Sulfide Phases Research Articles

GO nanosheets decorated with SnS nanoparticles: excellent photocatalytic performance under visible-light irradiation.

In this study, pristine SnS and SnS/reduced graphene oxide nanostructures were synthesized using a simple and cheap co-precipitation method. To investigate the effect of graphene oxide concentration on the structural and optical properties and photocatalytic activity, SnS/graphene oxide nanocomposites were prepared with different concentrations of graphene oxide (5, 15, and 25 wt%). The synthesized nanostructures were analyzed using X-ray diffraction, FESEM, Raman spectroscopy, UV-Vis spectroscopy, photoluminescence techniques, and electrochemical impedance spectroscopy. The results of the XRD analysis confirmed the orthorhombic phase of tin sulfide for all nanostructures. The absence of a peak at 2θ = 10.21° for SnS/graphene oxide nanocomposites indicated that during the synthesis process, graphene oxide turns into reduced graphene oxide. The FESEM analysis results showed that surface cracking occurs for SnS/graphene oxide nanocomposites compared to pure graphene oxide sheets. This cracking of reduced graphene oxide sheets can act as sites for the growth of SnS nuclei on rGO. However, the presence of such nucleus sites for the growth of nanoparticles is an important factor in improving the photocatalytic efficiency of nanocomposites. The results of the Raman analysis of the nanocomposites show the highest reduction of oxygen for the SnS/rGO nanocomposite with 15 wt% concentration of graphene oxide, and this improves the conductivity and increases the separation of charge carriers. These results are confirmed by electrochemical impedance analysis with the longest lifetime (430 ns) and photoluminescence analysis with the least recombination of charge carriers for this nanocomposite. Therefore, the results of the research on the photocatalytic activity of the synthesized nanostructures for the decomposition of methylene blue under visible light irradiation show that the SnS/rGO nanocomposite has a higher efficiency than pristine SnS, and the optimal concentration of graphene oxide in the nanocomposites synthesized for 150 minutes to obtain the highest photocatalytic efficiency (more than 90%) was 15 wt%.

Tailoring the phase composition of carbon-coated nickel sulfides to achieve a high specific capacitance.

As significant transition metal sulfides, nickel sulfides integrated with carbon were successfully synthesized in the presence of polyethylenimine and glutaraldehyde with a solvothermal route at 180 °C followed by carbonization. Glutaraldehyde prevented complete sulfur loss and allowed the formation of a mixed phase of nickel sulfide. The electrochemical performances of pure NiS2, NiS@C0, NiS2/NiS@C1, and NiS2/NiS@C2 electrodes were tested by a series of measurements. The specific capacitances obtained from GCD analysis were 698, 1160, 1484, and 908 F g-1 at 1 A g-1 for NiS2, NiS@C0, NiS2/NiS@C1, and NiS2/NiS@C2 electrodes, respectively. The results implied that the NiS2/NiS@C1 electrode possessed the highest specific capacitances and this study can be a good reference for the preparation of other hybrid metal sulfides as pseudocapacitive electrode materials.

Crystal lattice defects in nanocrystalline metacinnabar in contaminated streambank soils suggest a role for biogenic sulfides in the formation of mercury sulfide phases.

