Iron Oxide Crystals Research Articles

NEW IRON CONTAINING HYBRID SILICATES FOR THE SELECTIVE REMOVAL OF ARSENIC OXYANIONS FROM CONTAMINATED WATER

A series of hybrid silicates containing iron oxides was synthesized via loading with hydrated iron oxide species (HFO) using a post precipitation mechanism from aqueous solution using different amounts of iron into the silica. The obtained materials were characterized by XRD, SEM, TEM, FTIR and low temperature nitrogen sorption. XRD analysis confirmed that HFO- Si was amorphous and iron oxide crystals in the silica cannot be detected due to both the lower size of HFO and the probability that occupying interstitial positions inside the silicate matrix. However, TEM image showed the presence of nano-sized HFO located inside the silicate matrix. The adsorption properties and selective efficiency of the synthesized materials were exam�ined in the removal of As (V) and As (III) species from contaminated water under different experimental conditions as well as in the presence of competing anions. The increasing iron loading enhanced the arsenic adsorption capacity of HFO-Si and the maximum arsenic removal was found to be 623 mg Fe/g silica after five successive loading times. The synthesized materials possess a unique adsorption capacity and their adsorption capacity reaches 303 mg As/g HFO-Si. Adsorption isotherm data for As (V) on HFO-Si fitted well the Langmuir equation. In addition, the intraparticle diffusion models fitted the experimental kinetic data, suggesting that the rate limiting step of adsorption is most probably diffusion of arsenic ions into pores. Further�more, the use of HFO-Si in column run and its easy regeneration makes it more sustainable to reuse several times to reduce the volume of arsenic laden waste.

A facile controlled in-situ synthesis of monodisperse magnetic carbon nanotubes nanocomposites using water-ethylene glycol mixed solvents

Abstract In this paper, a facile and controllable method for in-situ synthesis of the magnetic carbon nanotubes nanocomposites (Fe/CNTs) in water-ethylene glycol (EG) mixed solvents is reported by the deposition–precipitation method following annealing. The effect of water/EG ratio on the physico-chemical properties of magnetic Fe/CNTs is investigated by X-ray diffraction, transmission electron microscope, scanning electron microscopy, thermogravimetric analysis and physical property measurement system. The results indicate that the iron particle size distribution and grain size can be well-tuned by adjusting the water/EG ratio. With the variation of EG fraction in the mixed solvent, the nucleation, growth and crystallization of magnetic iron oxides with a controllable morphologies and particle sizes attached on the exterior surface of CNTs can be achieved. The as-prepared Fe/CNTs nanocomposites display superparamagnetic property at room temperature and the water/EG ratio determines the magnetization of the sample. Possible formation mechanism for magnetic Fe/CNTs is proposed based on the characterization results.

Rare Metal Chemistry, Microstructures, and Mineralogy of Coal Ash from Thermal Power Plants of Korea

Chemical and mineralogical properties of coal ash samples from the nine thermal power plants of Korea were investigated to acquire basic data for estimating the potential of rare metal recovery. Chemical compositions of coal ash were consistent with those of average shale and foreign coal ashes. However, there were small differences between the metal contents of domestic anthracitic and imported bituminous coal ashes. Unburned coal particles were much abundant in the ash of domestic anthracitic coal. Chalcophile elements were relatively enriched in the fly ash compared to bottom ash. Silicate glass was the major component of coal ash with minor minerals such as quartz, illite (muscovite), mullite, magnetite, lime, and anhydrite. Al and Si were the major components of the glass with varying contents of Ca, Fe, K, and Mg. Glass occurred in a form of porous sphere and irregular pumace-like grain often fused with iron oxide spheres or other glass grains. Iron oxide spheres were fine intergrowth of fast-grown iron oxide crystals in the matrix of silicate glass. Chemical, microstructural, and mineralogical properties would guide successful rare metal recovery from coal ash.

