Iron Mineral Phases Research Articles

Long term durability of Tc-bulk and Tc-coatings in various environmental conditions

Technetium metal is renowned for its inertness in environmental conditions, rendering it an optimal candidate for use as a container material for high-level radioactive waste. Alternatively, thin technetium electroplated coatings can be employed to prevent corrosion of steel containers and the subsequent biofouling that may result. The utilization of metallic technetium in the design of containers for radioactive waste in deep burial may be promising from two perspectives: firstly, in terms of increasing their stability, and secondly, in terms of the utilization of technetium, which is a macrocomponent of radioactive waste. In this study, the resilience of the metal technetium and its two derivative coatings (amorphous and crystalline) was assessed under various conditions, including exposure to fresh groundwater and seawater. The multifunctional strain Shewanella xiamenensis DCB-2-1, known for its ability to enzymatically reduce pertechnetate ions, was used to investigate the possibility of microbial biofouling of metallic technetium. Laboratory experiments have demonstrated that amorphous electrodeposited technetium is more susceptible to oxidation processes compared to its crystalline counterpart. Ultimately, the most durable form of technetium was metal foil. The potential for biofouling on Tc surfaces is largely attributed to the diverse nature of the specimens’ surface. Research conducted in the Barents Sea has revealed that the accumulation of iron, calcium, and magnesium mineral phases within the microbial biofilm may shield beta radiation, resulting in the establishment of macro-fouling (Balanus and Mutilus).

Coupled transformation pathways of iron minerals and natural organic matter related to iodine mobilization in alluvial-lacustrine aquifer

The complex of natural organic matter (NOM) and iron minerals in sediment is the main host and source of groundwater iodine. However, the transformation pathways of the complex remain unclear. The groundwater and sediment from the Hetao Basin were collected in this study to analyze multi-isotopes, NOM molecular characteristics, and iron mineral phases. The results showed that high-iodine groundwater was mainly observed in the discharge area, where biodegradation of NOM, sulfate reduction and methanogenesis occurred. Compared to the shallow clayey sediments, the confined sandy sediments had lower iodine content, a lower fraction of crystalline iron oxides, and a higher fraction of carbonate associated Fe(II) minerals, suggesting that the release of sediment iodine in the aquifer is related to the transformation of sediment Fe(III) hydroxides/oxides. Moreover, the molecular features of high-iodine groundwater NOM and sandy sediment NOM were characterized by a higher proportion of refractory compounds, suggesting that the reductive transformation of sediment Fe(III) hydroxides/oxides is fueled by degradable organic compounds. The microbial Fe-reducing and/or sulfate-reducing processes cause the enrichment of groundwater iodine in the form of iodide via the transformation of iodine species. These findings provide new insights into the genesis of high-iodine groundwater.

Nitrate and nitrite reduction by adsorbed Fe(II) generated from ligand-promoted dissolution of biogenic iron minerals in groundwater

Chemical denitrification by redox-active Fe(II) species is pivotal in the coupled iron and nitrogen cycles. The reductive dissolution of ferric minerals by ligand can generate Fe(II)-ligand complexes, but their reducing capability for electrophilic pollutants like nitrate and nitrite remains uncertain. Here, biogenic secondary iron minerals (SIM) after dissimilatory iron reduction were reductively dissolved by oxalate and the siderophore desferrioxamine B, and subsequently the partially-dissolved SIM (SIMD) effectively removed NO2− from groundwater via reduction, while exhibiting much lower reactivity towards NO3−. The dissolution and removal processes were well-fitted with the Kabai model and the pseudo-second-order adsorption model, respectively. The equilibrium NO2− removal capacity (qe) of SIMD reached 0.146–0.223 mmol/g, accompanied with the rate constants as 0.433–0.810 g/(mmol·h). The emission of N2O and NO verified the occurrence of chemical denitrification during NO2− removal by SIMD. From the perspective of Fe(II) reactivity, SIMD exhibited higher densities of surface Fe(II) and more negative Eh values than SIM, and these two indicators showed linear correlations with the removal rates. Combined with microscopic, electrochemical and spectral analysis, our results indicated the redox reaction of adsorbed Fe(II)-complexes with NO2− on SIMD surface. The concurrent substance biochar was also considered, as it indirectly influenced dissolution and pollutant removal by shifting the iron mineral phase in SIM from magnetite to goethite. These findings highlight the significant role of reductive dissolution of iron mineral in N transformation, expand the electron pool available to support chemical denitrification, and have implications for Fe and N cycling coupling with pollutant reduction.