At mercury (Hg)-contaminated sites, streambank erosion can act as a main mobilizer of Hg into nearby waterbodies. Once deposited into the waters, mercury from these soils can be transformed to MeHg by microorganisms. It is therefore important to understand the solid-phase speciation of Hg in streambanks as differences in Hg speciation will have implications for Hg transport and bioavailability. In this study, we characterized Hg solid phases in Hg-contaminated soils (100-1100 mg per kg Hg) collected from the incised bank of the East Fork Poplar Creek (EFPC) in Oak Ridge, TN (USA). The analysis of the soil samples by scanning electron microscopy-energy dispersive spectroscopy indicated numerous microenvironments where Hg and sulfur (S) are co-located. According to bulk soil analyses by extended X-ray absorption fine structure spectroscopy (EXAFS), the near-neighbor Hg molecular coordination in the soils closely resembled freshly precipitated Hg sulfide (metacinnabar, HgS); however, EXAFS fits indicated the Hg in the HgS structure was undercoordinated with respect to crystalline metacinnabar. This undercoordination of Hg-S observed by spectroscopy is consistent with transmission electron microspy images showing the presence of nanocrystallites with structural defects (twinning, stacking faults, dislocations) in individual HgS-bearing particles. Although the soils were collected from exposed parts of the stream bank (i.e., open to the atmosphere), the presence of reduced forms of S and sulfate-reducing microbes suggests that biogenic sulfides promote the formation of HgS nanoparticles in these soils. Altogether, these data demonstrate the predominance of nanoparticulate HgS with crystal lattice defects in the bank soils of an industrially impacted stream. Efforts to predict the mobilization and bioavailability of Hg associated with nano-HgS forms should consider the impact of nanocrystalline lattice defects on particle surface reactivity, including Hg dissolution rates and bioavailability on Hg fate and transformations.

UiO-66(-NH2) crystal-decorated Cu7S4 snowflake-like nanoarchitectures with synergistic charge migration for enhanced photocatalytic H2 evolution and N2 fixation

The fabrication of template-free dendritic copper sulphide phase-coupled metal–organic framework (MOF) heterostructures is an innovative approach for boosting light harvesting property and efficacy towards the photoreduction of atmospheric molecules.

Nickel Catalysts on Carbon-Mineral Sapropel-Based Supports for Liquid-Phase Hydrogenation of Nitrobenzene

Nickel catalysts with carbon-mineral supports derived from sapropel were synthesized; the effect exerted by the nature of the support (type of the initial sapropel) and active component precursor on the activity of the catalysts in the model reaction of liquid-phase nitrobenzene hydrogenation was studied. The catalysts, synthesized using the support with a smaller fraction of carbon, were more active irrespective of the precursor nature. The highest activity was observed for the catalysts synthesized from nickel nitrate and formate; nitrobenzene conversion was 65% and 51%, respectively, after 1 h of reaction. The catalysts retained high activity after six reaction cycles at 100% aniline selectivity. The presence of sulfur in the nickel precursor deteriorated the catalytic activity (convection less than 3%) due to formation of the sulfide phase.

Sedimentary cycling of zinc and nickel and their isotopes on an upwelling margin: Implications for oceanic budgets and paleoenvironment proxies

Zinc and Ni are essential micronutrients whose stable isotope systematics in marine sediments represent promising, but still developing, tracers of past ocean chemistry and biology. Sediments from upwelling continental margins have been identified as important sinks for Zn and Ni, driven by high productivity, incorporation of the metals into cells and organic carbon burial. At present, however, our understanding of how Zn and Ni isotope composition of upwelling sediments reflects specific processes in the water column is incomplete. Here, we present coupled Zn and Ni abundance and isotope data for both solid phase and porewater in a series of sediment cores collected on a shelf-to-slope transect across an oxygen minimum zone (OMZ) from the southwest African margin off Namibia.Zinc/Al and Ni/Al ratios in Namibian margin sediments are elevated relative to the lithogenic background, by factors of 1.4–2.4 and 1.7–5.7, respectively. Systematic relationships between solid phase Zn and Ni concentrations and organic carbon accumulation corroborate the view that authigenic Zn and Ni are mainly delivered to these sediments via export production from the photic zone. Corrections for detrital Ni are sometimes substantial, but authigenic δ60Ni values are within uncertainty of the modern deep ocean, at 1.38 ± 0.18 ‰ (mean and 1SD, n = 42). Authigenic δ66Zn is more variable, at −0.09 to 0.50 ‰, at or below the value for the deep ocean average. This latter observation can be attributed to Zn isotope fractionation during sequestration into authigenic ZnS phases in the sediments, either quantitatively, or partially.Porewater systematics are more complex and the profiles do not necessarily reflect the redox state of the sediment-porewater system at the time of sampling, but rather characteristics inherited from more reducing conditions in a temporally heterogeneous system. Porewater zinc concentrations (30–369 nM) are much higher than the deep ocean and increase with depth beneath the sediment–water interface. Despite this prominent increase in Zn concentrations, δ66Zn is rather constant and lighter than the deep ocean average, at 0.18 ± 0.06 ‰ (mean and 1SD, n = 33). These observations are most consistent with the buffering of the small porewater pool by the dissolution of a previously formed sulfide phase. Porewater Ni concentrations are closer to the deep ocean, mostly at 5–15 nM. The lightest porewater isotope compositions (δ60Ni as low as 0.15 ‰) are consistent with a Mn-oxide source of Ni, whereas the heaviest isotope compositions (up to 1.76 ‰) clearly reflect uptake of light Ni into sulfide at depth within the sediment.Our data, for the largest upwelling site in the modern ocean, add to sparse data from the eastern Pacific, and confirm that upwelling margin sediments bury Ni that is close to the deep ocean in isotope composition, but Zn that is generally lighter. The data thus confirm the importance of such margins in setting the heavy isotope composition of oceanic Zn. Sediments from this kind of setting hold significant potential for the construction of records of past oceanic Ni isotopes.

