Iron Sulfide Material Research Articles

Enhanced decomposition of H2S to H2 via iron sulfide nanoparticles: A comprehensive experimental and theoretical evaluation

Hydrogen sulfide (H2S), a common pollutant in both fossil and bio-based fuels, can be transformed into valuable hydrogen (H2) through a two-step thermochemical process known as sulfur looping. This scheme, derived from the chemical looping approach, employs a metal-sulfide-based sulfur carrier as a solid intermediate. Iron sulfide, a benign and abundant material, is a promising candidate as the sulfur carrier; however, it faces challenges related to its poor kinetic activity. In this study, we demonstrate the exceptional performance of nano-sized sulfur carriers for the sulfur looping scheme through comprehensive experimental and theoretical analyses. We synthesized iron sulfide nanoparticles that exhibit a remarkable ∼69% enhancement in reactivity over the bulk-sized sulfur carrier. This enhancement is attributed to the high surface area and the nanoscale effects that enhance intrinsic activity. Furthermore, for the first time, we evaluated the effect of co-feeding carbon dioxide (CO2), a prevalent component in industrial acid gas streams alongside H2S. Our combined thermodynamic, atomistic density functional theory (DFT), and experimental studies indicate that the presence of CO2 enhances the conversion of H2S. Additionally, to gauge the sulfur looping process’s superiority at a larger scale, we conducted comprehensive thermodynamic analyses under industrial acid gas conditions. These analyses reveal an improvement of ∼22 percentage points in energy efficiency and ∼8 percentage points in exergy efficiency over the state-of-the-art Claus process. This study, integrating experiments, atomistic DFT studies, and process simulations, provides valuable guidance in the design of high-performance sulfur carriers for efficient H2S splitting to H2.

Synthesis and application of iron sulfide−based materials to activate persulfates for wastewater remediation: a review

Rapid industrial development has led to excessive levels of various contaminants in natural water, which poses a challenge to the innovation of environmental remediation technology. In recent years, iron sulfide and its modified materials have attracted extensive attention in environmental remediation due to their high activity in advanced oxidation processes and widespread existence in anoxic environment. This paper reviewed the latest advances of the synthesis methods for iron sulfide and modified FeS. In addition, the application of persulfate activation by iron sulfide materials (FeS, FeSx, S−ZVI, FeS@Carbon materials and MFexSy) for contaminants remediation is also reviewed, and the enhancement of this system by photo irradiation, ultrasound, and microwave have also been concluded. Additionally, the interaction mechanism of iron sulfide and persulfate with contaminants was reviewed. Based on the above contents, we concluded that the long−term stability of iron sulfide, the toxicity to organisms of iron sulfide materials in the treated water, and the combination of FeS/PS with other assisted technologies should be focused in future.

Electrospun Fe1-xS@nitrogen-doped carbon fibers as anode material for sodium-ion batteries

Iron sulfide is a potential anode material for sodium-ion batteries because of its abundant natural resources and high theoretical specific capacity. However, they show poor cycling performance due to the serious volume change of iron sulfide materials during the process of charge and discharge. In this work, Fe1-xS particles are encapsulated in nitrogen-doped 1D carbon fiber material by an electrospinning/high-temperature vulcanization process. The carbon fiber skeleton effectively stabilized the structure of the material; The heteroelement doped carbon improved the electrical conductivity properties and capacitive sodium storage performance. Owing to the unique structure of nitrogen-doped 1D carbon fiber, the material obtains good cycling stability and rate capability. The optimized Fe1-xS@ nitrogen-doped carbon fibers (Fe1-xS@NCFs) material was used as the anode of the sodium-ion batteries and maintained a discharge capacity of 382 mAh g-1 after 100 cycles at 0.1 A g-1 and 330 mAh g-1 after 150 cycles at 1 A g-1.

Ultra-efficient and selective recovery of Au(III) using magnetic Fe3S4/Fe7S8

Gold is a highly valuable resource in our society, an efficient and selective recovery technology is necessary for gold recycling from wastes to alleviate resource shortage and environmental pollution caused by traditional mining activities. In this paper, Fe3S4/Fe7S8 materials were applied for Au(III) recovery for the first time, one of the materials showed ultra-high capacity (2020.7 mg/g). Various characterizations and adsorption tests proved its excellent properties, including high capacity and selectivity, good magnetism, low cost, and reusability. Characterization results revealed Au(III) is recovered on the adsorbents through in-situ reduction, and the reduction mechanism was studied through intensive XRD and XPS analyses. This work introduced magnetic iron sulfide materials in Au(III) recovery, and demonstrated its promising features.

