Green Rust Research Articles

Geochemical Decoupling of Iron and Zinc during Transformation of Zn-Bearing Ferrihydrite in Reducing Sediments.

The transformation of the mineral ferrihydrite in reducing environments, and its impact on the mobility of incorporated trace metals, has been investigated in model laboratory studies, but studies using complex soil or sediment matrices are lacking. Here, we studied the transformation of zinc (Zn)-bearing ferrihydrite labeled with 57Fe and mixed with natural sediments, incubated in reducing conditions for up to six months. We tracked the evolution of Fe and Zn speciation with 57Fe Mössbauer spectroscopy and with bulk and micro-X-ray absorption spectroscopy. We show that Fe was readily reduced and incorporated into a poorly crystalline mixed-valence Fe(II)-Fe(III) phase resembling green rust. In parallel, Zn was released in the surrounding porewater and scavenged by precipitation with available ligands, particularly as zinc sulfide (ZnS) or Zn-carbonates. Early in the mineral transformation process, the chemical behavior of Fe was decoupled from Zn, suppressing the impact of Zn on the rates and products of the ferrihydrite transformation. Our results underline the discrepancy between model experiments and complex field-like conditions and highlight the importance of sediment and soil geochemistry and ligand competition on the fate of divalent metal contaminants in the environment.

The role of iron(II) excess and phosphate to synthesize hydroxychloride green rust

Green rust (GR) is a chemically reactive mineral of interest for environmental remediation. However, the lack of stability of this compound is a major drawback for practical applications. In this study, the precipitation of hydroxychloride green rust type 1 (GR1Cl) from soluble FeII and FeIII species was studied by analyzing pH titration curves and employing XRD, Raman and Mössbauer spectroscopies to find optimal conditions for synthesizing GR1Cl. Using the stoichiometric condition for FeII-FeIII corresponding to the [FeII3FeIII(OH)8]Cl compound, FeIIIO(OH)2.9Cl0.1 was formed in a first step during the addition of NaOH and then transformed into a mixture of GR1Cl and Fe3O4. The addition of phosphate anions (PO4) at a molar ratio PO4: Fe = 1: 10 in the initial solution was shown to avoid the formation of undesired magnetite. Interestingly, GR1Cl was also the only product without adding PO4 using an excess of FeII species in solution, i.e. for an initial ferric molar fraction x = FeIII: Fetot of 0.2. First experimental evidences of a hydroxyphosphate green rust type 2 GR2PO4 were also provided by XRD and Raman spectroscopy. Therefore, this work may attract interest for a better understanding of the geochemical cycle of iron and phosphate in natural environments such as hydromorphic soils or hydrothermal chimneys where fougerite, the mineral homologue of synthetic GR, is supposed to play a significant role.

Silicate coprecipitation reduces green rust crystal size and limits dissolution-precipitation during air oxidation

Green rusts (GR) are mixed-valence iron (Fe) hydroxides which form in reducing redox environments like riparian and wetland soils and shallow groundwater. In these environments, silicon (Si) can influence Fe oxides’ chemical and physical properties but its role in GR formation and subsequent oxidative transformation have not been studied starting at initial nucleation. Green rust sulfate [GR(SO4)] and green rust carbonate [GR(CO3)] were both coprecipitated from salts by base titration in increasing % mol Si (0, 1, 10, and 50). The minerals were characterized before and after rapid (24 h) aqueous air-oxidation by x-ray diffraction (XRD), scanning electron microscopy (SEM), Fe extended x-ray absorption fine structure spectroscopy (EXAFS), and N2-BET surface area. Results showed that only GR(SO4) or GR(CO3) was formed at every tested Si concentration. Increasing % mol Si caused decreased plate size and increased surface area in GR(CO3) but not GR(SO4). GR plate basal thickness was not changed at any condition indicating a lack of Si interlayering. Air oxidation of GR(SO4) at all % mol Si contents transformed by dissolution and reprecipitation into lepidocrocite and goethite, favoring ferrihydrite with higher % Si content. Air oxidation of GR(CO3) transformed into magnetite and goethite but increasing Si caused GR to oxidize while retaining its hexagonal plate structure via solid-state oxidation. Our results indicate that Si has the potential to cause GR to form in smaller particles and upon air oxidation, Si can either stabilize the plate structure or alter transformation to ferrihydrite.Graphical

