Metal Sulfide Deposits Research Articles

Quantifying pyrrhotite superstructures in copper-gold ore flotation through synchrotron X-ray diffraction analysis

Pyrrhotite, a significant sulfide mineral in base metal sulfide deposits, exists in various superstructures including magnetic (4C) and non-magnetic (5C and 6C) types. Identifying and quantifying pyrrhotite superstructures in an ore sample has been a challenge, hindering efforts to improve pyrrhotite rejection in copper–gold flotation. This study employed synchrotron X-ray powder diffraction (S-XRPD) analysis to quantify pyrrhotite superstructures in the concentrates obtained from flotation of a copper–gold ore after grinding with forged steel and 30% chromium grinding media. S-XRPD demonstrated a superior capability in detecting characteristic peaks of 4C, 5C and 6C pyrrhotite superstructures compared to conventional XRPD. Utilizing the Rietveld refinement method, the identified pyrrhotite superstructures were quantified. These findings were successfully validated through independent X-ray fluorescence analysis on elemental compositions. The quantification work demonstrated that 30% chromium grinding media enhanced the floatability of all pyrrhotite superstructures over forged steel grinding media and each pyrrhotite superstructure in the copper–gold ore resembled a copper sulfide mineral rather than pyrite in response to grinding media during flotation. This research highlights the potential of S-XRPD as an effective technique for identifying and quantifying pyrrhotite superstructures in ore samples and determining their flotation behaviors.

Active Electrochemical Catalysts for Ammonia and Hydrogen Evolution Reaction

An environmentally friendly alternative synthesis process is desired to produce NH3 with no CO2 emissions and low energy demand in a sustainable and ecological way in the future. The electrochemical method assisted by earth-abundant materials has been widely utilized for the chemical energy conversion. We have developed new earth-abundant layered structure metal sulfide based materials as active catalysts for electrochemically nitrogen reduction reaction. From electrochemical analysis, the Faraday efficiency of MoS2 and FeS2 for NRR can be achieve to~27% and 14% with good catalytic stability, respectively. The energy profile of the NRR reaction pathway on the catalysts will be performed by the density functional theoretical (DFT) calculation. Besides, there have been lots of studies on hydrogen evolution reaction (HER) catalytic activity using ultralow loading of Pt catalysts or even Pt single atom catalysts as well. However, Pt single atom deposited on the surface of the carbon or metal oxide material showed some drawbacks, such as high possibility of Pt desorption from the supported material in the electrolyte. Our work demonstrated that gold nanodendrites (Au NDs) with high facet surface was chosen as the supported materials for studying the relation between the low loading amount of Pt atoms and reaction mechanism of HER activity. Overall results provides a feasible approach to morphological control of metal sulfide and atomic deposition of Pt element on the specific substrate as active catalysts for NRR and HER applications, respectively.

Seafloor spreading and the delivery of sulfur and metals to Earth’s oceans

Abstract Circulating fluids within Earth’s mid-ocean ridge system cool and alter the oceanic crust, contribute distinct chemistry to the ocean, and generate economically and geologically important metal-sulfide deposits at the seafloor. Yet, we have few constraints on the characteristics of these fluids at peak subseafloor pressure and temperature conditions or how the primary variable, seafloor spreading, affects these fluids’ delivery of metals and sulfur to seawater. Here, we develop a new, robust technique for estimating the peak endowment of heat and dissolved sulfur, iron, and copper in subseafloor hydrothermal fluids and determining their fate as these superheated fluids rise to the seafloor. Calculations using this technique indicate that >20%–70% of sulfur, iron, and copper dissolved at peak subseafloor conditions are lost during upflow due to cooling and concomitant decreases in sulfide mineral solubility. The interpretation of these estimates within the geologic context of vent fields allows us to demonstrate a strong inverse relationship between seafloor spreading rate and peak pressure-temperature conditions, subseafloor heat loss, and the magnitude of subseafloor sulfide mineralization. Our results demonstrate the extent to which the secular variation of Earth’s mid-ocean ridge system over geologic time has impacted sulfide deposition rates and hydrothermal fluxes of sulfur and metals to the ocean.

