Coexistence Of Fe2 Research Articles

Mechanism of Germanium Adsorption by Iron Hydroxide Colloids during the Leaching Process of Secondary Zinc Oxide.

In the leaching process of secondary zinc oxide, there is a problem of germanium loss caused by the colloidal adsorption of germanium by iron hydroxide (Fe(OH)3) formed by Fe3+ hydrolysis. In response to this, this article elucidates the hydrolysis conditions of Fe3+ and the adsorption mechanism of the Fe(OH)3 colloid on germanium through theoretical analysis and simulation of the adsorption process. The coexistence of Fe3+ and H2GeO3 requires high acidity conditions (pH < 1.53 at 25 °C). The adsorption of germanium by the Fe(OH)3 colloid is a spontaneous exothermic entropy reduction process, which conforms to a pseudo-second-order kinetic model and includes three stages: fast, slow, and equilibrium. In addition, the adsorption process can be fitted by the Langmuir isotherm adsorption model, mainly consisting of monolayer and chemical adsorption. The Fe(OH)3 colloid has a great adsorption capacity for germanium at 328 K, and the equilibrium adsorption capacity is 261.15 mg/g in 40 min. During leaching, the adsorption of germanium by Fe(OH)3 colloids can be inhibited by increasing the reaction temperature, controlling the pH value of the solution system, and suppressing the formation of Fe3+ at the source. This study provides direction for how to suppress the adsorption of germanium by Fe(OH)3 colloids during the leaching process of secondary zinc oxide, which is of great significance for improving the germanium leaching efficiency and fully utilizing limited germanium resources.

Study on the Influence of Calcination Temperature of Iron Vitriol on the Coloration of Ancient Chinese Traditional Iron Red Overglaze Color.

Iron red, a traditional Jingdezhen overglaze color, is primarily colored with iron oxide (Fe2O3). In traditional processes, the main ingredient for the iron red overglaze color, raw iron red, is produced by calcining iron vitriol (FeSO4·7H2O). Analysis of ancient iron red porcelain samples indicates that the coloration is unstable, ranging from bright red to dark red and occasionally to black. Addressing this, the present study, from a ceramic technology standpoint, conducts a series of calcination experiments on industrial iron vitriol at varying temperatures. Utilizing methodologies such as differential scanning calorimetry-thermogravimetry (DSC-TG), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy with X-ray energy dispersive spectrometry (SEM-EDS), and optical microscopy (OM), this research scientifically explores the impact of iron vitriol's calcination temperature on the coloration of traditional Jingdezhen iron red overglaze color. The findings indicate that from room temperature to 550 °C, the dehydration of iron vitriol resulted in the formation of Fe2(SO4)3 and a minimal amount of α-Fe2O3, rendering the iron red overglaze color a yellowish-red shade. At 650 °C, the coexistence of Fe2(SO4)3 and α-Fe2O3 imparted a brick-red color to the iron red. As the temperature was elevated to 700 °C, the desulfurization of Fe2(SO4)3 produced α-Fe2O3, transitioning the iron red to an orange red. With further temperature increase to 750 °C, the particle size of α-Fe2O3 grew and the crystal reflectivity decreased, resulting in a purplish-red hue. Throughout this stage, the powder remained in a single α-Fe2O3 phase. Upon further heating to 800 °C, the crystallinity of α-Fe2O3 enhanced, giving the iron red overglaze color a dark red or even black appearance.

In-situ one-pot synthesis, characterization of magnetic hydrochar and its application as Fenton-like catalyst for the degradation of methylene blue dye