Microbial Reduction of Geogenic and Synthetic Goethite and Hematite

The microbial reduction of Fe(III) is a major component of Fe cycling in terrestrial and aquatic environments and is affected by the Fe(III) mineralogy of the system. The majority of the research examining the bioreduction of Fe(III) oxides by Fe(III)-reducing bacteria (IRB) has focused on the reduction of poorly crystalline Fe(III) phases, primarily ferrihydrite; however, crystalline Fe(III) oxides like goethite (α-FeOOH) and hematite (α-Fe2O3) comprise the majority of Fe(III) oxides in soils. This study examined the bioreduction of goethite and hematite of geogenic and synthetic origin by Shewanella putrefaciens CN2, a well-studied model IRB, in laboratory incubations. Overall, the rate and extent of Fe(II) production were greater for goethite than for hematite, and for geogenic Fe(III) oxides relative to their synthetic analogs. Although there was substantial production of Fe(II) (i.e., >5 mM Fe(II)) in many of the systems, X-ray diffraction analysis of the solids at the end of the incubation did not indicate the formation of any Fe(II)-bearing secondary minerals (e.g., magnetite, siderite, green rust, etc.). The results of this study demonstrate the variability in the extent of bioreduction of geogenic goethite and hematite, and furthermore, that synthetic goethite and hematite may not be good analogs for the biogeochemical behavior of Fe(III) oxides in aquatic and terrestrial environments.

Redox Dynamic Interactions of Arsenic(III) with Green Rust Sulfate in the Presence of Citrate

Redox Dynamic Interactions of Arsenic(III) with Green Rust Sulfate in the Presence of Citrate

Regulating the interlayer SO42--induced rebound of SeO42- in green rust coupled with iron nanoparticles for groundwater remediation

Green rust (GR) is an interlayer anion-containing Fe(II)/Fe(III) mineral material that is versatile in removing a series of ionic contaminants in water. Taking SeO42- (Se(VI)) as the target contaminant, this study identified that the removal processes of Se(VI) by GR could be divided into three stages: initial rapid interlayer exchange, followed by a rebound, and finally slow removal. In addition, as the percentage of SO42- in GR interlayer increased, the Se(VI) removal by GR gradually decreased. To mediate the SO42--induced rebound of Se(VI), the coupling of GR with iron nanoparticles (nFe0@GR) was proposed in this study and it was found that the removal efficiency of Se(VI) by nFe0@GR was 3.53 folds greater than that of GR. This study further revealed that the enhanced reactivity of nFe0@GR with Se(VI) could be attributed to the re-equilibration of SO42- driven by the formed GR in situ. Since it had a weaker electrostatic repulsion with interlayer SeO42- than pristine GR, the Se(VI) could be quickly removed by nFe0@GR without the rebound. Moreover, the nFe0@GR was demonstrated to be effective in immobilizing Se(VI) from simulated groundwater and has a great potential to reduce the risk of Se(VI) re-release into the environment.

Green Rust: A Potent Reductant for Unassisted Conversion of CO to Multicarbon Liquid Products

Green Rust: A Potent Reductant for Unassisted Conversion of CO to Multicarbon Liquid Products

Synthesis of membrane protein-like redox-active mineral «green rust» through size and hydrophobicity functionnalization with amino acids

Synthesis of membrane protein-like redox-active mineral «green rust» through size and hydrophobicity functionnalization with amino acids

Preparation of Oriented Nanoporous Magnetite Films by a Template-Free Solution Process from Iron Oxyhydroxide Films

