Fe-S Bond Research Articles

Understanding flotation processes at the atomic scale using density functional theory – A case study on adsorption of 2-Mercaptobenzothiazole on chalcopyrite and pyrite surfaces

Detailed understanding of the mechanism of interaction between collector molecules and gold and copper bearing minerals is essential to design novel ligands for enhanced recovery of these precious metals from their ores. Density functional theory calculations reveal that while the (001) and (100) surfaces of chalcopyrite undergo significant reconstruction, only rearrangement of atoms occurs on the (110), (112) and pyrite (100) surfaces. The thione tautomer of the well-known ligand, 2-mercaptobenzothiazole (MBT), adsorbed stronger on both pyrite and chalcopyrite surfaces than the thiol form, consistent with the quantum chemical descriptors such as larger EHOMO, smaller ELUMO and smaller Egap of thione. However, the adsorption of thione was stronger on pyrite due to the formation of Fe-S bonds with both the endo and exo-cyclic sulphur atoms while only one Fe-S exocyclic bond was formed on chalcopyrite. Such differential binding explains the observed selectivity of MBT towards pyrite in flotation. Insights from this work not only aid in understanding the mechanism of interaction of ligands with mineral surfaces, but also provides us a way to rationally design ligands with enhanced efficiency for selective recognition and separation of target minerals.

Estimations of Fe–N2 Intrinsic Interaction Energies of Iron–Sulfur/Nitrogen–Carbon Sites: A Deeper Bonding Insight by EDA-NOCV Analysis of a Model Complex of the Nitrogenase Cofactor

The MoFe7S9C1– unit of the nitrogenase cofactor (FeMoco) attracts chemists and biochemists due to its unusual ability to bind aerial dinitrogen (N2) at ambient condition and catalytically convert it into ammonia (NH3). The mode of N2 binding and its reaction pathways are yet not clear. An important conclusion has been made based on the very recent synthesis and isolation of model Fe(I/0)-complexes with sulfur-donor ligands under the cleavage of one Fe–S bond followed by binding of N2 at the Fe(0) center. These complexes are structurally relevant to the nitrogenase cofactor (MoFe7S9C1–). Herein, we report the EDA-NOCV analyses and NICS calculations of the dinitrogen-bonded dianionic complex Fe0–N2 (1) (having a CAr ← Fe π-bond) and monoanionic complex FeI–N2 (2) (having a CAr–Fe σ-bond) to provide a deeper insight into the Fe–N2 interacting orbitals and corresponding pairwise interaction energies (EDA-NOCV = energy decomposition analysis coupled with natural orbital for chemical valence; NICS = nucleus-independent chemical shifts). The orbital interaction in the Fe–N2 bond is significantly larger than Coulombic interactions, with major pairwise contributions coming from d(Fe) orbitals to the empty π* orbitals of N2 (three Fe → N2). ΔEint values are in the range of −61 to −77 kcal mol–1. Very interestingly, NICS calculations have been carried out for the fragments before and after binding of the N2 molecule. The computed σ- and π-aromaticity values are attributed to the position of the Fe atoms, oxidation states of Fe centers, and Fe–C bond lengths of these two complexes.

A Fe3N/carbon composite electrocatalyst for effective polysulfides regulation in room-temperature Na-S batteries

The practical application of room-temperature Na-S batteries is hindered by the low sulfur utilization, inadequate rate capability and poor cycling performance. To circumvent these issues, here, we propose an electrocatalyst composite material comprising of N-doped nanocarbon and Fe3N. The multilayered porous network of the carbon accommodates large amounts of sulfur, decreases the detrimental effect of volume expansion, and stabilizes the electrodes structure during cycling. Experimental and theoretical results testify the Fe3N affinity to sodium polysulfides via Na-N and Fe-S bonds, leading to strong adsorption and fast dissociation of sodium polysulfides. With a sulfur content of 85 wt.%, the positive electrode tested at room-temperature in non-aqueous Na metal coin cell configuration delivers a reversible capacity of about 1165 mA h g−1 at 167.5 mA g−1, satisfactory rate capability and stable capacity of about 696 mA h g−1 for 2800 cycles at 8375 mA g−1.