The widespread use of dyes in various industries has led to alarming levels of water pollution, posing significant environmental and health risks. This study presents biochar being a carbon-rich source, produced from Acacia koa pod covers has been used as a sustainable source to prepare Ak/BC-Fe3O4 magnetic nanocomposite, subsequently employed for Fenton-like degradation of methylene blue (MB) dye. FESEM-EDS revealed that the synthesized nanocomposite has a morphology of spherical magnetic nanoparticles being embedded on the biochar base and EDS further confirmed the synthesis of magnetic biochar by detecting only C, O, and Fe. The nanocomposite is mesoporous with a pore volume of 0.03204 cm3/g and a surface area of 7.11 m2/g as shown by the BET results. XRD substantiated the presence of an amorphous structure of biochar and the presence of ultra-small crystallites of Fe3O4 nanoparticles. FTIR signified the presence of specific functional groups for Fe–O and biochar whereas, XPS showed the peaks at 712.39 and 725.78 eV indicated the coexistence of Fe2+ and Fe3+. The nanocomposite is superparamagnetic with a saturation magnetization of 8.64 emu/g having remarkable magnetic separation capacity. Fenton-like degradation of MB dye in the presence of H2O2 revealed a first-order reaction with removal efficiency ranging between 82 and 96% in 120 min with convenient recycling ability for 7 cycles. Hence, this study underscores the outstanding characteristics and MB degradation efficiency of Ak/BC–Fe3O4, emphasizing its synthesis from sustainable plant biomass as a promising solution to address water pollution challenges associated with dye contamination.

Exploring Iron Oxide Catalysts for Acetone Hydrodeoxygenation: Making Use of an Earth-Abundant Resource

The catalytic performance of γ-Fe2O3 nanopowder was investigated in the acetone hydrodeoxygenation (HDO) reaction, an essential catalytic reaction in biomass valorization. Sequential reduction/oxidation thermal pre-treatments of the γ-Fe2O3 nanopowder induced significant structural and electronic modifications that directly impacted its catalytic performance. The co-existence of Fe3+/Fe2+/Fe0 sites led to different reaction pathways (C-C coupling, hydrogenolysis, hydrogenation, and (hydro)deoxygenation) that formed a wide range of products. The correlation of the catalytic and structural data provided a better understanding of C-O, C-C, and C-H bond activation under the HDO reactional stream in the presence of metallic and oxidized phases of iron. This study demonstrates the tunability of FeOx catalysts in the acetone HDO reaction to favor different reaction pathways and the formation of products. It highlights that tailoring active sites is crucial for developing selective and optimized catalysts for the HDO reaction.

Distinct effects of Fe3+ on the adsorption of chromate and arsenate: A comparison of iron-bearing ferrihydrite and nano-TiO2 absorbents

Fe3+, a particularly prevalent ion in acid mine drainage (AMD), has a substantial impact on the crystallization of iron-bearing minerals and the immobilization of multiple co-existing oxyanions such as Cr(VI) and As(V). To investigate the varied effects of Fe3+ on Cr(VI) and As(V), ferrihydrite (Fh) and nano-TiO2 were selected due to their superior adsorption effectiveness and distinctive stability. As a result of the dissolution of Fe3+ in Fh and its subsequent promotion to As(V) adsorption, As(V) adsorption capacity on Fh (124.0 mg/g) was twice that of TiO2 (62.76 mg/g). The co-existence of Fe3+ in the As(V) adsorption system greatly enhanced As(V) sorption on TiO2 (18.9–56.5%) and Fh (1.03–15.7%), and an additional Fe-As complex was confirmed to contribute extra As(V) removal on both Fh and TiO2 by the FTIR and EXAFS spectra. On the other hand, TiO2 (18.15 mg/g) and Fh (19.50 mg/g) exhibited nearly identical Cr(VI) adsorption capabilities, and the co-presence of Fe3+ even slightly blocked Cr(VI) sorption on Fh. The spectroscopic and modeling results showed that the monodentate Cr(VI) adsorption complex was blocked by Fe3+, but the outer-sphere and bidentate inner-sphere Cr(VI) surface complexes were unaffected. Additionally, in the ternary As-Cr-Fe adsorbate systems, Cr(VI) had little effect on the development of As-Fe surface complexes or precipitates. With the interference mechanisms, actual AMD wastewater adsorption on Fh and TiO2 was well explained and predicted. The findings would offer fresh perspectives on the bioavailability and fate of hazardous metal compounds in the AMD-polluted locations.