Nanoporous oxide films composed of nanocrystal assemblies with an aligned crystallographic orientation are key nanostructures for efficient interfacial reactions. However, a simple, template-free method for their formation remains a challenge. Layered metal hydroxide (LMH) films are a promising precursor for spontaneous formation of nanoporous oxide films.[1-4] LMHs have a layered structure comprising 2D sheets of edge-shared octahedral hydroxide, i.e., brucite structure, with or without interlayer anions and water molecules. Calcination of LMH results in dehydration, anion elimination, and volume shrinkage, leading to the spontaneous formation of nanoporous oxides.In this study, we have prepared nanoporous and ferrimagnetic magnetite (Fe3O4) films by using layered iron hydroxides, namely, green rust (GR), as a precursor. Generally, GR has a brucite-type structure containing Fe2+ and Fe3+ ions, and is highly susceptible to oxidation by oxygen in water and air, leading to the formation of iron oxyhydroxides (FeOOH). Here, GR films were electrochemically deposited on FTO substrates in an aqueous solution containing Fe2+ and NO3 − ions at room temperature. Drying the GR films in air resulted in the formation of two-type FeOOH films, depending on the electrodeposition condition. Characterization using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and FT-IR spectroscopy revealed that one is [010]-oriented γ-FeOOH films, and the other is [001]-oriented δ-FeOOH films. The obtained FeOOH films had a mille-feuille like morphology with 500–700 nm thickness. Heat treatment of these two-type FeOOH films under vacuum at 500 °C resulted in the formation of [110]- and [111]-oriented nanoporous Fe3O4 films. The obtained Fe3O4 films showed a ferrimagnetic behavior in VSM measurements and had a nanoporous structure comprising nanoparticles with 50–100 nm diameter.Finally, a possilble interpretation for the observed orientation relationships between the FeOOH and Fe3O4 was also discussed on the basis of pyrolysis intermediates of FeOOH and similarity in their atomic arrangements. References T. Shinagawa, M. Watanabe, T. Mori, J.-i. Tani, M. Chigane and M. Izaki, Inorg. Chem., 57, 13137 (2018).T. Shinagawa, M. Chigane and M. Izaki, ACS Omega, 6, 2312 (2021).T. Shinagawa, M. Chigane and M. Takahashi, Cryst. Growth Des., 22, 4122 (2022).T. Shinagawa, N. Kotobuki and A. Ohtaka, Nanoscale Adv., 5, 96 (2023). Figure 1

Enhanced Cr(VI) removal and stabilization from bioleached wastewater by zero-valent iron coupled with hetero and autotrophic bacteria

Zero-valent iron (Fe0) usually suffers from organic acid complexation and ferrochrome layer passivation in Cr(VI) removal from bioleached wastewater of Cr slag. In this work, a synergetic system combined Fe0 and mixed hetero/autotrophic bacteria was established to reduce and stabilize Cr(VI) from bioleached wastewater. Due to bacterial consumption of organic acid and hydrogen, severe iron corrosion and structured-Fe(II) mineral generation (e.g., magnetite and green rust) occurred on biotic Fe0 surface in terms of solid-phase characterization, which was crucial for Cr(VI) adsorption and reduction. Therefore, compared with the abiotic Fe0 system, this integrated system exhibited a 6.1-fold increase in Cr(VI) removal, with heterotrophic reduction contributing 3.4-fold and abiotic part promoted by hydrogen-autotrophic bacteria enhancing 2.7-fold. After reaction, the Cr valence distribution and X-ray photoelectron spectroscopy indicated that most Cr(VI) was converted into immobilized products such as FexCr1-x(OH)3, Cr2O3, and FeCr2O4 by biotic Fe0. Reoxidation experiment revealed that these products exhibited superior stability to the immobilized products generated by Fe0 or bacteria. Additionally, organic acid concentration and Fe0 dosage showed significantly positive correlation with Cr(VI) removal within the range of biological adaptation, which emphasized that heterotrophic and autotrophic bacteria acted essential roles in Cr(VI) removal. This work highlighted the enhanced effect of heterotrophic and autotrophic activities on Cr(VI) reduction and stabilization by Fe0 and offered a promising approach for bioleached wastewater treatment.