Desulfurization in high-sulfur bauxite with a novel thioether-containing hydroxamic acid: Flotation behavior and separation mechanism

Desulfurization is a critical problem in the efficient exploitation of high-sulfur bauxite resources. This study synthesized a novel thioether-containing hydroxamic acid (2-BTHA) by click-esterification-hydroxylamine oximation for flotation separation of pyrite from diaspore. DFT calculations indicated the functional groups of 2-BTHA were hydroxamate and thioether groups. Flotation results demonstrated 2-BTHA can effectively separate pyrite from diaspore under weak acidic conditions without adding vulcanizing agent. The UV-absorbance and surface energy tests explained introducing a thioether group improved the adsorption of Fe2+ on the collector, thus reducing its surface energy, hydrophilic index and free energy of bubble-mineral interaction, conducive to selective flotation. Zeta potential, infrared spectrum analyses and XPS further proved 2-BTHA could chemically adsorb on pyrite rather than on diaspore. It mainly reacted with pyrite surface Fe to form Fe-S bonds and five-membered hydroxamate-(O, O)-Fe rings. This research provides a potential multi-functional collector for green and efficient utilization of high-sulfur bauxite.

Synergistic desulfurization over graphitic N and enzyme-like Fe-N sites of Fe-N-C

By coupling P450 enzyme-like single-atom Fe-N center and graphitic N into N-doped carbon matrix, we precisely fabricated a robust Fe-N-C adsorbent for efficient, stable and reversible desulfurization, notably exceeding the counterparts of commercial carbon black, iron porphyrin and its hybrid. Our results disclosed that the adsorptive desulfurization mainly occurred in the atomic Fe-N and graphitic N sites via the formation of Fe-S bond between Fe3d and S3p orbitals, and N/S electrostatic interaction, respectively. The excellent desulfurization capability (34.03 mg S/g) of Fe-N-C not only originated from its effective adsorption sites, large surface area and abundant porosity, but also relied on the moderate binding strength between adsorption sites and organosulfur, which could be well optimized by modulating the pyrrolic/pyridinic N and graphitization structure, enabling its outstanding recyclability via a feasible cleavage of formed Fe-S and N-S bonds without obvious loss of activity. Moreover, Fe-N-C still maintained the 91.20% and 84.56% desulfurization selectivity, even in the presence of the interfacing substrates such as thiophene and 4,6-dimethyldibenzothiophene, respectively. This work would provide a new opportunity to metal-N-C with tunable site configuration and density for various selective adsorption and separation.

Silica improved formation of Fe(III)-S and electron-deficient effect in Fe-based catalysts to improve hydrodesulfurization

Electronic structure tuning is an effective strategy to activate transition metals. In this study, silica-promoted γ-Al2O3-supported Fe-based hydrodesulfurization catalysts of Fe species with electron loss were successfully prepared by transferring electrons from Fe to Si. The characterization results showed that the Fe-based hydrodesulfurization catalyst with the addition of silica modulated the structure and properties of the active metal, which not only improved the degree of sulfidation of the active metal but also promoted the generation of Fe(III)-S. The hydrodesulfurization rate of dibenzothiophene showed a remarkable rise from 38.4 to 83.2% at 673 K. Importantly, the formation of Fe(III)-S greatly stretched the bond length of Fe-S bonds, exhibiting an increase of approximately 21%, this facilitating the generation of coordinatively unsaturated active site. Finally, the HDS reaction performance of the Fe-based hydrodesulfurization catalysts was mainly influenced by the Fe(III)-S/Fe(II)-S ratio, with the most significant enhancement in the direct desulfurization reaction path. The results of this study provide a promising approach for the design and development of environmentally friendly and economical Fe-based catalysts in the field of clean fuels.

