Iron Surface Research Articles

Study on inhibition effect and mechanism of sodium humate in hematite reverse flotation

The inhibitor can improve the hydrophilicity of minerals and prevent minerals from interacting with collectors. It plays an important role in the reverse cation flotation of iron ore, and it has become the focus of current research to find efficient, environmental friendly and cheap inhibitors. Sodium humate (NaHA) is a product extracted from weathered Lignite by means of biodegradation and organic decomposition. In this study, this new inhibitor NaHA was used to separate hematite and quartz. The results of micro-flotation showed that an appropriate concentration of NaHA could selectively inhibit hematite and realize the effective separation of quartz and hematite. Zeta potential and adsorption measurement results showed that after treatment by NaHA, the negative shift of zeta potential of hematite was more obvious, and could prevent the further adsorption of dodecylamine (DDA). The adsorption capacity of NaHA on hematite surface was much greater than that on quartz surface. FTIR results showed that there was chemisorption of NaHA on the surface of hematite but no on the quartz. XPS analysis again confirmed that NaHA may adsorb on the surface of hematite through coordination with surface iron.

Dissolution of hydrogen in metals and casting alloys

Thermodynamic calculations have shown that hydrogen from atmospheric water vapors can penetrate aluminum, iron and copper, especially into their melts. Hydrogen atoms in these metals are in free and adsorbed states. Strong and dense oxide films on the surfaces of aluminum, iron and copper significantly reduce the solubility of hydrogen in these metals. Copper and iron nanocrystals more actively adsorb atomic hydrogen than aluminum nanocrystals. This is one of the main reasons for the weak solubility of hydrogen in aluminum and the large desorption of hydrogen atoms in the crystallization of aluminum compared to iron and copper.

Characterization of mechanical properties of TaC/Fe composite layer on gray cast iron by using nano-indentation

Abstract A TaC/Fe composite layer was prepared on a gray cast iron surface by using the interfacial reaction technique. The phase composition, microstructure and crystal structure of TaC/Fe composite layer were analyzed with X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The hardness and elastic modulus of TaC/Fe composite layer were examined by nano-indentation testing. The plastic deformation behavior of TaC/Fe composite layer was characterized with the index of creep stress. The results demonstrated that the intrinsic hardness and elastic modulus of TaC/Fe composite layer were 21 GPa and 413 GPa, respectively. During nano-indentation testing, the plastic deformation resistance of TaC/Fe composite layer decreased with the increase in load, while the plastic deformation resistance decreased as the loading rate rose.

Visualization of Hydrogen Penetration Generated in an Atmospheric Corrosion and a Crevice Corrosion

Hydrogen could form in the corrosion reaction and sometimes causes hydrogen-related deterioration of steel. Spatial distribution of hydrogen penetration in steels has been observed using a photocurrent mapping method. In this method, hydrogen penetrated from the backside of the steel sheet formed by the cathodic polarization or corrosion reaction causes an enhancement of photocurrent intensity under the photo-irradiation to the passive film in the anodic biased condition. This photocurrent enhancement may be provided by the photo-generated holes that oxidize hydrogen atoms efficiently on the passive film surface. This work conducted hydrogen penetration mapping using a photo-charge mapping method newly developed for rapid mapping measurement. In this method, a polarization current during single UV-light pulse irradiation was integrated to obtain the charge Q a, and then a charge Q b during the irradiation was subtracted to obtain a photo-charge Q PC = Q a-Q b for a single pulse. This process was performed by the electronics circuit controlled by the computer. Combination of pulse system and X-Y galvano-mirror-scanning device for a light beam emitted from pulse UV (405 nm, 0.2 W) pulse laser, rapid photocharge mapping was achieved, e.g., 24 s for 40 x 40 = 1600 pixel map. In the experiments, a Devanathan-type cell composed of a top cell of a humidity control room and a bottom electrochemical cell was constructed. A UV laser beam was induced to the bottom cell via a quartz window to scan the bottom iron surface. Fig. 1 shows an example of the time-transition of photocharge maps measured for an iron sheet. In the experiment, a droplet of NaCl solution was put on the surface, and the humidity of the top cell was changed to wet/dry/wet conditions. In the figure, a droplet grew with absorbing moisture at 48 ks, rust expanded and precipitated in the droplet at 131 ks, dried to form rust at 668 ks, and soaked again at 534 ks. In this process, penetration of hydrogen was observed at the bottom face. Initially, hydrogen appeared only at the center of the droplet and then expanded to the lateral direction by increasing the photocharge. Fig. 1. Time-transition of top images of an iron sheet (0.1 mmt) with a single NaCl solution droplet and photocharge maps measured for the bottom side of the iron sheet polarized at 0.7 V vs. Ag/AgCl in pH8.4 borate solution. Figure 1