Mineralogical and geochemical features of the Sirna Mn‐Fe deposit in the Kurdistan region, northeastern Iraq: Unveiling the formation of a Mn‐Fe silica gel plume via serpentinization hydrothermal mechanisms

AbstractThe study probes the mineralogical and geochemical features of manganese‐iron deposits located in the Sirna area, which is a part of the late Cretaceous Walash Group in the Zagros suture zone, situated in the Kurdistan region of northeastern Iraq. Our investigation comprised field surveys, examination of ore petrography, besides using x‐ray diffraction, SEM‐EDS analysis, x‐ray fluorescence analyses, and inductively coupled plasma mass spectrometry techniques conducted on a set of representative samples. A significant Mn‐Fe ovoidal ore body, extending across 25 meters in diameter, protrudes between the lower strata of soft gray shale and the upper strata of massive limestone within the Walash group. The deposit exhibits a distinct separation into three layers: a lower horizon characterized by abundance of oxide of silicon, an upper horizon enriched in manganese oxide, and a transition layer dominated by hematite (Fe2O3). From a geochemical perspective, there is a gradual decrease in Fe2O3 and SiO2 from the lower to the upper part of the deposit, while MnO, BaO, and SO3 demonstrate a gradual increase. The co‐association of Mn‐Fe‐mineralization in a small restricted tabular ore body suggests that they are genetically related. Within the Sirna manganese‐iron deposit, the prevalent manganese and iron mineral phases are braunite, hollandite, and hematite. Concurrently, the gangue minerals in this deposit encompass cryptocrystalline spheroidal quartz, barite, calcite, and apatite. The Sirna Mn‐Fe deposit exhibits geochemical characteristics such as elevated levels of MnO (reaching up to 68 wt.%) and significant Fe2O3 content (up to 45 wt.%) in the upper manganese and transitional iron horizons, respectively. The Co/Zn ratio (0.28), Ce/La ratio (1.78), low levels of transitional elements (Co + Ni + Cu <0.01 wt.%), and varying concentrations of Ba (up to 6.9 wt.%) suggest that the Siran Mn‐Fe deposit is likely originated from a manganese‐iron silica gel plume that separated from hydrothermal fluids linked to serpentinization. This process is thought to have occurred in the mantle wedge along subduction zone, typically within an arc tectonic environment. Moreover, the presence of remnants of micro‐organisms such as EPS layers, different types of filaments, which are densely covered by biominerals, are important evidence of microbial effect in the mineralization of Mn‐Fe in the study area.

Sorption of antimony(V) to naturally formed multicomponent secondary iron minerals: Sorption behavior and a comparison with synthetic analogs

Antimony (Sb) pollution in water has attracted extensive attention due to the biotoxicity of Sb. Secondary iron minerals readily sorb heavy metal(loid)s and critically affect their cycling in terrestrial environments. However, compared with synthetic pure iron mineral phases, little is known about the Sb sorption behavior and mechanism on natural secondary iron minerals (nSIMs) composed of various mineral phases. In this study, sorption experiments were conducted to investigate the Sb(V) sorption properties of nSIMs from an acid mine drainage zone and corresponding single-component synthetic secondary mineral phases and to compare their sorption behaviors and mechanisms. Spectroscopic analyses indicated that the nSIMs structurally resembled a hybrid of schwertmannite, jarosite and goethite. Sb(V) sorption on nSIMs, schwertmannite, goethite and jarosite was controlled by chemisorption, with maximum Sb(V) sorption capacities of 217.39, 233.65, 32.17 and 35.61 mg/g, respectively. nSIMs demonstrated an excellent Sb(V) sorption capacity equivalent to or greater than that of the single-component phases. XRD, FTIR and Raman analyses indicated that Sb(V) was immobilized on nSIMs mainly through ion exchange with structural SO42− and complexation interactions with surface FeO and FeOH; then, an FeOSb surface phase formed during the dissolution and further transformation of schwertmannite and jarosite into goethite. SEM revealed that nSIMs had an advantage in surface microstructure over the single components. These results suggested that despite the similarities in Sb(V) binding mechanism between nSIMs and schwertmannite, nSIMs might be more reactive for Sb(V) sorption since the nSIM components could mutually influence each other and facilitate Sb(V) sorption. This research suggests that nSIMs have potential for Sb(V) removal and helps elucidate the environmental behavior of Sb(V) associated with nSIMs.

