Sulfide Phases Research Articles

Role of Phosphorus and Triethylene Glycol Incorporation on the Activity of Model Alumina‐Supported CoMoS Hydrotreating Catalysts

AbstractEnvironmental regulations concerning fuel‐related sulfur emissions are currently experiencing worldwide expansion. This is motivating the research and development of improved hydrotreating (HDT) catalysts with carefully engineered synthesis methods that maximize activity as ultimate goal. In this contribution, the effect of phosphorus doping and triethylene glycol (TEG) incorporation on the genesis of the CoMoS phase of model HDT catalysts is assessed. Following a surface‐science approach, α‐Al2O3 single crystals with four orientations: C(0001), A(11 0), M(10 0), and R(1 02) are used as model supports of the traditional γ‐Al2O3 support for the study of active phase‐support interactions at the molecular scale. The model catalysts are prepared by traditional impregnation of a solution containing metal and phosphorus precursors and TEG. The catalysts are characterized in the sulfide phase by XPS, XAS, TEM, and AFM, revealing that the calcination step is key in the emergence of distinctive metal‐support interactions, which are directly related to the nature of alumina surface sorption sites. In addition, TEG incorporation on dried catalysts increases metal sulfidation and enhances promotion with respect to non‐additivated systems, especially at mild sulfidation temperatures. The catalytic activity of the model catalysts is tested in a thiophene hydrodesulfurization reaction, revealing the following activity trend with respect to alumina surface orientations: A ≫ M >R , C(0001). This trend is identical to the one observed for non‐phosphorus doped non‐TEG additivated model systems, confirming the predominance of surface effects on the catalytic activity over those exerted by P and TEG. By transposing these results to the industrial γ‐Al2O3 support, the (100) facet would provide surface sites that lead to better performing catalysts. This could result in the development of novel supports, engineered to expose surface sites that maximize hydrotreating activity.

New insights on the Escoural Orogenic gold district (Ossa-Morena Zone, SW Iberia): Geochemistry, fluid inclusions and stable isotope constraints from the Monfurado gold prospect

The Escoural gold district belongs to the Montemor-Ficalho metallogenic belt which is part of the Portuguese section of Ossa-Morena Zone (OMZ), at the SW of Iberia. The Escoural gold district includes twelve gold prospects and/or deposits largely controlled by the NW-SE Montemor-o-Novo Shear Zone (MNSZ) and associated fault zones, extending for approximately 30 km. Ubiquitously, gold-arsenopyrite-loellingite assemblages hosted in quartz-sericite-chlorite veins are found in most deposits, although, in the Monfurado prospect, the gold-bearing assemblages are more complex. This prospect is located in the vicinity of a Cambrian SEDEX-VMS iron deposit, from which massive and disseminated iron-ores hosted in marbles and calcsilicate rocks, were exploited. The interplay of the gold mineralizing processes with the iron-rich host rocks has favored gold deposition at the Monfurado prospect. Selected samples from six drill cores allowed to define two mineralizing events: the pre-ore and ore stages. Two types of gold mineralization characterize the ore-stage: i) massive sulfide horizons in which gold (Au = 85.6–86.3 wt%; Ag = 13.1–13.6 wt%) is hosted in arsenopyrite and pyrite or, seldomly, gold particles (Au = 91.8 wt%; Ag = 7.1 wt%) found in an arsenopyrite-rich layer; and ii) quartz-chlorite-pyrite veins crosscutting acid metavolcanic rocks with rhyolite-rhyodacite affinities, in which gold (Au = 80.5–82.9 wt%; Ag = 16.8–18.7 wt%) is found as fracture filling in pyrite, sometimes accompanied by Bi-Te phases. Arsenopyrite geothermometer suggests that for type i the overall deposition temperature falls within the range of 188 °C to 372 °C. Type ii mineralization lacks arsenopyrite, and for this reason, thermodynamic constraints were gathered from fluid inclusions and chlorite geothermometer. CH4-rich fluid inclusions are ubiquitous in transgranular fluid inclusion planes, suggesting that reduced fluids percolated the rocks that host type ii mineralization. The reduced fluids support the transport of gold in sulfide complexes, such as AuHS- and Au(HS)-2. Furthermore, secondary H2O-NaCl fluid inclusions (Lw2) were found, with mean salinities of 6.0 eq. w(NaCl) and mean homogenization temperature of 226 °C, with corresponding pressures of 3.0 MPa, thus suggesting late hydrostatic regimes. Chlorite geothermometer results are in the range of 229 °C and 309 °C, agreeing with the fluid inclusion homogenization temperatures for Lw2 fluids.Sulfur isotope (δ34S) analysis of representative sulfide phases collected from both mineralization types, revealed signatures ranging from 8.5 ‰ and 10.6 ‰, indicating a single sulfur source. The gathered results suggest that although fluid transport is structurally controlled by MNSZ activity, the sulfidation reactions promoted by fluid-rock interactions are the main control on gold deposition from type i mineralization. It is further suggested that a coeval gold-event can lead to the deposition of two different types of mineralization, related to distinct gold deposition mechanisms.The tectonic and geodynamic settings in which the Escoural gold district developed correlate it to worldwide Palaeozoic orogenic gold deposits, with the Monfurado prospect being an example of the complexity of such geological settings.