Cation distribution, Fe2+/Fe3+ valence states and oxygen vacancies detection in the Y2.98Er0.02Fe5−yCryO12 compound

The appropriate physical properties of yttrium iron garnet (YIG), make it an excellent soft magnetic material for applications in microwave, magneto-optical devices, and spintronic. In this sense, the scientific community has made and continues to make numerous investigations to improve the YIG properties. Here, we have presented a study on the cation's distribution, valence states and oxygen vacancies (OV) in the Y2.98Er0.02Fe5−yCryO12 (0.00 ≤ y ≤ 0.05) compound. The coral type structures were observed by Transmission Electron Microscopy (TEM), whereas the Selected Area Electron Diffraction (SAED) confirmed the YIG crystalline nature, by means of bright points corresponding to the (004), (123), (024), (224), (022) and (112) YIG family planes. The valence states of the different atoms and oxygen vacancies defects were identified by the deconvolution of the X-ray Photoelectron Spectroscopy (XPS) spectra. For all YIG samples, the coexistence of Fe3+ and Fe2+ ions were observed and the Fe2+ cations and OV decrease as the Cr3+ cations concentration increases. By using the Electronic Paramagnetic Resonance (EPR) measurements, was detected the magnetic contribution of the Fe cations, while an isotropic line obtained near to 3440 Oe was associated with the Cr3+ cations presence. Finally, an increase of the Cr content led to a decrease in the saturation magnetization (Ms), which was explained in terms of the cation’s occupation, obtained from a phenomenological model.

Fabrication of novel magnetic Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite synthesized by a simple ultrasonic-assisted route for organic dye removal using Fenton-like reaction.

Fenton-like degradation of contaminants is considered to be a feasible method for eliminating environmental pollution. In this study, a novel ternary Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite was fabricated using a novel ultrasonic-assisted technique, and investigated as a Fenton-like catalyst for the removal of tartrazine (TRZ) dye. The nanocomposite was synthesized by first coating the SiO2 shell around the Mg0.8Cu0.2Fe2O4 core via a Stöber-like process to form Mg0.8Cu0.2Fe2O4/SiO2. Then, a simple ultrasonic-assisted route was used to synthesize Mg0.8Cu0.2Fe2O4/SiO2/CeO2 nanocomposite. This approach provides a simple and environmentally friendly way to produce this material without the use of any additional reductants or organic surfactants. The fabricated sample demonstrated excellent Fenton-like activity. The efficiency of Mg0.8Cu0.2Fe2O4 was significantly enhanced by the incorporation of SiO2 and CeO2, and complete removal of TRZ (30mg/L) was achieved within 120min using 0.2g/L of Mg0.8Cu0.2Fe2O4/SiO2/CeO2. The scavenger test shows that the main active species is the strong oxidizing of hydroxyl radicals (HO•). Consequently, the Fenton-like mechanism of Mg0.8Cu0.2Fe2O4/SiO2/CeO2 is explained based on the coexistence of Fe3+/Fe2+, Cu2+/Cu+, and Ce4+/Ce3+ redox couples. The removal efficiency of TRZ dye remained around 85% after the third recycling run, revealing that the nanocomposite could be employed to eliminate organic contaminants in water treatment. This research opened up a new avenue for expanding the practical application of new-generation Fenton-like catalysts.

Magnetic Properties of FeBO3 in the Low-Spin State

Changes in the magnetic properties of FeBO3 single crystals in the course of spin crossover occurring with increasing pressure up to 63 GPa are studied both experimentally and theoretically. Simultaneous measurements of the nuclear diffraction and nuclear forward scattering spectra make it possible to detect the antiferromagnetic high-spin state at low pressures up to 48 GPa and to reveal the antiferromagnetic state within the range characterized by the coexistence of Fe3+ ions in the high-spin and low-spin states, which occurs at pressures from 48 to 54 GPa, where the hysteresis takes place. Above 58 GPa, only the low-spin state is observed, whereas the magnetic order is absent down to 9 K. An analysis of changes in the exchange interactions manifesting themselves at spin crossover suggests that there exist competing ferromagnetic and antiferromagnetic contributions nearly compensating each other. A possible Néel temperature in the low-spin state does not exceed 7 K; thus, an ordered state cannot be observed in our experiments.

