Passivation Of Iron Research Articles

Synergetic effect of pyrrhotite and zero-valent iron on Hg(Ⅱ) removal in constructed wetland: Mechanisms of electron transfer and microbial reaction

Effective removal of mercury (Hg) from wastewater is significant due to its high toxicity, especially methylmercury (MeHg). Reducing of Hg(II) to Hg(0) in constructed wetlands (CWs) using iron-based materials is an effective strategy for preventing the formation of MeHg. However, the surface passivation of zero-valent iron (ZVI) limits its application. Herein, synergetic ZVI and pyrrhotite were utilized to enhance Hg removal in CWs. Results indicated that the removal of total Hg, dissolved Hg, and particulate Hg in CWs with ZVI and pyrrhotite were improved by 21.68 ± 0.76 %, 13.02 ± 0.88 %, and 22.27 ± 0.76 % compared to that with single ZVI or pyrrhotite. Pyrrhotite increased the surface corrosion of ZVI, thereby facilitating the process of iron reduction. The redox of iron promoted the generation of EPS, which could provide electrons for Hg(II) reduction. The sulfur also participates in electron transfer by driving the methylation of Hg and provides sulfides to form FeS-Hg complexes and HgS precipitation. The abundance of key enzymes that involved in iron reduction and Hg transformation was enhanced with the addition of ZVI and pyrrhotite. The synergetic of pyrrhotite and ZVI enhances the removal of Hg in CW, offering a promising technology for high-efficiency treatment of Hg.

Linear dependence of potential drop at the passive film/solution interface on film-formation potential and pH: Combining first-principles calculations with experiments

Potential drop at the oxide film/solution interface plays a critical part in numerous electrochemical processes, especially for the passivated metal-electrolyte system, affecting the passive film breakdown and the pitting initiation. There are still some controversies over the dependence of potential drop at the passive film/solution interface (φf/s) on potential and pH of electrolyte. Herein, we develop a model presenting the linear dependence of φf/s on both potential and pH, as represented by φf/s=φf/s(V=0,pH=0)0+αV+βpH. By analyzing the surface charge (i.e., point of zero charge, pHpzc) and performing first-principles calculations, we provide the insights into the effect of potential and pH on the φf/s, and into the linear relation between φf/s with pH beyond the Nernst relation that is attributed to the role of point defects in pHpzc of passive film on iron. In addition, two methods, e.g., a combination of Mott-Schottky measurement with first-principles, contact angle titration, are suggested to determine the values of α, β and φf/s(V=0,pH=0)0, respectively. The study of passivity of iron in borate buffer solutions validates our model.

Crystal structure-dependent evaluation of chloride ions resistance of iron passivation film in reinforced concrete at the nanoscale

In reinforced concrete, the passivation film refers to the spontaneous formation of an ultra-thin film of corrosion product on a metal's surface that acts as a barrier to additional chemical reactions and is extraordinarily helpful in mitigating corrosion damage. However, the Cl ions can significantly harm the completeness of the passivation film and thus facilitate the corrosion process. In view of the complexity of the passivation film composition, in this work, the Cl attack process of typical structures of passivation films (α-Fe2O3, β-Fe2O3 and γ-Fe2O3) is studied by Bonn-Oppenheimer molecular dynamics and density functional theory. It is found that the β-Fe2O3 and γ-Fe2O3 have the best and worst resistance of Cl ions, respectively. The reduced gradient density analyses indicate that the Cl ions can break chemical bonds of passivation film by creating Cl–Fe bonds. The details of binding energy and electron localization analyses prove that the rank of the strength of binding is γ-Fe2O3 > α-Fe2O3 > β-Fe2O3. Moreover, Different from the surface adsorption of α-Fe2O3 and β-Fe2O3, γ-Fe2O3 adsorbs Cl ions into the matrix, which also results in the formation of more chemical bonds. Further analyses of the density of states also confirm the bonding formation in the Cl ions attack process. This work suggests that the increase in the proportion of β-Fe2O3 in the composition of the passivation film is a potential approach for inhibiting corrosion. And also an effective method for evaluating the performance of passivation films is also proposed, especially since it is extremely difficult to evaluate given its nanometer characteristics.