Distribution of Te, As, Bi, Sb, and Se in Mid-Ocean Ridge Basalt and Komatiites and in Picrites and Basalts from Large Igneous Provinces: Implications for the Formation of Magmatic Ni-Cu-Platinum Group Element Deposits

Abstract In magmatic nickel-copper-platinum-group element (PGE) deposits, the PGEs are found both in solid solution in base metal sulfides and as platinum group minerals (PGMs). Apart from S, the most common elements that the PGEs combine with to form PGMs are Te, As, Bi, Sb, and Sn (TABS). Whether the TABS play a role in collecting the PGEs or simply partition into the sulfide liquid along with the PGEs and later combine with PGEs when the sulfide phase becomes saturated with PGMs is not currently clear. This is in part because the concentrations of TABS in the magmas (picrites and basalts from large igneous province and komatiites) that form these types of deposits are not well established, and hence it is not evident whether the magmas contain sufficient TABS to control PGEs. In order to establish the concentrations of Te, As, Bi, Sb, and Se (TABS+) in these rock types and to document the processes affecting these concentrations, we have determined TABS+ concentrations in komatiites, in mid-ocean ridge basalt, and in picrites and basalts from large igneous provinces. Using TABS+ mantle-normalized diagrams, the affects of different mantle sources, crystal fractionation, crustal assimilation, degassing, and alteration are considered. We estimate the concentrations of TABS+ in komatiites to be approximately twice primitive mantle values. In picrites the concentrations vary: approximately 10 times primitive mantle values for As and Sb and decreasing through Bi to Te from 7 to 2 times primitive mantle. Assimilation of S-bearing sedimentary rocks is thought to be important in triggering sulfide saturation leading to the formation of Ni-Cu-PGE deposits. Assimilation of such sediments would enrich the magma in Th over Nb and in As, Sb, and Bi. Evidence of assimilation in the form of TABS and Th enrichment is clear in the PGE reef deposits of the Bushveld and Stillwater Complexes, but the deposits do not contain sufficient TABS to control the PGEs. This is also true in the Norilsk-Talnakh Ni-Cu-PGE deposits. However, at Norilsk degassing of the magma has resulted in the loss of TABS, which results in negative As, Bi, Se, and Te anomalies on primitive mantle-normalized plots.

Metals in Avachinsky peridotite xenoliths with implications for redox heterogeneity and metal enrichment in the Kamchatka mantle wedge

