Hydroxysulphate Green Rust Research Articles

Formation of Fe(III)-containing mackinawite from hydroxysulphate green rust by sulphate reducing bacteria

The interactions between Fe(II–III) hydroxysulphate GR( SO 4 2 - ) and sulphate reducing bacteria (SRB) were studied. The considered SRB, Desulfovibrio desulfuricans subsp. aestuarii ATCC 29578, were added with GR( SO 4 2 - ) to culture media. Different conditions were envisioned, corresponding to various concentrations of bacteria, various sources of sulphate (dissolved SO 4 2 - + GR( SO 4 2 - ) or GR( SO 4 2 - ) alone) and various atmospheres (N 2:H 2 or N 2:CO 2:H 2). In the first part of the study, CO 2 was deliberately omitted so as to avoid the formation of carbonated compounds, and GR( SO 4 2 - ) was the only source of sulphate. Cell concentration increases from ∼4 × 10 7 to ∼7 × 10 8 cells/mL in 2 weeks. The evolution with time of the iron compounds, monitored by Raman spectroscopy and X-ray diffraction, showed the progressive formation of a FeS compound, the Fe(III)-containing mackinawite. This result is consistent with the association GR( SO 4 2 - )/SRB/FeS observed in rust layers formed on steel in seawater. In the presence of CO 2 and additional dissolved sulphate species, a rapid growth of the bacteria could be observed, leading to the total transformation of GR( SO 4 2 - ) into mackinawite, found in three physico-chemical states (nanocrystalline, crystalline stoichiometric FeS and Fe(III)-containing), and siderite FeCO 3.

Reductive transformation and mineralization of an azo dye by hydroxysulphate green rust preceding oxidation using H 2O 2 at neutral pH

In this study, the reactivity of hydroxysulphate green rust ( GR ( SO 4 2- ) ) toward reductive transformation, oxidative degradation and mineralization of organic compounds was evaluated using Methyl Red (MR) as model pollutant. The GR ( SO 4 2- ) was synthesized by co-precipitation method and characterized by X-ray diffraction (XRD), Mössbauer spectroscopy and Fourier Transform Infrared (FTIR) analyses. Reductive decolourization of MR solution occurred in the presence of GR ( SO 4 2- ) , while no total organic carbon (TOC) decay was observed during the equilibration time. Significant TOC removal (87%) was noted when H 2O 2 was added to the GR ( SO 4 2- ) / MR mixture after the preliminary reduction step. UV–Vis analysis, dissolved iron and H 2O 2 concentration measurement, and batch sorption test showed that the heterogeneous Fenton-like reaction is the main mechanism by which the pollutant was mineralized. Increasing of H 2O 2/Fe(II) ratio did not affect significantly the mineralization rate of MR. However, slight decolourization of MR and absence of TOC abatement were noted when both MR and H 2O 2 were simultaneously mixed with the GR ( SO 4 2- ) . XRD analysis, Mössbauer spectroscopy and FTIR spectroscopy revealed that the oxidation end-products of GR ( SO 4 2- ) were mainly a poorly crystallized goethite when GR was oxidized after equilibrating with MR in solution. However, a badly crystallized iron oxide was formed when GR was immediately oxidized. In all cases, the interlayer anion ( SO 4 2- ) was ejected from GR structure to aqueous solution. These results suggest that the GR ( SO 4 2- ) / H 2 O 2 system could be used to promote the reduction/oxidation reaction of organic pollutants.

