Immobilization of Acidithiobacillus ferrooxidans on sulfonated microporous poly(styrene–divinylbenzene) copolymer with granulated activated carbon and its use in bio-oxidation of ferrous iron

The immobilization efficiencies of Acidithiobacillus ferrooxidans cells on different immobilization matrices were investigated for biooxidation of ferrous iron (Fe^2 +) to ferric iron (Fe^3 +). Six different matrices were used such as the polyurethane foam (PUF), granular activated carbon (GAC), raw poly(styrene–divinylbenzene) copolymer (rawSDVB), raw poly(styrene–divinylbenzene) copolymer with granular activated carbon (rawSDVB-GAC), sulfonated poly(styrene–divinylbenzene) copolymer (sulfSDVB) and sulfonated poly(styrene–divinylbenzene) copolymer with granular activated carbon (sulfSDVB-GAC). The sulfSDVB-GAC polymer showed the best performance for Fe^2 + biooxidation. It was used at packed-bed bioreactor and the kinetic parameters were obtained. The highest Fe^2 + biooxidation rate (R) was found to be 4.02 g/L h at the true dilution rate (D_t) of 2.47 1/h and hydraulic retention time (τ) of 0.4 h. The sulfSDVB-GAC polymer was used for the first time as immobilization material for A. ferrooxidans for Fe^2 + biooxidation.     

Formation of schwertmannite and its transformation to jarosite in the presence of acidophilic iron-oxidizing microorganisms

Schwertmannite [Fe₈O₈(OH)₆SO₄] and jarosite [XFe₃(SO₄)₂(OH)₆] were synthesized from FeSO₄-mineral salts solutions that were inoculated with acidophilic iron-oxidizing bacteria (Acidithiobacillus ferrooxidans). Schwertmannite was transformed to NH₄⁺/H₃O⁺ jarosite upon increasing the aging time (19 to 40 days), temperature (36 to 45 °C), or the ammonium concentration (11.4 to 111.4 mM) in acid (about pH 2.0) media. Thus, in this phase transformation, metastable schwertmannite served as a solid phase precursor for jarosite formation. Scanning electron microscope and chemical analyses showed that the morphology, specific surface area and chemical composition of the jarosites thus produced varied depending on the experimental conditions. Because the surface areas and the molar ratios of Fe:S in the two Fe(III) hydroxysulfates are different, the transformation of schwertmannite to jarosite impacts the biogeochemistry of Fe and S as well as minor and trace metals in acid mine drainage.     

Biosynthesis of schwertmannite by Acidithiobacillus ferrooxidans cell suspensions under different pH condition

Oxidation of FeSO₄ solution with initial pH in the range of 1.40–3.51 by Acidithiobacillus ferrooxidans LX5 cell at 26 °C and subsequent precipitation of resulting Fe(III) were investigated in the present study. Results showed that the oxidation rate of Fe(II) was around 1.2–3.9 mmol l^? 1 h^? 1. X-ray diffraction (XRD) indicated that the formed precipitates were composed of natrojarosite with schwertmannite when the initial pH was 3.51, while only schwertmannite was produced when initial pH was in the range of 1.60–3.44 and no precipitate occurred when initial pH ≤ 1.40. Scanning electron microscope (SEM) analyses showed that precipitates formed in solution with initial pH 3.51 were spherical particles of about 0.4 µm in diameter and had a smooth surface, whereas precipitates in solution with initial pH ≤ 3.44 were spherical particles of approximately 1.0 µm in diameter, having specific sea-urchin morphology. Specific surface area of the precipitates varied from 3.42 to 23.45 m² g^? 1. X-ray fluorescence analyses revealed that schwertmannite formed in solution with initial pH in the range of 2.00–3.44 had similar elemental composition and could be expressed as Fe₈O₈(OH)_4.42(SO₄)_1.79, whereas Fe₈O₈(OH)_4.36(SO₄)_1.82 and Fe₈O₈(OH)_4.29(SO₄)_1.86 as its chemical formula when the initial pH was 1.80 and 1.60, respectively.     