Unveiling the crucial role of iron mineral phase transformation in antimony(V) elimination from natural water

Antimony (Sb) in natural water has long-term effects on both the ecological environment and human health. Iron mineral phase transformation (IMPT) is a prominent process for removing Sb(V) from natural water. However, the importance of IMPT in eliminating Sb remains uncertain. This study examined the various Sb–Fe binding mechanisms found in different IMPT pathways in natural water, shedding light on the underlying mechanisms. The study revealed that the presence of goethite (Goe), hematite (Hem), and magnetite (Mag) significantly affected the concentration of Sb(V) in natural water. Elevated pH levels facilitated higher Fe content in iron solids but impeded the process of removing Sb(V). To further our understanding, polluted natural water samples were collected from various locations surrounding Sb smelter sites. Results confirmed that converting ferrihydrite (Fhy) to Goe significantly reduced Sb levels (<5 μg/L) in natural water. The emergence of secondary iron phases resulted in greater electrostatic attraction and stabilized surface complexes, which was the most likely cause of the decline of Sb concentration in natural water. The comprehensive findings offer new insights into the factors governing IMPT as well as the Sb(V) behavior control.

Pore structure and fractal dimension analysis of ancient city wall bricks in China

Comprehensive quantitative characterization of the pore structures of ancient city wall bricks is important for predicting the durability of historical masonry buildings. However, in most previous studies, only one or two methods were used to analyse the pore structures of fired clay bricks. In this study, mercury intrusion porosimetry (MIP), low-temperature nitrogen adsorption (LTNA), and low-field nuclear magnetic resonance (LF-NMR) were used to characterize the pore structure and fractal dimension of nine different ancient city wall bricks. The results show that the surface relaxivity of ancient bricks measured via the Hahn spin echo (HSE) in LF-NMR ranged from 1.55 to 1.75 μm/s. Furthermore, the porosity of the blue bricks measured via LF-NMR were much lower than that obtained via the gravimetric method owing to a higher number of paramagnetic iron mineral phases. LTNA was not suitable for describing pore size distribution of ancient bricks as the pore diameters were mainly concentrated in the range of 100–1000 nm. The pore structures of ancient bricks in dried and water-saturated states were different, the pore size of the white bricks obtained via LF-NMR was smaller than the MIP-derived pore-throat size by a factor of approximately 2.

Intracellular biotransformation and disposal mechanisms3d cancer cells.

Magnetosomes are magnetite nanoparticles biosynthesized by magnetotactic bacteria. Given their potential clinical applications for the diagnosis and treatment of cancer, it is essential to understand what becomes of them once they are within the body. With this aim, here we have followed the intracellular long-term fate of magnetosomes in two cell types: cancer cells (A549 cell line), because they are the actual target for the therapeutic activity of the magnetosomes, and macrophages (RAW 264.7 cell line), because of their role at capturing foreign agents. We show that cells dispose of magnetosomes using three mechanisms: splitting them into daughter cells, excreting them to the surrounding environment, and degrading them yielding less or non-magnetic iron products. A deeper insight into the degradation mechanisms by means of time-resolved X-ray absorption near-edge structure (XANES) spectroscopy has allowed us to follow the intracellular biotransformation of magnetosomes by identifying and quantifying the iron species occurring during the process. In both cell types there is a first oxidation of magnetite to maghemite and then, earlier in macrophages than in cancer cells, ferrihydrite starts to appear. Given that ferrihydrite is the iron mineral phase stored in the cores of ferritin proteins, this suggests that cells use the iron released from the degradation of magnetosomes to load ferritin. Comparison of both cellular types evidences that macrophages are more efficient at disposing of magnetosomes than cancer cells, attributed to their role in degrading external debris and in iron homeostasis. This article is protected by copyright. All rights reserved.