Carbon dioxide and weak magnetic field enhance iron-carbon micro-electrolysis combined autotrophic denitrification

Combining iron-carbon micro-electrolysis and autotrophic denitrification is promising for nitrate removal from wastewater. In this study, four continuous reactors were constructed using CO2 and weak magnetic field (WMF) to address challenges like iron passivation and pH stability. In the reactors with CO2 + WMF (10 and 35 mT), the increase in total nitrogen removal efficiency was significantly higher (96.2 ± 1.6 % and 94.1 ± 2.7 %, respectively) than that of the control (51.6 ± 2.7 %), and Fe3O4 converted to low-density FeO(OH) and FeCO3, preventing passivation film formation. The WMF application decreased the N2O emissions flux by 8.7 % and 20.5 %, respectively. With CO2 + WMF, the relative enzyme activity and abundance of denitrifying bacteria, especially unclassified_Rhodocyclaceae and Denitratisoma, increased. Thus, this study demonstrates that CO2 and WMF optimize the nitrate removal process, significantly enhancing removal efficiency, reducing greenhouse gas emissions, and improving process stability.

Improvement strategy of citrate and biochar assisted nano-palladium/iron composite for effective dechlorination of 2,4-dichlorophenol.

Rapid passivation and aggregation of nanoscale zero-valent iron (nZVI) seriously limit its performance in the remediation of different contaminants from wastewater. To overcome such issues, in the present study, nano-palladium/iron (nPd/Fe) was simultaneously improved by biochar (BC) prepared from discarded peanut shells and green complexing agent sodium citrate (SC). For this purpose, a composite (SC-nPd/Fe@BC) was successfully synthesized to remove 2,4-dichlorophenol (2,4-DCP) from wastewater. In the SC-nPd/Fe@BC, BC acts as a carrier with dispersed nPd/Fe particles to effectively prevent its agglomeration, and increased the specific surface area of the composite, thereby improving the reactivity and stability of nPd/Fe. Characterization results demonstrated that the SC-nPd/Fe@BC composites were well dispersed, and the agglomeration was weakened. The formation of the passivation layer on the surface of the particles was inhibited, and the mechanism of SC and BC improving the reactivity of nPd/Fe was clarified. Different factors were found to influence the reductive dichlorination of 2,4-DCP, including Pd loading, Fe:C, SC addition, temperature, initial pH, and initial pollutant concentration. The dechlorination results revealed that the synergistic effect of the BC and SC made the removal efficiency and dechlorination rate of 2,4-DCP by SC-nPd/Fe@BC reached to 96.0 and 95.6%, respectively, which was better than that of nPd/Fe (removal: 46.2%, dechlorination: 45.3%). Kinetic studies explained that the dechlorination reaction of 2,4-DCP and the data were better represented by the pseudo-first-order kinetic model. The reaction rate constants followed the order of SC-nPd/Fe@BC (0.0264min-1) > nPd/Fe@BC (0.0089min-1) > SC-nPd/Fe (0.0081min-1) > nPd/Fe (0.0043min-1). Thus, SC-nPd/Fe@BC was capable of efficiently reducing 2,4-DCP and the dechlorination efficiency of BC and SC synergistically assisted composite on 2,4-DCP was much better than that of SC-nPd/Fe, nPd/Fe@BC and nPd/Fe. Findings suggested that SC-nPd/Fe@BC can be promising for efficient treatment of chlorinated pollutants.

Corrosion Potential Oscillation of Iron Electrodes in Nitric Acid

Although iron dissolves in diluted nitric acid solutions, it does not dissolve in concentrated solutions because of surface passivation. When a small amount of water is added to a concentrated solution, the dissolution and passivation of iron occur alternately, and the amount of gaseous products generated by nitric acid reduction varies in an oscillatory manner. During the corrosion process, the corrosion potential of iron oscillates spontaneously. In this study, we investigated the factors that cause oscillations in corrosion potential through electrochemical measurements using a three-electrode system and numerical simulations. The study revealed that an N-shaped negative differential resistance characteristic of iron oxidation plays a vital role in the oscillation of the corrosion potential and, simultaneously, the reduction of nitric acid results in oscillation. We considered metal corrosion has essential factors resulting in oscillatory instability. Thus, the corrosion potentials of various metals are expected to oscillate spontaneously under the appropriate conditions.

A Tale of Nickel-Iron Batteries: Its Resurgence in the Age of Modern Batteries

The nickel-iron (Ni-Fe) battery is a century-old technology that fell out of favor compared to modern batteries such as lead–acid and lithium-ion batteries. However, in the last decade, there has been a resurgence of interest because of its robustness and longevity, making it well-suited for niche applications, such as off-grid energy storage systems. Currently, extensive research is focused on addressing perennial issues such as iron passivation and hydrogen evolution reaction, which limit the battery’s energy density, cyclability, and rate performance. Despite efforts to modify electrode composition and morphology, these issues persist, warranting a deeper look at the development story of Ni-Fe battery improvements. In this review, the fundamental reaction mechanisms are comprehensively examined to understand the cause of persisting issues. The design improvements for both the anode and cathode of Ni-Fe batteries are discussed and summarized to identify the promising approach and provide insights on future research directions.