Cover Feature: Redox Properties of Iron Sulfides: Direct versus Catalytic Reduction and Implications for Catalyst Design (ChemCatChem 12/2022)

The Cover Feature shows two different natural sceneries where iron sulfides play a key role in mediating chemical reductions. One where the reactions are catalytic, nitrogenase and another where the chemical reduction is direct, hydrothermal vents. The two reactions are sometimes confused. In their Research Article, C. F. Garibello et al. explore the relationship between direct and catalytic reduction of nitrite to ammonia using a “test set” of iron sulfide materials, including amorphous irons sulfide, greigite, pyrite and troilite. XAS results show the changes in the structure of the materials after reaction, and the ammonia quantification allows us to explore the selectivity of reduction products. Amorphous iron sulfide shows the greatest selectivity for NH3/NH4+ production as both a direct reductant and a catalyst, while the most stable minerals (troilite and pyrite) show the largest differences between catalytic and direct reduction. More information can be found in the Research Article by C. F. Garibello et al.

Synthesis, modular composition, and electrochemical properties of lamellar iron sulfides

A new class of layered iron sulfide materials offers tunable composition and properties for electrochemical energy storage.

Iron Sulfide Materials: Catalysts for Electrochemical Hydrogen Evolution

The chemical challenge of economically splitting water into molecular hydrogen and oxygen requires continuous development of more efficient, less-toxic, and cheaper catalyst materials. This review article highlights the potential of iron sulfide-based nanomaterials as electrocatalysts for water-splitting and predominantly as catalysts for the hydrogen evolution reaction (HER). Besides new synthetic techniques leading to phase-pure iron sulfide nano objects and thin-films, the article reviews three new material classes: (a) FeS2-TiO2 hybrid structures; (b) iron sulfide-2D carbon support composites; and (c) metal-doped (e.g., cobalt and nickel) iron sulfide materials. In recent years, immense progress has been made in the development of these materials, which exhibit enormous potential as hydrogen evolution catalysts and may represent a genuine alternative to more traditional, noble metal-based catalysts. First developments in this comparably new research area are summarized in this article and discussed together with theoretical studies on hydrogen evolution reactions involving iron sulfide electrocatalysts.

Rapid formation of iron sulfides alters soil morphology and chemistry following simulated marsh restoration

Many marshes show signs of degradation due to fragmentation, lack of sediment inputs, and erosion which may be exacerbated by sea level rise and increasing storm frequency/intensity. As a result, resource managers seek to restore marshes via introduction of sediment to increase elevation and stabilize the marsh platform. Recent field observations suggest the rapid formation of iron sulfide (FeS) materials following restoration in several marshes. To investigate, a laboratory microcosm study evaluated the formation of FeS following simulated restoration activities under continually inundated, simulated drought, and simulated tidal conditions. Results indicate that FeS horizon development initiated within 16 days, expanding to encompass >30% of the soil profile after 120 days under continuously inundated and simulated tidal conditions. Continuously inundated conditions supported higher FeS content compared to other treatments. Dissolved and total Fe and S measurements suggest the movement and diffusion of chemical constituents from native marsh soil upwards into the overlying sediments, driving FeS precipitation. The study highlights the need to consider biogeochemical factors resulting in FeS formation during salt marsh restoration activities. Additional field research is required to link laboratory studies, which may represent a worst case scenario, with in-situ conditions.

Insight into the Nature of Iron Sulfide Surfaces During the Electrochemical Hydrogen Evolution and CO2 Reduction Reactions.

Greigite and other iron sulfides are potential, cheap, earth-abundant electrocatalysts for the hydrogen evolution reaction (HER), yet little is known about the underlying surface chemistry. Structural and chemical changes to a greigite (Fe3S4)-modified electrode were determined at -0.6 V versus standard hydrogen electrode (SHE) at pH 7, under conditions of the HER. In situ X-ray absorption spectroscopy was employed at the Fe K-edge to show that iron-sulfur linkages were replaced by iron-oxygen units under these conditions. The resulting material was determined as 60% greigite and 40% iron hydroxide (goethite) with a proposed core-shell structure. A large increase in pH at the electrode surface (to pH 12) is caused by the generation of OH- as a product of the HER. Under these conditions, iron sulfide materials are thermodynamically unstable with respect to the hydroxide. In situ infrared spectroscopy of the solution near the electrode interface confirmed changes in the phosphate ion speciation consistent with a change in pH from 7 to 12 when -0.6 V versus SHE is applied. Saturation of the solution with CO2 resulted in the inhibition of the hydroxide formation, potentially due to surface adsorption of HCO3-. This study shows that the true nature of the greigite electrode under conditions of the HER is a core-shell greigite-hydroxide material and emphasizes the importance of in situ investigation of the catalyst under operation to develop true and accurate mechanistic models.