Geochemical Response of Surface Environment to Mining of Sn-Pb-Zn Sulfide Deposits: A Case Study of Dachang Tin Polymetallic Deposit in Guangxi

The rational development of mineral resources provides necessary materials for economic development, but environmental pollution caused by mining activities is an inevitable consequence. Here, we present a case study of Chehe Town in Guangxi, an area with integrated metals mining and smelting. The geochemical distribution, migration, and transformation behaviors of Cd and other heavy metals were studied in detail by systematically collecting surface media such as atmospheric dust, surface water and stream sediments, ores, tailings, mine drainage, soil, and crops in and around the mining area. We used these data to explore the geochemical response of the surface environment to mining and smelting of metal sulfide deposits. The annual flux of Cd and other heavy metals near the mining and smelting sites was high. Due to the topography, heavy metals in the atmosphere are mainly transported via vertical deposition, influencing areas downwind for 25 km. The mine drainage exceeded As and Zn standards but had little impact on the surface water. The surface water quality was good, without acidification. Risks due to ore were much higher than that for tailings. Heavy metals buffered by surrounding carbonate rocks and secondary minerals mainly migrated as solid particles, resulting in the contamination of stream sediment by heavy metals. In mountainous areas, rivers are mainly affected by topography, flowing fast and dominated by downcutting, which caused heavy metal pollution in the sediment have a limited effect on the soil near the river. Heavy metal concentrations in the cultivated soil were greatly influenced by external input such as substantial atmospheric dust. However, only Cd accumulated in the crops, with very high concentrations in rice, but safe and edible levels in corn. Thus, in the mining area, the most sensitive to heavy metals was the atmospheric environment. High concentrations of heavy metals beyond the ore district are mainly concentrated in the sediment, with distant impacts. Therefore, it is necessary to monitor and control risks associated with sediment transport, conduct treatment, and adjust crop planting. The soil, river, and agriculture respond differently to mining activities, but the risk is low and can be managed as needed.

An Early Cretaceous magmatic-hydrothermal origin of the Shanhou stratabound Pb-Zn deposit in Fujian Province of southeast China: Constraints from hydrothermal titanite U-Pb dating and C-O-S-Pb isotopes

Stratabound base metal sulfide deposits within Neoproterozoic metavolcanic rocks and skarns in the Fujian Province are important Zn-Pb producers in China. To date, the inability to determine absolute ages and proper sources of Pb-Zn mineralization has led to conflicting ore genetic models. These include the metamorphosed volcanogenic massive sulfide (VMS) model, which predicts that the Pb-Zn mineralization was synchronous with submarine volcanic activity, and the Early Cretaceous magmatic-hydrothermal skarn model. The Shanhou deposit (2.56 Mt ore @ 6.8 % Pb + Zn) in the central Fujian Province, the southeastern coastal area of China, consists of twelve stratabound massive Pb-Zn sulfide orebodies hosted in hydrothermally altered metavolcanic rocks of the Neoproterozoic Dongyan Formation. No intrusive body that could have contributed to the formation of the calc-silicate mineral-dominated wall rocks and Pb-Zn ores has been found spatially associated with the Shanhou deposit, and the origin of the mineralizing fluids, sulfur, and metals has not yet been identified previously. Here we present in-situ U-Pb ages of hydrothermal titanite and C-O-S-Pb isotopes of gangue and ore minerals to constrain the timing and origin of the Pb-Zn mineralization. Three hydrothermal stages can be identified: pyroxene (prograde stage I), epidote + chlorite + titanite (retrograde stage II), and quartz + calcite + polymetallic sulfides (quartz-calcite-sulfide stage III). In-situ LA-ICP-MS U-Pb isotopic analyses of hydrothermal titanites coexisting with sulfides in two massive ore samples yield indistinguishable ages of 145 ± 13 Ma and 144 ± 9 Ma, overlapping the 152 to 145 Ma emplacement age of granitic rocks in the central Fujian area. The results show that the Shanhou Pb-Zn deposit is significantly younger than the Neoproterozoic host (meta)volcanic rocks, arguing against a Neoproterozoic VMS genetic model as suggested by some previous researchers. The δ34S (V-CDT) values of pyrrhotite, pyrite, marcasite, chalcopyrite, sphalerite, and galena in the massive sulfide ores range from −2.9 to 6.9 ‰, indicating that the sulfur at Shanhou is mainly of magmatic origin. Sphalerite separates have 206Pb/204Pb ratios of 17.782 to 17.782, 207Pb/204Pb ratios of 15.585 to 15.593, and 208Pb/204Pb ratios of 38.376 to 38.407, which are similar to those of the host rocks, indicating that the ore-forming materials were derived from the host rocks. Calcite in sulfide ores has δ13CV-PDB values of −7.8 to −4.3 ‰ and δ18OV-SMOW values of 6.1 to 9.5 ‰, suggesting a magmatic origin for the ore-forming fluids. It is concluded that the Shanhou stratabound Pb-Zn deposit is a metasomatic skarn-like deposit associated with a possible hidden Early Cretaceous felsic intrusion at depth, rather than a metamorphosed VMS deposit.

