Formation Of Hematite Research Articles

The Influence of the Thermal Treatment of Copper Slag on the Microstructure and Performance of Phosphate Cements.

In general, phosphate cements have a very rapid setting reaction at room temperature. The same holds for copper slag-based phosphate cements. This means that using them as a binder, for instance as mortar, is always possible on a small scale, but very difficult on a large scale. In this paper, the heat treatment of the copper slag was shown to be an effective way to increase the setting time and keep the mix workable for an adequate period. The main objective of this research was to examine the changes in the phase composition of quenched copper slag after exposure to 500 °C and to evaluate the impact of these changes on the reactivity of the material in an acidic environment, as well as on the mechanical properties, microstructure, and structure of the produced phosphate cement materials. Various experimental methods were utilized to characterize the raw materials and the obtained phosphate cementitious materials, including isothermal microcalorimetry (TAM Air), thermogravimetric analysis (TGA), infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), as well as the determination of the chemical composition using X-ray fluorescence (XRF) and the particle size distribution. Furthermore, compressive strength tests were conducted to gauge the mechanical resistance of the materials. The main findings of this work revealed that subjecting the copper slag to a thermal treatment of 500 °C induced a partial transformation in its structure. The high temperature caused the oxidation of some of the divalent iron oxide in the slag, leading to the formation of hematite. This treatment increased the setting time and reduced the reactivity of the copper slag with phosphoric acid, ultimately enabling the production of a dense phosphate-based cementitious material with outstanding mechanical properties. The compressive strength of the newly developed cement was recorded to be greater than 78.9 MPa after 7 days, and this strength continued to increase, reaching 82.5 MPa after 28 days.

Investigation of the beneficiation of refractory ferromanganese ores “Zhomart” deposits

In order to provide ferroalloy production with high-quality raw materials, the need to develop technologies for processing of low-grade manganese and ferromanganese ores is becoming increasingly important. In view of the change in the quality characteristics of ores, the decrease in manganese content and the ability to beneficiation by traditional methods, it is necessary to consider new approaches and technological solutions. The article presents data from a study on the beneficiation of refractory iron-manganese ore from the Zhomart deposit. The mineralogy, physical and mechanical properties, and granulometric composition of the ore were determined. The results of a study on gravitational beneficiation using a laboratory pulsator with a pneumatic drive and a laboratory 2-chamber diaphragm jigging machine and magnetic beneficiation of ore with a high-intensity magnetic field are presented. Iron-containing concentrate (Fe-45% and Mn-6.5% is mainly represented by hematite mixed with non-metallic minerals quartz and calcite) and iron-manganese concentrate (Mn-21.7% and Fe-21.1% in the form of hematite, Brownite and pyrolusite, also mixed with quartz and calcite). The concentrates are not suitable for smelting manganese-containing ferroalloys but can be used in the process of electrothermal beneficiation with selective carbothermal reduction of iron in an ore-thermal furnace. The smelting products can be manganese cast iron and iron-free, low-phosphorus limiting manganese slag with a high ratio of manganese to iron.

Crystal structure refinement, low- and high-temperature X-ray diffraction and Mössbauer spectroscopy study of the oxoborate ludwigite from the Iten'yurginskoe deposit.