Removal of arsenic from contaminated soils by combining tartaric acid with dithionite: An efficient composite washing agent

In the context of the increasing global problem of arsenic (As) contamination in soils, an efficient remediation method is urgently needed to alleviate it. In this study, a composite washing agent consisting of 0.2 mol L−1 dithionite and 0.05 mol L−1 tartaric acid (TA) in a 1:1 mixing volume ratio was prepared and used in the remediation of arsenic-contaminated soils. The results showed that the removal efficiency of arsenic was 62.47% in soil 1 at a concentration of 134 mg kg−1 and 70.08% in soil 2 at a concentration of 70 mg kg−1. Dithionite achieved greater release of the arsenic associated with amorphous hydrous oxides of iron and aluminium (F3) and arsenic associated with crystalline hydrous oxides of iron and aluminium (F4) forms of arsenic by the reductive dissolution of iron oxides, while also reducing Fe3+. TA released some arsenic in the specifically adsorbed (F2) and F3 forms through acidic effects. The mechanism of arsenic removal from the composite washing agent was found to be a synergistic effect between dithionite and TA. The TA complexation formed Fe-TA complexes with Fe2+ in solution, preventing the formation of new iron mineral phases and reducing the readsorption or precipitation of arsenic to the soil surface. Meanwhile, the formation of Fe-TA complexes kept the iron oxides dissolved, allowing more iron oxide-bound arsenic (F3 +F4) to be released. This study showed that combining TA with dithionite is a promising technology for remediating arsenic-contaminated soils because of its high efficiency.

Iron (oxyhydr)oxides are responsible for the stabilization of Cu and Zn in AMD after treatment with limestone.

The formation and transformation of secondary iron (oxyhydr)oxides and their role in the stabilization of copper (Cu) and zinc (Zn) in acid mine drainage (AMD) after limestone treatment are worth studying to better understand the impacts of limestone AMD treatment. In this study, the wastewater from a copper mine ditch was sampled. Two different doses of limestone (S: 5.33 g L-1 and SS: 8.00 g L-1) were applied to adjust the pH range of the sampled AMD. The concentrations of Fe, Cu and Zn in the supernatant and the levels of iron (oxyhydr)oxides and heavy metals in AMD sediments were dynamically monitored for 300 days to analyze the transformation of the secondary iron mineral phase and the role iron (oxyhydr)oxides play in the removal and stabilization of Cu and Zn. The results showed that the pH rose rapidly to 6.82, decreased to 5.82 on the 150th day, and finally decreased to approximately 4.63 by the 300th day, when the dosage of limestone (S) was 5.33 g L-1. Goethite was the main form of iron oxides in the sediments. As the incubation time increased, so did the content of crystalline Fe (oxyhydr)oxides. In addition, the Cu and Zn content in the fraction of crystalline Fe (oxyhydr)oxides increased as the corresponding iron (oxyhydr)oxide increased. When the high dosage of limestone (8.00 g L-1 or SS) was applied, the pH remained at approximately at 7.46 during the whole period and goethite and lepidocrocite were present in the sediment. Amorphous/ poorly crystalline Fe-oxyhydroxide was the main product after SS limestone dosage, indicating that the risk of Cu and Zn reactivation in the sediment was higher with a higher limestone treatment dosage.