Peridotite xenoliths from the Avachinsky volcano in southern Kamchatka contain diverse assemblages of native metals and intermetallic compounds associated with primary olivine and orthopyroxene and metasomatic amphibole. Mineral compositions in Avachinsky xenoliths (Mg-rich olivine and low-Al enstatite associated with Cr-spinel) coupled with common absence of primary clinopyroxene and low bulk Al2O3 and CaO contents, suggest a depleted mantle wedge beneath the southern segment of the Kamchatka volcanic arc.Metallic phases in Avachinsky xenoliths occur as euhedral to anhedral grains in fractures andirregularly shaped voids in Fe-Mg silicates as well as micro-particles localized along boundaries between oivine and orthopyroxene. Siderophile metal assemblage is composed of platinum, iron and gold along with Cr-Fe and W-Fe-Mn alloys. Chalcophile metals include native copper, bismuth, lead and zinc along with Cu-Ag, Cu-Sn, Cu-Sn-Au, Ag-Au, Cu-Ag-Au and Ni-Cu-Ag-Au intermetallic compounds. Metals in Avachinsky xenoliths are associated, both spatially and texturally, with magnetite, rutile, galena, cassiterite, Cu-Ag-bearing Sb-Bi-Pb sulfide phase, AgS and non-stoichiometric Cl-bearing silver compound. Siderophile metals were introduced by primitive metasomatizing melts into low fO2 domains in the mantle wedge below the Kamchatka arc. Phase relations in the Cu-Ag-Au system suggest high-temperature (>900 °C) origin for Cu-Ag-Au intermetallic compounds in Avachinsky xenoliths. While Cu-Ag-Au alloys precipitated from metal-rich, mantle-derived silicate melts, low-melting point chalcophile metals and their minerals (Ag, Bi, Sb, Zn, Pb, Sn) were deposited in the sub-Kamchatkan mantle from hydrous slab fluids under reduced conditions. Metal assemblages in Avachinsky xenoliths further attest to reducing conditions in some subduction systems and potentially indicate existence of extreme redox gradients at sufficiently small scales in sub-arc mantle wedge environments.

A new non-stoichiometric quaternary sulfide Ba3.14(4)Sn0.61(1)Bi2.39(1)S8: Synthesis, crystal structure, physical properties, and electronic structure

We report the syntheses of single crystals and polycrystalline phase of a new quaternary sulfide, Ba3.14(4)Sn0.61(1)Bi2.39(1)S8, by the high-temperature sealed tube method. A single-crystal X-ray diffraction study established that the title compound is non-stoichiometric and crystallizes in the orthorhombic D2h16-Pnma space group with cell parameters of a ​= ​12.4479(7) Å, b ​= ​4.3140(2) Å, c ​= ​28.7860(17) Å, and Z ​= ​4. The crystal structure is composed of infinite chains of ∞1[Sn(1)0.61Bi(1)0.39S3]2.39− and ∞1[Bi(2)Bi(3)S5]4− stripes, which are separated by Ba2+ cations. The optical absorption study of the polycrystalline Ba3.2Sn0.6Bi2.4S8 sample showed a direct bandgap of 1.4(1) eV, indicating the semiconducting nature. The thermal conductivity study showed that polycrystalline Ba3.2Sn0.6Bi2.4S8 has an extremely low thermal conductivity of ∼0.30 ​W/mK at 773 ​K. The first-principles theoretical studies of electronic structure and nature of chemical bonding in Ba3Sn0.62Bi2.38S8 are performed within the framework of DFT.

Method for analyzing HR-TEM micrographs to propose and/or describe structures and their interaction in crystalline materials

A general and versatile method for the analysis and processing of HR–TEM data useful for several applications is presented. The first utility is to identify the structures seen in the micrographs; also can be extended to propose the interaction of structure dynamics between various phases; and also it can be hybridized with the chemical method to make a proposal of new structure and/or phase. The general method consisted of four steps: 1) micrograph pretreatment, 2) measurement of planar distances, 3) structure identification, and 4) structure corroboration. Crystallographic planes were immediately identified by comparing the interplanar distances. Next, crystallographic data were collected from the Crystal Structures Database (ICSD) and introduced into Diamond software to visualize the planes in each structure. In addition, from the zone axis point of view it must show the planes aligned, similar as is observed in the HR–TEM micrograph.•It was possible establish the growth mechanism of the different structures by identifying how is the structural interaction between the different oxides and sulfide phases.•Method was successful applied to propose a new TiCoMoS sulfide phase through HR–TEM results.•The method can also be extended to other areas where structural studies with HR–TEM are viable, such as biology, electronics, among others.