This paper reports an investigation of the chemistry, crystal structure refinement and thermal behavior (80-1650 K) of ludwigite from the Iten'yurginskoe deposit (Eastern Chukotka, Russia). Its chemical composition was determined by electron microprobe analysis, giving an empirical formula (Mg1.70Fe2+0.29Mn0.01)Σ2.00(Fe3+0.90Al0.08Mg0.02)Σ1.00O2(BO3). A refinement of the crystal structure from single-crystal X-ray diffraction data (SCXRD) was provided for the first time for ludwigite from this deposit (R = 0.047). The structure can be described as a framework composed of [MO6]n- octahedra and isolated [BO3]3- triangles located in triangular interstices of the framework. Based on a comprehensive analysis of SCXRD and Mössbauer spectroscopy data, the M1 site is occupied by Mg, M2 and M3 by Mg and Fe2+, M4 by Fe3+, Mg and Al. There are also oxo-centered [O4M4]n+ and [O2M5]n+ polyhedra building up a framework with the [BO3]3- triangles located in its hexagonal interstices. No indications of magnetic ordering are found in the temperature range investigated. The Fe2+ → Fe3+ oxidation occurs above 600 K, and is accompanied by a decrease of the unit-cell parameters and subsequent incomplete solid-phase decomposition with the formation of hematite, warwickite and magnetite. The mineral melts at temperatures above 1582 K. The thermal expansion of ludwigite is slightly anisotropic, which is explained by a dense packing of the [MO6]n- octahedra as well as a virtually perpendicular orientation of the oxo-centered double chains to each other. At room temperature, maximum expansion is along the c axis (αc = 9.1 × 10-6 K-1) and minimum expansion is in the ab plane (αa = 8.6 × 10-6, αb = 7.6 × 10-6 K-1), which is due to the preferred orientation of the [BO3]3- triangles. A comparison of the thermal behavior of three oxoborates of the ludwigite group, namely azoproite (Mg,Fe2+)2(Fe3+,Ti,Mg,Al)O2(BO3), vonsenite (Fe2+,Mg)2(Fe3+,Mn2+,Sn,Al)O2(BO3) and ludwigite (Mg,Fe2+,Mn)2(Fe3+,Al,Mg)O2(BO3), is provided.

Understanding the growth mechanism of Al-bearing hematite nanoparticles via two-dimensional oriented attachment

Hematite occurs ubiquitously in nature and is important for controlling the migration and conversion of various nutrients and pollutants. The morphology of hematite is a key factor affecting its reactivity. Naturally occurring hematite usually contains an amount of aluminum (Al) impurities. Al has a significant effect on the morphology of hematite. However, the details of Al-bearing hematite formation and the role of Al in the morphological evolution remain poorly understood. In this work, a series of Al-bearing hematite were synthesized using hydrothermal methods. Their growth process was followed by examining the intermediate products harvested at different intervals of reaction time using the XRD and electron microscopy. DFT calculations were used to investigate the effect of Al on the stability of hematite {001} and {110} crystal facets. The results indicate that the formation of Al-bearing hematite follows two stages: the initial nucleation of hematite nuclei and the subsequent ripening of nuclei into nanoplates. The nucleation process involves the formation of ferrihydrite, followed by the amorphous nanoparticles undergoing phase transition into more thermodynamically stable hematite nuclei. In the ripening stage, hematite nuclei aggregate into single-crystalline hematite particles through oriented attachment and then crystallize into nanoplates. The surface energy of the {110} crystal facet is higher than the {001} crystal facet at high concentrations of Al, which promotes oriented attachment of {110} facets between hematite nuclei. The proposed mechanism in this article not only provides deep insight into the formation of naturally occurring hematite but also a path for the efficient fabrication of environmentally friendly iron oxide materials.

Fluoride-free, simple, and environmentally friendly extraction of mixed oxides of niobium and tantalum from the Nigerian and Rwandan columbite-tantalite concentrates

We report a fluoride-free comparative study with promising results of an alkali-assisted roasting with KOH and water-based leaching of the Nigerian and Rwandan columbite-tantalite concentrates and application of guanidine carbonate to extract Nb and Ta as mixed oxides. The results proved that the alkali-assisted roasting the sample with KOH at optimum conditions, (250 °C, 100 % flux-to-concentrate ratio, 1 h), facilitated open-up of the (Nb–Ta)-minerals and induced their water solubilities. However, the Nigerian sample seems to be highly soluble relatively to the Rwandan sample. In all investigated cases, most of tin and iron in form of cassiterite and hematite and other impurities remained in the residue and their dissolutions decreased as temperature increased. Guanidine carbonate was used to extract both Nb and Ta dissolved in the pregnant leach solution of the Nigerian and Rwandan columbite-tantalite concentrate samples. The (Nb–Ta)-guanidine precipitate with purity of more than 95.0 % was recovered from leach liquor solution of −250 µm size fraction containing Nb (48.5 %), Ta (47.5 %), with Fe (2.6 %) and Mn (0.1 %) for N-Nass Con sample. For R-KMY Con sample, similar precipitate with purity of more than 94.0 % with chemical compositions of Nb (28.45 %), Ta (65.75 %) along with Fe (3.32 %) and Mn (0.77 %) was obtained from leach liquor of +250 µm size fraction. The amorphous (Nb–Ta)-guanidine precipitate was then calcined at 900 °C and converted the metals into their mixed oxides with high purity (more than 99%) and removed the guanidine as evidenced with their crystallographic peaks. The study presents a potential alternative to HF and promising opportunity for the sustainable extraction of Nb and Ta while the world is shifting toward clean energy.