Biogeochemical Permeable Barrier Based on Zeolite and Expanded Clay for Immobilization of Metals in Groundwater

Groundwater samples contaminated with potentially toxic elements (PTE), including metals and nitrate ions, were collected at a depth of 8–10 m from the Siberian Chemical Plant multicomponent waste storage. The possibility of developing a permeable biogeochemical barrier with zeolite and lightweight expanded clay aggregate (LECA) was investigated. The mass fraction and properties of several metals (Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg and Pb) were determined to investigate their fixation on the chosen materials at the given experimental conditions. It was established that metals in sulfide or phosphate forms can be effectively immobilized via biomineralization on LECA, whereas metals from the non-chalcogen group are primarily retained in the form of phosphates. The formation of biogenic deposits of iron sulfide, which serve as a sorption–precipitation phase during the immobilization of the majority of metals, is an important aspect of the LECA loading process. The use of LECA and zeolite in the form of a two-component barrier is feasible based on the data obtained. It is assumed that metal immobilization processes occur due to sorption mechanisms in the zone of zeolite loading. Microbial nitrate removal and the formation of iron sulfide phases under reducing conditions, which form a geochemical barrier for metals, are expected in the LECA zone.

Geochemical controls on mobilization of metals from a 100-year-old waste rock pile and implications for selection of cover amendments

Reclamation of mine waste rock piles typically consists of constructing a cover with amendments to improve conditions for vegetation. However, cover amendments have potential to mobilize metals in waste by introducing new chemicals and altering pH and redox conditions. This study evaluates metal phases in a 100-year-old waste rock pile with high metals content (3.5% lead by weight, 0.8% zinc, and 0.75% copper) and the potential for these metals to be mobilized by several cover materials and amendments (topsoil, spent brewery grain, biochar, compost, commercial soil media, and phosphate). Laboratory testing indicates that metals have weathered from their initial metal sulfide phases (galena, sphalerite, chalcopyrite), and are now also present as sulfates, phosphates, carbonates, and phases associated with manganese/iron oxides. Sequential extraction tests demonstrated that the largest extractable fraction of metals is associated with manganese/iron oxides (37% of lead by weight, 22% of copper, and 26% of zinc), suggesting an environmental risk should geochemically reducing conditions develop and mobilize metals in the pile after cover construction. Testing of specific cover materials demonstrated that metals mobilization also occurs from low pH (as with spent brewery grain), formation of stable aqueous metal–organic complexes (as with spent brewery grain and compost), and ligand exchange (as with phosphate amendment). Results of this study demonstrate the importance of identifying metal phases present in a waste rock pile prior to selecting cover amendments.