Spatial variation of soil magnetic susceptibility in relation to different emission sources in southern Poland

The study in the area surrounding the Rybnik urban agglomeration (southern Poland) was conducted to determine the influence of various emission sources on the occurrence of local magnetic anomalies observed in the forest topsoils. For this reason field measurement of volume-specific magnetic susceptibility (κ) was conducted in forest topsoil on the area of study. The measurements were performed twice: directly on the surface and after removal of forest litter to see the influence of the litter on the magnetic signal measured on the soil surface. The maps of surface distribution of κ value revealed that magnetic anomalies were observed 2.0km around the residential areas dominated by low emission sources, 2.1km around the coke plant, 2.8km around the old steelworks, 1.4km around the coal-mining waste heaps, and 4.0km around the combined heat and power plant and coal mines. On the 43% of the study area, the topsoil magnetic susceptibility was between 50 and 100×10−5 SI units; on the 5.2% of the area, κ value was between 100 and 200×10−5 SI units; and on the 1.2% of the research area, the κ value was over 200×10−5 SI units. Also the vertical distribution of technogenic magnetic particles (TMPs) along the topsoil profile was analysed using topsoil 30cm cores. Two κ value maxima were observed in the soil profile. The upper one (κaverage=333.9×10−5 SI units) was found in either the Oa or Ah subhorizons at the depth of 3cm to 8cm dependently of thickness of organic horizon. The lower one (κaverage=53.4×10−5 SI units) was observed in the B or C horizon at the depth of 19cm to 23cm. The upper maxima was of anthropogenic origin with large content of the magnetic fraction (magnetic spherules), whereas the lower maxima containing isometric crystals of iron oxides was of pedogenic or geogenic origin. The soil magnetometry seems to be a useful tool in identification of anthropogenic “hot spots” caused by industrial and urban dust deposition from different emission sources.

Fe K-Edge X-ray Absorption Fine Structure Determination of γ-Al2 O3 -Supported Iron-Oxide Species.

The structure of FeOx species supported on γ-Al2 O3 was investigated by using Fe K-edge X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al2 O3 and co-gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α-Fe2 O3 particles at an Fe loading of above 10 wt %, whereas the formation of iron-oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K-edge XAFS was characterized by a clear pre-edge peak, which indicated that the FeO coordination structure deviates from central symmetry and that the degree of FeOFe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K-edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron-oxide monomer on the γ-Al2 O3 surface.

Effect of sample pretreatment on the fractionation of arsenic in anoxic soils.

Using by sequential extraction procedures to obtain the chemical forms of arsenic in soils can provide useful information for the assessment of arsenic mobility and bioavailability in soils. However, sample pretreatments before the extraction probably have some effects on the fractionation of arsenic in soils. Impact of sample pretreatments (freeze-drying, oven-drying, air-drying, and the fresh soil) on the fractionation of arsenic in anoxic soils was investigated in this study. The results show that there are some differences for arsenic fractions in soils between by drying pretreatments and by the fresh soil, indicating that the redistribution among arsenic fractions in anoxic soils occurs after drying pretreatments. The redistribution of arsenic fractions in anoxic soils is ascribed to the oxidation of organic matter and sulfides, the crystallization of iron (hydr)oxides, the ageing process, and the diffusion of arsenic into micropores. The freeze-drying is the best drying method to minimize the effect on the fractionation of arsenic in anoxic soils, while air-drying is the worst one. Drying pretreatments are not recommended for the fractionation of arsenic in anoxic soils with high concentration of iron.

Occurrence of iron and aluminum sesquioxides and their implications for the P sorption in subtropical soils

The effect of the pedo-climatic variation in qualitative and quantitative soil sesquioxide contents and soil phosphorus (P) sorption capacities has been studied. In four soils (samples from A horizons) located along a southern Brazilian environmental gradient (EG) shown a decrease in crystallized iron oxides with the increase of altitude. Hematite and goethite were found at low EG altitudes in association with low soil organic carbon content, and goethite–ferrihydrite and gibbsite were found at high altitudes in association with high organic carbon content. The adsorbed soil P (measured by the remaining P) was predicted by the goethite content, and the desorbed P (measured by successive P extractions using anion exchange resin membranes) was predicted mainly by the goethite and clay content. In subtropical soils, even a smooth environmental gradient could determine the qualitative and quantitative iron and aluminum sesquioxide distributions that control soil P sorption capacities.

Magnetite Fe3O4 nanoparticles and hematite α-Fe2O3 uniform oblique hexagonal microdisks, drum-like particles and spindles and their magnetic properties