Migration Features and Regularities of Heavy Metals Transformation in Fresh and Marine Ecosystems (Peter the Great Bay and Lake Khanka)

Peter the Great Bay and Lake Khanka are among the most important structural and industrial fishing parts of the Far East coastal ecosystem, which are used by a number of countries such as Russia, China, Korea, Japan, etc. At the same time, the active use of water resources, as well as industrial activities deployed on the coastal part of these reservoirs, are accompanied by a constant flow of pollutants into the water area. Among them, one can include heavy metals; their entry and migration are currently not fully controlled. There exists an important scientific and ecological task to study the features of heavy metal migration and transformation in natural objects. Bottom sediments act as a substrate for hydrobionts and, at the same time, serve as accumulators of pollutants, so that they can be used as the main component of the coastal-shelf ecosystem. The geochemical assessment of the behavior of heavy metals in the bottom sediments of Ussuri Bay and Amur Bay (Sea of Japan) and Lake Khanka (Xingkai) has been performed. Qualitative and quantitative elemental compositions of the bottom sediments have been established by means of the inductively coupled plasma-mass spectrometry (ICP-MS), atomic absorption spectrometry (AAS), and X-ray fluorescence analysis (XRF), whereas a correlation with the concentration of elements in seawater above sediments has been provided. The main phases of anthropogenic components as well as their relationship with an increased content of heavy metals have been established using X-ray diffraction analysis (XRD). Average values of the concentration of elements in the bottom sediments of Peter the Great Bay decrease in the following row: Fe > Cu > Cr > Zn ≥ Pb > Mn > Ni, and for Lake Khanka: Pb > Cu > Mn > Fe > Cr > Zn > Ni. Here, the excessive contents of Cr, Fe, Cu, Zn, and Pb in sea bottom sediments by 6, 32, 7, 3, and 4 times as compared with background values are the result of the formation of a large amount of carbonate and iron-oxide phases. At the same time, it was shown that, during the transition from the estuarine (coastal) area of river flow to the central (closer to the outlet to the ocean), the concentration of biogenic metals (Ni, Zn, Pb, Cu) generally decreased 2–4-fold along the profile, which was associated with the formation of their hydroxides and carbonates in the area of mixing of freshwater and seawater followed by that of complex compounds or absorption. A significant anthropogenic impact is observed in the lake sediments, which is demonstrated by the excess of Pb concentration by 6700 times, as compared with the Clarke number of the lithosphere. The non-uniform distribution of heavy metals along the core profile has been established, which is related to different contents of aluminosilicate and iron oxide phases in the form of hematite and magnetite. The sedimentation rate has been established by means of granulometric and radiometric analysis and equaled to 0.45 mm/year in Ussuri Bay, 1.6 mm/year in Amur Bay, and 0.43–0.50 mm/year in Lake Khanka. By calculating the distribution coefficients of heavy metals in the ‘water–deposits’ system, some features of migration and accumulation of individual elements have been established. To assess the potential pollution of the marine areas, the geoaccumulation index (Igeo) and the pollution factor (Kc) have been calculated. In comparison with the maximum permissible concentrations of the Russian Federation (MPC), the World Health Organization (WHO), the US Environmental Protection Agency (US EPA), and environmental protection agencies of China and Japan, Peter the Great Bay has an excess of Mn—2-fold, Fe—2-fold, Zn—3-fold, whereas in Lake Khanka, the situation is even less favorable, in particular, the excess of Mn is 79-fold, Fe—35-fold, Cu—2-fold, Zn—3–4-fold, which is clearly determined by the closeness of the water basin and the lack of water exchange. In comparison with the lithosphere Clarke number, the sediments of both water basins, as well as the coastal soil of the lake, are enriched with Pb and depleted with Cr, Ni, and Zn. The highest values of Igeo in both water basins have been observed for Pb, and equaled 12–16 in Peter the Great Bay and 6000 in Khanka Lake. Based on the data obtained, the areas with the greatest pollution caused by natural and anthropogenic factors have been identified.