Halogen characteristics and their implications for geochemical exploration in the Qujia gold deposit, Laizhou, Jiaodong

The ore-forming fluids in the Jiaodong gold deposits are characterized by low to medium salinities and Au-HS complexes are the predominant Au species in the fluid. The role of halogen elements in geochemical exploration for the gold deposits is still unclear. This study takes the Qujia gold deposit as an example to explore the issue. Scatter plots and 3D modeling were conducted based on the geochemical data of 1130 borehole samples. The halogen characteristics are governed by fluid-rock interactions, and rock types and heterogeneity. Nevertheless, the halogen characteristics in the alteration zone along the Jiaojia fault zone are still interesting and appealing. In the mineralized zone along the Jiaojia fault, the F and Cl concentrations generally reduce with a decrease in depth; F anomalies evolved from strong positive anomalies at deep depths to negative anomalies at shallow depths; positive Cl anomalies appeared in the upper part or above the mineralized zone while negative Cl anomalies appear in the middle and lower parts of the mineralized zone. The zonation pattern may be attributed to the preferential replacement of OH− by F− due to the acidic pH and the intense beresitization. The consumption of halogen elements may cause the destabilization of metal-Cl complexes and increase the pH of ore-forming fluid, and the deposition of metal sulfides further results in the destabilization of Au-HS complexes and Au deposition. Therefore, F, Cl, and F/Cl ratio can be jointly used as exploration indicators for the geochemical exploration only if rock types, and characteristics of hydrothermal fluid and alteration are examined in advance.

The geochemistry of zinc and copper stable isotopes in marine hydrothermal brine pools: Perspectives from metalliferous sediments of the Atlantis II Deep, Red Sea

This study provides a zinc and copper stable isotope characterization (δ66Zn, δ68Zn, and δ65Cu) of metalliferous seafloor sediments from the Atlantis II Deep, a hydrothermally influenced brine basin in the Red Sea. Samples collected from box cores that capture the entire stratigraphy in the Deep have δ66Zn and δ65Cu values of −0.31 to 0.34 ‰ (0.02 ‰ median) and − 1.81 to 1.02 ‰ (−0.34 ‰ median) relative to the JMC-Lyon and NIST SRM 976 standards, respectively. These results suggest enrichments of light stable isotopes in sediments compared to the hydrothermal inputs to the basin, which likely overlap the mantle-like isotopic signatures of basalts beneath the Deep. Such shifts to lower δ66Zn and δ65Cu values are consistent with widespread metal sulfide deposition from the brines because sulfide anions preferentially consume the light stable isotopes of zinc and copper. However, this interpretation contrasts with observations in the open ocean, where the fractionation of zinc and copper stable isotopes is strongly influenced by biological utilization and organic matter. Previous studies proposed that metal deposition in the Atlantis II Deep is also driven by adsorption onto iron oxides/hydroxides and their weakly crystalline (Si-)Fe-OOH precursor phases within the brines. However, because this process should accumulate heavy zinc and copper stable isotopes, its influence on isotopic fractionation is likely limited. Controls by metal sulfide precipitation are also indicated by spatial covariations between δ66Zn and concentrations of zinc and copper, that is, δ66Zn values increase whereas metal contents decrease with distance away from hydrothermal venting. Comparable trends are lacking for copper isotopes, perhaps because of additional influence by redox processes or, compared to zinc, a much stronger influence by adsorption onto (Si-)Fe-OOH phases, particularly in areas distal to hydrothermal venting where reduced sulfur could be scarce. Collectively, our results from the Atlantis II Deep indicate that zinc and copper stable isotopes could provide information about base and precious metals deposits from similar paleoenvironments. Firstly, zinc and copper stable isotopes shed light on metal sourcing and accumulation processes. Secondly, mineral precipitation in hydrothermally influenced brine pools produces zinc stable isotope patterns that, at least theoretically, could be of interest in mineral exploration at sub-basin and deposit scales.