Corrosion Behaviour of an Epoxy Resin Reinforced with Aluminium Nanoparticles

During exploitation, the properties of the epoxy coating deteriorate and therefore, it is necessary to modify it with metal particles. In this paper, spherical aluminium nanoparticles (Al NP) of 100 nm with 99.9% purity were used to modify the epoxy coating for the better corrosion protection of grey cast iron. Pure Al has a high corrosion resistance and can form a thin protective film that prevents its further oxidation, thus, becoming inert and environmentally friendly. To examine these facts, different concentrations (0.5, 0.75, 1.0, 3.0, and 6.0 wt.%) of Al nanoparticles were dispersed in the epoxy coating. The surface of the modified nanocomposite coating was analysed using scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Furthermore, the physical properties such as colour, thickness, hardness, and adhesion to the cast iron surface were tested as well. The same properties were tested by exposing the sample plates to corrosive conditions in the climate chamber. Their anticorrosion properties were investigated using electrochemical impedance spectroscopy (EIS) by their immersion in 3.5 wt.% NaCl solution as a corrosive medium. The coating with 0.75% Al NP showed the best corrosion resistance after 10 days of exposure in salt water, while the sample with 1.0% Al NP showed the best corrosion resistance after exposure to the icing/deicing process.

Effect of multi-component gases on the behavior and mechanism of carbon deposition in hydrogen-rich blast furnaces

Hydrogen-rich blast furnace is considered an advanced technology in the iron and steel industry for reducing carbon emissions at the source. The CO utilization is instead reduced due to the severe carbon deposition behavior after hydrogen enrichment. This paper quantitatively investigated the effect of CO–H2–H2O–N2 multi-component on carbon deposition behavior, and a formation mechanism of deposited carbon was proposed finally. The results revealed that the optimum temperature range for carbon deposition was about 470–900 °C, and the maximum rate of carbon deposition was reached at 550–700 °C. At 600 °C, the carbon deposition rate for 100%CO and 40%CO–60%N2 were 0.54 g/d and 0.13 g/d, respectively. The aggravating effect of H2 to carbon deposition was 5.2 times that of H2O. Whereas the carbon deposition will be constrained in low CO and high H2 environment. The SEM showed that the morphology of the deposited carbon was filamentous, its formation mechanism on the iron surface is: (a) Adsorption of gases on the iron surface, (b) Formation of Fe3C layer, (c) Deposition of graphite layer, (d) Decomposition of Fe3C layer, (e) Formation of Fe3C–Fe + C (diss.) catalytic particles, (f) Formation of filamentous carbon, (g) Carbon activity in metallic Fe-filamentous carbon.

Fabrication and Characterization of Bimetal Sulfide Hybrid Ag/S-ZVI for Dechlorination of Trichloroethylene