Enhanced removal of Sb(V) by iron‐spent bleaching earth carbon binary micro‐electrolysis system: performance and mechanism

AbstractBACKGROUNDIn this work, the construction of a zero‐valent iron‐loaded spent bleaching earth carbon binary micro‐electrolysis system (Fe0/SBE@C) was first developed for antimony(V) (Sb(V)) removal in water.RESULTSFe0/SBE@C at 4:1 Fe‐to‐SBE@C mass ratio can obtain satisfactory Sb(V) removal and less Fe dissolution under acid (pH 3) and neutral (pH 7) conditions. Sb(V) removal by Fe0/SBE@C accorded with a second‐order kinetic model. Activation energy of Fe0/SBE@C reaction for Sb(V) removal was 27.61 kJ mol−1. Optimal reaction conditions forecasted by the response surface method (RSM) was a dosage of 0.19 g L−1, a temperature of 45 °C and initial pH of 4.0, contributing to Sb(V) removal of 98.2%. Clearly, SO42− and Cl− (as electrolytes) had no obvious effect on Sb(V) removal; CO32−, PO43− and SiO32− showed obvious inhibition, likely due to iron passivation (pH > 10.5) and formation of precipitation (e.g., FeCO3, Fe(OH)2 and Fe2(SiO3)3); N2 atmosphere was more conducive to Sb(V) removal.CONCLUSIONSb(III) concentration in the solution was almost zero without adjusting the initial pH. It was deduced that Sb(V) removal in Fe0/SBE@C micro‐electrolysis system was probably the combined result of adsorption, coagulation and electrochemical reduction. © 2023 Society of Chemical Industry (SCI).

Reduced graphene oxide supported Fe/Ni bimetallic nanoparticles for the rapid adsorption and dechlorination of 2,4-dichlorophenol

Agglomeration and passivation of nanoscale zerovalent iron (nZVI) can result in significant decrease of reactivity with contaminants. In this paper, reduced graphene oxide supported Fe/Ni bimetallic composites (Fe/Ni@rGO) were synthesized. Electron microscopy characterization showed that the spherical Fe/Ni bimetallic nanoparticles with the size of 70–150 nm were successfully loaded on the graphene sheets and mainly distributed at the edges and folds of the graphene sheets. The agglomeration of nZVI decreased significantly and more active sites were exposed. The removal efficiency of 2,4-dichlorophenol by nZVI, reduced graphene oxide supported nZVI (Fe@rGO) composites and Fe/Ni@rGO composites were 14.4%, 71.8% and 95.0% within 180 min, respectively. The results showed that when the pH was 5–7 and humic acid concentration was 60 mg/L, the removal efficiency of 2,4-dichlorophenol was higher. According to the correlation coefficient R2, the removal of 2,4-dichlorophenol by Fe/Ni@rGO followed the pseudo second order model instead of the pseudo first order model. The anti-oxidation and cycle test showed that Fe/Ni@rGO composites had high stability and recycling value. The removal mechanism of 2,4-dichlorophenol by Fe/Ni@rGO composites was the synergistic effect of adsorption by rGO and dechlorination by Fe/Ni.

A method for using the residual energy in waste Li-ion batteries by regulating potential with the aid of overvoltage response

The value of considerable residual energy in waste Li-ion batteries (WLIBs) is always neglected. At present, "this energy" is always wasted during the discharge process of WLIBs. However, if this energy could be reused, it would not only save a lot of energy but also avoid the discharge step of recycling of WLIBs. Unfortunately, the instability of WLIBs potential is a challenge to efficient utilization of this residual energy. Here, we propose a method that could regulate the cathode potential and current of the battery by simply adjusting the solution pH to utilize 35.08%, 88.4%, and 84.7% of the residual energy for removing heavy metal ions from wastewater, removing Cr (VI) from wastewater, and recovering copper from the solution, respectively. By taking advantage of the high internal resistance R of WLIBs and the sudden change of battery current I caused by iron passivation on the positive electrode of the battery, this method could induce the response of overvoltage η (η = IR) inside the battery at different pH levels to regulate the cathode potentialµ of the battery to the three intervals. The potential ranges of the battery cathode corresponding to pH < 3.4, pH ≈ 3.4, and pH > 4 were µ > -0.47V, -0.47V < µ < -0.82V, and µ < -0.82V, respectively. This study provides a promising way and theoretical basis for the development of technologies for reusing residual energy in WLIBs.