Nanostructured NaFeS2 as a cost-effective and robust electrocatalyst for hydrogen and oxygen evolution with reduced overpotentials

One of the biggest challenges currently in the field of energy generation and conservation is to develop a stable, scalable and cost-effective electrocatalyst with reduced overpotentials for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This unprecedented effort presents a robust, non-costly ternary alkali metal-based chalcogenide (NaFeS2) as an effective and highly active electrocatalyst prepared by the hydrothermal method. The monocrystalline nature of the NaFeS2 nanostructures was shown using SAED patterns. The differences in the atomic radii of Na and Fe favors the formation of Fe-S bonds largely contributing to the enhanced electrocatalytic activity of NaFeS2. Further, a decrease in the kinetic energy of the catalytic reaction increases the electrocatalytic property of NaFeS2. We also highlighted the contribution of the high surface area, the Fermi level and the d-orbitals of Fe in enhancing the OER. NaFeS2/NF shows a current density of 200 mA cm−2 with a small potential of 1.60 V and an overpotential of 370 mV indicating that the material possesses a remarkable electrocatalytic activity outperforming other electrocatalysts in the category. Further, by displaying a potential of −220 mV, NaFeS2/NF attained a current density of −100 mA cm−2, demonstrating a significantly improved HER performance of the electrocatalyst. Also, at a potential of −220 mV, the material exhibited a high stability at a continuous electrolysis of about 30 h. The density functional theory (DFT) calculations indicated that out of the possible adsorption sites on the NaFeS2 surface, only (010) and (100) exhibit catalytically preferential adsorption energy (EH) values, which are eventually responsible for the superior electrocatalytic activity. Finally, both the experimental studies and the DFT calculations complement each other and present NaFeS2 as a potentially promising bifunctional electrocatalyst for water splitting applications, which can be scaled-up and deployed for large-scale hydrogen productions.

DFT insights into the sulfidation mechanism of Fe-impurity smithsonite

The sulfidation-flotation of Fe-bearing smithsonite is still a challenge in practice. Currently, theoretical understandings on reagents adsorption on impurity-bearing mineral surface are still lacking. Here we first systematically investigated the adsorption of HS on perfect and Fe-impurity smithsonite (101) surfaces in the absence and presence of H2O by density-functional theory (DFT). We found Fe-impurity dramatically changed the structure and electronic properties of smithsonite surface. In the absence and presence of H2O, the adsorption energies of HS on Fe-bearing smithsonite surface were all lower than those of perfect surface. The Mulliken bond populations and DOS analysis results showed that the formed Fe-S bonds on Fe-impurity smithsonite surface were less stable than the Zn-S bonds formed on the perfect surface. Meanwhile, the competitive adsorption capacity of H2O and HS on perfect and Fe-impurity surfaces was different. The interaction of H2O and HS to TZn site on perfect surface was in the order of HS > H2O while that to TFe site on TFe-impurity surface was H2O > HS, and the adsorption of HS was depressed. Furthermore, S-OH was contained in the sulfidation product of BFe-impurity surface, and the hydrophobicity of the formed sulfidation film greatly decreased, which was also not conducive to the sulfidation-flotation.

Mesoporous sulfur-doped CoFe2O4 as a new Fenton catalyst for the highly efficient pollutants removal

Herein, mesoporous sulfurized CoFe2O4 (S-CoFe2O4) was developed and applied as a new Fenton catalyst. As a result, the sulfurization for CoFe2O4 could significantly improve the Fenton performance, compared with the non-sulfurized CoFe2O4. The enhanced removal efficiencies of pollutants in Fenton process catalyzed by S-CoFe2O4 was attributed to the elevated specific area and decreased electron transfer resistance of S-CoFe2O4. The DFT calculations further confirmed that the increased charge densities of FeS bond and CoS bond could contribute to the existences of species of Fe and Co in S-CoFe2O4 with the low valence, which were more favorable to the H2O2 activation. Furthermore, electron paramagnetic resonance (EPR) tests showed that the OH and O2− were the main generated radicals during the H2O2 activation process. This work provided a new strategy for the synthesis and application of an efficient non-precious metal Fenton catalyst.