Sulfidated and bimetal modification can improve the reactivity and selectivity of zero-valent iron in contaminant removal. However, previous studies were focused on unilateral material approaches. In this article, a new hybrid composite Ag/S-ZVI was prepared by doping elemental silver on surface of sulfidated nanoscale zerovalent iron (S-nZVI). The results of X-Ray Diffraction (XRD), energy dispersive spectrometer (EDS) and X-ray Photoelectron Spectroscopy (XPS) indicated Ag was dispersed on the surface of S-nZVI. Scanning electron microscope (SEM) images displayed Ag/S-ZVI was irregular clusters with rough surfaces, small agglomeration, and quasi-spherical in shape. The removal of TCE by Ag/S-ZVI was 90.4% within 20 min. The reaction rate constant <i>K<sub>obs</sub></i> of Ag/S-ZVI was 2.59 times or 1.85 times of nZVI or S-nZVI, respectively. Cycling experiments showed that Ag/S-ZVI had good recycling ability, and the removal rate of TCE reached 72.6% at the third cycle. The addition of Ag<sup>+</sup> makes S-nZVI as an abundant and efficient source of reducing electrons. The Fe<sup>0</sup> core can break C-Cl bonds by releasing electrons and the surface layer of Ag favors the transfer efficiency of electrons. Such study provides an efficient and robust ternary system for the remediation of TCE in groundwater.

Pencil graphite supported nano zero-valent iron for removal of levofloxacin from aqueous solution: Effects of pH, kinetic and biological activity

A highly efficient, and potentially recyclable antibacterial composite was prepared in an efficient simple process. Antimicrobial levofloxacin (LEV) was used to functionalize the surface of nano zero-valent iron (Fe0) supported by pencil graphite (PG). The surface morphology, elemental composition, particle size, and removal efficiency of the PG-Fe0 composite were confirmed by UV, FTIR, EDX, SEM, TEM, and XRD techniques. The potential influence of pH, adsorbate concentration, contact time, and temperature on the removal efficiency of LEV by the magnetic composite (PG-Fe0) from an aqueous solution was investigated. The well-known established models were used to examine the adsorption isotherms, and the results showed that the kinetic adsorption data fit well with the pseudo-second-order model, with the highest removal efficiency achieved from pH 5–7 (85%). The maximum adsorption capacity qmax on the surface of Fe0-PG for LEV was obtained using the Langmuir isotherm at pH 6.5 (66.3 mg/g) and pH 8 (11.4 mg/g). All adsorption thermodynamic parameters at pH 6.5 suggested a chemisorption endothermic natural process ΔHo(44.4 kJ/mol), and the negative value of free Gibbs energy indicated a spontaneous process at an ambient temperature. Furthermore, the removal efficiency of the PG-Fe0 composite was better than that of the Fenton-like catalyst performance for both Fe0 and PG-Fe0. Reusability and antibacterial activity of adsorbed LEV on the surface of PG-Fe0 were investigated against various types of gram-positive bacteria; (E. faecalis, S. epidermidis, and S. aureus) and gram-negative; (E. coli, K. pneumonia, and P. Mirabilia) via agar well diffusion method. Finally, the magnetic feature of the PG-Fe0-LEV composite has numerous potential for recovery and reuse.

Investigation of graphite formation in metal matrix

A new way of preparing graphite/silicon carbide-reinforced metal composite materials is presented. SiC and pure iron diffusion couple were heated to 720 ℃ and held at such temperature for 60 s to prove the concept. The experimental result shows that a graphite layer successfully forms on the surface of pure iron. The kinetic simulation was carried out using Thermal-Calc software, showing potential graphite formation in an iron matrix. The simulation result indicates that graphite can also form inside an iron matrix within 60 s at 720 ℃.

Performance and interaction mechanism of a new highly efficient benzimidazole-based epoxy resin for corrosion inhibition of carbon steel in HCl: A study based on experimental and first-principles DFTB simulations

Thanks to their excellent properties, epoxy resins are the first choice for many engineering applications. In this regard, herein, a new epoxy resin, namely 1-(oxiran-2-ylmethyl-1H-benzo[d]imidazole (BIZ epoxy), was synthesized and characterized by nuclear magnetic resonance (1H, 13C NMR) and Fourier transform infrared-attenuated total reflection (FTIR-ATR)) techniques. The corrosion inhibition properties of prepared epoxy resin for carbon steel (CS) in 1.0 mol/L HCl were evaluated using electrochemical and scanning electron microscope (SEM) techniques. Furthermore, reactivity and interaction mechanisms between epoxy resin molecule and the iron surface were investigated using quantum chemical parameters (QCPs) and Density-Functional Tight-Binding (DFTB). Electrochemical studies by potentiodynamic polarization curves (PPC) and electrochemical impedance spectroscopy (EIS) showed that the BIZ epoxy acted as a barrier against the acid corrosion of CS with an inhibition efficiency of 93 % at 1 mmol/L. The adsorption of BIZ epoxy followed the Langmuir adsorption isotherm and was found to be a physicochemical process. The SEM analysis showed a significant difference in surface morphology of CS after inhibition due to the formation of a protective barrier. DFTB simulation of BIZ epoxy – Fe(110) surface revealed the formation of a chemical bond and several long-range van der Waals interactions. The projected density of states (PDOS) of isolated and adsorbed systems confirmed the physicochemical nature of interactions between inhibitor molecule and Fe(110) surface.