Understanding the isotopic composition of sedimentary sulfide: A multiple sulfur isotope diagenetic model for Aarhus Bay

Measurement of the multiple sulfur isotopes (³²S/³³S/³⁴S) enables the calibration of microbial biosignatures and provides a unique diagnosis of S-based metabolic processes: sulfate reduction, disproportionation, and sulfide oxidation. All three metabolisms carry distinct geochemical consequences for S cycling in modern systems, and are particularly powerful for paleoenvironmental interpretations if their respective contributions can be separated. To hone those interpretations and to further develop a quantitative context for understanding early diagenetic sulfur cycling, we constructed a multiple S isotope reactive transport model for the sediments of a geochemically well-characterized system (Aarhus Bay, Denmark). The model reconciles pore water and solid phase concentration profiles of the major species associated with Fe/S/C cycling, and uses multiple S isotope systematics to predict the isotope profiles of the major S species, including pore water sulfate, free sulfide and solid phase pyrite. We note that very large fractionations associated with sulfate reduction (³⁴ε_sr = 70‰) are required to reproduce the observed pore water profiles, and we reconcile these fractionations with low temperature theoretical predictions for isotope equilibrium fractionation. The minor sulfur isotope values (noted as Δ³³S) of sulfate increase at shallow depths within the Aarhus Bay core, and decrease when sulfate drops below 10 mM. Values (Δ³³S) for sulfide decrease nearly monotonically towards seawater sulfate values near the zone of sulfate depletion. Pyrite Δ³³S values are nearly uniform downcore (0.170 ± 0.010‰) despite a ∼10‰ enrichment in surface versus deep pyrite δ³⁴S values. Sulfate reduction is the most important process controlling S isotope pore water distributions, with modest contributions from oxidative S cycling. Further, microbial sulfate reduction demonstrates large fractionations typically not expected for shallow, organic rich (TOC ∼ 4%) continental margin systems.

Structure and properties of two-phase Cd-=SUB=-x-=/SUB=-Pb-=SUB=-1-x-=/SUB=-S/CdS films obtained by chemical deposition from the ethylenediamine-citrate system

Polycrystalline films of CdxPb1-xS (0≤ x≤0.05) substitutional solid solutions with a cubic structure B1 (Fm3m space group) containing amorphous cadmium sulfide were obtained by chemical bath deposition. Upon reaching a critical concentration of the cadmium salt in the reactor, the films consisted of substitutional solid solution and cubic CdS with the B3 structure (F43m space group). Scanning electron microscopy established the morphological features associated with the secondary nucleation and formation of the cadmium sulfide phase. The structural characteristics of the films have been calculated by a full-profile analysis of X-ray diffraction patterns. We have revealed the correlation between phase and elemental composition of CdxPb1-xS/CdS films with their voltage and current photosensitivity. Based on the received data, we have assumed the role of the individual CdS phase for the photoconductivity mechanism of CdxPb1-xS solid solutions. Keywords: chemical bath deposition, thin films, solid solutions, cadmium sulfide, photosensitivity, current-voltage characteristics.

ВЛИЯНИЕ ПРЕДШЕСТВЕННИКОВ НИКЕЛЯ НА АКТИВНОСТЬ КАТАЛИЗАТОРОВ НА ОСНОВЕ УГЛЕРОД-МИНЕРАЛЬНОГО НОСИТЕЛЯ ИЗ САПРОПЕЛЯ В РЕАКЦИИ ЖИДКОФАЗНОГО ГИДРИРОВАНИЯ НИТРОБЕНЗОЛА

Nickel catalysts on carbon mineral supports obtained from sapropel were synthesized, the influence of the nature of the supports (type of the initial sapropel) and the precursor of the active component on the activity of the catalysts under study in the model reaction of liquid-phase nitrobenzene hydrogenation was studied. It is shown that catalysts based on a mineral support are more active than those based on an organic one, regardless of the nature of the precursor. When comparing the precursors, it was found that the most active catalysts are those obtained using nitrate and nickel formate. The presence of sulfur in the composition of the nickel precursor leads to a decrease in the activity of the catalyst as a result of the formation of the sulfide phase.

An ab-initio study on the thermodynamics of disulfide, sulfide, and bisulfide incorporation into apatite and the development of a more comprehensive temperature, pressure, pH, and composition-dependent model for ionic substitution in minerals