Double bond effects induced by iron selenide as immobilized homogenous catalyst for efficient polysulfides capture

• A double bond effect based on selenide was introduced into Li-S batteries. • FeSe was applied as a host in Li-S battery for the first time. • The catalytic effect of FeSe@NC on solid–solid conversion is analyzed. The low utilization of sulfur and the shuttle effect accompanying the discharge process are the fundamental problems that hinder the development of lithium-sulfur (Li-S) batteries. Although the LiPSs loss and conversion are ameliorated by physical and chemical methods with the design of multi-functional host material structures, the problem of capacity attenuation has not been fundamentally solved. Seeking for reliable polar hosts with suitable adsorption capacity and good catalytic ability for the conversion process is still an issue with great challenge. Herein, a high-efficiency nitrogen doped carbon supported FeSe electrocatalyst derived from the carbon skeleton (FeSe@NC) is used as the sulfur host for Li-S batteries. During the discharge process, Fe-S and Li-Se bonds would be formed in pairs, thus forming a double bond effect to alleviate the shuttle effect. In particular, the FeSe@NC with good conductivity and double bond effect can catalytically accelerate capture/diffusion of polysulfides and improve the utilization of active substances from Li 2 S 2 to Li 2 S in solid-to-solid conversion. Thus, the FeSe@NC/S cathode exhibits an excellent capacity of 1087 mAh g −1 at 1C and 441 mAh g −1 at 5C. This work will inspire the optimization design of adsorption-electrocatalysis engineering of transition-metal-based composite materials for diverse applications.

Insights into the Two-Electron Reductive Process of [FeFe]H2 ase Biomimetics: Cyclic Voltammetry and DFT Investigation on Chelate Control of Redox Properties of [Fe2 (CO)4 (κ2 -Chelate)(μ-Dithiolate)

The electrochemical reduction of complexes [Fe2 (CO)4 (κ2 -phen)(μ-xdt)] (phen=1,10-phenanthroline; xdt=pdt (1), adtiPr (2)) in MeCN-[Bu4 N][PF6 ] 0.2 m is described as a two-reduction process. DFT calculations show that 1 and its monoreduced form 1- display metal- and phenanthroline-centered frontier orbitals (LUMO and SOMO) indicating the non-innocence of the phenanthroline ligand. Two energetically close geometries were found for the doubly reduced species suggesting an intriguing influence of the phenanthroline ligand leading to the cleavage of a Fe-S bond as proposed generally for this type of complex or retaining the electron density and avoiding Fe-S cleavage. Extension of calculations to other complexes with edt, adtiPr bridge and even virtual species [Fe2 (CO)4 (κ2 -phen)(μ-adtR )] (R=CH(CF3 )2 , H) or [Fe2 (CO)4 (κ2 -phen)(μ-pdtR )] (R=CH(CF3 )2 , iPr) showed that the relative stability between both two-electron-reduced isomers depends on the nature of the bridge and the possibility to establish a remote anagostic interaction between the iron center {Fe(CO)3 } and the group carried by the bridged-head atom of the dithiolate group.

Synergetic effect of spatially separated dual co-catalyst for accelerating multiple conversion reaction in advanced lithium sulfur batteries