Magnetite Fe3O4 nanoparticles and uniform hematite (α-Fe2O3) oblique hexagonal microdisks, drum-like particles, and spindles have been synthesized via a facile hydrothermal reaction route, in which the mixture solvents of ethylene glycol (EG) and water are used as reaction medium. The phase, size, shape and growth orientation of the synthesized iron oxide crystals were characterized by powder X-ray diffraction and electron microscopy. When the reaction medium is almost composed of EG, a lot of Fe3+ ions reduce to Fe2+ ions due to the effect of EG, resulting in the magnetite Fe3O4 nanoparticles. As the volume ratio of EG/water in the reaction medium is lower than 30:10, the reductive ability of EG is too low to reduce the Fe3+ ions to Fe2+ ions, leading to the hematite α-Fe2O3 crystals. Moreover, since the adsorption of EG on the crystals, the shape of the obtained hematite α-Fe2O3 crystals evolves from oblique hexagonal microdisks to drum-like particles, and spindles due to the decrease of EG in the mixture reaction medium solvent. The magnetic properties of the magnetite Fe3O4 nanoparticles and hematite α-Fe2O3 uniform microcrystals were also investigated by measuring the magnetic hysteresis loops.

Abstract 5380: Near-infrared-resonant IONP/Au2S core/satellites hybrid nanocomposite for imaging-guided photothermal therapy

Abstract Abstract: Photothermal therapy (PTT) using near-infrared-resonant nanomaterials including multifunctional probes with both therapeutic functions and imaging capabilities has gained great attention in recent years. However, various challenges still exist including the large size of gold nanoshells, the “melting” effect of gold nanorods, lack of imaging capability, and tedious multiple steps for making imaging-capable multifunctional probes. Consequently, it is desired to develop an effective PTT mediator with the following criteria: small size, photo stability, facile synthesis, low toxicity, and imaging capability. We report the design of a core/satellites hybrid nanocomposite with a highly crystallized iron oxide nanoparticle (IONP) core (10-20 nm) and multiple gold sulfide (Au2S) nanoparticle satellites (1-2 nm) attached to the IONP polysiloxane-containing polymer coating for imaging-guided photothermal cancer therapy. In this nanostructure, the multiple satellites (Au2S) enhance PTT, while the IONP core serves as both a photothermal mediator and magnetic resonance imaging (MRI) contrast agent to localize the tumor. To make these core/satellites nanocomposites we first modify the IONP polymer coating with (3-mercaptopropyl) trimethoxysilane followed by mixing with Au2S nanoparticles, which are made by mixing sodium sulfide (Na2S) and chloroauric acid (HAuCl4) at the designed ratio. After purification using a magnet, the TEM image shows that around 8-10 Au2S nanoparticles (1-2 nm average diameter) were attached to each IONP (15 nm in diameter). This core/satellites nanocomposite has obvious absorption in the near infrared (NIR) range and the absorption peak can be adjusted by the molar ratio of Na2S to HAuCl4. The developed nanocomposite exhibits an enhanced photothermal effects without any quenching under NIR laser light. Benefitting from the anti-biofouling polysiloxane-containing polymer coating for in vivo applications, the core/satellites nanocomposites effectively accumulate to xenograft tumor tissue (SUM-159, triple-negative breast tumor cell line) through the enhanced permeability and retention effect after tail vein injection. MRI imaging is used to locate the tumors. NIR triggered PTT, which is enhanced by the core/satellites nanoparticles within the tumor site, destroys the tumor cells, while the tumor tissues in control mice do not show any change under the same laser light irradiation. Our in vitro and in vivo data reveal that NIR-resonant IONP/Au2S core/satellites nanocomposites can be used as effective MRI imaging-guided photothermal cancer therapy. Correspondence should be addressed to: Duxin Sun, PhD, or Hongwei Chen, PhD, Department of Pharmaceutical Sciences, College of Pharmacy, The University of Michigan, 428 Church Street, Ann Arbor, MI 48109, Email: duxins@umich.edu (D. Sun); or hongweic@umich.edu (H. Chen) Citation Format: Hongwei Chen, Joseph Burnett, Xiaoqing Ren, Feng Ni, Yi Wei, Hayley Paholak, Duxin Sun. Near-infrared-resonant IONP/Au2S core/satellites hybrid nanocomposite for imaging-guided photothermal therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5380. doi:10.1158/1538-7445.AM2014-5380

Early kaolinization of detrital Weald facies in the Galve Sub-basin (Central Iberian Chain, north-east Spain) and its relationship to palaeoclimate