On Stability of High-Surface-Area Al2O3, TiO2, SiO2-Al2O3, and Activated Carbon Supports during Preparation of NiMo Sulfide Catalysts for Parallel Deoxygenation of Octanoic Acid and Hydrodesulfurization of 1-Benzothiophene

NiMo sulfide catalysts were prepared by the impregnation of high surface area supports with an aqueous solution made of NiCO3·2Ni(OH)2, MoO3 and citric acid, followed by freeze drying and sulfidation in H2S/H2 mixture. N2 physisorption and X-ray diffraction were selected to investigate the amphoteric oxides Al2O3 and TiO2, acidic SiO2-Al2O3 and activated carbon supports, fresh prepared sulfide NiMo catalysts and spent catalysts after model parallel reaction of octanoic acid deoxygenation and 1-benzothiophene hydrodesulfurization. The studied mesoporous amphoteric oxides Al2O3 and TiO2 did not lead to highly active NiMo catalysts due to the low hydrothermal stability of these supports during the preparation of the active sulfide phase and deoxygenation reaction. The most active catalyst based on oxidic support was the NiMo sulfide supported on acidic mesoporous SiO2-Al2O3, which was explained by the increased stability of this support to the water and CO/CO2 mixture during the activation of the sulfidic phase and deoxygenation reaction. The extraordinarily high stability of the activated carbon support led to outstanding activities of the sulfidic NiMo/C catalyst.

Microwave induced rapid surface amorphization of metal oxide nanowire into sulfides shell for electronically modulated efficient hydrogen evolution catalyst

Order/dis-order atomic arrangements in crystalline/amorphous structure possess a complementing effect in electro-catalysis as the former one can offer a long-range electronic conducting path, whereas the latter is rich with active sites. However, atomic level interfacing of crystalline and amorphous structures is extremely challenging and thus often end-up with uncontrolled secondary deposition one above another. Here, we are reporting second-scale atomic rearrangement of crystalline oxide nanowire surface into amorphous molybdenum sulfide shell that displayed excellent hydrogen evolution activity. Employing transient heating by microwave-activated graphene filament, surface atoms of molybdenum tungsten oxide (MoWO) nanowire can be arrested in either an amorphous or crystalline state during their sulfidation. Such a nanowire structure consisting of crystalline oxide core-amorphous sulfide shell shows excellent catalytic activity for hydrogen evolution reaction (HER) and exhibits an overpotential of 136 mV at 10 mA cm−2 in the acid electrolyte, which is much lower than the overpotential of parent oxide nanowire (356 mV) and its fully sulfurized crystalline counterpart (163 mV). As-developed catalyst also shows competitive HER performance with excellent alkaline and neutral electrolytes stability, thereby qualifying it as a pH universal catalyst. A detailed density functional theory calculation reveals oxide core promoted activation of multiple sites of amorphous sulfide phase, which provide key insights of electronic modulation via crystalline/amorphous interfacial structure for HER catalysis. This rapid and highly facile technique can lay the platform for the development of generic crystalline/amorphous core-shell nanostructure and their possible use as cost-effective and efficient catalysts.

Tin Removal from Tin-Bearing Iron Concentrate with a Roasting in an Atmosphere of SO2 and CO

The tin could be volatilized and removed effectively from the tin-bearing iron concentrate while roasted in an atmosphere of SO2 and CO. The reduction of SO2 by CO occurred in preference to the SnO2 and Fe3O4, and the generated S2 could sulfurize the SnO2 to an evaporable SnS, which resulted in the tin volatilization. However, the Fe3O4 could be sulfurized simultaneously, and a phase of iron sulfide was formed, retaining in the roasted iron concentrate. It decreased the quality of the iron concentrate. In addition, the formation of Sn-Fe alloy was accelerated as the roasting temperature exceeded 1100 °C, which decreased the Sn removal ratio. An appropriate SO2 partial pressure and roasting temperature should be controlled. Under the condition of the roasting temperature of 1050 °C, SO2 partial pressure of 0.003, CO partial pressure of 0.85, and residence time of 60 min, the tin content in the roasted iron concentrate was decreased to 0.032 wt.% and the sulfur residual content was only 0.062 wt.%, which meets the standard of iron concentrate for BF ironmaking.