Abstract The enhanced chemical immobilization and catalytic conversion of polysulfides (LiPS) intermediates are considered a promising solution to improve the electrochemical performance in lithium-sulfur batteries. However, the role of catalysts on catalytic mechanism of distinctive selectivity is still not understood and overlooked. Herein, a dual-functional strategy, composed of Fe3O4 nanoparticles/hierarchical porous carbon (Fe3O4/HPC) cathode and FeP/HPC modified separator, is proposed to improve anchoring and catalyzing of LiPS, ensure uniform Li2S deposition and reduce the dead sulfur. The systematic theoretical calculation reveals that the Fe3O4 has the stronger binding energy with LiPS (Li2S4 and Li2S6) due to the Fe-S bonds and Li-O bonds. The variations in the catalytic performance of Fe3O4 and FeP are due to the shifts of p band center. Especially, Fe3O4 and FeP tend to selectively catalyze the solid-liquid reaction and liquid-liquid-solid conversion, respectively. Thus, the synergistic effects of dual-catalysts in spatial separation help to achieve excellent cycling stability with an ultralow capacity decay rate of 0.083% over 1000 cycles at 1 C. Even with a high areal sulfur loading of 5.73 mg cm−2 and a cruel current density of 0.01 C, the cells can still keep a low shuttle factor of 0.08, demonstrating the effective inhibition of shuttle effect. This work offers novel insights for designing a dual-functional structure in lithium-sulfur batteries.

Insights into the selective adsorption mechanism of a multifunctional thioether-containing hydroxamic acid on separation of wolframite from fluorite

Both thioether and hydroxamate groups are excellent iron ligands. Herein, to improve the properties of hydroxamic acid and the recovery of tungsten-minerals, a surfactant containing thioether and hydroxamate groups, 2-(benzylthio)-acetohydroxamic acid (BTHA), was introduced to separate wolframite from fluorite. The properties, predicted by Density Functional Theory (DFT) calculations and Molecular Dynamics (MD), indicated that BTHA, as a multifunctional surfactant (i.e., thioether and hydroxamate groups), could enhance its hydrophobicity and selectively adsorb on the desired mineral surfaces. The experimental results of micro-flotation and contact angles confirmed BTHA had a strong collecting ability and good selectivity toward wolframite versus fluorite. The adsorption mechanism, surveyed through zeta potential, solution chemical analysis and XPS, demonstrated only electrostatic adsorption on fluorite surfaces, while chemisorption and hydrogen bonding would be produced on wolframite surfaces. The thioether and hydroxamate groups could co-absorb onto wolframite's surfaces to form FeS bonds and five-membered hydroxamate-(O, O)-Fe rings.

Piezoelectric field-promoted heterogeneous sono-Fenton performance of MoS2/α-Fe2O3 heterojunction structure

The limited FeIII/FeII cycle in iron-based heterogeneous catalysts is one of the main technical obstacles to the heterogeneous Fenton-like application. This work demonstrates the catalytic performance improvement of MoS2/α-Fe2O3 heterojunction in the Fenton-like reaction, specifically in the sono-Fenton reaction. The rate constant of degrading Acid Orange 7 (AO7) with MoS2/α-Fe2O3 heterojunction presents ca. 26.0 and 14.8 times higher than those with pristine α-Fe2O3 and MoS2 catalysts, respectively. Experiments with the addition of various scavengers demonstrated that 1O2, O2−, and OH are the dominant, sub-dominant, and least-dominant ROS in the reaction, respectively. The reaction mechanism is further proposed on account of the characterization and experimental results. MoS2 participates in the Fenton-like reaction as a catalyst; besides, the FeS bond observed at the interface accelerates the FeIII/FeII cycle by enhancing the electron transfer from Mo to Fe. Notably, ultrasonic irradiation evokes a piezoelectric potential on the surface of MoS2, which reduces the interfacial barrier height of MoS2/α-Fe2O3 heterojunction, accelerating the electron transfer through the FeS bond and thus dramatically boosting the sono-Fenton activity. These findings could provide an alternative strategy to enhance the iron-based heterogeneous Fenton catalytic reactivity.

