Crystalline Iron Oxides Research Articles

Characterization of biotite drugs used in traditional medicine

Temperature-induced mineral alterations are extensively used in traditional pharmaceutical industry. Studies on the traditional heating methods for enhancing pharmaceutical properties and on the toxicity of mineral-based medicines are limited. This study focuses on the effect of thermal alterations on mineralogical and chemical changes of biotite with respect to two traditional drugs (Abhrak Bhasma and Abhrak Chendhuram). Samples of the drugs and heat-treated and untreated biotite minerals were characterized using X-ray diffraction analysis, Fourier-transform infra-red spectroscopy, thermogravimetric analysis and differential scanning calorimetry. Total and water-soluble cation concentrations of drugs were measured using atomic absorption spectrometry. The study reveals that the degree of collapsing the biotite structure increased with the thermal oxidation process that produced nanoparticles of crystalline and amorphous iron oxides and secondary silicates. The thermal products of biotite had nano-crystallinity and high water solubility. The study suggests that modern pharmaceuticals can be developed from mineral-based traditional drugs.

Synergistic approach towards the sustainable management of heavy metals in wastewater using mycosynthesized iron oxide nanoparticles: Biofabrication, adsorptive dynamics and chemometric modeling study

In our study, novel mycosynthesis of ferromagnetic, monodispersed, spherical, crystalline iron oxide nanoparticles (IO-NPs) of 73.05 ± 15.47 nm were biofabricated using manglicolous fungi Aspergillus tubingensis (STSP 25) isolated from rhizospheric sediment samples of Avicennia officinalis which was sustainably utilised for the removal of Pb (II), Ni (II), Cu (II), and Zn (II) from wastewater. The elemental and XRD characterisation had shown Fe2O3 (hematite) nature of the IO-NPs which were aqua stable due to deposition of extracellular fungal bio molecules onto them. Initial batch adsorption studies revealed that at pH 6 in 313 K temp, 1 g/L of IO-NPs could able to remove >90 % of heavy metals from the aqueous matrix. This was further confirmed through muti-factor chemometric approach which involved RSM and ANN module. RSM and ANN analysis inferred that 98.0037 % of Pb (II), 96.4502 % of Ni (II), 92.1984 % of Cu (II), and 93.9913 % of Zn (II) ions were adsorbed from 9.66 mg/L of heavy metals on 1 g/L concentration of IO-NPs in 308.25 K temperature at pH 6. Adsorptive dynamics indicated the process of adsorption was kinetically spontaneous and thermodynamically it followed endothermic reaction, where metallic ions got chemisorbed on the monolayer interface of IO-NPs. The overall process followed the Langmuir isotherm model and Pseudo-second order kinetics. The Adsorbing potentiality of IO-NPs for Pb (II), Ni (II), Cu (II), and Zn (II) was found to be 9.206 mg/g, 9.666 mg/g, 8.335 mg/g and 9.106 mg/g respectively. Reusability study showed IO-NPs had high regeneration capability till five adsorption/desorption cycle.