Aluminium substitution in iron(II–III)-layered double hydroxides: Formation and cationic order

The formation and the modifications of the structural properties of an aluminium-substituted iron(II–III)-layered double hydroxide (LDH) of formula Fe 4 II Fe ( 2 - 6 y ) III Al 6 y III (OH) 12 SO 4, 8H 2O are followed by pH titration curves, Mössbauer spectroscopy and high-resolution X-ray powder diffraction using synchrotron radiation. Rietveld refinements allow to build a structural model for hydroxysulphate green rust, GR(SO 4 2−), i.e. y=0, in which a bilayer of sulphate anions points to the Fe 3+ species. A cationic order is proposed to occur in both GR(SO 4 2−) and aluminium-substituted hydroxysulphate green rust when y<0.08. Variation of the cell parameters and a sharp decrease in average crystal size and anisotropy are detected for an aluminium content as low as y=0.01. The formation of Al-GR(SO 4 2−) is preceded by the successive precipitation of Fe III and Al III (oxy)hydroxides. Adsorption of more soluble Al III species onto the initially formed ferric oxyhydroxide may be responsible for this slowdown of crystal growth. Therefore, the insertion of low aluminium amount ( y∼0.01) could be an interesting way for increasing the surface reactivity of iron(II–III) LDH that maintains constant the quantity of the reactive Fe II species of the material.

Formation of the Fe(II–III) hydroxysulphate green rust during marine corrosion of steel associated to molecular detection of dissimilatory sulphite-reductase

Accelerated corrosion phenomena of carbon steel constantly immersed in seawater could be simulated in situ via a galvanic coupling of the samples with steel port structures. Three harbours located on different seas and various conditions of immersion were considered so as to study the eventual correlation between dissimilatory sulphite-reductase genes and sulphate-containing corrosion products. In each case, after 6 or 12 months, the rust layers proved to be made of an inner black layer, close to steel surface, and an orange outer layer. Scanning electron microscopy, chemical analyses by inductively coupled plasma/atomic emission spectroscopy, X-ray diffraction and micro-Raman spectroscopy were used to obtain a detailed characterisation of these layers. The inner one proved to be mainly composed of iron sulphides FeS and Fe(II–III) hydroxysulphate green rust GR ( SO 4 2 - ) , the outer one of Fe(III) oxyhydroxides, with lepidocrocite γ-FeOOH as a major component. The molecular detection of dissimilatory sulphite-reductase, the key enzyme in dissimilatory sulphate reduction by micro-organisms, was applied for the first time to rust layers. This detection was positive in most cases, especially for the inner part of the rust layers. This demonstrates that sulphate reducing bacteria are associated to GR ( SO 4 2 - ) inside the rust layers, GR ( SO 4 2 - ) more likely playing the role of a source of sulphate. The systematic presence of iron sulphides also testifies the activity of sulphate reducing bacteria and/or thiosulphate reducing bacteria.

Fate of nickel ion in (II-III) hydroxysulphate green rust synthesized by precipitation and coprecipitation

In order to investigate the efficiency of sulfate green rust (GR2) to remove Ni from solution, GR2 samples were synthesized under controlled laboratory conditions. Some GR2 samples were synthesized from Fe(II) and Fe(III) sulfate salts by precipitation. Other samples were prepared by coprecipitation, of Ni(II), Fe(II) and Fe(III) sulfate salts, i.e., in the presence of Ni. In another sample, Ni(II) sulfate salt was added to pre-formed GR2. After an initial X-ray diffraction (XRD) characterization all samples were exposed to ambient air in order to understand the role of Ni in the transformation of the GR2 samples. XRD was repeated after 45 days. The results showed that Nious GR2 prepared by coprecipitation is isomorphous to Ni-free GR2, i.e. Ni is incorporated into the crystalline structure. Fe(II) was not replaced by Ni(II) in the crystalline structure of GR2 formed prior to exposure to solution-phase Ni. This suggests Ni was adsorbed to the GR2 surface. Sulfate green rust is more efficient in removing Ni from the environment by coprecipitation.

Influence of silicate ions on the formation of goethite from green rust in aqueous solution

We investigated the influence of silicate ions on the formation of goethite converted from hydroxysulphate green rust, which was synthesized by neutralizing mixted solution of Fe 2(SO 4) 3 and FeSO 4 with NaOH solution, by O 2 in an aqueous solution. The pH and oxidation–reduction potential of the suspension and the Fe and Si concentrations in supernatant solutions were analyzed. X-ray diffraction results for the solid particles formed during the conversion were consistent with the results of the solution analyses. The results indicated that silicate ions suppressed the conversion from green rust to α-FeOOH and distorted the linkages of FeO 6 octahedral units in the α-FeOOH structure.