Atomic Force Microscopy and Raman Microspectroscopy Investigations of the Leaching of Chalcopyrite (112) Surface

The aim of this study was to determine the reactivity of the chalcopyrite (112) surface under industrially relevant leaching conditions. Leaching of the chalcopyrite (112) surface was carried out at approximately pH 1 and in the presence of 0.01 M ferric or ferrous. The atomic force microscopy (AFM) and Raman microspectroscopy analyses suggested that the chalcopyrite (112) surface was relatively inert, with no formation of elemental sulfur observed over 42 days of leaching. In addition, it was found that the distribution of Fe-S and Cu-S bonds was always negatively correlated, as revealed by Raman analysis. This suggested that the breakage of the Fe-S and Cu-S bonds did not occur concurrently at a specific reaction site. The rate of variation of surface roughness, as reflected by AFM data, also suggested that leaching of the chalcopyrite (112) surface in the ferric or ferrous solution medium likely occurred more rapidly in the initial stage (fewer than seven days) than in the later stage (after seven days).

Model Complexes Elucidate the Role of the Proximal Hydrogen-Bonding Network in Cytochrome P450s.

Cytochrome (Cyt) P450s are an important class of enzymes with numerous functions in nature. The unique reactivity of these enzymes relates to their heme b active sites with an axially bound, deprotonated cysteine (a "cysteinate") ligand (chemically speaking a thiolate). The heme-thiolate active sites further contain a number of conserved hydrogen-bonds (H-bonds) to the bound cysteinate ligand, which have been proposed to tune and stabilize the Fe-S bond. In this work, we present the low-temperature preparation of five ferric heme-thiolate nitric oxide (NO) model complexes that contain one tunable hydrogen-bond to the bound thiolate ligand. We show that the presence of a H-bond has a dramatic effect in stabilizing the thiolate ligand against direct reaction with NO. This observation reinforces the important protective role of H-bonds in Cyt P450s. We further demonstrate that H-bond strength tunes thiolate donor strength, which, in turn, controls the N-O and Fe-NO stretching frequencies and hence, bond strengths. We observe a direct correlation between the Fe-NO and N-O stretching frequencies, indicative of a thiolate σ-trans effect (interaction). Here, very small changes in H-bond strength lead to a surprisingly large effect on the FeNO unit. This result implies that subtle changes in the Cys-pocket of a Cyt P450 can strongly affect reactivity. Importantly, using the Fe-NO/N-O correlation established here, the thiolate donor strength in heme-thiolate enzyme active sites and model complexes can be quantified in a straightforward way, using NO as a probe. This spectroscopic correlation provides a quantitative measure of the thiolate's "push" effect, which is important in O2-activation (Compound I formation) in Cyt P450s in general.

Mechanism for the Bio-Oxidation and Decomposition of Pentlandite: Implication for Nickel Bioleaching at Elevated pH

This work investigated the effects of Fe3+, H+ and adsorbed leaching bacteria on the bioleaching of pentlandite. Collectively, an integrated model for the oxidation and decomposition of pentlandite was built to describe the behaviors of different components in a bioleaching system. Proton ions and ferric ions could promote the break and oxidation of Ni-S and Fe-S bonds. The iron-oxidizing microorganisms could regenerate ferric ions and maintain a high Eh value. The sulfur-oxidizing microorganisms showed significant importance in the oxidation of polysulfide and elemental sulfur. The atoms in pentlandite show different modification pathways during the bioleaching process: iron transformed through a (Ni,Fe)9S8 → Fe2+ → Fe3+ → KFe3(SO4)2(OH)6 pathway; nickel experienced a transformation of (Ni,Fe)9S8 → NiS → Ni2+; sulfur modified through the pathway of S2−/S22− → Sn2− → S0 → SO32− → SO42−. During bioleaching, a sulfur-rich layer and jarosite layer formed on the mineral surface, and the rise of pH value accelerated the process. However, no evidence for the inhibition of the layers was shown in the bioleaching of pentlandite at pH 3.00. This study provides a novel method for the extraction of nickel from pentlandite by bioleaching at elevated pH values.

Synthetic Metallodithiolato Ligands as Pendant Bases in [FeIFeI], [FeI[Fe(NO)]II], and [(μ-H)FeIIFeII] Complexes.