Thermodynamic interaction and iron passivation mechanism of copper–cobalt sulfide concentrates during pressure leaching

Thermodynamic interaction and iron passivation mechanism of copper–cobalt sulfide concentrates during pressure leaching

Effect of carbon addition on the passivity of hypoeutectic high chromium cast irons.

The effect of adding C on the passivity of hypoeutectic high chromium cast iron (HCCI) was investigated in a pH 8.4 boric-borate buffer solution. The microstructure of HCCI is composed of austenite and carbide phases, whose fractions and chemical compositions are influenced by the amount of C added. Electrochemical and surface analyses revealed that the addition of C in the HCCI increased the defect densities in the n-type and p-type semiconductive oxide layers on the austenite and carbide phases, respectively.

Promotion of nitrogen removal in a zero-valent iron-mediated nitrogen removal system operated in co-substrate mode

In this study, the performance and mechanism of nitrogen removal were investigated in a zero-valent iron-mediated nitrogen removal system operated in co-substrate mode with sodium acetate as the organic carbon source. The results showed that the additional organic matter had the capacity to promote NH4+-N and total inorganic nitrogen (TIN) removal with efficiencies of 91.09% and 84.10%, and increases of 60.06% and 75.32% compared with the control group, respectively. The organic matter also stimulated the production of extracellular polymer substances that reduced the passivation and toxicity of iron to microorganisms. The ammonia oxidation activity was 2.5 times higher than that in the control group, and the anammonia oxidation activity and denitrification activity were substantially higher than in the control group with TIN removal efficiencies of 1.02 and 1.19 mgN/(gVSS·d), respectively. In addition, the organic matter increased the enrichment of the heterotrophic denitrification bacterium Diaphorobacter and facultative iron salt-based bacterium Dechloromonas.

Performance, Reaction Pathway and Kinetics of the Enhanced Dechlorination Degradation of 2,4-Dichlorophenol by Fe/Ni Nanoparticles Supported on Attapulgite Disaggregated by a Ball Milling-Freezing Process.

Attapulgite (ATP) disaggregated by a ball milling–freezing process was used to support Fe/Ni bimetallic nanoparticles (nFe/Ni) to obtain a composite material of D-ATP-nFe/Ni for the dechlorination degradation of 2,4-dichlorophenol (2,4-DCP), thus improving the problem of agglomeration and oxidation passivation of nanoscale zero-valent iron (nFe) in the dechlorination degradation of chlorinated organic compounds. The results show that Fe/Ni nanoparticle clusters were dispersed into single spherical particles by the ball milling–freezing-disaggregated attapulgite, in which the average particle size decreased from 423.94 nm to 54.51 nm, and the specific surface area of D-ATP-nFe /Ni (97.10 m2/g) was 6.9 times greater than that of nFe/Ni (14.15 m2/g). Therefore, the degradation rate of 2,4-DCP increased from 81.9% during ATP-nFe/Ni application to 96.8% during D-ATP-nFe/Ni application within 120 min, and the yield of phenol increased from 57.2% to 86.1%. Meanwhile, the reaction rate Kobs of the degradation of 2,4-DCP by D-ATP-nFe/Ni was 0.0277 min−1, which was higher than that of ATP-nFe/Ni (0.0135 min−1). In the dechlorination process of 2,4-DCP by D-ATP-nFe/Ni, the reaction rate for the direct dechlorination of 2,4-DCP of phenol (k5 = 0.0156 min−1) was much higher than that of 4-chlorophenol (4-CP, k2 = 0.0052 min−1) and 2-chlorophenol (2-CP, k1 = 0.0070 min−1), which suggests that the main dechlorination degradation pathway for the removal of 2,4-DCP by D-ATP-nFe/Ni was directly reduced to phenol by the removal of two chlorine atoms. In the secondary pathway, the removal of one chlorine atom from 2,4-DCP to generate 2-CP or 4-CP as intermediate was the rate controlling step. The final dechlorination product (phenol) was obtained when the dechlorination rate accelerated with the progress of the reaction. This study contributes to the broad topic of organic pollutant treatment by the application of clay minerals.