Promoting the transformation of green rust for As immobilization with Acidovorax sp. strain BoFeN1

Microbially mediated Fe(II) oxidation has a great potential for attenuating arsenic (As) mobility in an anoxic groundwaters. Green rust (GR), a common Fe(II)-bearing phase in such environments, could be easily oxidized into Fe (oxyhydr)oxides through microbial activity. This study focused on Acidovorax sp. strain BoFeN1, an anaerobic nitrate-reducing Fe(II)-oxidizing (NRFO) bacterium, to promote the transformation of GR. In biotic GR transformation experiments, magnetite formation occurred at [As]ini = 5 mg/L while lepidocrocite and goethite were formed at [As]ini = 10 mg/L. In the absence of bacterium, the GR persisted throughout the 120-h experiment. Meanwhile, with the addition of strain BoFeN1, the final aqueous As concentration significantly decreased from 0.237 to 0.004 mg/L (C0 = 5 mg/L) and from 1.457 to 0.096 mg/L (C0 = 10 mg/L) at 120 h. It was indicated that strain BoFeN1 played a crucial role in promoting the GR transformation and enhancing As immobilization. Further investigations revealed that the role of strain BoFeN1 extended beyond Fe-oxidation. With nitrite (the intermediate of nitrate bioreduction) as oxidizer, lepidocrocite/goethite were formed in the chemical-oxidation system, excluding magnetite. In the Bio - [As]ini = 5 mg/L, the occurrence of lepidocrocite via the bio-oxidation of Fe(II) in GR at 24 h, along with the metabolism of strain BoFeN1 reducing nitrate accompanied with H+ consumption, it should be reasonably deduced that the alkaline micro-environment of periplasm induced by strain BoFeN1 were vital for the transformation of lepidocrocite to magnetite triggered by trace Fe(II). However, in the Bio - [As]ini = 10 mg/L, more As adsorbed on GR inhibiting the adsorption of bacterium, so the alkaline micro-environment had no obvious effect on such transformation. This study helps to understand the interdependence between GR and anaerobic NRFO bacterium, and provides a new perspective for more effective As remediation strategies in anoxic groundwaters.

Episodic hydrothermal supply and microbial anaerobic Fe(II) oxidation in early Archean ocean: Insights from precursor mineral compositions of the 3.46 Ga Marble Bar Chert, Pilbara Craton, Western Australia

The 3.46 Ga Marble Bar Chert (MBC) from the Pilbara Craton in Western Australia is known as the oldest chert on Earth. The origin of its Fe minerals was investigated to decipher the geochemistry and redox conditions of the early Archean ocean, as well as to explore the possible microbial contribution to the earliest sedimentary processes on Earth. However, the composition of the precursor minerals in the MBC remains poorly understood, giving rise to controversies on its genesis. Here we performed high-resolution petrographic, laser Raman, Mössbauer, X-ray diffraction, and Mn K-edge X-ray absorption near edge structure spectroscopic studies on two typical types of finely laminated MBC, grey-black chert and red chert. The grey-black chert contains considerable amounts of siderite, carbonaceous materials, and minor phyllosilicates and hematite. By contrast, the red chert contains high hematite and silicates, minor siderite and rare carbonaceous materials. Microcrystals in the cores of chert polyhedral are among the earliest mineral phases without signs of alterations, recrystallisation, erosion or replacement histories. Ferrihydrite, greenalite, siderite, and green rust are possible precursors of Fe-bearing minerals in the MBC. Their respective proportion in each lamina was regulated by pH, Fe(II)-oxidation rate, DIC, and Fe(II) content in the seawater. Approximately half Fe in the MBC primary minerals existed as Fe(III), indicating the existence of indigenous Fe(II)-oxidation in the Paleoarchean seawater. The element Mn in the MBC is primarily Mn(II) coordinated with O, suggesting a reduced depositional environment and hence implying the involvement of anaerobic microbial Fe(II)-oxidation in the formation of the MBC. Collectively, the grey-black laminae with abundant carbonaceous materials reflect limited Fe(II)-oxidation and increased dissolved inorganic carbon content likely due to enhanced hydrothermal CO2 supply, while the red laminae with considerable hematite represent substantial Fe(III)-supply due to rapid indigenous anaerobic Fe(II)-oxidation.