Structural, Electrical, and Magnetic Properties of Hexagonal Lu0.5−xZrxSc0.5FeO3 Ceramics

Hexagonal Lu0.5−x Zr x Sc0.5FeO3 polycrystalline samples are synthesized by conventional solid‐state reaction. Effects of slight Zr4+ ions substitution on the structural distortion and magnetoelectric properties are investigated. The coexistence of Fe2+ and Fe3+ is checked by X‐ray photoelectron spectroscopy (XPS). X‐ray diffraction (XRD) and Raman spectrum (RS) microstructural analysis reveal that all samples are in the hexagonal structure with the polar space group of P6 3 cm. With x increasing slightly, the tilting of FeO5 bipyramids and the bending of rare‐earth atomic layers are suppressed. The Néel temperature T N of antiferromagnetic (AFM) transition is decreased, whereas the weak ferromagnetic (WFM) order is strengthened. The permittivity ε r of the samples is significantly increased. A dielectric anomaly near T N in Lu0.45Zr0.05Sc0.5FeO3 may indicate magnetoelectric coupling. It is attributed to the spin–phonon coupling as is evidenced by the Raman phonon modes. The improvement of dielectricity and magnetoelectric coupling is explained by considering the Dzyaloshinskii–Moriya interaction, structural distortion, and the incremental ratio of Fe2+ ions. These results provide an idea for sensitive control of electric and magnetic properties in related materials.

New two-layer Ruddlesden\u2014Popper cathode materials for protonic ceramics fuel cells

New two-layer Ruddlesden—Popper (RP) oxide La0.25Sr2.75FeNiO7−δ (LSFN) in the combination of Sr3Fe2O7−δ and La3Ni2O7−δ was successfully synthesized and studied as the potential active single-phase and composite cathode for protonic ceramics fuel cells (PCFCs). LSFN with the tetragonal symmetrical structure (I4/mmm) is confirmed, and the co-existence of Fe3+/Fe4+ and Ni3+/Ni2+ couples is demonstrated by X-ray photoelectron spectrometer (XPS) analysis. The LSFN conductivity is apparently enhanced after Ni doping in Fe-site, and nearly three times those of Sr3Fe2O7−δ, which is directly related to the carrier concentration and conductor mechanism. Importantly, anode supported PCFCs using LSFN-BaZr0.1Ce0.7Y0.2O3−δ (LSFN-BZCY) composite cathode achieved high power density (426 mW·cm−2 at 650 °C) and low electrode interface polarization resistance (0.26 Ω·cm2). Besides, distribution of relaxation time (DRT) function technology was further used to analyse the electrode polarization processes. The observed three peaks (P1, P2, and P3) separated by DRT shifted to the high frequency region with the decreasing temperature, suggesting that the charge transfer at the electrode-electrolyte interfaces becomes more difficult at reduced temperatures. Preliminary results demonstrate that new two-layer RP phase LSFN can be a promising cathode candidate for PCFCs.

Cation mixing in Wadsley-Roth phase anode of lithium-ion battery improves cycling stability and fast Li+ storage

Developing advanced electrode materials with high stability and high ion-diffusion rate is vital for the success of high-rate lithium-ion batteries (LIBs). However, the commonly used modification strategies such as carbon coating, nanoarchitecture engineering, and introducing oxygen vacancies are unavoidably meeting with the problems of high cost and complicated preparation process. Herein, we report cation-mixing effect enhanced fast Li+ storage in Wadsley-Roth phase Fe-Ti-Nb oxide (FTNO) materials by a facile solution combustion method. Co-existence of Fe3+ and Ti4+ in the crystallographic shear structure leads to enhanced cation-mixing effect with cations short-range order (SRO) in FTNO materials, thus resulting in outstanding capabilities of fast Li+ storage/diffusion, robust structure and low charge transfer resistance compared with the analogues of FeNb11O29 and Ti2Nb10O29. Consequently, a high-capacity retention of 71.8% is achieved upon 10 000 cycles at 10 C. Most importantly, the feasibilities of FTNO are also systematically verified in various practical electrochemical energy storage devices containing conventional lithium-ion full battery (FTNOǁLiFePO4), high-power lithium-ion hybrid capacitor [FTNOǁactive carbon (AC)], and novel dual-ion battery [FTNOǁmesocarbon microbeads (MCMB)]. It is worth noting that the FTNOǁMCMB with high output voltage of 3 V delivers a capacity of 105.7 mAh g−1, implying a great potential of FTNO applied in dual-ion batteries.