Chemical vapor deposition of two-dimensional transition metal sulfides on carbon paper for electrocatalytic hydrogen evolution catalytic activity

Chemical vapor deposition of two-dimensional transition metal sulfides on carbon paper for electrocatalytic hydrogen evolution catalytic activity

Preparation of nickel/copper sulfides from metal-organic frameworks. Applications to energy storage in a symmetric supercapacitor and electrocatalytic methanol oxidation

A hybrid of nickel and copper sulfides was synthesized by using metal-organic frameworks. The prepared composite (Ni3S2/CuxS) was then mixed with multi-walled carbon nanotubes to form MWCNTs@Ni3S2/CuxS. Several methods were used for characterization of the prepared composite. Electrochemical studies showed a great improvement in capacitive properties of graphite foil (GF) when modified by MWCNTs@Ni3S2/CuxS. In a three-electrode system, the specific capacitance was estimated from galvanostatic charge-discharge experiments to be 1388.7 F g−1 at a current density of 1 A g−1 with cycling stability of ∼ 100% (10,000 cycles). In two electrode system (symmetric supercapacitor, SSC), a wide working voltage range (2.4 V) was obtained in aqueous alkaline solution. Moreover, MWCNTs@Ni3S2/CuxS showed great electrocatalytic effect in methanol oxidation reaction (current density 346.7 mA cm−1 in methanol, 0.5 M). Chronoamperometric oxidation of methanol on MWCNT@Ni3S2/CuxS/GCE showed a current lose< 16% after 14,000 s (∼ 4 h). Chronopotentiometry at a constant current density (22.3 mA cm−2) showed a highly stable potential after 14,000 s (drift<8%). The excellent capacitive and electrocatalytic properties of MWCNTs@Ni3S2/CuxS were attributed to deposition of metal sulfides on metal-organic frameworks which prevented their agglomeration, and effective synergy among Ni3S2, MOF-derived-CuxS and MWCNTs.

Chemical vapor deposition of two-dimensional transition metal sulfides on carbon paper for electrocatalytic hydrogen evolution

Hydrogen is considered one of the most likely alternative clean energy fuel to traditional fossil fuels. One of the most attractive hydrogen production strategies is water splitting, but the need for expensive Pt precious metal catalysts to catalyze the hydrogen evolution reaction (HER) is a problem. Recently, two-dimensional transition metal dichalcogenides (TMDs), especially MoS2, have attracted intense interest as a non-precious metal HER catalyst due to their low cost and relatively high catalytic activity. However, their poor electron conductivity and the limited number of active sites at their edges have greatly limited their overall catalytic performance. We report the direct growth of three representative TMDs (MoS2, NbS2 and WS2) on a conductive carbon paper substrate using chemical vapor deposition and have studied the effects of temperature and gas flow rate on their morphology and structure. All the as-grown TMDs have a 2D nanosheet morphology and were aligned perpendicular to the carbon paper. The WS2 nanosheets had the smallest sheet size with a diameter of ca. 100-200 nm and, more interestingly, were assembled into a one-dimensional nanofiber, leading to the highest HER activity. Additional electrochemical cathodic activation further improved the HER activity of the TMDs, and the structural changes after the activation were investigated by TEM combined with in-situ electrochemical Raman spectroscopy. The activated NbS2 contained large triangular or truncated triangular S vacancy areas, which is distinctly different from the individual S vacancies in MoS2.