Are we on a path to solar cells that utilize iron?

By mass, iron is the most common element on earth and the most widely utilized metal in industry. Over 30 years of research have shown that iron is a poor choice for practical applications in solar energy conversion. Hematite and other ferric oxide polymorphs are competent for water oxidation in photoelectrochemical cells, but just barely. Photovoltaics based on iron oxide or sulfide materials are inefficient and the inclusion of even trace iron in silicon significantly lowers the efficiency of today’s commercial photovoltaics. In dye-sensitized solar cells (DSSCs), inclusion of an iron center in a dye molecule results in devices with poor efficiencies that are of no practical value.1 Iron-based materials and compounds function for light-driven electron transfer and catalysis, but just well enough to give some hope to highly optimistic scientists in academic labs. In the final analysis, iron consistently continues to disappoint and one can safely conclude that it is best to keep iron out of solar cells. Until now Harlang et al.2 found that the iron compound shown in Figure 1 harvests sunlight through most of the visible region with subsequent excited state electron transfer to a TiO2 semiconductor with efficiencies >90%. Such a breakthrough in efficiency is remarkable, particularly when one considers the decades of prior research that failed to accomplish anything even close. This breakthrough raises the question, are we on a path to solar cells that utilize iron? Before addressing this question, it is worthwhile to consider the impact an iron center has on a dye molecule.

Cr(VI)-contaminated groundwater remediation with simulated permeable reactive barrier (PRB) filled with natural pyrite as reactive material: Environmental factors and effectiveness

Permeable reactive barriers (PRBs) are efficient technologies for in situ remediation of contaminated groundwater, the effectiveness of which greatly depends on the reactive media filled. Natural pyrite is an iron sulfide material with a very low content of iron and sulfur, and a mining waste which is a potential material for Cr(VI) immobilization. In this study, we conducted a series of batch tests to research the effects of typical environmental factors on Cr(VI) removal and also simulated PRB filled with natural pyrite to investigate its effectiveness, in order to find a both environmentally and economically fine method for groundwater remediation. Batch tests showed that pH had the significant impact on Cr(VI) removal with an apparently higher efficiency under acidic conditions, and dissolved oxygen (DO) would inhibit Cr(VI) reduction; a relatively high initial Cr(VI) concentration would decrease the rate of Cr(VI) sorption; ionic strength and natural organic matter resulted in no significant effects on Cr(VI) removal. Column tests demonstrated that the simulated PRB with natural pyrite as the reactive media was considerably effective for removing Cr(VI) from groundwater, with a sorption capability of 0.6222mg Cr per gram of natural pyrite at an initial Cr(VI) concentration of 10mg/L at pH 5.5 in an anoxic environment.

Critical coagulation in sulfidic sediments from an east-coast Australian acid sulfate landscape

Sulfidic clays are agriculturally and environmentally important. In this work we examine the impacts of electrolytes and pH on the behaviour of colloidal clay mineral particles extracted from such sediments. The distribution of ferrous iron released by pyrite oxidation, aluminium by acidic weathering and cations in soils and pore waters in the field are reported. The behaviour of open-structured sulfidic colloidal clay mineral particles in response to changes in solution ionic composition were studied; (i) to evaluate the effects of natural oxidation of iron sulfide material in pedogenic development, and (ii) to investigate the response of these sediments to changes in pore water ionic composition as an option for soft sediment engineered dewatering. Photon correlation spectroscopy (PCS) was used to quantify these effects. As expected, Mg 2+ and Ca 2+ were more effective in inducing coagulation of the colloidal clay mineral particles than Na +; however, the effect was more pronounced than theoretically expected according to DLVO theory. Comparing the presence/absence of protons in cation saturated experiments showed new evidence for the formation of H-colloidal clay mineral particle complexes that resist competitive cation exchange. The critical concentrations of acidic cations required for mass rapid aggregation in these experiments is comparable to the pore water composition within the soil profile where structural collapse has already occurred.