Role of crystalline iron oxides on stabilization of inositol phosphates in soil

Inositol phosphates selective retention in soil is related to their great affinity to iron (Fe) oxides, with which they interact by the formation of ligand exchange complexes. Soils contain from amorphous to crystalline Fe oxides forms, as goethite (Gt), whose effect on inositol phosphates retention is well-known. The contribution of other widespread crystalline Fe oxides as haematite (Hm), magnetite (Mt) and maghemite (Mh) is instead less known. These oxides display different phosphorus (P) retention and release capacities due to their specific surface properties and stability towards protons, organic acids and complexing agents. We therefore investigated: i) the extent and mechanisms of myo-inositol hexaphosphate (InsP6) and inorganic phosphate (Pi) adsorption on Gt, Hm, Mt and Mh, also studying the computational geometries of InsP6 molecule; ii) the reversibility of the reaction as affected by pH and in the presence of citrate; iii) the efficiency of NaOH-EDTA on P extraction. Compared to Gt, Hm retained less InsP6, due to the distribution of superficial –OH groups allowing for the interaction of two phosphate groups instead of four, as for Gt. Mt and Mh retained more InsP6 than Hm, also through precipitation processes due to a partial dissolution of the oxides caused by InsP6. Desorption of InsP6 in the pH range 3.5–8.5 was negligible, except for Hm, while citrate led to larger desorption, with no release from Gt. NaOH-EDTA extraction of InsP6 was instead particularly effective from Gt and less from the other oxides. The four crystalline Fe oxides thus showed different capacity to retain organic P in the form of InsP6 as a function of surface properties and stability of the mineral-P complexes, therefore influencing the extent of release, accumulation and turnover in soils.

Shifts in the bacterial community along with root-associated compartments of maize as affected by goethite

Root-associated compartments, including rhizosphere soil, rhizoplane soil, and the endosphere, are found to harbor distinguished bacterial populations and community composition, but how microbiome in these rhizo-compartments are affected by edaphic variables remains largely unknown. Goethite is a prevalent crystalline iron (hydr)oxide mineral of the soil matrix and strongly interact with microbial communities. The objective of our study was to determine how goethite (α-FeOOH) amendment assemble bacterial communities in the rhizo-compartments of Maize (Zea mays. L). Using sequencing of microbial 16S ribosomal RNA gene amplicons, we revealed that goethite amendment into soil enriched Actinobacteria and depleted Proteobacteria in all rhizo-compartments. Also, goethite enlarged the differences in the alpha diversity (Chao) between rhizo-compartments, with much lower mean diversity in the endosphere and rhizoplane compared with rhizosphere soil, indicating a higher selection of the microbiome assemblage. This was supported by beta Nearest Taxon Index (βNTI > + 2), indicating that changes in environmental conditions progressively increase the strength of selection. It suggests that variable selection (a deterministic process) was the dominant process influencing the microbial assembly in soil amended with goethite. According to the distance-based linear modeling (distLM), the assemblage of bacterial communities in the rhizosphere compartments was regulated by specific edaphic variables, with the major contributors being goethite (62%), total C (52%), soil pH (50%), and FeOM (25%). Stabilization of rhizosphere C in the presence of goethite would be the selective step for its accessibility and consequent microbial community. For instance, the keystone microorganisms, e.g., Pseudomonas, had more negative links within the goethite added co-occurrence network, indicating its mutual exclusions and outcompete other microbes in C/nutrients limited conditions. Thus, goethite narrows the composition of rhizosphere mainly due to “gate selection” effects on rhizodeposits, which limited microbial penetrance into inner-compartments, consequently assemble the rhizosphere bacterial community via deterministic process.

Phosphate competition with arsenate on poorly crystalline iron and aluminum (hydr)oxide mixtures

Phosphate competes with arsenate for sorption sites on poorly crystalline iron and aluminum (hydr)oxides. The competition has implications e.g. for the management of arsenic-contaminated soil and water. Phosphate competition with arsenate on mixed phases containing both iron and aluminum (hydr)oxides has rarely been investigated. Here, the phosphate competition with arsenate on mixtures of poorly crystalline aluminum hydroxide (Alhox) and ferrihydrite (Fh), was investigated in batch experiments at pH 6.5. X-ray absorption spectroscopy (XAS) was performed on the phosphorus and arsenic K edges, which offered a unique insight in the partitioning of arsenate and phosphate on mixed Alhox-Fh sorbents. Under the studied conditions the sorption capacity of the mixed sorbents (per mol Al or Fe) increased at higher Alhox to Fh ratios. The XAS measurements provided direct evidence that phosphate competed more effectively with arsenate for sorption sites on Alhox than on Fh. For example, in a mixture with 50% of both sorbents and with similar additions of arsenate and phosphate, 71% of the oxyanions adsorbed on Fh and 46% on Alhox were arsenate. Consequently, phosphate may mobilize arsenate more easily from mixed iron-aluminum matrices that are rich in aluminum.