Facile Preparation of Fe3O4@SiO2 Derived from Iron-Rich Sludge as Magnetic Catalyst for the Degradation of Organic Contaminants by Peroxymonosulfate Activation

Iron-rich sludge, generated during flocculation/sedimentation processes by using Fe-based coagulant in drinking water treatment plants, could be used as a precursor to prepare an effective peroxymonosulfate (PMS) activator (Fe3O4@SiO2) for the ciprofloxacin (CIP) degradation via facile hydrothermal treatment. The catalytic performances of raw iron-rich sludge and Fe3O4@SiO2 were evaluated. The removal rate of CIP in Fe3O4@SiO2/PMS system increased from 44.7% to 82.8% within 60 min compared with the raw iron-rich sludge. The effects of PMS, catalyst loadings, temperature, and initial pH on the CIP degradation were examined, demonstrating that acidic conditions and higher temperatures were beneficial for CIP degradation. Both sulfate radicals (SO4•−) and hydroxyl radicals (•OH) contributed to the CIP degradation, and SO4•− was predominated in the Fe3O4@SiO2/PMS system, which was confirmed by the result of electron paramagnetic resonance (EPR) analysis and radical quenching tests. The mechanisms of the PMS activation process by Fe3O4@SiO2 were elucidated, and the influencing factors were among which the role of the iron mineral phase was emphatically explored. This study provides a facile method to convert the recycled waste iron-rich sludge to magnetic heterogeneous catalysts for CIP degradation with PMS activation.

Improvement of the thermal properties of alkali-activated fly ash after high temperature by the Fe-based solid wastes

Compared with Portland cement, AAM was selected as the high-temperature resistant material. But there is still a trend toward a significant reduction in compressive strength at 600 ℃ and 800 ℃. Thus, in this paper, the Fe-based solid wastes, i.e., copper slag and iron tailing, were used to improve the compressive properties of fly ash-based AAM after high temperatures. The result shows that the residual compressive strength of the Fe-based solid waste samples is higher than that of the blank sample. The residual compressive strength increases by about 20 % at 800 ℃. Though the results of SEM-EDS, MIP, and XPS experiments, the mechanism of the effect of Fe-based solid wastes on the AAM could be summarized as follows: the iron element in the Fe-based solid waste samples is more concentrated after high temperature, which may be caused by the melting of the original iron mineral phase into a new mineral phase, filling the crack gap. And the formation of the Fe-O-Si amorphous phase would improve the densification of samples, resulting in the improvement of compressive strength.

The mechanism of suspension reduction on Fe enrichment with low-grade carbonate-containing iron ore

Carbonate-containing iron ore is a refractory iron resource with a complex symbiotic relationship between iron minerals and gangue. An efficient suspension magnetizing roasting technology was proposed to extract the iron mineral from the carbonate-containing iron ore. The results demonstrated that a concentrate containing 67.20% total Fe and 83.35% iron recovery was obtained under the optimal conditions: the roasting temperature at 550 °C for 15 min with a CO concentration of 15 at.%, a total gas flow of 400 mL/min, and the grinding size of the roasted product was −0.045 mm accounting for 85.39 wt%. The phase transformation and microstructure evolution of the samples before and after roasting were characterized. The investigation revealed that the iron mineral phases were selectively transformed from weakly magnetic hematite and siderite to strongly magnetic magnetite, disrupting the particle structure. Subsequently, the iron mineral was effectively enriched into concentrate via magnetic separation.

Microbially Induced Anaerobic Oxidation of Magnetite to Maghemite in a Hydrocarbon‐Contaminated Aquifer