Special direct route for efficient transfer hydrogenation of nitroarenes at room temperature by monatomic Zr tuned α-Fe2O3

Determining the route of a heterogeneous catalytic reaction is an important step in studying the reaction mechanism as well as improving reaction activity. As for the widely reported transfer hydrogenation of nitroarenes to aniline, many reported works have made simple judgements about the reaction route based on the “direct route” and “condensation route” proposed by Haber in 1898. Herein, detailed mechanistic experiments and DFT calculations helped us identify a special direct reduction route that goes through Ph-NO2 → Ph-NHOH → Ph-NH2 without the widely recognized Ph-NO intermediate for the transfer hydrogenation of nitroarenes to anilines by monatomic Zr tuned α-Fe2O3. In this catalytic system, Zr0.025Fe0.975Oy-350 can achieve complete transfer hydrogenation of nitroarenes at room temperature, where the parent α-Fe2O3 is inactive. Accompanying spectroscopic characterizations and calculations illustrate that the incorporation of Zr into the crystal lattice of α-Fe2O3 can effectively reduce the electron cloud density of surface iron species. The resulting special Fe(3+α)+-O(2+β)--Zr(4-γ)+ structure has greatly enhanced Lewis acidity, that promotes the decomposition of N2H4·H2O to form active [H] for the reduction of nitroarenes. Moreover, the structure is also beneficial for the adsorption of nitroarene with weakening of the NO bond. The present work can be extended to the application of non-noble metal oxides in the transfer hydrogenation of nitrobenzene under mild condition, and provides a significant method for exploring the reaction process of a heterogeneous catalytic reaction.

Acidithiobacillus ferrooxidans and mixed Acidophilic microbiota oxidation to remove sulphur impurity from iron concentrate

This study reports the bacterial properties of mixed Acidophilic microbiota with sulfur as electron donor and Acidithiobacillus ferrooxidans (A. ferrooxidans) with FeS2 as electron donor and conducted microbial desulfurization experiments. The results showed that mixed Acidophilic microbiota and A.ferrooxidans could effectively reduce the sulfur content in iron concentrate, with the desulfurization efficiency of 79.8 % and 45.7 % in 30 days. And the recovery rates were above 90 % and 88 % respectively. The results of the Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) showed that both bacteria oxidized the iron concentrate and removed the sulfur-containing impurity from the surface of the ore sample. According to the enrichment of elemental phosphorus on the sulfur of the ore sample, it can be deduced that the bacteria were oxidized. After the leaching of A.ferrooxidans, it was found that jarosite was generated, which was consistent with the conclusion of Stereomicroscope morphological observation. Based on X-ray photoelectron spectroscopy analysis, it was concluded that mixed Acidophilic microbiota could reduce the deposition on the surface of iron concentrate after the leaching of sulfate and improve the bioleaching efficiency. The conversion route of sulfur was identified to be from S2-/S22- to Sn2-/S0, and finally SO42-. In conclusion, a model for the oxidation of iron concentrate by A.ferrooxidans and Mixed Acidophilic Microbiota during bioleaching has been proposed.