Organic molecule functionalized lead sulfide hybrid system for energy storage and field dependent polarization performances

A wet chemical route is reported for synthesising organic molecule stabilized lead sulfide nanoparticles. The dielectric capacitance, energy storage performances and field-driven polarization of the organic–inorganic hybrid system are investigated in the form of a device under varying temperature and frequency conditions. The structural analysis confirmed the formation of the monoclinic phase of lead sulfide within the organic network. The band structure of lead sulfide was obtained by density functional theory calculation that supported the semiconductor nature of the material with a direct band gap of 2.27 eV. The dielectric performance of the lead sulfide originated due to the dipolar and the space charge polarization. The energy storage ability of the material was investigated under DC-bias conditions, and the device exhibited the power density values 30 W/g and 340 W/g at 100 Hz and 10 kHz, respectively. The electric field-induced polarization study exhibited a fatigue-free behaviour of the device for 103 cycles with a stable dielectric strength. The study revealed that the lead sulfide-based system has potential in energy storage applications.

Early Au-rich sulfide liquid saturation explains the low Au endowment of continental intraplate alkaline magmas

Abstract Alkaline magmatic systems formed in intraplate settings have a low Au endowment, contrasting with the high Au fertility of alkaline magmatic systems in arc and rift settings, which host numerous Au-rich porphyries and Cu-Au and Au-Ag epithermal deposits. Among other factors, the Au fertility of a magmatic system is determined by the Au concentration of the ore-forming magma, which is strongly controlled by the amount and chemistry of magmatic sulfides that fractionated during magma differentiation. To better explore the factors controlling the low Au endowment of alkaline magmatic systems formed in intraplate settings, we studied magmatic sulfide and silicate melt inclusions hosted in various phenocrysts from the Mont-Dore Massif (France). The magmatic system was saturated with Cu-poor, Au-rich sulfide liquid during its differentiation from basanite to trachyandesite, leading to a strong depletion of both Cu and Au in the residual melt. This presumably reduced the capacity of the magmatic system to form Au-rich magmatic-hydrothermal deposits. Such evolution contrasts with previous studies conducted in sulfide-saturated magmatic systems formed in arc settings, where an Au-poor monosulfide solid solution was the main sulfide phase to crystallize, only marginally affecting the Au budget of those systems. We conclude that the observed saturation of Au-rich sulfide liquid during evolution of the studied volcanic products could explain the low Au endowment of intraplate alkaline magmatic systems.

Features of the presence of precious metals in the zinc production clinker

The paper considers the features of gold deportments in technogenic raw materials – aged clinker of zinc production at the Belovsky zinc plant (Belovo, Kemerovo Region). The Belovsky plant operated from 1930 to 2003 using zinc concentrates from the Salairsky ore mining and processing plant. After the plant shutdown, clinker dumps were stored at the plant’s mill site and were repeatedly washed with acidic solutions to isolate copper. This form of storage and leaching led to the transformation of precious metal deportments in clinker, which currently makes it difficult to extract gold. The gold content in clinker is at the level of 2–3 g/t, which makes gold recovery profitable. The presence of carbon in clinker complicates the use of known methods of both analytical detection of gold and its recovery. A method is proposed for determining the deportment and content of gold taking into account the fact that gold may be present in the form of free fine gold, as well as gold finely disseminated in iron and its oxides, in sulfide phases, in the quartz-silicate part of clinker and in the carbonaceous phase. It was shown that gold deportments in clinker change depending on the storage conditions and preceding acid treatment, and this affects the choice of the material processing flow chart. The share of gold available for leaching is at least 40 %. The increased associativity of gold with the coal (flotation-active) phase and the sorption activity of coal significantly interfere with the study into the properties of gold deportments in clinker, which requires preliminary carbon removal.