Nano scale visualization of enhanced adsorption and distribution of humic acid on hematite: Effect of Pb(II) ions

The interactions between soil organic matter (SOM) and minerals are key processes controlling the organic carbon (OC) stability in the environment, but the underlying mechanisms responsible for OC distribution on minerals are still not clear. In this study, a common crystalline iron oxide, hematite, and a typical SOM component, humic acid (HA), were chosen to explore, at the nano and even sub-nano scales, HA adsorption and distribution on hematite under the impact of Pb(II) ions. Adsorption experiments and spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) coupled with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) demonstrated that Pb(II) enhanced the adsorption of HA on hematite, but the nano scale distributions of HA varied between experimental conditions. The Cs-STEM, EDS, and the EELS analyses clearly unveiled that, with the presence of Pb(II), the hematite aggregates became more dispersed, and HA was not only adsorbed on the edges hematite nanoparticles, but also was localized in the extended areas away from the hematite particles/aggregates, which resulted in a heterogeneous distribution of OC in hematite-HA systems. Our imaging methods provided direct visualization of the mineral-SOM-metal interactions at nano scales, which shed lights on the underlying mechanisms for OC stabilization in natural environments and can enable more robust constraints in the models of organic matter-mineral interactions.

Iron fractions responsible for the variation of Cd bioavailability in paddy soil under variable pe+pH conditions

Iron (Fe) in soil is closely related to cadmium (Cd) uptake by rice plants, and soil pe + pH significantly influences Fe redox behavior. This study aimed to explore the influential mechanisms of varying pe + pH conditions on the transformation of iron oxides in the rhizosphere and the subsequent effect on Cd accumulation in rice plants. A two-month pot experiment was conducted to investigate the effect of soil pe + pH on the fractions of iron oxides and formation of iron plaque (IP), as well as the effect of these changes on Cd uptake by rice plants (Oryza sativa L.). Different irrigation strategies, 70% water holding capacity (DY), continuous flooding (FL), and alternate flooding/drying weekly (AWD), were used to achieve various soil pe + pH levels. The results showed that low pe + pH conditions (under the FL and AWD treatments) were more beneficial to the transformation of crystalline iron oxides into amorphous forms in rhizosphere soil and the precipitation of IP on rice roots. The increase of amorphous iron oxides resulted in the reduction of Cd availability in rhizosphere soil by immobilizing more Cd on Fe oxides. Moreover, Cd adsorbed on rice root surfaces reacted with IP, inhibiting Cd soil-to-root transport. The two mechanisms combinatively functioned at decreasing Cd concentration in rice shoots by 14.1–33.1% at low pe + pH conditions compared to that of the high pe + pH (DY treatment). These results indicate that lowering soil pe + pH effectively reduced Cd accumulation in rice plants, probably through the immobilization of amorphous Fe oxides on Cd and sequestration of iron-plaque on Cd.

Selective catalytic reduction of NO by NH3 over Fe2O3-promoted V2O5/TiO2-based catalysts with high Fe2O3-to-V2O5 ratios