Preliminary chemical and mineralogical characterization of tailings from base metal sulfide deposits in Serbia and North Macedonia

Tailings of old mines often contain metals, which were not of economic interest or could not be recovered with the existing technology at the time of active mining. This is especially true for metals that often occur as by-products in Cu-Pb-Zn-(Ag-Au) ores as Sb, Mo, Ge, and In. A fundamental characterization of some tailings is presented in terms of their mineralogy and content of valuable metals which could be extracted to finance a possible remediation and improve the supply of the EU with critical metals. Tailings from active and abandoned mines in Serbia (Bor, porphyry Cu/Au; Krivelj, porphyry Cu/Au; Blagodat, hydrothermal Pb-Zn; Lece, epithermal Au; Rudnik, hydrothermal/skarn Pb-Zn) and North Macedonia (Sasa, Pb-Zn; Probištip, Pb-Zn; Bučim, porphyry Cu; Lojane, fault-bound vein-type low-temperature As, Sb, Cr at the contact of rhyolite and serpentinite) were studied. Analysis for major and trace elements used a multi-method approach (lithium borate fusion and ICP-MS/OES analysis, gravimetric analysis, instrumental neutron activation analysis, total digestion ICP-OES, infrared spectroscopy) with mineral identification by scanning electron microscopy. Concentrations of the major commodity elements (Cu, Pb, Zn, Au, Ag) varies within several orders of magnitude depending on mineralogy and ore type. Critical metals (Co, Ga, Ge, Sb) contents are low with some exceptions. Some tailings contain moderate to elevated potentially toxic element levels (As, Cd, Pb, Tl). For the sample from Probištip which yielded the highest valuable metal concentrations (&gt;5000 ppm Pb, 4020 ppm Zn), a heavy mineral concentrate of the sand size fraction (0.06 mm to 0.5 mm) was produced and analyzed by SEM and LA-ICP-MS for additional rare phases and trace elements. In all tailings studied, additional milling would be needed to separate ore from gangue minerals. Increasing metal prices might facilitate feasibility studies for some of the localities in the future, despite the limited quantitative information about the characterized tailings.

Experimental Determination on the Deactivation Kinetics of Residue Hydroprocessing in a Two-Stage Fixed Bed Loaded with HDM and HDS Catalysts

Residue catalytic hydrogenation was carried out in a two-stage downflow fixed-bed reactor system, with a HDM catalyst in the first stage and HDS catalyst in the second one, to mimic the industrial operation. The experiments were run at five sets of temperatures (395 °C (first reactor)/405 °C (second reactor), 400 °C/410 °C, 405 °C/415 °C, 410 °C/420 °C, and 420 °C/430 °C). It was found that the initial stage deactivation was mainly caused by the rapid deposition of coke. Gradually, the deposition of metal sulfides leads to a slow deactivation in the middle stage of operation. A deactivation model that considers the catalyst activity as a function of TOS was proposed and applied to the hydrotreating reaction. The deactivation parameters of HDCCR, HDS, HDNi, and HDV in the two reactors were obtained by fitting the experimental data at the outlet of the two reactors. According to the deactivation curves of catalysts, it is proposed that the deactivation of HDM catalyst is faster than that of HDS catalyst, and multi-bed hydrogenation can effectively increase the catalyst life.

Complex Effects of Assimilation on Sulfide Saturation Revealed by Modeling with the Magma Chamber Simulator: A Case Study on the Duluth Complex, Minnesota, USA