A set of samples from the Camarillas Formation (Barremian, Weald facies) in the Galve Sub-basin (Central Iberian Chain, north-east Spain) was studied to determine the origin of the abundant kaolinitic clays and their relationship to the sedimentary environment, palaeoclimate and diagenetic processes. The samples were examined by X-ray diffraction and scanning and transmission electron microscopy, with special emphasis on clay-mineral characterization. The analysed materials are a mixture of detrital (quartz, micas, and K-feldspars) and authigenic phases (kaolinite, Fe-oxides, gibbsite, dickite, and calcite). Therefore, the mineralogy of the rocks reflects the source area, the sedimentary conditions, and the diagenetic evolution. The most abundant authigenic phases are kaolinites. The combination of XRD and electron microscopy shows that the kaolinites are well crystallized and have as high a degree of ordering as those formed by weathering in palaeosols; this clay formed the rock matrix, intergrowths with muscovite, and vermicular booklets that replaced detrital silicates as a consequence of intense dissolution processes. The diagenetic processes have recrystallized kaolinites in the sandstones, producing larger crystallinity indices and dickite. In contrast, kaolinites from the claystones and siltstones probably reflect formation by weathering. The kaolinitization process described, associated with the crystallization of gibbsite and iron oxides, is in agreement with the relatively warm and humid conditions described for the Iberian Range basin in the early Barremian.

Sticking behavior of iron ore–coal pellets and its inhibition

Most previous studies on iron ore–coal pellets (ICPs) have focused on their reduction, but studies on their sticking behavior have not been reported. The sticking behavior of iron ore–coal pellets (ICPs) at high temperatures under a load of 0.1MPa was studied. Temperature was determined to be an important factor that affects the sticking behavior: the sticking increased with increasing temperature; the sticking index was 89.28% at 1373K but only 4.78% at 1223K. The sticking mechanism results from the intergrowth of metallic iron and ferrous oxide crystals between pellet boundaries. High-melting-point materials formed by the combination of MgO and FexOy, can effectively prevent this intergrowth of iron, and the addition of a dolomite powder coating reduces the sticking index from about 90% to about 10%. The addition of limestone and iron ore powder was not found to have any beneficial effect of sticking inhibition.

Disruptive chemical doping in a ferritin-based iron oxide nanoparticle to decrease r2 and enhance detection with T1-weighted MRI.

Inorganic doping was used to create flexible, paramagnetic nanoparticle contrast agents for in vivo molecular magnetic resonance imaging (MRI) with low transverse relaxivity (r2). Most nanoparticle contrast agents formed from superparamagnetic metal oxides are developed with high r2. While sensitive, they can have limited in vivo detection due to a number of constraints with T2 or T2*-weighted imaging. T1-weighted imaging is often preferred for molecular MRI, but most T1-shortening agents are small chelates with low metal payload or are nanoparticles that also shorten T2 and limit the range of concentrations detectable with T1-weighting. Here we used tungsten and iron deposition to form doped iron oxide crystals inside the apoferritin cavity to form a WFe nanoparticle with a disordered crystal and un-coupled atomic magnetic moments. The atomic magnetic moments were thus localized, resulting in a principally paramagnetic nanoparticle. The WFe nanoparticles had no coercivity or saturation magnetization at 5 K and sweeping up to ± 20,000 Oe, while native ferritin had a coercivity of 3000 Oe and saturation at ± 20,000 Oe. This tungsten-iron crystal paramagnetism resulted in an increased WFe particle longitudinal relaxivity (r1) of 4870 mm(-1) s(-1) and a reduced transverse relaxivity (r2) of 9076 mm(-1) s(-1) compared with native ferritin. The accumulation of the particles was detected with T1-weighted MRI in concentrations from 20 to 400 nm in vivo, both injected in the rat brain and targeted to the rat kidney glomerulus. The WFe apoferritin nanoparticles were not cytotoxic up to 700 nm particle concentrations, making them potentially important for targeted molecular MRI.

Morphology-selective crystallization of cocatalysts on cuprous oxide with improved photocatalytic activity

Morphology-selective crystallization of manganese, nickel and iron oxides on pre-synthesized cubic cuprous oxide for photocatalysis is reported. Manganese oxide formed nanorods lying down on the surfaces of Cu2O while nickel oxide formed monodisperse nanospheres. Iron oxides formed vertically aligned nanosheets. Deposition of the iron oxide nanosheets resulted in dramatically improved photocatalytic activities.

Highly crystallized iron oxide nanoparticles as effective and biodegradable mediators for photothermal cancer therapy.