Both initial concentrations of Fe(II) and monovalent cations jointly determine the formation of biogenic iron hydroxysulfate precipitates in acidic sulfate-rich environments

In order to accurately predict the types of biogenic iron hydroxysulfate precipitates in acidic, sulfate-rich environments facilitated by Acidithiobacillus ferrooxidans, different initial concentrations of Fe^2 +, K⁺, Na⁺, and NH₄⁺ are selected and tested in batch experiments for the formation of the precipitates. The critical equations of jarosite formation in FeSO₄–K₂SO₄–H₂O system or FeSO₄–(NH₄)₂SO₄–H₂O system could be described as Y = ? 22120.8077 ? 0.04257x + 0.006170x² (R² = 0.9979) or Y = 0.03540 ? 0.002950x + 7.407E ? 5x² (R² = 0.9934), respectively, where Y is the threshold or critical values of the molar ratio of Fe/K or Fe/NH₄ for jarosite formation, and x (mmol/L) is the initial concentration of Fe(II). Schwertmannite is the sole biogenic secondary ferric mineral when molar ratio of Fe/K or Fe/NH₄ is higher than Y in the system with a given initial Fe(II) concentration. The precipitates are an admixture of schwertmannite and jarosite, or pure jarosite when the Fe/M molar ratio is lower than Y. The crystallinity of the secondary ferric minerals increased with the increase of initial Fe(II) concentration in the medium with a fixed K⁺ concentration. It is observed that the capacity of monovalent cation in promoting jarosite formation is K⁺ > NH₄⁺ > Na⁺, as exhibiting that the capacity of K⁺ in this process is about 75 and 200 times greater than NH₄⁺ and Na⁺, respectively. Obviously, both the initial concentration of Fe(II) and molar ratio of Fe to monovalent cation determine the types of biogenic iron hydroxysulfate precipitates.     

Structural and magnetic properties of Ba0.7Sr0.3Fe12 − 2x Co x Ti x O19 M-type hexaferrites

We have studied the effect of “double” substitution in Ba_0.7Sr_0.3Fe_{12 ? 2x} Co _x Ti _x O₁₉ on the structural and magnetic properties of M-type barium hexaferrite. The basic composition of Ba_{1 ? x} Sr _x Fe₁₂O₁₉ obtained by heat-treating carbonate-hydroxide precipitates has been optimized (x = 0.3). 2Fe³⁺ → Co²⁺ + Ti⁴⁺ substitutions considerably reduce the coercive force (H _c) and increase the magnetization (M _s) relative to Ba_0.7Sr_0.3Fe₁₂ O₁₉.     

Etude de la cinetique d'oxydation de magnetites finement divisees. I - Influence de la substitution par l'aluminium

The kinetics of finely divided, (Fe²⁺Fe³⁺_2?xAl³⁺_x)O₄ type (0 ? x ? 2), substitution magnetites oxidation into metastable phase γ(Fe³⁺_1?yAl³⁺_y)₂O₃ (x = 3y) has been accounted for by means of the law of diffusion, under variable working conditions, of the cationic vacancies generated at solid-gas interface with a diffusion coefficient that decreases when the stoichiometric difference is high. The crystallites size and the trivalent substituant percentage increases, in both cases, slow down the reaction rate.     

The nature of Schwertmannite and Jarosite mediated by two strains of Acidithiobacillus ferrooxidans with different ferrous oxidation ability

Jarosite and Schwertmannite are iron-oxyhydroxysulfate materials. These materials gain increasing interest in geological and metallurgical fields. Especially, for it can effectively scavenge heavy metals, less toxic ions and better biocompatibility, the application potential in environment becomes more and more intriguing. In this study, the nature of Jarosite and Schwertmannite mediates synthesized by two strains of Acidithiobacillus ferrooxidans with different ferrous oxidation ability is investigated. The precipitates are characterized by SEM, XRD, FTIR, and TG/DSC analysis. The materials are varied in color, shape, surface area, elemental composition and crystallinity. The crystallinity of precipitate produced by A. ferrooxidans 23270 with lower oxidation ability in optimized medium is significantly better than the precipitate produced by A. ferrooxidans Gf. A. ferrooxidans Gf will tend to mediate the formation of Schwertmannite with the decreasing of monovalent cation concentration in optimized medium. Cr(VI) adsorption capacity difference exists among the four materials. The adsorption efficiency of Schwertmannite is higher than Jarosite. Adsorption capacity of the materials formed by A. ferrooxidans Gf is higher than that of A. ferrooxidans 23270. Adsorption capacity decreases with the increasing of crystallinity.     

Microstructural characterization of terbium-doped ceria

The microstructures of Ce_1−xTb_xO_2−δ (0.10 ≤ x ≤ 0.50) sintered samples were studied systematically using transmission electron microscopy. The sintered samples consist of not only fluorite-structured matrix but also nano-sized precipitates. Correspondingly, diffuse scattering and extra reflections related to the precipitates were observed in the selected area diffraction patterns. The composition of the precipitates was studied quantitatively by electron energy-loss spectroscopy, indicating that the precipitates have higher Tb concentration than that of the matrix. Furthermore, Tb³⁺ and Ce³⁺ cations were observed to segregate in the precipitates.     