The development of ligands with specific stereo- and electrochemical requirements that are necessary for catalyst design challenges synthetic chemists in academia and industry. The crucial aza-dithiolate linker in the active site of [FeFe]-H2ase has inspired the development of synthetic analogues that utilize ligands which serve as conventional σ donors with pendant base features for H+ binding and delivery. Several MN2S2 complexes (M = Ni2+, [Fe(NO)]2+, [Co(NO)]2+, etc.) utilize these cis-dithiolates to bind low valent metals and also demonstrate the useful property of hemilability, i.e., alternate between bi- and monodentate ligation. Herein, synthetic efforts have led to the isolation and characterization of three heterotrimetallics that employ metallodithiolato ligand binding to di-iron scaffolds in three redox levels, (μ-pdt)[Fe(CO)3]2, (μ-pdt)[Fe(CO)3][(Fe(NO))II(IMe)(CO)]+, and (μ-pdt)(μ-H)[FeII(CO)2(PMe3)]2+ to generate (μ-pdt)[(FeI(CO)3][FeI(CO)2·NiN2S2] (1), (μ-pdt)[FeI(CO)3][(Fe(NO))II(IMe)(CO)]+ (2), and (μ-pdt)(μ-H)[FeII(CO)2(PMe3)][FeII(CO)(PMe3)·NiN2S2]+ (3) complexes (pdt = 1,3-propanedithiolate, IMe = 1,3-dimethylimidazole-2-ylidene, NiN2S2 = [N,N'-bis(2-mercaptidoethyl)-1,4-diazacycloheptane] nickel(II)). These complexes display efficient metallodithiolato binding to the di-iron scaffold with one thiolate-S, which allows the free unbound thiolate to potentially serve as a built-in pendant base to direct proton binding, promoting a possible Fe-H-···+H-S coupling mechanism for the electrocatalytic hydrogen evolution reaction (HER) in the presence of acids. Ligand substitution studies on 1 indicate an associative/dissociative type reaction mechanism for the replacement of the NiN2S2 ligand, providing insight into the Fe-S bond strength.

Ab Initio molecular dynamics of the dissolution of oilfield pyrite scale using borax

Iron sulfide scales, particularly pyrite, form in oil and gas underground tubing and surface equipment thus blocking the flow of fluids and halting production. Therefore, the development of physicochemical processes for scale removal is of pivotal relevance. In this work, Ab Initio Molecular dynamics simulations have been employed to investigate the use of borax as a scale removal agent and understand the molecular level features in the dissolution of pyrite using a borax solution. Geometry analysis, radial distribution function, and near neighbor analysis tools have been used to analyze the data. The reported results show that potassium ion is preferentially bonding with the sulfur atoms in the top layer of the pyrite surface rather than with iron, thus being the predominant factor that accounts for pyrite dissolution. The KS bonds evolve dynamically exposing the whole pyrite surface. The presence of the chelating agent would prevent the formation of FeS bonds. It is proposed that borax, in conjunction with chelating agents, could be used for removing the pyrite scale and consequently boosting production in the upstream sector.

Decomposition of the binuclear nitrosyl iron complex with thiosulfato ligands in aqueous solutions: Experimental and theoretical study

In this work, transformations of the anionic binuclear tetranitrosyl iron complex with thiosulfato ligands (Na2[Fe2(S2O3)2(NO)4]·4H2O) (1) have been studied in aqueous anaerobic and aerobic solutions. Under anaerobic conditions, complex 1 was shown to undergo intramolecular isomerization, in addition to NO generation, due to embedding of the oxygen atom of the thiosulfato ligand in the Fe-S bonds. The complex becomes more stable, so its further transformation, including NO release, is unlikely. The model for the complex decomposition has been suggested, and reaction rate constants have been calculated using the kinetic modeling method.As follows from the experimental data, under aerobic conditions, complex 1 is oxidized and becomes a more effective NO donor. Due to the incorporation of the oxygen atom into the Fe-S bonds, mononuclear nitrosyl intermediates are formed, which have a typical EPR signal (g = 2.03).