AbstractThe mineral apatite, Ca10(PO4)6(F,OH,Cl)2, incorporates sulfur (S) during crystallization from S-bearing hydrothermal fluids and silicate melts. Our previous studies of natural and experimental apatite demonstrate that the oxidation state of S in apatite varies systematically as a function of oxygen fugacity (fO2). The S oxidation states –1 and –2 were quantitatively identified in apatite crystallized from reduced, S-bearing hydrothermal fluids and silicate melts by using sulfur K-edge X-ray absorption near-edge structure spectroscopy (S-XANES) where S 6+/ΣS in apatite increases from ~0 at FMQ-1 to ~1 at FMQ+2, where FMQ refers to the fayalite-magnetite-quartz fO2 buffer. In this study, we employ quantum-mechanical calculations to investigate the atomistic structure and energetics of S(-I) and S(-II) incorporated into apatite and elucidate incorporation mechanisms.One S(-I) species (disulfide, S22−) and two S(-II) species (bisulfide, HS−, and sulfide, S2−) are investigated as possible forms of reduced S species in apatite. In configuration models for the simulation, these reduced S species are positioned along the c-axis channel, originally occupied by the column anions F, Cl, and OH in the end-member apatites. In the lowest-energy configurations of S-incorporated apatite, disulfide prefers to be positioned halfway between the mirror planes at z = 1/4 and 3/4. In contrast, the energy-optimized bisulfide is located slightly away from the mirror planes by ~0.04 fractional units in the c direction. The energetic stability of these reduced S species as a function of position along the c-axis can be explained by the geometric and electrostatic constraints of the Ca and O planes that constitute the c-axis channel.The thermodynamics of incorporation of disulfide and bisulfide into apatite is evaluated by using solid-state reaction equations where the apatite host and a solid S-bearing source phase (pyrite and Na2S2(s) for disulfide; troilite and Na2S(s) for sulfide) are the reactants, and the S-incorporated apatite and an anion sink phase are the products. The Gibbs free energy (ΔG) is lower for incorporation with Na-bearing phases than with Fe-bearing phases, which is attributed to the higher energetic stability of the iron sulfide minerals as a source phase for S than the sodium sulfide phases. The thermodynamics of incorporation of reduced S is also evaluated by using reaction equations involving dissolved disulfide and sulfide species [HnS(aq)(2−n) and HnS(aq)(2−n); n = 0, 1, and 2] as a source phase. The ΔG of S-incorporation increases for fluorapatite and chlorapatite, and decreases for hydroxylapatite, as these species are protonated (i.e., as n changes from 0 to 2). These thermodynamic results demonstrate that the presence of reduced S in apatite is primarily controlled by the chemistry of magmatic and hydrothermal systems where apatite forms (e.g., an abundance of Fe; solution pH). Ultimately, our methodology developed for evaluating the thermodynamics of S incorporation in apatite as a function of temperature, pH, and composition is highly applicable to predicting the trace and volatile element incorporation in minerals in a variety of geological systems. In addition to solid-solid and solid-liquid equilibria treated here at different temperatures and pH, the methodology can be easily extended to different pressure conditions by just performing the quantum-mechanical calculations at elevated pressures.

Структура и свойства двухфазных слоев Cd-=SUB=-x-=/SUB=-Pb-=SUB=-1-x-=/SUB=-S/CdS, полученных химическим осаждением из этилендиамин-цитратной системы

Polycrystalline films of CdxPb1−xS (0 ≤ x ≤ 0.05) substitutional solid solutions with a cubic structure B1 (Fm3 ̅m space group) containing amorphous cadmium sulfide were obtained by chemical bath deposition. Upon reaching a critical concentration of the cadmium salt in the reactor, the films consisted of substitutional solid solution and cubic CdS with the B3 structure (F43 ̅m space group). Scanning electron microscopy established the morphological features associated with the secondary nucleation and formation of the cadmium sulfide phase. The structural characteristics of the films have been calculated by a full-profile analysis of X-ray diffraction patterns. We have revealed the correlation between phase and elemental composition of CdxPb1−xS/CdS films with their voltage and current photosensitivity. Based on the received data, we have assumed the role of the individual CdS phase for the photoconductivity mechanism of CdxPb1−xS solid solutions.