Ferrihydrite transformation impacted by coprecipitation of lignin: Inhibition or facilitation?

Lignin is a common soil organic matter that is present in soils, but its effect on the transformation of ferrihydrite (Fh) remains unclear. Organic matter is generally assumed to inhibit Fh transformation. However, lignin can reduce Fh to Fe(II), in which Fe(II)-catalyzed Fh transformation occurs. Herein, the effects of lignin on Fh transformation were investigated at 75°C as a function of the lignin/Fh mass ratio (0-0.2), pH (4-8) and aging time (0-96 hr). The results of Fh-lignin samples (mass ratios = 0.1) aged at different pH values showed that for Fh-lignin the time of Fh transformation into secondary crystalline minerals was significantly shortened at pH 6 when compared with pure Fh, and the Fe(II)-accelerated transformation of Fh was strongly dependent on pH. Under pH 6, at low lignin/Fh mass ratios (0.05-0.1), the time of secondary mineral formation decreased with increasing lignin content. For high lignosulfonate-content material (lignin:Fh = 0.2), Fh did not transform into secondary minerals, indicating that lignin content plays a major role in Fh transformation. In addition, lignin affected the pathway of Fh transformation by inhibiting goethite formation and facilitating hematite formation. The effect of coprecipitation of lignin on Fh transformation should be useful in understanding the complex iron and carbon cycles in a soil environment.

Effects of Coexisting Anions on the Formation of Hematite Nanoparticles in a Hydrothermal Process with Urea Hydrolysis and the Congo Red Dye Adsorption Properties

Crystalline hematite nanoparticles as adsorbents for anionic Congo red dye were prepared by a hydrothermal process using urea hydrolysis. To examine the effects of coexisting anions in a solution on the formation of hematite nanoparticles, different iron(III) salts, including iron chloride hexahydrate, iron nitrate nonahydrate, iron sulfate n-hydrate, ammonium iron sulfate dodecahydrate, and basic ferric acetate, were employed as iron-ion sources. After the hydrothermal treatment of the solution, consisting of an iron salt and urea at 423 K for 20 h, a single phase of hematite was formed from the iron-nitrate solution. The results suggested that the hydrothermal formation of hematite depended on the stability of iron complexes formed in the starting solution. The average crystallite size and median diameter of hematite nanoparticles also depended on the coexisting anions, suggesting that the appropriate selection of the coexisting anions in the starting solution can allow for control of the crystallite size and particle diameter of hematite nanoparticles. The Congo red adsorption kinetics and isotherms of the hematite nanoparticles were described by the Elovich model and Langmuir model, respectively. The adsorption thermodynamics parameters were estimated, which suggested an exothermic and spontaneous process. The results demonstrated good adsorption properties for Congo red adsorption.

Crystallization between (100) Goethite and (001) Orientation of Hematite – A Review