Fe2O3-promoted V2O5-WO3/TiO2 catalysts with high Fe2O3-to-V2O5 ratios (3.4–6) have been prepared for the selective reduction of NO with NH3 (NH3-SCR) and extensively characterized using various spectroscopic measurements. No crystalline iron oxides were indicated even for 8% Fe2O3-promoted V2O5-WO3/TiO2 but α-Fe2O3 crystallites were observed in a XRD pattern for 7.04 % Fe2O3-promoted WO3/TiO2. Both Raman and XPS measurements suggest the formation of FeOV species which may make a better N2 selectivity in NH3-SCR reaction at high temperatures. All Fe2O3-promoted catalysts showed a great depression on N2O formation. At temperatures >400 °C, samples with 5.46 and 8% Fe2O3 (Fe2O3/V2O5 ratio = 3.4 and 5) gave significantly lower N2O production levels compared with the unpromoted and lower Fe2O3 loading catalysts. However, increasing in Fe2O3 loading resulted in a decrease in high temperature deNOx activity due to the oxidation of NH3 into NO. All the 3.4 and 5 ratio catalysts after a hydrothermal aging at 550 °C for 10 h gave NO removal activity and N2O formation similar to those measured over non-aged ones. However, such an aging at 750 °C could lead to a considerable increase in N2O formation even for the 5.46 % Fe2O3-promoted catalyst. Fe2O3-promoted V2O5/TiO2-based catalysts could catalyze the reduction of gas-phase N2O by NH3 adsorbed strongly, suggesting that this reaction may be a major route to greatly suppress N2O formation, consistent with infrared studies showing a reaction between N2O and surface NH3 species strongly adsorbed on the catalysts. This surface reaction could readily occur from a temperature as low as 250 °C.

Effects of metal cation substitution on hexavalent chromium reduction by green rust

Chromium contamination is a serious environmental issue in areas affected by leather tanning and metal plating, and green rust sulfate has been tested extensively as a potential material for in situ chemical reduction of hexavalent chromium in groundwater. Reported products and mechanisms for the reaction have varied, most likely because of green rust’s layered structure, as reduction at outer and interlayer surfaces might produce different reaction products with variable stabilities. Based on studies of Cr(III) oxidation by biogenic Mn (IV) oxides, Cr mobility in oxic soils is controlled by the solubility of the Cr(III)-bearing phase. Therefore, careful engineering of green rust properties, i.e., crystal/particle size, morphology, structure, and electron availability, is essential for its optimization as a remediation reagent. In the present study, pure green rust sulfate and green rust sulfate with Al, Mg and Zn substitutions were synthesized and reacted with identical chromate (CrO42−) solutions. The reaction products were characterized by X-ray diffraction, pair distribution function analysis, X-ray absorption spectroscopy and transmission electron microscopy and treated with synthetic δ-MnO2 to assess how easily Cr(III) in the products could be oxidized. It was found that Mg substitution had the most beneficial effect on Cr lability in the product. Less than 2.5% of the Cr(III) present in the reacted Mg-GR was reoxidized by δ-MnO2 within 14 days, and the particle structure and Cr speciation observed during X-ray scattering and absorption analyses of this product suggested that Cr(VI) was reduced in its interlayer. Reduction in the interlayer lead to the linkage of newly-formed Cr(III) to hydroxyl groups in the adjacent octahedral layers, which resulted in increased structural coherency between these layers, distinctive rim domains, sequestration of Cr(III) in insoluble Fe oxide bonding environments resistant to reoxidation and partial transformation to Cr(III)-substituted feroxyhyte. Based on the results of this study of hexavalent chromium reduction by green rust sulfate and other studies, further improvements can also be made to this remediation technique by reacting chromate with a large excess of green rust sulfate, which provides excess Fe(II) that can catalyze transformation to more crystalline iron oxides, and synthesis of the reactant under alkaline conditions, which has been shown to favor chromium reduction in the interlayer of Fe(II)-bearing phyllosilicates.

Exchange Bias in FePt-FePt3 Thin Films by Controlled Phase Transition of Blended Nanoparticle Building Blocks.