Poly(2-ethyl-2-oxazoline) coating of additively manufactured biodegradable porous iron

Additively manufacturing of porous iron offers a unique opportunity to increase its biodegradation rate by taking advantage of arbitrarily complex porous structures. Nevertheless, achieving the required biodegradation profile remains challenging due to the natural passivation of iron that decrease the biodegradation rate. Moreover, the biocompatibility of iron is reported to be limited. Here, we address both challenges by applying poly(2-ethyl-2-oxazoline) coating to extrusion-based 3D printed porous iron. We characterized the specimens by performing in vitro biodegradation, electrochemical measurements, time-dependent mechanical tests, and in vitro cytocompatibility assays. The coated porous iron exhibited a biodegradation rate that was 2.6× higher than that of non-coated counterpart and maintained the bone-mimicking mechanical properties throughout biodegradation. Despite the formation of dense biodegradation products, the coating ensured a relatively stable biodegradation (i.e., 17% reduction in the degradation rate between days 14 and 28) as compared to that of non-coated specimens (i.e., 43% drop). Furthermore, the coating could be identified even after biodegradation, demonstrating the longevity of the coating. Finally, the coated specimens significantly increased the viability and supported the attachment and growth of preosteoblasts. Our results demonstrate the great potential of poly(2-ethyl-2-oxazoline) coating for addressing the multiple challenges associated with the clinical adoption of porous iron.

Corrosion electrochemistry of metallic iron in reduced ilmenite with ammonium chloride solution

Separation of iron and titanium by reduction-corrosion method from ilmenite had the advantages of less pollution, simple process, and low cost compared with other methods. To identify the determinants for corrosion reaction of reduced ilmenite, the corrosion electrochemistry of metallic iron in ammonium chloride solution was carried out. The metallic iron was oxidized to form dense Fe2O3 and Fe3O4 in NH4Cl solution at pH of 3.60, resulting in the passivation of metallic iron electrode surface. However, the anode passivation film was destroyed by the chloride ions in the NH4Cl solution, which promoted the corrosion reactions of metallic iron. The corrosion of metallic iron in the 1.60 wt.% NH4Cl solution was controlled by the cathode reaction with a control degree of 95.86%. Decreasing the cathodic polarization could improve the corrosion rate of metallic iron. The decrease of pH value in electrolyte promoted the anode reaction of metallic iron in the NH4Cl solution and reduced the passivation of metallic iron. The Ca2+ and Mg2+ ions in electrolyte increased the difficulty of the metallic iron corrosion reaction. The Fe(OH)3 accumulated in electrolyte slowed down the corrosion reaction rate of metallic iron.

Anaerobic in Situ Removal of Bio-Sponge Iron Passivation Layer to Restore Phosphorus Removal Performance of Sbr

Anaerobic in Situ Removal of Bio-Sponge Iron Passivation Layer to Restore Phosphorus Removal Performance of Sbr

Anaerobic in Situ Removal of Bio-Sponge Iron Passivation Layer to Restore Phosphorus Removal Performance of Sbr

Anaerobic in Situ Removal of Bio-Sponge Iron Passivation Layer to Restore Phosphorus Removal Performance of Sbr

Anaerobic in Situ Removal of Bio-Sponge Iron Passivation Layer to Restore Phosphorus Removal Performance of Sbr

Anaerobic in Situ Removal of Bio-Sponge Iron Passivation Layer to Restore Phosphorus Removal Performance of Sbr

Electrochemical Oscillation during Dissolution of Iron in High Concentration of Nitric Acid

Electrochemical oscillations are attractive phenomena from the viewpoint of dynamic self-organization of molecular systems. In general, an N-shaped negative differential resistance (N-NDR) plays a crucial role in the appearance of oscillations because it gives rise to oscillatory instability [1]. Most of the oscillations can be classified into an N-NDR type or “hidden” N-NDR (HN-NDR) type oscillator. The former shows current oscillations under potential controlled conditions and hysteresis loops under current-controlled conditions, whereas the latter shows not only current oscillations but also potential oscillations.Iron dissolves in aqueous HNO3 solutions, accompanied by hydrogen evolution reaction. This dissolution reaction is written as follows:Fe → Fe2+ + 2e- (1)2H+ + 2e- → H2. (2)On the other hand, the dissolution does not take place in concentrated HNO3 solutions (i.e., 13 M HNO3) because of the formation of a passivation film on the surface. However, when the concentration of HNO3 is approximately 10 M, the dissolution and passivation of iron occur alternatively. In other words, only when an iron wire is immersed in a high concentration of HNO3, the rest potential of the iron wire oscillates spontaneously. This phenomenon is of interest because its appearance does not require any external devices.In this work, to clarify the mechanism of the spontaneous oscillation, we observe the surface of an iron wire during the oscillation using a high-speed camera (Figure 1) and measure electrochemical impedance spectra. From these studies, we can say that the oscillation is an HN-NDR type, which will be discussed in the presentation. Reference M. Orlik, Self-Organization in Electrochemical Systems I, Springer-Verlag Berlin Heidelberg, Berlin (2012). FIGURE CAPTION Figure 1 Time course of rest potential of an iron electrode in 10 M nitric acid and snapshots of the electrode. Figure 1