In-situ groundwater remediation of contaminant mixture of As(III), Cr(VI), and sulfanilamide via electrochemical degradation/transformation using pyrite

Electrochemical advanced oxidation processes (EAOPs) are effective in removing persistent contaminants from groundwater. However, their practical applicability depends significantly on various site-specific characteristics. Therefore, the primary objective of this investigation was to study the feasibility of EAOPs and pyrite, which is a sulfide mineral, to effectively remove the mixture of arsenic (As (III)), chromium (Cr (VI)), and sulfanilamide in groundwater. We conducted a comparison of three systems: (1) EAOP alone, (2) pyrite alone, and (3) a combined EAOP and pyrite system. In EAOP alone, sulfanilamide was effectively oxidized (80%), while the electrochemical transformation of As(III)/Cr(VI) into As(V)/Cr(III) was limited. In just the pyrite system, As(III), Cr(VI), and sulfanilamide were adsorbed onto the surface of pyrite (60%, 20%, and 18%). Neither the EAOP nor the pyrite system alone could effectively treat the contaminants mixture. Nonetheless, the combined system completely removed As(III), Cr(VI), and sulfanilamide by the synergistic reaction. This could be attributed to the formation of green rust, a natural adsorbent mineral produced as a reaction of dissolved iron, generated via electrochemical pyrite oxidation, with the groundwater electrolyte (e.g., CO3 or SO4). This system harmonized the combined approach of EAOP and pyrite to effectively eliminate both organic and inorganic contaminants. Environmental implicationA paper proposed electrochemical oxidation (EO) with pyrite to remove both organic and inorganic contaminants from groundwater. The removal performance of the combined system was evaluated, and the synergistic mechanism was revealed. The combination of EO and pyrite with synergistic removal effectively removed the mixture of both contaminants. This could be attributed by the formation of green-rust by electrochemical activation for pyrite. Compared to the single system of EO and pyrite alone, the combined system with EO and pyrite improved removal performance. Results suggested that the combined system could be used for green groundwater remediation.

Fast degradation of vinyl chloride by green rust and nitrogen-doped graphene

Carbonaceous materials catalyze reductive dechlorination of chlorinated ethylenes (CEs) by iron(II) materials providing a new approach for the remediation of CE polluted groundwater. While most CEs are reduced via β-elimination, vinyl chloride (VC), the most toxic and recalcitrant CE, degrades by hydrogenolysis. The significance of carbon catalysts for reduction of VC is well documented for iron(0) systems, but hardly investigated with iron(II) materials as reductants. In this study, a layered iron(II)‑iron(III) hydroxide sulfate (green rust) was used as reductant for VC, with an N-doped graphene (NG), prepared by co-pyrolysis of graphene and urea, as catalyst. VC (80 μM) was completely reduced to ethylene within 336 h in the presence of 5 g Fe/L GR and 5 g/L NG pyrolyzed at 950 °C, following pseudo-first-order kinetics with a rate constant of 0.017 h−1. Dosing experiments demonstrated that dechlorination of VC takes place on the NG phase. Monitoring of hydrogen formation, cyclic voltammetry, and quenching experiments demonstrated that atomic hydrogen contributes significantly to the dehalogenation reaction, where NG is critical for formation of atomic hydrogen. CE competition experiments demonstrated the presence of specific VC reduction sites with hydrogenolysis being unaffected by concurrent β-elimination reactions. The system exhibited excellent performance in natural groundwaters and in comparison with iron(0) systems. This study demonstrates that GR + NG is a promising system for remediation of VC contaminated groundwater, and the mechanistic part of the study can be used as a reference for subsequent studies.