Abstract The purposes of this study were: (1) to review the preparation and characterization of the intergrowth between goethite and hematite crystals; and (2) to propose a schematic diagram of the epitaxial relationships among three sets of (100) goethite twin crystals associated with the (001) orientation of the hexagonal prism of hematite. The Fe(ClO4)3 solution was prepared and aged at 70°C, which precipitated goethite initially and produced hematite later with prolonged aging. Goethite and hematite aged for 20 days were observed as star-shaped and hexagonal prisms, respectively. The results suggest that hematite could form later using goethite as a template surface. A selected area electron diffraction (SAED) pattern showed the epitaxial relationship among three sets of (100) goethite intergrowth crystals and hexagonal prisms with the (001) orientation of hematite. Goethite can be produced as lath-, X-, K-, or star-shaped crystals on the (100) orientation, depending on the Fe(ClO4)3 concentrations and the addition of HClO4 to Fe solution samples which were aged for a prolonged period at room temperature. The initial solubility products [(Fe3+)(OH–)3] of the sample solution, rather than the nature of the nuclei, are the key factors governing the formation of goethite or hematite. The addition of acids and high concentrations of iron solutions extend the secondary hydrolysis and induction period (IP) and favor the formation of hematite. The index of the SAED pattern of the star-shaped goethite intergrowth twin crystal has a (100) plane parallel to this basal plane and rotates at a 60° angle between two or three sets of lath-shaped goethite crystals, which share the (011) plane and form goethite twins with ‘interpenetrated’ crystal growth. Stereoscopic viewing using Oak Ridge Thermal Ellipsoid Plot (ORTEP) and CrystalMaker software was deployed to explore the relationship and configuration of oxygen atoms between pseudo-hexagonal (100) goethite associated with hexagonal (001) hematite lattice planes. A schematic diagram of the epitaxial relationship between star-shaped (100) goethite, which is acting as a template facilitating later precipitation of (001) hexagonal prisms of hematite on it, is presented.

Application of Deep Eutectic Solvents (DES) for the Synthesis of Iron Heterogeneous Catalyst: Application to Sulfamethoxazole Degradation by Advanced Oxidation Processes

The development of novel approaches to the remotion of pharmaceuticals in wastewater is a subject of concern due to their effect on living beings and the environment. Advanced oxidation processes and the use of relevant catalysts are feasible treatment alternatives that require further development. The development of suitable heterogeneous catalysts is a necessity. This work proposes the synthesis of an iron catalyst in a deep eutectic solvent (Fe-DES) composed of choline chloride and citric acid, which was physically and chemically characterized using SEM-EDS and TEM, FTIR, RAMAN, XRD and XPS. The characterisation confirmed the presence of iron in the form of hematite. Fe-DES was shown to be a multipurpose catalyst that can be applied in the removal of sulfamethoxazole as a reagent in the Fenton and electro-Fenton processes and as an activator of peroxymonosulfate (PMS) processes. After testing the catalyst with the aforementioned techniques, the best result was achieved by combining these processes in an electro-PMS, with great efficiency achieved by dual activation of the PMS with the catalyst and electric field, attaining total elimination at natural pH in 90 min. Furthermore, the degradation was confirmed by the detection of short-chain carboxylic acids (oxalic, succinic, and acetic) and reduction in toxicity values. These results confirm the suitability of Fe-DES to degrade high-priority pharmaceutical compounds.

The mobility of Cr(VI) on the ferrihydrite-Cr(VI) co-precipitates: The effect of co-existing tartaric acid and Cu(II)

Ferrihydrite is a crucial scavenger for hexavalent chromium (Cr(VI)) via coprecipitation processes. Foreign impurities widely exist in soils and sediments, which influence mineral recrystallization and transformation processes. Under the circumstances, the speciation and migration behavior of Cr(VI) will change accordingly. In this research, we explored the impact of tartaric acid and Cu(II) on ferrihydrite transformation, as well as the sequestration of Cr(VI) on iron minerals. Our results manifested that tartaric acid affected the valence of Cr on iron oxides. The adsorbed Cr(VI) was reduced to Cr(III) by tartaric acid on the surface of iron oxides and not released into the aqueous phase, which greatly reduced its toxicity. It was conducive to the conversion of ferrihydrite into hematite when tartaric acid concentration was 1.0 mM, because tartaric acid could facilitate the hematite nucleation to induce the generation of hematite from ferrihydrite. Moreover, Cu(II) promoted the formation of hematite and played a synergistic role in Cr(VI) fixation. Therefore, tartaric acid and Cu(II) are important factors decreasing the toxicity of Cr(VI) when considering Cr(VI) retention on iron minerals in complicated environments. This work has a vital implication for understanding the impact of the co-existent metals and organic substances on Cr(VI) retention in complex environments.