Chemical stability of hydroxysulphate green rust synthetised in the presence of foreign anions: carbonate, phosphate and silicate

Chemical stability of hydroxysulphate green rust synthetised in the presence of foreign anions: carbonate, phosphate and silicate

Monitoring structural transformation of hydroxy-sulphate green rust in the presence of sulphate reducing bacteria

The activities of bacterial consortia enable organisms to maximize their metabolic capabilities. This article assesses the synergetic relationship between iron reducing bacteria (IRB), Shewanella putrefaciens and sulphate reducing bacteria (SRB) Desulfovibrio alaskensis. Thus, the aim of this study was first to form a biogenic hydroxy-sulpahte green rust GR2(\( {\text{SO}}_{{\text{4}}} ^{{2 - }} \)) through the bioreduction of lepidocrocite by S. putrefaciens and secondly to investigate if sulfate anions intercalated in the biogenic GR2(\( {\text{SO}}_{{\text{4}}} ^{{2 - }} \)) could serve as final electron acceptor for a sulfate reducing bacterium, D. alaskensis. The results indicate that the IRB lead to the formation of GR2(\( {\text{SO}}_{{\text{4}}} ^{{2 - }} \)) and this mineral serve as an electron acceptor for SRB. GR2(\( {\text{SO}}_{{\text{4}}} ^{{2 - }} \)) precipitation and its transformation was demonstrated by using X-ray diffraction (DRX), Mossbauer spectroscopy (TMS) and transmission electron spectroscopy (TEM). These observations point out the possible acceleration of steel corrosion in marine environment in presence of IRB/SRB consortia.

Green rusts synthesis by coprecipitation of Fe II–Fe III ions and mass-balance diagram

A basic solution is progressively added to various mixed Fe II–Fe III solutions. The nature and the relative quantities of the compounds that form can be visualised in a mass-balance diagram. The formation of hydroxysulphate green rust {GR( SO 4 2 − )} is preceded by the precipitation of a sulphated ferric basic salt that transforms in a badly ordered ferric oxyhydroxide. Then octahedrally coordinated Fe II species and SO 4 2 − anions are adsorbed on the FeOOH surface and GR( SO 4 2 − ) is formed at the solid/solution interface. By using the same method of preparation, other types of green rust were synthesised, e.g. hydroxycarbonate green rust {GR( CO 3 2 − )}. Like other layered double hydroxides, green rusts obey the general chemical formula [ M II ( 1 − x ) M III x ( OH ) 2 ] x − ⋅ [ ( x / n ) A n − ⋅ m H 2 O ] x + with x ⩽ 1 / 3 . Al-substituted hydroxysulphate green rust consists of small hexagonal crystals with a lateral size ∼50 nm, which is significantly smaller than the size of the GR( SO 4 2 − ) crystals (∼500 nm). To cite this article: C. Ruby et al., C. R. Geoscience 338 (2006).

Formation of Hydroxysulphate Green Rust 2 as a Single Iron(II-III) Mineral in Microbial Culture

Although GR2(SO4 2-) can be easily formed by abiotic synthesis, the biotic formation of hydroxysulphate as a single iron(II-III) mineral in microbial culture and its characterization was not achieved. This study was carried out to investigate the sole formation of GR2(SO4 2-) during the reduction of γ-FeOOH by a dissimilatory iron-respiring bacterium, Shewanella putrefaciens CIP 8040T. Reduction experiments were performed in a non-buffered medium devoid of organic compounds, with 25 mM of sulphate and with a range of lepidocrocite concentrations with H2 as the electron donor under nongrowth conditions. The resulting biogenic solids, after iron-respiring activity, were characterized by X-ray diffraction (XRD), transmission Mössbauer spectroscopy (TMS) and electron microscopy (SEM and TEM). The sulphate has been identified as the intercalated anion by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In addition, the structure of this sulphate anion was discussed. Our experimental study demonstrated that, under H2 atmosphere, the biogenic solid was a GR2(SO4 2-), as the sole iron(II-III) bearing mineral, whatever the initial lepidocrocite concentration. The crystals of the biotically formed GR2(SO4 2-) are significantly larger than those observed for GR2(SO4 2-) obtained through abiotic preparation, < 15 μ m diameter as against 0.5–4 μm, respectively.