Synthesis and Properties Investigation of Non-equivalent Substituted W-Type Hexaferrite

A novel composed W-type hexaferrite Ba_1?x La _x Co₂Fe₁₆O₂₇ was rapidly synthesized via a sol–gel self-combustion reaction. The effects of lanthanum ions on the oxidation state of iron ions and cobalt ions in hexaferrite were explored by X-ray photoelectron spectroscopy. The changes of the Fe 2p X-ray absorption spectra indicated that the nonequivalent substitution can lead to the transition Fe³⁺→ Fe²⁺ in Ba_1?x La _x Co₂Fe₁₆O₂₇. However, the oxidation state of cobalt ions was maintained as Co²⁺. Moreover, the effects of La content on the phase composition, structural parameters, morphology, and static magnetic properties were also investigated in detail by using the X-ray diffractometer, scanning electron microscope, and vibrating sample magnetometer. The results indicated that the structural parameters decreased regularly with increasing the La content, and the magnetic properties were enhanced after substitution, which is beneficial for their application in various electrical devices employed for industrial and military applications.     

Oxidation of Fe–Si alloys in CO2–H2O atmospheres

Abstract

Iron and model alloys containing 1, 2, and 3wt% Si were reacted with dry and wet CO₂ gases at 800°C. All oxidised in dry CO₂ according to approximately linear kinetics. Additions of H₂O accelerated the reaction until steady-state parabolic kinetics were achieved. However, the effect of H₂O was small in the steady-state reaction stage of Fe – 3Si. Alloy reaction products were a duplex scale consisting of an outer FeO+Fe₃O₄ layer and an inner FeO+Fe₂SiO₄ layer, plus an internal oxidation zone, in all gases. In Fe – 1Si, amorphous SiO₂ precipitates in the internal oxidation zone grew with rod-like morphologies in all gases. However, internal amorphous SiO₂ precipitates grown in Fe – 2Si and Fe – 3Si formed network patterns. Internal penetration rates were initially rapid in Fe – 1Si, but slowed considerably at longer times. In Fe – 3Si, the internal oxidation zone grew wider in the first 20 h of reaction, and then remained constant in dry gas. In the wet gases this zone subsequently diminished, and disappeared after 50 h reaction.     

Cu-doping effect on structure and magnetic properties of Fe-doped ZnO powders

Fe-doped and Cu, Fe co-doped ZnO diluted magnetic semiconductors powders were synthesized by sol–gel method. The x-ray diffraction (XRD) results showed that Zn_0.97−xFe_0.03Cu_xO (x ≤ 0.02) samples were single phase with the ZnO-like wurtzite structure. X-ray photoelectron spectroscopy (XPS) showed that Fe²⁺ and Fe³⁺ existed in Zn_0.97Fe_0.03O, while Fe²⁺, Fe³⁺and Cu⁺, Cu²⁺ were found in Zn_0.95Fe_0.03Cu_0.02O. Both Zn_0.97Fe_0.03O and Zn_0.95Fe_0.03Cu_0.02O exhibited ferromagnetic performance at room temperature. But the Cu incorporation reduced the saturation magnetization of Fe-doped ZnO diluted magnetic semiconductors.     

Effect of NaOH Concentration and Adding Sequences on Structural and Magnetic Properties of Ni<Subscript>0.4</Subscript>Co<Subscript>0.6</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> Nanopowders Prepared Via Co-precipitation Route

Ni_0.4Co_0.6Fe₂O₄ nanopowders were prepared via the co-precipitation route followed by annealing treatment. The structural and magnetic properties of the as-synthesized samples were determined by XRD, FT-IR, TG-DSC, and PPMS measurements, respectively. The XRD patterns indicated a single-phase cubic spinel structure for all the Ni-Co ferrite samples, regardless of adding sequences of the reactants or NaOH concentration. The analysis of the XRD patterns revealed that the enhancement in lattice constant with increasing NaOH concentration is related to the prevention of oxidization of Co²⁺ ions in the Ni-Co ferrite lattice. The FT-IR spectra indicated that samples prepared in the B process have fewer impurities than those prepared in the A process. The enhancement in saturation magnetization with the increase in sodium hydroxide concentration could be attributed to the strengthening of super-exchange interaction between A and B sublattices, due to replacements of Co³⁺ ions (magnetic moment of 0 μ _B) by Co²⁺ ions (magnetic moment of 3 μ _B) at B sublattices. The obvious increase in the coercivity field with the increase in concentration of NaOH solutions can be interpreted in terms of enhancement of magneto-crystalline anisotropy that originated from gradual substitutions of Co³⁺ ions with Co²⁺ ions at the octahedral sites.     