Nanostructured composite thin films showing magnetic exchange coupling at the material interface have attracted great interest for the development of electronic components such as spin-valves. Besides the commonly performed fabrication of multilayer systems, the utilization of nanoparticle building blocks holds great potential for thin films with tailored magnetic properties and allows the facile but controlled combination of materials with complementary magnetic characteristics. In this work, we present the use of prefabricated highly crystalline iron platinum (fcc-FePt) and iron oxide (FexOy) nanoparticles for the preparation of nanocomposite thin films with varying compositions by wet processing from mixed dispersions. The resulting multiphase coatings showed high homogeneity, low surface roughness, and superparamagnetic behavior. By the variation of the amount of incorporated iron oxide, a precise adjustment of the magnetization at high field strength could be achieved. Furthermore, calcination under inert gas atmosphere resulted in a controlled phase transition of the magnetic phases and thus, in purely metallic coatings composed of ferromagnetic fct-FePt and antiferromagnetic fcc-FePt3, a decrease in surface roughness as well as high magnetic coercivity at room temperature. Field-cooling below the Néel temperature of fcc-FePt3 led to an exchange bias effect with a strong increase in coercivity and the characteristic hysteresis shift. In comparison to the literature, our nanocomposite thin films showed fully ordered phases without the occurrence of phase impurities, a distinctly higher coercivity, and an exchange bias shift of 38.7 mT.

Magnetic Vortex and Hyperthermia Suppression in Multigrain Iron Oxide Nanorings

Single-crystal iron oxide nanorings have been proposed as a promising candidate for magnetic hyperthermia application because of their unique shape-induced vortex-domain structure, which supports good colloidal stability and enhanced magnetic properties. However, the synthesis of single crystalline iron oxide has proven to be challenging. In this article, we showed that chemically synthesized multigrain magnetite nanorings disfavor a shape-induced magnetic vortex-domain structure. Our results indicate that the multigrain Fe3O4 nanorings with an average outer diameter of ~110 nm and an inner to outer diameter ratio of ~0.5 do not show a shape-induced vortex-domain structure, which was observed in the single-crystal Fe3O4 nanorings of similar dimensions. At 300 Ks, multigrain magnetite nanorings showed an effective anisotropy field of 440 Oe, which can be attributed to its high surface area and intraparticle interaction. Both calorimetric and AC loop measurements showed a moderate inductive heating efficiency of multigrain magnetite nanorings of ~300 W/g at 800 Oe. Our results shed light on the magnetic ground states of chemically synthesized multigrain Fe3O4 nanorings.

The Influence of Synthesis Parameters on Structural and Magnetic Properties of Iron Oxide Nanomaterials.

Magnetic iron oxides have been used in biomedical applications, such as contrast agents for magnetic resonance imaging, carriers for controlled drug delivery and immunoassays, or magnetic hyperthermia for the past 40 years. Our aim is to investigate the effect of pressure and temperature on the structural, thermal, and magnetic properties of iron oxides prepared by hydrothermal synthesis at temperatures of 100–200 °C and pressures of 20–1000 bar. It has been found that pressure influences the type of iron oxide crystalline phase. Thus, the results obtained by Mössbauer characterization are in excellent agreement with X-ray diffraction and optical microscopy characterization, showing that, for lower pressure values (<100 bar), hematite is formed, while, at pressures >100 bar, the major crystalline phase is goethite. In addition, thermal analysis results are consistent with particle size analysis by X-ray diffraction, confirming the crystallization of the synthesized iron oxides. One order of magnitude higher magnetization has been obtained for sample synthesized at 1000 bar. The same sample provides after annealing treatment, the highest amount of good quality magnetite leading to a magnetization at saturation of 30 emu/g and a coercive field of 1000 Oe at 10 K and 450 Oe at 300 K, convenient for various applications.