We report that highly crystallized iron oxide nanoparticles (HCIONPs) made by thermal decomposition and further coating with a polysiloxane-containing copolymer can be used as effective mediators for photothermal therapy. Irradiation of a HCIONP solution containing 0.5 mg mL-1 Fe, for instance, with an 885 nm diode laser at a power of 2.5 W cm-2, induces a temperature increase of 33 °C from room temperature, while water produced only a ∼3 °C increase as the control. In vivo studies are further evaluated for effective photothermal therapy using the as-prepared HCIONPs. Benefiting from the great antibiofouling property of the polymer coating and minimized hydrodynamic size (whole particle size: 24 nm), the nanoparticles intravenously administered to SUM-159 tumor-bearing mice can effectively accumulate within the tumor tissue (5.3% of injection dose) through the enhanced permeability and retention effect. After applying the same laser conditions to irradiate the tumors, complete tumor regression is observed within three weeks without disease relapse over the course of three months. Conversely, control mice exhibit continuous tumor growth leading to animal mortality within four weeks. To better understand the photothermal effect of HCIONPs and potentially improve their photothermal efficiency, we compare their photothermal effect and crystal structures with commercially available magnetic nanoparticles. Our data show that after applying the same laser to commercially available magnetic nanoparticles from FeREX at the same iron concentration, the temperature is only increased by 7.4 °C. We further use synchrotron-XRD and high-resolution TEM to compare the crystal structures of both magnetic nanoparticles. The data show that both magnetic nanoparticles are Fe3O4 but as-prepared HCIONPs are highly crystalline and have preferred lattice plane orientations, which may be the cause of their enhanced photothermal efficiency. Taken together, these data suggest that HCIONPs, with unique lattice orientations and small size as well as antifouling coating, can be used as promising mediators for photothermal cancer therapy.

Micro-investigation of EPICA Dome C bottom ice: evidence of long term in situ processes involving acid–salt interactions, mineral dust, and organic matter

The EPICA Dome C ice core (EDC) reached a final depth of 3260 m, at a maximum height of about 15 m above the ice–bedrock interface in December 2004. We present here data gained from a detailed investigation of selected samples of the deeper part of the core located below 3200 m and referred to as bottom ice. This part of the core has been poorly investigated so far mainly because there are significant challenges in interpreting paleo-records that were very likely modified by long term in situ processes. Our study combines high resolution ion chromatography, high resolution synchrotron X-Ray micro-fluorescence (micro XRF), scanning, and transmission electron microscopy. Our aim was to identify the long term physico-chemical processes at work close to the bedrock, to determine how they have altered the initial registers, and, ultimately to extract information on the very ancient Antarctic environment.The ubiquitous presence of nanometer iron oxide crystals at the surface of wind-borne dust aggregates containing also large amount of organic matter raises the possibility that the consolidation of windborne dust clusters formed during ice recrystallization could be related to microbial iron reduction and, thus, to the progressive reactivation of dormant bacterial activity in warming ice. Inclusions of size and number density increasing with depth observed in the 12 last meters (3248–3260 m) contain liquid and solid species, among them marine biogenic acids, numerous wind-borne dust aggregates and clusters of large reversible calcium carbonate particles precipitated once the inclusion was formed and often covered by secondary gypsum. The refreezing of slush lenses is discussed as a potential cause of the formation of such heterogeneous and complex mixtures. In addition to the very fine micrometer size minerals windborne from extra-Antarctic continental sources and often accreted in large aggregates, single medium size particles (a few to ca 20 μm and among them organic debris) are commonly encountered. Their size, surface shape, and mineralogy suggest that aerosol transport from Antarctic ice-free areas played a significant role at the time EDC bottom ice was formed. Concentrations and concentration ratios of biogenic sulfur species also advocate for the strengthening of peri-Antarctic meteorological patterns that favor the inland penetration of disturbed flow carrying local material. Very large well preserved mineral particles several tens of micrometers in diameter, and biotope relics in deeper ice close to 3260 m likely come from the sub-glacial environment.

Characterization of ash deposits from the boiler of Yenikoy coal-fired power plant, Turkey

Yenikoy power plant is a coal-fired electric power station with a 2×210 MW production capacity located in Mugla, Turkey. The plant burns a low quality, high calcium lignite, which causes significant operational problems due to slag formation in combustion units over time. This study aimed to characterize the ash deposits taken from one of the boilers of this particular power plant. The samples were collected from different elevations of the boiler and subjected to chemical, mineralogical and micro-textural analyses. Apart from Ca, significant concentrations of Fe, Al and Si were detected in ash deposits. Anhydrite was found to be the dominating crystalline phase and various forms of aluminosilicates, iron-oxide crystals and Fe–Ca bearing phases were also identified in the samples. The deposits basically consist of two layers; the inner layer characterized by a reddish-colored surface with high hematite content and the outer layer which was mostly in gray and light brown color due to the presence of high amount of calcium particles.