Competitive Formation of Hydroxycarbonate Green Rust 1 versus Hydroxysulphate Green Rust 2 in Shewanella putrefaciens Cultures

The formation of hydroxysulphate green rust 2, a Fe(II-III) compound commonly found during corrosion processes of iron-based materials in seawater, has not yet been reported in bacterial cultures. Here we used Shewanella putrefaciens, a dissimilatory iron-reducing bacterium to anaerobically catalyze the transformation of a ferric oxyhydroxide, lepidocrocite (γ-FeOOH), into Fe(II) in the presence of various sulphate concentrations. Biotransformation assays of γ-FeOOH were performed with formate as the electron donor under a variety of concentrations. The results showed that the competitive formation of hydroxycarbonate green rust 1 (GR1(CO3 2−)) and hydroxysulphate green rust 2 (GR2(SO4 2 −)) depended upon the relative ratio (R) of bicarbonate and sulphate concentrations. When R ≥ 0.17, GR1(CO3 2 −) only was formed whereas when R < 0.17, a mixture of GR2(SO4 2 −) and GR1(CO3 2 −) was obtained. These results demonstrated that the hydroxysulphate GR2 can originate from the microbial reduction of γ-FeOOH and confirmed the preference for carbonate over sulphate during green rust precipitation. The solid phases were characterized by X-ray diffraction, transmission Mössbauer spectroscopy and scanning electron microscopy. Diffuse reflectance infrared Fourier transform spectroscopy confirmed the presence of intercalated carbonate and sulphate in green rust's structure. This study sheds light on the influence of dissimilatory iron-reducing bacteria on microbiologically influenced corrosion.

Coprecipitation of Fe(II) and Fe(III) cations in sulphated aqueous medium and formation of hydroxysulphate green rust

Fe(II)–Fe(III) solutions having a variable Fe(III) molar fraction were titrated with a NaOH solution. Three plateau regions separated by two equivalent points characterise the pH titration curves. The nature and relative abundance of the phases that form during the first and second plateaux are predicted by using the positions of equivalent points in an iron-compound mass-balance diagram. A slowing down of the pH increase is observed at a point of titration curve called E∗ for solutions that have a Fe(III) molar ratio x Fe(III)=[ n Fe(III)/( n Fe(II)+ n Fe(III))] lower than ∼0.27=(2/7). It corresponds to the addition of ∼7±0.5 moles of OH − per mole of Fe(III). Mössbauer spectroscopy shows that the complete formation of green rust is achieved when exactly 7 moles of OH − per mole of Fe(III) are added. This quantity would be larger than expected to form [Fe II 4Fe III 2(OH) 12] 2+·[SO 4· mH 2O] 2−, if the {Fe(II)/Fe(III)} initial ratio is conserved. This excess is attributed to the adsorption of {[Fe II 4(OH) 8]SO 4} 2− layers on the ferric oxyhydroxide surface that dissolves it and thus forms the hydroxysulphate; this replaces Misawa's ad hoc green complex {Fe II m Fe III n O p [OH] q } (2 m+3 n−2 p− q) prior precipitation.