Geochemical and geochronological constraints on the gold-sulfide mineralization and host granitoid rocks in the Bulghah and Al-Maham prospects, central Arabian Shield, Saudi Arabia

Among several gold-sulfide deposits and prospects scattered in the Afif terrane of the Arabian Shield, the Bulghah and Al-Maham prospects are investigated to assess the spatial and temporal relationships between gold mineralization and the host lithologies and regional structures. Both prospects are hosted by the sulfide-bearing Hulayfah Group metavolcano-sedimentary successions, and are confined to cross-cutting granitoid intrusions. Tonalite-granodiorite and monzogranite from the two areas have geochemical characteristics of metaluminous to weakly peraluminous calc-alkaline I-type granitoids. Younger alkali feldspar granite in the Bulghah area exhibits geochemical features of A-type granite, likely formed in a post-collisional or transitional setting. ID-TIMS dating of zircons from two granodiorite samples from the Al-Maham prospect yielded 206Pb/238U ages of ∼662 and 651 Ma. A tonalite sample from the Bulghah mine area gave a concordia age of 674.8 ± 0.8 Ma (2σ; MSWD = 0.42), whereas the alkali feldspar granite sample has an age of ∼ 631 ± 1 Ma. The newly defined ages can be considered as the upper age limit of the auriferous quartz veins, evidently attendant to the Nabitah orogeny (∼680–640 Ma). Gold-bearing quartz veins in the two prospects are identical in terms of ore mineralogy, textures and paragenesis. Gold-bearing quartz veins are associated with intersecting veinlets and stockwork of arsenopyrite, pyrite, and less common pyrrhotite, chalcopyrite, and sphalerite. Recrystallized pyrite and arsenopyrite are ubiquitous in quartz veins, whereas pyrrhotite-chalcopyrite intergrowths in-fills or replacements prevail in the deformed host metavolcanic rocks. Free gold typically occurs as fine inclusions in quartz veins, commonly in deformed pyrite and arsenopyrite crystals. The sulfides of Al-Maham prospect have significantly higher Re-Os concentrations (ppb level), compared with those in the Bulghah prospect, and define an isochron with a Model-1 age of 360 ± 2 Ma and an initial 187Os/188Os ratio of 1.962 ± 0.032. The obtained Re-Os age and the crustal initial Os isotope ratio do not necessarily define the primary age of gold mineralization since ore textures indicate that pyrrhotite was a paragenetically late sulfide phase in both prospects. Alternatively, this age may be interpreted as the time of remobilization and recrystallization of older sulfides in response to Hercynian uplift and deformation (370–290 Ma), manifested as intermittently rejuvenated reverse faults elsewhere in the Arabian Shield.

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

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

A critical comparison between the Fungurume 8 and 88 Cu-Co deposits, Central African Copperbelt

The Fungurume 88 deposit located in the Tenke-Fungurume Mining (TFM) district is situated in the northern extent of the Central African Copperbelt (CACB). It is an unusual sedimentary stratiform copper (SSC) deposit of this area, since it contains high-grade hypogene carrollite mineralization in the SD-1b subunit of the lower Shales Dolomitique (SD) Formation of the Mines Subgroup. These lithologies are normally regarded as being barren to poorly mineralized, here however, they boast cobalt concentrations as high as 3 wt% along with Cu concentrations in excess of 4 wt%. Detailed logging of drill core revealed that the sediments of the Fungurume 88 deposit which host the anomalous SD-1b mineralisation differ in both grainsize and mineralogy to the well-recognised Long Facies sediments exhibited by the majority of deposits in the TFM district - including the overlying Fungurume 8 deposit. Petrographic studies have revealed several distinct sulphide textures including the dominant disseminated style, stratiform style, bedding parallel jack veins and crosscutting veins. These sulphides also exhibit distinct trace element compositions suggesting several episodes of mineralization and support a multiphase hypogene Cu-Co model. The specific timings of the mineralisation events are constrained to an early phase (probably contemporaneous with diagenesis and early lithification) as well as a later phase associated with quartz-carbonate-sulphide veining and possibly linked to the regional brecciation event, and thus, in support of existing literature, indicate the presence of at least two mineralizing fluids. Host rock geochemistry obtained from SEM analyses together with LA-ICP-MS analyses on sulphide phases have helped to constrain the mineralizing process in the Fungurume 88 deposit by corroborating fluid-rock interaction, sulphide mineral paragenesis and trace element variation. Drill core assay data has also revealed prominent zonation and segregation between Cu and Co and the latter’s local enrichment observed in the SD-1b subunit. Metal zonation of this kind has also been described in some deposits of the Zambian copperbelt and are therefore used as a proxy here. The detailed petrographic analyses on the host rock shows that the sediments of the Fungurume 88 deposit potentially belong to the Kalumbwe, Menda or a geochemically similar deep marine sedimentary facies rather than the usual Long Facies. This lithological variation was likely the key ingredient, providing an optimal reducing environment or “trap site” for the precipitation of carrollite and other copper sulphides in the SD-1b subunit. These geological and geochemical observations provide insights into the genesis for the Fungurume 88 deposit, understood in a context of the regional geology and Cu-Co mineralisation throughout the greater Copperbelt. Moreover, it highlights that the northern apex of the Lufilian arc and the broader CACB hold vast exploration potential for similar deeper-water sub-basins which may host significant, and yet-undiscovered metal (notably Co) resources.