Photocatalytic mechanism and performance of a novel wool flake–BiFeO3 nanosheet–TiO2 core–shell-structured composite photocatalyst

In this study, BiFeO3 (BFO) nanosheets ground from BFO particles were first incorporated with wool flakes to construct sandwich-like wool–BFO composites using the vibration-assisted ball milling technique in freezing conditions. The wool–BFO composites were then loaded with a thick layer of TiO2 nanoparticles to prepare the core–shell-structured wool–BFO–TiO2 composites using a hydrothermal synthesis process. The microstructure of the core–shell wool–BFO–TiO2 composites and its photocatalytic applications were systematically examined using a series of characterization methods. Trapping experiments and electron spin resonance spectra were also employed to judge the active radical species like superoxide radicals (·O2 −), singlet oxygen (1O2), holes (h+), and hydroxyl radicals (·OH) using benzoquinone, furfuryl alcohol, ethylenediamine tetraacetic acid, and tert-butanol as the scavengers, respectively. The photodegradation performance of the wool–BFO–TiO2 composites was measured using more resistant methyl orange (MO) dye as the pollutant model. In comparison with the wool–TiO2 or wool–BFO composites, the superior photocatalytic properties of the wool–BFO–TiO2 composites under visible light irradiation were attributed to the presence of mesopores and macropores, the large specific surface area and intimate interface between wool–BFO composites and TiO2 nanoparticles, the coexistence of Fe3+, Fe2+, Bi3+, Bi(3–x)+, Ti4+, and Ti3+species, and the strong visible light harvesting, thus leading to the fast separation of photogenerated electron–hole pairs. The wool–BFO–TiO2 composites could be used for the repeated photodegradation of organic pollutants and be recycled easily using a magnet. The active radical species of the wool–BFO–TiO2 composites were ·O2 − and 1O2 rather than ·OH and h+, which were involved in the photodegradation of MO dye under visible light irradiation.

Study of Delithiation Process Features in LixFe0.8M0.2PO4 (M = Mg, Mn, Co, Ni) by Mössbauer Spectroscopy

Studies of lithium iron phosphates doped with Mg, Mn, Co, and Ni were carried out at different stages of electrochemical charging using 57Fe Mössbauer spectroscopy. A multispectrum fitting method was used to analyze spectra measured at different temperatures. This made it possible to detect and characterize various local states of iron cations with different cationic environments. The feature of the charging process that is caused by doping the samples is established. Doping of LiFePO4 leads to the formation of a large interphase boundary between lithiated and delithiated regions where Fe2+ and Fe3+ cations coexist. Magnetic moments of divalent iron cations that are located near this boundary exhibit relaxation properties. Based on the obtained results, a new model of charge and discharge processes for doped samples was proposed explaining the increase of the charge/discharge rate. Within the framework of this model, regions with increased and decreased concentrations of divalent ions are formed inside the particles of a cathode material during delithiation and lithiation, respectively. The coexistence of Fe2+ and Fe3+ ions and, as a consequence, the formation of lithium defects at interphase boundaries determine the increase in electronic and ionic conductivity at interfaces and rapid diffusion of lithium ions in the samples.

Modulating the Structure and Magnetic Properties of ε-Fe2O3 Nanoparticles via Electrochemical Li+ Insertion.