Black shales and mesozonal quartz vein‐hosted Au: The Truchas Syncline, Spain and the Harlech Dome, Wales, a comparative study

A comparative study of quartz vein‐hosted gold occurrences associated with Palaeozoic metapelites in two areas of Wales and Spain combines new, previously unpublished and published data. Metamorphic grade is greenschist in both areas, but very low‐grade indicators in the host metapelites distance the environment from the greenschist/amphibolite transition zone required for some orogenic gold occurrences. Basin fertility for Au is indicated by the presence of auriferous pyrites in the protolith black shales in Spain. Only minor igneous activity has taken place in both study areas. Mineral parageneses are similar, with early sulphide phases characterized by As/Co and later auriferous phases by Cu/Pb/Zn sulphides. Mesozonal P–T conditions apply at deposition in both terranes. In Spain, mineralisation typically occurs in quartzites near to the metapelites, but not where the veins are in contact with them, and extensional faulting appears to be a stronger control over mineralisation than geochemical interaction with metapelite wall‐rocks. In Wales, both structural and geochemical factors (C content of the wall‐rocks and coupled oxidation of NH4 ions substituted in wall‐rock phyllosilicates to produce CH4 and N2) could have a role in Au deposition. In both areas, minor cross‐fault systems between larger faults are typical hosts of the mineralisation. Assignment is made to different subtypes of the orogenic gold model but these subtypes share the characteristic of a local source. This has implications for exploration methodology in epizonal/anchizonal metapelite‐dominated terranes, where indicators of basin fertility for Au within the protolith itself assume importance.

Cable bacteria activity and impacts in Fe and Mn depleted carbonate sediments

The metabolic activities of cable bacteria enable the oxidation of sulfide to sulfate in anoxic sediment at depth through long distance electron transport coupled to the reductions of O2 and NO3−/NO2− in surface sediment. The spatial separation of oxidation and reduction half reactions requires modification of diagenetic models that assume electron donors and acceptors are coupled with each other locally within sedimentary deposits. In this study, we show that cable bacteria can become established and remain metabolically active in sulfidic, but Fe, Mn, and solid phase sulfide-depleted, carbonate muds from Florida Bay, USA. Sediment surface pH maxima reflecting electrogenic metabolism developed between 1 and 3 weeks in sediment incubated in laboratory microcosms with oxic overlying water. Cable filament cell abundances varied over time, with the increase initially focused within the subsurface, but by the end of experiments, cell abundances increased both in subsurface and oxic surface sediment. The development of cable bacteria activity in carbonate muds demonstrates that long-distance electron transport metabolism can utilize subsurface dissolved sulfide (e.g., H2S) as a sole reductant source for sustained periods without transition to Fe-sulfide and apparently without formation of an intermediate suboxic region associated with Fe and Mn cycling. H2S consumption occurs initially within the O2-NO3− rich oxic – suboxic zone and transitions to a dominant, but not exclusive, subsurface cable bacteria anodic zone. Once established, cable bacteria significantly altered sediment carbonate cycling. Thermodynamic calculations demonstrated that aragonite and hi-Mg-calcites were supersaturated (Ω ∼2.0–3.2) in the surface sediment layer (< 0.25 cm depth) and were undersaturated (Ω ∼ 0.2) in the anodic zone (1–2 cm depth). Hi-Mg-calcites and aragonite likely precipitated in the surface sediment and dissolved in the anodic region, the dissolution confirmed by elevated porewater Ca2+, Mg2+ concentrations. P cycling was coupled to remineralization of organic matter, carbonate mineral cycling, and apparently intracellular accumulation of polyphosphates. Thus, cable bacteria may play an important role in the acquisition of P by seagrasses in carbonate deposits where P is otherwise limited by irreversible adsorption and authigenic mineral precipitation.

High-pressure phase relations in the system Fe–Ni–Cu–S up to 14 GPa: implications for the stability of sulfides in the earth’s upper mantle