To the study of economic activities of the population of the Saka period in Central Kazakhstan (on the materials of traceological studies)

The Tasmola Culture of Central Kazakhstan, dated to the 8th–5th centuries BC, was discovered more than half a century ago by M.K. Kadyrbaev. He studied dozens of kurgans, on the materials of which he characterized the mortuary rites and funerary equipment of the new culture at a high professional level. On the basis of the materials from the burial sites, he for the first time considered the features of the economic activity of the population of the Saka period in Central Kazakhstan. Recent materials, including those obtained from the settlements, make it possible to largely extend the existing conclusions and assumptions of those years. At the settlement of Abylai, located in the territory of the Karaganda Region of the Republic of Kazakhstan, six seasons of archaeological excavations were carried out in 2016–2021. First results of the traceological analysis of stone tools from this site have already been published by the authors. In this paper, we report the results of the traceological study of a new series of stone tools from the Abylai settlement. In 2021, 254 stone objects were examined, functions of 202 of which were determined. As the analysis showed, 185 tools were used in various economic areas. The remaining 15 items were identified as kitchen utensils; there was also one mortar for grinding paints and one small altar (‘credence’), which is very often found in the burials of this culture. The 185 tools are divided into 5 classes, each of which belongs to a certain area of economic activity (ancient industries). Among those, 92 articles (49.73 % of the total number) are tools for the earthworks. Fifty articles (27.03 %) belong to the class of grinding tools. These are pestles and upper and lower grindstones, which were used for grinding plant products. Next 26 tools (14.05 %) were used in the processing of skins (tanning industry). Thirteen tools (7.03 %) were used in metalworking, including the work with iron products. Four tools (2.16 %) were used to process bone and wood. Among the results obtained, of a particular importance are the finds of numerous hoes and grating tools, as well as tools for metalworking, on which traces of iron surface are clearly identified. In addition to the whetstones, used for dressing knives and other iron objects, the new series of tools contains stone anvils, on the working surface of which some iron scale preserves.

Visualization of Coupling Current and Immersion Potential of Iron Surface Corroding Beneath the Ice in the Temperature Cycling under the Freezing Point

A test specimen, comprising 100 iron wires of 1 mmφ diameter arranged in a 10 × 10 matrix, was exposed to temperature cycling between 0°C and −20°C. NaCl solution (0.1 wt%) was dropped on the surface to form an ice droplet, and the coupling current of each iron electrode against the other 99 electrodes was measured sequentially to obtain a coupling current map. The average coupling current of 100 electrodes varied with temperature cycling. The coupling current increased at a relative humidity > 65% in the absence of an ice droplet, which was similar to atmospheric corrosion at a room temperature higher than the freezing point. When an ice droplet exists, the coupling current increased with increasing temperature and did not depend on relative humidity. This behavior was interpreted as the formation of a thin solution layer of concentrated NaCl solution at the interface between the electrode surface and ice due to the exclusion of NaCl from the growing ice crystal of pure water. From the coupling current map, the inner area of the iron electrodes beneath the ice droplet tended to be a cathode, whereas the outer and surrounding area tended to be an anode. An open circuit potential map was also measured using a quasi-Ag/AgCl electrode placed on the specimen surface. The potential of the inner area was less noble than the outer and surrounding areas and shifted in a less noble direction with temperature. The ice droplet shrank during the temperature cycling and left rust on the surface.

Facile encapsulation of nano zero-valent iron with calcium carbonate: synthesis, characterization and application for iron remediation.

In this study, CaCO3 was used as a modifier for nano zero-valent iron (nZVI) surface to prevent rapid aggregation and effectively utilized for iron remediation from aqueous solution. Surface chemistry and morphology of CaCO3 encapsulated nZVI (CaCO3-nZVI) before and after treatment of contaminant iron solution were characterized by scanning electron microscopy-energy dispersive X-ray (SEM-EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The mechanisms of surface modification as well as iron remediation were well depicted with the help of these characterisation tools. Iron removal efficacy of 96.4% was achieved with 0.25g/L adsorbent dose for an influent iron of 0.5mg/L at pH 10 after a 3h treatment process. When the influent concentration was increased to 10mg/L, the removal capacity decreased to 92.1%. The study demonstrates that CaCO3 and nZVI in the encapsulated nanoparticle have a significant synergistic effect. The pseudo-second- order reaction kinetics and Freundlich isotherm model correctly portrayed the experimental data for iron removal by CaCO3-nZVI. The CaCO3-nZVI is a viable option for iron removal from various aqueous media due to its facile preparation, high iron removal capability, and reusability.