In situ arsenic immobilisation for coastal aquifers using stimulated iron cycling: Lab-based viability assessment

Arsenic (As) is one of the most harmful and widespread groundwater contaminants globally. Besides the occurrence of geogenic As pollution, there is also a large number of sites that have been polluted by anthropogenic activities, with many of those requiring active remediation to reduce their environmental impact. Cost-effective remedial strategies are however still sorely needed. At the laboratory-scale in situ formation of magnetite through the joint addition of nitrate and Fe(II) has shown to be a promising new technique. However, its applicability under a wider range of environmental conditions still needs to be assessed. Here we use sediment and groundwater from a severely polluted coastal aquifer and explore the efficiency of nitrate-Fe(II) treatments in mitigating dissolved As concentrations. In selected experiments >99% of dissolved As was removed, compared to unamended controls, and maintained upon addition of lactate, a labile organic carbon source. Pre- and post-experimental characterisation of iron (Fe) mineral phases suggested a >90% loss of amorphous Fe oxides in favour of increased crystalline, recalcitrant oxide and sulfide phases. Magnetite formation did not occur via the nitrate-dependent oxidation of the amended Fe(II) as originally expected. Instead, magnetite is thought to have formed by the Fe(II)-catalysed transformation of pre-existing amorphous and crystalline Fe oxides. The extent of amorphous and crystalline Fe oxide transformation was then limited by the exhaustion of dissolved Fe(II). Elevated phosphate concentrations lowered the treatment efficacy, indicating joint removal of phosphate is necessary for maximum impact. The remedial efficiency was not impacted by varying salinities, thus rendering the tested approach a viable remediation method for coastal aquifers.

Evolution of Chemical Composition and Modeling of Growth Nonmetallic Inclusions in Steel Containing Yttrium.

The programs WYK_Stal and Bi-Growth, developed at AGH-UST, Kraków, Poland, were used for simulating the refining process, the formation of non-metallic inclusions, and their growth. The Fe-Y-Al-O-S-Ca system in pre-oxidized steel was analyzed, where yttrium formed precipitates from both O and S. When first Al and second Y were added to steel, the proportion of Al2O3 inclusions remained constant. This resulted in higher yttrium losses for oxide formation, whereas the sulfur content promoted sulfide phase formation. The introduction of yttrium at the end of refining contributed to reducing the consumption of this element in the non-metallic phase formation. The addition of aluminum and then calcium were sufficient to achieve a high degree of deoxidation and desulfurization. Calculations performed with WYK_Stal for both (a) and (c) versions of the model showed that the sulfide phase was constituted by CaS and FeS (model c) and CaS (model (a)). The participation of the calcium sulfide phase turned out to be dominant in the inclusions. Their presence was also identified in the slag phase. Simulations of the growth of complex oxide and oxo-sulfide inclusions using the Bi_Growth program showed that the yttrium content of the steel has a decisive role in the formation of complex oxide inclusions and the final oxygen content of the steel. In contrast, for the growth of oxide-sulfide inclusions, the character of growth is determined by the sulfur content of steel.

Temperature-Sensitive Localized Surface Plasmon Resonance of α-NiS Nanoparticles.