The Adsorption of Heavy Metals by Tochilinite, an Iron Sulfide Material Produced by Chemical Precipitation: Analysis Using a Simple Theory of Chemisorption

This paper describes the adsorption of heavy metals Cd, Pb, Cu, and Zn by a tochilinite‐like material composed of alternating layers of Fe1−xS and Fe(OH)2. The layers are thin, being of atomic dimension. The material was produced by chemical precipitation together with some magnetite, Fe3O4, which renders the material magnetic. The results were analyzed with a simple chemisorption model which contained two parameters g(=mass of the heavy metal adsorbed/mass of adsorbent added) and C, a kinetic term with dimensions, l.mg−1.h−1., h is the time elapsed in hours. The fitting procedure works well with values of g>1, in some cases. However, according to the simple theory g and C should be constant independent of MA, the mass of adsorbent added: the constancy predicted was not observed. From the variation of g and C with MA the conclusion was that for a more complete understanding of the adsorption process, in addition to chemisorption adsorption‐desorption processes must be included. We wish to acknowledge the help of Mr. Harry Childs, sadly, now deceased, who funded much of this work and who financially supported RGL. We also wish to acknowledge useful conversations with Dr. G.J. Daniell (University of Southampton) on the statistical methods used in this work and S.J.P. Watson for discussions on the subject of chemisorption.

The removal of the pertechnetate ion and actinides from radioactive waste streams at Hanford, Washington, USA and Sellafield, Cumbria, UK: the role of iron-sulfide-containing adsorbent materials

In previous work the adsorption of a number of radioactive ions from solution by a strongly-magnetic iron sulfide material has been studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake is rapid and the loading on the adsorbent is high due to the high surface area of the adsorbent and because many of the ions are chemisorbed. The structural properties have been examined using high-resolution imaging and electron diffraction, by transmission electron microscopy (TEM). The magnetisation versus field and temperature, extended X-ray absorption fine-structure (EXAFS) spectroscopy, X-ray absorption near edge structure (XANES) spectroscopy and neutron diffraction have been reported previously. The surface area is of the order of 400–500 m 2 g −1, as determined by the adsorption of heavy metals, the magnetic properties, neutron scattering and transmission electron microscopy. Following the success of the biologically-generated material, Lidzey at Bio Separation Ltd. was able to produce an iron sulfide material with the tochilinite structure which has similar adsorption properties for cations, but not anions, as the biologically-generated material but the Lidzey material is considerably cheaper to produce. One of the radionuclides of particular interest is the pertechnetate ion TcO 4 −. 99 Tc is a radionuclide determining the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion which can enter the food chain. This paper examines methods by which adsorbent materials containing iron sulfide can play a part in the extraction and the safe long-term storage of many radionuclides and in particular the pertechnetate ion occuring at the Hanford Plant, Washington, USA and the Sellafield Plant, Cumbria, UK.

ADSORPTION OF RADIOACTIVE METALS BY STRONGLY MAGNETIC IRON SULFIDE NANOPARTICLES PRODUCED BY SULFATE-REDUCING BACTERIA

The adsorption of a number of radioactive ions from solution by a strongly magnetic iron sulfide material was studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake was rapid and loading on the adsorbent was high due to the high surface area of the adsorbent and because many of the ions were chemisorbed. The structural properties were examined with high-resolution imaging and electron diffraction by transmission electron microscopy. The adsorbent surface area was determined to be 400–500m2/g by adsorption of heavy metals, the magnetic properties, neutron scattering, and transmission electron microscopy. The adsorption of a number of radionuclides was examined at considerably lower concentration than in previous work with these adsorbent materials. A number of ions studied are of interest to the nuclear industry, particularly the pertechnetate ion (TcO4 −). 99Tc is a radionuclide thought to determine the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion, which can enter the food chain. This bacteria-generated iron sulfide may provide a suitable matrix for the long-term safe storage of the pertechnetate ion. Also, because of the prevalence of the anaerobic sulfate-reducing bacteria worldwide and, in particular, in sediments, the release of radioactive heavy metals or toxic heavy metals into the environment could be engineered so that they are immobilized by sulfate-reducing bacteria or the adsorbents that they produce and removed from the food chain.