Abstract Wall-rock assimilation can cause effective sulfide saturation in magmas and lead to the formation of base and precious metal sulfide deposits. Detailed assessments of how assimilation affects the sulfur content at sulfide saturation (SCSS) in magmas have been scarce because of the lack of suitable thermodynamic modeling tools. The Magma Chamber Simulator (MCS) is the first geochemical modeling software that accounts for thermodynamic wall-rock phase equilibrium in open magmatic systems experiencing recharge-assimilation-fractional crystallization. We used the MCS to model SCSS in a magmatic system corresponding to the parental melt of the Partridge River intrusion of the Duluth Complex, Minnesota. This intrusion hosts several Cu-Ni deposits in troctolitic and noritic rocks, which both show evidence of assimilation of the adjacent Virginia Formation black shale. Our simulations show that the dominantly troctolitic rocks can form via fractional crystallization if the parental melt is hydrous (≥ 1 wt % H2O), while gabbroic rocks dominate when the parental melt is H2O poor (≤ 0.14 wt % H2O). Formation of norite from the hydrous parental melt requires ~20–30% of selective assimilation of black shale partial melts or bulk assimilation of stoped blocks. In the fractional crystallization simulations, increasing the H2O content of the parental melt lowers SCSS. In the hydrous fractional crystallization scenarios, SCSS is lowered further by the depletion of FeO from the residual melt, owing to enhanced olivine stability. In the assimilation simulations, the residual melt in the magma subsystem becomes enriched in SiO2, Al2O3, K2O, and H2O with simultaneous depletion in FeO, MgO, CaO, and Na2O. These compositional changes promote sulfide saturation—an effect that is more pronounced in selective rather than in bulk assimilation scenarios. Trace element models, used as a proxy for the efficiency of sulfur assimilation, show that sulfur should behave as an incompatible element (DWR (S) ≤ 1) to wall rock in the selective assimilation simulations, i.e., enriched in early-assimilated wall-rock fluids and/or partial melts, in order to fulfill the natural sulfur isotope criteria of the Duluth Complex. Bulk assimilation may also be efficient enough to modify the sulfur isotope composition, but it requires a large amount of crystallization in the magma and is, hence, considered less likely to be the main process for sulfur assimilation. If wall-rock sulfur is effectively transported to the magma, in situ precipitation of sulfides without notable subsequent upgrading by dynamic processes could produce the sulfide grade of an average Cu-Ni deposit in the Partridge River intrusion.

Sulfate-limited euxinic seawater facilitated Paleozoic massively bedded barite deposition

Existing models for massively bedded barite (MBB) deposits (e.g., sedimentary exhalative and diagenetic/ cold-seep) satisfy some geological and geochemical observations, but none explain the Paleozoic clustering of MBB deposits in Earth history. Here we bring seawater redox history into the picture and propose a sulfate-limited euxinic seawater (SLES) model where hydrothermally sourced Ba2+ accumulates as dissolved ion while other metal ions precipitate as insoluble metal sulfides. A subsequent encounter of this Ba2+-rich water mass with a sulfate-bearing one results in the deposition of MBB, thus physically separated from the accompanied metal sulfide deposits. We tested the SLES model using early Cambrian MBB deposits in South China through petrographic and isotope analyses. Syngenetic sphalerite and barite layers show a clear separation. A wide range of 87Sr/86Sr values (0.7082 to 0.7120) of the MBB supports a mixing of seawater and hydrothermal sources. A large range of δ34S values (32.2 to 61.1‰) of the MBB and the occurrence of mineral hyalophane supports an overall sulfate-limited but sulfate-concentration temporally and spatially heterogeneous ocean. Our model established the genetic link between MBB deposits and the accompanied metal sulfide deposits in the Paleozoic. The dearth of MBB deposits before and after the Paleozoic is due to widespread ferruginous oceans with little sulfate and complete oxygenated oceans with too much sulfate, respectively. The Paleozoic clustering of the MBB deposits is a consequence of a critical redox transition in Earth history.

Molybdenum(IV) dithiocarboxylates as single-source precursors for AACVD of MoS2 thin films.

Tetrakis(dithiocarboxylato)molybdenum(IV) complexes of the type Mo(S2CR)4 (R = Me, Et, iPr, Ph) were synthesized, characterized, and prescreened as precursors for aerosol assisted chemical vapor deposition (AACVD) of MoS2 thin films. The thermal behavior of the complexes as determined by TGA and GC-MS was appropriate for AACVD, although the complexes were not sufficiently volatile for conventional CVD bubbler systems. Thin films of MoS2 were grown by AACVD at 500 °C from solutions of Mo(S2CMe)4 in toluene. The films were characterized by GIXRD diffraction patterns which correspond to a 2H-MoS2 structure in the deposited film. Mo-S bonding in 2H-MoS2 was further confirmed by XPS and EDS. The film morphology, vertically oriented structure, and thickness (2.54 μm) were evaluated by FE-SEM. The Raman E12g and A1g vibrational modes of crystalline 2H-MoS2 were observed. These results demonstrate the use of dithiocarboxylato ligands for the chemical vapor deposition of metal sulfides.