Increasing wear resistance of the protective bush-ing of the centrifugal pump made of gray cast iron by chemical-thermal treatment

Problem. The weak link that reduces the warranty time of centrifugal pumps is a unit that includes protective bushings and seals. The purpose of the bushings is to protect the rotor shaft from erosion, corrosion and wear. The bushing works under conditions of abrasive wear by elements of the seal packing and abrasive particles entering the liquid pumped by the pump. Due to accelerated surface wear, cast iron protective bushings do not satisfy the requirements service life. Goal. The purpose of the work is to increase wear resistance of pump parts made of gray cast iron by chemical and thermal treatment. Method. Metallographic studies of the structure were performed under a UIT MicroMet-D-101 microscope. Wear is studied using the roller-pad method on a friction machine. Sulfocyanation of cast iron samples was carried out in molten salts (K2CO3, CO(NH2)2, Na2S at 560°С at the bottom of the bath. Results. In the cast state, the microstructure of gray cast iron consists of ferrite, pearlite, double phosphide eutectic and lamellar graphite inclusions. The influence of exposure time during sulfocyanation in a bath with molten salts on the structure and properties of the formed surface layer was studied. The exposure was carried out for 2 hours, 3 hours 30 minutes and 6 hours. After exposure in the bath, a thin carbonitride layer is formed on the surface of the cast iron, and a layer consisting of iron sulfide is formed on top. Conducting wear tests showed that sulfocyanation increases the wear resistance of gray cast iron. An increase in the wear resistance of cast iron is provided by a hard carbonitride layer, and good workability – by a layer of iron sulfides, which acts as a lubricant. Scientific novelty. Increasing the exposure time during sulfocyanation in the bath for more than 3 hours 30 minutes does not affect the thickness of the carbonitride layer. Practical significance. As an optimal mode of sulfocyanation, exposure for 3 hours 30 minutes can be recommended, which provides a 4.8-fold increase in wear resistance.

Experimental, DFT and Theoretical Corrosion Study for 4-(((4-ethyl-5-(thiophen-2-yl)-4H-1,2,4-triazole-3-yl)thio)methyl)-7,8-dimethyl-2H-chromen-2-one

In this work, 4-(((4-ethyl-5-(thiophen-2-yl)-4H-1,2,4-triazole-3-yl)thio)methyl)-7,8-dimethyl-2H-chromen-2-one was synthesized by acetone-mediated condensation of 4-ethyle-5-(thiophen-2-yl)-4H-1,2,4-triazole-3-thiol and 4-(chloromethyl)-7,8-dimethyl-2H-chromen-2-one. The molecule results (3) were experimentally characterized using FT-IR, 1H-, and 13C NMR spectroscopy. Density Functional Theory (B3LYP/cc-pVDZ) was used to investigate the ideal molecule structure, vibrational frequencies, and 1H with 13C NMR (theoretically) chemical shifts. Theoretical and experimental spectroscopy results were compared and agreed with each other, which indicated the validity of the used developed molecular structure. The Dipole moment, hardness, softnes, electronegativity, electrophilicity index, nucleophilicity index, and chemical potential as electronic structural parameters linked to corrosion inhibition efficacy were investigated for the prepared compound. Furthermore, the fraction of transferred electrons was calculated to determine the interaction between the iron surface and organic molecules. The results indicated a favorable relationship between organic-based corrosion inhibitors and quantum chemical parameters processes. The corrosion inhibitors' behavior can be predicted without the need for experimental investigation.

Performances and enhanced mechanisms of nitrogen removal in a submerged membrane bioreactor coupled sponge iron system.