Bone char switch on reductive dehalogenation of trichloroethene by series of Fe(II)-bearing minerals: The balance between kinetics and electron efficiency

Fe(II)-bearing minerals might be able to drive the attenuation of chlorinated ethene in soil and groundwater, however, with relatively slow kinetics. In this study, bone char(BC) was selected as an efficient and benign catalyst to prepare composites with three different Fe(II)-bearing minerals (Green rust (GR), Fe(OH)2 and FeS), respectively, for enhanced trichloroethylene (TCE) dehalogenation. The kinetics experiment demonstrated that the presence of BC could effectively switch on the TCE dehalogenation by these solids, while these Fe(II)-bearing minerals alone can barely reduce any TCE. Surprisingly, the Fe(OH)2-BC showed fastest TCE reduction rate, followed by GR-BC and FeS-BC in sequence. Acetylene was confirmed as the major dehalogenation products while other chlorinated byproducts were hardly detected. The electron efficiency (ηe) for TCE reduction was further calculated and compared among these BC amended systems, the results show that the highest ηe value was recorded in GR-BC system as 33.14% with high loading of TCE. Solid phase characterization confirmed that the high loading of amorphous Fe(II) on the BC surface might effectively improve the TCE dehalogenation kinetics, while the well crystallized Fe(II)-bearing minerals would increase the electron efficiency. According to this mechanism, it might be possible to achieve balance between kinetics and electron efficiency. Stress resistance test in real groundwater matrix and life cycle analysis (LCA) was conducted to further verify the application potential of these composites.

Performance and Surface Modification of Cast Iron Corrosion Products by a Green Rust Converter (Mimosa tenuiflora Extract)

One of the alternative materials used for conducting conservation treatment of iron artifacts is the rust converter, since it generates barrier properties and more stable oxides. The protective properties and surface modifications from using Mimosa tenuiflora extract as a green rust converter on a gray iron oxide layer were studied. The surface characterization was carried out using a Scanning Electron Microscope coupled to an energy-dispersive X-ray spectrometer (SEM-EDS), along with infrared spectroscopy (IR), Raman spectroscopy, X-ray Diffraction (XRD), and Water Contact Angle (WCA). Electrochemical characterization was performed with an Electrochemical Impedance Spectroscope (EIS) using 3.5 wt.% NaCl as the electrolyte. According to the results of the Raman spectroscopy and XRD, the layer of corrosion products formed after 90 days in the atmosphere was composed of goethite, lepidocrocite, maghemite, hematite, and magnetite. The surface of the corrosion products was transformed with the rust converter into an amorphous and microcracked layer. By IR, the Fe-O and C-O-Fe bonds associated with the iron chelate were found with absorption bands at 1540 and 1567 cm−1, respectively. By XRD, a modification of the magnetite crystallinity was observed. Finally, the Water Contact Angle and the protective capacity of the corrosion products were improved by the presence of the rust converter.

Reaction mechanisms and diagnostic mineralogy of intertidal steel corrosion: An X-ray photoelectron spectroscopy study

The products of intertidal and super tidal (splash zone) corrosion on steel piles have been characterised at 3 UK sites with contrasting environmental conditions in order to determine corrosion reaction mechanism and if a common mechanism for accelerated low water corrosion occurs across sites. Intertidal corrosion samples at Shoreham and Newhaven ports show an internal composition of iron mono- and bi-sulphide, with intermediate sulphur oxidation state compounds, and an outer surface dominated by iron oxides and oxyhydroxides with a component of iron sulphates. The FTIR spectra are characteristic of sulphate green rust. In contrast, samples from Southend have all sulphur species below detection levels and are dominated by iron oxides and oxyhydroxides. Carbon binding energy spectra are consistent with the development of biofilms at all sites except for a splash zone sample at Southend. The results demonstrate a common mechanism for ALWC at Newhaven and Shoreham, involving the action of sulphate-reducing bacteria generating iron sulphides on the steel surface. These are subsequently oxidised to produce sulphate green rust, which may in turn oxidise to produce lepidocrocite. At Southend differences in environment are inferred to restrict the activity of sulphate reducing bacteria, resulting in direct oxidation of steel to generate iron oxyhydroxide gels, which subsequently recrystallise, dehydrate and oxidise to goethite, magnetite and ultimately hematite in both splash zone and intertidal samples. The multi-technique approach used here characterises the full range of corrosion products.