Preparation of ferric oxide modified diatomite and its application in the remediation of As(III) species from solution

A new iron oxide–diatomite system was synthesized in one pot by mixing natural diatomite with a ferrous sulfate solution at room temperature. The characterization of the materials (Diatom–Fe) by XRD and chemical analysis revealed that iron (29%w/w) was crystallized under goethite phase (α-FeOOH). Analysis conducted by SEM further highlighted the preferential presence of goethite on the surface of diatomite, which involves hydrogen bonding between diatomite surface silanol groups and ion species. The mechanism of formation of goethite is suggested to occur through the precipitation of ferrous ions by hydroxyls ions followed by the oxidation of the iron species to yield first to lepidocrocite (γ-FeOOH) then goethite that is thermodynamically more stable. Within this mechanism, the contribution of calcium carbonate through its dissolution into hydroxyls species is evidenced by XRD and FTIR analyses. The remediation properties of Diatom–Fe towards arsenite species cations were investigated in batch jar tests for 24h at auto-equilibrium pH. The materials showed a noticeable higher As (III) sorption capacity (16mg/g) than the native diatomite (0.5mg/g). These results can be explained by the strong affinity of arsenites to goethite which is further emphasized by the dispersion of the iron oxide crystals on diatomite surface.

Natural Nanomaterials: Reappraising the Elusive Structure of the Nano-Sized Mineral Ferrihydrite through X-Ray Absorption Spectroscopy at the Iron K-Edge

Ferrihydrite is natural ferric oxyhydroxide occurring exclusively nanocrystalline. With ideal formula 5 Fe2 O3 . 9 H2 O, ferrihydrite is quite abundant in sediments, weathering crusts and mine wastes, being characteristic of red pre-soils formed by loose weathered rock plus mineral debris (regoliths) and commonly designated as “2-line” or “6-line” on the basis of the broadened maxima observed in the X-ray diffraction pattern. Synthetic nanocrystalline “6-line” ferrihydrite was recently studied through methods based on atomic-pair distribution functions disclosing the possible occurrence of icosahedral clusters formed by twelve octahedra centred by an inner tetrahedron, all filled by Fe 3+ ions. However, Mössbauer studies were inconclusive about the existence of 4-coordinated iron, thus suggesting that the tetrahedral cation may well be Si4+. In view of such structural uncertainty, a XANES study at the Fe K-edge was undertaken on ferrihydrite from a regolith to ascertain the occurrence of tetrahedral iron. Comparison with data collected from well crystallized iron oxide and hydroxide minerals where Fe 3+/2+ ions occur in octahedral and tetrahedral coordination is described and the results so far obtained are discussed, showing that supplementary study is needed on the elusive structure of ferrihydrite.

Synthesis, Self-Assembly, and High Performance in Gas Sensing of X-Shaped Iron Oxide Crystals

X-shaped goethite iron oxide crystals were synthesized by a surfactant-free mild hydrothermal synthesis method with the aid of fluorine ions. The X-shaped goethite crystals could readily self-assemble into microscopic hollow spheres through an oil-water interface induced self-assembly method. X-shaped hematite crystals were obtained by phase topotactic transformation of the goethite precursors. The gas sensor properties of X-shaped hematite iron oxide were investigated, and the mechanism for excellent sensor properties was discussed.

Physicochemical factors affecting leaching of laterite ore in hydrochloric acid

The effect of physicochemical factors on laterite ore leaching in hydrochloric acid was investigated in this study. The results showed that the valuable metals such as nickel and cobalt could be extracted effectively at the leaching conditions as follows: acid concentration was 8mol/L, the particle size of samples were 100% passing 0.15mm, the stirring speed was 300rpm, leaching temperature was 353K, S/L ratio was 1:4 and leaching duration was 2h. The extraction of nickel and iron presented a linear correlation, which demonstrated nickel associated in iron ore, and cobalt dissolution was not consistent with iron dissolution which indicated that the distribution of cobalt were not uniform in the iron oxide crystals and existed in other minerals, and this result had also been demonstrated by mineralogical studies. To investigate the stability of different minerals in the leaching condition listed above as well as the influence of nickel and cobalt on their dissolution in such condition, the minerals dissolution order was studied by X-ray diffraction (XRD) according to determination of the leaching residues and chemical composition of the leaching solution, and the result order was goethite>lizardite>magnetite>hematite.