Base metal sulfides (Fe–Ni–Cu–S) are ubiquitous phases in mantle and subduction-related lithologies. Sulfides in the mantle often melt incongruently, which leads to the production of a Cu–Ni-rich sulfide melt and leaves a solid residue called monosulfide solid solution (mss). However, the persistence of crystalline sulfide phases like mss in the Earth’s mantle at higher temperatures and pressures deep within the Earth has long been up for debate, as the presence of both mss and sulfide melt in mantle rocks implies the fractionation of chalcophile elements during mantle melting. Recent studies have shown that the average mantle sulfide (45 wt.% Fe, 16 wt.% Ni, 1 wt.% Cu, and 38 wt.% S), is fully molten at average mantle potential temperatures (1300–1400 ^{circ }C) up to 8 GPa (ca. 240 km). However, sulfide inclusions found in diamonds show a broad compositional spectrum, ranging from Ni-poor and Fe-rich (eclogitic), to Ni-rich and Fe-poor sulfides (peridotitic), with their Cu contents being generally low. The wide compositional variety of diamond-hosted sulfide inclusions raises the possibility that results on the melting properties obtained from this average mantle sulfide compositional may not reflect that found in those inclusions. As such, further investigation of the melting properties of sulfides from a wide compositional range is necessary. Here, we present the results of an experimental study where the melting properties of typical sulfide compositions found in diamond inclusions associated with eclogites and peridotites have been determined. Experiments have been carried out between 0.1 MPa and 14 GPa, and between 920 and 1590 ^{circ }C, on box muffle furnaces, end-loaded piston cylinder, and multi-anvil apparatuses. Results show that solid mss in Fe-rich, Ni-poor sulfide inclusions associated with eclogites persist to higher pressures and temperatures compared to their less-refractory, more Ni-rich peridotitic counterparts to the depth of the mantle transition zone (410 km depth). Our results have implications for the recycling of chalcophile elements during subduction-related processes and the entrapment of sulfides in diamonds.

Technology for processing phosphogypsum into a fluorescent dye based on calcium sulfide

Objectives. There is considerable economic demand for products obtained by processing phosphogypsum. In particular, calcium sulfide-based materials having luminescent properties are the object of intensive study due to the wide range of possibilities for their use. The alloying of the structure of calcium sulfide with cations of rare earth elements leads to the appearance of a glow having various colors. However, the high cost of such phosphorescent materials is due to the high chemical purity of the reagents required for their synthesis. The development of efficient methods for obtaining calcium sulfide-based luminescent materials from phosphogypsum is part of an integrated approach to solving the problem of synthesizing economically demanded materials from production waste.Methods. The synthesized materials were studied using X-ray phase analysis and scanning electron microscopy. Photos of the samples were taken under illumination with an incandescent lamp or a fluorescent ultraviolet lamp.Results. According to X-ray phase analysis, phosphogypsum is mainly comprised of calcium sulfate dihydrate and calcium sulfate hemihydrate. Heat treatment of a phosphogypsum sample at a temperature of 1073 K is accompanied by the formation of anhydrous calcium sulfate. In the presence of a reducing agent, a composite material is formed containing a phase of anhydrous calcium sulfate and calcium sulfide. Due to the calcium sulfide content, phosphogypsum has luminescent properties when heat-treated in the presence of various reducing agents, including activated carbon, wood charcoal, vegetable oil, citric acid, starch, and sucrose.Conclusions. Optimal technological conditions for obtaining a composite material exhibiting luminescent properties are revealed. The successful synthesis of phosphor from without nonpretreated phosphogypsum is demonstrated. Optimal technological conditions for obtaining a composite material exhibiting luminescent properties are as follows: heat treatment temperature is 1073–1173 K; isothermal holding time is 60 min; reducing agent quantity is 37–50% (mol). The study results are widely applicable to processing wastes obtained from large-scale chemical production involving the production of a highly demanded inorganic product.

A multi-methodological approach for mineral exploration and predictive metallurgy: the case of the Pilar gold deposit at the Quadrilátero Ferrífero, Brazil