Interactions of Perrhenate (Re(VII)O4−) with Fe(II)-Bearing Minerals

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)O4−) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReO4 with magnetite (Fe3O4), siderite (FeCO3), vivianite (Fe3(PO4)2•8H2O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)O6 octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReO4− in sedimentary environments requires further investigation.

Fenton-like system of UV/Glucose-oxidase@Kaolin coupled with organic green rust: UV-enhanced enzyme activity and the mechanism of UV synergistic degradation of photosensitive pollutants

This study introduces the UV/glucose-oxidase@Kaolin (GOD@Kaolin) coupled organic green rust (OGR) system (UV/OGR/GOD@Kaolin) to investigate the promotion of glucose oxidase activity by UV light and its synergistic degradation mechanism for photosensitive pollutants, specifically targeting the efficient degradation of 4-chlorophenol (4-CP). The enzyme system demonstrates its ability to overcome drawbacks associated with traditional Fenton systems, including a narrow pH range and high localized concentration of H2O2, by gradually releasing hydrogen peroxide in situ within a neutral environment. In the presence of UV radiation under specific conditions, enhanced enzyme activity is observed, resulting in increased efficiency in pollutant removal. The gradual release of hydrogen peroxide plays a crucial role in preventing unwanted reactions among active substances. These unique features facilitate the generation of highly reactive species, such as Fe(IV)O, •OH, and •O2−, tailored to efficiently target the organic components of interest. Additionally, the system establishes a positive iron cycle, ensuring a sustained reactive capability throughout the degradation process. The results highlight the UV/OGR/GOD@Kaolin system as an effective and environmentally friendly approach for the degradation of 4-CP, and the resilience of the enzyme extends the system's applicability to a broader range of scenarios.

Influence of Cr(III) on the formation and transformation of corrosion products of steel in marine environments

A fundamental approach is used to better understand the influence of Cr on the resistance of low alloy steel to marine corrosion. It focuses on the formation and transformation of corrosion products of steel in seawater-like electrolytes. Fe(OH)2 precipitates are then prepared by mixing a solution of NaCl, Na2SO4·10H2O, FeCl2·4H2O or FeCl2·4H2O + CrCl3·6H2O (so that Cr = 8% and Fe = 92%), with a solution of NaOH. The initial concentration ratio of reactants, Q=frac{2[{{{rm{Fe}}}}^{2+}]+3[{{{rm{Cr}}}}^{3+}]}{[{{{rm{OH}}}}^{-}]}, is set at Q = 0.88, 1, and 1.136. In a first approach, the obtained aqueous suspension is stirred, at a controlled temperature of 25 ± 0.5 °C, to be oxidized by air. The resulting oxidation product is characterized by XRD and Raman spectroscopy. In a second approach, the Fe(OH)2 precipitates are aged one week in suspension in anoxic conditions, filtered, mixed as a wet paste with glycerol and set as a thin compact layer on the sample holder of a X-ray diffraction system. The oxidation process of Fe(OH)2 is then monitored in situ during the acquisition of the X-ray diffractogram. The obtained results demonstrate that Cr(III) hinders the formation of green rust compounds, hence hindering the formation of γ-FeOOH, i.e., the main oxidation product of green rust compounds. The other oxidation pathways of Fe(OH)2, which lead to Fe3O4 or α-FeOOH, are thus favored. Nevertheless, Cr(III) favors mainly the solid state transformation pathway of Fe(OH)2, thus promoting α-FeOOH via the formation of poorly ordered Fe(III) oxyhydroxides, namely feroxyhyte and ferrihydrite.