Sponge iron is a potential material for nitrogen removal, but lack of a study about nitrogen removal in a membrane bioreactor (MBR) coupled with sponge iron. The performances and mechanisms of nitrogen removal of SI-MBR were investigated and compared it with that in GAC-MBR. The results showed that the average rate of organic matter removal in the SI-MBR was 92.74%, which was higher than that in the GAC-MBR (87.48%). And the average effluent NO2--N and NO3--N concentration in the SI-MBR (0.02mg/L and 3.73mg/L) was lower than that in the GAC-MBR (0.05mg/L and 7.51mg/L). Meanwhile, the highest nitrification rate and denitrification rate was respectively 3.544±0.25 mg/(g VSS·h) and 6.643±0.2 mg/(g VSS·h) in the SI-MBR, which was higher than that (3.094±0.25 mg/(g VSS·h) and (6.376±0.2 mg/(g VSS·h)) in the GAC-MBR. Additionally, the bacterial activities (e.g., DHA activity and respiratory activity) were obviously enhanced through the iron ion from sponge iron. The bacterial community in the SI-MBR system was more richness and diverse than that in the GAC-MBR. Ultimately, the mechanisms of enhanced biological nitrogen removal with sponge iron in MBR were analyzed. On the surface of sponge iron, the DIRB and FOB could use the iron ion from sponge iron as the electron transfer to improve the nitrogen and organic removal. With sponge iron, there is not only the nitrification bacteria and heterotrophic denitrifying microorganism enriched, but also the autotrophic denitrifying bacteria abounded obviously. The autotrophic denitrifying bacteria could use Fe(II) as an electron donor to achieve denitrification and enhance the nitrogen removal.

Theoretical understanding of water adsorption on stepped iron surfaces

Nanoscale zero-valent iron (nZVI) has attracted significant interest due to its high capability in groundwater remediation. Understanding the interaction between water and nZVI is essential to optimizing its performance. While stable stepped surfaces may play a unique role in nZVI during their practical applications due to their higher reactivity, the interactions between water and stepped surfaces are still rarely investigated. Here we applied density functional theory (DFT) to study the adsorption properties of water on stable stepped Fe(210) and Fe(211) surfaces with the consideration of the van der Waals correction. Our results revealed that the adsorption strength of molecular water is enhanced on surface Fe atoms with lower coordination numbers (CN). Accordingly, the water has a stronger interaction on the stepped surface after the dissociation into H and OH. The stepped surface can facilitate water dissociation by greatly reducing dissociation energy barriers. Since water adsorption and dissociation are the first stage of iron oxidation by water, our DFT results demonstrate that the water adsorption on stepped iron surface may determine the lifetime of nZVI. Our findings, therefore, suggests the passivation of stepped surface can be a practical approach to improve the performance of nZVI.

Underestimation about the Contribution of Nitrate Reducers to Iron Cycling Indicated by Enterobacter Strain.

Nitrate-reducing iron(II) oxidation (NRFO) has been intensively reported in various bacteria. Iron(II) oxidation is found to be involved in both enzymatic and chemical reactions in nitrate-reducing Fe(II)-oxidizing microorganisms (NRFOMs). However, little is known about the relative contribution of biotic and abiotic reactions to iron(II) oxidation for the common nitrate reducers during the NRFO process. In this study, the typical nitrate reducers, four Enterobacter strains E. hormaechei, E. tabaci, E. mori and E. asburiae, were utilized as the model microorganisms. The comparison of the kinetics of nitrate, iron(II) and nitrite and N2O production in setups with and without iron(II) indicates a mixture of enzymatic and abiotic oxidation of iron(II) in all four Enterobacter strains. It was estimated that 22−29% of total oxidized iron(II) was coupled to microbial nitrate reduction by E. hormaechei, E. tabaci, E. mori, and E. asburiae. Enterobacter strains displayed an metabolic inactivity with heavy iron(III) encrustation on the cell surface in the NRFOmedium during days of incubation. Moreover, both respiratory and periplasmic nitrate-reducing genes are encoded by genomes of Enterobacter strains, suggesting that cell encrustation may occur with periplasmic iron(III) oxide precipitation as well as the surface iron(II) mineral coating for nitrate reducers. Overall, this study clarified the potential role of nitrate reducers in the biochemical cycling of iron under anoxic conditions, in turn, re-shaping their activity during denitrification because of cell encrustation with iron(III) minerals.