Characteristics of iron oxide rust prepared by peracetic acid and its removal of heavy metals in water

Fe2O3 is an especially promising material for water purification as it shows high heavy metal adsorption capacity. However, the high cost of commercial Fe2O3 makes it difficult to be widely used in developing countries. Herein, we probe the heavy metal removal performance of iron oxide rust. Rust was grown on iron nails in a controlled manner using peracetic acid (CH3CO3H), a safe and environment-friendly oxidizer. Arsenic was selected as an example of a heavy metal contaminant in this study. XRD and EDS analysis revealed that the iron oxide prepared with peracetic acid was nearly amorphous Fe2O3. Amorphous iron oxide is reported to show higher reactivity than crystalline iron oxide. The BET specific surface area of prepared Fe2O3 is 71 m2/g, which is larger than that of commercial Fe2O3, and the average pore diameter is 73 Å. Oxidized nails are highly effective for removing heavy metals: about 90% of 1ppm arsenic in water was removed at the residence time of 20 minutes, and the removal rate of 90% is maintained after 10 back-to-back arsenic removal experiments at the same residence time. Iron oxide prepared in this study can remove, per 1 cm2, up to 0.114 mg of arsenic.

Evaluation of nutrient index using manganese as a measure of fertility status of soils under different cropping systems of punjab in North-Western India

Due to intensive cropping, improper agricultural practices and use of high grade chemical fertilizers, the areas gradually tend to show depletion of macro and micronutrients which has an adverse impact on quality and quantity of crops. Therefore, this study was undertaken in three districts of Punjab (north-western India) with the aim of assessing the fertility status of soils of major cropping systems through nutrient index criteria. A total of 150 surface soil samples were collected from various blocks of three districts of Punjab located in the north-western region of India from major cropping systems viz ., rice-wheat (Ludhiana district), maize-wheat (Ropar district) and cotton-wheat (Mansa district). These samples were analyzed for pH, electrical conductivity (EC), soil organic carbon (SOC), cation exchange capacity (CEC), sand, silt, clay, DTPA-extractable manganese (DTPA-Mn) and different Mn fractions of variable solubility. In soils, with DTPA-Mn content (>5.0 mg kg-1 soil), the concentration of water soluble + exchangeable Mn (WSEXMn), specifically adsorbed Mn (SpAD-Mn), oxides bound Mn (OX-Mn), amorphous iron oxide bound Mn (AFeOX-Mn), crystalline iron oxide bound Mn (CFeOX-Mn) and organic matter bound Mn (OM-Mn) fractions was significantly higher as compared to soils with DTPA-Mn content ( 5.0 mg kg-1 soil), respectively. The EC was low in all DTPA-Mn categories. Organic carbon status was medium in all soils with different DTPA-Mn categories.

Amorphous iron oxide–selenite composite microspheres with a yolk–shell structure as highly efficient anode materials for lithium-ion batteries

Yolk-shell structured transition metal compounds have intrinsic structural advantages as anode materials and have been synthesized in a highly crystalline form. Thus, development of a synthesis process for a yolk-shell structure with an amorphous state, that displays high structural stability and fast ionic diffusion, is a notable research subject, with wide applications in fields such as energy storage. Herein, a novel approach for synthesizing amorphous materials with a yolk-shell structure using several facile phase transformation processes is presented. Crystalline iron oxide microspheres with a yolk-shell structure were formed by oxidation of the spray-dried product at 400 °C. Using the pitch/tetrahydrofuran solution infiltration method, pitch-infiltrated iron oxide was selenized at 350 °C to form a crystalline iron selenide-C composite. The following partial oxidation process at 375 °C produced a yolk-shell structured amorphous iron oxide-selenite composite. The amorphous characteristics, the yolk-shell structure, and the formation of a heterostructured interface from iron selenite during the initial cycle contributed to high electrochemical kinetic properties and excellent cycling performance of the iron oxide-selenite composite. The amorphous iron oxide-iron selenite yolk-shell microspheres exhibited enhanced reversible capacities, cycling stability, and remarkable electrochemical kinetic properties when compared to crystalline iron oxide.