Determination of fluorine concentrations in mineralizing fluids of the Hansonburg, New Mexico Ba-F-Pb district via SEM-EDS analysis of fluid inclusion decrepitates

The Hansonburg, New Mexico district in the southwestern U.S.A. contains anomalously fluorite rich carbonate-hosted base metal sulfide deposits. A long-standing hypothesis for this fluorite enrichment is that the Hansonburg mineralizing fluids were correspondingly enriched in F relative to the typical sedimentary brines that formed carbonate-hosted base metal deposits.The purpose of the present study was to test this hypothesis by determining the F concentration in fluid inclusions hosted by drusy quartz that paragenetically overlaps fluorite. The fluid inclusions were thermally decrepitated creating evaporative solute mounds, which were then analyzed via scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDS). Fluorine was detected in all evaporative solute mounds analyzed, equating to fluid inclusion F concentrations of 320 to 2500 ppm. These F concentrations are significantly greater than the F concentrations of tenth's to 10s of ppm F typical of sedimentary brines. Further, these high F concentrations indicate that the Hansonburg mineralizing fluid must have been very acidic during the time of fluorite mineralization with a pH of 1 to 2.4. This pH is much lower than the pH of 4.3 to 5.1 predicted in earlier studies and also much lower than the pH of 4 to 5.5 considered typical of carbonate-hosted ZnPb mineralizing fluids. High mineralizing fluid F concentrations in combination with low pH would have provided conditions favorable for the formation of the observed Hansonburg mineral assemblage, i.e. fluorite-barite rich and metal sulfide mineral poor.

Spatial and temporal variations of Cu and Cd mobility and their controlling factors in pore water of contaminated paddy soil under acid mine drainage: A laboratory column study

Acid mine drainage (AMD) poses a potential threat to human health worldwide, due to its high content of inorganic contaminants including heavy metals. Nevertheless, AMD is commonly used for irrigation of paddy soils. To determine the extent to which AMD affects contaminant levels in such practices, the effect of continuous AMD flooding on pH, redox potential Eh and the migration of Cu and Cd in contaminated paddy soil was studied in column experiments. By means of simulated AMD, dynamic changes of Cu and Cd concentrations in pore water were measured and the controlling factors pH, Eh and presence of Fe, dissolved organic carbon and sulfate were determined over a period of 60 days. Minerals in the soil were assessed by means of an Eh-pH diagram and solid-phase mineral detection. During continuous flooding with AMD-simulated water the soil pH increased, while Eh decreased over time. After 60 days the soil pH stabilized. Cu and Cd concentrations in the pore water negatively correlated with pH and with sulfate concentrations. Five-step sequential extraction illustrated that the fraction of exchangeable Cu increased significantly during AMD flooding. The overall content of Cu increased from initially 0.29 mg/g to 0.41 mg/g, while the content of Cd decreased from 9.2 mg/g to approximately 7.2 mg/g. Mobility factors were calculated and these conformed that Cd mobility significantly increased in contaminated soils during continuous AMD flooding. Our findings indicate that the release of Cu and Cd under AMD flooding can increase potential environmental risks, even though they lead to formation of metal sulfide deposits under anaerobic conditions. The presented data improves our understanding of the impact of overlying water conditions on the mobility of toxic metals in contaminated paddy soils.

Liquid electrolyte design for metal‐sulfur batteries: Mechanistic understanding and perspective

AbstractMetal‐sulfur batteries have received intensive research attention owing to their potential to achieve higher energy density and lower cost than conventional Li‐ion batteries. However, metal‐sulfur batteries suffer from a fundamental challenge, the shuttle effect, the crossover of soluble reaction intermediates polysulfide leading to low efficiency and poor cycle life. Electrolyte design becomes the center of the sulfur redox chemistry since it dictates the properties of the soluble polysulfide intermediates in metal‐sulfur batteries. Here, we discuss the influence of electrolytes on sulfur reactions and cell performance, focusing on the polysulfide chemistry including polysulfide solubility and metal sulfide deposition. Based on the extensive analysis of literature, we highlight the design requirement of electrolytes to enable optimized sulfur reaction kinetic and realize high‐performance metal‐sulfur batteries.image

Ferrocene addition for suppression of hydrogen sulfide formation during thermal recovery of oil sand bitumen