Oxidation character of chlorite from Byrapur chromite deposit,India — A57Fe Mössbauer evaluation

Chlorite occurring in tremolite-chlorite schist rock of Byrapur chromite deposit of southern India has been investigated by⁵⁷Fe Mössbauer spectroscopy along with XRD, IR and EPMA analyses. From XRD and EPMA results the chlorite is identified as clinochlore. The fit of Mössbauer spectrum (at room temperature) shows five symmetric doublets for iron. Based on hyperfine parameters three doublets are assigned to Fe²⁺ attrans andcis positions of talc layers, and Fe²⁺ at brucite layer. The remaining two doublets are attributed to Fe³⁺ attrans position and Fe³⁺ at tetrahedral site. The Mössbauer result suggests that the Fe³⁺ in octahedral sites of this chlorite was caused by oxidation after chloritization. The chlorite of Byrapur area was less oxidized compared to the chlorite of Sukinda chromite deposit of eastern India.     

A Novel Synthesis,Structural, Morphological,and Opto-magnetic Characterizations of Magnetically Separable Spinel Co x Mn1−x Fe2O4 (0 ≤ x ≤ 1) Nano-catalysts

Spinel Co _x Mn_1?x Fe₂O₄ (0≤x≤1) nano- crystals were successfully synthesized by a simple microwave-assisted combustion method. High-resolution scanning electron microscopy (HR-SEM) and transmission electron microscopy (HR-TEM) analysis was used to study the morphological variations and found the particle-like nanocrystal morphologies. Energy dispersive X-ray (EDX) results showed that the composition of the elements were relevant as expected from the combustion synthesis. Powder X-ray diffraction (XRD) analysis showed that all composition was found to have cubic spinel-type structure. Average crystallite size of the samples was found to be in the range of 10.36–21.16 nm. The lattice parameter decreased from 8.478 to 8.432 Å with increasing Co²⁺ content. Fourier transform infrared (FT-IR) spectra showed two strong absorption peaks observed at lower frequency (～435 to ～800 cm^?1), which can be assigned to the M–O (Mn, Co, and Fe) bonds. UV-Visible diffuse reflectance spectroscopy (DRS) shows that the energy band gap of pure MnFe₂O₄ is 1.78 eV and with increase in the Co²⁺ ion, it increases from 1.87 to 2.33 eV. Addition of Co²⁺ in MnFe₂O₄ reduces the particle size, which can be confirmed by the blue shift in the photoluminescence (PL) spectra. Vibrating sample magnetometer (VSM) results that confirmed a weak ferromagnetic behavior for all composition with saturation magnetization values in the range of 50.05 ±04 to 67.09 °03 emu/g. All composition of spinel Co _x Mn_1?x Fe₂O₄ nano-crystals were successfully tested as catalyst for the oxidation of benzyl alcohol to benzaldehyde, which has resulted 87.32 and 94.28 % conversion efficiency of MnFe₂O₄ and Co_0.6Mn_0.4Fe₂O₄, respectively.     

Hysteresis analysis of Co-Ti substituted M-type Ba-Sr hexagonal ferrite

The magnetic, crystallographic properties and grain morphology of synthesized Ba_0.5Sr_0.5Co_xTi_xFe_{(12 − 2x)}O₁₉ ferrite have been investigated by XRD, SEM and VSM. XRD and SEM confirm M-type hexagonal crystal structure. X-ray diffraction indicates expansion of hexagonal unit cell with substitution of Co²⁺ and Ti⁴⁺ ions. The microstructure governs increase in density and intergrain connectivity with substitution. The preferential site occupancy of substituted Co²⁺ and Ti⁴⁺ ions results in rapid decline of anisotropy field, hysteresis loops also revealed same effect of substitution. Coercivity and remanence magnetization can be easily controlled by varying substitution while maintaining high saturation magnetization, making it useful for recording media.     

Preparing particulate magnetites with pigment properties from suspensions of basic iron(III) sulphates with the structure of jarosite

The transformation of a suspension of hydronium jarosite, H₃O⁺Fe₃(SO₄)₂(OH)₆, into Fe₃O₄ (magnetite) of pigment quality is described. The process consists in the neutralization of the hydronium jarosite suspension in FeSO₄ aqueous solutions with NH₃ and subsequent thermal treatment of this mixture at controlled pH and temperature.     