Genesis and classification of soils from granitic hills in southern Brazil

Southern Brazil abounds with granitic hills capped by intricately distributed soils most of which have been classified as Entisols or Inceptisols in medium- and small-scale soil surveys. However, field observations have revealed substantial texture gradients that are consistent with better-developed soils; also, the physical, chemical and mineralogical properties of the soils suggest that they are only slightly to moderately weathered. In this work, we examined the influence of formation-related factors and processes in soils from two granite toposequences. The eight soil profiles studied for this purpose were shallow, their C horizons occurring at depths of less than 100 cm. The low degree of flocculation and the fine/total clay ratio of the soils suggest that lessivage, which contributed to the development of the texture gradient in six of the profiles, was the main pedogenic process responsible for the formation of these soils. The soils at topographically high points were dystrophic or allitic, whereas those at low points were eutrophic. Based on their Ki values, the soils were weathered to a medium extent, which is in conflict with their low clay activity and cation exchange capacity. On the other hand, the Fed/Fes ratios of the soils were consistent with strong weathering, which in turn was consistent with their pH and exchangeable Al values. The iron oxides contents increased with increasing depth in the profiles as a result of lessivage. Feo/Fed ratios were suggestive of a prevalence of crystalline iron oxides. Increased substitution of Al in Fe oxides in the topographically higher soils further confirmed their increased weathering. Based on the foregoing, the soils were classified as Ultisols/Alfisols, Entisols and Inceptisols, the last series being less frequent than suggested by existing soil surveys. The transitional nature of these soil classes reflected in the presence of Ultisols/Alfisols with a thin B horizon, and also of argilluvic Inceptisols.

Study of the Mobilization of Uranium Isotopes in a Sandstone Aquifer in Combination with Groundwater Data

This work is part of a research project that aims to develop a method for combined radiocarbon and uranium-isotope dating of groundwater. The specific objective of this study was to investigate the mobility of uranium isotopes in the various mineral phases of rocks of an aquifer of sandy-clay deposits of the Vendian in the northwest of Russia, for which a partial extraction procedure was used. Representative aliquots of each core sample were treated with various reagents: distilled water, low mineralized fresh natural groundwater, minopolycarboxylic acid chelating agent (0.05 M EDTA), 0.5M HCl, 15 M HNO3, as well as total digestion, and the U isotope data for each procedure are reported in this study. The following mineral phases of core samples were characterized: sorbed material, carbonate minerals, amorphous iron oxides, partially soluble aluminosilicates and crystalline iron oxides, totally digestible aluminosilicates and a clay/quartz resistate. Red-colored siltstones and sandstones were depleted in uranium in relatively readily soluble mineral phases. The concentration of sorbed uranium was established in the range 15.8 ± 2.1–30.5 ± 3.9 μg/kg and carbonate minerals contained even less uranium. For iron hydroxides and the most readily soluble aluminosilicates, uranium concentrations were in the range 168 ± 24–212 ± 28 μg/kg. The most insoluble fraction contained uranium in the range 1.65 ± 0.21–4.32 ± 0.45 mg/kg. In green-colored siltstones, the concentration of sorbed uranium was much higher in the range 106 ± 14–364 ± 43 μg/kg. Carbonate minerals and amorphous iron oxides contained uranium in the range 1.91 ± 0.21–2.34 ± 0.26 mg/kg. In aluminosilicates and a clay/quartz resistate, uranium concentrations were in the range 5.6 ± 0.5–16.8 ± 1.4 mg/kg. Elevated values of 234U:238U activity ratio prevailed in the sorbed material and iron hydroxides. In aluminosilicates and clay/quartz resistate, the values decreased. This indicates the replacement of primary sedimentogenic uranium by secondary hydrogenic uranium sorbed on the surface of minerals and coprecipitation with iron hydroxides. The results obtained made it possible to carry out preliminary quantitative estimates of the retardation factor and recoil loss factor of uranium in the groundwater of siltstones and sandstones of the studied Vendian aquifer.

Goethite Reduction by a Neutrophilic Member of the Alphaproteobacterial Genus Telmatospirillum.