Influence of montmorillonite incorporation on ferrihydrite transformation and Cr(VI) behaviors during ferrihydrite-Cr(VI) coprecipitates aging

Hexavalent chromium (Cr(VI)) is a pollutant with high migration ability, and the destiny of Cr(VI) is highly correlated with ferrihydrite (Fh). Montmorillonite (Mt) is a clay mineral abundantly presents in nature. Although Cr(VI) adsorption on montmorillonite or ferrihydrite has been studied, Cr(VI) behaviors during the Fh-Cr-Mt coprecipitates transformation still remain unknown. In this study, calcium montmorillonite (Ca-Mt) or sodium montmorillonite (Na-Mt) was coprecipitated with ferrihydrite and Cr(VI). Effect of Ca-Mt (or Na-Mt) incorporation on coprecipitates transformation and Cr(VI) behaviors during aging were investigated. The results showed that Ca-Mt or Na-Mt incorporation inhibited the transformation of ferrihydrite in Fh-Cr-Ca-Mt or Fh-Cr-Na-Mt at the initial pH of 5.0, 7.0 and 9.0. During aging, two kinds of Mt were supposed to interact with Fh to form the FeOSi and FeOAl bonds, and thus the formation of hematite and goethite were limited. By testing the Cr(VI) distribution in each phase of coprecipitates during transformation, delay on Cr(VI) migration and redistribution could be found in systems added with montmorillonite, and Cr(VI) was retained in coprecipitates to a greater extent compared with the systems without montmorillonite addition. The results of this study contribute to increasing our knowledge about the role of clay minerals on the coprecipitates transformation when they coexist at different pH values. It is also significant for the heavy metals polluted sites repairing.

乾式機械的処理を利用した無溶媒均一沈殿法によるヘマタイトナノ粒子の合成

Hematite (α-Fe2O3) nanoparticles were synthesized by a solvent-free homogeneous precipitation method using urea hydrolysis via dry mechanical treatment of urea and ferric nitrate nonahydrate for activation. This novel method consists of high-energy ball milling of the raw materials and subsequent heating of the activated liquid precursor, which can provide smaller-sized nanoparticles than conventional methods. The milling and heating conditions were systematically investigated in detail. It was found that the hematite formation can be promoted by milling ferric nitrate nonahydrate and urea simultaneously under dry conditions even when relatively gentle milling and heating treatments were employed. The hematite nanoparticles had a similar crystallite size and particle diameter regardless of the conditions. This method can contribute to large-scale environmentally-friendly synthesis of fine hematite nanoparticles.

Controls of normal diagenesis on poroperm parameters in red beds: examples in Miocene Muddy Creek Formation, Mesquite basin, USA and upper Devonian Old Red Sandstone, Orcadian basin, Scotland

General diagenetic patterns in Miocene Muddy Creek Formation and upper Devonian Old Red Sandstone (ORS) can be characterized as follows: i) early diagenesis characterized by the formation of early hematite, carbonate, and clay cement; ii) burial diagenesis followed by the formation of quartz and feldspar overgrowths, poikilotopic calcite and pore-filling clays; iii) late diagenesis characterized by the formation of late hematite replacing previous poikilotopic carbonate cement. Normal diagenesis has a significant impact on poroperm parameters as indicated by the destruction of pore spaces from cementation and intergranular pressure solution. Early cementation in unburied sandstones of the Muddy Creek Formation reduces sample porosities to 2÷20% of the total rock volume. Cementation destroyed the original porosity of studied sandstones through pore occlusion due to the formation of equant and meniscus calcite cement. Point-count data indicate that the intergranular cement of studied samples ranges between 22 and 44%; in contrast, the intergranular porosities range from 2÷20% of the total rock volume. These consequently indicate that the intergranular volumes that are considered to represent the original porosities of studied samples, ranged from 35÷50% of the total rock volume. Completely pore-occluding poikilotopic calcite cement in the upper Old Red Sandstone reduces poroperm values to as low as 5% porosity and 0.003 mD permeability. Late reddening is caused by replacive hematite cement in the calcite. In addition, normal diagenesis also has an impact on porosity enhancement due to dissolution in the studied red beds. This improves porosity and permeability by as much as 14% and 254 mD in the upper ORS.