Formation of the Fe(II)–Fe(III) hydroxysulphate green rust during marine corrosion of steel

Rust layers formed on steel sheet piles immersed 1 m above the mud line for 25 years were analysed by Raman spectroscopy, scanning electron microscopy and elemental X-ray mappings (Fe, S, O). They consist of three main strata, the inner one mainly composed of magnetite, the intermediate one of iron(III) oxyhydroxides and the outer one of hydroxysulphate green rust GR(SO 4 2−). Simulations of GRs formation in solutions having large [Cl −]/[SO 4 2−] ratios revealed that the hydroxysulphate GR(SO 4 2−) was obtained instead of the hydroxychloride GR(Cl −), as demonstrated by X-ray diffraction and transmission Mössbauer spectroscopy analyses. Measurements of the [S], [Fe] and [Cl] concentrations allowed us to establish that GR(SO 4 2−) formed along with a drastic impoverishment of the solution in sulphate ions; the [Cl −]/[SO 4 2−] ratio increased from 12 to 240. The GR, acting like a “sulphate pump”, may favour the colonisation of the rust layers by sulphate reducing bacteria.

Structure of the Fe(II-III) layered double hydroxysulphate green rust two from Rietveld analysis

Synthetic samples of the iron(II-III) hydroxysulphate known as green rust two were obtained by aerial oxidation of iron(II) hydroxide precipitates and studied using chemical and thermal analyses, transmission Mössbauer spectroscopy and powder X-ray diffraction. The ideal formula is Fe II 4Fe III 2(OH) 12SO 4·∼8H 2O. The structure is trigonal, P 3 ̄ m1 with cell parameters a=0.5524 1 nm, c=1.1011 3 nm, V=0.29097 nm 3 and Z=1/2. It is characterised by the succession of positively charged hydroxide sheets [Fe II 4 Fe III 2(OH) 12] 2+ and negatively charged interlayers composed of the sulphate anions and water molecules, [SO 4·∼8H 2O] 2−. These interlayers are made of two planes of H 2O and SO 2− 4, in contrast with those found in the rhombohedral green rust one compounds, which are made of a single plane. A superstructure ( a=a 0 3 ) is found along the [110] direction of the parent hexagonal unit cell, where a 0 is the lattice parameter of Fe(OH) 2, and due to an ordering of the sulphate anions in the interlayers.

Coprecipitation thermodynamics of iron(II–III) hydroxysulphate green rust from Fe(II) and Fe(III) salts

Iron(II–III) hydroxysulphate GR(SO 4 2−) was prepared by precipitating a mixture of Fe(II) and Fe(III) sulphate solutions with NaOH, accompanied in most cases by iron(II) hydroxide, spinel iron oxide(s) or goethite. Its [Fe(II)]/[Fe(III)] ratio determined by transmission Mössbauer spectroscopy was 2±0.2, whatever the initial [Fe(II)]/[Fe(III)] ratio in solution. Proportion of Fe(OH) 2 increased when the initial [Fe(II)]/[Fe(III)] ratio increased, whereas proportion of α-FeOOH or spinel oxide(s) increased when this ratio decreased. GR(SO 4 2−) is metastable vs. Fe 3O 4 except in a limited domain around neutral pH. Precipitation from solutions containing both Fe(II) and Fe(III) dissolved species seems to favour GRs formation with respect to stable systems involving iron (oxyhydr)oxides.

Synthesis of Fe(II-III) hydroxysulphate green rust by coprecipitation

Abstract Iron(II-III) hydroxysulphate precipitates were prepared in absence of other compounds by coprecipitation that consists of mixing solutions of iron(II) and iron(III) salts with NaOH solution in adequate proportions. Precipitates were characterised by transmission Mossbauer spectroscopy (TMS), XRD, TEM and AFM. Mossbauer spectrum measured at 15 K was composed of Fe(II) and Fe(III) doublets with δ=1.33 and 0.51 mm s−1, and Δ=2.88 and 0.43 mm s−1, respectively. The Fe(II)/Fe(III) ratio of 2 is independent of the solution ratio set at 3 that confirms the composition, [FeII4FeIII2(OH)12]2+·[SO2−4 ·m H2O]2−. XRD analysis led to hexagonal unit cell parameters of aH=bH=0.318±0.004 nm and cH=1.090±0.004 nm. The value aH=0.314±0.002 nm was obtained by TEM diffraction pattern corresponding to ( h k 0 ) planes and displayed a distribution of hexagonal plates (10