In tropical iron ore regions, biologically mediated reduction of crystalline iron oxides drives ongoing iron cycling that contributes to the stability of surface duricrusts. This represents a biotechnological opportunity with respect to post-mining rehabilitation attempts, requiring re-formation of these duricrusts. However, cultivated dissimilatory iron reducing bacteria typically reduce crystalline iron oxides quite poorly. A glucose-fermenting microbial consortium capable of reducing at least 27 mmol/L goethite was enriched from an iron duricrust region. Metagenome analysis led to the recovery of a metagenome assembled genome (MAG) of an iron reducer belonging to the alphaproteobacterial genus Telmatospirillum. This is the first report of iron reduction within the Telmatospirillum and the first reported genome of an iron-reducing, neutrophilic member of the Alphaproteobacteria. The Telmatospirillum MAG encodes putative metal transfer reductases (MtrA, MtrB) and a novel, multi-heme outer membrane cytochrome for extracellular electron transfer. In the presence of goethite, short chain fatty acid production shifted significantly in favor of acetate rather than propionate, indicating goethite is a hydrogen sink in the culture. Therefore, the presence of fermentative bacteria likely promotes iron reduction via hydrogen production. Stimulating microbial fermentation has potential to drive reduction of crystalline iron oxides, the rate limiting step for iron duricrust re-formation.

In-situ generation of multi-homogeneous/heterogeneous Fe-based Fenton catalysts toward rapid degradation of organic pollutants at near neutral pH.

In this study, an in-situ generated multi-homogeneous/heterogeneous Fe-based catalytic system was developed, which exhibited a high efficiency for the production of •OH and rapid degradation of various organic pollutants in a near neutral pH range (5-8). The mechanism for the rapid decomposition of H2O2 and the generation of •OH were investigated in detail. The results indicated that, besides the introduced Fe2+, the in-situ generated various iron species including Fe(OH)+, Fe(OH)2, Fe3+, ferrihydrite (Fh), γ-FeOOH and α-FeOOH as well as FeII/Fh, FeII/γ-FeOOH and FeII/α-FeOOH could simultaneously act as homogeneous and heterogeneous Fenton reaction catalysts. The dropwise addition manner of Fe2+ greatly improved the catalytic efficiency of Fe2+ ions in near neutral pH environment, while the in-situ generated nanosized Fh, γ-FeOOH and α-FeOOH could supply numerous active catalytic sites. After degradation, the ferrous ions could be transformed to various crystalline iron oxides by the catalytic phase transformation. This study presents a method towards the rational design of novel Fenton catalysts for wastewater treatment.

Application of chemical and biological tests for estimation of current state of a tailing dump and surrounding soil from the region of Tarniţa, Suceava, Romania.

This paper presents the results from a study on the current state of tailing dump, surrounding soil and water in the region of Tarniţa-Suceava, Romania. A number of chemical analyses and germination tests were applied in an attempt to estimate the ability of soil to maintain the plants growing, the bioavailability, and heavy metals uptake. Total heavy metals, exchangeable metals, acidity, and carbon and nitrogen content were determined. A modified sequential extraction method was used to determine geochemical phase distribution of heavy metals. The most abundant heavy metals in the studied samples were Cu, Zn, and Pb. Elevated concentrations of As were also found. The results from sequential extraction revealed that up to 51% of copper was retained by amorphous and crystalline iron oxides in soil. Higher content of lead was noticed in amorphous iron oxide fraction. The heavy metal concentration in river water during dry season varied from 0.13 mg/L (Fe) to 4.2 mg/L (Zn) and was below the maximum contamination level for drinking water. The soil toxicity and heavy metal bioavailability of tailing dump material and surrounding soils were studied by germination tests. The germinated plantlets on the studied soils were found to accumulate elevated concentrations of heavy metals thus indicating the bioavailability of soil contaminants. Soil decontamination by distilled water or magnesium nitrate solution was found to be efficient enough to improve the capability of the studied soils to support the germination process.