The presented work shows a synthesis route to obtain nanoparticles of the hexagonal α-NiS phase and core–shell particles where the same material is grown onto previously prepared Au seeds. In the bulk, this nickel sulfide phase is known to exhibit a metal–insulator type phase transition (MIT) at 265 K which drastically alters its electrical conductivity. Since the produced nanoparticles show a localized surface plasmon resonance (LSPR) in the visible range of the electromagnetic spectrum, the development of their optical properties depending on the temperature is investigated. This is the first time an LSPR of colloidal nanoparticles is monitored regarding such a transition. The results of UV–vis absorbance measurements show that the LSPR of the particles can be strongly and reversibly tuned by varying the temperature. It can be switched off by cooling the nanoparticles and switched on again by reheating them above the transition temperature. Additional to the phase transition, the temperature-dependent magnetic susceptibility of α-NiS and Au-NiS nanoparticles suggests the presence of different amounts of uncompensated magnetic moments in these compounds that possibly affect the optical properties and may cause the observed quantitative differences in the LSPR response of these materials.

Microscopic analysis for the oxidation of sulphide-bearing aggregate.

Mortar samples were prepared with sulphide-bearing aggregates and tested for the potential of aggregate oxidation followed by sulphate attack. Scanning Electron Microscopy and its associated Energy Dispersive X-Ray analysis were used to analyze the developed phases in the tested samples to confirm that the obtained expansion is attributable to sulphate attack. The Energy Dispersive X-Ray analysis helped identify sulphide phases in aggregates and evidence of sulphate attack in mortars. Ettringite was detected and confirmed in the mortars with sulphide-bearing aggregates suggesting that the test conditions are suitable for reproducing the damaging mechanism of sulphide oxidation.

On the contribution of the cobalt sulfide phase to the global activity of industrial-type CoMo/Al2O3 catalysts in the HDS of DBT

To analyze if the HDS activity is the result of contributions of both CoMoS and cobalt sulfides phases, a series of CoMo/Al2O3 catalysts with increasing Co/(Co+Mo) ratios (r = 0.1, 0.2, 0.3 and 0.4) prepared by simultaneous impregnation, and composites formed with the CoMo/Al2O3 catalysts and Co/Al2O3, were tested in the hydrodesulfurization of dibenzothiophene. The catalysts were characterized by UV–Visible–NIR and infrared of adsorbed CO spectroscopies. The results showed that the amount of CoMoS adsorbing sites remains basically the same in the series of promoted catalysts, while an increase of the precursor of cobalt sulfide is observed. The activity experiments showed that the addition of Co/Al2O3 to Mo/Al2O3 or CoMo/Al2O3 catalysts promotes both the MoS2 and CoMoS phases, and that the rate constants of CoMo/Al2O3 r = 0.2 and CoMo/Al2O3 r = 0.3 can be closely reproduced with composites of CoMo/Al2O3 r = 0.1 with different amounts of Co/Al2O3, indicating that the increased activity in the series of Co-promoted catalysts is related to the presence of cobalt sulfide. It was evidenced that Co-promoted catalysts are complex systems in which several surface species contribute to the global hydrodesulfurization activity and that cobalt sulfide, far from being a spectator in HDS catalysis, has in fact a secondary but significant role in the global performance of industrial-type CoMo/Al2O3 hydrodesulfurization catalysts. All these contributions must be optimized to obtain highly active and selective hydrodesulfurization catalysts.

Li4.3AlS3.3Cl0.7: A Sulfide-Chloride Lithium Ion Conductor with Highly Disordered Structure and Increased Conductivity.

Mixed anion materials and anion doping are very promising strategies to improve solid-state electrolyte properties by enabling an optimized balance between good electrochemical stability and high ionic conductivity. In this work, we present the discovery of a novel lithium aluminum sulfide–chloride phase, obtained by substitution of chloride for sulfur in Li3AlS3 and Li5AlS4 materials. The structure is strongly affected by the presence of chloride anions on the sulfur site, as the substitution was shown to be directly responsible for the stabilization of a higher symmetry phase presenting a large degree of cationic site disorder, as well as disordered octahedral lithium vacancies. The effect of disorder on the lithium conductivity properties was assessed by a combined experimental–theoretical approach. In particular, the conductivity is increased by a factor 103 compared to the pure sulfide phase. Although it remains moderate (10–6 S·cm–1), ab initio molecular dynamics and maximum entropy (applied to neutron diffraction data) methods show that disorder leads to a 3D diffusion pathway, where Li atoms move thanks to a concerted mechanism. An understanding of the structure–property relationships is developed to determine the limiting factor governing lithium ion conductivity. This analysis, added to the strong step forward obtained in the determination of the dimensionality of diffusion, paves the way for accessing even higher conductivity in materials comprising an hcp anion arrangement.