AbstractIron mineral transformations occurring in hydrocarbon‐contaminated sites are linked to the biodegradation of the hydrocarbons. At a hydrocarbon‐contaminated site near Bemidji, Minnesota, USA, measurements of magnetic susceptibility (MS) are useful for monitoring the natural attenuation of hydrocarbons related to iron cycling. However, a transient MS, previously observed at the site, remains poorly understood and the iron mineral phases acting as reactants and products associated with this MS perturbation remain largely unknown. To address these unknowns, we acquired mineral magnetism measurements, including hysteresis loops, backfield curves, and isothermal remanent magnetizations on sediment core samples retrieved from the site and magnetite‐filled mineral packets installed within the aquifer. Our data show that the core samples and magnetite packs display decreasing magnetization with time and that this loss in magnetization is accompanied by increasing bulk coercivity consistent with decreased average grain size and/or partial oxidation. Low‐temperature magnetometry on all samples displayed behavior consistent with magnetite, but samples within the plume also show evidence of maghemitization. This interpretation is supported by the occurrence of shrinkage cracks on the surface of the grains imaged via scanning electron microscopy. Magnetite transformation to maghemite typically occurs under oxic conditions, here, we propose that maghemitization occurs within the anoxic portions of the plume via microbially mediated anaerobic oxidation. Mineral dissolution also occurs within the plume. Microorganisms capable of such anaerobic oxidation have been identified within other areas at the Bemidji site, but additional microbiological studies are needed to link specific anaerobic iron oxidizers with this loss of magnetization.

Past, present and future global influence and technological applications of iron-bearing metastable nanominerals

Iron-bearing nanominerals such as ferrihydrite, schwertmannite, and green rust behave as metastable precursors leading to the formation of more thermodynamically stable iron mineral phases (e.g., jarosite, goethite, hematite, and magnetite). However, this transformation may last from days to tens or even hundreds of years, making them the most predominant iron-bearing minerals at environmental conditions and at the human time scale. The present review characterizes ferrihydrite, schwertmannite, and green rust nanominerals according to their main physical and chemical properties, and at both nano- and meso-scales. It also presents a comprehensive review of the multiple past and present Earth environments where these nanominerals have played, and still play, a pivotal role in the geochemistry, mineralogy and environmental nanogeosciences of these environments. Finally, the present and future technological applications of these nanominerals as well as their role in the generation of a more sustainable human-Earth relationship is discussed, with a special emphasis on their use in new circular economies and green based technologies.

In situ arsenic immobilisation for coastal aquifers using stimulated iron cycling: Lab-based viability assessment

Arsenic (As) is one of the most harmful and widespread groundwater contaminants globally. Besides the occurrence of geogenic As pollution, there is also a large number of sites that have been polluted by anthropogenic activities, with many of those requiring active remediation to reduce their environmental impact. Cost-effective remedial strategies are however still sorely needed. At the laboratory-scale in situ formation of magnetite through the joint addition of nitrate and Fe(II) has shown to be a promising new technique. However, its applicability under a wider range of environmental conditions still needs to be assessed. Here we use sediment and groundwater from a severely polluted coastal aquifer and explore the efficiency of nitrate-Fe(II) treatments in mitigating dissolved As concentrations. In selected experiments >99% of dissolved As was removed, compared to unamended controls, and maintained upon addition of lactate, a labile organic carbon source. Pre- and post-experimental characterisation of iron (Fe) mineral phases suggested a >90% loss of amorphous Fe oxides in favour of increased crystalline, recalcitrant oxide and sulfide phases. Magnetite formation did not occur via the nitrate-dependent oxidation of the amended Fe(II) as originally expected. Instead, magnetite is thought to have formed by the Fe(II)-catalysed transformation of pre-existing amorphous and crystalline Fe oxides. The extent of amorphous and crystalline Fe oxide transformation was then limited by the exhaustion of dissolved Fe(II). Elevated phosphate concentrations lowered the treatment efficacy, indicating joint removal of phosphate is necessary for maximum impact. The remedial efficiency was not impacted by varying salinities, thus rendering the tested approach a viable remediation method for coastal aquifers.

Extraction of vanadium from low-vanadium grade magnetite concentrate pellets with sodium salt

This study reported the extraction of vanadium from low-vanadium grade magnetite concentrate pellets using sodium salt. 71.1% of vanadium can be extracted under the following optimal conditions: pelletizing with 5 wt% Na2CO3, preheating at 1050 °C for 10 min, roasting at 1250 °C for 10 min, and water leaching at 120 °C for 120 min with a liquid:solid ratio of 5:1 (mL/g) in the bench-scale experiment. XPS and SEM-EDS results showed that part of trivalent vanadium was not oxidized completely during the sodium salt roasting and still occurred in the iron mineral phase; consequently, this part of vanadium was retained in the leached iron ore. The sodium salt roasting parameters are consistent with those of the iron ore oxidized pellets produced by grate-kiln or straight-grate methods; thus, the production efficiency of sodium salt roasting for vanadium extraction can be improved significantly. Pilot-scale experiment was further performed to verify the feasibility of the recommended method in a traveling grate, a better vanadium extraction ratio of 79.1% was achieved.