The reduction of chromate ions by Fe(II) layered hydroxides

Abstract. The reduction of chromate ions by Fe(OH)2 and the iron (II)-iron (III) hydroxysulphate green rust, GR(SO42-), was studied to evaluate whether such synthetic layered hydroxides and the corresponding natural green rust mineral could be involved in the natural attenuation of contaminated environments. The resulting Cr (III) bearing phases, which would govern the subsequent behaviour of chromium, were clearly characterised. Both compounds proved to be very reactive and oxidised instantaneously while chromate ions were reduced to Cr (III) as evidenced by X-ray photoelectron spectroscopy. Mass balance (ICP-AES) demonstrated that the Fe/Cr ratio inside the solid end product was equal to the initial Fe/Cr ratio. The solid phases, analysed by X-ray diffraction, Raman and Mossbauer spectroscopies were identified as Cr-substituted poorly crystallised iron (III) oxyhydroxides in both cases, more precisely δ-FeOOH when starting with Fe(OH)2 and ferrihydrite when starting with GR(SO42-).

Chemical composition and Gibbs standard free energy of formation of Fe(II)-Fe(III) hydroxysulphate green rust and Fe(II) hydroxide

AbstractThe redox potential and pH of aerated suspensions of iron(II) hydroxide in sulphate–containing aqueous solutions are measured during the oxidation process. Plateaux corresponding to the equilibrium conditions between Fe(OH)2(s) and Fe(II)-Fe(III) hydroxysulphate GR2(SO2-4)(s) on the one hand, and between GR2(SO2-4)(s) and FeOOH(s) on the other hand, are displayed. Potentiometry, voltammetry, pH-metry and Mössbauer spectroscopy are applied to follow all reactions. The thermodynamic meaning of the measured potential of the first plateau which corresponds to the GR2(SO2-4)(s)/Fe(OH)2(s) equilibrium is demonstrated. The chemical composition of GR2(SO2-4)(s) is found to be FeII4 FeIII2(OH)12SO4·nH2O all along the oxidation process, implying that this compound must be considered as a pure phase with a well-defined composition. The Gibbs standard free energy of formation or chemical potential μ°[GR2(SO2-4)(s)] in ‘anhydrous form’ (n = 0) is determined at −3790±10 kJ mol-1. A consistent value of μ°[Fe(OH)2(s)] at −490±1 kJ mol-1 is obtained.

Chemical Composition and Gibbs Standard Free Energy of Formation of Fe(II)-Fe(III) Hydroxysulphate Green Rust and Fe(II) Hydroxide

Chemical Composition and Gibbs Standard Free Energy of Formation of Fe(II)-Fe(III) Hydroxysulphate Green Rust and Fe(II) Hydroxide

IDENTIFICATION OF GREEN RUST COMPOUNDS IN THE AQUEOUS CORROSION PROCESSES OF STEELS ; THE CASE OF MICROBIALLY INDUCED CORROSION AND USE OF 78 K CEMS

Fe(II)-Fe(III) hydroxy-sulphate Green Rust 2, GR2(SO4–), is obtained by microbially induced corrosion of steel. Transmission Mossbauer spectroscopy (TMS) was used to characterise the corrosion products of steel sheet piles under the biofilm at low sea-water level in a harbour. To understand the process, iron coupons maintained in aqueous solutions of 4 M NaCl and 0.1 M NaHCO3 of pH 7.4 were studied by X ray diffraction and conversion electron Mossbauer spectroscopy (CEMS) at 78 K. The Fe(II)-Fe(III) hydroxy-carbonate, GR1(CO3–), covers the surface, as predicted by the Eh-pH diagram.