ε-Fe2O3, a metastable phase of iron oxide, is widely known as a room-temperature multiferroic material or as a superhard magnet. Element substitution into ε-Fe2O3 has been reported in the literature; however, the substituted ions have a strong site preference depending on their ionic radii and valence. In this study, in order to characterize the crystal structure and magnetic properties of ε-Fe2O3 in the Fe2+/Fe3+ coexisting states, Li+ was electrochemically inserted into ε-Fe2O3 to reduce Fe3+. The discharge and charge of Li+ into/from ε-Fe2O3 revealed that Li+ insertion was successful. X-ray magnetic circular dichroism results indicated that the reduced Fe did not exhibit site preference. Increasing the Li+ content in ε-Fe2O3 resulted in decreased saturation magnetization and irregular variation of the coercive field. We present a comprehensive discussion of how magnetic properties are modified with increasing Li+ content using transmission electron microscopy images and considering the Li+ diffusion coefficient. The results suggest that inserting Li+ into crystalline ε-Fe2O3 is a useful tool for characterizing crystal structure, lithiation limit, and magnetic properties in the coexistence of Fe2+/Fe3+.

Effect of yttrium doping on the structure, dielectric multiferroic and magnetodielectric properties of Bi5Ti3FeO15 ceramics

Multiferroic Bi5−xYxTi3FeO15 (BYTF-x, x = 0, 0.1, 0.3, 0.5, 0.7) ceramics were synthesized through the conventional solid-state reaction. The structure, dielectric, multiferroic and magnetodielectric properties of BYTF-x were investigated in detail. X-ray diffraction confirmed that all the samples were layered Aurivillius structure. Upon increasing Y content, the grain size of samples slightly decreases. The dielectric permittivity increased with Y doped. The Y doping has no effect on microstructural changes of plate-like grains which verified though field-emission scanning electron microscopy. The minimum remanent polarization (2Pr = 2.48 μc/cm2) was observed in BYTF-0.3 ceramic and the maximum magnetodielectric coefficient value of 1.23% was obtained in BYTF-0.3 ceramic perhaps result from the coexistence of Fe2+ and Fe3+. Additionally, weak ferromagnetic is only found in BYTF-0.3 ceramic. The ferromagnetism can be attributed to ferromagnetic double exchange interactions (Fe2+–O–Fe3+) and the spin canting of tilting FeO6 octahedra via the Dzyaloshinskii–Moriya interaction. These results indicate that Y doping Aurivillius phase may be the potential candidates for exploring superior room-temperature multiferroics.

Adsorption of Cr(VI) on Al-substituted hematites and its reduction and retention in the presence of Fe2+ under conditions similar to subsurface soil environments

Aluminum substitution is common in iron (hydr)oxides in subsurface environments, and can significantly modify mineral interactions with contaminants. However, few studies investigate Cr(VI) adsorption and its subsequent mobility on Al-substituted iron (hydr)oxide surfaces. Here shows that Al substitution gradually modifies hematite crystals from {101}, {112}, {110} and {104} faceted rhombohedra to {001} faceted plates, resulting in a general decrease in Cr(VI) adsorption density and favoring of monodentate mononuclear over bidentate binuclear Cr(VI) adsorption complexes. Consequently, the mobility of Cr(VI) might be increased in environments with an abundance of Al-containing iron (hydr)oxides. However, pre-adsorption of Fe2+ on hematite promotes Cr(VI) adsorption, reduction and fixation, and Al-substituted hematite removes more Cr(VI) than pure hematite. Similarly, although addition of Fe2+ to Cr(VI)-adsorbed hematite remobilizes a small proportion of Cr, it greatly increases the proportion of Cr fixed. As the coexistence of Fe2+ and iron (hydr)oxides is common in subsurface environments, Al-containing iron (hydr)oxides will promote Cr(VI) uptake and retention, with a significant proportion fixed as Cr(III), limiting Cr mobility and toxicity. These results offer new insights into how iron (hydr)oxides might control the behaviors of other high-valence redox-sensitive contaminants, and provide a platform for modeling such processes in complex soil and sediment systems.

Visualization and high sensitivity detection of Fe3+ and Cu2+ based on glutathione functionalized gold nanoclusters.