Nanosized strongly-magnetic bacterially-produced iron sulfide materials

Using sulfate-reducing bacteria and a novel bioreactor strongly magnetic iron sulfide material has been produced. TEM studies reveal that a substantial fraction of the material consists of particles of a few nanometres in diameter. Normal X-ray diffraction showed no lines. Neutron scattering revealed some Bragg peaks and peaks in the radial distribution which may be associated with the results from the extended X-ray absorption fine structure (EXAFS). At small angles the neutron scattering revealed that a large fraction of the sample had particle diameters of the order of 2 nm. EXAFS gave results consistent with the neutron scattering. The trapped magnetisation was monitored as the temperature was slowly increased from 4.2 K. 75% of the trapped flux was lost between 4.2 and 20 K. Some particles remained blocked at 300 K showing hysteresis, but with an applied field greater than 1 T the magnetisation was linear with the field. This material is an excellent adsorbent for many metal ions.

Characterization of lacustrine iron sulfide particles with proton‐induced X‐ray emission

Black particles, collected by filtration (1.2‐µm pore size) from the anoxic waters of a soft‐water lake, were examined by a scanning proton microprobe which permitted quantitative elemental analysis by proton‐induced X‐ray emission (PIXE) and Rutherford backscattering (RBS). There was a uniform distribution of sulfur across the filter, but Fe, and to a lesser extent, Mn, was localized in ∼5‐µm‐diameter clusters. Elemental analysis with 1‐µm‐diameter beams revealed that the Fe clusters were mainly comprised of iron oxides. Iron sulfide material not in the Fe clusters had stoichiometric proportions of Fe1.0S0.60P0.60Ca0.24K0.14. Although a purely biogenic origin for P, Ca, and K cannot be ruled out, the composition is consistent with the particles originating as authigenic iron oxides which react with sulfide as they sink through the water column. The iron sulfide particles are richer in Cu (4,000 ppm) and Zn (6,000 ppm) than the iron oxides, suggesting that these elements are also concentrated as their insoluble sulfides. The coexistence of iron oxides and sulfides indicates that either the supply of sulfide is limiting or that some iron oxide particles are unreactive.

Case Study of a Multiple Sand Waterflood, Hewitt Unit, OK

Summary Synthetic two-component mixtures (uraninite and iron sulfide) as well as native uranium ores obtained from Texas and Wyoming have been examined. Physical/chemical ore properties are correlated with observed laboratory leach response. Data show a large inherent selectivity of oxidant for uranium in the early stages of a leach period. Uranium head grade was found to increase in a nearly linear fashion with hydrogen peroxide concentration in the leach solution. As uranium in the ore is depleted, uranium response decreases and the oxidant serves mainly to leach iron sulfide gangue material. Introduction Uranium historically has been mined by two methods, open pit (strip) or underground shaft mining. These two methods require high-grade uranium deposits to justify the large investment of personnel and material required to process the uranium into saleable form. New reserves of high-grade uranium ore are not being discovered in large quantities, indicating the need to locate new types of uranium deposits to fill future demands of the nuclear power industry. New sources of uranium exist in the form of low-grade ore deposits approximately 60 to 600 m below ground level. Recovery of some of these low-grade deposits became economically feasible when the price of uranium increased in the early 1970's. It is too costly, however, to mine these uranium deposits by conventional techniques (i.e., open pit or underground shaft), so a new mining method was developed. This new method is known as in-situ leaching or solution mining and involves selective leaching of the uranium from the ore deposit by use of a special solution injected into the ore body. Ore body composition and leach solution chemistry have a large effect on uranium recovery and are investigated in this study. Chemistry Uranium present in an ore body is generally in the reduced tetravalent (U+4) state and first must be oxidized to the more soluble hexavalent (U+6) state before it can be leached. Various oxidants are available, with hydrogen peroxide and molecular oxygen being the most widely used in commercial practice. Aside from uranium, an ore body contains other oxidant-consuming species such as pyritic iron sulfides and carbonaceous material (Table 1). Uranium leach chemistry can be described best by the following equations, with hydrogen peroxide (H2O2) as oxidant. (1) (2) (3) (4) (5) Eqs. 1 and 2 describe uranium oxidation and solubilization, respectively. Oxidant is added to a leach solution composed of either sodium or ammonium carbonate, and is injected into the ore body. Dissolved uranium is transported through the ore body to the recovery wells in the form of a uranyl carbonate complex. Eqs. 1 through 5 show that more oxidant can be consumed by oxidation of the iron sulfide and carbonaceous gangue materials than by uranium itself. JPT P. 937^