-phase structures. Cation exchange reactions (CERs), in particular with copper sulfide templates, have been extensively investigated for the synthesis of multicomponent heteronanoparticles with unconventional structural features. Because copper cations within the host copper sulfide templates are stoichiometrically released with incoming foreign cations in CERs to maintain the overall charge balance, the complete absence of Cu cations in the nanocrystals after initial CERs would mean that further compositional variation would not be possible by subsequent CERs. Herin, we successfully retained a portion of Cu cations within the silver sulfide (Ag2S) and gold sulfide (Au2S) phases of Janus Cu2-xS-M2S (M = Ag, Au) nanocrystals after the CERs, by partially suppressing the transformation of the anion sublattice that inevitably occurs during the introduction of external cations. Interestingly, the subsequent CERs on Janus Cu1.81S-M2S (M = Ag, Au), by utilizing the remnant Cu cations, allowed the construction of Janus Cu1.81S-AgxAuyS, which preserved the initial heterointerface. The synthetic strategy described in this work to suppress the complete removal of the Cu cation from the template could fabricate the CER-driven heterostructures with greatly diversified compositions, which exhibit unusual optical and catalytic properties.

In‐depth study of a speiss/matte sample from Castillo de Huarmey, North Coast of Peru, and its implications for the pre‐Columbian production of arsenic bronze in the Central Andes

AbstractThis study aims to characterize the phase composition and chemistry of the speiss/matte sample from the Metallurgist's Burial at Castillo de Huarmey and to use the information derived from these analyses to infer the temperatures, furnace conditions, and ores associated with the smelting processes, which created the speiss/matte sample. For this purpose, a number of geochemical analyses were performed on the spies/matte fragment: analysis of the general chemical composition (handheld X‐ray fluorescence spectrometry [hhXRF], X‐ray photoelectron spectroscopy [XPS]), analysis of the chemical composition in the micro area (field emission scanning electron microscope with an energy dispersive spectroscopy detector [FE‐SEM‐EDS], field emission electron probe microanalysis [FE‐EPMA]), analysis of the mineral composition (X‐ray diffraction [XRD]), and analysis of the phase composition (Raman spectroscopy). Chemical and mineralogical analyses of the speiss/matte specimen determined that the specimen is composed of distinct arsenide, arsenate, sulfide, and glass phases. During the smelting process, the charge material consisted mainly of Cu, Fe, and As sulfides. Arsenopyrite is the most likely candidate as the mineral source of arsenic. In addition, temperatures of at least 1200°C were achieved during the smelting process, with smelting occurring over a relatively short timeframe given that effective density separation of speiss and matte phases was not achieved.

Interplay Between Ni and Brønsted and Lewis Acid Sites in the Hydrodesulfurization of Dibenzothiophene.

Ni-MoS2/γ-Al2O3 catalysts are commonly used in hydrotreating to enhance fossil fuel quality. The extensive research on these catalysts reveals a gap in understanding the role of Ni, often underestimated as an inactive sulfide phase or just a MoS2 promoter. In this work, we focused on analyzing whether well-dispersed supported nickel nanoparticles can be active in the hydrodesulfurization of dibenzothiophene. We dispersed Ni by Strong Electrostatic Adsorption (SEA) method across four supports with different types of acidity: silica (~ neutral acidity), γ-Al2O3 (Lewis acidity), H+-Y zeolite, and microporous-mesoporous H+-Y zeolite (both with Brønsted-Lewis acidity). Our findings reveal that Ni is indeed active in dibenzothiophene hydrodesulfurization, even with alumina and silica as supports, although their catalytic activity declines abruptly in the first hours. Contrastingly, the acid nature of zeolites imparts sustained stability and performance, attributed to robust metal-support interactions. The efficacy of the SEA method and the added mesoporosity in zeolites further amplify catalytic efficiency. Overall, we demonstrate that Ni nanoparticles may perform as a hydrogenating metal in the same manner as noble metals such as Pt and Pd perform in hydrodesulfurization. We discuss some of the probable reasons for such performance and remark on the role of Ni in hydrotreatment.

Compositional alteration of low dimensional nickel sulfides under hydrogen evolution reaction conditions in alkaline media

Developing cost-effective electrodes for electrochemical water splitting with minimal kinetic losses remains a primary challenge in water electrolysis. Nickel-based dichalcogenides, particularly sulfides, have emerged as promising candidates for the hydrogen evolution reaction (HER). However, the stability of various nickel sulfide (NixSy) phases under cathodic potentials in alkaline electrolytes is subject to debate. In this study, we investigate the HER activity and durability of both 2-dimensional (2D) and 3-dimensional (3D) NixSy nanostructures with diverse chemical compositions. Through cross-correlation analysis of spectroscopic and electrochemical characterization data, we elucidate the transformation behavior of these materials under operating conditions. Our findings reveal that NiS2 tends to undergo conversion to nickel hydroxide (Ni(OH)2), while Ni-rich phases like Ni3S4 and NiS exhibit greater stability. Furthermore, we demonstrate that in 3D nanostructures, the initial formation of a protective hydroxide layer on the surface inhibits further sulfide transformation. This nickel sulfide/hydroxide composite shows an improved HER activity with lower onset potential (−0.25 V), Tafel slope (105 mV s−1), and charge transfer resistance (17.3 Ω).