In this paper, a glutathione functionalized gold nanocluster (GSH-AuNCs) was prepared. GSH-AuNCs can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide to produce a blue-green ox-TMB. By using its peroxidase activity and the GSH-AuNCs-TMB-H2O2 system, the visualization of Fe3+ and Cu2+ and the high sensitivity detection of Fe3+ and Cu2+ can be realized according to the change of absorbance value and color of the system. The results showed that the sensitivity of the system to detect Fe3+ and Cu2+ in industrial wastewater reached 1.25 × 10-9 M and 1.25 × 10-10M, respectively. At the same time, the chelating agents NH4F and EDTA · 2Na were introduced to realize the selective detection of the two ions under the coexistence of Fe3+ and Cu2+ ions.

Multiferroic properties of aurivillius structure Bi4SmFeTi3O15 thin films

Bi4SmFeTi3O15 thin films were coated on (111)Pt/Ti/SiO2/Si substrates by the sol–gel method. X-ray diffraction analysis shows the films have a single-phase four-layered Aurivillius structure with the space group of A21am. The remarkable physical property of Bi4SmFeTi3O15 thin films are the presence of multiferroic properties at room temperature with the remnant polarization (2Pr) ~ 48 μC/cm2 and saturated magnetization (Ms) ~ 0.43 emu/cm3. Moreover, at room temperature, magnetoelectric coupling that may be derived from the charge order of Fe3+ and Fe2+ is observed. Magnetodielectric coefficient and magnetoelectric coefficient are respectively 0.78% at 0.5 T and 41.16 mV/cmOe at 0.9 T. The coexistence of Fe2+ and Fe3+ was confirmed with both X-ray photoelectron spectra and dielectric relaxation spectrum.

Layered Nb-REE ores in the Tomtor Complex (Arctic Siberia): Formation conditions

We study a unique deposit of Nb-REE ores that occur as three orebodies overlying weathered rocks of the Tomtor ultramafic alkaline-carbonatite complex in the northern Sakha Republic (Yakutia). The formation conditions of the rich Tomtor ores remain poorly constrained. Our hypothesis is that these ores, composed of detrital and authigenic minerals, were deposited in a hydrothermal lake. The Eh-pH parameters of water are reconstructed from REE distribution in ores and in monazite, with reference to results of thermodynamic calculations. The stability fields of hydrous Ce, La, and Nd phosphates in the Pourbaix diagrams are proximal in a region within a small range of pH (4-6) and Eh (-0.25 -+0.25 V). Monazite apparently formed by dehydration of the precursor phase of hydrous REE phosphate. This inference is supported by coexistence of Fe3+ and Fe2+ minerals.

Extracellular Biomineralization of Gold by Delftia tsuruhatensis GX-3 Isolated from a Heavy Metal Contaminated Paddy Soil

The use of microorganisms in geochemical gold recycling was considered recently. To explore the feasibility of gold biomineralization in this study, bacteria GX-3 were isolated from a heavy metal contaminated paddy soil in Guangxi province, China. This sulfur-reducing bacteria, Delftia tsuruhatensis, can survive in toxic Au3+ solution. Alkaline conditions (pH 8.0) and 35 °C were optimal for GX-3 cultivation. Nanoparticle formation was promoted by the coexistence of Fe3+. Field-emission scanning electron microscopy and transmission electron microscopy (TEM) images of GX-3 showed the presence of spherical particles, ranging from 50 to 100 and 200 to 500 nm in diameter, respectively, that stuck together and distributed around the surface of the bacteria as well as outside the cell. These nanoparticles were identified as gold according to the TEM–energy dispersive X-ray spectroscopy analysis. Here, bacterial extracellular solute-binding protein and/or porin should account for the gold nanoparticle formation and the detoxification in aqueous system as it transports electrons to Au3+ for nanoparticle precipitation. The ubiquitous nature of bacteria in near-surface environments and the rapid precipitation of gold by the sulfur-reducing bacterium suggest that these bacteria could be responsible for the wide bioaccumulation of gold in natural systems.