Gold exploration is generally based on methods such as soil, stream and drill core geochemistry and geophysical techniques, but X-ray diffraction (XRD) and the Rietveld method-based mineral quantification are seldomly used. Here, a multi-methodological approach coupling traditional drill core macroscopic description and multi-element analysis, scanning electron microscopy/energy-dispersive X-ray fluorescence spectrometry (SEM/EDS), and electron probe microanalysis (EPMA) with XRD/Rietveld method and statistical techniques is presented as a useful tool for deposit characterization, mineral exploration and predictive metallurgy purposes. The Pilar gold deposit, situated in the Quadrilátero Ferrífero province, Brazil, was used as a case study for the proposed multi-methodological approach. Carbonate-facies banded iron formations (BIFs) and schist sequences showing an intense quartz and sulfide hydrothermal alteration represent the host rocks of Pilar mineralized intervals, which may be identified by three signatures: Au-As-W-S-quartz-chlorite-pyrrhotite-arsenopyrite-calcite for schists, and Au-As-quartz-chlorite-arsenopyrite-pyrrhotite and Au-Ag-S-Te-quartz-chlorite-pyrrhotite for BIFs. Within the mineralized BIFs, the expected average Au grades and gold textures vary according to the signature. In As-poor BIFs, gold is only observed within the structure of sulfide and telluride phases. On the other hand, native gold is present in As-rich BIF samples, which usually contain relatively higher Au grades, compared to the As-poor BIFs. Native gold is also identified in mineralized schists, whose average Au grades are similar to those of As-poor BIFs. Therefore, the proposed multi-methodological approach is useful in providing the following information: geochemical-mineralogical signatures and the expected average Au grades and mode of occurrence of gold for each one of these signatures. At Pilar, the geochemical-mineralogical behavior of mineralized zones is directly linked to Au grades and textures. In terms of a practical workflow, this study illustrates that, after the multi-methodological approach is applied and the representativeness of the ore-petrography is tested, the general described behavior of gold within each group of ores can be used for mineral exploration and metallurgical purposes without the need of repeated SEM/EDS and EPMA analyses. Instead, the average Au grades and the gold textures may be predicted solely by the signature definition based on the drill core geochemical-mineralogical analyses.

A Role for Crustal Assimilation in the Formation of Copper-Rich Reservoirs at the Base of Continental Arcs

Abstract Understanding the behavior of chalcophile elements during the evolution of arc magmas is critical to refining models for the formation and distribution of porphyry copper deposits used in mineral exploration. Because magmas in continental arcs undergo copper depletion during their early differentiation, a widely held hypothesis posits that the removed copper is locked at the base of the crust in copper-rich cumulates that form due to early sulfide saturation. Testing this hypothesis requires direct evidence for such copper-rich reservoirs and a comprehensive understanding of the mechanisms driving sulfide saturation. Interaction between oxidized magmas and reducing crustal material in island arcs has been shown to be an efficient process causing sulfide saturation. However, the extent to which crustal assimilation impacts the flux of chalcophile elements during magmatism in thick continental arcs remains to be established. Here, we provide a deep perspective into these problems by studying a suite of subarc cumulate rocks from the Acadian orogen, New England (USA). These cumulates record the imprint of subduction zone magmatism and represent the residues left behind during the genesis of intermediate to evolved Acadian magmas (ca. 410 Ma). We find that the most primitive Acadian cumulates are enriched in copper (up to ~730 µg g–1) hosted by sulfide phases, providing direct evidence for the formation of lower crustal copper-rich reservoirs. The Acadian cumulates reveal a wide range of δ34S values, from –4.9‰ in the ultramafic rocks to 8‰ in the most evolved mafic rocks. The negative δ34S values observed in the most primitive and copper-rich cumulates (avg –3‰) reflect the assimilation of isotopically light sulfur from surrounding sulfidic and graphite-bearing metasedimentary rocks (δ34S of –19 to –12‰), whereas the more evolved cumulates with positive δ34S signatures may have formed from different magma batches that experienced less sediment assimilation. The assimilation of these reducing metasedimentary rocks caused a critical drop in oxygen fugacity (~DFMQ –2.5 to –1.9; FMQ = fayalite-quartz-magnetite buffer) in the evolving magmas, ultimately leading to extensive sulfide saturation and the consequent formation of copper-rich subarc cumulates. Assimilation-driven sulfide saturation may be a common process at the root of thickened arc crusts that triggers the formation of lower crustal copper-rich reservoirs, which play a pivotal role in the fate of copper during arc magmatism. Thus, deeply buried reducing metasedimentary crustal material at the base of continental arcs can act as a barrier to the magmatic flux of chalcophile elements and may play a crucial role in the genesis and distribution of porphyry copper deposits.