Recycling iron from oolitic hematite via microwave fluidization roasting and magnetic separation

Oolitic hematite is an iron ore resource with complex refractory characteristics, abundant reserves, and significant recycling value. In this study, a clean and innovative microwave fluidization roasting method was developed. Iron concentrate with an iron grade of 58.72% and iron recovery of 89.32% was obtained via microwave pretreatment at 1050 °C for 2 min, followed by magnetization roasting at 650 °C for 5 min at a CO content of 30% and total gas volume of 700 mL/min. A vibrating-sample magnetometer analysis indicated that the saturation magnetization increased from 0.33 A·m2/kg for the raw ore to 42.52 A·m2/kg for the roasted products. Scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed that microwave pretreatment promoted the formation of microcracks at the interfaces between minerals, offering the advantages of a rapid reaction and phase transformation during the magnetization roasting. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses indicated that the iron mineral phase was selectively transformed from weakly magnetic hematite into strongly magnetic magnetite and that the iron mineral was effectively recycled from the roasted samples via magnetic separation.

Polycrystalline texture causes magnetic instability in greigite

Magnetic stability of iron mineral phases is a key for their use as paleomagnetic information carrier and their applications in nanotechnology, and it critically depends on the size of the particles and their texture. Ferrimagnetic greigite (Fe3S4) in nature and synthesized in the laboratory forms almost exclusively polycrystalline particles. Textural effects of inter-grown, nano-sized crystallites on the macroscopic magnetization remain unresolved because their experimental detection is challenging. Here, we use ferromagnetic resonance (FMR) spectroscopy and static magnetization measurements in concert with micromagnetic simulations to detect and explain textural effects on the magnetic stability in synthetic, polycrystalline greigite flakes. We demonstrate that these effects stem from inter-grown crystallites with mean coherence length (MCL) of about 20 nm in single-domain magnetic state, which generate modifiable coherent magnetization volume (CMV) configurations in the flakes. At room temperature, the instability of the CVM configuration is exhibited by the angular dependence of the FMR spectra in fields of less than 100 mT and its reset by stronger fields. This finding highlights the magnetic manipulation of polycrystalline greigite, which is a novel trait to detect this mineral phase in Earth systems and to assess its fidelity as paleomagnetic information carrier. Additionally, our magneto-spectroscopic approach to analyse instable CMV opens the door for a new more rigorous magnetic assessment and interpretation of polycrystalline nano-materials.

Selection of a hydrometallurgical process for rare earths extraction from a Brazilian monazite

This work describes the processing of a monazite concentrate containing iron mineral phases in order to recover the rare earth elements (lanthanum was taken as representative for REEs) with minimum iron interference. Three classical routes were tested: acid leaching, alkaline conversion and acid baking. Control of iron bearing mineral phases was performed during REEs leaching. The most important variables of each process were determinated using experimental design planning. The acid leaching presented high lanthanum extraction but this route was not selective as high Fe extraction was found. Leaching temperature was the most important variable. Alkaline conversion presented medium-to-high lanthanum extraction and a relatively selectivity for iron. Temperature was also the most important variable. Temperature was also the most important variable for the acid baking route, but the amount of acid added to the system and the leaching time were also relevant for iron extraction. High yields were achieved for lanthanum, together with moderate yields for iron. The choice of the best route was determined using the Desirability Function as multiresponse methodology. The alkaline conversion route presented the best combined recovery and selectivity results for lanthanum (with a maximum of 77 wt%) and iron extraction (below 5 wt%).