Possible Formation Mechanism of Lunar Hematite

Hematite, a ferric mineral with diagnostic features in the visible and infrared spectral range, has recently been discovered in the polar regions of the Moon by the Chandrayaan-1 Moon Mineralogy Mapper (M3). The oxygen involving the oxidization process producing lunar hematite is supposed to originate from the Earth’s upper atmosphere, and hematite with different ages may have preserved information on the oxygen evolution of the Earth’s atmosphere in the past billions of years. The discovery of lunar hematite may provide insight into the understanding of the oxidation products on the Moon and other airless bodies. In this work, we analyze hematite abundance distribution in the lunar polar regions, showing that the content of hematite on the lunar surface increases with latitude, and is positively correlated with surface water abundance. We suggest that the latitude dependence of hematite is derived from the latitude dependence of water, which indicates that water may play an essential role in the formation of hematite. The correlation between hematite and the optical maturity parameter (OMAT) was analyzed and a significant positive correlation was observed, which suggests that the hematite in the polar regions is the result of gradual and persistent oxidation reactions. In addition, based on the analysis of oxygen particles in the Earth wind, it was found that O+ and O2+ are much more abundant, suggesting that low-energy O+ or O2+ ions escaping from the upper atmosphere of the Earth may play a crucial role in the formation of hematite in the lunar polar regions.

Enhanced immobility of Pb(II) during ferrihydrite-Pb(II) coprecipitates aging impacted by malic acid or phosphate.

Metastable ferrihydrite is omnipresent in environments and can influence the fate of Pb(II) during ferrihydrite transformation. Ferrihydrite is rarely pure and often coexists with impurities, which may influence the mineralogical changes of ferrihydrite and Pb(II) behavior. In this work, we investigated the effect of malic acid or phosphate on Pb(II)-ferrihydrite coprecipitates (Fh-Pb) transformation and the subsequent fate of Pb(II) during the 10-day aging of Fh-Pb. Results showed that both malic acid and phosphate retarded Fh-Pb transformation and prevented the release of Pb(II) from Fh-Pb back into solutions. Pb(II) was beneficial to goethite formation by inhibiting hematite formation while both malic acid and phosphate inhibited goethite formation since they could act as templates of nucleation. Besides, malic acid and phosphate improved the proportion of non-extracted Pb(II) during Fh-Pb transformation, indicating that Pb(II) was incorporated into secondary minerals. Pb(II) could not replace Fe(III) within the crystal lattice due to its large radius but was occluded into pores and defect structures within the secondary mineral lattices. This work can advance our understanding of the influences of malic acid and phosphate on Pb(II) immobility during Fh-Pb aging.

On the thermal and hydrothermal stability of spinel iron oxide nanoparticles as single and core-shell hard-soft phases

The thermal and hydrothermal stability of oleate-capped nanosized spinel iron oxides is of primary importance for the plethora of applications and environments for which they are employed. An in-situ XRD and ex-situ autoclave treatments have been set up for monitoring the thermal and hydrothermal stability in different samples. In detail, spinel iron oxide nanoparticles (NPs) were studied as (i) single-phase alone at three different sizes (about 6, 10, and 15 nm); (ii) as core in a core-shell architecture having cobalt ferrite as shell, at different core sizes (about 6 and 10 nm); (iii) as shell in a core-shell architecture with cobalt ferrite as core, at different shell thicknesses (about 3 and 4 nm). The Rietveld refinement of the diffraction patterns and 57Fe Mössbauer spectroscopy have been exploited to monitor the evolution of the structural parameters and the hematite fraction. Moreover, transmission electron microscopy has permitted to deepen the morphological details on the phases. The spinel iron oxide-hematite transition has been found size- and time-dependent for the single-phase iron oxide NPs (360–455 °C). The transition temperature has increased significantly when iron oxide is incorporated in a core-shell architecture, both as core (630 °C) and shell (520 °C), suggesting a stabilizing effect of cobalt ferrite. The hydrothermal stability of iron oxide and core-shell NPs has been found dependent on water content, time, and temperature, with a reducing effect of pentanol toward the formation of magnetite from maghemite, highlighted by 57Fe Mössbauer spectroscopy. The synergic effects of cobalt ferrite and pentanol have limited the formation of hematite, leading to the obtainment of magnetite-covered cobalt ferrite NPs upon the hydrothermal treatment.