Double electron exchange in Fe1−xO : A Mössbauer study

Mössbauer spectroscopy investigations have been performed at room temperature upon Fe_1−xO samples with 0.05 ⩽ x ⩽ 0.094 which have been previously characterized by X-ray diffraction and thermomagnetic analysis and the composition of which have been determined by thermogravimetric oxidation to Fe₂O₃.A model allowing to calculate the amount of Fe³⁺ ions has been proposed; it assumes a fast electron exchange over iron atoms in octahedral sites between Fe²⁺ and Fe³⁺. The amount of Fe³⁺ ions calculated from the Mössbauer data agrees very well with those obtained directly from the thermogravimetric analysis.     

Biological Metabolism Synthesis of Metal Oxides Nanorods from Bacteria as a Biofactory toward High‐Performance Lithium‐Ion Battery Anodes

Increasing awareness toward environmental remediation and renewable energy has led to a vigorous demand for exploring a win‐win strategy to realize the eco‐efficient conversion of pollutants (“trash”) into energy‐storage nanomaterials (“treasure”). Inspired by the biological metabolism of bacteria, Acidithiobacillus ferrooxidans (A. ferrooxidans) is successfully exploited as a promising eco‐friendly sustainable biofactory for the controllable fabrication of α‐Fe₂O₃ nanorods via the oxidation of soluble ferrous irons to insoluble ferric substances (Jarosite, KFe₃(SO₄)₂(OH)₆) and a facile subsequent heat treatment. It is demonstrated that the stable solid electrolyte interphase layers and marvelous cracks in situ formed in biometabolic α‐Fe₂O₃ nanorods play important roles that not only significantly enhance the structure stability but also facilitate electron and ion transfer. Consequently, these biometabolic α‐Fe₂O₃ nanorods deliver a superior stable capacity of 673.9 mAh g^?1 at 100 mA g^?1 over 200 cycles and a remarkable multi‐rate capability that observably prevails over the commercial counterpart. It is highly expected that such biological synthesis strategies can shed new light on an emerging field of research interconnecting biotechnology, energy technology, environmental technology, and nanotechnology.     

Optical and structural investigations on iron-containing phosphate glasses

The article reports the preparation and complex characterization of iron-containing phosphate glasses considered to be ecological materials, as they contain non-toxic compounds related to environment. The oxide system Li₂O?CMgO?C(CaO)?CAl₂O₃?CP₂O₅?C(FeO/Fe₂O₃) was investigated in respect to its structural changes caused by MgO replacement with CaO and by the iron addition. UV?Cvis?CNIR (ultraviolet?Cvisible?Cnear infrared) spectroscopy as well as thermo-gravimetric (TG) measurements, differential thermo-analysis (DTA), X-ray diffraction (XRD) analysis, electronic paramagnetic resonance (EPR), and Mossbauer (nuclear gamma resonance) spectroscopy have been used to investigate redox states and coordination symmetry of iron, together with vitreous network changes during the heat treatment up to 1000 °C. UV?Cvis?CNIR transmission spectroscopy revealed no structural modifications when MgO was substituted by CaO, but noteworthy absorption bands attributed to Fe²⁺/Fe³⁺ species. TG analysis made in the 20?C1000 °C range shows low weight loss accompanied by several thermal effects, as evidenced by DTA. XRD patterns for the glass samples heat treated at about 700 °C revealed the presence of different phosphate crystalline phases containing Mg, Al, and Fe ions. EPR spectroscopy revealed the presence of paramagnetic Fe³⁺ ions and the change of the first coordination symmetry, when the samples are heated below the vitreous transition temperature. Mossbauer spectroscopy has evidenced two paramagnetic species, Fe²⁺ and Fe³⁺, both in octahedral coordination symmetry and a clustering process supported by only Fe³⁺ ions.     

Photocatalytic degradation of formaldehyde by nanostructured TiO2 composite films

Interest in the photocatalytic oxidation of formaldehyde from contaminated wastewater is growing rapidly. The photocatalytic activity of the nanocrystalline Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film for the degradation of formaldehyde solution under visible light was discussed in this study. The films were characterised by field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy, X-ray diffraction (XRD), BET surface area, UV–Vis absorption spectroscopy, and photoluminescence spectroscopy. The FE-SEM results revealed that the Fe³⁺/F^? co-doped TiO₂–SiO₂ film was composed of uniform round-like nanoparticles or aggregates with the size range of 5–10 nm. The XRD results indicated that only the anatase phase was observed in the film. Compared with a pure TiO₂ film and a singly modified TiO₂ film, the Fe³⁺/F^? co-doped TiO₂–SiO₂ composite film showed the best photocatalytic properties due to its strong visible light adsorption and diminished electrons-holes recombination.