The occurrence of H2S during thermal recovery production becomes one of the biggest challenges. While various industrial processes can remove H2S at the surface, to prevent the formation of H2S in reservoir is much less successful. Ferrocene was chosen as the likely target reagent after a review of iron compound volatility and environmental considerations. To evaluate this, closed system gold tube pyrolysis experiments were conducted on an Athabasca oil sand at 350–650 °C to examine gas compositions with and without ferrocene addition. Slightly higher hydrocarbon gas yields have been observed from samples with ferrocene addition likely caused by ferrocene decomposition. Yields of carbon dioxide (CO2) are higher in plain oil sand samples before 550 °C but the trend was reversed afterwards with more CO2 being generated from ferrocene addition ones. H2S yields in samples without ferrocene increase from background value at 350 °C to the highest amount at 450 °C then disappear above 625 °C. Thermal decomposition of organosulfur compounds is supposed to be the main route for the occurrence of H2S in the sulfur-rich bitumen pyrolysis. Ferrocene is proved to be powerful H2S removal reagent as no H2S can be detected from ferrocene addition samples. The reactions of ferrocene with H2S may form iron sulfides, cyclopentadiene and hydrogen. Complete, rapid, and predictable reactions and inert reaction products make ferrocene as an ideal in situ H2S scavenger, while the potential for the deposition of metal sulfides may reduce the permeability. Ferrocene is widely available for industry, however, the unit cost has not been assessed in this study.

Mechanisms and rates of pyrite formation from hydrothermal fluid revealed by iron isotopes

Critical to interpreting iron isotope signatures in hydrothermal sulfide minerals is the accurate knowledge of Fe isotope fractionation factors, both kinetic and at equilibrium, between the fluid and minerals. Here we report Fe isotope fractionation between pyrite and aqueous saline fluid from in-situ pyrite precipitation experiments performed at 400–450 °C and 400–800 bar in a wide range of pH (2.5–4.8) and salt content (0.05–2.0 mol NaCl/KCl per kg of fluid). Our measurements show that while apparent bulk chemical equilibrium (in terms of total dissolved Fe concentration) between the FeCl2-bearing fluid and crystalline pyrite is attained within a few days, the Fe isotope fractionation values between the fluid and mineral (expressed as Δ57Fefluid-pyrite = δ57Fefluid – δ57Fepyrite) exhibit large variations, from about –0.6 to +1.0‰, depending on the elapsed time (1–30 days) and fluid composition (mostly pH, sulfur solubility, and di- and tri-sulfur radical ion concentration). Yet these values remain significantly higher, by 0.5–2‰, than equilibrium isotope fractionation inferred from β-factors of pyrite and the dominant iron chloride species in solution FeCl2(H2O)20(aq), generated in this study using Density Functional Theory (DFT) modeling (Δ57FeFeCl2(H2O)2-pyrite ≈ –1.25 ± 0.25‰ at 300–450 °C). The lack of isotope equilibrium between fluid and pyrite in this study and other recent work demonstrates that the fluid-pyrite Fe isotope exchange is kinetically controlled even at elevated temperatures (≥300 °C), allowing rate patterns to be identified. Our time-series data, combined with other available measurements at 300–350 °C, provide evidence for two major distinct kinetic regimes of fluid-pyrite Fe isotope exchange: (1) a fast and short (<10–20 days) initial step, likely controlled by Fe (poly)sulfide aqueous precursors that transfer their isotope signature to rapidly precipitating pyrite resulting in apparent isotopic disequilibrium between the FeCl2-dominated fluid and pyrite, (2) followed by a slower and longer second step of pyrite recrystallization, growth, and isotope re-equilibration with the fluid. The derived Fe isotope exchange rate constants suggest that more than 1 year is required to isotopically equilibrate pyrite with hydrothermal fluid at temperatures of 300–450 °C. Our new data provide direct interpretation of the Fe isotope ratios in fluids and sulfide minerals from modern submarine hydrothermal vents, which are characterized by fast (hours to days) pyrite precipitation. Furthermore, our results may enable estimating, using Fe isotope signatures, the dynamics of relatively short (<year-scale) mineralizing events in ancient hydrothermal metal sulfide deposits that cannot be assessed using more traditional dating approaches.