Enhancement of electrical conductivity, optical band gap and ferromagnetic properties by co-doping of Co and Ti ions in canted antiferromagnetic hematite (α-Fe2O3) system

The Co and Ti ions have been co-doped at the sites of Fe3+ ions of α-Fe2O3 (hematite) structure by employing mechanical alloying technique and post heat treatment of the as-alloyed material under vacuum and air. The ratio of Co and Ti ions has been maintained at 50:50 in order to compensate charge disproportionate effect in the composition of α-Fe2-xTix/2Cox/2O3 (x = 0.2, 0.4, 0.6). The X-ray diffraction pattern and Raman spectra at room temperature have confirmed the formation of hematite (rhombohedral) structure as the major phase and a minor amount of TiO2 phase in some of the prepared samples. X-ray photoelectron spectra (XPS) have provided useful information of the chemical environment and electronic charge state of the metal (Co, Ti, Fe) ions in the lattice structure. The XPS spectra confirmed tetra-valence charge state of Ti ions, whereas a mixed valence charge state of Fe3+(Co2+) and Fe(2+δ)+(Co(3−δ)+) has been indicated for the Fe and Co ions. The mixed valence charge states indicated the enhancement of covalent character of the metal-oxygen bonds. In this work, details of the lattice structure, chemical composition, charge state of ions, optical, electrical and magnetic properties have been presented.

The Geochemical Effect of Impact Processing of Polar Regolith on the Moon

The paper considers the geochemical effects of impact processing of the polar regolith of the Moon. It contains an admixture of water ice, which can (should?) provide conditions for possible chemical reactions. To date, only one geochemical effect was reliably found—the formation of hematite Fe2O3, which is uncharacteristic for relatively low selenographic latitudes. In the work, a thermodynamic analysis of the conditions required for the formation of hematite is carried out. It is shown that this requires the presence of free oxygen, which (this is a possible option) can accumulate during the dissipation into outer space of hydro gen formed during water decomposition. The specific process or processes of hematite formation require fur ther study. It is very likely that impact processing of polar regolith also leads to hydration of silicate glasses and to the formation of heavy hydrocarbons. The dissipation of free hydrogen into outer space, which, apparently, is formed in these processes, should lead to an increase in the deuterium content in the remaining hydrogen. The Н2О ice of the polar regolith likely contains a significant amount of heavy water. Future inves tigations in the polar regions of the Moon, especially with the delivery of samples to Earth, should confirm or refute these conclusions and assumptions.

A new iron recovery and dephosphorization approach from high‑phosphorus oolitic iron ore via oxidation roasting-gas-based reduction and magnetic separation process

Deep dephosphorization of high‑phosphorus oolitic iron ore (HPOIO) is extremely difficult because of its refractory characteristics. A new approach for simultaneous iron recovery and dephosphorization from HPOIO by oxidation roasting–gas-based reduction (ORGR) and magnetic separation process was developed. The underlying mechanism was investigated using thermodynamic calculations, X-ray diffraction (XRD), and scanning electron microscopy combined with energy dispersive spectroscopy (SEM–EDS). The results showed that the powdery reduced iron produced contained 91.37% iron and 0.14% phosphorus, and the iron recovery was 92.81%, which is an ideal for steelmaking. The addition of Na2CO3 formed nepheline, which promoted the formation and coarsening of hematite during oxidation. Concurrently, Na2CO3 reacted with the phosphorus in the iron minerals and fluorapatite to form sodium calcium phosphate, which was embedded in hematite with a simple relationship. Hematite was subsequently converted into metallic iron, sodium calcium phosphate was not reduced, and metallic iron and phosphorus were separated efficiently.